科创中国

Published studies in regard to coupler systems have been mainly focused on the manufacturing process or coupler strength issues. With the ever increasing of tonnage and length of heavy haul trains, lateral in-train forces generated by longitudinal in-train forces and coupler rotations have become a more and more significant safety issue for heavy haul train operations. Derailments caused by excessive lateral in-train forces are frequently reported. This article studies two typical coupler systems used on heavy haul locomotives. Their structures and stabilizing mechanism are analyzed before the corresponding models are developed. Coupler systems models are featured by two distinct stabilizing mechanism models and draft gear models with hysteresis considered. A model set which consists of four locomotives and three coupler systems is developed to study the rotational behavior of different coupler systems and their implications for locomotive dynamics. Simulated results indicate that when the locomotives are equipped with the type B coupler system, locomotives can meet the dynamics standard on tangent tracks; while the dynamics performance on curved tracks is very poor. The maximum longitudinal in-train force for locomotives equipped with the type B coupler system is 2000 kN. Simulations revealed a distinct trend for the type A coupler system. Locomotive dynamics are poorer for the type A case when locomotives are running on tangent tracks, while the dynamics are better for the type A case when locomotives are running on curved tracks. Theoretical studies and simulations carried out in this article suggest that a combination of the two types of stabilizing mechanism can result in a good design which can significantly decrease the relevant derailments.

通过对三相异步电机功率因数控制器的工作原理分析,找出双向晶闸管的输出电压与其可控角之间的关系,提出了将功率因数控制器对晶闸管控制角控制计算转换为对时间控制的新控制算法.分析触发时间与输出电压之间的关系及触发方法,电机负载、功率因数与节能之间的关系,提出了功率因数控制器控制算法的两种控制方案,给出了控制算法程序框图,使单片机的软件设计实施方案更加方便.

The existing research on improving the hydraulic performance of centrifugal pumps mainly focuses on the design method and the parameter optimization.The traditional design method for centrifugal impellers relies more on experience of engineers that typically only satisfies the continuity equation of the fluid.In this study,on the basis of the direct and inverse iteration design method which simultaneously solves the continuity and motion equations of the fluid and shapes the blade geometry by controlling the wrap angle,three centrifugal pump impellers are designed by altering blade wrap angles while keeping other parameters constant.The three-dimensional flow fields in three centrifugal pumps are numerically simulated,and the simulation results illustrate that the blade with larger wrap angle has more powerful control ability on the flow pattern in impeller.The three pumps have nearly the same pressure distributions at the small flow rate,but the pressure gradient increase in the pump with the largest wrap angle is smoother than the other two pumps at the design and large flow rates.The pump head and efficiency are also influenced by the blade wrap angle.The highest head and efficiency are also observed for the largest angle.An experiment rig is designed and built to test the performance of the pump with the largest wrap angle.The test results show that the wide space of its efficiency area and the stability of its operation ensure the excellent performance of the design method and verify the numerical analysis.The analysis on influence of the blade wrap angle for centrifugal pump performance in this paper can be beneficial to the optimization design of the centrifugal pump.

目的 研究胎儿颜面部角度孕期发育规律,探讨测量胎儿颜面部角度在产前诊断小下颌畸形中的应用价值.方法 选择20~36孕周正常胎儿188例,应用经腹三维超声测量胎儿颜面部角度,采用SPSS 13.0软件分析颜面部角度正常值范围,Person相关系数(r)评估胎儿颜面部角度与孕周相关性;对比小下颌畸形胎儿颜面部角度与正常组差异.结果 20~36孕周正常胎儿颜面部角度与孕周无相关性,r=0.001,P=0.757.胎儿颜面部角度均值是62.37°,标准差为6.23°.颜面部角度小于49.9°诊断为小下颌畸形.6例小下颌畸形胎儿颜面部角度均小于49.9°.结论 应用三维超声检测胎儿颜面部角度,为产前诊断小下颌畸形提供一种客观定量的检测方法.

安氏Ⅱ类错胎是正畸临床中常见的错胎畸形,促进颞下颌关节(TMJ)和下颌骨的生长改建是正畸治疗追求的目标.许多学者针对逐步和一次最大程度前移下颌对矫治效果及TMJ改建的影响进行了大量的临床及实验研究.本文就此作一综述.

There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.

目的通过对安格尔Ⅱ类1分类错胎临界病例正畸前后的牙胎模型同行评估等级(PAR)指数分析,评估这类患儿拔牙与否的正畸治疗效果,为临床医师制定矫治计划提供参考.方法选择83例平均年龄(12.6±1.1)岁的安格尔Ⅱ类1分类错胎临界病例为研究对象,其中拔牙57例,非拔牙26例,应用PAR指数对其治疗前后的牙胎模型进行评分,比较拔牙组与非拔牙组矫治前后错胎的分值变化,进而评估两组正畸治疗的效果.结果安格尔Ⅱ类1分类错验临界病例不论拔牙与否,治疗后的加权PAR指数总分均较治疗前明显减小,加权PAR指数减少率均大于70%,且两组之间的加权PAR指数总分差异无统计学意义;治疗效果明显改善者为96.39%(80/83).结论安格尔Ⅱ类1分类错胎临界病例拔牙与否,均可在牙胎关系方面收到较好的治疗效果.