In order to reduce the noise and vibration of the diesel engine,it is crucial to exactly identify the engine noise source character.Based on "two-microphone" method,the sound intensity measurement of a vehic...In order to reduce the noise and vibration of the diesel engine,it is crucial to exactly identify the engine noise source character.Based on "two-microphone" method,the sound intensity measurement of a vehicle four-stroke diesel engine was carried out in a hemi-anechoic chamber.Then the sound intensity contour maps were obtained from the measurement results and the main noise components of different frequencies on all the measurement surfaces were picked out to construct contour maps.By analysizing the relationship between the characteristics of contour maps and the space distribution of the engine compartment,the major sources of the exterior radiation noise of the diesel engine were identified.The results provided a creditable basis for improving the noise performance of the engine in the next phase.展开更多
For anti-jamming and anti-countermeasure techniques of the sonar receiver, the response characteristics of the automatic gain control （AGC） circuit and the survivability of the prime circuit under strong interferenc...For anti-jamming and anti-countermeasure techniques of the sonar receiver, the response characteristics of the automatic gain control （AGC） circuit and the survivability of the prime circuit under strong interference are analyzed by simulations and experiments. An AGC simulation model based on the voltage control amplifier VCA810 prototype is proposed. Then static and dynamic simulations are realized with single frequency signal and linear frequency modulated （LFM） signal commonly used in the active sonar. Based on intense sound pulse （ISP） interference experiments, the real-time response characteristics of each module of the receiver are studied to verify the correctness of the model as well as the simulation results. Simulation and experiment results show that, under 252 dB/20 μs ISP interference, the specific sonar receiver will produce sustained cut top oscillation above 30 ms, which may affect the receiver and block the regular sonar signal.展开更多
目的检索并再评价声音对NICU早产儿生长发育影响的系统评价,为临床医务人员临床决策及早产儿健康干预策略的持续改进提供参考。方法计算机检索The Cochrane Library、Embase、PubMed、Web of Science、万方、中国知网、维普和中国生物...目的检索并再评价声音对NICU早产儿生长发育影响的系统评价,为临床医务人员临床决策及早产儿健康干预策略的持续改进提供参考。方法计算机检索The Cochrane Library、Embase、PubMed、Web of Science、万方、中国知网、维普和中国生物医学文献数据库,检索关于声音对NICU早产儿影响的系统评价/Meta分析/荟萃分析,检索时间为建库至2023年5月。2名研究人员应用AMSTAR对文献进行方法学质量评价后,通过GRADE进行证据整理与分级。结果初检文献405篇,最终纳入文献20篇,AMSTAR质量评价结果表明,高等质量文献有5篇,其余15篇均为中等质量,纳入文献的总体方法学质量较低。采用GRADE系统对20篇系统评价的79条结局指标的证据质量评价结果显示,12条证据为中等质量,34条证据为低等质量,33条证据为极低质量。结论声音干预有利于改善NICU早产儿的相关生理指标、睡眠效率、行为状态、神经行为及大脑发育,可促进早产儿健康恢复,但系统评价的方法学质量和证据的质量均较低,临床实践需谨慎采纳有关证据,并逐步进行更加规范、严谨的研究。展开更多
基金supported by programfor the Top Young Academic Leaders of Higher Learning Institutions of Shanxi(2009)Natural Science Foundation of Shanxi Province,China(No.2010011031-2)
文摘In order to reduce the noise and vibration of the diesel engine,it is crucial to exactly identify the engine noise source character.Based on "two-microphone" method,the sound intensity measurement of a vehicle four-stroke diesel engine was carried out in a hemi-anechoic chamber.Then the sound intensity contour maps were obtained from the measurement results and the main noise components of different frequencies on all the measurement surfaces were picked out to construct contour maps.By analysizing the relationship between the characteristics of contour maps and the space distribution of the engine compartment,the major sources of the exterior radiation noise of the diesel engine were identified.The results provided a creditable basis for improving the noise performance of the engine in the next phase.
基金supported by the National Natural Science Foundation of China (10974154)the National Innovation Project of China for Undergraduates (101069935)
文摘For anti-jamming and anti-countermeasure techniques of the sonar receiver, the response characteristics of the automatic gain control （AGC） circuit and the survivability of the prime circuit under strong interference are analyzed by simulations and experiments. An AGC simulation model based on the voltage control amplifier VCA810 prototype is proposed. Then static and dynamic simulations are realized with single frequency signal and linear frequency modulated （LFM） signal commonly used in the active sonar. Based on intense sound pulse （ISP） interference experiments, the real-time response characteristics of each module of the receiver are studied to verify the correctness of the model as well as the simulation results. Simulation and experiment results show that, under 252 dB/20 μs ISP interference, the specific sonar receiver will produce sustained cut top oscillation above 30 ms, which may affect the receiver and block the regular sonar signal.
文摘目的检索并再评价声音对NICU早产儿生长发育影响的系统评价,为临床医务人员临床决策及早产儿健康干预策略的持续改进提供参考。方法计算机检索The Cochrane Library、Embase、PubMed、Web of Science、万方、中国知网、维普和中国生物医学文献数据库,检索关于声音对NICU早产儿影响的系统评价/Meta分析/荟萃分析,检索时间为建库至2023年5月。2名研究人员应用AMSTAR对文献进行方法学质量评价后,通过GRADE进行证据整理与分级。结果初检文献405篇,最终纳入文献20篇,AMSTAR质量评价结果表明,高等质量文献有5篇,其余15篇均为中等质量,纳入文献的总体方法学质量较低。采用GRADE系统对20篇系统评价的79条结局指标的证据质量评价结果显示,12条证据为中等质量,34条证据为低等质量,33条证据为极低质量。结论声音干预有利于改善NICU早产儿的相关生理指标、睡眠效率、行为状态、神经行为及大脑发育,可促进早产儿健康恢复,但系统评价的方法学质量和证据的质量均较低,临床实践需谨慎采纳有关证据,并逐步进行更加规范、严谨的研究。
