城市轨道交通调线调坡测量中圆隧道横断面测量方法的探讨

介绍了城市轨道交通在调线调坡测量中圆隧道结构横断面测量的两种不同的方法,并以上海市轨道交通2号线东延伸段工程调线调坡测量为例,对这两种方法进行分析比较.     

Direct neutron spectrum measurement to validate Zr(n,2n) reaction cross-section at 14 MeV

Lithium zirconate, Li₂ZrO₃, is known as a candidate blanket material in a fusion reactor. Various neutronics benchmark experiments for zirconium have thus been carried out so far. According to the independent benchmark studies by two parties, the neutron spectrum calculations show fairly large overestimation for most evaluated nuclear data libraries. However, the reason has not yet been made clear up to now. The author's group expects it would be due to a problem of evaluation for the ^natZr(n,2n) reaction cross-section, because the cross-section measurement is basically not possible with the foil activation method for zirconium isotopes except for ⁹⁰Zr.In the present study, two neutrons emitted from ^natZr(n,2n) reaction have been measured directly to investigate the reason for the above overestimation. The measurement was done with our own special technique of detecting angle-correlated neutrons by the coincidence detection technique and the pencil-beam DT neutron source of FNS, JAEA. Angle-correlated energy differential cross-sections for ^natZr(n,2n) reaction were successfully measured. The obtained total cross-section above the emitted neutron energy of 800 keV was fairly larger than the one evaluated in JENDL-3.3. The total cross-section of ^natZr(n,2n) reaction was estimated by extrapolating the spectrum down to zero energy taking into account the nuclear temperature. The estimated cross-section value with the nuclear temperature of 1 MeV, which is larger than the one adopted in JENDL-3.3, was in acceptable agreement with JENDL-3.3. It is suggested from the result that the disagreement pointed out in the previous benchmark studies may be due to inappropriate nuclear temperature used in the evaluation. Further investigation of the nuclear temperature employed in the nuclear data evaluation should thus be carried out once again.     

A new cross-section generation model in the FAST code system and its application to gas- and sodium-cooled Generation IV fast reactors

The cross-section generation scheme employed in the 3D spatial kinetics PARCS code included in the FAST code system being used and developed at the Paul Scherrer Institute (PSI) is currently based on region-wise macroscopic cross-sections for reference conditions and their first-order derivatives with respect to the state variables. Since for some transients, feedback effects may likely not in this way be precisely approximated in their interrelations, this standard method was recently complemented for (hex, z) geometry by a more rigorous cross-section representation scheme. The main idea behind the new approach within the FAST code system is that of preparing sets of microscopic cross-sections for a studied design. The full library consisting of such isotopic tables is generated based on using the ECCO cell code of the code system ERANOS developed by the French Atomic Energy Commission (CEA) for a suitable range of temperatures and background cross-sections (σ₀) on a common grid. In the paper, this σ₀-model is described. In addition, within a detailed verification study needed due to its complexity, it is extensively compared to the standard method for both steady-state and transient conditions. Thereby use is made of current Generation IV fast-spectrum concepts. Reactivity and power evolution indicate overall good agreement of the two methods. Such a good consistence in various transient situations for systems characterized by different neutron spectra gives a large degree of confidence in the correct implementation and suitability of the microscopic cross-section methodology. Therefore, besides for the safety analysis of advanced fast-spectrum core concepts in general, it is foreseen, within the FAST code system, to use the σ₀-model for the assessment of uncertainty propagations in transient calculations in conjunction with the available ERANOS isotopic covariance matrices. The new development makes it also in principle possible to use the PARCS code as a reactor kinetics solver for severe accident analysis, allowing through the use of microscopic cross-sections to account for relocation of the core material during the accident.     

短鞘丝匀度的判知

本文阐述了利用无鞘丝截面非常扁平的特征判断短鞘丝匀度的若干方法。认为短鞘丝匀度可根据生丝非常扁平、其直径离散性大等特征进行判知。     

Characteristics of cross-sectional atom probe analysis on semiconductor structures

The laser-assisted Atom Probe has been proposed as a metrology tool for next generation semiconductor technologies requiring sub-nm spatial resolution. In order to assess its potential for the analysis of three-dimensional semiconductor structures like FinFETs, we have studied the Atom Probes lateral resolution on a silicon, silicon-germanium multilayer structure. We find that the interactions of the laser with the semiconductor materials in the sample distort the sample surface. This results in transient errors of the measured dimensions of the structure. The deformation of the sample furthermore leads to a degradation of the lateral resolution. In the experiments presented in this paper, the Atom Probe reaches a lateral resolution of 1-1.8 nm/decade. In this paper we will discuss the reasons for the distortions of the tip and demonstrate that with the present state of data reconstruction severe quantification errors limit its applicability for the quantitative analysis of heterogeneous semiconductor structures. Our experiments show that reconstruction algorithms taking into account the time dependent nanostructure of the tip shape are required to arrive at accurate results.     

Evaluation of mass transport performance in heterogeneous gaseous in-plane spiral reactors with various cross-section geometries at fixed cross-section area

Due to its compactness, high heat and mass transfer rate and ease of manufacture, coiled/spiral tube has been widely used in process industries, especially as heat exchangers and chemical reactors. This study addresses the mass-transport enhancement and reaction performance in in-plane spiral reactor with various cross sections geometries, i.e. circular, half-circular, rectangular, square, trapezoidal and triangular, at fixed cross-section area at several Reynolds numbers. The mass transfer performance is compared with those of straight channel counterpart. Laminar flow of gas with catalytic reactions is investigated using a validated three-dimensional computational fluid dynamics (CFD) model. The results suggest that spiral ducts offer better reaction performance as compared to straight duct, especially at higher Reynolds number. However, it imposes higher pressure drop. Amongst various cross-section, the coil reactor with half-circular geometry yields the highest reaction performance. This study can provide insight for design guidelines of high performance coiled reactor.     

Investigation of through-plane morphologies of multiblock copolymers based on poly(arylene ether sulfone)s

Through-plane morphologies of multiblock copolymers based on poly(arylene ether sulfone)s were investigated by transmission electron microscopy (TEM) and through-plane conductivity measurements using a 4-probe method. The measured results showed that proton conductivity increased with a longer block length and that the optimal block length ranged from 5 to 7 K. TEM cross-sectional images also supported these results, indicating that a block length of 10 K is too well organized to conduct through-plane ion carriers.     

高层建筑电气设计中几个问题的思考与处理

在高层建筑电气设计中,楼梯走廊灯、设备房照明、小区路灯等的双电源自动切换开关可以用接触器构成,给出了自复式和手动自复式两种双电源自动切换开关控制电路;对较小的单相负荷可采用由微型接触器构成的双电源单相切换开关。给出了高层建筑楼梯灯的控制方案。分析了高层建筑中水泵房、空调冷水机组设备房的中性线截面偏大的问题,提出单相负荷配电线路和动力配电线路分开供电,和减小N线截面,保护断路器加附件两种解决方案。     

塑性应变极限状态下I形和矩形管截面变形分析

通常在钢结构弹塑性设计中会假设大多数受压横截面中具有"全塑性铰"。基于平衡条件提出的用于计算塑性极限状态下结构内力的公式,不能计算出这种极限状态下各种内力组合下结构的整体变形。针对矩形管截面和双轴对称I形截面的弹塑性分析提出一个简单模型。该模型考虑了横截面塑性应变极限状态下的结构整体变形(轴向变形和弯曲曲率)与相应内力(轴力和弯矩)的关系。利用这个模型可以对横截面延性进行真实的评估。     

绕弱轴的循环弯矩作用下高厚比较大的H型钢—柱试验研究

对恒定轴力和绕弱轴循环弯矩共同作用下的9根高厚比较大的H型钢梁-柱进行了试验研究。考虑横截面的不同类别,翼缘和腹板选择不同的宽厚比,并提出一套可靠的试验方案。试验结果表明,局部屈曲在所有未发生整体屈曲的试件的破坏中占主导地位。对于绕弱轴的弯曲,H型钢件表现出良好的塑性变形能力,由此可判定现行规范中H型钢的分类方法不适用于绕弱轴弯曲的情况。此外,研究发现,翼缘或腹板的宽厚比以及轴向力的比例对滞回特性的影响互相依赖,因此应视为交互作用。