主轴回转误差分析仪校准方法

针对超精密机床主轴回转误差分析仪校准难的问题,分析了主轴回转误差分析仪的系统组成及测量原理,提出了一种基于示值误差、线性度、重复性等主要计量特性的校准方法;搭建了一种专用的校准装置,该装置采用纳米微动台进行位移驱动,采用高精度激光干涉仪作为计量标准,测量线符合阿贝原则,能够在普通实验环境条件下实现:位移范围±1mm内最佳测量能力优于10 nm,10 min内示值稳定性优于2 nm;进行了主轴回转误差分析仪校准试验,给出了不确定度评定方法。该校准方法及装置能够满足主轴回转误差分析仪以及各种纳米级位移传感器及仪器的溯源需要。

Engineering graphitic carbon nitride with expanded interlayer distance for boosting photocatalytic hydrogen evolution

Regulating interlayer distance is a crucial factor in the development of two‐dimensional(2D)nanomaterials.A 2D metal‐free photocatalyst,such as graphitic carbon nitride(g‐C3N4),exhibits morphology‐and microstructure‐dependent photocatalytic activity.Herein,we report a straightforward and facile route for the preparation of unique lamellar g‐C3N4,by co‐firing melamine and ammonium chloride via microwave‐assisted heating.Through the decomposition of NH4Cl,the evaporation of NH3 gas can effectively overcome van der Waals forces,expanding the interlayer distance of g‐C3N4,thereby creating a lamellar structure consisting of nanosheets.Compared with bulk g‐C3N4,the NH3‐derived lamellar g‐C3N4 exhibits a larger specific surface area and enhanced optical absorption capability,which increase photocatalytic hydrogen production because of the highly active structure,excellent utilization efficiency of photon energy,and low recombination efficiency of photogenerated charge carriers.This study provides a simple strategy for the regulation of the g‐C3N4 microstructure toward highly efficient photocatalytic applications.

Nonlinear distortion analysis for multisine excitation constrained by power spectral density

Nonlinear distortion introduced by an amplifier when subjected to a multisine excitation decreases the measurement accuracy in many metrological and measurement areas. In this paper, we performed qualitative and quantitative analyses of the nonlinear distortion with the multisine excitations constrained by a constant power spectral density. We present the numerical results with respect to different tone spacings,nonlinear orders, harmonic phases and tone distributions. Moreover, three as-pects of contributions are made to further reveal the distortion mechanism. First, we find that the type Ⅱ components for Schr- oeder-phase multisines distribute uniformly but not all in anti-phase to the type I components for the second order nonlinearity. Second,we simulate the variance of the type I and Ⅱ components and their summation to explain the principle of reducing the type Ⅱ distortion by averaging the results obtained using multiple realizations of random-phase multisines. Third, we observe a special distortion distribution mechanism for the Schroeder-phase multisine excitation The results contribute to a better estima-tion and understanding of the nonlinear distortion.

Three-dimensional atomic force microscopy based on tailored cantilever probe with flared tip

In order to meet the requirements of nondestructive testing of true 3D topography of micro-nano structures,a novel three-dimensional atomic force microscope(3D-AFM)based on flared tip is developed.A high-precision scanning platform is designed to achieve fast servo through moving probe and sample simultaneously,and several combined nanopositioning stages are used to guarantee linearity and orthogonality of displacement.To eliminate the signal deviation caused by AFM-head movement,a traceable optical lever system is designed for cantilever deformation detection.In addition,a method of tailoring the cantilever of commercial probe with flared tip is proposed to reduce the lateral force applied on the tip in measurement.The tailored probe is mounted on the 3D-AFM,and 3D imaging experiments are conducted on different samples by use of adaptive-angle scanning strategy.The results show the roob-mean-square value of the vertical displacement noise(RMS)of the prototype is less than 0.1 nm and the high/width measurement repeatability(peak-to-peak)is less than 2.5 nm.

Effects of pinholes on zerooffset of single-axis normal-tracking measurement system

A single-axis normal-tracking measurement system is proposed, which can solve the problem of measuring large curved surface. According to Collins formula, the tilt dependent error of the measurement system is studied, which uses Gaussian beam as the light source. By theoretical analysis and numerical simulation, the influence of the error is presented. The results show that there is the difference between point source and Gaussian beam for differential confocal microscopy. The opti-mal diameter of pinhole can be determined by the mathematical model and the actual parameters of the measurement system. The optimal pinhole diameter of this measurement system is 20 to 35 pm for 633 nm wavelength light source.

Seasonal Variations of Hydrochemical Characteristics of Groundwater in Changping Plain, Beijing

Changping Plain, located in the northwest of Beijing, has become an important groundwater recharge area for the Beijing Plain and an important source for the urban water supply. In this study, groundwater samples were collected during the dry and wet seasons in 2015 from 24 monitoring wells distributed in Changping Plain. A Piper-Tri-linear diagram, a Schoeller diagram, a Gibbs diagram, and the isotope technique were used to investigate the temporal and spatial variations in the concentrations of groundwater hydrochemicals and the sources of groundwater recharge. The results indicated： 1） seasonal variations in the concentrations of HCO3^–, Ca^2＋, and Na^＋ were significant; the spatial variations of these ions were more dramatic in the dry season than in the wet season due to the dilution effect of precipitation; 2） Most groundwater samples had a HCO3-Ca-Mg based hydrochemical type and a few had a HCO3-Na-K based hydrochemical type; the hydrochemical type tended to evolve from HCO3-Ca-Mg based to HCO3-Na-K based in some monitoring wells that showed distinct seasonal variation; 3） the groundwater in the study area originated mainly from atmospheric precipitation, and it is affected by evaporation and concentration processes.