Lanthanide-doped upconversion nanocrystals (UCNCs) have recently become an attractive nonlinear fluorescence material for use in bioimaging because of their tunable spectral characteristics and ...exceptional photostability. Plasmonic materials are often introduced into the vicinity of UCNCs to increase their emission intensity by means of enlarging the absorption cross-section and accelerating the radiative decay rate. Moreover, plasmonic nanostructures (e.g., gold nanorods, GNRs) can also influence the polarization state of the UC fluorescence--an effect that is of fundamental importance for fluorescence polarization-based imaging methods yet has not been discussed previously. To study this effect, we synthesized GNR@SiO2 @CaF2 :Yb3+ ,Er3+ hybrid core-shell-satellite nanostructures with precise control over the thickness of the SiO2 shell. We evaluated the shell thickness-dependent plasmonic enhancement of the emission intensity in ensemble and studied the plasmonic modulation of the emission polarization at the single-particle level. The hybrid plasmonic UC nanostructures with an optimal shell thickness exhibit an improved bioimaging performance compared with bare UCNCs, and we observed a polarized nature of the light at both UC emission bands, which stems from the relationship between the excitation polarization and GNR orientation. We used electrodynamic simulations combined with Förster resonance energy transfer theory to fully explain the observed effect. Our results provide extensive insights into how the coherent interaction between the emission dipoles of UCNCs and the plasmonic dipoles of the GNR determines the emission polarization state in various situations and thus open the way to the accurate control of the UC emission anisotropy for a wide range of bioimaging and biosensing applications.
Ultrafine/nano WC–Co cemented carbide is widely used because of its high hardness, strength, toughness, and other comprehensive properties. However, WC grain growth during preparation is a persistent ...issue that hinders the development of this type of cemented carbide. In this context, we review current research on the preparation of ultrafine/nano WC–Co composite powder and sintering methods of ultrafine/nano cemented carbide. The correlation between grain growth and densification during sintering is analyzed. The key technologies inhibiting WC grain growth are explored and discussed, and the synergism between transition metal carbides and rare-earth element mixtures is found to effectively inhibit the growth of WC grains and improve the general performance of ultrafine/nano WC–Co cemented carbide. Finally, future research directions and development trends of ultrafine/nano WC–Co cemented carbides are presented.
Micro/nanoplastic pollution in the water environment has received great attention worldwide. The rapid identification and analysis of micro/nanoplastics are crucial steps for monitoring animal safety ...and protecting human health. Herein, we developed a novel surface-enhanced Raman spectroscopy (SERS) sensor based on Co3O4/Co3S4/AgNPs array substrate for the detection and analysis of micro/nanoplastics. The semiconductor heterojunction-induced charge transfer, enhanced together with the electromagnetic enhancement of plasmon AgNPs, endow the sensor with high sensitivity, thus achieving exceptional analytical and detection capability for polystyrene (PS) nanospheres of different sizes ranging from 1 µm to 1 nm. The limits of detection (LOD) for PS nanospheres (size of 1 µm and 800 nm) was as low as 25 µg/mL, even with a portable Raman spectrometer. Additionally, the periodic Co3O4/Co3S4/AgNPs array generated high repeatability of Raman signals with relative standard deviation (RSD) values less than 7.6%. As proof of this concept, we further demonstrated the simulation detection of PS in actual water samples. We measured the SERS spectra of the different sizes and concentrations of PS spiked in lake water and city water. The results showed that the sensing platform realized trace detection of PS nanospheres in lake water with a detection limit of 14 µg/mL, and a quantitative detection of PS with linear relationship (R2 = 0.962). This SERS sensor has demonstrated fast analysis of PS nanospheres, which can provide a solid basis for the qualitative and quantitative detection of various micro/nanoplastics in the real water environments.
This article investigates the <inline-formula><tex-math notation="LaTeX">\eta</tex-math></inline-formula>-exponential stabilization and positivity of the controlled discrete-time polynomial fuzzy ...model (DPFM) system with time delay. <inline-formula><tex-math notation="LaTeX">\eta</tex-math></inline-formula>-exponential polynomial copositive Lyapunov candidate is proposed to detect the system stability under the convergence (decay) rate. Static output feedback fuzzy controller is then synthesized to assure the DPFM closed-loop system with time delay. We propose Chebyshev membership functions (CMFs) to approach the primary membership function and attenuate the conservativeness of <inline-formula><tex-math notation="LaTeX">\eta</tex-math></inline-formula>-exponential stability formulation and positivity analysis. Chebyshev norm approximation error is utilized to introduce the error between CMFs and primary membership functions using slack matrices. A numerical example is presented to validate the proposed methods.
This work explores the polynomial fuzzy stabilization for positive systems. The traditional quadratic Lyapunov function and basic stability analysis may not be favourable for stability investigation ...due to the absence of the positivity property and membership functions. Therefore, a fuzzy co-positive polynomial Lyapunov–Krasovskii (FCPL) function which considers the positivity is proposed firstly through an imperfect premise matching (IPM) approach. Secondly, the symbol transfer technique which takes into account fuzzy membership knowledge relaxes the stability conditions. The number of symbols is reduced by two constraints: (1) the last and next moments of the membership functions of the FCPL function; (2) membership functions of the fuzzy model and the controller. Finally, the polynomial fuzzy controller with symbols is obtained. Two examples are implemented to verify the proposed methods.
•Favourable fuzzy co-positive polynomial Lyapunov–Krasovskii functional candidate: we propose a FCPL candidate to favour the relaxed stability. The original membership function elements in stability conditions are retained and the information of membership function is considered to relax the results.•Solvable polynomial fuzzy controller whose feedback gains with nonlinear polynomial terms: the controller is designed whose feedback gains with polynomial terms of system states and membership characteristics. Adequate nonlinear information is considered and it makes the controller design process robust.•Favourable symbol transfer technique design: the symbol transfer technique is employed for reducing the stability conservativeness. Membership grades are carried by symbols in the control. The next moment of membership functions is replaced by the symbol to solve the non-convex problem.
Nonlinear switched positive systems with time delay are universally found in practical applications. However, with the consideration of the switching signal, the constraints of positivity and the ...existence of the time delay make the control of this special system much more complicated. In this paper, a novel exponential stability analysis which can tighten the bounds of switching dwell time is proposed under the switched positive polynomial fuzzy control scheme. Firstly, the polynomial fuzzy model represents the dynamic characteristics of nonlinear switched positive systems with time delay, which can sufficiently promote the approximation capability, thereby simplifying the model structure. Secondly, the switched polynomial state fuzzy (SPSF) controller is designed based on the principle of the premise variable mismatching to enhance the design flexibility, and matrix decomposition is proposed to overcome the obstacle caused by the non-convexity conditions both in positive and stable conditions. In addition, as the existing switching control theory is relatively conservative which leads to a high bound of dwell time, a switched fuzzy copositive Lyapunov-Krasovskii function (SFCLKF) with the upper bound of the derivative of the membership function and a Taylor expansion technique are together incorporated in positive switched stability analysis to obtain tight bound of dwell time and relax conditions. At last, two simulation examples are provided to validate proposed methods.
This article proposes a novel Lyapunov stability analysis for a class of switched nonlinear systems under the mode-dependent average dwell time (MDADT) switching signals. For the first time, a ...polynomial fuzzy model is used to describe the nonlinearity of the switched systems instead of a Takagi-Sugeno fuzzy model, which can represent a wider range of nonlinear plants. As existing advanced results are relatively conservative and lead to that tighter bounds on the dwell time are not easy to be obtained, therefore, the stability analysis for switched systems is still quite challenging. In this article, to tackle this problem, by developing a polynomial multiple Lyapunov function (MLF) approach and exploring the feature of the membership functions, relaxed stability conditions are derived for the switched polynomial fuzzy-model-based control systems. In particular, the polynomial MLF is guaranteed radially unbounded by a two-step procedure, making traditional quadratic MLF a specific case, thereby improved stability conditions can be established in the form of sum-of-squares. Moreover, the new algorithm for multivariate Chebyshev membership functions based on linear programming is proposed to introduce the information of membership functions and further relax the stability conditions to obtain tighter bounds on MDADT. Finally, a simulation example demonstrates the effectiveness of the developed techniques.
A composite photoelectrode, prepared by spin-coating silicon nanowires with nickel ferrite nanoparticle co-catalysts, exhibited a TC degradation of 90.24 %, nearly 5 times higher than that of pure ...silicon nanowires, indicating a significant enhancement in electrode performance.
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•NiFe2O4/SiNWs type-II heterojunction with good visible light response separates the carriers efficiently.•The degradation of TC by the optimized NiFe2O4/SiNWs composite reached 90.24 %, which is 4.73 times higher than that of SiNWs.•The transformation products and mechanism of TC degradation by NiFe2O4/SiNWs heterojunction have been proposed and verified.
Silicon nanowires (SiNWs), with their simple fabrication process and large surface area, show promise as photoelectric materials. However, their limited charge separation efficiency and light absorption properties hinder its further development. Therefore, it is necessary and meaningful to improve its performance by cocatalyst modification. Herein, NiFe2O4/SiNWs heterojunctions were successfully synthesized by an efficient and convenient spin-coating method, and a photoelectrocatalytic degradation system based on NiFe2O4/SiNWs heterojunction was constructed for the degradation of TC under the conditions of simulated light and applied voltage. UV-NIR, LSV and EIS experimental results demonstrate that the composite exhibits higher light absorption, stronger photocurrent density, and lower carrier recombination, resulting in significantly enhanced photoelectrocatalytic activity. Consequently, NiFe2O4/SiNWs heterojunction as the photoelectrocatalyst achieved a TC degradation rate of 90.24 % with a kinetic constant (k) of 0.01202 min−1, which was 4.73 and 10.27 times higher than those for pure SiNWs under identical conditions. Further experimental and theoretical results confirmed that the OH provided by NiFe2O4 as a co-catalyst played a dominant role in the degradation process, which significantly improved the degradation efficiency of TC by SiNWs. This work confirms the synergistic catalytic effect between NiFe2O4 and SiNWs, opening up new possibilities for exploring composite photoanodes with diverse co-catalysts for antibiotic wastewater treatment.
A sensitive solid semiconductor-based surface-enhanced Raman spectroscopy (SERS) substrate can realize recyclable and portable detection of organic pollutants. In this paper, TiO2 nanosheets (NSs) on ...FTO glass substrate were synthesized by a simple and controllable hydrothermal method, followed by decoration of plasmonic Ag nanoparticles (AgNPs), and further deposition of graphene oxide (GO). The GO and AgNPs co-modified TiO2 substrate showed improved signal reproducibility, longer-term stability, and higher detection sensitivity than that of TiO2 counterparts. Note that, the optimized TiO2-Ag-GO substrate can also be utilized to discriminate multiple organic pollutants with a portable Raman instrument. The limit of detection (LOD) for crystal violet (CV), rhodamine 6 G (R6G) and malachite green (MG) was 10−9 M, 10−8 M, and 10−7 M, respectively. Moreover, the solid substrate was applied to discern low concentrations of CV residue (10−8 M) on crayfish’s shell and thiram residue (10−6 M) on grape skin. As a proof of concept, multiplex detections were also demonstrated. More significantly, the better photocatalytic degradation performance of the TiO2-Ag-GO makes the solid substrate reuse for 10 cycles. The solid SERS substrate may have great potential for practical applications and resource-confined detections.
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•The GO and AgNPs co-modified TiO2 (TiO2-Ag-GO) nanosheet substrate was fabricated by a simple and controllable manner.•The substrate showed improved signal reproducibility, longer-term stability, and higher detection sensitivity.•The substrate can be utilized to discriminate multiple organic pollutants in real-world sample surface.•Multiplex detections are also demonstrated even on a portable Raman device.•It shows great potential for practical applications and resource-confined detections.
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