Quantitative Analysis of Heavy Metals in Water Based on LIBS with an Automatic Device for Sample Preparation

Abstract Heavy metals in water can be deposited on graphite flakes, which can be used as an enrichment method for laser-induced breakdown spectroscopy （LIBS） and is studied in this paper. The graphite samples were prepared with an automatic device, which was composed of a loading and unloading module, a quantitatively adding solution module, a rapid heating and drying module and a precise rotating module. The experimental results showed that the sample preparation methods had no significant effect on sample distribution and the LIBS signal accumulated in 20 pulses was stable and repeatable. With an increasing amount of the sample solution on the graphite flake, the peak intensity at Cu I 324.75 nm accorded with the exponential function with a correlation coefficient of 0.9963 and the background intensity remained unchanged. The limit of detection （LOD） was calculated through linear fitting of the peak intensity versus the concentration. The LOD decreased rapidly with an increasing amount of sample solution until the amount exceeded 20 mL and the correlation coefficient of exponential function fitting was 0.991. The LOD of Pb, Ni, Cd, Cr and Zn after evaporating different amounts of sample solution on the graphite flakes was measured and the variation tendency of their LOD with sample solution amounts was similar to the tendency for Cu. The experimental data and conclusions could provide a reference for automatic sample preparation and heavy metal in situ detection.

Effects of automatic variable preload device on performance of spindle

To increase the machine accuracy by improving the stiffness of bearings,a preload was applied to bearings.A variable preload technology was necessary to perform machining processes in both low and high speed regions.An automatic variable preload device was fabricated using an eccentric mass.By installing the fabricated device on a spindle,the effect of the automatic variable preload device on the performance of the spindle was analyzed.In the results of the vibration measurement of the spindle,the vibration is increased by 20%-37% according to measurement points at the maximum rotation speed of 5 000 r/min.And,in the results of the noise measurement of the spindle,the spindle rotation speed is increased by about 1.9% and 1.5% at the front and side of the spindle,respectively.Based on the results of this analysis,an improved method that reduces such effects on the performance of the spindle is proposed.

Research on Cam-linkage Mechanism of Automatic Piecing Device

The principle of an automatic piecing device is presented, and the mathematic model of a specific combined mechanism of the automatic piecing device is analysed. The kinematics and dynamics equation of the combined mechanism is established on the basis of the mathematic model. By the virtual prototype technology, the motion of this mechanism is simulated, whose result is post-processed by ADAMS. To improve the output motion, according to the simulation output and automatic piecing device's practical working condition, the optimisation of the cam mechanism is carried out by finite difference method. The simulation result of this combined mechanism turns out in accordance with its theoretical analysis of virtual prototype in this research, which, therefore, lays a principle basis for the further study of automatic piecing device.

Performance of automated CT ASPECTS in comparison to physicians at different levels on evaluating acute ischemic stroke at a single institution in China

Background:Our aim was to evaluate the sensitivity and specificity of the automated computer-based Alberta Stroke Program Early CT Score(e-ASPECTS)for acute stroke patients and compare the result with physicians at different levels.Methods:In our center,e-ASPECTS and 9 physicians at different levels retrospectively and blindly assessed baseline computed tomography(CT)images of 55 patients.Sensitivity,specificity,receiver-operating characteristic curves,Bland–Altman plots with mean score error,and Matthews correlation coefficients were calculated.Comparisons were made between the scores by physicians and e-ASPECTS with diffusion-weighted imaging(DWI)being the ground truth.Two methods for clustered data were used to estimate sensitivity and specificity in the region-based analysis.Results:In total,1100(55 patients×20 regions per patient)ASPECTS regions were scored.In the region-based analysis,sensitivity of e-ASPECTS was better than junior doctors and residents(0.576 vs 0.165 and 0.111,p<0.05)but inferior to senior doctors(0.576 vs 0.617).Specificity was lower than junior doctors and residents(0.883 vs 0.971 and 0.914)but higher than senior doctors(0.883 vs 0.809,p<0.05).E-ASPECTS had the best Matthews correlation coefficient of 0.529,compared to senior doctors,junior doctors,and residents(0.463,0.251,and 0.087,respectively).Conclusions:e-ASPECTS showed a similar performance to that of senior physicians in the assessment of brain CT of acute ischemic stroke patients with the Alberta Stroke Program Early CT score method.