开展脉冲重复间隔(Pulse Repetition Interval,PRI)模式识别工作是电子支援系统的一项重要任务。现代复杂电磁环境下,受雷达辐射源部署和接收设备本身影响,雷达脉冲丢失率极高,导致分选后PRI序列调制规律被破坏,现有的PRI模式识别方法...开展脉冲重复间隔(Pulse Repetition Interval,PRI)模式识别工作是电子支援系统的一项重要任务。现代复杂电磁环境下,受雷达辐射源部署和接收设备本身影响,雷达脉冲丢失率极高,导致分选后PRI序列调制规律被破坏,现有的PRI模式识别方法准确率不足。针对上述问题,从PRI序列还原角度出发,并结合PRI序列本质是时序序列的特点,提出GAIN-LSTM(Generative Adversarial Imputation Nets and Long Short Term Memory)网络架构,其先对丢失脉冲位置进行补全操作,恢复PRI调制规律,然后对还原后PRI序列进行调制模式识别。仿真结果表明,提出的GAIN-LSTM网络架构在脉冲丢失率70%时仍保持95%的正确识别率。展开更多
目的探讨孕期膳食模式与增重过多(excessive gestational weight gain,eGWG)的关联。方法研究对象来自同济母婴健康队列(Tongji Maternal and Child Health Cohort,TMCHC),孕早期产检时纳入孕妇,测量身高、体重,问卷调查收集孕前体重及...目的探讨孕期膳食模式与增重过多(excessive gestational weight gain,eGWG)的关联。方法研究对象来自同济母婴健康队列(Tongji Maternal and Child Health Cohort,TMCHC),孕早期产检时纳入孕妇,测量身高、体重,问卷调查收集孕前体重及其它基本信息,定期随访称量体重,计算孕期总增重,并判定是否为eGWG;采用食物频率问卷(food frequency questionnaire,FFQ)进行膳食调查;用主成分分析法识别孕期膳食模式;Logistic回归估计膳食模式与eGWG风险的关联,计算比值比及95%可信区间(OR,95%CI);采用贝叶斯核机器回归(Bayesian Kernel Machine regression,BKMR)方法验证膳食模式与eGWG的关联。结果4815名孕妇中,3010名(62.5%)判定为eGWG;提取的5种主要膳食模式分别为“蔬菜类”“动物肉-米麦类”“蛋奶-坚果类”“大豆-鱼类”和“粗粮-水果-零食-菌藻类”;与得分最低四分位Q1相比,在“蔬菜类”模式中Q4组孕妇eGWG的OR为0.82(95%CI:0.68,0.99,P-trend=0.033),在“蛋奶-坚果类”模式中Q4组孕妇eGWG的OR为1.46(95%CI:1.21,1.75,P-trend<0.001);BKMR模型证实“蛋奶-坚果类”过多是eGWG的独立危险因素,在“蔬菜类”是独立保护因素,奶制品和坚果、特别是酸奶摄入过多,对eGWG起到重要作用;在“蔬菜类”饮食中,橙黄色蔬菜的保护作用最为显著。结论为避免eGWG,孕妇应遵循平衡膳食原则,适宜摄入坚果、酸奶等高能量密度食物,注意增加蔬菜的摄入量,尤其应增加橙黄色蔬菜的比例。展开更多
To evaluate the effects of maternal pre-pregnancy body mass index （pre-BMI） and gestational weight gain （GWG） on neonatal birth weight （NBW） in the population of Chinese healthy pregnant women, attempting to gui...To evaluate the effects of maternal pre-pregnancy body mass index （pre-BMI） and gestational weight gain （GWG） on neonatal birth weight （NBW） in the population of Chinese healthy pregnant women, attempting to guide weight control in pregnancy. A retrospective cohort study of 3772 Chinese women was conducted. The population was stratified by maternal pre-BMI categories as underweight （〈18.5 kg/m2）, normal weight （18.5-23.9 kg/m2）, overweight （24.0-27.9 kg/m2）, and obesity （〉28.0 kg/m2）. The NBW differences were tested among the four groups, and then deeper associations among maternal pre-BMI, GWG, and NBW were investigated by multivariate analysis. NBW increased significantly with the increase of maternal pre-BMI level （P〈0.05）, except overweight to obesity （P〉0.05）. The multivariate analysis showed that both pre-BMI and GWG were positively correlated with NBW （P〈0.05）. Compared with normal pre-BMI, underweight predicted an increased odds ratio of small-for-gestational-age （SGA） and decreased odds ratio for macrosomia and large-for-gestational-age （LGA）, and the results were opposite for overweight. With the increase of GWG, the risk of SGA decreased and the risks of macrosomia and LGA increased. In addition, in different pre-BMI categories, the effects of weight gain in the first trimester on NBW were different （P〈0.05）. NBW is positively affected by both maternal pre-BMI and GWG, extreme pre-BMI and GWG are both associated with increased risks of abnormal birth weight, and maternal pre-BMI may modify the effect of weight gain in each trimester on NBW. A valid GWG guideline for Chinese women is an urgent requirement, whereas existing recommendations seem to be not very suitable for the Chinese.展开更多
This paper demonstrates the analysis of antenna pattern and gain for different designs of full-wave dipole antenna feeding techniques. Seven such techniques were studied and analyzed;symmetrical dual feeding in phase,...This paper demonstrates the analysis of antenna pattern and gain for different designs of full-wave dipole antenna feeding techniques. Seven such techniques were studied and analyzed;symmetrical dual feeding in phase, symmetrical dual feeding out of phase, asymmetrical dual feeding in phase, asymmetrical dual feeding out of phase, symmetrical triple feeding in phase and symmetrical triple feeding out of phase. Symmetrical dual feeding in phase produced high gain as compared to the single and center-fed antennas. An improvement of about 3 to 3.5 dB was achieved comparing to center tap fed and off center fed. It was found that an asymmetrical dual feeding in-phase provides good performance, considering the directivity, pattern, and input impedance. A 2.46 dB gain has been attained. It was found that a symmetrical triple feeding provides an overall best performance with respect to gain, radiation pattern, beam width and input impedance.展开更多
如何快速而准确地评估天线阵面结构变形对电性能的影响是工程上亟需解决的关键问题。文中根据某大型相控阵天线设计了3种规格的阵列天线,按照典型的天线阵面碗状变形,分别采用HFSS数值计算方法和有源阵元方向图(Active Element Pattern,...如何快速而准确地评估天线阵面结构变形对电性能的影响是工程上亟需解决的关键问题。文中根据某大型相控阵天线设计了3种规格的阵列天线,按照典型的天线阵面碗状变形,分别采用HFSS数值计算方法和有源阵元方向图(Active Element Pattern, AEP)计算方法计算阵元Z向误差和指向误差对电性能的影响。结果表明:当Z向偏差小于λ/20(λ为波长)时,碗状变形对副瓣电平和波束宽度的影响显著,对增益影响较小;当Z向偏差增大到λ/20时,天线增益明显恶化;随着阵元规模的增大,得益于阵元互耦效应,碗状变形对电性能的影响减弱。AEP计算方法忽略了阵元方向图的差异性及互耦效应,导致其计算精度不如HFSS数值计算方法的计算精度高,特别是副瓣计算结果差异明显。该研究可为相控阵天线结构设计参数的确定提供指导。展开更多
文摘开展脉冲重复间隔(Pulse Repetition Interval,PRI)模式识别工作是电子支援系统的一项重要任务。现代复杂电磁环境下,受雷达辐射源部署和接收设备本身影响,雷达脉冲丢失率极高,导致分选后PRI序列调制规律被破坏,现有的PRI模式识别方法准确率不足。针对上述问题,从PRI序列还原角度出发,并结合PRI序列本质是时序序列的特点,提出GAIN-LSTM(Generative Adversarial Imputation Nets and Long Short Term Memory)网络架构,其先对丢失脉冲位置进行补全操作,恢复PRI调制规律,然后对还原后PRI序列进行调制模式识别。仿真结果表明,提出的GAIN-LSTM网络架构在脉冲丢失率70%时仍保持95%的正确识别率。
文摘目的探讨孕期膳食模式与增重过多(excessive gestational weight gain,eGWG)的关联。方法研究对象来自同济母婴健康队列(Tongji Maternal and Child Health Cohort,TMCHC),孕早期产检时纳入孕妇,测量身高、体重,问卷调查收集孕前体重及其它基本信息,定期随访称量体重,计算孕期总增重,并判定是否为eGWG;采用食物频率问卷(food frequency questionnaire,FFQ)进行膳食调查;用主成分分析法识别孕期膳食模式;Logistic回归估计膳食模式与eGWG风险的关联,计算比值比及95%可信区间(OR,95%CI);采用贝叶斯核机器回归(Bayesian Kernel Machine regression,BKMR)方法验证膳食模式与eGWG的关联。结果4815名孕妇中,3010名(62.5%)判定为eGWG;提取的5种主要膳食模式分别为“蔬菜类”“动物肉-米麦类”“蛋奶-坚果类”“大豆-鱼类”和“粗粮-水果-零食-菌藻类”;与得分最低四分位Q1相比,在“蔬菜类”模式中Q4组孕妇eGWG的OR为0.82(95%CI:0.68,0.99,P-trend=0.033),在“蛋奶-坚果类”模式中Q4组孕妇eGWG的OR为1.46(95%CI:1.21,1.75,P-trend<0.001);BKMR模型证实“蛋奶-坚果类”过多是eGWG的独立危险因素,在“蔬菜类”是独立保护因素,奶制品和坚果、特别是酸奶摄入过多,对eGWG起到重要作用;在“蔬菜类”饮食中,橙黄色蔬菜的保护作用最为显著。结论为避免eGWG,孕妇应遵循平衡膳食原则,适宜摄入坚果、酸奶等高能量密度食物,注意增加蔬菜的摄入量,尤其应增加橙黄色蔬菜的比例。
基金Project supported by the National Natural Science Foundation of China(Nos.81370725 and 81370726)the Natural Science Foundation of Zhejiang Province(No.LQ14H040004)the Key Discipline of Obstetrics of Zhejiang Province,China
文摘To evaluate the effects of maternal pre-pregnancy body mass index （pre-BMI） and gestational weight gain （GWG） on neonatal birth weight （NBW） in the population of Chinese healthy pregnant women, attempting to guide weight control in pregnancy. A retrospective cohort study of 3772 Chinese women was conducted. The population was stratified by maternal pre-BMI categories as underweight （〈18.5 kg/m2）, normal weight （18.5-23.9 kg/m2）, overweight （24.0-27.9 kg/m2）, and obesity （〉28.0 kg/m2）. The NBW differences were tested among the four groups, and then deeper associations among maternal pre-BMI, GWG, and NBW were investigated by multivariate analysis. NBW increased significantly with the increase of maternal pre-BMI level （P〈0.05）, except overweight to obesity （P〉0.05）. The multivariate analysis showed that both pre-BMI and GWG were positively correlated with NBW （P〈0.05）. Compared with normal pre-BMI, underweight predicted an increased odds ratio of small-for-gestational-age （SGA） and decreased odds ratio for macrosomia and large-for-gestational-age （LGA）, and the results were opposite for overweight. With the increase of GWG, the risk of SGA decreased and the risks of macrosomia and LGA increased. In addition, in different pre-BMI categories, the effects of weight gain in the first trimester on NBW were different （P〈0.05）. NBW is positively affected by both maternal pre-BMI and GWG, extreme pre-BMI and GWG are both associated with increased risks of abnormal birth weight, and maternal pre-BMI may modify the effect of weight gain in each trimester on NBW. A valid GWG guideline for Chinese women is an urgent requirement, whereas existing recommendations seem to be not very suitable for the Chinese.
文摘This paper demonstrates the analysis of antenna pattern and gain for different designs of full-wave dipole antenna feeding techniques. Seven such techniques were studied and analyzed;symmetrical dual feeding in phase, symmetrical dual feeding out of phase, asymmetrical dual feeding in phase, asymmetrical dual feeding out of phase, symmetrical triple feeding in phase and symmetrical triple feeding out of phase. Symmetrical dual feeding in phase produced high gain as compared to the single and center-fed antennas. An improvement of about 3 to 3.5 dB was achieved comparing to center tap fed and off center fed. It was found that an asymmetrical dual feeding in-phase provides good performance, considering the directivity, pattern, and input impedance. A 2.46 dB gain has been attained. It was found that a symmetrical triple feeding provides an overall best performance with respect to gain, radiation pattern, beam width and input impedance.
文摘如何快速而准确地评估天线阵面结构变形对电性能的影响是工程上亟需解决的关键问题。文中根据某大型相控阵天线设计了3种规格的阵列天线,按照典型的天线阵面碗状变形,分别采用HFSS数值计算方法和有源阵元方向图(Active Element Pattern, AEP)计算方法计算阵元Z向误差和指向误差对电性能的影响。结果表明:当Z向偏差小于λ/20(λ为波长)时,碗状变形对副瓣电平和波束宽度的影响显著,对增益影响较小;当Z向偏差增大到λ/20时,天线增益明显恶化;随着阵元规模的增大,得益于阵元互耦效应,碗状变形对电性能的影响减弱。AEP计算方法忽略了阵元方向图的差异性及互耦效应,导致其计算精度不如HFSS数值计算方法的计算精度高,特别是副瓣计算结果差异明显。该研究可为相控阵天线结构设计参数的确定提供指导。
