醇类选择性催化氧化的研究进展

醇类选择性氧化制备相应羰基（醛或酮）化合物是有机合成中的重要反应。综述醇类选择性催化氧化的研究现状,主要有液均相氧化、液多相氧化和水/有机两相催化氧化,对所用催化剂发展状况和反应机理分别进行阐述。均相催化氧化催化剂难于从反应体系分离,造成成本过高,而且污染环境。大部分多相催化剂来自均相催化剂的负载,活性中心分布不均匀,结构不明确,存在活性组分易从载体上脱落和流失的现象,导致催化剂活性下降。以水作溶剂,不仅清洁无污染,且产物和催化剂容易分离,催化剂可以循环使用,从经济和环保角度值得大力推广,但该体系价格昂贵,反应条件不够温和,还需进一步改进。因此,多相催化氧化和水/有机两相催化氧化相对于均相催化剂有更广阔的发展和应用空间,是今后的研究方向。     

Challenges and opportunities for productivity improvement studies in linear,repetitive, and location-based scheduling

Despite theoretical advancements in alternative project planning methods the extent of their practical implementation varies strongly; it has been limited especially in the US construction industry. The family of linear, repetitive, and location-based scheduling techniques holds significant but barely substantiated promise by containing multiple variables of interest for integrated analysis and optimization. Yet it is necessary to provide empirical evidence that using such techniques can improve productivity to increase credibility and acceptance by practitioners, because claims of conceptual superiority are only sporadically supported with detailed measures. An analysis is performed to identify relevant decision-making variables, extract challenges that currently limit the corpus of quantitative productivity studies on alternative scheduling to its insufficient size, and reveal opportunities to expand it in breadth and depth. Variables are categorized by their relevance to time, activity, resource and location, as well as the managerial approach. Challenges include the diverse definitions of productivity itself, issues related to achieving generalizability, and the detailed steps of data collection, preparation, and analysis. Opportunities include the guidance from existing but rare studies and well-established research methods such as case studies that can be applied. This is illustrated with a sample project of a high-rise apartment building in Brazil. If alternative methods can be proven to be measurably better for specific applications, there might be a paradigm shift from merely defaulting to traditional but problematic network-based scheduling toward consciously choosing the planning method based on its potential benefits for a project.     

关于风景园林施工与养护的研究

社会的快速前进使居民的生活水平有了显著地提高,居民对生活氛围的要求也在不断增加,风景园林的设计及保养水平在居民选择居住区中的重要性越来越高。绿地的设计和建造不仅能有效提高城市的氛围,更为创建生态型城市提供了物质条件。     

公平的多方并发签名方案

Tonien等在ISC2006上首次提出了多方并发签名体制,但Xie和谭指出Tonien等的方案并不满足公平性,进而分别重新构造了多方并发签名方案。分别对Xie和谭的多方并发签名方案进行了分析,指出他们的方案也不满足公平性,进而正式定义了公平多方并发签名的安全模型,并基于双线性对及多方密钥协商技术重新构造了一个多方并发签名方案。分析表明,在随机预言模型下,假设CDH问题是难解的,新方案同时满足正确性、不可伪造性、模糊性、并发性和公平性,并且与同类方案相比,新方案在签名长度、计算量、通信代价方面效率较高。     

Transport priorities,risk perception and worry associated with mode use and preferences among Norwegian commuters

There is currently scant research on the role of transport priorities, risk perception and worry for travel mode use and preferences. The present study aims to examine these factors in relation to mode use and preferences among Norwegian commuters. A web-based survey was conducted in a randomly obtained representative sample of daily commuters in the extended greater Oslo area (n = 690). The results showed that those who prioritized efficiency and flexibility tended to commute by car, while those who prioritized safety and comfort used public (e.g. metro, tram, and train) or active (e.g. walking and cycling) transport. In a free choice scenario, the respondents who prioritized flexibility reported a preference for using a car, whereas those who prioritized safety and comfort preferred public and active transport for their commuter travels. Risk perception of high impact events, such as terrorism and major accidents, as well as risk perception related to personal impact risks (theft, violence etc.) were related to car use on commuter travels. Transport-related worry exerted weak influences on mode use and preferences. Increased speed on rail transport and more frequent departures may be effective in reducing car use on commuter travels. Risk communication should focus on highlighting the low risk of experiencing security and safety issues in the public transport sector, and this message should be complemented by efforts to reduce the probability of negative events affecting public transport.     

The analysis of the current–voltage characteristics of the high barrier Au/Anthracene/n-Si MIS devices at low temperatures

The Au/Anthracene/n-Si/Al MIS device was fabricated on the basis of anthracene film covalently bonded to a Si substrate. The MIS device showed Schottky behavior with barrier heights of 0.85 eV and ideality factors of 1.88 at 300 K. The barrier height of the Au/n-Si has increased after deposition of the anthracene layer onto Si. Temperature dependent current–voltage (I–V) measurements were performed on the Au/Anthracene/n-Si/Al MIS diodes in the range 140–300 K. From the temperature dependence of forward bias I–V, the barrier height was observed to increase with temperature. However, the ideality factor decreased with increasing temperature. The values of activation energy (E_a) and Richardson constant (A*) were determined as 0.24 eV and 7.57 × 10⁻⁶ A cm⁻² K⁻² from the slope and the intercept at ordinate of the linear region of Richardson plot, respectively. The increase of the series resistance R_s with the fall of temperature was attributed to lack of free carrier concentration at low temperatures.     

Single and multilayered a-SiOx:H (x < 1) thin film samples analyzed by optical absorption and small-angle X-ray scattering

Hydrogenated amorphous silicon oxygen alloy thin films (a-SiO_x:H) were prepared on glass and crystalline silicon substrates, with two different oxygen contents: x = 0.15 and x = 0.32. The deposition was realized in an RF-PECVD reactor by using the plasma of the gas mixture SiH₄ and CO₂ with tunable flow rates. The optical characterization data of the single layers were received from the optical transmittance experiments. Multilayered samples were designed upon the results of the single layers. In depositing the multilayers the repetition of the a-SiO_0.15:H/a-SiO_0.32:H kernel-pair was used. The samples were prepared as 25-pair of λ/4 layers, 3-pair of λ/4 layers and 3-pair of λ/2 layers. The inner morphologies and nanostructural contents of the films were investigated by Small-Angle X-ray Scattering (SAXS) method.     

Permeability properties of concretes with high reactivity metakaolin and calcined impure kaolin

This study reports the findings of an experimental study carried out on transport properties of the concretes modified with different calcined non purified kaolins (CK) and commercially available high reactivity metakaolin (MK). CK used in this study were obtained by calcining impure ground kaolins from four different quarries located on kaolin beds of different morphological and geological formations in Turkey. However, commercially available MK produced by thermal treatment of high purity kaolin from Czech Republic was used as reference material. In concrete mix design, the cement was replaced with 5, 10, 15, and 20 % by weight of CK or MK. The gas permeability, water permeability, water sorptivity, and chloride permeability tests were performed at the end of 28 and 90 days of curing periods. The results indicated that the concretes incorporated with different types of calcined kaolins had comparable performance in permeability with MK modified concrete, depending mainly on the type and amount of the mineral admixture used. Moreover, all of the concretes incorporation MK or CK had considerably better permeability than plain concrete regardless of the replacement level.