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1.
A new measurement method for mass property parameters 总被引：1，自引：0，他引：1
Mass property parameters (mass, center of mass, moment of inertia) are important technology parameters of aircraft. The traditional mass and center of mass measurement uses centroid units, and the moment of inertia measurement torsion units, which can only get results in installing direction. Because of the structural reasons, there is a need to get all high accurate physical parameters in clamping once. To solve this problem, this study merges centroid units and torsion units into one composite unit, installs a table which can tilt and rotation to measure the moment of inertia in different conditions. The moment of inertia and product of inertia relative to three axis are calculated by the method of coordinate transformation. Measurement theory of mass, center of mass and mass moment of inertia are described, the main reason of causing measurement errors is discussed, and the measurement accuracy affected by tilt error is analyzed. 相似文献
2.
中国生态退耕重要阶段耕地面积时空变化分析 总被引：2，自引：1，他引：1
为了兼顾生态退耕过程中的生态安全和食物安全,开展中国生态退耕政策实施重要阶段(1999—2008)的耕地时空变化特点的研究十分必要。根据各省市级耕地增减变化数据,利用分布重心计算模型和分区比较方法,探讨了中国耕地面积时空变化的总体特征。结果表明,从区域尺度分析,研究时段内耕地面积减少幅度排序为：西部＞东部＞中部;生态退耕政策实施的重要阶段可划分为2个时期：一是生态退耕前期,以耕地面积急剧减少、面积分布重心向东移动为特征;二是生态退耕后期,以耕地面积缓慢减少、面积分布重心向北迁移为特点;生态退耕、农业结构调整和建设用地占用所造成的耕地变化,对耕地面积分布重心迁移的影响较大。研究结果提示,建设用地占用优质耕地是制约中国耕地整体生产能力提高的重要因素,而耕地分布重心向北移动使生态退耕的成效面临挑战。 相似文献
3.
Deformation equations of thin-walled open-profile members considering distortion and its application
In order to simplify the analysis of thin-walled open-profile bars, a method is presented in which the analysis is split into two parts, dominated by in-plane and out-plane loading effects respectively. This article focuses on the out-plane loading effects. Based on bending theory of thin plate with small deflection, each slab or strip is analyzed separately and the results are integrated into vectors, in which, the deformation shapes and equilibrium conditions are simplified appropriately, thus leading to the slabs' out-plane bending resistance system of thin-walled bars, which reflects the properties of the bar's distortion and torsion. By composing the slabs in-plane tension-bending resistance system and the slabs' out-plane bending resistance system, deformation equations of thin-walled open-profile bars considering distortion are deduced. In order to set up the finite bar element method, stiffness equation and equivalent nodal forces of internode loadings are deduced. Comparative analysis with finite shell element method indicates the high efficiency and accuracy of this method. 相似文献
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In order to correctly describe the lateral torsion buckling and warping deformations, and to satisfy the incremental virtual displacement principle, the solution of equilibrium differential equations under stretch bending, compression bending, pure bendin 相似文献
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The torsion vibration of main transmission system of 1 450 rolling mill is tested:The torsion vibration frequency and amplification coefficient of torque are obtained.Basing on part of the measured date and theoretical analysis,the measure is developed for preventive method;it is of important theoretic sense and high engineering practical value for reducing accident and controlling torsion vibration. 相似文献
7.
Microstructures, Reaction Kinetics and Properties of Reaction Between Magnesium and Silica Glass 
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下载免费PDF全文 In earlier calculation models,the stiffness centers in frame-shear wall structures have been located by the structural torsion stiffness.However,the results are illogical owing to the difference between the distortion character and the shears distribute mechanism of the frames and shear walls.In this paper,a new formula for calculating story stiffness is introduced,which can consider the stiffness of the frames and shear walls at the same time.The structural stiffness centers,the torsion eccentric distances and torsion effect are calculated,and the stiffness of elements is considered also.It is shown that the concept of the presented stiffness model is clear and the results are reasonable,which can be used to calculate the appreciative torsion effect. 相似文献
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DUAN Shao guang 《保鲜与加工》2003,(6):121-124
Professor Venzo de Sabbata is a famous Italian physicist in the world. He is engaged with a series of creating research works about the general relativity theory applying to astrophysics, and achievies glorious successes. The author pays attention to his works in this field, especially his paper titled "Is it dark matter necessary to explain galaxy rotation curves?"In order to coincide with the astrophysical observations, Milgrom adopted a new foundamental acceleration a 0 to modify the Newtonian Dynamics (MOND).Meanwhile Sabbata explored another approach wisely by introducing the innate related torsion with intrinsic spin of the particle into the general relativity theory, and showed penetratively that without use of dark metter for explanation,the foundamental accelerations a max and a min will be derived from the quantum effect yielded by the torsion. They are the nice results which can be derived from an accurate solution of the related equations in the Einstein Cartan general relativity theory. 相似文献
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基于县域单元的我国水稻生产时空动态变化 总被引：11，自引：0，他引：11
水稻是我国最重要的粮食作物之一, 阐明近几十年来水稻的时空动态变化特征, 对于优化水稻布局、促进水稻生产的可持续发展具有重要意义。本研究基于1985年以来的县域水稻生产数据, 分析了我国水稻产量、面积和单产的时空动态变化特征和水稻生产重心迁移轨迹, 在此基础上量化了水稻面积和单产对总产的贡献度。结果发现, 我国水稻产量变化以49年周期为主, 21年为辅, 面积变化周期为26年, 单产变化周期为60年; 1985—2015年间, 在水稻种植区域内, 近50%地区产量上升, 约70%播种面积减少, 80%以上区域单产增加; 我国水稻产量、面积重心分别向东北方向迁移229 km和225 km, 而东北稻作区产量、面积重心分别向北偏东方向迁移238 km和242 km; 我国水稻生产主导因素中单产占比由56.3%下降至28.3%, 面积由34.7%上升至63.1%。结果表明, 全国各稻作区单产提升、东北早熟单季稻区面积增加、华中双单季稻区和华南双季稻区面积减少是我国水稻种植面积变化的主要特征。因此, 合理布局我国水稻的种植面积和持续提高的水稻单产是稳定和提升我国水稻产量的主要措施, 充分利用光热资源、提高机械化程度和比较效益是促进我国水稻生产发展的关键途径。 相似文献
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This paper first introduces the main reasons that cause torsion under the earthquake, then compares the provisions of several Codes (Chinese new and old Code, American Code, and European Code) about the torsion effect and anti-torsion design under the earthquake. 相似文献
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Wang Mingfei 《保鲜与加工》1998,(6):18-22
After the second world war pedestrian streets began to be built in European cities, at the age of seventies pedestrian street became very popular in western countries.In the nineties our country started into the planning and construction of pedestrian streets.On the basis of analysing the reasons for the development of pedestrian streets at home and abroad and the typology of pedestrian environment,this paper presents the main points of planning and design of pedestrian space in city center. 相似文献
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韩冉冉 《农产品加工．学刊》2012,(6):60-63
农产品资源浪费一直是我国现阶段存在的一大问题,其主要原因是物流环节不能很好地服务于这一产业。通过收集和分析我国农产品物流及农产品物流中心选址问题的研究,提出了成本最低法的农产品物流中心选址模型,通过用模糊综合评价法构建其指标体系,最后用实证分析对其验证可行。 相似文献
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【研究目的】探讨胰岛素样生长因子（IGF1）对生长60 d的梅花鹿鹿茸体外培养不同代数鹿茸生长中心细胞的影响。【方法】分离、培养生长60d的梅花鹿鹿茸生长中心细胞,将培养第2 代、5 代、8 代细胞经含有不同浓度的IGF1（0,1,3 和10 nM）作用,在培养24 h后用3H-胸腺嘧啶核苷掺入测定法检测每分钟衰变数（DPM）值。【结果】全部IGF1处理组都显著高于对照组（p<0.01）。不同浓度IGFⅠ处理组的平均值和最高值都是离体培养2 代的细胞的DPM最高（分别为31918和39818 DPM/mg蛋白）,培养5 代的细胞（分别为5455和6815 DPM/mg蛋白）已大大地下降;到了第 8代的（分别为4030和4838 DPM/mg蛋白）又有进一步的下降。【结论】IGF1能够促进鹿茸生长中心细胞分裂增殖,生长60 d鹿茸的生长中心细胞在离体培养,不同培养时期的鹿茸生长中心细胞对IGFⅠ刺激的敏感度不同。 相似文献
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为了解决原有检索技术已经不能满足国家农业科学数据共享中心检索需求的问题,在总结原有网站搜索引擎方法的基础上,研究了Lucene这种开源代码全文检索引擎工具包的原理及使用方法,探讨了利用Lucene工具包在国家农业科学数据共享中心站内构建海量数据检索引擎的方法,并在科学数据共享中心网站中选取三个有代表性的大、中、小型数据库,依照上述方法建立了基于Lucene工具包的搜索引擎,以此为基础进行不同大小数据库搜索效率对比实验,最后,将实验结果与传统的数据检索方法在相应数据库搜索时所得到的结果相比较。实验结果表明：基于Lucene的搜索引擎在检索效率上明显占优,实际应用效果也是令人满意的。 相似文献
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In mechanical design and application, in order to calculate torsion angle and shear stresses of prismatic bars with seetorial cross-section undergoing extemal couples, the numerical method is presented. The torsion equation is nonhomogeneous partial differential equation. First, using the method of separation of variables, torsion stress function is acquired in polar coordinate. Then, the method of boundary collocation is improved to calculate the undetermined parameters. Finally,approximate numerical solutions of stress function and shear stresses in cross-section are obtained. It is given the several calculation results of shear stresses of prismatic bars with different vertex angles. These results show that the method has some precision and application feasibility in engineering design. The method of separation of variables is combinied with the method of boundary collocation simplified calculation process. 相似文献
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中国同期作物空间格局变化分析——以小麦和油菜为例 总被引：2，自引：1，他引：2
小麦和油菜是我国非常重要的两种大宗作物,它们的空间格局变化历来备受关注。利用1980 -2014年间小麦、油菜的面积数据,以省级行政区为研究单元,采用Pearson相关系数和GIS空间几何重心分析技术,结合同期作物之间的竞争性用地关系,对油菜和小麦的空间分布格局及其变化特征进行分析。研究结果表明:我国小麦近三十年空间格局的总体变化不明显但是省际分布特别不均衡,其分布重心一直位于河南省境内;油菜的面积重心自1980年以来从湖北省境内不断地向南推移,目前分布在湖南省境内。受同期作物之间竞争性用地关系的影响,在陕西、青海、湖北、湖南、四川等地,油菜、小麦的面积变化表现出明显的“消-长”关系,彼此呈显著负相关。 相似文献
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基于县域单元粮食生产空间演变与重心变化的测算分析——以广东省为例 总被引：1，自引：1，他引：0
本研究采用县域数据,以广东省121个县（区）作为研究对象,分析2000—2019年粮食生产空间演变的动态路径以及重心变化以及2000—2019年广东粮食生产的重点区域和西南地区粮食生产的变化。结果表明：中部偏东的趋势较强,并逐渐以珠三角为中心向四周移动,总体呈现“东、西扩张、北波动、珠三角收缩”的态势。此外,粮食生产逐步向重点县转移,产粮10大县产量占广东省22%~25%,产粮前20位的产量占广东省的40%~43%,产粮前40位的产量占广东省的63%~68%,但近年来保持相对稳定。 相似文献
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Modern economy depends on money,but money is created by the bank system.So,as the main body of finance institution in one state,banks have the importance influence upon the economy of one country.Center bank constitutes the money policy and executes the money policy in one country,then it is the core of the whole financial system.But the validity for the money policy must rely on the activity of commercial banks to the money policy.Being based on the money policy transmitting mechanism,this Article analyzes how to establish a kind of bargain relation between Center bank and commercial bank so that commercial bank may work hard toward the aim of the money policy for the center bank under the asymmetric information,which was the bases of the Commercial Banks' innovation. 相似文献
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Based on the study of effec t of torsion vibration natrual frequency on rollingmill main transmission system , the sensibility formula of natural frequency related to design parameter is given,By the means of programming, analysis and calculation have been carried out on 2300rolling mill main transmission system,It provides theoretical asis for dynamic optimizing transmis sion svstems. 相似文献