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排序方式: 共有266条查询结果,搜索用时 31 毫秒
21.
Magda A Akl Ayman M Atta Abd El-Fatah M Yousef Mohamed I Alaa 《Polymer International》2013,62(12):1667-1677
Stabilized and dispersed superparamagnetic porous nanogels based on sodium acrylate (AA‐Na) and acrylamide (AM) in a surfactant‐free aqueous system were synthesized via solution polymerization at room temperature. The formation of magnetite nanoparticles was confirmed and their properties characterized using Fourier transform infrared spectroscopy. Extensive characterization of the magnetic polymer particles using transmission electron microscopy (TEM), dynamic light scattering and zeta potential measurements revealed that Fe3O4 nanoparticles were incorporated into the shells of poly(AM/AA‐Na). The average particle size was 5–8 nm as determined from TEM. AM/AA‐Na nanoparticles with a diameter of about 11 nm were effectively assembled onto the negatively charged surface of the as‐synthesized Fe3O4 nanoparticles via electrostatic interaction. Crosslinked magnetite nanocomposites were prepared by in situ development of surface‐modified magnetite nanoparticles in an AM/AA‐Na hydrogel. Scanning electron microscopy was used to study the surface morphology of the prepared composites. The morphology, phase composition and crystallinity of the prepared nanocomposites were characterized. Atomic force microscopy and argon adsorption–desorption measurements of Fe3O4.AM/AA indicated that the architecture of the polymer network can be a hollow porous sphere or a solid phase, depending on the AA‐Na content. © 2013 Society of Chemical Industry 相似文献
22.
Christ Mary Anne G.; Lahey Benjamin B.; Frick Paul J.; Russo Mary F.; McBurnett Keith; Loeber Rolf; Stouthamer-Loeber Magda; Green Stephanie 《Canadian Metallurgical Quarterly》1990,58(6):840
Early motherhood (r?=?.33) with the number of Diagnostic and Statistical Manual of Mental Disorders (DSM-III) symptoms of conduct disorder in a sample of 253 boys (aged 6–13 yrs) who had been referred to outpatient clinics. The following models were compared using path analysis: (1) Teenage motherhood, parental antisocial personality, and socioeconomic status (SES) each contribute uniquely to the prediction of childhood conduct problems; (2) teenage motherhood mediates the association of SES and parental antisocial personality with child conduct problems; and (3) teenage motherhood is spuriously related with child conduct problems because of common associations with SES and parental antisocial personality. Model (3) best fit the data. Similar results were obtained whether maternal age at the birth of the firstborn child or the proband child was used to define maternal age and when teenage motherhood was defined as giving birth at 相似文献
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24.
Marina Serantoni Elisa Mercadelli Anna Luisa Costa Magda Blosi Laura Esposito Alessandra Sanson 《Ceramics International》2010,36(1):103-106
Sub-micrometer powder (100–150 nm diameter) of Yb-doped yttrium oxide was obtained, for the first time, by microwave-assisted polyol (diethylene glycol, DEG) method. This method is based on fast and homogeneous increase of temperature, due to the microwave heating, and on addition of the hydrolysing agent (water) at high temperature. This promotes a fast nucleation followed by a controlled growth of nuclei. Different procedures were used to process the as-synthesized powders. In some cases washing by ultrapure water was used to dissolve nitrate and DEG by-products, this treatment allowed the use of a lower calcination temperature (150–200 °C less) to obtain the crystalline phase. Analysis of the calcined powder showed different levels of structures: from nanocrystal (10–15 nm), to primary particles (100–150 nm), to micrometer soft aggregates (2–4 μm). The microwave-assisted polyol method resulted an easy way to dope yttria with the desired amount of Yb3+. This work was carried out in order to prepare particles to be used as rare-earth doped Y2O3 and YAG polycrystalline transparent ceramic for laser source applications. 相似文献
25.
Aflatoxin M1 in pasteurized and ultrapasteurized milk with different fat content in Mexico 总被引:1,自引:0,他引:1
High per capita milk consumption in Mexico indicated a strong need for documentation of aflatoxin M1 (AFM1) levels in milk. A survey of 580, 2-liter samples (n = 290), was conducted to quantify AFM1 using high-performance liquid chromatography, considering two maximum tolerance levels (0.05 and 0.5 microg/liter). We relate aflatoxin levels in the seven most consumed brands from different regions, with two processes (pasteurized and ultrapasteurized), different expiration dates, and different fat content: whole fat (28, 30, and 33 g), half-skimmed (10, 16, and 20 g), light (1, 2, and 4 g), and with vegetable oil. Pasteurization and ultrapasteurization did not diminish AFM1 contamination present at levels of 0 to 8.35 microg/liter in 40% of the milk samples at concentrations > or = 0.05 microg/liter and in 10% of the samples at > or = 0.5 microg/liter. Statistically significant relationships were AFM1 contamination with brand (P = 0.002 at the > or = 0.05 microg/liter level and P = 0.034 at the > or = 0.5 microg/ liter level) and higher AFM1 levels with mild or warm seasons of the year (P = 0.0003). Samples with greater fat content had slightly more probability (P = 0.067) of being contaminated by AFM1 at the > or = 0.5 microg/liter level. The milk with the lowest contamination of AFM1 was a brand imported as powder and rehydrated in Mexico. 相似文献
26.
A problem of a modelling of vibrations of thin plates with a functionally graded macrostructure and a tolerance-periodic microstructure in planes parallel to the plate midplane is analysed. The proposed model, based on the Kirchhoff plate theory assumptions and additional hypothesis of the tolerance averaging technique [Wo?niak et al., editors. Thermomechanics of heterogeneous solids and structures. Tolerance averaging approach. ?ód?, University Press, Technical University of ?ód?; 2008], describes the effect of the microstructure size on dynamic behaviour of the plate. In this paper, as an example there are analysed free vibration frequencies of a functionally graded plate band. These frequencies are obtained in the framework of two proposed models—the tolerance model and the asymptotic model, using the known Ritz method. 相似文献
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28.
G. E. Mitchell W. I. Furman E. V. Lychagin A. Yu. Muzichka G. V. Nekhaev A. V. Strelkov E. I. Sharapov V. N. Shvetsov Yu. I. Chernuhin B. G. Levakov V. I. Litvin A. E. Lyzhin E. P. Magda B. E. Crawford S. L. Stephenson C. R. Howell W Tornow 《Journal of research of the National Institute of Standards and Technology》2005,110(3):225-230
Although crucial for resolving the issue of charge symmetry in the nuclear force, direct measurement of nn-scattering by colliding free neutrons has never been performed. At present the Russian pulsed reactor YAGUAR is the best neutron source for performing such a measurement. It has a through channel where the neutron moderator is installed. The neutrons are counted by a neutron detector located 12 m from the reactor. In preliminary experiments an instantaneous value of 1.1 × 1018/cm2s was obtained for the thermal neutron flux density. The experiment will be performed by the DIANNA Collaboration as International Science & Technology Center (ISTC) project No. 2286. 相似文献
29.
Burke Jeffrey D.; Loeber Rolf; White Helene Raskin; Stouthamer-Loeber Magda; Pardini Dustin A. 《Canadian Metallurgical Quarterly》2007,116(2):249
The authors examined the prediction from inattention to tobacco use among 2 cohorts (ages 7 and 13) of a community sample followed to young adulthood. Changes in self-reported tobacco use were tested with marginal transitional regression models, using parent and teacher ratings of inattention, hyperactivity-impulsivity, and other psychopathology, along with other factors, as predictors. Inattention, but not hyperactivity-impulsivity, significantly predicted adolescent tobacco use and young adult daily tobacco use. Peer substance use, parental substance use, and conduct disorder also predicted increases in tobacco use. African American ethnicity was strongly protective against later tobacco use. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
30.
An easy procedure for the preparation of solutions containing certain types of reactive dye and their subsequent application on cotton is described. This procedure takes advantage of the expected high reactivity of these dyes, which have adjacent hydroxy and amino groups in the molecule, and strives to evade the problems usually associated with the preparation and application of such dyes in the solid form. Several factors that affect the colour strength of reactive dyeings thus obtained are investigated. Possible disadvantages when applying this procedure are discussed. 相似文献