《中国科学》编辑委员会

(以姓氏笔划为序)主编:周光召副主编:丁乃刚 白以龙 孙枢 吴祖泽 严陆光 杨乐 杨芙清 徐光宪 阎隆飞     

《中国科学》编辑委员会

(以姓氏笔划为序)主编:周光召副主编:丁乃刚 白以龙 孙枢 吴祖泽 严陆光 杨乐 杨芙清 徐光宪 阎隆飞     

《中国科学》编辑委员会

(以姓氏笔划为序)主编:周光召副主编:丁乃刚 白以龙 孙枢 吴祖泽 严陆光 杨乐 杨芙清 徐光宪 阎隆飞梁栋材委员:     

有机-无机纳米复合水凝胶*

本文综述了近年来有机-无机纳米复合水凝胶领域的研究进展。针对无机成分的不同种类及复合形式,本文将目前已见报道的有机-无机纳米复合水凝胶划分为三类,分别为层状硅酸盐纳米插层复合水凝胶、粘土交联纳米复合水凝胶和二氧化硅纳米杂化复合水凝胶。阐述了三类纳米复合水凝胶的发展趋势,特别就它们的合成方法进行了详细归纳与总结。在此基础上,介绍了纳米无机成分对复合水凝胶的性能增强机理,并就三者之间的增强差异进行了说明。     

《中国科学》编辑委员会

主 编:严东生副主编:丁乃刚 白以龙 孙枢 许孔时 庄巧生 吴文俊 吴阶平 邹承鲁 周光召徐光宪 涂光炽 高景德委 员:丁国瑜 马大猷 万哲先 于景元 王元 王之江 王世强 王永炎 王补宣王思敬 王梓坤 王绶琯 文圣常 方圻 史绍熙 母国光 石元春 石钟慈     

我对总结性复习的一些认识和体会

(一)对總结性复習的目的和意义的認識 中学化学教学大纲(草案)中指出“为使学生得到系統概念,巩固既得知識,大綱中在每学年終了都規定了复習时間(教师也可移用其中一部分时間作学期复習)。”“敌师决不能把规定的复習时間移作講授新课之用。”又指出“高中最后一学期的总复習,教师必須予以     

《中国科学》编辑委员会

主编:周光召副主编:丁乃刚 白以龙 孙枢 吴祖泽 严陆光 杨乐 杨芙清 徐光宪 阎隆飞梁栋材委员:丁同仁 丁国瑜 丁德文 于景元 马志明 马宗晋 王之江 王元 王世强王志新 王补宣 王思敬 王越 王梓坤 王淀佐 毛河光 文圣常 方世璧方守贤 方圻 石元春 石钟慈 卢佩章 卢强 叶大年 叶叔华 叶恒强     

LF-NMR和MRI对干制虾仁复水过程水分状态及品质变化的研究

采用低场核磁(LF-NMR)及其成像技术(MRI)研究干制虾仁在25℃复水过程中的水分含量、分布及状态变化,并通过线性回归分析不同复水时间干制虾仁的LF-NMR参数与质构特性及复水率的相关性。实验结果表明,干制虾仁复水过程中存在结合水、不可移动水和自由水3个组分峰,随着复水时间的增加,结合水无明显变化,而自由水、不易流动水含量增加,且自由度增加,流动性增大。LF-NMR参数(T_(22)、T_(23)、A_(22)、A_(23)和A_(Total))和硬度、咀嚼性、弹性、凝聚性以及复水率有极显著的相关性(R~2≥0.613),为干制虾仁复水过程中品质的快速无损预测提供了一种新方法。     

层状纳米纤维素膜/PVA复合水凝胶的制备与力学性能研究

采用叠层复合与物理相分离的方法制备了层状纳米细菌纤维素(BC)膜/聚乙烯醇( PVA)复合水凝胶.研究了聚乙烯醇的质量百分数、BC膜的复合层数以及制备条件对复合水凝胶力学性能的影响;通过扫描电镜( SEM)观察比较了复合水凝胶中BC膜层与PVA界面结合情况.结果表明,复合水凝胶的力学性能与PVA的质量百分数和BC膜含水...     

微波场中化学试剂复介电系数及其温度特性

利用微波腔体微扰法，在３．０ＧＨｚ频点测定了二十一种常用化学试剂的复介电系数及其中几种典型试剂复介电系数的温变特性，在此基础上分析了不同极性化学试剂复介电参数温变的一些规律及其与分子结构间的内在联系。     

新型农村养老保险对居民消费的影响评估

新型农村养老保险制度是一项面向农村的影响深远的重要民生工程。本文基于农业农村部每年对约350个县（村）2万户农户的固定观察数据,从居民消费的角度评估新农保政策的影响。研究发现,新农保政策对居民消费有显著的促进作用,参与新农保使居民消费支出提高4%,2009年折合户均消费可以增加700元,折算新农保项目财政支出带来的消费支出系数为1.86,远远高于平均的边际消费倾向0.36;新农保缴费额度每增加1倍,农户消费支出提高约5.9%。机制检验表明,收入效应和预期效应都会使新农保促进居民消费,而预期的影响尤其重要。此外,新农保政策对户主年龄较大的家庭、户主受教育程度较高的家庭、家庭收入相对较低的家庭的消费促进作用更强。本文的研究表明,新农保政策的实施不但有利于农村社会保障体系的完善,也有利于降低未来预期不确定性,提高农村居民消费水平。     

Dehydration of zinc hydroxide precipitate produced by neutralization of weakly concentrated zinc sulfate solutions with aqueous ammonia

Method for dehydration of zinc-containing products is suggested. The method makes lower the energy expenditure in filtration, drying, and calcination, diminishes the expenditure of reagents, and improves ecological characteristics of the process.     

Hypothalamic control of energy expenditure and thermogenesis

Energy expenditure and energy intake need to be balanced to maintain proper energy homeostasis. Energy homeostasis is tightly regulated by the central nervous system, and the hypothalamus is the primary center for the regulation of energy balance. The hypothalamus exerts its effect through both humoral and neuronal mechanisms, and each hypothalamic area has a distinct role in the regulation of energy expenditure. Recent studies have advanced the understanding of the molecular regulation of energy expenditure and thermogenesis in the hypothalamus with targeted manipulation techniques of the mouse genome and neuronal function. In this review, we elucidate recent progress in understanding the mechanism of how the hypothalamus affects basal metabolism, modulates physical activity, and adapts to environmental temperature and food intake changes.Subject terms: Molecular neuroscience, Endocrine system and metabolic diseases     

Optimised uncertainty at minimum overall cost to achieve fitness-for-purpose in food analysis.

An optimised uncertainty (OU) methodology is described, that balances the uncertainty of measurements on food against the cost of the measurements and the other expenditure that may arise as a consequence of the possible misclassification of the food. Measurement uncertainty from the sources of primary sampling and chemical analysis is estimated using an existing technique, which is based on the taking of duplicated samples and duplicated analyses. The input information required for the OU method is the actual costs of sampling and analysis, and the expected costs that could arise from either the 'false positive' or 'false negative' classification of batches of food. A loss function is then constructed that calculates the 'expectation of loss' which will arise for a given uncertainty of measurement. This function has a minimum value of cost at an optimal value of uncertainty, which can be estimated numerically. Application of this OU method to a case study on the determination of aflatoxin levels in pistachio nuts has demonstrated this minimum value. Below the optimum value of uncertainty, the costs increased due to higher measurement costs. Above the optimum value, the costs increased due to increasing probability of expenditure on consequences such as unnecessary rejection of the batch, potential litigation or loss of corporate reputation because of undetected contamination. A second stage of the OU method optimises the division of the expenditure on the measurement between that on sampling and that on analysis. The technique is demonstrated as a useful new approach for judging the fitness-for-purpose of chemical measurements in the food industry. Several areas for further development of the technique are identified. By matching the expenditure on the measurement against that caused by the misclassification of the food, the OU method has the potential to reduce overall expenditure whilst ensuring an appropriate reliability of measurement.     

现代国家治理下的国际税收竞争再思考

传统国际税收竞争理论的贡献在于揭示了税负差异对资本和劳动力的经济影响,但也存在着对商品税关注相对有限、缺乏对政府收入结构的考虑以及忽视经济运行所依附的政治机制等局限。在现代国家治理框架下,国际税收竞争不仅影响生产要素的流动和社会成员对税收依据的认识,约束政府对社会资源的控制,而且使社会成员对财政支出的合理性和公共资金的使用效率更为关注。面对国际税收竞争,中国有必要在降低所得税负担的同时统筹考虑商品税税率的调整,完善税收确立方式并提高税收的可观察性和财政支出的透明度,通过预算改革和财政体制的优化提高财政资金使用效率,避免非税收入的扩张弱化税制改革的减负效应。     

Foam Separation of Nickel and Copper Ions from Dilute Aqueous Solutions

The minimal expenditure of anionic surfactant, sodium dodecyl sulfate, required for decreasing concentrations of nickel and copper ions to the maximum permissible concentration was determined experimentally. A possibility of selective recovery of nickel ions by foam separation with sodium dodecyl sulfate under conditions of complex formation of copper cations with thiosulfate anions was studied.     

Potential and Current Distributions in Chlorine Diaphragm Electrolyzers with Gas Removal from the Back Side of External Electrodes and Possibility of Electrolysis Intensification

The cell voltage balance components of monopolar and bipolar electrolyzers were analyzed on the basis of calculations in terms of a mathematical model of the potential and current distributions along the cell height and tests of a laboratory electrolyzer of industrial height. Ways to diminish energy expenditure and to intensify diaphragm electrolysis of aqueous sodium chloride solutions were substantiated theoretically and experimentally.     

CO2 removal by PSA: an industrial view on opportunities and challenges

CO₂ removal from gaseous streams is one of the most important separation tasks in this decade. Adsorption processes can contribute in a wide range to this topic, thus an enormous effort is performed respectively in research and industry. In two scenarios the competitiveness of pressure swing adsorption (PSA) and vacuum pressure swing adsorption technology is assessed: Carbon capture from hydrogen production by steam methane reforming for enhanced oil recovery and CO₂ removal from direct reduction processes for iron making. Additionally, industrial requirements, project as well as operation driven, have to be considered. Robustness and stable operation is as important as optimized captial expenditure and operational expenditure. Considering economical and operational aspects PSA processes are the most attractive alternatives in the presented scenarios.     

Current trends in finite-time thermodynamics

The cornerstone of finite-time thermodynamics is all about the price of haste and how to minimize it. Reversible processes may be ultimately efficient, but they are unrealistically slow. In all situations-chemical, mechanical, economical-we pay extra to get the job done quickly. Finite-time thermodynamics can be used to develop methods to limit that extra expenditure, be it in energy, entropy production, money, or something entirely different. Finite-time thermodynamics also includes methods to calculate the optimal path or mode of operation to achieve this minimal expenditure. The concept is to place the system of interest in contact with a time-varying environment which will coax the system along the desired path, much like guiding a horse along by waving a carrot in front of it.     

Effect of Composition and Structure of Aqueous Monoethanolamine Solutions on Carbon Dioxide Sorption and Desorption in Purification of Gas Mixtures

Possibility of raising the efficiency of the monoethanolamine purification of gas mixtures to remove carbon dioxide is demonstrated with consideration for the real intermolecular interactions and the structuring in the absorbent solution. The composition and structure of individual aqueous monoethanolamine solutions with various concentrations and of the same solutions saturated with carbon dioxide were examined. The methods of viscometry and conductometry demonstrated that, at monoethanolamine concentrations exceeding 12 ± 2 wt %, micelles are formed on the background of the existence of associates with intermolecular hydrogen bonds. This necessitates use of high temperatures (120?140°C) in the stage of carbon dioxide desorption. It was found that using a 12 wt % aqueous solution of monoethanolamine in purification of gas mixtures makes it possible to lower the desorption temperature of carbon dioxide to 90°C. This process is more efficient than the standard technology of CO₂ removal from a 30 wt % monoethanolamine solution. This is so because, in addition to a lower expenditure of heat, the extraction of carbon dioxide grows by 16% at a simultaneous decrease in the absorbent expenditure by at least a factor of 2.5.