基于模态综合法与动态凝聚的滚珠丝杠进给系统状态空间建模与实验验证

以往研究中为便于机械传动环节与控制系统的集成建模,常将滚珠丝杠进给系统简化为简单机械模型,其在动态性能精确求解等方面存在不足。针对这一问题,充分考虑滚珠丝杠进给系统的结构柔性以及丝杠螺母副的耦合特性,构建滚珠丝杠进给系统多柔体动力学模型;在此基础上,综合模态综合法和动态凝聚法,对进给系统有效简化动力学信息准确提取,加快模型降阶收敛和凝聚自由度响应求解速度,推导得到滚珠丝杠进给系统的状态空间缩聚模型。基于内置传感器信号的动态性能试验测试,对模型的正确性进行验证,其一阶固有频率计算误差为5.54%,实验和仿真计算得到的输入扭矩与输出转速间的频响曲线在一阶频率处极点坐标分别为32.83 d B和35.16 d B。该研究为实现滚珠丝杠进给系统与伺服控制系统的高效高精度集成建模提供了重要的理论基础和方法指导。

用有限元法计算特征值问题的一种新的动态凝聚方法

有限元法是常用的建模方法,由于所建模型具有较大的自由度,通常需要进行降阶处理.一般来讲,模型前几阶特征值和特征向量可以较精确地得到,利用所得到的特征值和主振型分量(在特征向量中与所给定的主自由度对应的振型分量),本文提出了一种新的动态凝聚方法,该方法是通过迭代方式,利用所得到的特征值和主振型分量对Guyan降阶法所得到的降阶模型进行修正.与同类方法相比,本文方法具有较高的计算精度和很小的计算量,且迭代收敛的稳定性很好.最后本文给出了一个计算实例.

周期性多孔结构特征值拓扑优化

为了实现尺度关联周期性多孔结构的隔振性能优化,提出一种周期性多孔结构特征值拓扑优化方法。基于子结构动态凝聚方法对多孔结构的刚度和质量矩阵进行缩减,采用局部水平集函数(LLSF)对多孔结构进行几何隐式描述,以最大化前6阶特征值为目标函数,以结构体积分数为约束条件,建立周期性多孔结构特征值拓扑优化模型,采用优化准则法对拓扑优化模型进行求解,并研究了多孔结构特征值拓扑优化的尺度效应。研究表明,该方法能有效实现尺度关联的二维和三维周期性多孔结构的特征值拓扑优化,并能大幅提高特征值拓扑优化的计算效率。

Single DNA Condensation Induced by Hexammine Cobalt with Molecular Combing

We investigated the interaction between DNA and hexammine cobalt III [Co（NH3）6]3＋ by a simple molecular combing method and dynamic light scattering. The average extension of A- DNA-YOYO-1 complex is found to be 20.9μm, about 30% longer than the contour length of the DNA in TE buffer （10 mmol/L Tris, 1 mmol/L EDTA, pH=8.0）, due to bis-intercalation of YOYO-1. A multivalent cation, hexammine cobalt, is used for DNA condensation. We find that the length of DNA-[Co（NH3）6]3＋ complexes decrease from 20.9 μm to 5.9μm as the concentration of the [Co（NH3）6]3＋ vary from 0 to 3 μmol/L. This observation provides a direct visualization of single DNA condensation induced by hexammine cobalt. The results from the molecular combing studies are supported by dynamic light scattering investigation, where the average hydrodynamic radius of the DNA complex decreases from 203.8 nm to 39.26 nm under the same conditions. It shows that the molecular combing method is feasible for quantitative conformation characterization of single bio-macromolecules.

Phase of Two-Component Bose-Einstein Condensates with a Coupling Drive

By using the invariant theory, we study the phases of two-component Bose-Einstein condensates with a coupling drive under the case that the strength of the interatomic interaction in each condensate equals the interspecies interaction. The dynamical and geometric phases are presented respectively. The Aharonov-Anandan phase is also obtained under the cyclical evolution.

基于智能分区的草原资源资产清查价格体系优化

【目的】在全民所有自然资源资产清查背景下,从均质区划分、清查价格指标体系以及价格修正体系等多个方面探究草原资源资产价格体系的优化路径,构建体系优化框架并验证其科学性与实用性。【方法】基于青海省草地资源清查196892条图斑的21条属性字段数据,遴选出草地类型、草地面积、干草产量、草原等级等指标,以乡镇为最小区域单元,基于动态凝聚约束集群和分区的区域化方法划分青海省省级草原均质区,采用分等级、分类别定价的思路引入草原等级调整系数和草地分类价格,形成一套“国家级均质区-省级均质区-乡镇”多层级自上而下的青海省草原资源资产价格体系。【结果】基于本文框架所构建的草原资源资产价格体系,青海省的4个国家级草原均质区经细化得到23个省级草原均质区,分区数目合理,各区域间的草原资源特征具有明显差异;在此基础上细分得到的乡镇级草地价格介于国家均质区草地价格30%上下限之间。【结论】本文提出以自然资源资产领域知识为驱动,智能分区算法为核心的草原资源资产清查价格体系优化框架,可支撑自然资源资产清查技术体系构建,助力自然资源资产清价值量核算工作。

Energetics and kinetics of direct phase conversion from graphite to diamond

The atomistic mechanism for direct conversion of graphite to diamond is a long-standing problem in condensed matter physics. The newly identified cold-compressed graphite phases of M, W and 0 carbon provide a crucial link to understand the graphite-to- diamond phase transformation. We demonstrate by ab initio calculations that pressure has a dual role in lowering the conversion barrier and enhancing the production stability during the first-stage cold-compressed phase conversion of graphite toward the intermediate metastable M, W and 0 carbon phases. However, it has little effect on the relative enthalpy and high conversion barrier during the second-stage conversion process toward the diamond polytypes, showing a temperature dominated conversion process. These results may give explanation regarding the necessity of high pressure and high temperature during the graphite-to- diamond reaction.