基于改进价值当量因子的北京市生态-经济协调度实证分析

从城市生态经济系统协调的视角,构建生态系统服务价值和生态经济协调度指数测算模型框架。以北京市16个辖区为基本研究单元,基于修正后的当量因子法,利用北京市2009—2018年土地利用相关数据,对北京市辖区10年间的生态系统服务价值进行了动态估算,并分析了10年间生态-经济协调度的变动规律。研究结果表明:近10年人类活动或自然环境变化对未利用土地的影响最大,其次是建设用地、园地、耕地、水域及水利设施用地、草地、林地;生态系统服务总价值均呈现总体增长趋势,密云区、怀柔区、延庆区占比前三;大部分地区生态经济协调度总体上升为较高协调,局部生态经济协调度没有改善,整体生态经济协调度较好。并根据北京市的生态服务价值与土地利用动态变化特点,综合考虑生态-经济协调度发展等级分类等情况,提出北京市生态-经济协调发展及土地利用优化的对策和措施。     

Global warming: Efficient policies in the case of multiple pollutants

This article investigates efficient policies against global warming in the case of multiple greenhouse gases. In a dynamic optimization model conditions for an efficient combination of abatement activities are derived. It is shown how this solution can be decentralised by a system of emission charges. Since the determination of the charge rates should be based on a long time horizon, the impact of sequential planning methods is explored. The parameters of the model are specified with respect to the main greenhouse gases (carbon dioxide, methane, nitrous oxide, chlorofluorocarbons) and a scenario for an efficient charge system is calculated. For the main emission sources the tax base and the likely range of tax rates is derived. The results illustrate that efficient policy measures against global warming will not only affect the use of fossil fuels but will also impose a considerable burden on modern agriculture specialising in livestock and in intensive farming techniques.     

静载行星轮系误差对行星轮载荷分配的影响

本文以2K—H 型行星齿轮传动装置为研究对象,将太阳轮与行星轮、行星轮与内齿圈之间的啮合轮齿用相当轮齿啮合刚度的弹簧代替,引入了当量啮合误差的概念,分析了静载条件下各制造误差和装配误差对行星轮间载荷分配的影响,这将有助于行星齿轮传动装置的均载设计和动力学分析。     

齿轮径向和切向误差分析与精度设计

本文重点对齿轮制造误差中的径向和切向误差进行了较深入的分析,简要介绍了齿轮精度设计的一般原则。     

Does food aid have disincentive effects on local production? A general equilibrium perspective on food aid in Ethiopia

This paper examined impacts of food aid on domestic food production employing a computable general equilibrium modelling technique and using data from Ethiopia. The simulation experiments have shown that food aid has unambiguous disincentive effects on domestic food production. The removal of food aid caused a modest increase in food prices but this stimulated food production. Employment and income generation effects of the latter outweighed the adverse effect of the former. Consequently, the removal of food aid led to improvements in aggregate household welfare. Contrary to some concerns in the food aid literature that any reduction in food aid would hurt the poor, the simulation experiments suggested that actually poor rural households and urban wage earners are the ones who benefit most in absence of food aid but entrepreneurs are more likely to encounter a marginal welfare decline. We have distinguished between in-kind food aid and cash equivalent transfers in order to isolate the disincentives that in-kind transfers would make to domestic production from those that are related to household purchasing power problem. The expansionary effect of removing food aid becomes significantly larger when it is accompanied by cash equivalent payments because the latter would provide demand side stimulus to agriculture while the removal of in-kind transfers would stimulate supply side, with the supply and demand side effects reinforcing each other. In our modelling framework, the only adverse effect would be a modest deterioration in the external current account, because the expansionary effects of food aid would cause imports to rise but exports to fall.     

“Probability of risk aversion” and other applications of derivatives of the certainty equivalent

“Probability of risk” aversion is principally concerned with reactions to scaling up of probabilities of non-zero values of a non-positive random variable by a common factor. Decreasing probability-of-risk aversion is defined and shown to be equivalent to ordinary risk aversion. Implications of this for insurance are pointed out. The sort of scaling involved is the same as that involved in “self-protection,” and it is shown that, for any expenditure on self-protection, say x, a concave utility function will prefer a coinsurance policy, costing x, which leaves probabilities unchanged, but scales down loss amounts by the same proportion as probabilities are scaled under self-protection. Properties of several comparative concepts of decreasing risk aversion are established. Derivatives of the certainty equivalent (CE) are used to elucidate well-known comparative static results in models of expected utility maximization. Finally, the study proves that concavity of the CE implies convexity of the coefficient of absolute risk aversion and examines the role of curvature of the CE in exploring relationships between properties of risk vulnerability, properness, and standardness.

基于ANSYS Workbench叶轮叶片流固耦合分析

以离心泵叶轮为研究对象,设定不同的两种工况(120/160L/s),基于Navier-Stokes方程和SST k-ω湍流模型,构建两者的内流场模型,次而根据其受力建立叶轮叶片的静力平衡方程,设置边界条件,施加载荷,最后求解得出结果。在流场的数值模拟中,由于考虑到离心力及流场对叶片的表面压力的影响,将内流场网格连接CFX模组进行流场模拟。在结构场中,导入CFX计算得出的水压力数值,最后求解得到叶片在两个工况下的应力应变情况。分析结果表明,叶轮叶片都能在两种工况下正常的运行。     

How much could be saved in Chinese hospitals in procurement of anti-hypertensives and anti-diabetics?

Background: Efficient use of government funding has been increasingly relevant for the success and sustainability of ongoing health-system reform in China; however, as there is no generic substitution policy, patients and basic health-insurance programs pay more for public-preferred brand originators. Such phenomenon is especially typical in public hospitals. The objective of this study is to estimate the potential cost savings in procurement by Chinese public hospitals when switching from brand originators of anti-hypertensive and anti-diabetic medications to their generic equivalents between 2012–2014.

Method: IMS Health volume and value consumption data (IMS China Hospitals Audit system 2012–2014) were used, which covered all Chinese hospitals with 100 beds and above. The top 60% IMS volume consumption of respective anti-hypertensive and anti-diabetic medication with unique dosage form and strength were included. The potential cost savings were calculated from a switch of brand originators with their generic equivalents on the Chinese and international market. An independent sample t-test was conducted to compare the difference of proportion of cost savings in value between the Chinese and international market.

Results: An average of 44% (US$44 million) and 87% (US$90 million) and a total of US$1.4 and 2.8 billion (2014?US$) could be saved from a switch from originator brand anti-hypertensives and anti-diabetics to domestically and internationally available generic equivalents, respectively. The differences of cost savings (in proportion) between domestic and international market were statistically significant (α?=?0.005, p?=?0.003, p?=?0.002, p?=?0.000).

Conclusion: Expensive brand originators dominated the anti-hypertensive and anti-diabetic market in Chinese hospitals between 2012–2014. Preference of brand originators wastes a huge amount of health resources in China and these limited resources could have been used more efficiently. As one of the world’s key generic suppliers, if China wants to use its health resource more efficiently on medicines, comprehensive measures are needed to address both demand-side (consumers’ low trust in the quality of local generics) and supply-side barriers (health professionals’ preference of brand originators).     

NO-FREE-LUNCH EQUIVALENCES FOR EXPONENTIAL LÉVY MODELS UNDER CONVEX CONSTRAINTS ON INVESTMENT

We provide equivalence of numerous no-free-lunch type conditions for financial markets where the asset prices are modeled as exponential Lévy processes, under possible convex constraints in the use of investment strategies. The general message is the following: if any kind of free lunch exists in these models it has to be of the most egregious type, generating an increasing wealth. Furthermore, we connect the previous to the existence of the numéraire portfolio , both for its particular expositional clarity in exponential Lévy models and as a first step in obtaining analogues of the no-free-lunch equivalences in general semimartingale models, a task that is taken on in Karatzas and Kardaras (2007) .