旋转圆板冲击现象的实验研究

在研究法向冲击速度对圆板碰撞恢复系数影响的基础上,应用高速摄像系统对伴有旋转速度圆板的冲击行为进行了实验研究,分析了不同法向冲击速度下旋转角速度对碰撞恢复系数的影响.通过确定变形量系数与旋转角速度的相关性,应用数值解析方法得出了不同法向冲击速度及旋转角速度下的碰撞恢复系数,得到了旋转角速度与碰撞恢复系数的相互关系.结果表明,数值计算结果与实验结果具有良好的一致性.     

Real-time rapid prediction of variations of Earth’s rotational rate

Real-time rapid prediction of variations of the Earth＇s rotational rate is of great scientific and practical importance. However, due to the complicated time-variable characteristics of variations of the Earth＇s rotational rate （i.e., length of day, LOD）, it is usually difficult to obtain satisfactory predictions by con- ventional linear time series analysis methods. This study employs the nonlinear artificial neural net-works （ANN） to predict the LOD variations. The topology of the ANN model is determined by minimizing the root mean square errors （RMSE） of the predictions. Considering the close relationships between the LOD variations and the atmospheric circulation movement, the operational prediction series of axial atmospheric angular momentum （AAM） is incorporated into the ANN model as an additional input in the real-time rapid prediction of LOD variations with 1-5 days ahead. The results show that the LOD prediction is significantly improved after introducing the operational prediction series of AAM into the ANN model.     

Influence of the instability of angular velocity of the rotating carrier itself on the stability of silicon micromachined gyroscope

In order to find out the influence of the instability of angular velocity of the rotating carrier itself on the stability of silicon micromachined gyroscope, the digital models for relative error of the high and low damping gyroscope＇s output signal are given respectively, based on the motion equations of the silicon micromachined gyroscope. Theory proves that the output signal error of the silicon micromachined sensor is mainly caused by the instability of damping factor and the angular velocity of the rotating carrier itself. The experiment result indicates that the error of proportionality coefficient of output voltage which is caused by the instability of the angular velocity of the rotating carrier itself reaches to 4.1%. Theoretical demonstration and experimental verification show that the instability of angular velocity of the rotating carrier itself has an important effect on the stability of low damping silicon micromachined gyroscope.     

挤压速度对Ti6Al4V钛合金等通道转直角挤压过程 影响的数值模拟

采用Deform-3D有限元软件,对样品初始温度为900℃的Ti6Al4V钛合金等通道转直角挤压在0~5 mm/s的下压速度范围内进行了数值模拟。模拟计算结果表明：在相同的挤压速度下,试样通过转角后的温度降低速率减小;挤压速度越大,挤压过程所需的荷载越低,应变累积越小,等效应力越低,应力集中现象越少,挤压过程中试样的温降越小;本研究条件下,挤压速度值选定为5 mm/s。     

轨道运动方程数值解的加速算法

针对卫星轨道受大气阻力摄动的运动方程,提出了一种数值加速算法,该算法实现简单、计算量不大、精度高,适合于各类卫星轨道方程的求解。     

动量因子对BP算法的影响

本文对BP神经网络算法进行了讨论,并通过实例分析了几种改进算法的实用性．结果表明,适当的改进动量因子和隐单元个数将加快网络的收敛性,提高预测能力．     

Effects and complications of placement of motility coupling post in porous polyethylene orbital implants

Objective： To investigate the effects and complications of primary and secondary placements of motility coupling post （MCP） in the unwrapped porous polyethylene orbital implant （PPOI） following enucleation. Methods： We investigated 198 patients who received PPOI implantation following the standard enucleation procedure in the First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China, from 2002 to 2004. These patients were subgrouped into PPOI-only patients （112 cases, received PPOI following enucleation）, primary MCP patients （46 cases, received primary placement of MCP during PPOI operation）, and secondary MCP patients （40 cases, received secondary placement ofMCP 6 months after the initial surgery）. Effects and complications among these three groups were compared. Results： The PPOI-only patients took shorter treatment course when compared with other two MCP groups （P〈0.001）, without significant difference noted between the two MCP groups. However, the two MCP groups had better prosthetic motility than PPOI-only group （P〈0.001）, without significant difference between the two MCP groups. In the early stage, 2 eyes in the PPOI-only group and l eye in the primary MCP group had PPOI infection. In PPOI-only group, 3 （2.68%） eyes had PPOI exposure, which occurred after fitting the prostheses; 4 eyes （8.70%） in primary MCP group and 1 eye （2.50%） in secondary MCP had PPOI exposure, which occurred before fitting the prostheses. After prosthesis was fit successfully, the excessive discharge and granuloma were 33.9% and 1.79% in PPOI group-only, 53.3% and 8.9% in primary MCP group, and 52.5% and 7.5% in secondary MCP group, respectively. Conclusion： Both primary and secondary placements of MCP into the PPOI following enucleation can help patients to obtain desirable prosthetic motility, but may be associated with more complications. The primary placement of MCP with skilled operation in selected patients is more recommendable than secondary plac     

螺旋槽干气密封润滑气膜角向涡动的稳定性分析

螺旋槽干气密封操作的稳定性和可靠性与其槽形参数密切相关,优化槽形参数一直是该领域研究的热点。应用PH线性化方法及变分运算干气密封螺旋槽内瞬态微尺度流动场的非线性雷诺方程,得到了气膜角向涡动刚度的解析式。继而利用复数转换和迭代法对稳态下气膜边值问题进行求解,求得了气膜涡动刚度的近似解析解。通过动态稳定性分析,获得了不同介质粘度、压力和转速下稳定性最佳的螺旋角数值。研究结果表明：随介质压力和转速增大,气膜涡动刚度越大,稳定性越好。     

海王星特洛伊小天体动力学

特洛伊小天体与行星同享一个轨道,并与太阳、行星在空间构成等边三角形,最早为人们所知的特洛伊小天体是位于木星轨道上并位于木星前(后)方60°的两群小天体.而海王星特洛伊小天体则是近20年来太阳系内最重要的发现之一.观测证据表明海王星特洛伊小天体的总数量和总质量远超过木星特洛伊小天体和主带小行星,是太阳系内仅次于柯伊伯带的第二大小天体集群.它们一方面具有独特的轨道特征,另一方面又联系着海王星轨道内、外的空间,自然而然地成为检验太阳系起源与演化的试金石.我们简要介绍了对海王星特洛伊小天体的观测结果、对它们的轨道动力学和起源研究的进展.     

典型轴手性D分子F被H取代的衍生物结构特性的理论研究

使用密度泛函理论的b3lyp方法,在b3lyp/6-31+g(d,p)理论水平上对D分子手性对映体D1的F被H取代的几种衍生物结构、红外振动频率、分子前线轨道进行了理论研究.结果表明:它们的解离产物及手型转变机制会不同;三种衍生物分子的HOMO和LUMO轨道,主要来源于骨架C原子p电子的贡献,F原子的p电子和手性C原子所在环上的H的s电子对前线分子轨道有很小的贡献.