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From the outbreak on December 19, 2019, to the current normalization of the epidemic, people stay at home for entertainment. The popularity of short videos has increased dramatically, and the use of Douyin has skyrocketed. This paper analysed the development strategy of Douyin, and further explored the power of brand equity on Douyin use intention by applying the theoretical knowledge and qualitative analysis of the influence of brand equity on purchase intention and the SWOT analysis method. SWOT analysis was used to analyse the impact of brand equity on the willingness to use Douyin, and the conclusion was drawn that in terms of SO, the intuitive and eye-catching the brand image of Douyin and the positive development of brand virtual character image improved the willingness to use. In WT, Douyin’s negative brand association and high-end brand positioning reduced the desire to use. Therefore, Douyin needed to improve in purifying the network environment and enhancing user participation in third - and fourth-tier cities.

Stability of explicit FDTD algorithm is limited by the established relationship which results in computation duration unacceptable in certain circumstances. To enhance the development of FDTD algorithm, unconditionally stable scheme is implemented to overcome such problem, especially for the open region simulation. Here, for bandpass simulation of anisotropic magnetized ferrite material, complex envelope (CE) method and its modified scheme are employed into the implementation. Generally speaking, the proposed scheme incorporates the alternating direction implicit (ADI) with the CE method during the simulation obtaining the bandpass ADI form in perfectly matched layer (PML) regions. Meanwhile, the proposed scheme establishes the bandpass calculation method of constitutive relationship in ferrite material regions. Such method can also be employed into the unmagnetized isotropic materials and other media. Through ferrite slab model and ferrite waveguide structure, accuracy, absorption and efficiency are demonstrated in the bandpass open region simulation numerically. The proposed scheme can not only benefit an impressive performance but also maintain both of stability and accuracy with decrement of iteration steps which can be proved to be an unconditionally stable implementation. Meanwhile, it also alleviates time increment problem within implicit schemes of small time steps. Thus, benefits of the proposed scheme can be summarized from the following categories: 1) Enhanced absorption and efficiency for the ADI procedure. 2) Decrement of duration with a small time step. 3) Bandpass form inside the magnetized ferrite material. 4) Extensively employment in different kinds of materials.

Popularizing community and home early caries screening is essential for caries prevention and treatment. However, a high-precision, low-cost, and portable automated screening tool is currently lacking. This study constructed an automated diagnosis model for dental caries and calculus using fluorescence sub-band imaging combined with deep learning. The proposed method is divided into two stages: the first stage collects imaging information of dental caries in different fluorescence spectral bands and obtains six-channel fluorescence images. The second stage employs a 2-D-3-D hybrid convolutional neural network combined with the attention mechanism for classification and diagnosis. The experiments demonstrate that the method has competitive performance compared to existing methods. In addition, the feasibility of transferring this approach to different smartphones is discussed. This highly accurate, low-cost, portable method has potential applications in community and at-home caries detection.

A theoretical model considering the interface shear deformation is developed to investigate the bending properties of graphene substrates coated with nano-film. This paper presents a closed-form solution for predicting the bending properties of graphene substrates coated with nano-film. Based on the proposed model, we investigate the effects of the interface shear stiffness and the boundary conditions on the bending properties of graphene substrates. A parameter study was carried out analyzing the mechanical behaviors of the graphene substrates. As a result, a parametric study is conducted to show the importance of interface shear transfer mechanisms. The interface shear stress and the deflection of the graphene substrates are largely affected by the interface shear stiffness, the concentrated load position and the boundary conditions of loading. Restraint against bending deflection of graphene nanoribbons coated with nanofilm under the lateral load can be easily investigated using the present theory. The theoretical investigation on the bending behavior provides a useful reference for understanding the interfaces shear deformation in graphene substrates.

To overcome the conflict between limited space and the requirement for high gain antennas, a novel high aperture efficiency antenna array consisting of surface wave end-fire antennas is proposed based on the three-dimensional aperture principle. By introducing longitudinal dimension into the calculation of the regular aperture antenna gain, the two-dimensional aperture principle is expanded into the three-dimensional aperture principle. Meanwhile, the directivity and gain of the array could increase without increasing the aperture area. The aperture efficiency of the array could be more than 100% in this situation. The gain of the surface wave end-fire element antenna is 9.5 dBi. The proposed 3 × 3 square antenna array with the size of 1.5λ × 1.5λ × 2.24λ obtains a gain of 15.3 dBi and its aperture efficiency reaches 120%.

Based upon the approximate Crank–Nicolson (CN) algorithms and the higher order (HO) concept, unconditionally stable perfectly matched layer (PML) implementations are proposed for electromagnetic problems in the finite-difference time-domain (FDTD) lattice. The approximate CN algorithms include the CN direct-splitting (CNDS) and CN approximate-factorization-splitting (CNAFS). The proposed schemes take advantage of the approximate CN algorithms in terms of eliminating the Courant–Friedrichs–Levy stability condition and maintaining the computational accuracy. By introducing the HO concept to the PML formulation, the absorbing performance can be enhanced during the simulation. Furthermore, to cope with the existence of half-time-step problems in simulating the anisotropic magnetized plasma, a modified ADE method is proposed at the integer time step. Thus, the modified ADE method can be directly employed in the approximate CN algorithms. Numerical examples and experiments are carried out to demonstrate the effectiveness, efficiency, and performance. Through the results, it can be observed that the computational efficiency and absorbing performance can be significantly improved. Meanwhile, it can be concluded that the CNAFS-PML and CNDS-PML algorithms show higher accuracy and considerable efficiency, respectively, when the time step surpasses far beyond the CFL condition.

By incorporating the higher-order concept with the perfectly matched later (PML) scheme, unconditionally stable approximate Crank–Nicolson algorithm is proposed for plasma simulation in open region problems. More precisely, the proposed implementation is based on the CN Direct-Splitting (CNDS) procedure for the finite-difference time-domain (FDTD) unmagnetized plasma simulation. The unmagnetized plasma can be regarded as frequency-dependent media which can be calculated by the piecewise linear recursive convolution (PLRC) method. The proposed implementation shows the advantages of higher-order concept, CNDS procedure, and PLRC method in terms of improved absorbing performance, enhanced computational efficiency, and outstanding calculation accuracy. Numerical examples are introduced to indicate the effectiveness and efficiency. It can be concluded from results that the proposed scheme shows considerable efficiency, accuracy, absorption, and unconditional stability.

People spend about 5-8 hours per day on phones, causing circadian disruption and eye fatigue, thus raising a great need for comfort and health. Most phones have eye protection modes, claiming a potential eye protection effect. To examine the effectiveness, we investigated the color quality, namely gamut area and just noticeable color difference (JNCD), and circadian effect, namely equivalent melanopic lux (EML) and melanopic daylight efficacy ratio (MDER), characteristics of two smartphones: iPhone 13 and HUAWEI P30, in normal and eye protection mode. The results show that the circadian effect is inversely proportional to color quality when the iPhone 13 and HUAWEI P30 changed from normal to eye protection mode. The gamut area changed from 102.51% to 82.5% sRGB and 100.36% to 84.55% sRGB, respectively. The EML and MDER decreased by 13 and 15, and, 0.50 and 0.38, respectively, affected by the eye protection mode and screen luminance. The EML and JNCD results in different modes show that the eye protection mode benefits the nighttime circadian effect at the cost of the image quality. This study provides a way to precisely assess the image quality and circadian effect of displays and elucidates the tradeoff relationship between them.

By incorporating higher order formulation with perfectly matched layer (PML) implementation, unconditionally stable computationally efficient locally one-dimensional (LOD) algorithm with improved absorption is proposed for simulating ground penetrating radar and its open region problems in finite-difference time-domain (FDTD) algorithm. To take advantages of these methods, the proposed implementation shows characteristics of maintaining considerable accuracy, enhancing computational efficiency and improving the entire absorption. These above-mentioned advantages are illustrated through the ground penetrating radar related problem in open regions. It can be concluded from the calculation results that the proposal shows advantages of higher order formulation, PML implementation and LOD procedure which are efficient in remarkable accuracy, considerable efficiency and improved absorption with increment of CFLNs. Meanwhile, the simulation results also indicate that the proposal is an unconditionally stable procedure with the dissatisfaction of Courant-Friedrichs-Levy stability condition.

For the simulation of gyrotropic plasma structure with fine geometry details along a single direction in open regions, the hybrid implicit-explicit (HIE) algorithm with improved absorbing boundary condition is modified based on the finite-difference time-domain (FDTD) algorithm. More precisely, incorporating the perfectly matched layer (PML) formulation, the higher order concept and the HIE procedure, the proposed implementation shows its significant superiority in terms of efficiency, accuracy and absorption. To simulate the unique anisotropic characteristic inside the gyrotropic plasma regions, the bilinear transform (BT) method is employed during the calculation. The effectiveness can be further demonstrated theoretically and numerically. Through the results, it can be concluded that the proposed scheme exhibits remarkable behaviors in the gyrotropic plasma open region problems. It can not only obtain considerable accuracy compared with the theoretical solution but also receive better absorption and efficiency compared with the published work. In addition, the results also indicate that the proposed scheme can maintain the stability of the algorithm with dissatisfaction of the Courant-Friedrichs-Levy condition between time step and mesh size.

With the unique flexibility or ductility, and efficient low-cost manufacturing process, flexible electronic devices have attracted a growing interest in scientific research and industry with applications in wearable electronic devices, stretchable antennas, flexible displays, and energy devices. Flexible conductive film (FCF), which functionalizes in building connections between different components of the devices, is key constitutions in flexible devices. We prepared the flexible conductive film with a diameter of approximately 60 nm and a length of 20 μm of silver nanowires (AgNWs) as the fillers and thermopolyurethane (TPU) as the matrix by solution blending and tape casting method. Further, self-made fluorinated decyl polyhedral oligomeric silsesquioxane (F-POSS) as hydrophobic layer was deposited on the AgNWs-TPU conductive film by immersing method. We systematically studied the properties of electronic conductivity, electrothermal response and infrared radiation (IR) thermal response performances, and superhydrophobic performance of AgNWs-TPU conductive films. The experimental results reveal that as the mass content of AgNWs reaches 30 wt%, the film displays good conductivity, and the resistivity of the film with 40 wt% AgNWs is 0.07 Ω·mm. AgNWs-TPU conductive film has good electrothermal response and IR thermal response performances. The water contact angle of the AgNWs-TPU conductive film with superhydrophobic layer reaches 155.29° ± 1.03 and superhydrophobic AgNWs-TPU conductive film slightly improves the reliability and tensile strength of the AgNWs-TPU conductive film. Our experimental results indicate that the superhydrophobic flexible conductive films prepared in this experiment can be applied to wearable flexible devices.

In order to efficiently simulate the symmetrical structures in the cylindrical coordinate system, the implementation of the complex frequency-shifted perfectly matched layer based on the body of revolution finite-difference time-domain algorithm is proposed for analysing the magnetised ferrite microwave structures. To improve the computational efficiency in the magnetised ferrite domain compared with the existing calculation methods, the bilinear Z-transform for the simulation of the dispersion relationship of the magnetised ferrite is proposed. The proposed implementations can not only improve the computational efficiency but also obtain a considerable absorbing performance. Numerical examples based on the magnetised ferrite microwave structures are carried out to demonstrate the effectiveness and efficiency of the proposed formulations.

An unconditionally stable and efficient higher order complex frequency-shifted perfectly matched layer (CFS-PML) based on the Crank–Nicolson-approximate-decoupling (CNAD) algorithm is proposed for truncating the finite-difference time-domain (FDTD) computational domain filled with the left-handed materials (LHMs). The proposed higher order CFS-PML is implemented by the bilinear transform (BT) approach and the LHMs are solved by the trapezoidal recursive convolution (TRC) method. A numerical example is provided to validate the effectiveness of the proposed implementation. The results show that the proposed CFS-PML not only has better absorbing performance compared with the first-order CNAD CFS-PML and the alternating-direction-implicit (ADI) CFS-PML but also takes advantage of the unconditional stability of the original Crank–Nicolson algorithm.

Active echo cancellation is an efficient method for reducing the target detected probability. The radar cross section (RCS) of the target detected by radar after using the active echo cancellation method is defined as the active radar cross section (ARCS). The ARCS concept, which may be used to evaluate reflection of the target under the effect of multiple antennas, is employed to design and achieve echo cancellation. In this paper, numerical simulation for active echo cancellation using antennas is designed. The direction of the radiation source is obtained by means of dual antenna angle measurement. Active echo cancellation is implemented by adjusting the radiation power and phase of the echo cancellation antenna. By using the proposed dual antenna structure, ARCS in the direction of the object facing the radiation source and its vicinity is significantly reduced. In addition, the effect of antenna position on reflection cancellation is discussed. From these simulation results, we conclude that the proposed method is efficient in reducing the target scattering intensity. Such investigation can be extensively applied into designing active echo cancellation strategies.

An unconditionally stable implementation of the higher order complex frequency-shifted (CFS) perfectly matched layer (PML) is proposed for the Crank-Nicolson-approximate-decoupling (CNAD) finite-difference time-domain (FDTD) scheme. The proposed higher order CFS-PML, which is implemented by the auxiliary differential equation (ADE) method, not only has better performance than the first-order PML but also maintains the unconditional stability of the origin Crank-Nicolson (CN) algorithm. The unmagnetised plasma, which can be expressed by the Drude medium and implemented by the piecewise linear recursive convolution (PLRC) method, is truncated by the proposed PML scheme. A numerical example is provided to validate the effectiveness of the proposed formulations.

In this work, we investigated the luminous and melanopic efficiency of the radiation (LER/MER) performances of phosphor-converted LEDs (PC LEDs) with tunable spectral characteristics, namely peak wavelength, full width at half maximum (FWHM), and emission intensity. We constructed theoretical PC LED spectra based on the characteristics extracted from the database of IES TM-30-15, analyzed the relations between LER/MER and different spectral characteristics, and proposed spectral composition strategies at various correlated color temperatures (CCTs). Results showed that both MER and LER are linear with the FWHM of phosphor within the peak wavelength range in practical use, but the change in values by tuning emission intensity varies with spectral compositions. Hence, different spectral characteristics should be considered comprehensively. We further explored the trade-off between luminous and melanopic efficiency. Lowering the FWHM of phosphor and the intensity distribution of the blue LED can obtain higher LER and low circadian effect at lower CCT. As CCT increases, considering color rendering and the increase in the blue intensity distribution, besides reducing FWHM, tuning the peak wavelength close to the peak wavelength of V(&lambda, ) helps to reduce the circadian effect. These investigations provide optimization strategies for ideal melanopic and luminous performance of PC LED light sources.

In order to analyze the scattering properties in multi-radiator problems, the active radar cross section (ARCS) concept is proposed under complex electromagnetic (EM) environments. The corresponding calculation methods and formulation are proposed by incorporating the monostatic radar cross section (RCS) concept with external disturbances. By introducing the phase characteristics into the ARCS concept, the coherent problems can be accurately solved. Through analyzing the external disturbance and the radar waves by employing the finite element method, the coherent and the incoherent characteristics of the external disturbance can be simulated in complex structures. Numerical examples and an experiment are carried out to further demonstrate the effectiveness of the proposed ARCS concept. The results demonstrate that the proposed ARCS concept obtains better universality compared with the existing incoherent multi-radiator formulation. Meanwhile, the ARCS can be identical with the solution which is obtained by the single radar wave. Compared with the existing incoherent methods for external disturbances calculations, the proposed ARCS concept is more rational. Through the experiment, the effectiveness of the calculation method and formulation is further demonstrated and validated.

Flexible conductive films were prepared via a convenient blending method with thermoplastic polyurethane (TPU) as matrix and nanocrystalline cellulose (NCC) modified chemically reduced graphene oxide (RGO/NCC) as the conductive fillers. The relationships between the electrical and thermal properties as well as the tensile strength and electrothermal response performance of the composite film and the mass content of reduced graphene oxide (RGO) and the initial TPU concentration were systematically investigated. The experimental results show that the resistivity of the composite film with the mass content of RGO/NCC of 7 wt% and an initial TPU concentration of 20 wt% is the minimum of 8.1 &Omega, ∙mm. However, the thermal conductivity of composite film with mass content of RGO/NCC of 5 wt% and the initial TPU concentration of 30 wt% reaches a maximum of 0.3464 W&middot, m&minus, 1&middot, K&minus, 1, which is an increase of 56% compared with pure TPU. The tensile strength of the composite films with mass contents of RGO of 3 wt% prepared with the initial TPU concentrations of 20 wt% reaches the maximum of 43.2 MPa, which increases by a factor of 1.5 (the tensile strength of the pure TPU is 28.9 MPa). The composite conductive film has a fast electrothermal response. Furthermore, superhydrophobic composite conductive films were prepared by immersing the composite conductive film into fluorinated decyl polyhedral oligomeric silsesquioxane (F-POSS) ethanol solution. The water contact angle of the superhydrophobic composite conductive film reaches 158.19&deg, and the resistivity of the superhydrophobic composite film slightly increases and still has good conductivity.

Based on the alternating direction implicit (ADI) procedure, leapfrog formulation, and a higher order PML scheme, we propose an unconditionally stable perfectly matched layer (PML) algorithm with improved absorption to treat open regions in a finite computational domain with improved overall performance. The proposed algorithm performed well compared to other algorithms during simulations. We further demonstrated the proposed scheme’s effectiveness using numerical examples. We found that the proposed scheme had enhanced effectiveness and improved the absorption during the whole simulation. Furthermore, it was able to break the stability condition, proving that it is an unconditionally stable scheme.

According to the two-dimensional aperture principle, directivity and gain are expected to be proportional to the aperture area of an antenna or antenna array. Our simulations and measurements of an end-fire radiation antenna array overturn this conventional wisdom. The gain of an end-fire antenna array is found to be much higher than that calculated by the two-dimensional aperture principle. We introduce a length component into the two-dimensional aperture principle and propose a three-dimensional aperture principle. A four-element end-fire antenna array is designed and measured to verify the correctness of this new principle. The three-dimensional aperture principle opens a pathway to novel types of aperture utilization.

Graphene-based thermoplastic polyurethane (G-TPU) composite materials were prepared and used for the fabrication of G-TPU film. The thermal conductivity and infrared radiation (IR) response and self-healing performances of the G-TPU film were studied. The experimental results reveal that the thermal conductivity of the TPU film was improved through the incorporation of graphene and increases with increasing of the graphene mass content. The G-TPU film displays a good IR thermal response characteristic. After heated by IR illumination, the temperatures of the G-TPU composite film incorporation of graphene of 0.2 wt% and 1.5 wt%, reach to 92.9 °C and 109.1 °C respectively. When the graphene mass content is in the range 0.6 wt% - 1.2 wt%, the crack on the G-TPU film can be completely healed via IR illumination.

In order to investigate the influence of multi-radiators, active scattering characteristics, which can be reflected by the active radar cross section (ARCS), are investigated by incorporating the multi-radiators with the radar-radiator. The proposed implementation takes advantage of the ARCS concept in terms of considerable accuracy and close to reality especially in the complex electromagnetic environment. The metal sphere model is analyzed to demonstrate the effectiveness of the proposed implementation. Several procedures are employed during the investigation. The ARCS of the metal sphere model is compared with its radar cross section with a single radar-radiator. The frequency characteristic of the ARCS for a metal sphere model with multi-radiators is calculated. The changes in the ARCS with different phases, field intensities, field polarization directions are given. An example is given to illustrate the change in the maximum detection range caused by multi-radiators. Through the results, it can be concluded that the active scattering characteristics of the metal sphere model can be significantly influenced by the multi-radiators.

We fabricated graphene-thermopolyurethane (G-TPU) flexible conductive film by a blending method and systematically investigated the electrical, thermal and self-healing properties of the G-TPU flexible conductive film by infrared light and electricity. The experimental results demonstrate that the G-TPU composite films have good conductivity and thermal conductivity in the appropriate mass content of graphene in the composite film. The composite films have the good electro-thermal and infrared light thermal response performances and electro-thermal response performance is closely related to the mass content of graphene in the composite film, but the infrared light thermal response performance is not. The scratch on the composite film can be completely healed, using electricity or infrared light. The healing efficiency of the composite film healed using infrared light is higher than that of using the electricity, while the healing time of the composite film is shorter. Regardless of the self-healing method, the temperature of the self-healing is a very important factor. The self-healing conductive composite film still exhibits a good conductivity.