电子书包支持的体验学习活动设计与应用研究

旨在研究电子书包支持的体验学习的活动模型和应用效果。首先通过理论分析提出了电子书包支持的体验学习活动模型,并设计了《校园植物知多少》等3个教学专题,之后在某小学进行了试点实验研究。研究结果表明,电子书包支持的体验学习模型确实有助于提高学生的认知体验、行为体验和情感体验的参与度。     

Catalytic activity of dispersed CuO phases towards nitrogen oxides (N2O, NO, and NO2)

A systematic reactivity study of N₂O, NO, and NO₂ on highly dispersed CuO phases over modified silica supports (SiO₂–Al₂O₃, SiO₂–TiO₂, and SiO₂–ZrO₂) has been performed. Different reaction paths for the nitrogen oxide species abatement were studied: from direct decomposition (N₂O) to selective reductions by hydrocarbons (N₂O, NO, and NO₂) and oxidation (NO to NO₂). The oxygen concentration, temperature, and contact time, were varied within suitable ranges in order to investigate the activity and in particular the selectivity in the different reactions studied. The support deeply influenced the catalytic properties of the active copper phase. The most acidic supports, SiO₂–Al₂O₃ and SiO₂–ZrO₂, led to a better activity and selectivity of CuO for the reactions of N₂O, NO, and NO₂ reductions and N₂O decomposition than SiO₂–TiO₂. The catalytic results are discussed in terms of actual turnover frequencies starting from the knowledge of the copper dispersion values.     

酯对钼系Ziegler-Natta催化剂引发丁二烯聚合的影响

以MoCl_4(Mo)为主催化剂,甲苯氧基二异丁基铝(Al)为助催化剂,在加氢汽油溶剂中,研究了8种酯对丁二烯(Bd)聚合的影响。结果表明,凡是能够溶解在酯中的Mo与Al所组成的二元催化体系,大多能很好地引发Bd聚合,并有较高的催化活性。酯的主要作用是增加Mo在加氢汽油中的溶解性,对聚合物的分子量影响不大,对微观结构几乎无影响。     

Obesity: Prevalence,Theories, Medical Consequences,Management, and Research Directions

Obesity and its associated disorders are a growing epidemic across the world. Many genetic, physiological, and behavioral factors play a role in the etiology of obesity. Diet and exercise are known to play a valuable role in the treatment and prevention of obesity and associated disorders such as hypertension, heart disease, and diabetes. Therefore, the purpose of this review is to examine the prevalence, etiology, consequences, and treatment of obesity.     

Influence of polymer molecular weight on selected thermodynamic properties of polymer/solvent systems and the application of the UNIFAC theory

The intrinsic viscosities of eleven narrow molecular weight distribution polystyrene samples ranging from number-average molecular weight 1820 to 1 292 000 have been determined in pure solvents of tetrahydrofuran and chloroform with a Ubbelohde No. 1 viscometer at 25°C. By combining the original and modified Fox-Flory viscosity treatments, respectively, with the Flory-Huggins Lattice theory, the interaction parameters were calculated. With the aid of original and modified UNIFAC methods the solvent activity, clustering function of the solvent, and the interaction parameter were computed and compared with the experimental data. It was established that the influence imposed by the polymer molecular weight on the activity of the solvent, the clustering function of solvent, and interaction parameter is insignificant. The modified UNIFAC method satisfactorily predicted the solvent activity as illustrated by previous investigators. However, both UNIFAC methods failed to predict the interaction parameter.     

The significance of defect chemistry for the rate of gas–solid reactions: three examples

Three examples are revisited in which the reaction rate could be reliably correlated with point defect chemistry highlighting the role of point defects as acid–base active centers. In the case of dehydrohalogenation of tertiary butyl chloride, AgCl becomes increasingly active as heterogeneous catalyst, if AgCl is homogeneously or heterogeneously doped. By such a procedure the silver vacancy concentration is adequately increased. The oxygen incorporation into SrTiO₃ offers an example in which the surface mechanism in terms of adsorbed species, oxygen vacancies and electronic centers has been elucidated. Appropriate surface coatings give rise to significant catalytic effects. Increasing iron (acceptor) doping not only changes the point defect chemistry but also the nature of the rate determining step. Lastly, the electrocatalytic function of Sr-doped LaMnO₃ is considered as regards oxygen reduction reaction and O²⁻ incorporation into Y-doped ZrO₂ in the context of solid oxide fuel cells. Again the defect chemistry is of prime importance for the reaction rate.     

Synthesis,characterization, and antitumor activity of poly(maleic anhydride‐co‐vinyl acetate‐co‐acrylic acid)

The ternary copolymerization of maleic anhydride (MA), vinyl acetate (VA), and acrylic acid (AA) [P(MA‐co‐VA‐co‐AA)], which is considered to be an acceptor–donor–acceptor system, was carried out in 1,4‐dioxane with benzoyl peroxide as an initiator at 70°C under a nitrogen atmosphere. Constants of complex formation for the monomer systems in the study were determined by UV–visible (hydrogen‐bonding complex) and ¹H‐NMR (charge transfer complex) methods, respectively. The results show that polymerization of the P(MA‐co‐VA‐co‐AA) system proceeds by an alternating terpolymerization mechanism. It is shown that the synthesized copolymers have typical polyelectrolyte behavior, ability for reversible hydrolysis–anhydrization reactions, and semicrystalline structures. In these cases, including radical polymerization, and formation of semicrystalline structures, the hydrogen‐bonding effect plays a significant role. The in vitro cytotoxicities of the synthesized terpolymer and alternating copolymer were evaluated using Raji cells (human Burkitt lymphoma cell line). The antitumor activities of prepared anion‐active copolymers were studied using methyl–thiazol–tetrazolium colorimetric assay and 50% of the cytotoxic dose of each copolymer and terpolymer were calculated. Hydrolyzed P(MA‐co‐VA‐co‐AA) and P(MA‐alt‐AA) copolymers have sufficiently high antitumor activity, which depends on the amount of hydrogen‐bonding carboxylic groups and their regular distribution in the side chain of functional macromolecules. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3425–3432, 2006     

Observations on the estimation of scavenging activity of phenolic compounds using rapid 1,1-diphenyl-2-picrylhydrazyl (DPPH<Superscript>•</Superscript>) tests

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.     

Optimization of the sputter-deposited platinum cathode for a direct methanol fuel cell

The electrodes prepared by a sputtering method were evaluated as the cathodes for direct methanol fuel cells (DMFCs). Pt loading below 0.25 mg cm⁻² achieved higher mass activities than that of 0.5 mg cm⁻² prepared by the paste method, which was general conventional method. However, an increase in Pt loading reduced the catalyst activity for the oxygen reduction reaction (ORR). This result may suggest an increase in only electrochemically inactive Pt. Pt utilization efficiency can be found about ten times higher at Pt loading of 0.04 mg cm⁻². Moreover, addition of Nafion to sputter-deposited Pt cathodes is found possible to improve the catalyst activity for the ORR, but the excess Nafion over the optimum condition reduces the active sites.     

Oil and fat hydrolysis with lipase fromAspergillus sp.

Hydrolysis of olive oil, soybean oil, mink fat, lard, palm oil, coconut oil, and a hydrogenated, hardened oil with lipase from anAspergillus sp. has been studied. The lipase had high specific activity (60,000 U/g) and did not show any positional specificity. The lipase proved to be a more effective catalyst than Lipolase fromA. oryzae, with an optimal activity at 37°C and pH 6.5–7.0. It was activated by Ca²⁺ but inactivated by organic solvents such as isopropanol and propanone. All substrates examined could be hydrolyzed to corresponding fatty acids with this enzyme at concentrations of 5–30 U/meq with yields of 90–99% in 2–24 h. The degree of hydrolysis was almost logarithmically linear with reaction time and occurred in two stages. The lipase was stable and could be repeatedly recycled for hydrolysis.