密文策略属性加密中的撤销控制方案

在云环境下使用数据共享功能时，由于云环境的复杂性，需要对数据进行安全保护和访问控制，这就要求使用加密机制。基于密文策略属性的加密（CP-ABE）是当前广泛使用的加密机制，它可以根据用户的属性来设置访问权限，任何具有合格访问权限的用户都可以访问数据。然而云是一个动态环境，有时可能只允许具有访问权限用户中的一部分用户访问数据，这就需要用户权限的撤销机制。然而，在CP-ABE中，访问权撤销或用户撤销是一个冗长且代价高昂的事件。所提出方案根据对CP-ABE流程的改进，在原密文中嵌入了可灵活控制的用户个人秘密，使得用户权限撤销时既不要求使用新访问策略的用户撤销数据，也不要求对数据进行重新加密，大幅减少撤销时的计算成本。与知名CP-ABE撤销方案对比，所提出方案的计算成本更低且具有良好的安全性。     

Monolithiation of 5,5′‐Dibromo‐2,2′‐bithiophene Using Flow Microreactors: Mechanistic Implications and Synthetic Applications

The lithiation of 5,5′‐dibromo‐2,2′‐bithiophene with one equivalent of an alkyllithium such as n‐BuLi or s‐BuLi was studied by varying the residence time in flow microreactors. With a short residence time, the product 2,2′‐bithiophene (3) derived from dilithiation was obtained preferentially and a significant amount of the starting material 5,5′‐dibromo‐2,2′‐bithiophene remained unchanged. An increase in the residence time caused a higher yield of the product 5‐bromo‐2,2′‐bithiophene derived from monolithiation with expense in the yields of 2,2′‐bithiophene and 5,5′‐dibromo‐2,2′‐bithiophene. The lithiation using MeLi gave the product 5‐bromo‐2,2′‐bithiophene preferentially even with a very short residence time.     

Sustainable hydrogen roadmap: A holistic review and decision-making methodology for production,utilisation and exportation using Qatar as a case study

Hydrogen is seen as a promising and inevitable energy carrier in the transition towards a carbon-free energy era. This study reviews the potential for carbon-free hydrogen production, utilisation and exportation from the State of Qatar. The study aims to introduce a roadmap for current and future exploration of carbon-free hydrogen production and exportation from Qatar, for which an assessment of several available alternatives for the production of hydrogen in Qatar is performed. These alternatives include the use of natural gas as a feedstock for hydrogen production through steam methane reforming (SMR), solar integrated steam methane reforming with carbon capture, as well as the possibilities for hydrogen production from electrolysis using renewables and ammonia as another intermediate. The potential of each alternative is reviewed based on selected technical, economic and environmental criteria. The findings of this review study indicate that the production and exportation of blue ammonia currently present the best pathway for Qatar, while green hydrogen is expected to become as competitive as blue ammonia in the mid-future. It is widely accepted that as the technologies associated with clean hydrogen production improve, and the cost of renewable energy falls, green hydrogen will become quite competitive in the region.     

Evaluation of China's new energy vehicle policy texts with quantitative and qualitative analysis

As one of the strategic emerging industries, the new energy vehicle (NEV) industry receives strong support from the Chinese government. The Chinese government has formulated a large number of policies to promote the development of NEV industry. Evaluating and analyzing the NEV policies are of great significance for improving policy formulation. In this study, we comprehensively analyze 253 NEV policy texts by employing quantitative and qualitative methods. We present the policy instrument types and semantic structure characteristics of policy texts based on the content analysis. The advantages and disadvantages of policy texts are identified by using a quantitative evaluation model. Our results show that the most frequently used policy instrument is regulatory, and the main policy objective is the demand-pull. The policies with higher scores are more comprehensive. Three suggestions are put forward to improve NEV policies.     

Popularity of patent commercialization policies: Iran as a case

Commercialization of technologies has attracted increasing attention over the past years due to its role in improving national competitiveness. Iran has not been an exception as the country's policy-makers have been actively engaged in crafting national policies to facilitate and promote commercialization of technologies. The popularity of the existing policies in this field, however, has not been properly researched. Our research, by following a survey study methodology, aims for the first time to address this gap. The study looks at popularity of governmental policies aimed at supporting commercialization of patented technologies in Iran, based on the careful study of 10 cases of successfully commercialized patented technologies in Iran. Our results indicate that the commercialization process of the studied patented technologies was very much affected by some company/technology-specific characteristics. The study shows that the two policy measures with the highest perceived popularity were the financial supports and the services offered by incubation centers. Our results also show that some of the existing supportive policy measures did not serve the intended purposes and some other measures need to be fine-tuned, as far as the studied cases are concerned, such as frequently held invention and innovation exhibitions and the government-supported media coverage.     

The effect of economic policy uncertainty on stock-commodity correlations and its implications on optimal hedging

Motivated by previous studies documenting significant return and volatility effects of economic policy uncertainty (EPU) on the stock market, this study examines whether EPU has an effect on the dynamic conditional correlations between stock and commodity returns. Our findings point to a positive and significant effect of EPU on stock-commodity correlations with particularly stronger effects in the case of energy and industrial metals. The EPU effect is stronger during weak economic conditions, while VIX as a proxy of market uncertainty is generally found to be insignificant. Finally, we show that the EPU effect on correlations has investment implications as well, implied by a significant effect on optimal hedge ratios in commodities in order to mitigate stock market risks. Our results underscore the importance of selective hedging strategies in which risk managers base the timing and size of their hedging programs on future price expectations, conditional on the level of policy uncertainty state and prevalent economic conditions.     

The foundations of a policy for the use of social robots in care

Should we deploy social robots in care settings? This question, asked from a policy standpoint, requires that we understand the potential benefits and downsides of deploying social robots in care situations. Potential benefits could include increased efficiency, increased welfare, physiological and psychological benefits, and experienced satisfaction. There are, however, important objections to the use of social robots in care. These include the possibility that relations with robots can potentially displace human contact, that these relations could be harmful, that robot care is undignified and disrespectful, and that social robots are deceptive. I propose a framework for evaluating all these arguments in terms of three aspects of care: structure, process, and outcome. I then highlight the main ethical considerations that have to be made in order to untangle the web of pros and cons of social robots in care as these pros and cons are related the trade-offs regarding quantity and quality of care, process and outcome, and objective and subjective outcomes.     

法西斯政权下的意大利公共住房政策和建设实践

本文讨论了在墨索里尼集权统治下意大利公共住房政策的演变,以及米兰的公共住房建设实践的特点,提出国家住房政策往往会受多方面因素影响。     

兼容二元:中国县镇乡发展的基本判断与路径选择

新型城镇化的国家战略对于县、镇、乡是一次新的发展机遇。通过更大数量和更基层的县城、镇等的发展,将城市资本与数量众多的县、镇、乡的土地、劳动力等资源集合起来,能够进一步生产和扩大市场,维持社会稳定。结合城乡关系过程的政治经济分析和历史讨论,作者提出县镇乡"兼容二元"的发展路径。但县、镇、乡的发展不仅仅与市场有关,它们的发展也不仅仅是被整合入全球经济生产链的问题。它们的开放或内生性发展对于地方的文化发展、大地景观、生活方式与价值理念、环境状况等都将有巨大影响,这仍然需要进一步讨论。     

Challenges for technology diffusion policy to achieve socio-economic goals

The aim of this contribution is to analyze the challenges for technology diffusion policies to achieve expected socio-economic goals and to deduce conclusions for an adequate policy design. Based on hypotheses from theoretical contributions, we review two rather distinct technology fields. One is biobased products, the other health technologies with bioethanol and magnetic resonance imaging respectively as case studies in order to derive rather general insights regarding those policies. The case studies highlight the difficulties in achieving the aimed societal goals by promoting technology diffusion. The dominant innovation design (e.g. techniques or resources used) which diffuses or its application fields (e.g. indication, patient characteristics) differ from those assumed in impact assessments and side-effects which occur in other markets. The direct linkage of policy measures to societal criteria may avoid some of those undesired developments but may have side effects of their own, such as trade distortions or shifting the environmental burden to other activities. However, there is considerable scope for improvement in policy design compared to the status-quo. Overall, a more balanced policy mix regarding various socio-economic goals is vital and unintended side effects have to be considered more in decision making.