简介:仪表放大器是精密增益模块,广泛应用于许多工业、测量、数据采集和医疗应用。本文针对FX620仪表放大器芯片在高温下出现振荡现象,利用返回比分析方法对电路的增益裕度和相位裕度进行分析,最终通过仿真计算得到在出现故障的应用电路中常温相位裕度小于45°相位裕度标准,环路处于欠稳定状态。在温度发生变化时对运放的增益和相位产生了一定影响,导致出现了输出振荡现象。针对这一故障原因提出了增加输出端隔离电阻阻值的解决措施,完善了电路设计上的缺陷。改进后的环路相位裕度值增加使得环路稳定性增加,环路有足够的冗余来补偿温度变化带来的影响。
简介:1994年2月4日,日本成功地发射了第一枚H—Ⅱ运载火箭。这次发射成功预示着日本的宇航事业美好的发展前景。H—Ⅱ运载火箭将做为日本九十年代到下世纪初的主要空间运载系统。它最显著的技术特点主要体现在它的第一级发动机LE—7和第二级发动机LE—5A。这两种发动机均以液氢为燃料,液氧为氧化剂。独特的发动机设计特点,使得H—Ⅱ运载火箭跻身于世界航天技术行列中并成为其中的佼佼者。LE—7和LE—5A是以LE—5发动机的技术为基础发展起来的。LE—5发动机是完全依靠日本技术研制出的第一种低温发动机,并成功地应用在H—Ⅰ运载火箭的第二级上。本文着重介绍日本低温发动机研制的历史,展示这些发动机独特的设计以及研制中所遇到的技术问题。
简介:一、引言目前,河南省已经全面展开地籍调查工作,控制测量工作任务饱满,研究如何在保证地籍调查工作精度的情况下提高工作效率很有必要。随着GPS软、硬件的完善与发展,GPS技术已经基本上取代了常规测量方法建立各种类型和等级控制网。采用GPS布设一般等级控制网时,在每个测站上观测时间一般在1~2个小时,即使利用GPS进行一、二级导线测量,一般也要观测40分钟以上。如果采用快速静态定位方法,观测时间可以缩短到20分钟,生产效率大幅度提高。本文以邓州市D级网测量为例,利用静态(观测2小时)和快速静态(观测20分钟)定位观测两套数据,分别进行数据传输、数据处理、基线解算和网平差,然后对网平差报告进行比较,得出预定结论。具体介绍了快速静态定位特点、作业组织模式、快速静态作业技术要求、数据处理、网平差及精度检验。
简介:AbstractObjective:The prevalence of midline birth defects, such as gastroschisis, has increased worldwide, over the last few decades. This study aims to explore the prevalence, maternal epidemiological characteristics, and natural history of neonates affected by gastroschisis at the University Hospital of León city, Nicaragua.Methods:Data were collected from the birth defect surveillance system of the Hospital Oscar Danilo Rosales (HEODRA). The analysis included all pregnancies that had gastroschisis complications between January 1 and December 31, 2020. The prevalence of gastroschisis was calculated according to maternal age. The mothers were interviewed, and the clinical records of the newborns were reviewed.Results:Among the 4,460 deliveries included in this study, four cases of gastroschisis were identified, including three live births and one stillbirth. The gastroschisis rate was 8.9 per 10,000 live births (95% confidence interval [CI]: 0.18-17.8). The prevalence among mothers younger than 20 years and those older than 20 years was 26.4 (95% CI: -3.43 to 56.25) and 3.01 (95% CI: 2.89-8.90)/10,000 births, respectively. Mothers of gastroschisis-affected fetuses were of rural origin (n = 3), had normal body mass indexes (n = 3), were exposed to tobacco and wood smoke (n = 2), and one was exposed to pesticides during the periconceptional period. Primary closure of the gastroschisis was performed on one patient, and complex gastroschisis for intestinal perforation was observed in another patient. The mean hospitalization duration was 33 days, and two patients were discharged alive.Conclusions:Gastroschisis was a significant birth defect among children delivered at HEODRA in 2020. Its prevalence in Nicaragua was higher than that in other countries in the region. All complicated pregnancies were young women with unplanned pregnancies, from rural areas, with exposure to secondhand smoke, and without vitamin supplements before or during the first trimester of pregnancy. Only 67% of infants survived after hospital discharge.