催化光度法测定伊文思蓝褪色反应速率常数——推荐一个物理化学新实验

介绍了一个关于复杂反应动力学测量的物理化学实验。基于亚硝酸钠作用下溴酸钾氧化伊文思蓝褪色反应,通过测量不同初始反应条件下系统吸光度随时间的变化情况,推导伊文思蓝和溴酸钾的分级数,探讨亚硝酸钠对反应的加速作用,并根据不同温度下的测量数据计算表观反应活化能。本实验可依据学时安排开设为基础性实验或综合设计性实验。两个学期的教学实践表明,作为综合设计性实验,本实验可加强学生对表观速率常数、表观活化能以及催化作用的认识,并促进学生综合实验能力的培养;此外,本实验也可适当精简后作为基础性实验项目“丙酮碘化反应”的替代方案,能克服该实验中存在的反应速率较快不易记录实验数据、碘不易清洗污染比色皿等问题。

Research on the Brand Construction of Agritourism Enterprise in Chongqing

Agritourism is a modern agricultural model,which is combination of agriculture and rural tourism. Its goal is to carry on the culture of farming and achieve economic efficiency. To achieve this goal,brand building is very important. However,most companies have the same goods and services in the development process. Managers lack brand awareness,and enterprises lack core competitiveness. To solve these problems,the agritourism enterprises must change their management concepts,establish brand awareness,improve quality of service,increase the cultural connotation of products and services,and strengthen marketing efforts to achieve the overall improvement of modern agricultural brand.

犬前肢鳞状上皮癌1例

报告一例犬前肢鳞状上皮癌病例。患病动物为5岁雄性欧第犬。发现右前肢肘关节下有凸起肿块,渐进性生长,持续半年有余。手术切除肿块后固定送检,常规H&E染色后,组织学检查发现肿块内有大量肿瘤细胞成分,癌巢大小不一,形态不规则,具有复层鳞状上皮的层次结构,其中心已形成角化珠。诊断为鳞状上皮癌。

Research on the Longitudinal Transmission Mechanism of Prices for Urban Vegetable Supply Chain-Based on the Empirical Research in Chongqing

This paper mainly introduces the longitudinal transmission mechanism of urban vegetable prices in Chongqing area. On the basis of the supply chain theory,the " farm price- wholesale price- retail price" of vegetables in Chongqing has been identified as the research object. Through statistical analysis,it is found that the above three types of price show a modest annual fluctuation of 7- 12% from 2008 to2013. Later,the paper focuses on the empirical research on the weekly price data in 2013 applying the co-integration theory,which reveals that the farm price of vegetables is largely influenced by themselves; the wholesale price of vegetables is mainly affected by their own price,the production price and the retail price of the earlier stage without the current influence of the production price; and the retail price of vegetables is also affected by their own price,but is not affected by the their current local price and the wholesale price. Vegetable prices have shown an obvious positive transmission mechanism in the links from production to retail,but the feedback effect of retail on production is not brought into play.

Tailoring properties of hybrid perovskites by domain-width engineering with charged walls

Charged ferroelectric domain walls are fascinating electrical topological defects that can exhibit unusual properties.Here,in the search for novel phenomena,we perform and analyze first-principles calculations to investigate the effect of domain width on properties of domains with charged walls in the photovoltaic material consisting of methylammonium lead iodide hybrid perovskite.We report that such domains are stable and have rather low domain wall energy for any investigated width(that is,up to 13 lattice constants).Increasing the domain width first linearly decreases the electronic band gap from≃1.4 eV to about zero(which therefore provides an efficient band-gap engineering),before the system undergoes an insulator-to-metal transition and then remains metallic(with both the tail-to-tail and head-to-head domain walls being conductive)for the largest widths.All these results can be understood in terms of:(i)components of polarization along the normal of the domain walls being small in magnitude;(ii)an internal electric field that is basically independent of the domain width;and(iii)rather negligible charge transfer between walls.These findings deepen the knowledge of charged ferroelectric domain walls and can further broaden their potential for applications,particularly in the context of halide perovskites for photovoltaics.

Effects of temperature on conversion of Li2CO3 to LiOH in Ca（OH）2 suspension

The effects of temperature on the convecsion of Li2 CO3 Co LiOH in a Ca（OH）2 suspension were investigated. Li2CO3 microplates were used as the Li source. The results showed that Li2CO3 was converted to LiOH via in situ ion-exchange and dissolution-precipitation routes. The formation of mixed CaxLiz-2xCO3 inter- mediate species confirmed that at 25℃ need/e-like CaCO3 was formed heterogeneously on the Li2CO3 surface via in situ ion-exchange. At 60-100℃, isolated CaCO3 agglomerates were formed homogeneously via dissolution-precipitation. Temperature increases accelerated the dissolution and conversion of Li2 CO3 to LiOH, producing solutions with high [CO32-1][Ca^2＋] ratios; this favored homogeneous precipitation of isolated CaCO3 agglomerates,

Displacement Current in Domain Walls of Bismuth Ferrite

In 1861,Maxwell conceived the idea of the displacement current,which then made laws of electrodynamics more complete and also resulted in the realization of devices exploiting such displacement current.Interestingly,it is presently unknown if such displacement current can result in large intrinsic ac current in ferroic systems possessing domains,despite the flurry of recent activities that have been devoted to domains and their corresponding conductivity in these compounds.Here,we report firstprinciples-based atomistic simulations that predict that the transverse(polarization-related)displacement currents of 71°and 109°domains in the prototypical BiFeO_(3) multiferroic material are significant at the walls of such domains and in the GHz regime,and,in fact,result in currents that are at least of the same order of magnitude than previously reported dc currents(that are likely extrinsic in nature and due to electrons).Such large,localized and intrinsic ac currents are found to originate from low-frequency vibrations at the domain walls,and may open the door to the design of novel devices functioning in the GHz or THz range and in which currents would be confined within the domain wall.