碳化混凝土再碱化控制理论研究的探讨

再碱化技术应用于实践必须解决的一个重要问题是再碱化过程的控制.在综合分析国内外相关研究的基础上,首先,对不同研究者所做的研究进行了剖析,分析了其研究的路线方法;然后,从控制理论研究的不同方面分析展示了其研究进展;最后,深入分析了各研究,揭示了其中不足之处,指出了再碱化控制理论的发展现状,为进一步研究提供参考.     

企业新雇员工作态度的结构模型及其验证研究

在对已有研究进行回顾的基础上，提出了一个关于企业新雇员工作态度的结构模型，并利用LISREL8软件采用模型生成方法，通过调查所收集数据对该模型进行验证。经过修正的最后模型表明：组织社会化通过工作适应对新雇员的工作态度产生间接影响，新雇员主观感知到的员工一组织匹配则对其工作态度产生直接影响。     

混凝土低温性能表征技术和研究方法综述

液化天然气(LNG)贸易的繁荣加剧了LNG储罐的需求.以混凝土代替9％镍钢制备"全混凝土"LNG储罐可降低46％的成本和缩短33％的工期并提高结构的耐久性,此技术具有重大经济和科学意义.全混凝土LNG储罐在服役过程中面临的最大风险是温度波动(-40～-165℃)和低温冻融循环(室温至-170℃).目前,低温环境(-40～-197℃)中混凝土的失效机理尚不清楚.低温环境孔隙中的水结冰会引起混凝土孔结构、热导率、热应变、渗透性能和失效过程中能量释放行为的变化.低温环境混凝土性能的演变机制还处于研究初期,采用先进的表征技术和高效的研究方法从多角度探究孔隙中水结冰和混凝土宏观性能演化的内在联系,是明确低温环境混凝土劣化机理的有效策略.本文对低温环境混凝土的表征技术(核磁共振技术(NMR)、X射线计算机断层扫描技术(μ-CT)、差分扫描量热技术(DSC)、低温扫描电子显微技术(LTSEM)、声发射技术(AE)和激光闪光法(LFA))及研究方法(热应变测试和渗透性测试)进行综述,并对超高性能混凝土(UHPC)的低温性能进行总结.在低温环境中,利用NMR技术和DSC技术可原位分析混凝土孔隙中水的结冰行为.其中,NMR技术可研究孔隙中水状态的演化;DSC技术基于热流数据可量化表征孔隙中冰的体积.μ-CT技术可探究冻融前后孔隙和裂缝的三维形态.LTSEM技术可获取孔隙中冰体的微观形貌.热应变测试和AE技术结合使用可明确混凝土热变形与失效过程中能量释放之间的相关性.通过降低孔隙率、含水率和剔除粗骨料,可使UHPC具有优异的耐低温性能.目前,低温环境中混凝土的导热性能和渗透性能仍缺少全面研究,采用LFA技术可测定低温环境混凝土的热导率.本文系统归纳了低温环境混凝土的表征技术和研究方法,有助于深入理解低温环境混凝土的失效机理和研制高耐久性的全混凝土LNG储罐.     

Cyclic and Linear Structures of C13: A Computational Study

Abstract

Recently, a linear structure of C₁₃ was observed and its infrared spectrum recorded. Computations of the linear and cyclic structures of C₁₃ are thus presented. The computations are performed at ab initio level using the standard 6-31G? basis set. Electron correlation is treated by density functional theory (Becke3LYP) and perturbation treatment (MP2=FC). With the density-functional approach the standard 6-311G? and 6-311G(2d,p) basis sets are applied, too. In all the treatments the cyclic structure (C _2v symmetry) is located about 90 kJ/mol below the linear form (D _∞h symmetry), while a tricyclic structure is considerably higher in energy (about 280 kJ/mol above the monocyclic species). Even at high temperatures the linear form represents less than 10% of the equilibrium isomeric mixture. Computed IR spectra are also reported. The stability evaluation corresponds to the findings of ion chromatography.     

Cyclic and Linear Structures of C13: A Computational Study

Recently, a linear structure of C₁₃ was observed and its infrared spectrum recorded. Computations of the linear and cyclic structures of C₁₃ are thus presented. The computations are performed at ab initio level using the standard 6-31G* basis set. Electron correlation is treated by density functional theory (Becke3LYP) and perturbation treatment (MP2=FC). With the density-functional approach the standard 6-311G* and 6-311G(2d,p) basis sets are applied, too. In all the treatments the cyclic structure (C_2v symmetry) is located about 90 kJ/mol below the linear form (D_∞h symmetry), while a tricyclic structure is considerably higher in energy (about 280 kJ/mol above the monocyclic species). Even at high temperatures the linear form represents less than 10% of the equilibrium isomeric mixture. Computed IR spectra are also reported. The stability evaluation corresponds to the findings of ion chromatography.     

基于全站仪测距的超声波液位计检校方法的提出和研究

通过全站仪的精确测距功能,对量程较大的超声波液位计进行检较,既能保证使用标准器的使用准确度,又能提高工作效率.     

Comparative Study of Laser Doppler Vibrometer and Capacitive Air‐coupled Transducer for Ultrasonic Propagation Imager and the New Development of an Efficient Ultrasonic Wavenumber Imaging Algorithm

Damage detection techniques using guided waves have been studied for decades with very few successful real‐world applications. The recent development with the full wavefield technique using the Ultrasonic Propagation Imager (UPI) is one of those few exceptions. In this paper, we study two non‐contact sensors: the laser Doppler vibrometer and the capacitive air‐coupled transducer in the context as the sensing modules for the UPI. The aim of this paper is to provide a comprehensive study for optimisation of the two sensors, as well as a comparison between them for use in the UPI. First, the parameters for laser ultrasonic measurement of each sensor were studied: surface treatment, measurement angle and stand‐off distance in the case of the laser Doppler vibrometer and measurement angle, lift‐off distance and bias voltage in the case of the capacitive air‐coupled transducer. Two optimised sensors were then compared in terms of their ability to detect damages using the UPI. Also, in this paper, we presented the ultrasonic wavenumber imaging (UWI) algorithm with the new development towards an efficient implementation. The uniqueness of the UWI algorithm with the capability of damage size estimation makes this algorithm very attractive for the future study with full wavefield signal processing.     

金属及合金熔点热物性动态测试新方法研究

利用物质熔化与凝固过程中导热逆(或反)问题原理，在建立了相界面移动与两相热物理性质关系的基础上，提出了一种新颖的热物性动态测试方法，即由相变速率动态测试热物性参数。由于是对熔点高的金属进行测试，故不能采用解析求解，而是运用数值求解；并用铅、锌、铝等已知热物性的金属对此方法进行了评定，测试结果与参照值误差不超过3％；还对相变导热系数未知的铅锑、铅锡、铋锡、铝硅、铝铜5种共晶合金进行了测试，其结果具有较高的参考价值。该方法的优点在于测试过程中所求热物性参数与相界面位置是由精确的传热方程所约束，故测量较简便，结果准确、可靠、误差小，并可测得多个热物性数据。     

Evaluation of Concrete Distributed Cracks by Ultrasonic Travel Time Shift Under an External Mechanical Perturbation: Study of Indirect and Semi-direct Transmission Configurations

Techniques based on non-linear acoustics have been proven sensitive to micro-defects in heterogeneous materials, such as concrete, but their implementation on-site is very restrictive. Ultrasonic travel time shift, a technique where a high frequency ultrasonic wave probes the medium while a low frequency elastic wave disturbs it to create a “time delay”, is a new promising technique that may be used efficiently on-site. This technique is based on nonlinear behaviour of concrete. Moreover, this technique offers the possibility of evaluating linear parameter, such as ultrasonic pulse velocity of direct waves. The scope of this paper is to study the applicability of the technique at different level of concrete damage and define its advantages, limitations in order to optimize its use. Because of the large dimensions, the geometry and limited access to various faces of existing structures, the transducers often have to be set on the same side. Two types of configurations, the indirect transmission (with incident waves at 90^°) and the semi-direct transmission (with incident waves at 45^°), were studied with cement base samples at different levels of damage (generated by freeze-thaw cycles). Up to now, test results have shown that time-shift is more sensitive when used in an indirect configuration of transmission rather than in a semi-direct configuration. Overall, the non-linear time-shift technique is much more sensitive to the initiation of cracking than linear indicators and its versatility (different indicators for different levels of damage) is of interest for rapid testing of structures.     

Behavior of a PCM at Varying Heating Rates: Experimental and Theoretical Study with an Aim at Temperature Moderation in Radionuclide Concrete Encasements

Phase-change materials (PCMs) can store/release thermal energy within a small temperature range. This is of interest in various industrial applications, for example, in civil engineering (heating/cooling of buildings) or cold storage applications. Another application may be the moderation of temperature increases in concrete encasements of radionuclides during their decay. The phase-change behavior of a material is determined by its heat capacity and the peak it exhibits near a phase change. We analyze the behavior of such peaks for a selected PCM at heating rates varying between \(0.1\,^{\circ }\hbox {C}\cdot \hbox {min}^{-1}\) and \(1\,^{\circ }\hbox {C}\cdot \hbox {min}^{-1}\), corresponding in real situations to different decay rates of radionuclides. We show that experimentally measured peaks can be plausibly described by an equilibrium theory that enables us to calculate the latent heat and phase-change temperature from experimental data.     

Optimization of Dry Machining Parameters for High-Purity Graphite in End-Milling Process by Artificial Neural Networks: A Case Study

The machining factors affecting the tool wear and the surface roughness produced in the end-milling process are generally the cutting speed, the feed rate, the depth of cut, etc. This article focused on finding an optimal cutting parameter setting of high-purity graphite under dry machining conditions by an artificial neural network and the Sequential Quadratic Programming method [1 Fletcher , R. Practical methods of optimizations . Vol. 1, Unconstrained Optimization, and Vol. 2 Constrained Optimization ; John Wiley and Sons , 1981 . [Google Scholar]]. This algorithm yielded better performance than the traditional methods such as the Taguchi method and the Design of Experiments (DOE) approach. Additionally, the tool worn surfaces after machining were examined with tool electron microscopy (TEM) to observe the tool wear mechanisms.     

博士生培养质量及其影响因素研究——基于Nature全球博士生调查的实证分析

采用博士生自我报告的能力提升衡量博士生培养质量是“以学生为中心”理念下的普遍趋势。基于Nature期刊2019年全球6812名博士生调查数据发现:第一,中国博士生感知的培养质量低于全球水平,尤其是学术能力培养相较于所对比的国家还有较大提升空间。第二,博士生每周学习投入时间越多,导生关系越融洽,导师指导和导师外其他人的指导越好,学术会议参与的机会越多,学术发表越多,科研基金越充裕,合作机会越多,社交环境和保健福利越好,以及职业生涯指导与建议越有帮助,博士生培养质量越高。第三,影响博士生学术能力提升的因素与培养质量的影响因素高度重合。第四,和学术能力不同,通用能力的提高更多受到沟通合作活动的影响。     

Ultrasonic Characteristics and Severity Assessment of Lung Ultrasound in COVID-19 Pneumonia:A Retrospective,Observational Study

The clinical application of lung ultrasound (LUS) in the assessment of coronavirus disease 2019 (COVID-19) pneumonia severity remains limited.Herein,we investig...     

基于L2-投影及日H1-投影进行不可压缩粘性流体数值模拟的比较:案例分析

本文的主要目的是讨论不可压缩粘性流体的Navier-Stokes方程的数值模拟.本文所用的方法足对时间用一阶精度算子分裂离散化,对空间度是用Uzawa方法对L2-投影及日H<,1>-投影求解Stokes问题,以及利用类波动方程方法求解平流问题.这两种投影格式都很容易实现.我们利用它们求解经典顶盖驱动方腔流问题直至雷诺数7500都取得了一致结果.当雷诺数处十区间[8575,8590](对应[8600,8625])时,运用L2-投影(对戍H1投影)得到的结果具有时间周期性,这表明Hopf分支的产生.当雷诺数为10000时,存在两个主导频率相互作用.     

重型血友病甲基因诊断新技术的研究及其应用

远用长距离ＤＮＡ扩增技术成功地检测出凝血八因子ＦⅧ基因倒位缺陷患者，并检出该倒位的女性携带者。     

基于L^2-投影及H^1-投影进行不可压缩粘性流体数值模拟的比较：案例分析

本文的主要目的是讨论不可压缩粘性流体的Navier-Stokes方程的数值模拟。本文所用的方法是对时间用一阶精度算了分裂离散化,对空间度是用Uzawa方法对L2-投影及H1-投影求解Stokes问题,以及利用类波动方程方法求解平流问题。这两种投影格式都很容易实现。我们利用它们求解经典顶盖驱动方腔流问题直至雷诺数7500都取得了一致结果。当雷诺数处于区间[8575,8590](对应[8600,8625])时,运用L2-投影(对应H1-投影)得到的结果具有时间周期性,这表明Hopf分支的产生。当雷诺数为10000时,存在两个主导频率相互作用。