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Facing the characteristics of big data in modern industrial system, manually retrieving the data from many different batches of vibration signals for modal analysis will cause low data utilization and low efficiency. At the same time, under cutting condition, the harmonic component generated by the rotating excitation of machine tool interferes the auto-identification of structural modal parameters from a large number of vibration signals. Therefore, to realize the auto-identification of structural dominant modal parameters from large amounts of different batches vibration data under cutting condition, a new weighted-SSA (singular spectrum analysis) method is proposed in this paper. First, multi batch on-site vibration signals are decomposed, and the eigenvalue and matrix are extracted through singular value decomposition. Then, based on the variance filtering of principal component analysis, a half principal component analysis is proposed to extract the weighted vector of the eigen matrix. and clustering is adopted to average the noise reduction signals, to realize the automatic screening of a large amount of data and the automatic distinction of modal parameters. Third, the identified dominant mode of the structure with weak link is optimized through the genetic algorithm, to achieve the suppression of spindle tool system vibration. Finally, the cutting tests are conducted to verify the feasibility and effectiveness of the auto-identification and optimization method.

In five-axis machining, drastic change of tool axis has negative effects on machining efficiency and quality. Our published work proposed a unified mathematical framework to generate smooth tool-axis field and implemented in 1D domain (Yan et al., J Manuf Syst 48:30–37, 2018). In this paper, we extend the mathematical framework to 2D domain and the framework is an integral functional problem converting diverse machining requirements, such as gouge and collision free, smoothness, into mathematical expressions. A tool-axis vector field (TAVF) defined on the freeform surface is calculated by optimizing the integral functional problem. The surface is discrete into triangular mesh, and the discrete TAVF calculation problem is solved by a numeric 2D finite element method (FEM). Subsequently, the proposed algorithm is implemented to generate field-generated tool path (FGTP). The tool path has been used in machining hub of blade disk (blisk). The blisk is a complex workpiece that impellers should be gouge avoided. Machining experiments indicate that tool path generated by the proposed algorithm can avoid collision and improve smoothness on the whole surface. The freeform surface machining quality is highly improved compared with that machined by region-partitioned tool path (RPTP).

Water-soluble, high quantum yield, green color carbon quantum dots (CQDs) are prepared by acid reflux with the use of coke powders as a carbon source. The CQDs are characterized by UV–Vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscope, fourier transform infrared spectrophotometer and x-ray diffraction. The analysis includes the evaluation of key variables with effect in the synthetic process of the quantum yield (QY) of CQDs: the reaction temperature and time, the volume of mixed acid (concentrated H2SO4 and HNO3) and the pH value on the structure and properties of as-prepared CQDs. The results revealed that the optimal hydrothermal synthesis conditions for obtaining CQDs are reaction at 100 °C for 8 h, with the volume of mixed acid is 16 mL, at pH value 9. The prepared CQDs have the activity of peroxidase-like and that quantum yield(QY)reached 34.27%.

Nitrogen dopants on carbon materials play vital roles in metal-free carbon catalysis, while the role of pyridinic nitrogen (NP) or graphitic nitrogen (NG) is still on debate. In this work, N-doped ...

Me N C catalysts have received intensive scientific interest as non-noble-metal single-atom catalysts (SAC) for electrochemical- and thermocatalytic reactions. However, the lack of understanding of its properties hinders further improvement of the catalytic performance. An interesting issue is the molecular details of the reaction involving more than one reactant, since the activation of the second reactant is inevitably affected by the first one on SAC. Here, we synthesized Co N C SACs for the aerobic oxidation of benzyl alcohol (BA) to benzaldehyde. The catalyst exhibited excellent activity for this reaction, among the most active non-noble-metal catalysts. Differently from particulate metal or metal oxide catalysts, the Co N C SAC displayed “self-poisoning” due to the strong competitive adsorption of BA to O2, as revealed by kinetics experiments and density functional theory calculations. Moreover, we rationalized the poisoning effect of polar moieties, including organic solvents and aqueous solutions, on the SAC. These results shed light on the catalytic behavior of aerobic oxidation of BA on the molecular level and enable the rational design of catalytic organic synthesis over Co N C SACs.

Using L-glutathione (GSH) as a capping agent, ZnSe/GSH quantum dots (QDs) were prepared under microwave irradiation and irradiated under dark, ultraviolet light and incandescent light, respectively. The properties and interaction of different lights irradiated ZnSe/GSH QDs and bovine serum albumin (BSA) were studied systematically. The fluorescence (FL) spectra results reveal that the quenching mechanism are all the static quenching in nature. The quenching constant (Ksv) and binding constant (K) value of different irradiated ZnSe/GSH QDs and BSA all increased with the change of light types from dark to incandescent light and UV light. The number of binding site (n) is close to 1 at different temperatures. The lighting types influence the enthalpy and entropy changes. The Fourier transform infrared (FTIR) spectra indicate that the light induced GSH ligand will facilitate photocatalytic oxidation on the surface of ZnSe/GSH QDs. The circular dichroism (CD) results show that the α-helicity content of BSA decreases from 60.34%, 59.31%, to 58.79% under UV lighting, incandescent lighting and dark conditions. The interaction results of different lights illuminated ZnSe/GSH QDs with BSA by CD spectra method matches well with that by FL and FTIR spectra. That is, the interaction of ZnSe/ GSH QDs and BSA from strong to weak is UV light, incandescent light and dark in sequence.

The typical tool path of turning freeform surfaces is spiral. Usually, this kind of tool path only can deal with continuous surfaces within a circular area. If the designed surfaces are not continuous, the spiral tool path will break, which will lead to a significant increase in servo following error of ultraprecision lathe during machining. In order to reduce the servo following error, the processing speed needs to be significantly reduced, which will greatly decrease the machining efficiency. To solve this problem, a smooth tool path interpolation algorithm in the non-cutting area for ultraprecision turning discontinuous multi-freeform-surfaces is proposed. In addition, more than circular area, this method can generate smooth tool paths for discontinuous generic surfaces of quasi-revolution based on the optimized space Archimedean spiral. Finally, the effectiveness and adaptability of the method are proved through two examples.

Carbon nanotubes (CNTs) have received intensive scientific interests as a metal-free catalyst for the oxidation reactions of hydrocarbons in the liquid phase. However, its application in the liquid reaction is limited by the costly catalyst filtration process. Herein, a structured CNT catalyst was fabricated via growing CNTs on Ni foams with a porous Al2O3 coating layer. The resultant structured CNTs were used both as catalysts and as stirrer in a rotating foam stirrer reactor. The catalytic performance was evaluated in the production of cumene hydroperoxide by the aerobic oxidation of cumene. Under optimized experimental conditions, the cumene conversion reached 25.1%, 14% higher than that of commercial CNTs in a slurry reactor. The excellent adhesion strength of CNTs on the foam and catalytic stability in 5 runs of recycling were demonstrated, opening a new way to employing CNTs as a metal-free catalyst in the liquid phase reactions.

Dual-transition-metal oxide (DTMO) nanostructures are emerging materials for lithium-ion battery (LIB) anodes with improved structural stability, electronic conductivity and electrochemical performance compared to their single-metal counterpart. Herein, composites of graphene with DTMOs (MFeO, M = Co, Mn, Zn) were controllably prepared by harnessing the synthesis atmospheres and the nanoscale diffusion couple. Their composition and morphology were characterized by TEM, EDS mappings, XRD and XPS. The NH3 treatment resulted in the formation of hollow DTMO nanoparticles on nitrogen-doped graphene, while H2 and Ar gave graphene-supported hollow and solid DTMO particles, respectively. Electrochemical tests were applied to compare the performance of these composites as LIB anodes. The superior anode performance DTMO electrodes was demonstrated to the corresponding iron oxide composite. CoFe2O/RGO composites exhibit excellent rate capability and high-rate cycling stability for lithium storage, due to its stable solid structure. However, the hollowing of DTMO particles cannot elevate the capacity and stability, due to the interfacial resistance and structural changes upon cycling.