元认知缺陷观理论在计算机辅助大学英语视听说教学中的应用

本文把元认知缺陷观理论引入计算机辅助下的大学英语视听说教学中。学习困难的元认知缺陷观最早由Joseph Torgesen提出。其基本观点是,学习困难儿童的学习策略没有得到较好的发展,尤其是元认知策略具有严重的缺陷,从而导致其学业成就水平低下。研究表明英语视听说学习困难的学生的元认知水平明显比优生低,对学习困难学生进行元认知的干预,可以显著地提高他们的英语视听说成绩。

内部控制质量对企业运营目标的影响:来自应收账款内部控制缺陷的证据

笔者以2011—2016年沪深两市A股上市公司为样本,以缺陷观衡量内控质量,通过检验应收账款内部控制缺陷对应收账款管理的影响研究了内部控制质量对企业运营目标的效应。研究了应收账款内控缺陷对运营效率和效果的直接影响和对综合运营绩效的影响,并细化讨论账户层缺陷与公司层缺陷对运营目标直接影响与综合影响的不同效应。检验结果发现,存在应收账款相关内部控制缺陷的公司,其应收账款周转率显著差于行业平均水平,当年增加的坏账准备大于无应收账款缺陷的公司;存在任何类型内控缺陷的公司,其总资产收益率与净资产回报率均低于行业平均水平;公司层应收账款缺陷对直接运营效率和效果具有显著负效应,但账户层缺陷不存在这种关系;公司层任何类型内控缺陷相对于账户层缺陷对公司整体运营目标产生的负向影响更大。在控制了自选择偏差后,前述结论成立。扩展研究发现,应收账款流动资产占比、公司复杂性、公司年限和审计师等因素显著影响应收账款内控缺陷。本研究为内部控制质量对运营目标的影响提供了新的证据,丰富了内控经济后果研究,账户层与公司层缺陷的研究有助于企业寻找改善内控的重点及完善自我披露,对应收账款内控缺陷影响因素的研究为防控特定类型内控缺陷提供了思路。

Measurement and analysis of defects in high-performance concrete with three-dimensional micro-computer tomography

In order to investigate the effects of two mineral admixtures （i. e., fly ash and ground slag）on initial defects existing in concrete microstructures, a high-resolution X-ray micro-CT（ micro-focus computer tomography）is employed to quantitatively analyze the initial defects in four series of highperformance concrete （HPC）specimens with additions of different mineral admixtures. The nigh-resolution 3D images of microstructures and filtered defects are reconstructed by micro- CT software. The size distribution and volume fractions of initial defects are analyzed based on 3D and 2D micro-CT images. The analysis results are verified by experimental results of watersuction tests. The results show that the additions of mineral admixtures in concrete as cementitious materials greatly change the geometrical properties of the microstructures and the spatial features of defects by physical-chemistry actions of these mineral admixtures. This is the major cause of the differences between the mechanical behaviors of HPC with and without mineral admixtures when the water-to-binder ratio and the size distribution of aggregates are constant.

Site occupation evolution of alloying elements in Ni_3 V phase during phase transformation in Ni_(75)Al_(4.2)V_(20.8)

Based on the microscopic phase-field model, the correlation between site occupation evolution of alloying elements in Ni3V-DO22 phase and growth of Ni3Al-L12 phase was studied during the phase transformation of Ni75Al4.2V20.8. The results demonstrate that the growth of L12 phase can be divided into two stages： at the early stage, the composition of alloying elements in DO22 phase almost remains unchanged; at the late stage, the compositions of Ni and Al decrease while V increases in DO22 phase. Part of alloying elements for L12 phase growth are supplied from the site occupation evolution of alloying elements on three kinds of sublattices in DO22 phase. Ni is mainly supplied from V sublattice, and part of Al is supplied from NiⅠ and V sites at the centre of DO22 phase. The excessive V from the decreasing DO22 phase migrates into the centre of DO22 phase and mainly occupies V and NiII sites. It is the site occupation evolution of antisite atoms and ternary additions in DO22 phase that controls the growth rate of L12 phase at the late stage.

Effects of Al and Ca on microstructure and surface defect of magnesium alloy thin strip

Mg-Al-Zn alloy thin strips were prepared by vertical twin-roll casting.Effects of Al and Ca on the microstructure and the surface defects of the thin strips were investigated.The results show that with the increase of Al content,the quantity of surface cracks of the thin strips increases rapidly and their locations are moved to the center of the thin strips.The alloy melts with more than 0.10%Ca(mass fraction)stick on the roller and a poor surface quality of the thin strips appears.With the increase of Al content,the microstructure of the thin strips evolves from singleα-Mg phase,characterized by the uniform and equiaxed recrystallization grains, to the combination of dendriticα-Mg with Al supersaturatedα-Mg.The minor addition of Ca can obviously refine the grains of Mg-3Al-1Zn thin strip because the formation of Al2Ca and the finest grains are obtained by adding 0.08%Ca.

评析哈耶克“法治下的自由”

本文试从分析哈耶克对"自由"的定义入手并进一步对这一定义提出自己的看法,最后从对自由的保障角度阐述哈耶克的法治思想。

Adaptive Observer-Based Fault Estimate for Nonlinear Systems

An approach for adaptive observer-based fault estimate for nonlinear system is proposed.H-infinity theory is applied to analyzing the design method and stable conditions of the adaptive observer, from which both system state and fault can be estimated. It is proved that the fault estimate error is related to the given H-infinity track performance indexes,as well as to the changing rate of the fault and the Lipschitz constant of the nonlinear item.The design steps of the adaptive observer are proposed.The simulation results show that the observer has good performance for fault estimate even when the system includes nonlinear terms, which confirms the effectiveness of the method.

Single-walled carbon nanotube networks for ethanol vapor sensing applications

Networks of pristine high quality single walled carbon nanotubes （SWNTs）, the SWNTs after Ar-plasma treatment （from 2 to 12 rain） and carbon nanobuds （CNBs） have been tested for ethanol vapor sensing. It was found that the pristine high quality SWNTs do not exhibit any ethanol sensitivity, while the introduction of defects in the tubes results in the appearance of the ethanol sensitivity. The CNB network showed ethanol sensitivity without plasma treatment. Both CNB and low defect （after 3 min treatment） SWNT networks exhibit significant drift in the resistance baseline, while heavily plasma-treated （9 min） SWNTs exhibited high ethanol vapor sensitivity without the baseline change. The mechanisms of the ethanol sensitivity and stability after the plasma irradiation are attributed to the formation of sensitive dangling bonds in the SWNTs and formation of defect channels facilitating access of the ethanol vapor to all parts of the bundled nanotubes.