Solidification Mechanism of Pb and Cd in S2--Enriched Alkali-Activated Municipal Solid Waste Incineration Fly Ash.

S2--enriched alkali-activator (SEAA) was prepared by modifying the alkali activator through Na2S. The effects of S2--enriched alkali-activated slag (SEAAS) on the solidification performance of Pb and Cd in MSWI fly ash were investigated using SEAAS as the solidification material for MSWI fly ash. Combined with microscopic analysis through scanning electron microscopy (SEM), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR), the effects of SEAAS on the micro-morphology and molecular composition of MSWI fly ash were studied. The solidification mechanism of Pb and Cd in S2--enriched alkali-activated MSWI fly ash was discussed in detail. The results showed that the solidification performance for Pb and Cd in MSWI fly ash induced by SEAAS was significantly enhanced first and then improved gradually with the increase in dosage of ground granulated blast-furnace slag (GGBS). Under a low GGBS dosage of 25%, SEAAS could eliminate the problem of severely exceeding permitted Pb and Cd in MSWI fly ash, which compensated for the deficiency of alkali-activated slag (AAS) in terms of solidifying Cd in MSWI fly ash. The highly alkaline environment provided by SEAA promoted the massive dissolution of S2- in the solvent, which endowed the SEAAS with a stronger ability to capture Cd. Pb and Cd in MSWI fly ash were efficiently solidified by SEAAS under the synergistic effects of sulfide precipitation and chemical bonding of polymerization products.

Mechanical behavior analysis of fully grouted bolt under axial load.

Based on the idea of discretization and the force balance analysis of each mass spring element, a spring-element analysis method for bolt is proposed. By analyzing the mechanical behavior of the bond interface of the fully grouted bolt, three coupling models of the bond interface, the slider model, the spring model and the spring-slider model, are proposed. Using the spring-element method, five load transfer models, namely the slider model, the spring model, the modified spring model, the spring-pulled slider model, and the spring-slider model, were deduced. And get the bolt displacement distribution function, axial force distribution function and shear stress distribution function under each model. The five proposed models are verified, analyzed and discussed by using the pull-out test of the smooth steel bolt and the threaded steel bolt. It is verified by experiments that this study is helpful to comprehensively understand the mechanical behavior of fully grouted bolts under axial load. The proposed spring element analysis method is simple and easy to understand and the results are reasonable.

Domain Adaptation With Self-Supervised Learning and Feature Clustering for Intelligent Fault Diagnosis.

Domain adaptation indeed promotes the progress of intelligent fault diagnosis in industrial scenarios. The abundant labeled samples are not necessary. The identical distribution between the training and testing datasets is not any more the prerequisite for intelligent fault diagnosis working. However, two issues arise subsequently: Feature learning in domain adaptation framework tends to be biased to the source domain, and unreliable pseudolabeling seriously impacts on the conditional domain adaptation. In this article, a new domain adaptation approach with self-supervised learning and feature clustering (DASSL-FC) is proposed, trying to alleviate the issues by unbiased feature learning and pseudolabels updating strategy. Taking different transformation methods as pretext, the transformed data and its pretext train a neural network in an SSL way. As to pseudolabeling, clusters are taken as the auxiliary information to correct the network predicted labels in terms of the "strong cluster" rule. Then, the updated pseudolabels and their confidence are enforced to further estimate the conditional distribution discrepancy and its confidence weight. To verify the effectiveness of the proposed method, the experiments are implemented on intraplatform and interplatforms for simulating the practical scenarios.

Strengthening Mechanism for the Mechanical Properties of Cement-Based Materials after Internal Nano-SiO2 Production.

This study focuses on overcoming the agglomeration issue of nano-SiO2 powder in cement, facilitating the strengthening mechanism of cement-based materials. A nano-SiO2 precursor solution (NSPS) was added to cement-based materials to replace nano-SiO2 powder. The influencing laws of the alkalinity and dosage of the NSPS on the mechanical properties of cement were investigated. Further, the strengthening mechanism of the mechanical properties of cement-based materials after internal nano-SiO2 production was analysed. The results show that (1) when the alkalinity of the precursor solution is a weak acid (pH = 6), the compressive strength of cement-based materials after internal nano-SiO2 production is 25%~36% higher than that of pure cement-based materials and 16%~22% higher than that of cement-based materials with silica fume; (2) when the solid content of SiO2 in the current displacement solution is about 0.16% of the cement mass, the compressive strength of the prepared cement-based material is the highest. With the continuous increase in the solid content of SiO2 in the precursor solution, the compressive strength of cement-based materials after internal nano-SiO2 production decreases but is always greater than the compressive strength of the cement-based material mixed with nano-SiO2 micro powder. According to a microstructural analysis, nano-SiO2 particles that precipitate from the precursor solution can facilitate the hydration process of cement and enrich the gel products formed on the cement particle surface. In addition, new network structures among cement particles are formed, and precipitated nano-SiO2 particles fill in the spaces among these cement particles as crystal nuclei to connect the cement particles more tightly and compact the cement-based materials. This reinforces the mechanical properties of cement-based materials.

The Stabilization Mechanism of Nano-SiO2 Precursor Solution.

The issues associated with the fabrication of nano-silica (NS) mineral powder, such as high cost and agglomeration, can be effectively mitigated by using a precursor solution of NS as the external mixture of cement-based materials. Based on the liquid-phase preparation of NS mineral powder, its preparation technology was thoroughly investigated herein. The precursor solution of NS was synthesized using acid media (HCL, HNO3, HBO3, HCOOH, CH3COOH)-the acetic acid concentration was 1~15%-and siliceous materials. (The concentration of sodium silicate was 20~38%). In addition, the pH value (pH4~pH8) of the precursor solution was measured using a pH detector. The indexes of NS, such as precipitation time, morphology, and distribution, were observed to formulate a preparation technique for the precursor solution of NS that possessed the best results for the precipitation of nanoparticles. From the acquired results, it was demonstrated that acetic acid solution (concentration ≤ 3%) and sodium silicate solution (concentration ≤ 25%) were mixed into a solution with pH = 6, which was the optimum mixing ratio for the precursor solution of NS. The prepared precursor solution of NS was also added to the Ca(OH)2 saturated solution, and the precursor solution became active from a stable state. Then, NS particles were precipitated in an alkaline solution and reacted with Ca(OH)2 to form calcium silicate gel, which made the solution increasingly turbid and generated many visible and uniformed flocculating substances. With time, gels were continuously produced, which then turn white. Similarly, NS particles can be precipitated when the precursor solution is added to cement paste, which reacts with the Ca(OH)2 to generate CSH gel and improve the compactness of the cement paste.

Numerical Parametric Study of Coda Wave Interferometry Sensitivity to Microcrack Change in a Multiple Scattering Medium.

The expansion of cracks in 3D printing concrete materials may lead to structural failure, so it is essential to monitor crack propagation development. Coda wave interferometry (CWI) has been proven to be sensitive to microcracks, however, the evolution pattern of ultrasonic coda waves during crack growth is still not clear. This paper reports a numerical study of the sensitivity and feasibility of CWI for monitoring microcrack growth in heterogeneous materials. A two-phase concrete model, which contains microcracks with different angles and lengths, was developed using the finite element analysis software ABAQUS. The relative velocity change (Δv/v) and the decorrelation coefficient (Kd) at different crack increments were quantitatively analyzed. The numerical simulation results show that coda waves are sensitive to microcrack length as well as the crack angle. The Δv/v increases linearly with the increase of the length of a single microcrack, and the Kd could be linked to the crack length quadratically. Furthermore, a quantitative functional relationship between the CWI observations (Kd, Δv/v) and the angle of the crack to the source/receiver and the relative length growth of the crack are established. In addition, the nonlinear relationship between slope and angle can be fitted with a sinusoidal function. The reported results quantitatively assess the coda wave variation pattern during crack propagation, which is important for the promotion and application of CWI technology.

Application of LC-MS/MS method for determination of dihydroartemisin in human plasma in a pharmacokinetic study.

Aim: Dihydroartemisinin (DHA) was also found therapeutic potential for the treatment of systemic lupus erythematosus (SLE). To assess the pharmacokinetic profile of DHA, the concentration of DHA in plasma of SLE patients needed be accurately determined based on a rapid and reliable analytical method. Experimental method & results: Developed method utilizes stable isotope-labeled internal standards and SPE method for sample preparation, applied XBridge C18 column (2.1 × 50 mm, 3.5 µm) for chromatography separation. Detection of the analytes was achieved by an AB Sciex 4000 mass spectrometer under positive electrospray ionization mode. The method was validated in accordance with international guidelines on bioanalytical methods validations. Conclusion: DHA concentrations in human plasma of Chinese SLE patients were quantified by developed LC-MS/MS (no. 2016L02562).