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21.
Dan Donescu Raluca Somoghi Catalin Ilie Spataru Doina Manaila-Maximean Denis Mihaela Panaitescu Eugeniu Vasile Cristina L. Nistor 《Colloid and polymer science》2013,291(10):2345-2358
The work describes a study for preparing polystyrene (PSt) and polymethyl methacrylate (PMMA) latex, containing magnetite (Fe3O4), covalently bounded to the polymeric chains. The magnetite was functionalized with various alkoxysilanes containing double bonds: vinyltriethoxysilane (VTES), methacryloyl propyl trimethoxysilane (MPTS) and vinyldimethylethoxysilane (VMe2TES). The ferrite-silane composite forms higher average size particles with MPTS than with VTES. Ferrite functionalized with VMe2TES forms stable latexes with both PSt and PMMA polymers. PSt forms also stable latexes with ferrite functionalized with VTES but unstable with ferrite functionalized with MPTS. 相似文献
22.
Doina Dragan Simona Cucu-Man Alin C. Dirtu Raluca Mocanu Luc Van Vaeck 《International journal of environmental analytical chemistry》2013,93(11):833-842
Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs), such as DDT and analogues, hexachlorocyclohexane (HCH) isomers and hexachlorobenzene (HCB), were measured in surface soils and sediments from Eastern Romania. Thirty-nine soil samples from the forested zone, eight soil samples from a municipal waste-disposal site, and 10 sediment samples from the Bahlui River along the Iassy city were analysed using accelerated solvent extraction (ASE) and gas chromatography coupled to electron capture detection or mass spectrometry. The low mean concentrations of OCPs (11–31 and 22–84?ng?g?1 for HCHs and DDTs, respectively) and PCBs (8–43?ng?g?1) in soil samples from the forested zone suggest that contamination at most of these sites occurred predominantly through atmospheric transport from zones where these compounds were used and subsequently through atmospheric deposition. Contrarily, soil samples collected in the vicinity of a waste-disposal site near Iassy contained higher mean levels of PCBs (278?ng?g?1, range 34–1132?ng?g?1) than OCPs (6 and 101?ng?g?1 of soil for HCHs and DDTs, respectively). The sediment samples collected along the Bahlui river throughout the Iassy city revealed higher mean levels of PCBs (59?ng?g?1, range 24–158?ng?g?1) compared with OCP levels (2 and 37?ng?g?1 of soil for HCHs and DDTs, respectively). Furthermore, PCB profiles and concentrations in the sediment samples varied considerably along the river due to a wide variety of sources, such as different industries and waste sites. Although their sources are difficult to evaluate, the presence of POPs at most sites (especially at the waste-disposal site) may constitute a potential health hazard. 相似文献
23.
The magnetic measurements performed on xFe2O3(1-x)[B2O3 · PbO] glasses show that for x 5 mol.% Fe2O3 the thermal variation of reciprocal susceptibility obeys a Curie behaviour. For higher iron content, at T 50 K, a nonlinear variation, typical for systems with random distribution of exchange interactions is observed. At greater temperatures than 50 K a Curie-Weiss behaviour is shown. The composition dependence of the Curie constants is analysed in correlation with the number of Fe3+ and Fe2+ ions as determined from Mössbauer effect measurements. A comparison with the data obtained in case of xFe2O3(1-x)[3B2O3 · PbO] glasses is made. 相似文献
24.
This paper studies the effective dielectric properties of heterogeneous materials of the type particle inclusions in a host medium, using the Maxwell Garnet and the Bruggeman theory. The results of the theories are applied at polymer-dispersed liquid crystal (PDLC) films, nanoparticles (NP)-doped LCs, and developed for NP-doped PDLC films. The effective permittivity of the composite was simulated at sufficiently high frequency, where the permittivity is constant, obtaining results on its dependency on the constituents’ permittivity and concentrations. The two models are compared and discussed. The method used for simulating the doped PDLC retains its general character and can be applied for other similar multiphase composites. The methods can be used to calculate the effective permittivity of a LC composite, or, in the case of a composite in which one of the phases has an unknown permittivity, to extract it from the measured composite permittivity. The obtained data are necessary in the design of the electrical circuits. 相似文献
25.
The effects of grape seeds polyphenols on SKH-1 mice skin irradiated with multiple doses of UV-B 总被引:1,自引:0,他引:1
Filip A Daicoviciu D Clichici S Bolfa P Catoi C Baldea I Bolojan L Olteanu D Muresan A Postescu ID 《Journal of photochemistry and photobiology. B, Biology》2011,105(2):133-142
The study investigated the protective activity of red grape seeds (Vitis vinifera L, Burgund Mare variety) (BM) extracts in vivo on multiple doses of ultraviolet radiation (UV)-B-induced deleterious effects in SKH-1 mice skin. Eighty 8-weeks-old female SKH-1 mice were divided into 8 groups: control, vehicle, UV-B irradiated, vehicle+UV-B irradiated, BM 2.5mg polyphenols (PF)/cm(2)+UV-B irradiated, BM 4 mg PF/cm(2)+UV-B irradiated, UV-B+BM 2.5mg PF/cm(2), UV-B+BM 4 mg PF/cm(2). The extract was applied topically before or after each UV-B exposure (240 mJ/cm(2)), for 10 days consecutively. The antioxidant activity of BM extract is higher than gallic acid (k(BM)=0.017, k(gallic acid)=0.013). Multiple doses of UV-B generated the formation of cyclobutane pyrimidine dimers (CPDs) and sunburn cells, increased glutathione peroxidase (GPx) and catalase (CAT) activities respectively glutathione (GSH) and IL-1β levels in skin. In group treated with 2.5mg PF/cm(2) before UV-B irradiation BM extract inhibited UV-B-induced sunburn cells, restored the superoxide dismutase (MnSOD) activity, increased insignificantly CAT and GPx activities and reduced IL-1β level. The BM 4.0 mg PF/cm(2) treatment decreased GSH level and reduced the percentage of CPDs positive cells in skin. Both doses of BM extract administered after UV-B irradiation increased the MnSOD and GPx activities and reduced the formation of sunburn cells in skin. Our results suggest that BM extract might be a potential chemo-preventive candidate in reducing the oxidative stress and apoptosis induced by multiple doses of UV-B in skin. 相似文献
26.
Mihaela Lupu Doina Macocinschi Virginia Epure Aurelia Ioanid Cristian Vasile Grigoras 《Journal of Macromolecular Science: Physics》2013,52(3):395-405
Poly(ether urethane)s containing different hard segments were investigated by viscometry, fluorescence spectra, polarizing optical microscopy, and scanning electron microscopy. The polarity dependence of the vibrational structure of the pyrene emission spectrum indicated the formation of aggregates at concentrations that are significantly below the critical concentrations that define the separation of dilute‐semidilute domains. Unlike the sample with 4,4'‐methylene diphenylene diisocyanate, the sample with 2,4‐tolylene diisocyanate in hard segments gives a fluorescence spectra in which the pyrene excimer appears. Supermolecular structures associated with the form of spherulites or of spherical micelles were detected by scanning electron microscopy. The results are discussed in correlation with viscometric data and optical microscopy. 相似文献
27.
In 1980 S.P. Han proposed a finitely terminating (in exact arithmetic) algorithm for solving an inconsistent system of linear inequalities in a least squares sense. This algorithm uses a singular value decomposition of a submatrix of the problem matrix on each iteration, making it impractical for all but only smaller problems. In this paper we show that a modification of Han's algorithm allows us to introduce an iterative approximation to the singular value decomposition solution. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
28.
Detlef Schrder Jessica Loos Helmut Schwarz Roland Thissen DorinV. Preda LawrenceT. Scott Doina Caraiman MaximV. Frach DiethardK. Bhme 《Helvetica chimica acta》2001,84(6):1625-1634
Electron‐transfer processes that involve single and doubly charged cations of corannulene (C20H10) and coronene (C24H12) are examined by three different mass‐spectrometric techniques. Photoionization studies give first‐ionization energies of IE(C20H10)=7.83±0.02 eV and IE(C24H12)=7.21 ±0.02 eV. Photoionizations of the neutrals to the doubly charged cations occur at thresholds of 20.1±0.2 eV and 18.5±0.2 eV for corannulene and coronene, respectively. Energy‐resolved charge‐stripping mass spectrometry yields kinetic energy deficits of Qmin(C20H=13.8±0.3 eV and Qmin(C24H=12.8±0.3 eV for the transitions from the mono‐ to the corresponding dications in keV collisions. Reactivity studies of the C20H and C24H dications in a selected‐ion flow‐tube mass spectrometer are used to determine the onsets for the occurrence of single‐electron transfer from several neutral reagents to the dications, affording two different monocationic products. With decreasing IEs of the neutral reagents, electron transfer to doubly charged corannulene is first observed with hexafluorobenzene (IE=9.91 eV), while neutrals with lower IEs are required in the case of the coronene dication, e.g., NO2 (IE=9.75 eV). Density‐functional theory is used to support the interpretation of the experimental data. The best estimates of the ionization energies evaluated are IE(C20H10)=7.83±0.02 eV and IE(C24H12)=7.21 ±0.02 eV for the neutral molecules, and IE(C20H)=12.3±0.2 eV and IE(C24H)=11.3±0.2 eV for the monocations. 相似文献
29.
LetA be the generator of a cosine functionC
t
,t R in a Banach spaceX; we shall connect the existence and uniqueness of aT-periodic mild solution of the equationu = Au + f with the spectral property 1 (C
T
) and, in caseX is a Hilbert space, also with spectral properties ofA.
This research was supported in part by DAAD, West Germany. 相似文献
30.
We consider a nonlinear homogenization problem for a Ginzburg–Landau functional with a (positive or negative) surface energy term describing a nematic liquid crystal with inclusions. Assuming that sizes and distances between inclusions are of the same order ?, we obtain a limiting functional as . We generalize the method of mesocharacteristics to show that a corresponding homogenized problem for arbitrary, periodic or non-periodic geometries is described by an anisotropic Ginzburg–Landau functional. We give computational formulas for material characteristics of an effective medium. To cite this article: L. Berlyand et al., C. R. Acad. Sci. Paris, Ser. I 340 (2005). 相似文献