Spatial variation in soil inorganic nitrogen across an arid urban ecosystem

We explored variations in inorganic soil nitrogen (N) concentrations across metropolitan Phoenix, Arizona, and the surrounding desert using a probability-based synoptic survey. Data were examined using spatial statistics on the entire region, as well as for the desert and urban sites separately. Concentrations of both NO₃-N and NH₄-N were markedly higher and more heterogeneous amongst urban compared to desert soils. Regional variation in soil NO₃-N concentration was best explained by latitude, land use history, population density, along with percent cover of impervious surfaces and lawn, whereas soil NH₄-N concentrations were related to only latitude and population density. Within the urban area, patterns in both soil NO₃-N and NH₄-N were best predicted by elevation, population density and type of irrigation in the surrounding neighborhood. Spatial autocorrelation of soil NO₃-N concentrations explained 49% of variation among desert sites but was absent between urban sites. We suggest that inorganic soil N concentrations are controlled by a number of ‘local’ or ‘neighborhood’ human-related drivers in the city, rather than factors related to an urban-rural gradient.     

弯曲液面的附加压强

本文主要从球形液面内、外的压强差和任意弯曲液面内、外的压强差两个方面推导 了弯曲液面的附加压强公式。     

Household debt and financial assets: evidence from Germany, Great Britain and the USA

Summary.  We explore the determinants of debt, financial assets and net worth at the household level by using survey data for Germany, Great Britain and the USA. To identify which households are potentially vulnerable to adverse changes in the economic environment, we also explore the determinants of a range of measures of financial pressure: the probability that a household has negative net worth; the debt-to-income ratio; mortgage income gearing; the saving-to-income ratio. Our empirical findings suggest that the poorest and the youngest households are the most vulnerable to adverse changes in their financial circumstances.     

我国中小企业面临的压力与对策

随着经济全球化的进一步发展,中国市场与国际市场逐渐融为一体,我国的中小企业将遇到更加激烈的竞争。我们必须抓住机遇,利用当前出现的国内外有利条件,制订应对挑战的策略,使中小企业在新环境里不断发展。     

高压微波催化合成肉桂酸甲酯

在硫酸铁铵的催化下 ,利用高压微波技术 ,快速合成了肉桂酸甲酯。最佳反应条件为 :甲醇和肉桂酸的摩尔比为 5 :1,催化剂用量为 2 .0g ,微波时间为 3min ,微波功率为 72 9W ,产率达93.8%。     

基于需求不确定性的供应链库存控制研究

通过建立需求不确定性环境下供应链成员的独立存货成本模型,运用模拟退火法对该模型进行52周的仿真,求解存货最佳订购数量与最佳再订购点,从而比较出不同存货控制策略的供应链存货总成本及订单满足率的差异。     

冠状动脉收缩期受压持续到舒张期的模拟实验分析

利用研制的心肌桥模拟装置,对冠状动脉受压迫状态建立了圆形收缩的实验模型,进行了冠状动脉受心肌桥压迫持续到舒张期情况下的血压和流量模拟实验.实验研究表明,冠状动脉面积收缩接近到原来的20%时,远段收缩压迅速与近段收缩压分离;当冠状动脉面积收缩到小于原来的20%时,近段收缩压迅速上升,远段压力从不稳定状态迅速过渡到收缩压呈反向分布状态.心率和近段血压范围不变时,流量随着收缩程度的增加而增加.     

国际基督教工会联合会与早期欧洲一体化

第二次世界大战后 ,作为欧洲压力集团之一的基督教工会通过其国际组织———国际基督教工会联合会 ,以个人活动和参与欧洲机构正式协商机制的方式 ,试图在欧洲早期一体化进程中维护基督教工会和工人的权利及利益。该组织的活动虽然取得了一定成就 ,但从总体上讲 ,其对欧洲经济政治一体化的影响仍然十分有限     

基于Poisson分布需求的两级零售系统最优订货策略

考虑由一个分销中心和N个零售商组成的两级分销库存系统．假设两级库存补充均采取周期订货策略，在每个零售商处的客户需求是随机的，且服从Poisson分布．当给定的某一货物缺货时，顾客愿意等待特别订货的概率是一确定的常数，在满足给定的客户服务水平的条件下，寻求该供应链总费用的最小化．对库存费用的计算进行了精确的推导，并且得到了最优的订货策略．最后给出了一个算例，根据所得到的公式由电子表格获得了两级最优库存水平．     

网络密度、高管注意力配置与企业绿色创新:制度压力的调节作用

本文整合社会网络理论、注意力基础观和新制度主义理论等,通过对282家制造企业的问卷调查,采用多元回归分析方法,探讨了网络密度和高管注意力配置的交互匹配对企业绿色创新的影响机制,以及制度压力在其中的调节作用。研究发现,在高密度网络中,高管采用注意力聚集策略对绿色创新有显著正向影响;而在低密度网络中,高管采用注意力分散策略对绿色创新有显著正向影响。规制压力和模仿压力均正向调节网络密度和高管注意力配置的交互作用对绿色创新的影响,但模仿压力的调节作用更强。通过构建不同制度压力情景下网络密度与高管注意力的交互作用对绿色创新影响的理论框架,本文推动社会网络理论、注意力基础观等成熟的理论成果从一般创新向绿色创新研究领域繁衍,为企业绿色创新加入与主流理论的对话做了努力,为企业在绿色创新过程中根据不同的制度压力,以及所嵌入的组织间网络密度情况,选择合适的注意力配置策略提供理论参考。