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101.
The effect of Mg-doping and Li overstoichiometry on the structural stability of LiCoO2 powders has been investigated with emphasis to voltammetric properties. Microparticle cyclic voltammetry (CV) conducted in caustic NaOH to best simulate a non-aqueous electrolyte shows a marked improvement of the structure stability of doped LiCoO2. In contrast to the unsubstituted LiCoO2 sample which shows voltammetric peaks associated to the well-known two-phase domain and monoclinic distortion reactions, in Li1.08Mg0.06CoO2, LiMg0.06CoO2 and Li1.08CoO2 samples these peaks are strongly suppressed providing direct evidence for the existence of a stable solid solution with negligible phase transitions in the reversible intercalation region (3.8-4.2 V vs. Li) as well as in the overcharged region. The effect is higher with Mg-doping, irrespective of the Li overstoichiometry. However, the concomitant presence of Mg and Li excess in the structure is important for obtaining small particle sizes. Since Mg-doping induces a quasi metallic behavior in the samples, whereas the Li excess may provide an higher initial capacity, it is suggested that the Li1.08Mg0.06CoO2 composition may be of interest as positive cathode for advanced Li-ion batteries. 相似文献
102.
The effect of oral administration, for 24 or 48 hr, of different octadeca fatty acids containing a 9,12-dienoic structure
on the fatty acid composition and Δ9 desaturation activity of liver microsomes of rat fed a fat-free diet was studied. The
ethyl esters of linoelaidic and γ-linolenic acids, the methyl ester of linoleic acid and free columbinic acid were administered
to rats maintained on a fat-free diet. The supplementation of the fat-free diet with linoelaidate produced no relevant changes
in the fatty acid composition pattern of liver microsomes and did not modify the percentage of conversion of palmitic to palmitoleic
acid. The addition of linoleate or γ-linolenate to the fat-free diet returned liver microsome Δ9 desaturation activity toward
the control and partially restored the liver microsome fatty acid spectrum found in the fat-free diet. Columbinic acid (5-trans-9-cis,12-cis-18∶3), which cannot be transformed into arachidonic acid, also decreased the Δ9 desaturation activity enhanced by the fat-free
diet and evoked changes in the microsomal fatty acid composition similar to those produced by the ω6 fatty acids. These results
suggest that the modulation of Δ9 desaturase activity evoked by dietary administration of unsaturated acids of ω6 series would
depend on thecis double bond configuration of these acids. 相似文献
103.
Nikolaos?Nenadis Maria?TsimidouEmail author 《Journal of the American Oil Chemists' Society》2002,79(12):1191-1195
Rapid 1,1-diphenyl-2-picrylhydrazyl (DPPH•) tests are often applied to classify the scavenging activity of phenolic compounds (AH). Published analytical protocols differ
in more than one experimental condition, and results for the relative order or magnitude of activity are often contradictory.
In this work, parameters such as duration of test, [AH]/[DPPH•] molar ratio, and solvent effects were examined and discussed. The test duration and the value of the [AH]/[DPPH•] ratio did not influence the order of activity among tested antioxidants. Ethanol, commonly used as solvent in such tests,
was compared with acetonitrile and tert-butyl alcohol. Solvent properties such as the ability to form hydrogen bonds with the AH seem to influence the level of the
relative activity (%RSA). Higher %RSA values were observed in ethanol. The activity of the most polar compounds was affected
the most, and in some cases (caffeic, dihydrocaffeic, and rosmarinic acids) the order of activity was changed owing to different
kinetics. Standardization of the analytical protocol should include a 20-min reaction period and a molar ratio that permits
attainment of a 60–80% RSA value for the most potent antioxidant. Solvent choice is critical for classifying activity. Safe
classification can be based only on results from kinetic studies. 相似文献
104.
Maria Jos O. C. Guimares Fernanda M. B. Coutinho Marisa C. G. Rocha Marcelo Farah Rosrio E. S. Bretas 《应用聚合物科学杂志》2002,86(9):2240-2246
The rheological and morphological properties of blends based on high‐density polyethylene (HDPE) and a commercial ethylene–octene copolymer (EOC) produced by metallocene technology were investigated. The rheological properties were evaluated in steady and dynamic shear experiments at 190°C in shear rates ranging from 90 s?1 to 1500 s?1 and frequency range between 10?1 rad/s and 102 rad/s, respectively. These blends presented a high level of homogeneity in the molten state and rheological behavior was generally intermediate to those of the pure components. Scanning electron microscopy (SEM) showed that the blends exhibit dispersed morphologies with EOC domains distributed homogeneously and with particle size inferior to 2 μm. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2240–2246, 2002 相似文献
105.
Maria Helena de Oliveira Nunes Victor Teixeira da Silva Martin Schmal 《Catalysis Letters》2004,97(1-2):1-8
There is a high industrial demand for MMA and DMA, however, the production of TMA is favored with the commercial catalysts. This work tested the methanol amination reaction with HZSM-5 and Cu/HZSM-5 zeolites (%Cu = 1.2, 3.7 and 6.0). Regarding the MMA selectivity, light differences were observed among Cu/HZSM-5 catalysts and pure zeolite, although the catalysts containing 3.7% copper was slightly more selective to MMA than the other metallic catalysts studied. From these results it is suggested that the metal loading present in the catalysts leads to a modification in the nature of the acidic sites, in particular, the selectivity depends on ratio Brönsted/Lewis acid sites. This modifications would facilitate the amines desorption during the reaction. 相似文献
106.
Induced Defensive Response of Myrtle Oak to Foliar Insect Herbivory in Ambient and Elevated Co2 总被引:2,自引:0,他引:2
The rising level of atmospheric CO2 has stimulated several recent studies attempting to predict the effects of increased CO2 on ecological communities. However, most of these studies have been conducted in the benign conditions of the laboratory and in the absence of herbivores. In the current study, we utilized large octagonal chambers, which enclosed portions of an intact scrub-oak community to investigate the interactive effects of CO2 and insect herbivory on myrtle oak, Quercus myrtifolia. Specifically, we assessed the effects of ambient and elevated CO2 (2x current concentrations) on percent foliar nitrogen, C:N ratio, total relative foliar tannin content, and the presence of leaf damage caused by leaf mining and leaf chewing insects that feed on myrtle oak. Total foliar N declined and C:N ratios increased significantly in oaks in elevated CO2 chambers. The percentages of leaves damaged by either leafminers or leaf chewers tended to be lower in elevated compared to ambient chambers, but they co-occurred on leaves less than expected, regardless of CO2 treatment. Leaves that had been either mined or chewed exhibited a similar wounding or defensive response; they had an average of 25 and 21% higher protein binding ability, which is correlated with tannin concentration, compared to nondamaged control leaves, respectively. While the protein-binding ability (expressed as total percent tannin) of leaves from elevated CO2 was slightly higher than from leaves grown in ambient chambers, this difference was not significant. 相似文献
107.
Prior to fertilization, mammalian sperm must undergo the acrosome reaction, which involves modifications of the plasma and
outer acrosomal membranes followed by vesiculation and release of the membranes. The membrane fraction that was released from
caudal boar sperm undergoing an in vitro acrosome-like reaction was isolated and characterized with respect to density, marker
enzymes and lipid composition. This membrane had a lower phospholipid/protein ratio (mg/mg) than the sperm plasma membrane,
whereas both membranes had similar molar sterol/phospholipid ratios. The major phospholipid was sphingomyelin, followed by
phosphatidylethanolamine and phosphatidylcholine, whereas in the plasma membrane the order was reversed; the two major phosphoglycerides
contained alkylacyl and alkenylacyl species in addition to the diacyl species. The released membrane also contained lower
amounts of cholesterol sulfate and unsaturated fatty acids than the plasma membranes. These results, in combination with our
studies on the changes of the sperm membranes during maturation and acrosome reaction, will allow a better understanding of
the mechanism of the sperm acrosome reaction. 相似文献
108.
Auguste Fernandes Maria Filipa Ribeiro Cristina Borges Joo Paulo Loureno Joo Rocha Zelimir Gabelica 《Microporous and mesoporous materials》2006,90(1-3):112-128
This study is aimed at exploring the ability of very small sized N-bearing molecules to generate and stabilize microporous aluminophosphates. Two new AlPO4-n materials, called IST-1 and IST-2, have been obtained in aqueous media using, as main template, methylamine (MA), directly added, or generated in situ from methylformamide (MF) degradation. While IST-1 topology proved to be novel, IST-2 appears structurally related to AlPO4-53(A). The obtained materials were characterized by powder XRD, TG/DSC, SEM and solid-state NMR. Tetraalkylammonium (TEA) cations were used as potential co-templates but only MA and water were found incorporated in the pore volumes of both structures, which argues for their true templating role. In IST-1, 13C solid-state NMR studies showed that half of MA species, presumably protonated, is H-bonded to framework oxygens while the other half surprisingly bonds directly to framework Al atoms. 13C NMR showed that only protonated MA occurs in IST-2 channels. TEA+ cations definitely do not play any specific template role. They indirectly favor the crystallization of IST-1 or IST-2 devoid from other crystalline or amorphous side phases, by interacting with part of the Al and P in solution and forming soluble [AlPO4(OH)]–[TEA,HMA] complexes, substantially modifying the compositions of gels precursors to each phase during nucleation and/or growth steps. While both IST-1 and IST-2 crystallize from gels of similar initial compositions, it was demonstrated that the new MA/T ratio (T = Al or P) obtained after in situ complexation was the key parameter that specifically governs the crystallization of each phase. 相似文献
109.
Pier Paolo Prosini Maria Carewska Silvera Scaccia Pawel Wisniewski Mauro Pasquali 《Electrochimica acta》2003,48(28):4205-4211
Amorphous LiFePO4 was obtained by lithiation of FePO4 synthesized by spontaneous precipitation from equimolar aqueous solutions of Fe(NH4)2(SO4)2·6H2O and NH4H2PO4, using hydrogen peroxide as oxidizing agent. Nano-crystalline LiFePO4 was obtained by heating amorphous nano-sized LiFePO4 for different periods of time. The materials were characterized by TG, DTA, X-ray powder diffraction, scanning electron microscopy (SEM) and BET. All materials showed very good electrochemical performance in terms of energy and power density. Upon cycling, a capacity fading affected the materials, thus reducing the electrochemical performance. Nevertheless, the fading decreased upon cycling and after the 200th cycle the cell was able to cycle for more than 500 cycles without further fading. 相似文献
110.
de Almeida Jhony Luiz Comunello Eros Sobieranski Antonio da Rocha Fernandes Anita Maria Cardoso Gabriel Schade 《Pattern Analysis & Applications》2021,24(3):907-914
Pattern Analysis and Applications - Digital holography is an imaging process able to recreate three-dimensional representations of objects from recording pattern interference among distinct waves.... 相似文献