In this paper, 3 mm 6061 aluminum alloy sheets were welded by laser MIG hybrid welding. Based on the experiment, the best welding parameters were determined to ensure the penetration welding. The detailed microstructu...In this paper, 3 mm 6061 aluminum alloy sheets were welded by laser MIG hybrid welding. Based on the experiment, the best welding parameters were determined to ensure the penetration welding. The detailed microstructure,tensile and fatigue fracture morphology and surface fatigue damage of the welded joints were analyzed by optical microscope(OM), scanning electron microscope(SEM) and energy dispersive spectrometer(EDS). The results show that there are two main kinds of precipitates, one is the long Si rich precipitates at the grain boundaries, the other is the intragranular Cu rich precipitates. The tensile test results show that the tensile strength of the joint is 224 MPa, which is only 70.2% of the base metal. Through the analysis of tensile fracture, there are great differences in the formation of tensile dimple. In the tensile-tensile fatigue test with a stress rate of 0.1, the conditional fatigue limits of base metal and welded joint are 101.9 MPa and 54.4 MPa, respectively. By comparing the fatigue fracture of the welded joints under different stress amplitudes, it was found that the main factor leading to the fracture of the joint is porosity. Through further analysis of the pore defects, it was found that there are transgranular and intergranular propagation ways of microcracks in the pores, and the mixed propagation way was also found.展开更多
A simple one-pot non-isocyanate route for synthesizing thermoplastic polyureas is presented. In situ urethanization was conducted from the ring-opening reaction of ethylene carbonate with poly(propylene glycol) bis(2-...A simple one-pot non-isocyanate route for synthesizing thermoplastic polyureas is presented. In situ urethanization was conducted from the ring-opening reaction of ethylene carbonate with poly(propylene glycol) bis(2-aminopropyl ether) and hexanediamine,m-xylylenediamine, or diethylene glycol bis(3-aminopropyl) ether at 100 °C for 6 h under normal pressure. Melt transurethane polycondensation was successively conducted at 170 °C under a reduced pressure of 399 Pa for different time periods. A series of nonisocyanate thermoplastic polyureas(NI-TPUreas) were prepared. The NI-TPUreas were characterized by gel permeation chromatography,FTIR, 1 H-NMR, differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray diffraction, atomic force microscopy,and tensile test. NI-TPUreas exhibited Mn of up to 1.67 × 104 g/mol, initial decomposition temperature over 290 °C, and tensile strength of up to 32 MPa. Several crystallizable NI-TPUreas exhibited Tm exceeding 98 °C. NI-TPUreas with good thermal and mechanical properties were prepared through a green and simple one-pot non-isocyanate route.展开更多
目的调查上海市浦东新区高东社区儿童青少年乙肝病毒感染现状及乙肝疫苗接种状况,为该社区的乙肝防控工作提供依据。方法 2016年3-4月,随机抽取高东社区幼儿园、小学及初级中学各1所,对每所学校每个年级抽取的1个班级中所有学生开展乙...目的调查上海市浦东新区高东社区儿童青少年乙肝病毒感染现状及乙肝疫苗接种状况,为该社区的乙肝防控工作提供依据。方法 2016年3-4月,随机抽取高东社区幼儿园、小学及初级中学各1所,对每所学校每个年级抽取的1个班级中所有学生开展乙肝病毒感染及乙肝疫苗接种相关问卷调查,同时采集静脉血进行乙肝血清指标及HBV DNA定量检测,分析该社区儿童青少年乙肝疫苗接种情况、乙肝病毒感染血清标志物分布情况及其影响因素。结果高东社区儿童青少年乙肝疫苗接种率95.50%(276/289),年龄组越小的儿童青少年乙肝疫苗接种率越高(P<0.01);10岁以下学生接种率高于≥10岁学生(P<0.01);HBsAg、HBcAb和HBsAb阳性率分别为1.04%(3/289)、1.38%(4/289)和32.18%(93/289);未接种乙肝疫苗及未全程接种者HBsAg和HBcAb阳性率均高于接种乙肝疫苗及全程接种者(P<0.05);女性HBcAb阳性率高于男性(P<0.05);≥10岁学生HBcAb阳性率高于3~<10岁学生(P<0.05);年龄组越大的儿童青少年HBsAb阳性率越低(P<0.01);HBsAb阳性学生抗体滴度水平分布以低水平(10 m IU/ml≤HBsAb<100 m IU/ml)为主(占81.33%,61/75),无年龄分布差异(P>0.05)。结论 2016年该社区儿童青少年的乙肝疫苗接种率高于95%,HBsAg、HBcAb阳性率较2012年上海市的调查结果下降明显。展开更多
为提高风电出力的预测精度,提出一种基于Bayes优化的长短期记忆人工神经网络(long-short term memory,LSTM)的预测模型。首先,利用经验模态分解对风电历史出力序列进行分解,并对各分量及原始数据分别提取8个统计特征量,与预测前6个时刻...为提高风电出力的预测精度,提出一种基于Bayes优化的长短期记忆人工神经网络(long-short term memory,LSTM)的预测模型。首先,利用经验模态分解对风电历史出力序列进行分解,并对各分量及原始数据分别提取8个统计特征量,与预测前6个时刻出力值共同组成预测特征集。然后,采用绳索算法(least absolute shrinkage and selection operator,LASSO)从预测特征集中提取具有统计意义的特征子集,作为预测模型的输入。最后,提出基于Bayes超参数寻优的LSTM网络优化方法,以提高预测精度。选取湖北某市风电出力历史数据进行预测实验,结果表明:相较于BP神经网络、SVM、RBF网络、GRNN网络等预测模型,所提模型预测精度较高,特征提取方法较为合理。展开更多
基金Project(51971129) supported by the National Natural Science Foundation of ChinaProject(19ZR1421200) supported by the Shanghai Natural Science Foundation,China。
文摘In this paper, 3 mm 6061 aluminum alloy sheets were welded by laser MIG hybrid welding. Based on the experiment, the best welding parameters were determined to ensure the penetration welding. The detailed microstructure,tensile and fatigue fracture morphology and surface fatigue damage of the welded joints were analyzed by optical microscope(OM), scanning electron microscope(SEM) and energy dispersive spectrometer(EDS). The results show that there are two main kinds of precipitates, one is the long Si rich precipitates at the grain boundaries, the other is the intragranular Cu rich precipitates. The tensile test results show that the tensile strength of the joint is 224 MPa, which is only 70.2% of the base metal. Through the analysis of tensile fracture, there are great differences in the formation of tensile dimple. In the tensile-tensile fatigue test with a stress rate of 0.1, the conditional fatigue limits of base metal and welded joint are 101.9 MPa and 54.4 MPa, respectively. By comparing the fatigue fracture of the welded joints under different stress amplitudes, it was found that the main factor leading to the fracture of the joint is porosity. Through further analysis of the pore defects, it was found that there are transgranular and intergranular propagation ways of microcracks in the pores, and the mixed propagation way was also found.
基金financially supported by the National Natural Science Foundation of China (No. 21244006)Beijing Natural Science Foundation (No. 2182056)
文摘A simple one-pot non-isocyanate route for synthesizing thermoplastic polyureas is presented. In situ urethanization was conducted from the ring-opening reaction of ethylene carbonate with poly(propylene glycol) bis(2-aminopropyl ether) and hexanediamine,m-xylylenediamine, or diethylene glycol bis(3-aminopropyl) ether at 100 °C for 6 h under normal pressure. Melt transurethane polycondensation was successively conducted at 170 °C under a reduced pressure of 399 Pa for different time periods. A series of nonisocyanate thermoplastic polyureas(NI-TPUreas) were prepared. The NI-TPUreas were characterized by gel permeation chromatography,FTIR, 1 H-NMR, differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray diffraction, atomic force microscopy,and tensile test. NI-TPUreas exhibited Mn of up to 1.67 × 104 g/mol, initial decomposition temperature over 290 °C, and tensile strength of up to 32 MPa. Several crystallizable NI-TPUreas exhibited Tm exceeding 98 °C. NI-TPUreas with good thermal and mechanical properties were prepared through a green and simple one-pot non-isocyanate route.
文摘目的调查上海市浦东新区高东社区儿童青少年乙肝病毒感染现状及乙肝疫苗接种状况,为该社区的乙肝防控工作提供依据。方法 2016年3-4月,随机抽取高东社区幼儿园、小学及初级中学各1所,对每所学校每个年级抽取的1个班级中所有学生开展乙肝病毒感染及乙肝疫苗接种相关问卷调查,同时采集静脉血进行乙肝血清指标及HBV DNA定量检测,分析该社区儿童青少年乙肝疫苗接种情况、乙肝病毒感染血清标志物分布情况及其影响因素。结果高东社区儿童青少年乙肝疫苗接种率95.50%(276/289),年龄组越小的儿童青少年乙肝疫苗接种率越高(P<0.01);10岁以下学生接种率高于≥10岁学生(P<0.01);HBsAg、HBcAb和HBsAb阳性率分别为1.04%(3/289)、1.38%(4/289)和32.18%(93/289);未接种乙肝疫苗及未全程接种者HBsAg和HBcAb阳性率均高于接种乙肝疫苗及全程接种者(P<0.05);女性HBcAb阳性率高于男性(P<0.05);≥10岁学生HBcAb阳性率高于3~<10岁学生(P<0.05);年龄组越大的儿童青少年HBsAb阳性率越低(P<0.01);HBsAb阳性学生抗体滴度水平分布以低水平(10 m IU/ml≤HBsAb<100 m IU/ml)为主(占81.33%,61/75),无年龄分布差异(P>0.05)。结论 2016年该社区儿童青少年的乙肝疫苗接种率高于95%,HBsAg、HBcAb阳性率较2012年上海市的调查结果下降明显。
文摘为提高风电出力的预测精度,提出一种基于Bayes优化的长短期记忆人工神经网络(long-short term memory,LSTM)的预测模型。首先,利用经验模态分解对风电历史出力序列进行分解,并对各分量及原始数据分别提取8个统计特征量,与预测前6个时刻出力值共同组成预测特征集。然后,采用绳索算法(least absolute shrinkage and selection operator,LASSO)从预测特征集中提取具有统计意义的特征子集,作为预测模型的输入。最后,提出基于Bayes超参数寻优的LSTM网络优化方法,以提高预测精度。选取湖北某市风电出力历史数据进行预测实验,结果表明:相较于BP神经网络、SVM、RBF网络、GRNN网络等预测模型,所提模型预测精度较高,特征提取方法较为合理。
