单参数单维度Rasch模型的优势与意义

相比多参数多维度IRT模型通过增加参数的方式来提升模型拟合度和解释度,Rasch模型流派强调"理论驱动研究"和"数据符合模型",推崇单参数单维度的测量模型能最大限度地减少额外因素对真实测量目的的影响和干扰,从而保证测量的客观性和准确性。Rasch模型关注测量目标与测量工具的对应关系,它的"简单"特性有助于研究者更准确地评估和解释被测目标与测量工具间的适配性,且在将非线性数据转化为等距数据时具有天然的优势。

基于MK-LSTM算法的盾构掘进参数相关性分析及结构变形预测

提出了MIC-K-median-LSTM(MK-LSTM)算法,用于对盾构掘进过程进行参数相关性分析和结构变形预测。首先,运用改进的MIC(MK)算法对涉及盾构掘进过程中的各参数与结构变形进行相关性分析;然后,在得到相关系数的基础上提出输入参数的修正方法;最后,通过LSTM模型对不同维度输入参数的预测效果进行分析,确定合理的输入参数维度。结果表明:盾构参数对既有结构变形的影响大于土体参数;MK算法可以有效降低计算复杂度和减小噪声对数据的影响,基于参数相关系数的数据前处理方法有利于提高模型的预测精度;MK-LSTM可以有效预测结构随时间的变形规律,考虑数据维度对预测精度的提升效果和计算效率的影响,进行实际工程预测时可以根据参数相关性大小进行维度删减。

Optical Fiber Instrument for Single-point Multi-parameter Measurement

A novel kind of optical fiber instrument for two channel measurement of temperature and displacement was developed. Four channel quartz fiber optics were employed to measure two channel signals of temperature and displacement simultaneously, and the operating efficiency of this instrument was greatly improved.

Investigations of 3D Surface Roughness Characteristic＇s Accuracy

The existing surface roughness standards comprise only two dimensions. However, the real roughness of the surface is 3D （three-dimensional）. Roughness parameters of the 3D surface are also important in analyzing the mechanics of contact surfaces. Problems of mechanics of contact surfaces are related to accuracy of 3D surface roughness characteristic. One of the most important factors for 3D characteristics determination is the number of data points per x and y axes. With number of data points we understand its number in cut-off length. Number of data points have substantial influence on the accuracy of measurement results, measuring time and size of output data file （especially along the y-axis direction, where number of data points are number of parallel profiles）. Number of data points must be optimal. Small number of data points lead to incorrect results and increase distribution amplitude, but too large number of data points do not enlarge range of fundamental information, but substantially increase measuring time. Therefore, we must find optimal number of data points per each surface processing method.

New criterion for rock joints based on three-dimensional roughness parameters

The shear behavior of rock joints is important in solving practical problems of rock mechanics. Three group rock joints with different morphologies are made by cement mortar material and a series of CNL(constant normal loading) shear tests are performed. The influences of the applied normal stress and joint morphology to its shear strength are analyzed. According to the experimental results, the peak dilatancy angle of rock joint decreases with increasing normal stress, but increases with increasing roughness. The shear strength increases with the increasing normal stress and the roughness of rock joint. It is observed that the modes of failure of asperities are tensile, pure shear, or a combination of both. It is suggested that the three-dimensional roughness parameters and the tensile strength are the appropriate parameter for describing the shear strength criterion. A new peak shear criterion is proposed which can be used to predict peak shear strength of rock joints. All the used parameters can be easily obtained by performing tests.

Effects of nonlinear strength parameters on stability of 3D soil slopes

Actual slope stability problems have three-dimensional(3D) characteristics and the soils of slopes have curved failure envelopes. This incorporates a power-law nonlinear failure criterion into the kinematic approach of limit analysis to conduct the evaluation of the stability of 3D slopes. A tangential technique is adopted to simplify the nonlinear failure criterion in the form of equivalent Mohr-Coulomb strength parameters. A class of 3D admissible rotational failure mechanisms is selected for soil slopes including three types of failure mechanisms: face failure, base failure, and toe failure. The upper-bound solutions and corresponding critical slip surfaces can be obtained by an efficient optimization method. The results indicate that the nonlinear parameters have significant influences on the assessment of slope stability, especially on the type of failure mechanism. The effects of nonlinear parameters appear to be pronounced for gentle slopes constrained to a narrow width. Compared with the solutions derived from plane-strain analysis, the 3D solutions are more sensitive to the values of nonlinear parameters.

A dimension-wise method for the static analysis of structures with interval parameters

A novel method for the static analysis of structures with interval parameters under uncertain loads is proposed, which overcomes the inherent conservatism introduced by the conventional interval analysis due to ignoring the dependency phenomenon. Instead of capturing the extremum of the structural static responses in the entire space spanned by uncertain parameters, their lower and upper bounds are calculated at the minimal and maximal point vectors obtained dimension by dimension with respect to uncertain parameters based on the Legend orthogonal polynomial approximation, overcoming the potential engineering insignificance caused by the optimization strategy. After performing its theoretical analysis, both the accuracy and applicability of the proposed method are verified.

Selective suspension of single layer graphene mechanochemically exfoliated from carbon nanofibres

This paper presents the first report of the successful ball-milling exfoliation of graphitic filaments （GANF~ carbon nanofibres） into single layer graphene. The addition of small amounts of solvent during the milling process makes it possible to enhance the intercalation of the exfoliating agent （melamine） between the graphene layers, thus promoting exceptional exfoliation. Advantage has also been taken of the fact that the Hansen solubility parameters of graphene are different from those of carbon fibres, which allows single and few-layer graphene to be suspended in a particular solvent, thus discriminating them from poorly exfoliated carbon nanofibres.