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141.
Jorge F. J. Coelho Ana M. F. P. Silva Anatoliy V. Popov Virgil Percec Mariana V. Abreu Pedro M. O. F Gonalves M. H. Gil 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2809-2825
Living radical polymerization of n‐butyl acrylate was achieved by single electron transfer/degenerative‐chain transfer mediated living radical polymerization in water catalyzed by sodium dithionate. The plots of number–average molecular weight versus conversion and ln[M]0/[M] versus time are linear, indicating a controlled polymerization. This methodology leads to the preparation of α,ω‐di(iodo) poly (butyl acrylate) (α,ω‐di(iodo)PBA) macroinitiators. The influence of polymerization degree ([monomer]/[initiator]), amount of catalyst, concentration of suspending agents and temperature were studied. The molecular weight distributions were determined using a combination of three detectors (TriSEC): right‐angle light scattering (RALLS), a differential viscometer (DV), and refractive index (RI). The methodology studied in this work represents a possible route to prepare well‐tailored macromolecules made of butyl acrylate in an environmental friendly reaction medium. Moreover, such materials can be subsequently functionalized leading to the formation of different block copolymers of composition ABA. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2809–2825, 2006 相似文献
142.
Ana I. R. N. A. Barros Artur M. S. Silva 《Monatshefte für Chemie / Chemical Monthly》2006,137(12):1505-1528
Summary. Several nitroflavone derivatives were synthesized by cyclodehydrogenation of 2′-hydroxychalcones and by the Baker-Venkataraman approach, starting from 2′-hydroxyacetophenones and benzoic acid derivatives. Nitroflavones synthesised by the first synthetic
approach were obtained in better global yields than those obtained by the later method. The structures of all new compounds
were elucidated by microanalyses, 1D and 2D NMR, IR, and mass spectroscopic measurements. 相似文献
143.
Marcos F. de Campos Marília Emura Fernando J.G. Landgraf 《Journal of magnetism and magnetic materials》2006
Electrical steels, when submitted to operation, present continuous decrease of their magnetic properties, depending on the carbon content. This effect is attributed to the increase of the size of carbides, a process also known as coarsening or Ostwald Ripening. Loss separation can offer a better understanding of this phenomenon. Experimental results show that all effect of aging is inside the hysteresis loss component, with the excess losses unaffected. The carbon content in electrical steels should be less than 25 ppm to avoid magnetic aging. 相似文献
144.
Seppo Hassi Manfred Mö ller Henk de Snoo 《Proceedings of the American Mathematical Society》2006,134(10):2885-2893
The class of Nevanlinna functions consists of functions which are holomorphic off the real axis, which are symmetric with respect to the real axis, and whose imaginary part is nonnegative in the upper halfplane. The Kac subclass of Nevanlinna functions is defined by an integrability condition on the imaginary part. In this note a further subclass of these Kac functions is introduced. It involves an integrability condition on the modulus of the Nevanlinna functions (instead of the imaginary part). The characteristic properties of this class are investigated. The definition of the new class is motivated by the fact that the Titchmarsh-Weyl coefficients of various classes of Sturm-Liouville problems (under mild conditions on the coefficients) actually belong to this class.
145.
Ricardo de Souza Pereira Nivaldo AntÔnio Parizotto Vitor Baranauskas 《Applied biochemistry and biotechnology》1996,59(2):135-143
Different strains of baker’s yeast(Saccharomyces cerevisiae) were imaged with an atomic force microscope (AFM). The images of uncoated and nonfixed samples were reproducible with high-constrast
and nanometer-resolution. Molecules from the polysaccharide surface of the cell wall were pictured and the distance of atoms
was measured. The preparation of samples was easy, suggesting that AFM is a useful tool in this type of analyses. 相似文献
146.
Summary The problem of robust stabilization of internally delayed uncertain systems via sliding mode controllers (SMC's) is studied
in this paper. The robustness property and assymptotic stability of the system are discussed. Some sufficient conditions for
the design of SMC and the switching hyperplane are given. Further generalization results, which lead to a simple design and
implementation, are made for the system being described in companion form. A method is suggested for the elimination of limit
cycles in systems being regulated by a relay SMC while allowing the generation of sliding motion and thus ensuring the closed-loop
asymptotic stability. 相似文献
147.
Electroanalytical and chromatographic determination of pentachlorophenol and related molecules in a contaminated soil: a real case example 总被引:1,自引:0,他引:1
L. Codognoto V. G. Zuin D. de Souza J. H. Yariwake S. A. S. Machado L. A. Avaca 《Microchemical Journal》2004,77(2):177-184
Electroanalytical and chromatographic methodologies have been applied for the determination of pentachlorophenol (PCP) and some of its derivatives in real soil samples contaminated by industrial discharge. The analytes were extracted with hexane from soil samples collected at different points of the site and mixed to produce a representative sample. Square wave voltammetry (SWV) experiments were carried out on either a boron-doped diamond (BDD) electrode or a gold ultramicroelectrode (Au-UME) in an analyte composed by the Britton-Robinson (B-R) buffer at pH 5.5 with the direct addition of proper amounts of the extract. The voltammetric responses revealed an irreversible anodic peak at approximately 0.80 V vs. Ag/AgCl with a peak current showing a linear dependence on PCP concentration. This linear relationship yielded a detection limit (DL) of 2×10−8 mol l−1 (or 5.5 μg l−1) for the BDD electrode and 6.9×10−8 mol l−1 (18.4 μg l−1) for the Au-UME, while the independently measured HPLC detection limit was 1.1×10−8 mol l−1 (3.0 μg l−1). The application of electroanalytical and chromatographic methodologies in the analysis of soil extracts revealed, besides the PCP responses, signals for some related molecules such as o-tetrachlorobenzoquinone (o-chloranil), hexachlorobenzene and tetrachlorophenol. Recovering experiments for PCP showed a concentration of 27.5 mg kg−1 for the electroanalytical determinations and 26.8 mg kg−1 for the HPLC analysis, values exceedingly high if considering that the maximum residue limit established for natural waters by the Brazilian Environmental Agency is 10 μg l−1. 相似文献
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