低温产品标准的技术要求制定方法

介绍了选择产品标准的技术要求的基本原则和依据。阐述了低温产品应根据实际需要从环境适应性、使用性能、理化性能、稳定性、健康安全和环境保护、耗能指标、外观和感观要求、材料要求和工艺要求等方面规定产品标准的性能要求。     

数学建模竞赛论文的写作方法

本文针对数学建模竞赛论文的评阅要求和近年来参赛论文的实际情况,首先简要介绍了科技论文的写作规范,然后详细说明了竞赛论文的写作方法和注意事项,可供拟参加数学建模竞赛的学生和指导老师参考。     

Lift and power requirements of hovering insect flight

Lift and power requirements for hovering flight of eight species of insects are studied by solving the Navier-Stokes equation numerically. The solution provides velocity and pressure fields, from which unsteady aerodynamic forces and moments are obtained. The inertial torque of wing mass are computed analytically. The wing length of the insects ranges from 2 mm (fruit fly) to 52 mm (hawkmoth); Reynolds numbers Re (based on mean flapping speed and mean chord length) ranges from 75 to 3850. The primary findings are shown in the following: (1) Either small (R = 2mm, Re = 75), medium (R ≈ 10 mm, Re ≈ 500) or large (R ≈ 50 mm, Re ≈ 4 000) insects mainly employ the same high-lift mechanism, delayed stall, to produce lift in hovering flight. The midstroke angle of attack needed to produce a mean lift equal to the insect weight is approximately in the range of 25° to 45°, which is approximately in agreement with observation. (2) For the small insect (fruit fly) and for the medium and large insects with relatively small wingbeat frequency (cranefly, ladybird and hawkmoth), the specific power ranges from 18 to 39W·kg^-1 , the major part of the power is due to aerodynamic force, and the elastic storage of negative work does not change the specific power greatly. However for medium and large insects with relatively large wingbeat frequency (hover fly, dronefly, honey bee and bumble bee), the specific power ranges from 39 to 61 W·kg^-1 , the major part of the power is due to wing inertia, and the elastic storage of negative work can decrease the specific power by approximately 33%. (3) For the case of power being mainly contributed by aerodynamic force (fruit fly, cranefly, ladybird and hawkmoth), the specific power is proportional to the product of the wingbeat frequency, the stroke amplitude, the wing length and the drag-to-lift ratio. For the case of power being mainly contributed by wing inertia (hoverfly, dronefly, honey bee and bumble bee), the specific power (without elastic storage) is proportional to the product of the cubic of wingbeat frequency, the square of the stroke amplitude, the square of the wing length and the ratio of wing mass to insect mass.     

Study on the radiation problem caused by electron beam loss in accelerator tubes

The beam dynamic code PARMELA was used to simulate the transportation process of accelerating electrons in S-band SW linacs with different energies of 2.5, 6 and 20 MeV. The results indicated that in the ideal condition, the percentage of electron beam loss was 50% in accelerator tubes. Also we calculated the spectrum, the location and angular distribution of the lost electrons. Calculation performed by Monte Carlo code MCNP demonstrated that the radiation distribution of lost electrons was nearly uniform along the tube axis, the angular distributions of the radiation dose rates of the three tubes were similar, and the highest leaking dose was at the angle of 160° with respect to the axis. The lower the energy of the accelerator, the higher the radiation relative leakage. For the 2.5 MeV accelerator, the maximum dose rate reached 5% of the main dose and the one on the head of the electron gun was 1%, both of which did not meet the eligible protection requirement for accelerators. We adopted different shielding designs for different accelerators. The simulated result showed that the shielded radiation leaking dose rates fulfilled the requirement.     

工程项目承包服务业主需求重要度确定方法研究

工程服务质量日渐成为承包商企业提高竞争力并获得长期发展的一个重要因素.但传统的对工程服务质量的研究大都忽略了业主需求,对此,本文基于QFD(质量功能展开)理论,结合专家组与顾客双渠道的需求信息来源,提出了集成Kano模型与区间层次分析法的业主需求重要度的计算方法,提升了需求重要度确定的合理性并将顾客的需求偏好信息充分反映到计算过程中,使得承包商企业能够运用科学准确的业主需求信息提高自身服务质量.通过对算法的实际应用,得出业主需求重要度的排序,承包商可以根据该排序对自身服务质量进行评价与改进,证明了该方法可行且有效,具有一定的实践价值.     

An advanced higher-order theory for laminated composite plates with general lamination angles

This paper proposes a higher-order shear deformation theory to predict the bending response of the laminated composite and sandwich plates with general lamination configurations.The proposed theory a priori satisfies the continuity conditions of transverse shear stresses at interfaces.Moreover,the number of unknown variables is independent of the number of layers.The first derivatives of transverse displacements have been taken out from the inplane displacement fields,so that the C 0 shape functions are only required during its finite element implementation.Due to C 0 continuity requirements,the proposed model can be conveniently extended for implementation in commercial finite element codes.To verify the proposed theory,the fournode C 0 quadrilateral element is employed for the interpolation of all the displacement parameters defined at each nodal point on the composite plate.Numerical results show that following the proposed theory,simple C 0 finite elements could accurately predict the interlaminar stresses of laminated composite and sandwich plates directly from a constitutive equation,which has caused difficulty for the other global higher order theories.     

A reduced variable neighborhood search algorithm for uncapacitated multilevel lot-sizing problems

Multilevel lot-sizing (MLLS) problems, which involve complicated product structures with interdependence among the items, play an important role in the material requirement planning (MRP) system of modern manufacturing/assembling lines. In this paper, we present a reduced variable neighborhood search (RVNS) algorithm and several implemental techniques for solving uncapacitated MLLS problems. Computational experiments are carried out on three classes of benchmark instances under different scales (small, medium, and large). Compared with the existing literature, RVNS shows good performance and robustness on a total of 176 tested instances. For the 96 small-sized instances, the RVNS algorithm can find 100% of the optimal solutions in less computational time; for the 40 medium-sized and the 40 large-sized instances, the RVNS algorithm is competitive against other methods, enjoying good effectiveness as well as high computational efficiency. In the calculations, RVNS updated 7 (17.5%) best known solutions for the medium-sized instances and 16 (40%) best known solutions for the large-sized instances.     

运用Student T-Copula的极值理论度量我国商业银行的操作风险

银行操作风险损失数据具有厚尾性,同时不同损失事件之间具有相关性.依据巴塞尔委员会对操作风险损失类型的界定,利用从公开渠道收集的我国商业银行内部欺诈和外部欺诈损失数据.运用基于Studentt-Copula的极值理论研究我国商业银行面临的操作风险,得出极值理论的POT模型能够有效地捕捉损失厚尾性,计算出的VaR比较准确,只是不同的损失数据对阈值的选取存在一定差异.进一步研究表明采用Studentt-Copula刻画两种损失事件之间的相关性,能够有效地降低VaR,降幅甚至高达40%以上.既可以为银行节省大量经济资本,有利于日常经营,又可以准确计提经济资本,有利于监管当局的监管.     

The End of a Classical Ontology for Quantum Mechanics?

In this paper, I argue that the Shrapnel–Costa no-go theorem undermines the last remaining viability of the view that the fundamental ontology of quantum mechanics is essentially classical: that is, the view that physical reality is underpinned by objectively real, counterfactually definite, uniquely spatiotemporally defined, local, dynamical entities with determinate valued properties, and where typically ‘quantum’ behaviour emerges as a function of our own in-principle ignorance of such entities. Call this view Einstein–Bell realism. One can show that the causally symmetric local hidden variable approach to interpreting quantum theory is the most natural interpretation that follows from Einstein–Bell realism, where causal symmetry plays a significant role in circumventing the nonclassical consequences of the traditional no-go theorems. However, Shrapnel and Costa argue that exotic causal structures, such as causal symmetry, are incapable of explaining quantum behaviour as arising as a result of noncontextual ontological properties of the world. This is particularly worrying for Einstein–Bell realism and classical ontology. In the first instance, the obvious consequence of the theorem is a straightforward rejection of Einstein–Bell realism. However, more than this, I argue that, even where there looks to be a possibility of accounting for contextual ontic variables within a causally symmetric framework, the cost of such an account undermines a key advantage of causal symmetry: that accepting causal symmetry is more economical than rejecting a classical ontology. Either way, it looks like we should give up on classical ontology.     

基于核心素养的化学教学目标设计策略

以“化学中常用的物理量--物质的量”为例,介绍了课程目标、单元教学目标和课时教学目标的转化。结合教材内容,分析了基于核心素养制订教学目标的策略,分别有:基于三维目标升华的策略、基于双向细目表的策略和基于教学板块与学习任务的策略。