试用导数法判断曲线的对称性

利用函数的奇偶性和导数的有关概念,推导了几个用导数的方法判断函数图象对称性的结论,并通过实例验证了这些结论对判断一般曲线的对称性是方便可行的.     

金融深化与区域创新效率——基于跨国面板数据的分析

创新是引领发展的第一动力,是牵动经济社会发展全局的"牛鼻子",区域创新效率用创新的投入产出比衡量了一个地区的综合创新绩效,其影响因素存在多个方面。金融深化是衡量金融发展水平的重要指标。为研究各国金融深化与区域创新效率之间相互影响及其内在作用机制,作者首先借鉴多投入与多产出的DEA方法测算了80个国家的区域创新效率,然后使用Tobit模型对2011—2018年80个跨国面板数据进行实证分析。研究发现:金融深化与区域创新效率之间存在显著的"U"型曲线关系,即随着金融深化的提升,其对区域创新效率的影响将从"抑制"效应向"促进"效应转变。这是因为金融深化较低时,风险贷款和信用贷款发展滞后、风险投资渠道不完善以及金融结构和金融市场不健全导致多层次、立体化企业融资融券功能落后,从而抑制企业的创新效率。而金融深化较高时,风险投资渠道逐步完善、企业融资成本低、金融市场和金融结构完善,从而促进企业创新效率。研究还发现,各国经济水平的不同也会导致各国金融深化和区域创新效率有显著差异。作者将国家按照经济发展水平分为发达组和欠发达组,分组研究发现,金融深化对区域创新效率具有选择效应,即金融深化对欠发达国家创新效率具有"U"型曲线特征,而在发达组则不存在这种效应。原因在于:发达国家经济发展水平较高,金融结构和金融市场完善,风险投资渠道畅通无阻,金融深化提升区域创效率的影响不再呈现"抑制"效应。而在欠发达国家,经济发展水平较低,金融结构和金融市场发展水平正处于发展和完善的阶段。对于完善的金融市场和金融结构的部分,金融深化对区域创新效率的影响是"促进"效应,而对于不完善的部分,金融深化对区域创新效率的影响是"抑制"效应。为检验研究结果的稳健性,作者运用了滞后项检验、替代变量检验两种检验方法,检验结果具有稳健性,即随着金融深化的提升,其对区域创新效率的影响将从"抑制"效应向"促进"效应转变。因此,政府部门应该正确认识金融深化对区域创新效率的作用,完善创新体系,加强金融监管,防范化解金融风险,兼顾长期利益和短期利益,发挥金融深化对区域创新和经济增长的促进作用,推动金融体系更好适应新时代创新需求,以此来促进区域创新效率的提升。文章的研究结论对利用金融深化提高创新效率的发展中国家有启示和借鉴意义。     

Quantitative risk assessment-epidemic curve prediction model for leafy green outbreak investigation

The objective of this study was to leverage quantitative risk assessment to investigate possible root cause(s) of foodborne illness outbreaks related to Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) infections in leafy greens in the United States. To this end, we developed the FDA leafy green quantitative risk assessment epidemic curve prediction model (FDA-LG QRA-EC) that simulated the lettuce supply chain. The model was used to predict the number of reported illnesses and the epidemic curve associated with lettuce contaminated with STEC O157 for a wide range of scenarios representing various contamination conditions and facility processing/sanitation practices. Model predictions were generated for fresh-cut and whole lettuce, quantifying the differing impacts of facility processing and home preparation on predicted illnesses. Our model revealed that the timespan (i.e., number of days with at least one reported illness) and the peak (i.e., day with the most predicted number of reported illnesses) of the epidemic curve of a STEC O157-lettuce outbreak were not strongly influenced by facility processing/sanitation practices and were indications of contamination pattern among incoming lettuce batches received by the facility or distribution center. Through comparisons with observed number of illnesses from recent STEC O157-lettuce outbreaks, the model identified contamination conditions on incoming lettuce heads that could result in an outbreak of similar size, which can be used to narrow down potential root cause hypotheses.     

毛涤混纺织物折皱回复性能的探讨

根据标准的折皱回复测试实验,提出分析毛涤混纺织物的折皱回复性能与混纺比关系的理论曲线.实践证明,曲线在一定的范围内对涤棉等混纺织物具有适用性.