科创中国

以脂肪酶N435催化合成了PHS基脂肪族聚酯,研究了反应条件、溶剂及第三单体的引入对聚酯相对分子质量(Mn)的影响.结果表明:反应24 h后产物的Mn较高,Mw/Mn较小;反应温度为80℃时产物的Mn最高;N435以5%用量为最佳;适当增加二苯醚的用量有利于反应进行;丙三醇的加入可生成具有支化结构的聚酯,少量丙三醇、ε-CL和短链二醇的添加可提高聚酯的Mn,CHDM的空间结构不会影响酶催化聚合反应活性.

It is a common phenomenon that the cracks originating from a hole can cause structural damage in engineering.However,the fracture mechanics studies of hole edge crack problems are not sufficient.The problem of an elliptical hole with two collinear edge cracks of unequal length in an infinite plate under uniform tension at infinity is investigated.Based on the complex variable method,the analytical solutions of stress functions and stress intensity factors are provided.The stress distribution along the axes and the edge of the elliptical hole is given graphically.The numerical results show that there is obvious stress concentration near the hole and cracks,and the stresses tend to applied loads at distances far from the defect,which conform to Saint-Venant's principle.Hence,the stress functions are proved to be right.Under special conditions,the present configuration becomes the Griffith crack,two symmetrical cracks emanating from an elliptical hole,two cracks of unequal length emanating from a circular hole,a crack at the edge of a circular hole,or a crack emanating from an elliptical hole.Compared with available results,stress intensity factors for these special shapes of ellipses and cracks show good coincidence.The stress intensity factor for two cracks of unequal length at the edge of an elliptical hole increases with the crack length and the major-to-minor axis ratio of the elliptical hole.The stress distribution in an infinite plate containing an elliptic hole with unsymmetrical cracks is given for the first time.

通过对三相异步电机功率因数控制器的工作原理分析,找出双向晶闸管的输出电压与其可控角之间的关系,提出了将功率因数控制器对晶闸管控制角控制计算转换为对时间控制的新控制算法.分析触发时间与输出电压之间的关系及触发方法,电机负载、功率因数与节能之间的关系,提出了功率因数控制器控制算法的两种控制方案,给出了控制算法程序框图,使单片机的软件设计实施方案更加方便.

The idle time which is part of the order fulfillment time is decided by the number of items in the zone; therefore the item assignment method affects the picking efficiency. Whereas previous studies only focus on the balance of number of kinds of items between different zones but not the number of items and the idle time in each zone. In this paper, an idle factor is proposed to measure the idle time exactly. The idle factor is proven to obey the same vary trend with the idle time, so the object of this problem can be simplified from minimizing idle time to minimizing idle factor. Based on this, the model of item assignment problem in synchronized zone automated order picking system is built. The model is a form of relaxation of parallel machine scheduling problem which had been proven to be NP-complete. To solve the model, a taboo search algorithm is proposed. The main idea of the algorithm is minimizing the greatest idle factor of zones with the 2-exchange algorithm. Finally, the simulation which applies the data collected from a tobacco distribution center is conducted to evaluate the performance of the algorithm. The result verifies the model and shows the algorithm can do a steady work to reduce idle time and the idle time can be reduced by 45.63% on average. This research proposed an approach to measure the idle time in synchronized zone automated order picking system. The approach can improve the picking efficiency significantly and can be seen as theoretical basis when optimizing the synchronized automated order picking systems.

目的表皮干细胞是组织工程化皮肤的"种子细胞".文中研究碱性成纤维细胞生长因子(basic fibroblast growth factor,bFGF)、胰岛素样细胞生长因子-1(insulin-like growth factor-1,IGF-1)和转化生长因子仅(transforming growth factor a,TGFa)对人表皮干细胞增殖的影响.方法采用两步酶消化法和Ⅳ型胶原差速贴壁相结合的方法获得人原代表皮干细胞,将表皮干细胞分为A组(K-SFM)、B组(K-SFM+bFGF)、C组(K-SFM+IGF-1)及D组(K-SFM+TGFot)进行培养.比较不同组之间表皮干细胞的克隆形成率、生长增殖、生长曲线和细胞周期等指标.结果B组、C组及D组培养的表皮干细胞在细胞增殖、细胞克隆率方面检测结果均明显高于A组(P〈0.05);流式细胞仪检测B组、C组与A组及D组处于G0/G1细胞比例比较差异有统计学意义(P〈0.05).结论IGF-1、bFGF及TGF-a均对表皮干细胞的增殖有促进作用,IGF-1及bFGF对表皮干细胞表型的维持有较好的作用.

通过梳理搜索算法中出现的各种特征因子,提出一种更全面的特征因子分类方法,按其自身特点将特征因子划分为6类,分别是文字内容特征、Web拓扑特征、主题分布特征、文档类型特征、统计特征和时效性特征,并描述各特征项对主题相关性的作用、综合运用各类特征的通用化链接优先级计算公式以及特征选取原则.

食品供应链由多个行为主体连接组成,其中食品生产企业是供应链众多行为主体中最为关键的因子.食品生产企业的质量安全关系到整个食品供应链乃至食品行业的安全及消费者的健康.以食品供应链中的生产企业为研究对象,探讨影响生产企业质量的风险因素构成,并提出对应的治理措施.

随着石家庄市城市规模的扩大,越来越多的城市水文环境问题日益突出.在分析石家庄市目前水文环境的基础上,提出城市面临的水文问题:城市化进程的加快,对降水量、地下水位、灾害性天气、地表水环境、地下水水质等一系列水文参数产生影响,根据石家庄城市水文的特点,探讨其变化规律并采取相应的解决对策,对城市经济发展有重要意义.

科研中经常遇到涉及两个因素的实验,若两因素有交互作用,则需采用析因设计、正交设计等设计类型,但这些设计通常需要进行较多次实验.若在理论和专业上可以证明,实验中涉及到的两个因素不存在交互作用,或交互作用对观测结果的影响无统计学意义,并且特定实验条件(通常为各因素不同水平的一种组合)下实验数据的测定误差在专业上允许的范围之内,则可采用无重复实验的随机区组设计、无重复实验的平衡不完全随机区组设计、具有一个重复测量的单因素设计、无重复实验双因素设计和两因素嵌套设计.本文结合实例,重点介绍后两种实验设计类型.

探讨生长分化因子-9(GDF-9)及其mRNA在高雄激素多囊卵巢综合征(PCOS)大鼠模型中的表达.方法:43只雌性sD大鼠随机分组,实验组大鼠皮下注射脱氢表雄酮建立PCOS动物模型;采用放射免疫法测定血清性激素水平,结合大鼠模型卵巢组织HE染色的病理结构改变进行模型验证;采用免疫组织化学法检测大鼠卵巢组织GDF-9表达及定位,蛋白印迹法进-步观察GDF-9表达变化;逆转录PCR法检测GDF-9mRNA表达.结果:血清性激素水平及HE染色病理结果均提示模型建立成功.免疫组织化学结果显示实验组卵泡中GDF-9表达增强,卵巢间质GDF-9表达下降,实验组和对照组间卵泡和间质灰度值差异均有统计学意义(P〈0.05).蛋白印迹检测及PCR结果提示实验组GDF-9蛋白表达下降,而GDF-9mRNA表达与对照组比较无差异.结论:GDF-9表达及分布改变可能是PCOS发生发展的重要原因.