金属圆柱的瞬态电磁响应及宽带雷达截面的时域测量

采用实验性冲激雷达在实际空间中对导体圆柱进行了瞬态电磁脉冲响应测量,然后利用瞬态响应法由实测数据计算其宽带雷达截面和谐振频率。     

一种新型扭转振动压电陶瓷超声换能器

研究了一种新型扭转压电陶瓷超声换能器.基于机电类比原理,对切向极化的压电陶瓷薄圆环振子的扭转振动特性进行了研究,建立了其机电类比等效电路模型,从等效电路得出了环形振子的扭转振动频率方程的解析式及共振频率的计算公式.在此基础上,分析了换能器的共振与其几何尺寸间的关系;并利用有限元方法对压电陶瓷薄圆环扭转振动模态进行了分析.结果表明,在换能器压电陶瓷圆环内外半径比增大时,共振频率随之增大.     

Conditional Mutual Information‐Based Feature Selection Analyzing for Synergy and Redundancy

Battiti's mutual information feature selector (MIFS) and its variant algorithms are used for many classification applications. Since they ignore feature synergy, MIFS and its variants may cause a big bias when features are combined to cooperate together. Besides, MIFS and its variants estimate feature redundancy regardless of the corresponding classification task. In this paper, we propose an automated greedy feature selection algorithm called conditional mutual information‐based feature selection (CMIFS). Based on the link between interaction information and conditional mutual information, CMIFS takes account of both redundancy and synergy interactions of features and identifies discriminative features. In addition, CMIFS combines feature redundancy evaluation with classification tasks. It can decrease the probability of mistaking important features as redundant features in searching process. The experimental results show that CMIFS can achieve higher best‐classification‐accuracy than MIFS and its variants, with the same or less (nearly 50%) number of features.     

响应面法优化重组大肠杆菌全细胞合成D-苯基乳酸

研究利用重组大肠杆菌Escherichia coli BL21（DE3）/pET-28a-ldhD全细胞生物转化苯丙酮酸（phenylpyruvic acid,PPA）合成D-苯基乳酸（D-phenyllactic acid,D-PLA）的条件。通过Plackett-Burman试验设计,从影响细胞转化的6 种因素中筛选得出转化温度、底物浓度和磷酸钠缓冲液pH值对底物PPA摩尔转化率有显著影响;采用Box-Behnken试验设计和响应面优化,对该重组菌全细胞转化合成D-PLA的条件进行了优化。最佳分批转化条件：转化温度为38 ℃、底物浓度为42 mmol/L、磷酸钠缓冲液pH 7.0、菌体质量浓度20 g/L、葡萄糖质量浓度20 g/L。在该条件下反应0.5 h,底物摩尔转化率为65.32%。根据此最佳转化条件,经4 h的间歇补加底物转化获得D-PLA最终浓度为119 mmol/L（19.75 g/L）,生产率为4.94 g/（L·h）。