检索结果-南通市图书馆

在线全文

学校读者我要写书评

暂无评论

有限性与延展性:新中国国家安全思想的演进

国际安全研究 2025年第1期43卷 73-95,157页

作者：祁昊天赵书韫北京大学国际关系学院国家安全学系北京100871

文章从国家安全本体论、安全体系认识论与安全实践方法论三个维度考察新中国的国家安全思想,以社会主义革命和建设时期、改革开放和社会主义现代化建设新时期以及中国特色社会主义新时代进行时间分段,讨论新中国国家安全思想的演进。有... 详细信息

文章从国家安全本体论、安全体系认识论与安全实践方法论三个维度考察新中国的国家安全思想,以社会主义革命和建设时期、改革开放和社会主义现代化建设新时期以及中国特色社会主义新时代进行时间分段,讨论新中国国家安全思想的演进。有限性与延展性是这一演进过程中安全思想的连贯体现,分别涵盖了安全目标、认知与方法在各阶段静态与动态、横向与纵向的特征。虽然新中国在不同时期面临不同的安全环境和安全需求,安全形势愈加复杂,但是安全思想和实践总体符合安全有限、延展演进的特征。安全具有弹性但不可过载,不存在绝对安全的空间,而狭义的、单一领域或维度的安全亦无法有效支撑对国家安全的维护,特别是在愈加复杂和不确定的国家安全环境中更是如此。新中国国家安全思想“有限—延展”的演进特征反映了安全环境的客观变化与领导人主观能动的决策部署。

关键词：国家安全思想演进有限性延展性

在线全文

学校读者我要写书评

暂无评论

球轴承刚度斜弹簧计算方法

轴承 2025年第1期 69-75页

作者：赵联春赵纪辉晏丽明王东上海斐赛轴承科技有限公司上海201199 洛阳摩梯普润滑技术有限公司河南洛阳471611 上海斐耐润滑技术有限公司上海201612

针对传统轴承刚度计算方法计算过程复杂,计算结果正确性存疑的问题,提出了一种斜弹簧计算方法,以角接触球轴承为例,推导了受联合载荷、高速运转和仅受中心轴向载荷、中低速运转2种极端情形下的轴承刚度计算公式,斜弹簧计算方法整个过程... 详细信息

针对传统轴承刚度计算方法计算过程复杂,计算结果正确性存疑的问题,提出了一种斜弹簧计算方法,以角接触球轴承为例,推导了受联合载荷、高速运转和仅受中心轴向载荷、中低速运转2种极端情形下的轴承刚度计算公式,斜弹簧计算方法整个过程无需微分和矩阵运算,物理意义清晰,正确性能够自证,计算过程简洁,计算精度高。并与虚功原理法、刚度投影法、准静态模型的增量法进行对比,结果表明:与虚功原理法误差较小,进一步证明了斜弹簧计算方法的正确性;与刚度投影法、准静态模型的增量法误差较大,两者所依据的物理基础不实的计算结果正确性存疑。

关键词：滚动轴承角接触球轴承刚度弹簧载荷变形

Sun's Log-concavity Conjecture on the Catalan–Larcombe–french Sequence

同方期刊数据库博看期刊评论

在线全文

学校读者我要写书评

暂无评论

Acta Mathematica Sinica,English Series 2016年第5期32卷 553-558页

作者： james j.Y.zhao Center for Applied Mathematics Tianjin University

Let {Pn},n≥0 denote the Catalan-Larcombe-french sequence, which naturally came from the series expansion of the complete elliptic integral of the first kind. In this paper, we prove the strict log-concavity of the sequence { n√Pn}n≥1, which was originally conjectured by Z. W. Sun. We also obtain the strict log-concavity of the sequence {n√Vn}n≥1, where {Vn}n≥0 is the fennessey-Larcombe- french sequence arising from the series expansion of the complete elliptic integral of the second kind.

关键词： The Catalan-Larcombe-french sequence the fennessey-Larcombe-french sequence logconcavity three-term recurrence relation

A New Emission Mode of PSR B1859+07

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2023年第10期23卷 176-183页

作者： Tao Wang P.f.Wang j.L.Han Yi Yan Ye-zhao Yu feifei Kou National Astronomical Observatories Chinese Academy of SciencesBeijing 100101China School of Astronomy and Space Science University of Chinese Academy of SciencesBeijing 100049China The key Laboratory for Radio Astronomy and Technology Chinese Academy of SciencesBeijing 100101China Qiannan Normal University for Nationalities Duyun 558000China Xinjiang Astronomical Observatories Chinese Academy of SciencesUrumqi 830011China

Previous studies have identified two emission modes in PSR B1859+07: a normal mode that has three prominent components in the average profile, with the trailing one being the brightest, and an anomalous mode(i.e., the A mode) where emissions seem to be shifted to an earlier phase. Within the normal mode, further analysis has revealed the presence of two submodes, i.e., the cW mode and c B mode, where the central component can appear either weak or bright. As for the anomalous mode, a new bright component emerges in the advanced phase while the bright trailing component in the normal mode disappears. New observations of PSR B1859+07 using the fivehundred-meter Aperture Spherical Radio Telescope(fAST) have revealed the existence of a previously unknown emission mode, dubbed the Af mode. In this mode, all emission components seen in the normal and anomalous modes are detected. Notably, the mean polarization profiles of both the A and Af modes exhibit a jump in the orthogonal polarization angle modesin the bright leading component. The polarization angles for the central component in the original normal mode follow two distinct orthogonal polarization modes in the A and Af modes respectively. The polarization angles for the trailing component show almost the same but a small systematic shift in the A and Af modes, roughly following the values for the c W and cB modes. Those polarization features of this newly detected emission mode imply that the anomalous mode A of PSR B1859+07 is not a result of “phase shift”or “swooshes” of normal components, but simply a result of the varying intensities of different profile ***, subpulse drifting has been detected in the leading component of the Af mode.

关键词： (stars:)pulsars:individual(PSR B1859+07) polarization plasmas

ON THE A/D TYPE TWIN BOUNDARY IN 18R MARTENSITE Of A Cu-Zn-Al ALLOY

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 1997年第5期10卷 425-429页

作者： Zhang, j.X. Zheng, Y.f. Cai, W. zhao, L.C. Harbin Inst of Technology Harbin China

The A/D type twin boundary in a Cu-Zn-Al shape memory alloy appears curved under TEM and shows irregularly serrated steps under HREM. Crystallographic analysis shows that the macroscopic curve results from non-self-accommodation of the boundary, the deviation from exact twin orientation and a preferential orientation for lower boundary energy.

关键词： Aluminum alloys Copper alloys Crystallography Electron microscopy Martensite Zinc alloys

THE TYPE II DEfECT IN 18R MARTENSITE IN A Cu-Zn-Al ALLOY

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 1998年第1期11卷 29-32页

作者： j.X.Zhang Y.f.Zheng W.Cai L.C.zhao Harbin Inst of Technology Harbin China

Type H defect in 18R martensite in a Cu-Zn-Al alloy has been studied by high resolution electron microscopy. It was found that Type H defect is not fault internal to martensite plate; rather,it is a stack of plates A and C. The rare observation of Type H defect is considered to be due to the fact that thc slice is too thin to exist for self-accommodation.

关键词： shape memory alloy Cu-based alloy defect

Large eddy simulations of a turbulent mixing layer periodically excited with fundamental and third harmonic frequency

在线全文

学校读者我要写书评

暂无评论

Chinese journal of Aeronautics 2023年第5期36卷 33-40页

作者： jörg SCHLÜTER Dan zhao Abhishek SARKAR School of Engineering Deakin UniversityWaurn Ponds 3216Australia College of Engineering University of CanterburyChristchurch 8041New Zealand School of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingapore

A better understanding of the mixing behavior of excited turbulent mixing layers is critical to a number of aerospace *** studies of excited turbulent mixing layers focused on single frequency excitation or the excitation with fundamental and its second harmonic *** is a lack of detailed studies on applying low and higher frequency *** this study,we have performed large-eddy simulations of periodically excited turbulent mixing *** excitation consists of a fundamental frequency and its third *** have used phase-averaging to identify the vortex structure and strength in the mixing layer,and we have studied the vortex *** different vortex paring mechanisms are observed depending on the phase shift between the two excitation *** influence of these two mechanisms on the mixing of a passive scalar is also *** is found that exciting the mixing layer with these low and high frequencies has initially an adverse influence on the mixing process;however,it improves the mixing further downstream of the splitter plate with the excitation using a phase shift ofΔφ=πshowing the best mixing *** present works shed lights on the fundamental vortex dynamics,and has great potential for aeronautical,automotive and combustion engineering applications.

关键词： flow control flow excitation Large eddy simulations Turbulent mixing layer Vortex dynamics

He-enhanced heterogeneity of radiation-induced segregation in feNiCoCr high-entropy alloy

在线全文

学校读者我要写书评

暂无评论

journal of Materials Science & Technology 2022年第6期101卷 226-233页

作者： W.T.Lin G.M.Yeli G.Wang j.H.Lin S.j.zhao D.Chen S.f.Liu f.L.Meng Y.R.Li f.He Y.Lu j.j.Kai Department of Mechanical Engineering City University of Hong KongHong KongChina Institute of Nuclear&New Energy Technology Tsinghua UniversityBeijingChina Department of Physics Southern University of Science and TechnologyShenzhenChina Centre for Advanced Nuclear Safety and Sustainable Development City University of Hong KongHong KongChina School of Environmental Science and Engineering Southern University of Science and TechnologyShenzhenChina School of Materials Science and Engineering Shanghai UniversityShanghaiChina Nano-Manufacturing Laboratory(NML) City University of Hong Kong Shenzhen Research InstituteShenzhenChina

Radiation-induced segregation(RIS) is a typical non-equilibrium process that can dramatically alter the behavior of defect sinks and material properties under irradiation. However, RIS mechanisms have been rarely studied around small He bubbles owing to the technical challenges involved in direct measurements of local chemistry. Here, using state-of-the-art atom probe tomography, we report the RIS behavior near He bubbles in the fe Ni Co Cr high-entropy alloy that indicates Co segregates most strongly, followed by weaker Ni segregation, whereas fe and Cr are depleted almost to the same degree. Exceptionally, the magnitude of Co segregation around He bubbles is higher than previously measured values at voids and dislocation loops. Electron energy-loss spectroscopy was used to measure the He density and pressure inside individual bubbles. We demonstrate that He bubbles are over-pressurized at the irradiation temperature that could result in the vacancy bias and the subsequent vacancy-dominated RIS ***-principles calculations further reveal that there are repulsive interactions between He and Co atoms that may reduce the frequency of Co-vacancy exchange. As a result, He atoms likely retard Co diffusion via the vacancy mechanism and enhance the heterogeneity of RIS in Co-containing multicomponent alloys. These insights could provide the basis for understanding He effects in nuclear materials and open an avenue for tailoring the local chemical order of medium-and high-entropy alloys.

关键词： High-entropy alloy Radiation-induced segregation He bubbles Atom probe tomography Electron energy-loss spectroscopy

NUMERICAL SIMULATION Of A TWO-DIMENSIONAL SQUARE MOVING NEAR fREE SURfACE

在线全文

学校读者我要写书评

暂无评论

journal of Hydrodynamics 2001年第1期13卷 54-57页

作者： Hong, f.W. zhao, f. Zhou, L.D. China Ship Sci. Res. Cent. P. O. Box 116 Wuxi 214082 China

A body moving near the free surface is a focus in fluid dynamic research. Many numerical methods were developed for the simulation of the induced flow field. In this paper, a two-dimensional square moving near the free surface was simulated by the volume of fluid method (VOf). The flow field and drag exerted on the square were studied. The drag would increase due to the presence of the free surface. The iteration factor of the pressure interpolation of surface cells was modified, and through this modification the iteration became more stable. The capability of dealing with the large deformation of the free surface was raised.

关键词： Computational fluid dynamics Computer simulation Drag Numerical methods