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The boundary element method (BEM) is an efficient way to compute solutions of eddy current nondestructive evaluation (NDE) problems. However, in boundary element analysis of eddy currents, the computational accuracy and efficiency depend on the element discretization employed and are very sensitive to the liftoff distance and the relative geometry size between the detecting coil and object under evaluation or test. In this paper, the skin depth parameter is applied to study the element discretization effects on boundary element analysis for 3D eddy current NDE problems. The element discretization rules are concluded by conducting numerical experiments for different liftoff distances and relative probe sizes so that they can be adjusted to account for variations in these parameters, and validated against the analytical method, semi-analytical method, and experiments of some benchmark problems. With the help of the rules, the overall computational accuracy is improved while the cost is reduced for the BEM modeling of eddy current NDE problems.

A two-dimensional zinc(II)-based metal-organic framework [Zn • (BA) • (BBI)] was synthesized from 1,2-benzenediacetic acid and 1,1'-(1,4-butanediyl) bis(imidazole) via a solvothermal reaction. The crystal exhibits good chemical stability in the pH range from 2 to 12, and strong fluorescence with excitation/emission maxima of 270/290 nm. The crystal is shown to by a viable fluorescent probe for the detection of ascorbic acid (AA) and the antibiotics chloramphenicol (CHL) and ceftriaxone (CRO). Fluorescence intensity of crystal dispersion is significantly quenched with increasing concentrations of AA/CHL/CRO. Quenching occurs even in the presence of other substances. The assay is fast (5 s) and has a low detection limit (1.6 ppb for AA, 12 ppb for CHL and 3.9 ppb for CRO). The crystal still has a good quenching effect on AA/CHL/CRO after washing and using for five times. The response of the probe is related to the interplay between the MOF and analytes via energy absorption competition. Graphical abstractSchematic diagram of preparing Zn • (BA) • (BBI) and responding to target analytes. BA: 1,2-phenyldiacetic acid; BBI: 1,1'-(1,4-butanediyl)bis(imidazole); Zn • (BA) • (BBI): Crystal chemical formula.

Anodic aluminum oxide (AAO) thin film recently has been found as a new type of fluorescence enhancement nanomaterial. However, the mechanisms of the AAO thin film for the fluorescence enhancement have not been completely understood. Herein, the studies of its mechanisms are reported. Based on the experimental and modeling results, it has been found that the main contributing factor to the fluorescence enhancement is probably the plasmonic Al nanoparticles (NPs) embedded in the film, while the nanopore size and porosity of AAO thin film have a limited contribution. The characteristics of the enhancement have also been studied. It has been found that the enhancement is highly related to the gap between the fluorophore and the surface of the AAO thin film. Different excitation wavelength also results in different fluorescence enhancement. Using a simple model with a layer of Al NPs uniformly distributed in the thin film, the calculated enhancement factor of electric field and characteristics of the fluorescence enhancement match the experimental results.

Uniform Bi2WO6 pancakes were prepared via a solvothermal route in a solvent mixture of glycerol (Gly) and water (V/V = 1). A variety of techniques including scanning electron microscopy, transmission electron micrographs, X-ray powder diffraction, Brunauer–Emmett–Teller, FT-IR spectra, and UV–Vis diffuse reflectance spectra, were employed to characterize the structure and properties of the as-obtained Bi2WO6. It was found that Bi2WO6 pancakes showed prominent photocatalytic performance for the degradation of rhodamine B (RhB) under visible light (λ ≥ 420 nm) irradiation, which can be attributed to its good crystallization, large surface area, unique morphology and structural features.

A hydrophilic polypyrrole/tellurium (PPy/Te) nanocomposite was synthesized by a facile approach in which H2TeO3 was used as the oxidizing agent of pyrrole and then the elemental Te formed in situ catalyzed the polymerization of pyrrole. The morphology and structure of the products were characterized by a series of testing technology. The electrochemical property and impedance of the PPy/Te nanocomposite were studied by cyclic voltammetry and electrochemical impedance spectroscopy, respectively. Significantly, the charge-discharge measurement results show that the PPy/Te nanocomposite has high specific capacitance (2488 F/g, at 2 A/g) and good cyclability.

CdSe:Eu nanocrystals were successfully synthesized and characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectric spectroscopy. The CdSe:Eu nanocrystals showed enhanced green electrochemiluminescence (ECL) intensity when compared to pure CdSe nanocrystals. Further, the nanocrystals were used to design an ECL immunosensor for the detection of carcinoembryonic antigen (CEA) that has a linear response over the 1.0 fg·mL−1 to 100 ng·mL−1 CEA concentration range with a 0.4 fg·mL−1 detection limit. The assay was applied to the determination of CEA in human serum samples.

The cobalt sulfide/graphene oxide (CoS/GO) nanocomposite was synthesized by a simple hydrothermal reaction. The products as-synthesized were characterized by XRD, SEM, TEM, BET-BJH and TG. The electrochemical property and impedance of the CoS/GO nanocomposite were studied by cyclic voltammetry and EIS analysis, respectively. The results show that the presence of the GO enhances the electrode conductivity, and then improves the capacitance property of the CoS/GO nanocomposite. The galvanostatic charge/discharge measurement results show that the CoS/GO nanocomposite has a high specific capacitance (550 Fg-1) and long cycle life (over 1 000 cycles).

The combination of organic conducting polymer with inorganic semiconductor is one of the most important topics in developing photoelectric materials. In this work, bouquet-like polythiophene/tellurium (PTh/Te) nanocomposite was synthesized via the redox reaction of H2TeO3 and thiophene. The formation mechanism and effect factors of PTh/Te nanocomposite were discussed. It was found that the elemental Te formed in situ promoted the polymerization of thiophene, and the remainder H2TeO3 molecules adsorbed on the PTh chains made the nanocomposite soluble. The Z-scan test results show that the PTh/Te nanocomposite has a large two-photon absorption (TPA) cross-section and nonlinear optical (NLO) absorption coefficient.

This paper presents the adaptive cross approximation (ACA) algorithm to accelerate boundary element method (BEM) for eddy current nondestructive evaluation (NDE) problem. The eddy current problem is formulated by boundary integral equation and discretized into matrix equations by BEM. Stratton–Chu formulation is selected and implemented for the conductive medium which does not has low frequency breakdown issue. The ACA algorithm has the advantage of purely algebraic and kernel independent. It starts with hierarchically partitioning the object to get diagonal blocks, near blocks and far blocks. The far-block interactions which are rank deficient can be compressed by ACA algorithm meanwhile the elements for diagonal-block interactions and near-block interactions are stored and computed by BEM. We apply modified ACA (MACA) for more memory saving while keeping almost same accuracy compared with original ACA. For numerical testing, several practical NDE examples such as coil above a half space conductor, tube in a fast reactor and Testing Electromagnetic Analysis Methods (TEAM) workshop benchmark problem are presented to show the robust and efficiency of our method. With the aid of ACA, for electrically small problems, the complexity of both the memory requirement and CPU time for BEM are reduced to $$ O\left( {N\log N} \right). $$

Template-free method is used to facilely synthesize TiO2 hollow microspheres via one-step hydrothermal method. Interestingly, the TiO2 hollow microspheres have porous shell with thickness of about 450 nm. The formation mechanism of the hollow@porous TiO2 microspheres involves the formation and aggregation of TiO2 nanoparticles followed by oriented growth, etching of HF, and then Ostwald ripening and transformation process. The prepared TiO2 microspheres show a reversible capacity of ~170 mAh g−1 after 150 cycles at a current density of 0.6 C and also exhibit a good rate capability of 40.8 mAh g−1 at a current density of 24 C due to the unique hollow@porous structure, which can offer more sites for the storage and insertion of Li ions, and accelerate electrolyte diffusion and Li ions transport. The results also indicate that the as-prepared TiO2 material possesses excellent electrochemical performances, which may be an ideal anode material for lithium ion battery.

A novel molybdenum sulfide-chitosan/CdSe quantum dots (MoS2-CS/CdSe QDs) composite was prepared by a facile liquid chemistry procedure. The composition and morphology of the composite as-prepared were characterized by a series of measurements. The electrode modified with MoS2-CS/CdSe QDs composite has excellent electrochemiluminescence (ECL) property that benefited from the synergistic effect of MoS2 nanosheets, CdSe QDs, and CS molecules. Based on strong and stable ECL emission, the electrode as-modified was used as ECL sensor for the detection of uric acid (UA) and the results show that the detection linear range for UA is from 0.10 to 140 nM with the detection limit of 0.040 nM. Depending on its good sensitivity and selectivity, this ECL sensor was successfully applied to determine uric acid in urine sample.

A film of perovskite-type LaFeO3 nanoparticles (NPs) was deposited on fluorine-doped tin oxide (FTO) conducting glass via dipping-lifting and calcination. Scanning electron microscopy shows that the NPs are evenly distributed on the surface of the glass. The modified glass was further coated with antibody against human interleukin 6 (IL-6) to result in a photoelectrochemical immunosensor for IL-6. The well-established photoelectrochemical immunoassay has a linear current response in the range of 0.1 pg·mL−1 to 0.1 μg·mL−1 and a detection limit as low as 33 fg·mL−1.

The hierarchical flower-like β-In2S3 catalyst assembled from 2D nanosheets was prepared using an organic-component depletion method utilizing inorganic-organic hybrids indium diethyldithiocarbamate (In-DDTC) as a single-source precursor. The crystallization, morphology and composition of the as-synthesized β-In2S3 were characterized by XRD, SEM, TEM, EDS and XPS, respectively. The β-In2S3 possessed high specific surface area of 134.1 m2 g-1, adsorption capacity of 195.5 mg g-1 for methylene blue, and extreme photodecolorization speed under visible light irradiation for the complete removal of methyl orange (MO) dye within 15 min and tetracycline within 60 min. Although methyl orange concentration decreased quickly, the total organic carbon (TOC) decreased slowly. UV-vis and mass spectrometry (MS) were applied to analyze the intermediates coming from the photodecolorization of MO. In order to estimate the roles of active species during the decolorization of MO, trapping experiments were conducted to determine the main active species during the decolorization process. The results indicated that . O2 − radicals and e-1 were the key intermediates. This enhanced activity was attributed to its unique structures assembled from 2D nanosheets with thickness of ca. 5-7 nm, leading to high specific surface area, wide range of pore size distribution and great efficiency in absorbing light and electron/hole separation. The hierarchical flower-like β-In2S3 demonstrated great advantages in the treatment of various wastewater pollutants including textile dyes and antibiotics.

Olive-like BiVO4 microstructures with lengths of 600–1000 nm and widths of 300–600 nm have been synthesized via a facile and additive-free solvothermal method. Studies find that the type of solvent plays an important role in the morphology of the final products. Furthermore, Ag3PO4 nanocrystals are successfully deposited on monoclinic olive-like BiVO4 via in situ precipitation method. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectra, and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activities of the catalysts are evaluated by degradation of rhodamine B (RhB) and methylene blue (MB) under visible light (≥420 nm) irradiation. The experimental results suggest that catalytic activity of the composite photocatalysts is greatly influenced by the loading level of Ag3PO4. The molar ratio of 0.8:1.0 Ag3PO4-loaded BiVO4 exhibits higher photocatalytic activity in both the decolorization of RhB and MB than that of individual BiVO4 and P25. The observed improvement in photocatalytic activity is associated with the extended absorption in the visible light region resulting from the Ag3PO4 nanoparticles, and the effective separation of photogenerated carriers at the Ag3PO4/BiVO4 interfaces through the formation of heterojunction structure. The study provides a general and effective method in the fabrication of composite with sound heterojunctions that may show a variety of applications.

To explore the role of protective enzymes in cassava (Manihot esculenta Crantz) resistance to mites, transgenic cassava lines overproducing copper/zinc superoxide dismutase (MeCu/ZnSOD) and catalase (MeCAT1) were used to evaluate and molecularly confirm cassava resistance to Tetranychus cinnabarinus. Laboratory evaluation demonstrated that, compared with the control cultivar TMS60444 (wild type, WT), the survival, reproduction, development and activities of SOD and CAT in T. cinnabarinus feeding on transgenic cassava lines SC2, SC4, and SC11 significantly inhibited. Furthermore, the activities of SOD and CAT in transgenic cassava lines SC2, SC4, and SC11 damaged by T. cinnabarinus significantly increased. These findings were similar to the results in the mite-resistant cassava cultivars. Besides, field evaluation indicated that the transgenic cassava lines SC2, SC4, and SC11 were slightly damaged as the highly mite-resistant control C1115, while the highly mite-susceptible WT was severely damaged by T. cinnabarinus. Laboratory and field evaluation demonstrated that transgenic cassava lines were resistant to T. cinnabarinus, which directly confirmed that the increase in SOD and CAT activities was positively related to cassava resistance to T. cinnabarinus. These results will help in understanding the antioxidant defense responses in the cassava–mite interaction and molecular breeding of mite-resistant cassava for effective pest control.

By dipping-lifting in sol–gel solution and reducing process, the TiO2 composite film on the glass plate was first prepared. Then, the PbSe/BaTiO3/TiO2 composite film was fabricated by interface reaction with BaTiO3 and PbSe on the surface of TiO2 composite film. The characterization results show that the uniform porous TiO2 film is made up of the anatase crystal, and the PbSe/BaTiO3/TiO2 composite film is constructed by doping or depositing BaTiO3 and PbSe nanoparticles on the surface of TiO2 film. The photoelectrochemical measurement results indicate that the PbSe/BaTiO3/TiO2 composite film has an interesting photoelectrochemical conversion property.

The hierarchically shaped CuO-CeO2 composites were prepared through a facile solvothermal method without using any template. The as-prepared products were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and N2 adsorption–desorption analysis. In the characterization, we found that CuO-CeO2 composites were showed uniform size and morphology which were consisted of the secondary nanoflakes interconnected with each other. Most interestingly, the composites showed efficient performance to remove methyl blue and Congo red dyes from water with maximum adsorption capacities of 2131.24 and 1072.09 mg g−1, respectively. In addition, because of their larger surface area and the unique hierarchical structures, the adsorption performance of the CuO-CeO2 composites is much better than the materials of CuO and CeO2.

In this study, we report a facile approach to synthesize Cu2(OH)3NO3 nanosheets via simply sonochemical method, which showed high efficiency and selectivity towards the adsorption of organic dyes containing sulphonic groups. The structure and morphology of the nanosheets were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption–desorption isotherms, particle size and zeta potential analysis. The adsorption results indicated that the equilibrium data coincide very well with Langmuir isotherm, and the maximum adsorption capacities for Congo red, methyl blue and methyl orange were 1864, 1270 and 959 mg g−1, respectively. The kinetic data can be explained by pseudo-second-order model. The Cu2(OH)3NO3 nanosheets also demonstrated high selectivity towards the adsorption of dyes containing sulphonic groups from mixed dye solutions. The rational mechanism of adsorption was attributed to hydrogen bonding, electrostatic attractions and ion exchanges between the dye molecules and Cu2(OH)3NO3 in the adsorption process.

A new kind of Co-based ternary nanocomposites has been obtained via one step without any additional surfactant at zero centigrade degree. Some experimental parameters play crucial roles in determining the morphologies and homogeneity of the final products, such as reaction temperature and the introduction of Na2S2O3·5H2O. The samples were characterized by XRD, SEM, TEM, UV–Vis, XPS, and BET. The result reveals that the as-prepared samples are Co1.29Ni1.71O4–Co3S4–Co3O4 Co-based ternary nanocomposites with an elliptic morphology composed of numerous fold-shaped superthin films (average thickness of ca. 2 nm). Interestingly, the obtained nanocomposites display superior performance for the hydrogenation of p-nitrophenol at room temperature in the presence of NaBH4. More importantly, the as-prepared nanocomposites show the huge adsorption capacity for methyl blue at room temperature, reaches 1100 mg g−1. A kind of new-type Co-based ternary nanocomposites has been obtained via one step without surfactants at zero centigrade degree. The as-prepared nanocomposites display superior performance for the hydrogenation of p-nitrophenol in the presence of NaBH4 at room temperature.

We study the one-pot facile hydrothermal growth of ultralong silver-carbon (Ag-C) nanocables with Ag nanowires as the cores and carbon as the sheaths through the mediation of H2SO4 and without using an organic surfactant. In the investigation, Ag-C nanostructures were systematically and extensively examined as a function of both temperature and H2SO4 concentration to locate the optimal conditions for preparing ultralong, robust, and uniform Ag-C coaxial nanocables at T = 180 °C and 0.5 M H2SO4. The characterization clearly demonstrated a simple, efficient, and surfactant-free synthesis of Ag-C nanocables. In the hydrothermal process, glycerol acts as both reducing agent and carbon source, while H2SO4 mediates the directional growth of the silver nanowire core and assists the deposition of carbon. Moreover, the nanocables manifest unusual ferromagnetism at room temperature and a plausible mechanism of forming Ag-C nanocables was proposed as a result of the chain-like hydrogen sulfate compounds owing to the H2SO4 mediation.

A boundary integral equation (BIE) is developed for the eddy-current (EC) problems with Dirichlet boundary condition by considering the difference between the field without cracks and the one with cracks. Once the field and its normal derivative are given for the structure in the absence of cracks, normal derivative of the scattered field on the surface can be calculated by solving this integral equation numerically. For infinite-domain problems, this equation is more efficient than the conventional BIE due to a smaller computational region needed. Four kinds of two-dimensional EC problems have been solved using this integral equation. The surface impedance for different cases is presented in this paper. Numerical results are compared with analytical solutions and published numerical results. There are good agreements between them. Also, this concept can be extended to three-dimensional problems with other boundary conditions.

Graphene-like cobalt–nickel double hydroxide nanocomposites have been successfully prepared by a mild hydrolysis process at the room temperature. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. The results reveal that the as-prepared samples are composed of α-Co(OH)2 and α-Ni(OH)2, and contain numerous thin flakes with wrinkle structure, and the thickness of the flakes is ca. 1 nm. Magnetic measurements indicate that the as-prepared nanocomposites have a weak ferromagnetic behavior at the room temperature, which is due to a small content of metallic Co. The as-synthesized products emerge large specific surface area (260.1 m2 g−1) from the measurement of Brunauer–Emmett–Teller. Interestingly, compared to single components, the obtained nanocomposites have exhibited superiorly and enhanced catalytic activity to the hydrogenation of p-nitrophenol in the presence of excess sodium borohydride at room temperature. In addition, the adsorption property of the nanocomposites for methyl blue has also been examined.