Study on the radiation and self-absorption characteristics of plasma under various background gases.

The self-absorption effect is a primary factor responsible for the decline in the precision of quantitative analysis techniques using plasma emission spectroscopy, such as laser-induced breakdown spectroscopy (LIBS). In this study, based on the thermal ablation and hydrodynamics models, the radiation characteristics and self-absorption of laser-induced plasmas under different background gases were theoretically simulated and experimentally verified to investigate ways of weakening the self-absorption effect in plasma. The results reveal that the plasma temperature and density increase with higher molecular weight and pressure of the background gas, leading to stronger species emission line intensity. To reduce the self-absorption effect in the later stages of plasma evolution, we can decrease the gas pressure or substitute the background gas with a lower molecular weight. As the excitation energy of the species increases, the impact of the background gas type on the spectral line intensity becomes more pronounced. Moreover, we accurately calculated the optically thin moments under various conditions using theoretical models, which are consistent with the experimental results. From the temporal evolution of the doublet intensity ratio of species, it is deduced that the optically thin moment appears later with higher molecular weight and pressure of the background gas and lower upper energy of the species. This theoretical research is essential in selecting the appropriate background gas type and pressure and doublets in self-absorption-free LIBS (SAF-LIBS) experiments to weaken the self-absorption effect.

Non-contact bacterial identification and decontamination based on laser-induced breakdown spectroscopy.

As a new kind of modern military biological weapon, bacterial agents pose a serious threat to the public health security of human beings. Existing bacterial identification requires manual sampling and testing, which is time-consuming, and may also introduce secondary contamination or radioactive hazards during decontamination. In this paper, a non-contact, nondestructive and "green" bacterial identification and decontamination technology based on laser-induced breakdown spectroscopy (LIBS) is proposed. The principal component analysis (PCA) combined with support vector machine (SVM) based on radial basis kernel function is used to establish the classification model of bacteria, and the two-dimensional decontamination test of bacteria is carried out using laser-induced low-temperature plasma combined with a vibration mirror. The experimental results show that the average identification rate of the seven types of bacteria, including Escherichia coli, Bacillus subtilis, Pseudomonas fluorescens, Bacillus megatherium, Pseudomonas aeruginosa, Bacillus thuringiensis and Enterococcus faecalis reaches 98.93%, and the corresponding true positive rate, precision, recall and F1-score reaches 0.9714, 0.9718, 0.9714 and 0.9716, respectively. The optimal decontamination parameters are laser defocusing amount of -50 mm, laser repetition rate of 15-20 kHz, scanning speed of 150 mm/s and number of scans of 10. In this way, the decontamination speed can reach 25.6 mm2/min, and the inactivation rates for both Escherichia coli and Bacillus subtilis are higher than 98%. In addition, it is confirmed that the inactivation rate of plasma is 4 times higher than that of thermal ablation, meaning that the decontamination ability of LIBS mainly relies on the plasma rather than the thermal ablation effect. The new non-contact bacterial identification and decontamination technology does not require sample pretreatment, and can quickly identify bacteria in situ and decontaminate the surfaces of precision instruments, sensitive materials, etc., which has potential application value in modern military, medical and public health fields.

Ultra-repeatability measurement of calorific value of coal by NIRS-XRF.

Calorific value is an important indicator to evaluate the comprehensive quality of coal, and its real-time and rapid analysis is of great significance for optimizing the coal blending process and improving boiler combustion efficiency. Traditional assays are time-consuming, and prompt gamma neutron activation analysis (PGNAA) and laser-induced breakdown spectroscopy (LIBS) have certain limitations. In this paper, a novel technique for ultra-repeatability measurement of coal calorific value by combining near-infrared spectroscopy (NIRS) and X-ray fluorescence (XRF) is proposed. In this NIRS-XRF technology, the former can stably measure organic components such as C-H and N-H that are positively correlated with the calorific value, while the latter can stably measure inorganic elements such as Na, Al, Si, Ca, Fe, and Mn that are negatively correlated with the calorific value. The combination of the two can greatly improve the measurement repeatability of coal calorific value. In the quantitative analysis algorithm, a holistic-segmented prediction model based on partial least squares (PLS) is proposed, that is, the holistic model is used to roughly predict the calorific value and determine the segment accordingly, and then the corresponding segmented model is used to accurately predict the calorific value. The experimental results show that the root mean square error of prediction (RMSEP), the average relative error (ARE), and the standard deviation (SD) of this method for predicting the calorific value of coal are 0.71 MJ kg-1, 1.18% and 0.07 MJ kg-1 respectively. The measurement repeatability meets the requirements of the Chinese national standard. This calorific value measurement technology based on NIRS-XRF is safe, fast, and stable, providing a new way to optimize and control the utilization process of coal in coal washing plants, power plants, coking, and other industries.

Study on direct identification of bacteria by laser-induced breakdown spectroscopy.

Bacteria are everywhere in the natural environment. Although most of them are harmless, there are still some hazardous bacteria that will harm human health, so it is particularly important to identify bacteria quickly. Compared with traditional time-consuming and complicated identification methods, laser-induced breakdown spectroscopy (LIBS) is one of the potential technologies for rapid identification of bacteria. In this paper, six weakly active bacteria, including Escherichia coli, Enterococcus faecalis, Bacillus megaterium, Bacillus thuringiensis, Pseudomonas aeruginosa and Bacillus subtilis, are taken as analysis samples. The thawed bacteria are placed in deionized water, and then uniformly smeared on five kinds of substrates to verify the feasibility of using LIBS to identify these bacteria. Spectrum filtering, normalization and principal component analysis (PCA) are used to preprocess the spectra, and a multi-class identification method based on the one-against-all linear kernel function of support vector machine (SVM) is proposed to establish the prediction model. The identification performance is evaluated by using precision and recall. The experimental results show that high-purity graphite is the best substrate with the least interference to the LIBS spectrum of bacteria. The prediction precision of these six bacteria is 77.27%, 92.86%, 84.21%, 94.12%, 81.82% and 76.92%, respectively, recall is 85%, 100%, 94.12%, 80%, 81.82% and 75% respectively, and the identification rate is 84.17%. It can be seen that the direct identification of bacteria can be preliminarily realized by smearing bacteria on the graphite substrate and analyzing its LIBS spectra, which provides a feasible way for simple, rapid and on-site bacterial identification.

Thermodynamic and Economic Analysis of Oxy-Fuel-Integrated Coal Partial Gasification Combined Cycle.

A novel partial gasification combined cycle (PGCC) system integrating coal partial gasification, oxy-fuel combustion, combined cycle, and CO2 separation is proposed. The coal-CO2 partial gasification technology is introduced in the coal gasification unit, and the oxy-fuel combustion technology is employed in the char combustion unit and gas turbine (GT) unit. The thermodynamic and economic analysis of the proposed system is carried out, showing that both energy and exergy efficiency have an increasing/decreasing tendency when the recycled flue gas (RFG) ratio of char combustion and GT increase. When the RFG ratios of char combustion and GT are 0.43 and 0.34, energy and exergy efficiencies reach maximum values of 48.18 and 45.11%, respectively. The energy efficiency of the PGCC-Oxy system is higher than that of the integrated gasification combined cycle (IGCC)-Oxy system by approximately 3%. It can be concluded from the economic analysis that the total investment on the PGCC-Oxy system is 3272.71 million RMB, and the internal rate of return (IRR) and payback time is 8.07% and 12.38 years, respectively.