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排序方式: 共有695条查询结果,搜索用时 15 毫秒
621.
Gerardo Martínez Marián A. Gómez Carlos Marco Gary Ellis Rafael Gómez José L. Segura 《Journal of polymer science. Part A, Polymer chemistry》2008,46(20):6722-6733
The covalent attachment of [60] fullerene (C60) to isotactic polypropylene (i‐PP) is achieved by direct reaction in 1,2,4‐trichlorobenzene (TCB) solution in the presence of dicumyl peroxide (DCP). The chemically modified pendant C60/i‐PP polymers are soluble in chlorinated solvents and have been characterized by ultraviolet–visible and fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, differential scanning calorimetry, cyclic voltametry, and thermogravimetric analysis. From the results it can be concluded that the modification of i‐PP by grafting via a free‐radical reaction competes with the possibility of chain scission of i‐PP due to the presence of DCP. The functionalized polymers crystallize in the monoclinic crystal modification, and have high crystallinity. The incorporation of C60 significantly enhances the thermal stability of the i‐PP. Electrochemical measurements demonstrate good electron acceptor properties of the fullerenated i‐PP samples. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6722–6733, 2008 相似文献
622.
Two new analogs of the human lethal toxin polycavernoside A, polycavernoside C and C2 (0.1-0.2 mg for each), were isolated from the red alga, Gracilaria edulis. The relative stereostructure of polycavernoside C and the absolute structure of polycavernoside C2 were determined by spectroscopic analysis and synthesis of the model of their aglycon. 相似文献
623.
Fernanda Cristina Stenger Valdir Cechinel-Filho Christiane Meyre-Silva Tania Mari Belle Bresolin Clóvis Antonio Rodrigues 《Chromatographia》2009,69(Z2):183-187
Chitosan was modified with lauroyl chloride to prepare a solid support for the application of matrix solid-phase dispersion
(MSPD) for the extraction of flavonoids from the medicinal plant Aleurites moluccana. The laurylchitosan prepared by the homogenous and heterogeneous method, was characterized using analytical methods such
as potentiometric titration and infrared spectroscopy. The hydrophobic properties were studied by naphthalene incorporation.
The MSPD performance was evaluated by extraction of swertisin and 2″-O-rhamnosylswertisin from the leaves of A. moluccana. 相似文献
624.
Guillermo?García-Pérez M.?ángeles?SerranoEmail authorView authors OrcID profile Marián?Bogu?á 《Journal of statistical physics》2018,173(3-4):775-782
The \(\mathbb {S}^1\) model has been central in the development of the field of network geometry. It places nodes in a similarity space and connects them with a likelihood depending on an effective distance which combines similarity and popularity dimensions, with popularity directly related to the degrees of the nodes. The \(\mathbb {S}^1\) model has been mainly studied in its homogeneous regime, in which angular coordinates are independently and uniformly scattered on the circle. We now investigate if the model can generate networks with targeted topological features and soft communities, that is, inhomogeneous angular distributions. To that end, hidden degrees must depend on angular coordinates, and we propose a method to estimate them. We conclude that the model can be topologically invariant with respect to the soft-community structure. Our results expand the scope of the model beyond the independent hidden variables limit and can have an important impact in the embedding of real-world networks. 相似文献
625.
The \(\eta \,\rightarrow \,3\pi \) decays are a valuable source of information on low energy QCD. Yet they were not used for an extraction of the three flavor chiral symmetry breaking order parameters until now. We use a Bayesian approach in the framework of resummed chiral perturbation theory to obtain constraints on the quark condensate and pseudoscalar decay constant in the chiral limit. We compare our results with recent CHPT and lattice QCD fits and find some tension, as the \(\eta \,\rightarrow \,3\pi \) data seem to prefer a larger ratio of the chiral order parameters. The results also disfavor a very large value of the pseudoscalar decay constant in the chiral limit, which was found by some recent work. In addition, we present results of a combined analysis including \(\eta \,\rightarrow \,3\pi \) decays and \(\pi \pi \) scattering and though the picture does not changed appreciably, we find some tension between the data we use. We also try to extract information on the mass difference of the light quarks, but the uncertainties prove to be large. 相似文献
626.
Adriana Araújo de Almeida-Apolonio Fabiana Gomes da Silva Dantas Allan Belarmino Rodrigues Claudia Andréa Lima Cardoso Melyssa Negri Kelly Mari Pires de Oliveira 《Natural product research》2019,33(16):2363-2367
Cryptococcosis is an opportunistic disease with a worldwide distribution. This disease is caused by fungi of the genus Cryptococcus, and its treatment is limited to several antifungals. In this study, the antifungal, cytotoxic and mutagenic properties of ethanol extracts from the bark and leaves of Annona coriacea were evaluated against the standard Cryptococcus species and clinical yeast specimens. Both extracts of A. coriacea showed inhibitory activity of 1.5 mg/mL for all of the yeasts tested. The number of viable cells at the lowest tested concentration was 0.187 mg/mL. The extracts that were tested showed inhibitory activity and reduced the fungal growth of the Cryptococcus gattii species and Cryptococcus neoformans species complexes, suggesting that this plant may be an effective alternative treatment for cryptococcosis. 相似文献
627.
Sasaki M Takaishi S Miyasaka H Sugiura K Yamashita M 《Journal of the American Chemical Society》2005,127(43):14958-14959
Scanning tunneling microscopy (STM) has been measured in quasi-one-dimensional (Quasi-ID) bromo-bridged Ni(III) complexes. In the STM image of [Ni(pn)2Br]Br2 (pn = (R)-1,2-diaminopropane), the bright spots are fluctuated zigzags. Such a result indicates that the methyl groups of the pn ligands are not arranged on the right- and left-hand alternatively along the chains, but in the domain structures or fluctuated structures. This is the first direct observation of the disorder of the methyl group of pn ligands in real space. 相似文献
628.
We demonstrate the equivalence of all loop closed topological string amplitudes on toric local Calabi-Yau threefolds with computations of certain knot invariants for Chern-Simons theory. We use this equivalence to compute the topological string amplitudes in certain cases to very high degree and to all genera. In particular we explicitly compute the topological string amplitudes for 2 up to degree 12 and 1× 1 up to total degree 10 to all genera. This also leads to certain novel large N dualities in the context of ordinary superstrings, involving duals of type II superstrings on local Calabi-Yau three-folds without any fluxes.This research is supported in part by NSF grants PHY-9802709 and DMS-0074329 相似文献
629.
630.
Dumitrescu A Rudzevich VL Romanenko VD Mari A Schoeller WW Bourissou D Bertrand G 《Inorganic chemistry》2004,43(21):6546-6548
Persistent phosphinyl radicals featuring the 2,6-bis(trifluoromethyl)phenyl group were prepared and characterized. Their electronic structure was theoretically investigated, and their low-temperature dimerization into the corresponding diphosphines was found to be strongly inhibited when the sterically very demanding (tert-butyl)(trimethylsilyl)amino substituent was used. 相似文献