With Al2O3 and SiO2 as polishing medium, under different polishing conditions, e.g. with different polishing pressure, polishing time and polishing fluid, the influences of polishing treatment on the return loss of op...With Al2O3 and SiO2 as polishing medium, under different polishing conditions, e.g. with different polishing pressure, polishing time and polishing fluid, the influences of polishing treatment on the return loss of optical fiber connectors were investigated. The return loss of optical fiber connectors is 32CD*238dB before polishing. The results show that dry polishing（i.e. no polishing fluid） with Al2O3 has less influence on return loss of optical fiber connectors, while dry polishing with SiO2 reduces return loss to about 20dB because of the end-face of optical fiber contaminated. The wet polishing（i.e. using distilled water as polishing fluid） with Al2O3 or SiO2 can increase return loss to 45CD*250dB, but wet polishing with Al2O3 may produce optical fiber undercut depth of 80CD*2140nm. Wet polishing with SiO2 should be preferentially selected for optical fiber connectors and polishing time should be controlled within 20CD*230s.展开更多
【目的】明确不同培肥措施对麦玉轮作模式下作物产量、氮肥利用率及农田氮损失的影响,为土壤培肥提供科学依据。【方法】以中国麦玉轮作区为研究区域,在中国知网、Web of Science平台,搜集并筛选出64篇文献,提取其中的产量、氮素损失(...【目的】明确不同培肥措施对麦玉轮作模式下作物产量、氮肥利用率及农田氮损失的影响,为土壤培肥提供科学依据。【方法】以中国麦玉轮作区为研究区域,在中国知网、Web of Science平台,搜集并筛选出64篇文献,提取其中的产量、氮素损失(氨挥发、N2O排放、硝态氮淋溶)数据,采用整合分析(Metaanalysis)方法,对比分析常规单施化肥、常规化肥配合秸秆还田(秸秆还田)、有机肥替代部分化肥(有机替代)以及秸秆还田+有机替代4种施肥措施对作物产量、氮肥利用率以及农田氮损失的影响。【结果】常规单施化肥措施下,小麦和玉米产量均值分别为6.06和7.79 t/hm^(2),氮肥利用率分别为36.3%和34.2%;农田氮损失以淋溶和NH3挥发为主,且农田氮损失主要发生在玉米季,约占全年氮损失的57.7%。与常规单施化肥相比,秸秆还田显著提高小麦产量21.8%、玉米产量6.1%,但增加NH3挥发和N2O排放的风险。与常规单施化肥相比,有机替代显著降低了农田硝态氮淋失(小麦季39.6%、玉米季27.7%)和玉米季N2O排放(21.2%),但小麦产量存在较大波动,以20%~40%的替代比例增产效果最佳(3.6%)。与常规单施化肥相比,秸秆还田+有机替代小麦平均增产16.4%、玉米产量提高17.7%,玉米季硝态氮淋溶降低24.1%;与秸秆还田相比,秸秆还田+有机替代虽然显著提高了作物产量(小麦5.7%、玉米13.4%),但增加了玉米季N_(2)O排放(61.9%)。【结论】常规化肥措施下,秸秆还田、有机替代及秸秆还田+有机替代措施均能提高麦玉轮作体系的作物产量。不同措施的环境效应存在差异:秸秆还田虽能增产,但会导致农田氮排放量增加;有机替代措施具有较好的氮减排效果,但需合适的替代比例才能实现增产与减排的双重效益。值得注意的是,秸秆还田结合有机替代的增产效果最佳,但其农田氮减排效果相关研究较少,减排效果和机制尚不明确,有待进一步探究。展开更多
基于微带贴片天线在无线引信中的应用,设计了一种中心频率为7.2 GHz的同轴馈电圆形微带天线,该天线介质基片相对介电常数为εr=4.4,回波损耗小于-20 d B,天线增益大于5 d B。根据微带天线原理,通过HFSS软件设计的天线,实验结果表明:天...基于微带贴片天线在无线引信中的应用,设计了一种中心频率为7.2 GHz的同轴馈电圆形微带天线,该天线介质基片相对介电常数为εr=4.4,回波损耗小于-20 d B,天线增益大于5 d B。根据微带天线原理,通过HFSS软件设计的天线,实验结果表明:天线谐振频率、回波损耗等性能参数符合设计要求。展开更多
文摘With Al2O3 and SiO2 as polishing medium, under different polishing conditions, e.g. with different polishing pressure, polishing time and polishing fluid, the influences of polishing treatment on the return loss of optical fiber connectors were investigated. The return loss of optical fiber connectors is 32CD*238dB before polishing. The results show that dry polishing（i.e. no polishing fluid） with Al2O3 has less influence on return loss of optical fiber connectors, while dry polishing with SiO2 reduces return loss to about 20dB because of the end-face of optical fiber contaminated. The wet polishing（i.e. using distilled water as polishing fluid） with Al2O3 or SiO2 can increase return loss to 45CD*250dB, but wet polishing with Al2O3 may produce optical fiber undercut depth of 80CD*2140nm. Wet polishing with SiO2 should be preferentially selected for optical fiber connectors and polishing time should be controlled within 20CD*230s.
文摘【目的】明确不同培肥措施对麦玉轮作模式下作物产量、氮肥利用率及农田氮损失的影响,为土壤培肥提供科学依据。【方法】以中国麦玉轮作区为研究区域,在中国知网、Web of Science平台,搜集并筛选出64篇文献,提取其中的产量、氮素损失(氨挥发、N2O排放、硝态氮淋溶)数据,采用整合分析(Metaanalysis)方法,对比分析常规单施化肥、常规化肥配合秸秆还田(秸秆还田)、有机肥替代部分化肥(有机替代)以及秸秆还田+有机替代4种施肥措施对作物产量、氮肥利用率以及农田氮损失的影响。【结果】常规单施化肥措施下,小麦和玉米产量均值分别为6.06和7.79 t/hm^(2),氮肥利用率分别为36.3%和34.2%;农田氮损失以淋溶和NH3挥发为主,且农田氮损失主要发生在玉米季,约占全年氮损失的57.7%。与常规单施化肥相比,秸秆还田显著提高小麦产量21.8%、玉米产量6.1%,但增加NH3挥发和N2O排放的风险。与常规单施化肥相比,有机替代显著降低了农田硝态氮淋失(小麦季39.6%、玉米季27.7%)和玉米季N2O排放(21.2%),但小麦产量存在较大波动,以20%~40%的替代比例增产效果最佳(3.6%)。与常规单施化肥相比,秸秆还田+有机替代小麦平均增产16.4%、玉米产量提高17.7%,玉米季硝态氮淋溶降低24.1%;与秸秆还田相比,秸秆还田+有机替代虽然显著提高了作物产量(小麦5.7%、玉米13.4%),但增加了玉米季N_(2)O排放(61.9%)。【结论】常规化肥措施下,秸秆还田、有机替代及秸秆还田+有机替代措施均能提高麦玉轮作体系的作物产量。不同措施的环境效应存在差异:秸秆还田虽能增产,但会导致农田氮排放量增加;有机替代措施具有较好的氮减排效果,但需合适的替代比例才能实现增产与减排的双重效益。值得注意的是,秸秆还田结合有机替代的增产效果最佳,但其农田氮减排效果相关研究较少,减排效果和机制尚不明确,有待进一步探究。
