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简介：摘 要： 圆和椭圆是有关联的，椭圆具有圆的某些特性，比如特殊角 利用圆的这种特性，把椭圆周长公式推导出来，这个特性就是，不论圆的半径 R 是多少，当把四分之一的圆弧拉直后，它所对应的夹角 不变，因为这个特性适用于椭圆，所以椭圆的周长公式 L=4BC=4 就可以推导出来 。

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简介：AbstractObjective:To investigate the relationship between the concentration of L-carnitine in semen and sperm parameters and investigate the epigenetic profile in sperm cell after L-carnitine usage.Methods:From February 2017 to February 2018, 46 semen samples from asthenospermic males and 41 semen samples from healthy donors were acquired. Motility parameters were assessed using computer-assisted sperm analysis (CASA, n = 78) and the DNA fragmentation index (DFI) was evaluated through flow cytometry (n = 86), %DFI = % cells outside main population. Other oxidative stress markers, such as reactive oxygen species (ROS) levels (n = 86) and the mitochondria DNA copy numbers, were detected (n = 78). The concentration of L-carnitine and acetyl-L-carnitine was detected (n = 82), and methylation was analyzed (n = 30). After that, we collected 13 fresh semen samples from asthenospermic males and 23 fresh semen samples from healthy donors. These samples were used in a freeze-thaw model that was used to determine whether adding L-carnitine could change sperm progressive motility (n = 23), apoptosis index (n = 9), and methylation analysis (n = 7). In total, we have done 13 asthenospermia samples for Western blot, and except for the poor Western result, we analyzed 6 samples for H3K9ac detection, 7 samples for H3K9m3 and H3K27m3 detection, and immunofluorescence (n = 3). Finally, we had recruited 30 volunteers, and they were given oral administration of L-carnitine for 3 months and then collected semen samples at different time points for methylation analysis.Results:The concentration of acetyl-L-carnitine is negatively correlated with the %DFI value (r2 = 0.1090; P = 0.0026), and the concentration of acetyl-L-carnitine is positively correlated with sperm forward motility (r2 = 0.0543; P = 0.0458) and ROS (r2 = 0.1854; P < 0.0001), and the acetyl-L-carnitine level is negatively correlated with %DFI in asthenospermia (r2 = 0.1701; P = 0.0066), and the level of acetyl-L-carnitine in asthenospermic semen is significantly lower than the normal group (P = 0.0419). In addition, this study indicates that adding L-carnitine significantly improved sperm motility (P = 0.0325) and reduced sperm apoptosis (P = 0.0032). Importantly, Western blotting (P = 0.0429) and immunofluorescence staining results showed that the addition of L-carnitine reduced H3K9Me3 methylation level in sperm, respectively. Furthermore, semen samples from asthenospermic patients had reduced methylation levels in a specific region (16thP= 0.0003; 17thP= 0.0016) of the brain-derived neurotrophic factor (BDNF) promoter. The 16th methylation decreased with age (r2 = 0.1564; P = 0.0306), and the 17th methylation was decreased after treatment with L-carnitine for 28 days (P = 0.0341).Conclusion:L-carnitine can reduce the %DFI and also affect the methylation of the histone modification marker in sperm as a possible epigenetic regulator.

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简介：摘要：雨篷是设置在建筑物出入口上部用于遮雨的装置。本文分析了现有各种形式雨篷结构的受力性能和优缺点，创造性提出了一种全新的雨篷结构形式：L型雨篷刚架，克服了现有各种雨篷结构的缺点，并已成功的应用于实际工程中。

简介：【摘要】 梅钢 1780 热轧 L2 过程控制计算机系统是由上海宝信软件股份有限公司自主集成开发的， L2 过程控制计算机系统中的加热炉燃烧控制模型在计算板坯温度时需要使用到加热炉 DCS 系统中的一些数据，同时需要将模型计算的相关结果下发到 L1 加热炉 DCS 系统，这就需在 L2 过程控制计算机系统与 L1 加热炉 DCS 系统之间进行数据通讯。 本文 主要 介绍了 在上海宝信软件的 iPlature 平台下，利用其 iMultiLink 技术实现 L2 过程控制 计算机系统与 L1 加热炉 DCS 系统通讯的方法。

简介：摘要： 由于 GT063L2K1/032L2K1 型增压机机止推轴承 温度 值高 、 轴向位移超差 ， 严重威胁 增压机 安全运行 。文章主要介绍了该增压机的结构、技术参数，叙述了止推轴承温度 高、轴向位移超差 故障的分析过程、处理措施以及效果。

简介：摘要：自 L波段高空探测雷达广泛应用于气象观测业务以来，大幅提升了气象观测数据质量。但是， L波段雷达在实际运行中也会发生一些故障问题，影响观测业务的顺利开展。基于此，本文结合广西河池市气象局高空气象探测业务实际，重点对 L波段雷达常见故障进行分析，并给出了故障维修处理措施，提出了几点维护管理建议，以供同行参考。

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简介：摘要：本文根据北京市气象探测中心 L波段探空雷达运用实际，主要对 L波段气象探测雷达使用中常见故障问题进行分析，并给出相应解决办法，以供同行参考。

简介：摘要：从故障现象、原因分析以及解决方法三个

简介：摘要：在经济高速发展的大背景下，中国行业不断追求现代化和改革，建筑业也不断创新，以确保能够进一步提高建筑设计水平，加强建筑结构。其中，超高层建筑和高层建筑的连接结构引起了广大从业人员的兴趣，也吸引了大量企业或建筑师参与连体结构的设计和研发。本文主要分析了L型超高层建筑的结构设计。

简介：摘要:船舶副机飞车事故并非经常发生，如果是并入电网的副机发生飞车事故，极易造成全船失电和机损事故，对船舶安全航行影响很大。针对2019年某轮“