用FPGA实现异步串口与同步串口的转换

美国TI公司的TMS320C64xx系列DSP芯片的McBSP同步串口不具备与UART(通用异步收发器)异步串口直接通信的能力,为了解决这个问题,扩展DSP芯片的使用范围,文中介绍了一种新的用FPGA(现场可编程门阵列)来实现McBSP同步串口与UART异步串口之间相互转换的方法,通过必要的硬件连接和VHDL软件编程,实现了两种串口的转换,经测试,数据传输正确可靠。     

Estimation and Spatial-temporal Distribution Characteristics of PM2.5 Concentration by Remote Sensing in China in 2015

Air pollution characterized by PM2.5 pollutants poses severe challenges to the sustainable development of society and human health. Therefore, it is of great significance to clarify the spatial-temporal distribution and evolution of PM2.5 pollutants in China for regional joint prevention and control of PM2.5 pollutants. Based on the MODIS satellite aerosol products, meteorological basic data and PM2.5 pollutant monitoring site monitoring data, a geographically weighted regression model was established to simulate and estimate PM2.5 pollutant concentration in China in 2015 on the basis of aerosol and meteorological data pre-processing. In addition, the spatial distribution pattern, the seasonal evolution characteristics of PM2.5 pollutant concentration were analyzed. The results showed that: (1) the PM2.5 concentration values in China in 2015 as a whole showed obvious spatial zonal differentiation characteristics. The concentration of pollutants in the north is significantly higher than that in the south, and the areas with high PM2.5 concentrations are mainly concentrated in the Beijing-Tianjin-Hebei region, the Jianghuai plain, the Sichuan basin, and the Takaramalkan desert. The area has a wide spatial distribution and significant continuity; (2) The PM2.5 concentration in the fourth quarter showed obvious seasonal adaptive evolution characteristics. The PM2.5 concentration changed significantly in the season. PM2.5 pollution was the heaviest in the fourth quarter, followed by the first quarter of the third quarter and the lowest in the second quarter. The maximum occurred in the fourth quarter (165 μg/m³). The minimum appeared in the second quarter (4.3 μg/m³). Seasonal changes in PM2.5 concentrations were influenced by meteorological factors and human social activities; and (3) The accuracy of the inversion of PM2.5_{concentration by a multi-factorial, geographically weighted regression model was higher, with relative errors in the four quarters being 10.2%, 7.0%, 9.3%, and 8.6%, respectively.}     

漫湾水轮发电机转子磁极键装配出现的问题

本文针对漫湾水电站机组安装中，由于国家规范和厂家规程要求不明确，出现的对转子磁极键装配的不同认识和不合理施工方法，通过对机组各种状态下受力状况进行计算、分析，论述水轮发电机转子磁极键的装配要求及改进意见。     

深孔精加工中的自适应减振镗杆系统设计

针对深孔镗削精加工中高长径比镗杆存在较低的颤振稳定极限，导致容易发生颤振的问题，设计了一种自适应减振镗杆系统。通过调节O形环弹簧的轴向压缩，调谐附加质量阻尼减振器的固有频率，以最大化其动态刚度和适应大范围的长径比；利用电磁激振器和非接触式电容位移传感器自动测量镗杆的频响函数，并通过压缩O形环自适应调谐附加减振器的固有频率；最后，将镗杆频响函数的负实部最小化，以最大限度地提高无颤振切削深度。研究结果表明：安装减振器后镗杆频响函数的实部从-15.17μm/N缩小到-0.24μm/N,相当于动态刚度增大了63.2倍，且表面粗糙度得到明显改善。该系统能够覆盖相当宽的镗杆长径比范围，可适应各种实际安装需求。     

采用流场分析提高涡轮流量传感器性能的研究

以10 mm口径液体涡轮流量传感器为研究对象,经过对传感器内部流场进行分析,提出通过减小靠近叶片顶端的叶片受力面积,提高传感器测量性能的方法。从对特性曲线的分析出发,结合传感器数学模型,提出了一种利用不同流量点的仪表系数平方差Δ(K~2)评价传感器性能的方法。在此基础上,结合CFD仿真和传感器样机实验测试,研究了不同叶轮叶片形状参数对传感器性能的影响。实验结果表明:改变叶轮叶片形状能有效提高传感器的测量性能,切角参数为0.25时,传感器性能最优;此方法同样适用于其他口径涡轮流量传感器结构的优化。     

Critical stress of high‐density polyethylene during stress and photo‐oxidative aging

The long‐term photo‐oxidative aging behavior of high‐density polyethylene (HDPE) under different tensile stress was studied using a stress‐aging apparatus. The aging behavior was investigated through the methods of the surface morphology observation, gel content measurement, Fourier transform infrared spectroscopy, and creep behavior. It was found that stress has influence on the development of cracks and stress induces cracking through creep deformation. With increasing stress, the cracking time decreases in a reversed S‐shape curve way, and there is a critical stress near 7 MPa where the cracking time has a maximum decreasing rate. Meanwhile, the creep deformation increases rapidly when the stress exceeds the critical stress. The critical stress of HDPE is about 20–25% of breaking strength, and HDPE with low comonomer content has good dimensional stability when the stress is less than the critical stress, while HDPE with high comonomer content has a good performance when the stress exceeds the critical stress. This study may be useful for the rational selection of HDPE for the sheath material of bridge cable. POLYM. ENG. SCI., 55:2277–2284, 2015. © 2015 Society of Plastics Engineers     

桥梁工程实习教学改革探索

桥梁工程实习是土木工程专业实践性教学的重要内容之一,文章针对当前桥梁工程实习普遍存在的问题进行分析,并提出对策建议。根据教学过程的先后顺序,分析了桥梁工程认识实习、生产实习、毕业实习的各自特点以及学生的知识储备情况,从实习时间、实习内容、实习现场、实习管理等角度分析了实习存在的问题,剖析了问题存在的原因,提出了优选实习工点、建立实习基地、强化现场讲解、补充实习讲座、完善视频资源等系列改进措施。在近几年的实习实践中取得了良好的教学效果,可供同类实习教学参考。     

一种新型石英陶瓷辊的钢轴头联接技术

通过对多种瓷辊联接方式的对比,提出了一种新型的石英陶瓷辊的钢轴头联接技术,此种联接技术不仅可以提高瓷辊联接处的使用温度,从而扩展石英瓷辊的应用领域,还具有联接简单、可重复联接等特点。     

高反射光学薄膜的温度稳定性分析

利用高桥模型讨论了高反射光学薄膜的温度稳定性问题,理论上着重分析了高反射膜主反射光谱带边缘线性区域波长位置处反射率温度系数以及膜料和基底热物理参数对它的影响,得出该系数正比于膜料的热物理参数,而反比于基底的线性热膨胀系数.对于文中分析的样品,其温度稳定性受高折射率材料的折射率温度系数影响最大.     

磁通变换器的特性仿真及优化设计

利用三维有限元软件Maxwell对磁通变换器的静、动态特性进行仿真计算,并通过试验测量验证了仿真方法及结果的正确性。在此基础上分析了旁路、铁心工作点、线圈参数等因素对磁通变换器特性的影响,并综合各种因素进行了优化设计,达到了降低功耗、提高动作速度、减小体积的目的。