潜水环境噪声数据库设计与开发

随着人类水下活动和实验行为的增多,越来越多的应用需要借助水声探测技术和水声通信技术,而在潜水环境中,环境噪声是以上技术的重要制约因素。因而,了解相应海域的环境噪声特性并建立环境噪声数据库,将有助于该海域的航运、测绘、通信等水声技术的应用与发展。本文针对以上需求,提出一种噪声建模方法,并根据该方法设计和研究相应的潜水环境噪声数据库。实验证明本文提出的方法具有一定的可行性。     

黄土路堑边坡剥落病害发育规律研究

黄土边坡剥落病害威胁公路的安全,破坏公路边坡的生态环境。依据大量野外实际调查所获取的资料,对黄土地区黄土边坡剥落的分布特征及其特点进行了深入研究发现,黄土边坡剥落病害的发育与黄土边坡的极限坡率、边坡倾向、坡体黄土的粒度成分及含盐量、坡体土性及坡型相关。探讨了各因素对黄土边坡剥落病害发育的规律,研究结果可为黄土地区公路工程选线、勘察与设计提供依据。     

欧盟汽车商业化混合动力总成竞争力提升项目分析

欧盟开展汽车商业化混合动力总成竞争力提升,开发五辆示范车辆,包括乘用车、客车与卡车。相比2013年车辆,示范车辆的动力总成效率提高20%,重量和体积减少20%,成本增长控制在10%以内。     

动车组逻辑控制机箱热仿真及试验研究

针对动车组电气屏柜中逻辑控制机箱内继电器表面温度过高的问题,提出一种改善继电器表面温度的散热结构。通过仿真,分析了改进前后的逻辑控制机箱在全功率运行时继电器表面温度和逻辑控制机箱内腔温度的变化,并通过温升试验进行了验证。仿真和试验结果表明,散热结构对继电器表面温度和逻辑控制机箱内腔温度有一定的改善作用。     

圆弧形挡土墙整体土压力计算

针对计算挡土墙土压力时,因挡土墙转角处与长直墙的土压力不同,其转角处需用圆弧形挡土墙的土压力进行单独计算的问题.本研究提出将圆弧形挡土墙作为整体进行土压力计算的方法,基于库仑土压力理论和极限平衡理论,计算了挡土墙墙后滑动土体的破裂角,并用微积分计算沿墙身对称线上土压力的合力.同时考虑了墙背与墙后填土之间的摩擦力.研究结果表明:圆弧形挡土墙主动土压力及破裂角会随着墙土摩擦角的增大而减小.该计算方法可为挡土墙实际工程压力计算提供借鉴.     

浅谈当前施工企业财务管理

文中针对当前施工企业缺乏统筹预算体系、基础控制薄弱、考核制度不完善等问题,提出须树立员工收益最大化的新理念,建立完备的预算体系,人员、资金集中管理,实行责任成本管理,将集团贡献额和集团贡献产值比率两个新指标引入考核等一系列管理方式方法,以期提高企业经济运行质量,挖掘潜在经济效益。     

Asymmetric regular sampling SPWM method based on tangent-secant midpoint approximation applied to intermediate frequency inverter power supply北大核心CSCD

［Objective］In order to reduce the switching frequency of an intermediate frequency inverter power supply, ensure the quality of the output waveform and realize digitalization easily, a SPWM sampling method based on a tangent-secant midpoint approximation is proposed. ［Methods］It is proven by deduction that the quantitative relationship of the natural sampling method can be approximated, and a Matlab/Simulink simulation model is built. The algorithm is designed and applied to an intermediate frequency inverter device, and the correctness of the proposed method is verified in the two aspects of simulation and experiment. ［Results］The simulation results show that the total harmonic distortion (THD) of the output waveform based on the tangent-secant midpoint approximation method is 2.64%, lower than the 3.99% of the symmetrical regular sampling method. The waveform quality of the tangent-secant midpoint approximation method is obviously better than that of the symmetrical regular sampling method, as it not only reduces the switching frequency but also takes into account the requirements of THD. ［Conclusions］SPWM sampling based on tangent-secant midpoint approximation is applied to the intermediate frequency power supply and is able to effectively overcome the shortcomings of the low-quality output waveform and high switching frequency of the symmetrical regular sampling method. Both theoretical analysis and engineering practice verify the rationality and correctness of the proposed method, and it can be widely extended to the field of intermediate frequency power supply installation. © 2022 Journal of Clinical Hepatology. All rights reserved.