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551.
Mariagrazia Napoli Rosanna De Vita Ivano Immediata Pasquale Longo Gaetano Guerra 《先进技术聚合物》2011,22(4):458-462
The syntheses of low‐molecular‐weight polyethylene (PE), in the presence of catalysts based on five different metallocene frameworks, have been compared. High yields and low molecular masses, typical of industrially relevant PE waxes, can be easily achieved by using overpressure of hydrogen. Particularly suitable for the production of PE waxes are catalytic systems based on the C2 symmetric rac‐dimethyl‐silyl‐bis‐(2‐methyl‐4‐phenyl‐1‐indenyl)‐zirconium dichloride ( 1 ) and the C2v symmetric bis‐cyclopentadienyl‐zirconium dichloride ( 5 ). The wax yields can be substantially increased by increasing the MAO/Zr molar ratio. The control of the PE molecular weight allows an easy control of physical properties. In fact, as Mn increases in the range 103–104 g/mol, the degree of crystallinity decreases from nearly 85 to 60% while the melting temperature increases from 125°C up to 135°C. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
552.
Arsenic compounds are ubiquitous and widespread in the environment as a result of natural or anthropogenic occurrence. Fish are the major source of protein for human consumption. They are also a source of contamination, because of the amounts of heavy elements they can contain, some of which are highly toxic. Fish bones are high in calcium, which is an essential mineral for normal body function. It consists of water, organic material, and mineral matter. Chelating agents have been used clinically as antidotes for acute and chronic metal intoxications. In the present study, an attempt is made to investigate the bio-accumulation of arsenic and its effect on the biochemical and mineral contents of Labeo rohita bones using, Fourier transform infrared (FT-IR) spectroscopy. The results of the present study indicate that arsenic exposure induces significant reduction on the biochemical and mineral contents of the L. rohita bones. Further, the DMSA treatment significantly improves these levels. This shows that DMSA is an effective chelator for arsenic toxicity. Quantitative curve-fitting analyses of amide I band have proved useful in studying the nature and the extent of protein conformational changes. A decrease in α-helical and random coil structures and an increase in β-sheet structures have been observed due to arsenic exposure. In conclusion, the present study shows that the FT-IR spectroscopy coupled with second derivative and curve-fitting analysis gives useful information about the biochemical and mineral contents of the L. rohita bones. 相似文献
553.
554.
Imaging metallic multilayer structures through ultrafast optically driven excited electron transport
Received: 20 September 1998 / Revised version: 21 December 1998 相似文献
555.
Petrov G. M. Matte J. P. Pérès I. Margot J. Sadi T. Hubert J. Tran K. C. Alves L. L. Loureiro J. Ferreira C. M. Guerra V. Gousset G. 《Plasma Chemistry and Plasma Processing》2000,20(2):183-207
A self-consistent steady-state spatially averaged collisional-radiativemodel in which the rate coefficients involving electrons are calculatedfrom the solution to the electron Boltzmann equation has been developedfor describing an atmospheric pressure plasma in helium–nitrogen(He–N2) mixtures. The influence of small nitrogenconcentrations (typically less than 1%) on the discharge characteristicsis studied and compared with available experimental data. It is foundthat nitrogen is highly dissociated and that the density of metastablehelium atoms is considerably reduced by the presence of nitrogen, evenat such low concentrations. 相似文献
556.
PL. RM. Palaniappan K. S. Pramod V. Vijayasundaram 《Journal of Applied Spectroscopy》2008,75(5):752-758
Zinc is an essential metal for different physiological functions and becomes toxic when elevated concentrations are introduced
into the environment. In the present study, an attempt is made to analyze zinc-induced biochemical changes in the liver tissues
of freshwater fingerlings of Labeo rohita using Fourier Transformation Infrared Spectroscopy. Several important features have
been observed in the FTIR spectra of zinc-intoxicated liver tissues, namely, altered membrane lipid, altered protein profile,
and increased glycogen content, indicating an alteration in the lipid and protein profiles leading to modification in membrane
composition. Further, it is observed that acute exposure to zinc causes some alteration in protein profile with a decrease
in α-helix and an increase in random coil structure. Treatment with the chelating agent D-penicillamine reduces the biochemical
contents in the liver tissues. This shows that D-penicillamine is a good antidote for zinc toxicity.
Published in Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 746–752, September–October, 2008. 相似文献
557.
I.?A.?Santos R.?G.?Mendes J.?A.?Eiras J.?de?Los?S.?Guerra E.?B.?Araújo 《Applied Physics A: Materials Science & Processing》2009,95(3):757-760
The dielectric properties of Sr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films were carefully analyzed. In contrast to bulk samples which present three distinct dielectric
relaxation phenomena Sr0.75Ba0.25Nb2O6 thin films present only two of them. The suppression of the third anomaly can be mainly attributed to the narrow grain size
distribution of nanograins and weak tensile strains imposed to the film from the substrate. The whole set of results point
to the interpretation of a dielectric response characteristic of mesoscopic structure, which is composed of clusters and nanodomains. 相似文献
558.
A.C. Brasileiro-Vidal M.B. Melo-Oliveira G.M.G. Carvalheira M. Guerra 《Micron (Oxford, England : 1993)》2009,40(8):851-859
Conventional chromosome staining has suggested that more than 75% of the tomato chromosomes are constituted by heterochromatin. In order to determine whether more deeply stained proximal regions are classic heterochromatin, the distributions of C-bands and chromomycin A3 (CMA) bands, and the prophase condensation patterns, were analysed in tomato. In this and most other species of the tomato clade, the 5S and 45S rDNA sites were also localised. In tomato, CMA banding was similar to C-banding. After conventional staining, all species displayed large condensed heteropycnotic regions that did not correspond to C-bands or CMA bands. Analyses of the CMA banded karyotypes revealed a low heterochromatin content. Around 12–17% of the chromatin of tomato was CMA+ and 1/4 to 1/5 of this heterochromatin corresponded to 45S rDNA. In other species, the CMA+ heterochromatin showed extensive variation (8–35%), but was never near the values found in the literature for tomato. These data suggest the existence of three principal fractions of chromatin in tomato and related species: the late condensed euchromatin corresponding to the terminal regions of the chromosomes, the precocious condensed euchromatin that occupies the major part of the chromosomes and the constitutive heterochromatin that represents those regions revealed by C-bands. 相似文献
559.
A new concept of duality is proposed for multiobjective linear programs. It is based on a set expansion process for the computation of optimal solutions without scalarization. The duality gap qualifications are investigated; the primal–dual balance set and level set equations are derived. It is demonstrated that the nonscalarized dual problem presents a cluster of optimal dual vectors that corresponds to a unique optimal primal vector. Comparisons are made with linear utility, minmax and minmin scalarizations. Connections to Pareto optimality are studied and relations to sensitivity and parametric programming are discussed. The ideas are illustrated by examples. 相似文献
560.
Daniel Hernndez‐Guerra Anna Hlava
kov Chiranan Pramthaisong Ilaria Vespoli Radek Pohl Tom Slanina Ullrich Jahn 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(36):12570-12575
A mild, atom‐economic, and metal‐free α‐C?H amination of ethers using relatively stable nonafluorobutanesulfonyl (nonaflyl, Nf) azide as the aminating reagent to give N‐sulfonyl hemiaminals is reported. This enables unprecedented C(sp3) difunctionalization reactions, leading to diverse functionalized amino group containing compounds starting from simple ethers in one pot. 相似文献