Modern Physics Letters B

Structural colors engineering as a promising research area provides a high-resolution and environmental-friendly sustainable colors implementation. Here, metasurface-based concept was used to design waveguides and gratings of Si₃N₄ material on silicon dioxide substrates. The shift of reflection peaks can be controlled by structural parameters and efficiencies exceeded 90% with half height and width less than 10 nm. This induced structural color with superior saturation. Moreover, such nanostructures showed good sensitivity to polarization angle and incident angle of incident light. The proposed coloring devices look promising for applications in active color displays, imaging devices, and anti-counterfeiting and so on.

One important characteristic of complex networks is community structure. How to effectively divide the potential community structure of complex networks has been the focus of scholars because communities may have very different properties than the network. A community is usually defined as a collection of nodes with similar attributes. Generally, nodes in the same community are relatively densely connected to each other, compared with nodes from different communities. From the perspective of clustering, nodes in the same community can be considered as having higher similarities. Therefore, using graph clustering algorithms for community detection is theoretically feasible. Collaborative networks are special complex networks. A collaborative relationship tends to connect to multiple collaborators, which makes it hard to build collaborative networks by abstracting the collaboration into edges. Based on characteristics of the collaborative network, we expand the cluster similarity index and propose a gravitational coefficient index to measure the similarity of nodes and subsequently design community detection algorithms. Experiments using real datasets show that the proposed algorithm can obtain higher quality community partitioning results and avoid falling into local optimal solutions to obtain larger-scale communities than classical community detection algorithms.

In self-propelled particle models, the interactions are generally subject to some type of noise, which is introduced either during or after the interactions between the particles. Here, self-propelled particles are subject to two different types of noise. If the orientation between them is less than a certain rate $\beta$, a vectorial noise is introduced in each particle–particle interaction, otherwise, an angular noise is introduced in the average direction of motion, already calculated, of neighboring particles. We vary the rate $\beta$ over a wide range ($\beta <\pi$) and study the change in the nature of the phase transition. The product-moment correlation coefficient between the order parameter and the hybrid noise, is calculated. We found that in the combination of the two types of noise, the critical noise decreases with increasing the parameter $\beta$, and by analysis of the Binder cumulant we estimate the value of $\beta$ as from which begins to appear the effects of the vectorial noise on the phase transition.

In order to investigate the turbulence-induced acoustic characteristics of hydrofoils, the flow and sound field for a model NH-15-18-1 asymmetric hydrofoil were calculated based on the mixed method of large eddy simulation (LES) with Lighthill analogy theory. Unsteady fluid turbulent stress source around the hydrofoil were selected as the inducements of quadrupole sound. The average velocity along the mainstream direction was calculated for different Reynolds numbers $(Re)$. Compared to experimental measurements, good agreement was seen over a range of $Re$. The results showed that the larger the $Re$, the larger the vortex intensity, the shorter the vortex initial shedding position to the leading edge of the hydrofoil, and the higher the vortex shedding frequency $(f_s)$. The maximum sound pressure level (SPL) of the hydrofoil was located at the trailing edge and wake of the hydrofoil, which coincided with the velocity curl $(\omega )$ distribution of the flow field. The maximum SPL of the sound field was consistent with the location of the vortex shedding. There were quadratic positive correlations between the total sound pressure level (TSPL) and the maximum value of the vortex intensity $({\mathrm{\Gamma }}_{max})$ and velocity curl, which verified that shedding and diffusion of vortices are the fundamental cause of the generation of the quadrupole source noise.

In this paper, in order to analyze the coexistent multiple-stability of system, a fractional-order memristive Chua’s circuit with time delay is proposed, which is composed of a passive flux-controlled memristor and a negative conductance as a parallel combination. First, the Chua’s circuit can be considered as a nonlinear feedback system consisting of a nonlinear block and a linear block with low-pass properties. In the complex plane, the nonlinear element of the system can be approximated by a variable gain called a describing function. Second, compared with conventional computation, the describing function can accurately predict the hidden dynamics, fixed points, periodic orbits, unstable behaviors of the system. By using this method, the full mapping of the system dynamics in parameter spaces is presented, and the coexistent multiple-stability of the system is investigated in detail. Third, using bifurcation diagram, phase diagram, time domain diagram and power spectrum diagram, the dynamical behaviors of the system under different system parameters and initial values are discussed. Finally, based on Adams–Bashforth–Moulton (ABM) method, the correctness of theoretical analysis is verified by numerical simulation, which shows that the fractional-order delayed memristive Chua’s system has complex coexistent multiple-stability.

The temperature and concentration dependences of the transmission spectrum of an aqueous solution of agar are investigated. Measurements taken in the heating and cooling modes show strong thermal hysteresis in the spectral properties. Analysis of the results suggests that the formation of a gel network occurs in a much narrower temperature range than its collapse. The study of the temperature dependence of transmittance indicates that the association bispirals by cooling the solution and responsible for the formation of network occurs at temperature about $40^{\circ }$C. A breakdown of these associates by heating of the gel begins at $60^{\circ }$C and covers a wide temperature range. The gel point $T_g$ and the gel melting point $T_m$ increase with increasing polymer concentration, but for $T_m$ this dependence is stronger. Growth of turbidity (light scattering) of gel by increasing of agar concentration is due to the increasing of number and size of gel associates.

It is hard to achieve low bit error rate (BER) and high-quality signals in free-space optical (FSO) communication systems due to atmospheric link interference. For the sake of seeking solutions, we proposed an experimental scheme of free-space laser communication based on middle-wave infrared (MWIR) and near infrared (NIR) for obtaining atmospheric transmission characteristic in 1 km turbulence path. Compared with NIR waveband, MWIR-based scheme is more suitable for atmospheric FSO communication since it owns higher anti-interference ability for atmospheric attenuation, turbulence and skylight background noise. The experimental results may offer a significant reference for FSO communication in atmosphere link.

In this paper, water entry process of air launched AUV is investigated by employing fully coupled finite element method and arbitrary Lagrange–Euler formulation (FEM-ALE) and using penalty coupling technique. Numerical model is established to describe the hydrodynamic characteristics and flow patterns of a high-speed water entry AUV. The effectiveness and accuracy of the numerical simulation are verified quantitatively by the experiments of the earlier study. Selection of suitable advection method and mesh convergence study is carried out during experimental validation process. It is found that appropriate mesh size of impact domain is crucial for numerical simulations and second-order Van Leer advection method is more appropriate for high speed water entry problems. Subsequently, the arbitrary Lagrange–Euler (ALE) algorithm is used to describe the variation laws of the impact load characteristics with water entry velocities, water entry angles and different AUV masses. Dimensionless impact coefficient of AUV at different velocities calculated using ALE method is compared with SPH results. This reveals that ALE method can also simulate the water entry process accurately with less computational cost. This research work can provide beneficial reference information for structure design of AUV and for selection of the water entry parameters.

The charge distribution of fast multicharged ions passing through a matter is studied taking ion energy losses into account. Within the framework of the proposed method, we show that the changes in the charge exchange cross-sections, caused by the decreasing of ion energy, affect the process of the formation of the equilibrium ion charge distribution. The target thickness, required for obtaining the equilibrium ion charge distribution, reaches the maximum value for ions without electrons and hydrogen-like ions. The equilibrium target thickness increases with increasing in ion nuclear charge and energy and for fast heavy ions becomes comparable with their range.

The effect of room-temperature annealing on the basal-plane conductivity of YBCO single crystals is investigated after their irradiation with fast electrons. It is revealed that the excess conductivity $\mathrm{\Delta }\sigma (T)$ of the samples obeys an exponential temperature dependence in a broad temperature range $T_f<T<T^{\ast }$. Here, $T_f$ is the crossover temperature from the pseudogap to the fluctuation conductivity regime. The description of the excess conductivity with the expression $\mathrm{\Delta }\sigma \propto T/T^{\ast }exp({\mathrm{\Delta }}^{\ast }/T)$ can be interpreted in terms of the mean-field theory where $T^{\ast }$ corresponds to the mean-field transition temperature to the pseudogap state and the dependence $\mathrm{\Delta }\sigma (T)$ is described within the framework of the BCS-BEC crossover theory.

This paper presents the experimental investigation of the changes in the geometrical shape of femtosecond laser-induced plasma in air under different laser power, and its effects on supercontinuum white light generation and conical emission. When a femtosecond laser is focused into a tiny spot in air, optical breakdown of air molecules occurs and this leads to the generation of plasma filament whose geometrical size and shape depend on laser power. This process is then followed by two light-emitting processes, namely supercontinuum white light generation and conical emission, both of which scatter light that reveals the characteristics of the plasma filament. Our experiment shows that the laser-induced plasma becomes thinner and longer at high average laser power but appears thick and round at lower laser power. At higher laser power, conical emission which scatters laser light in the forward direction dominates the scattering process while at lower laser power, it is the scattering of supercontinuum white light in all directions that plays a bigger role. The intricate rainbow-like pattern formed on a white screen located far away in the forward direction reveals sophisticated nonlinear optical processes that take place in conical emission which slowly diminishes as the laser power is gradually reduced.

In this paper, the binding energy and photoionization cross-section of donor impurity state in $\mathrm{\text{GaN}}/{\mathrm{\text{Al}}}_x{\mathrm{\text{Ga}}}_{1-x}\mathrm{\text{N}}$ quantum dot structure are studied theoretically by using variational method. The variation of binding energy and photoionization cross-section with core and shell sizes at different impurity locations under hydrostatic pressure is calculated numerically. The results show that the binding energy decreases monotonously with the core size at different impurity locations for $\mathrm{\text{GaN}}/{\mathrm{\text{Al}}}_x{\mathrm{\text{Ga}}}_{1-x}\mathrm{\text{N}}$ core/shell quantum dot. In contrast, for the inverted core/shell quantum dot, the binding energy exhibits different trends with the increase of core size at different impurity locations. But the binding energy decreases monotonically with the shell size for both of them. Moreover, when the photon energy is approximately equal to the donor binding energy, the peak of the photoionization cross-section appears. There will be different peak shifts under different conditions, and its peak intensity increases with the increase of core and shell sizes. When the hydrostatic pressure is applied, the binding energy and the peak strength of the photoionization cross-section increase with the increase of the pressure.

An optically tunable terahertz (THz)-band shift in interference fringes based on an indium oxide structure was investigated. An interference phenomenon formed by the combination of partial-through measurements with a shift in the periodic peaks in a THz time-domain spectroscopy system was reported. When the THz beam passes through the edge of the material sample, equally spaced interference fringes are obtained in the frequency domain and these interference fringes can be varied using a 450 nm external continuous-wave laser. The peak of the THz interference fringe shifts by almost half a period. This work offers the ability to observe THz-band interference fringes in the frequency domain and shows that these interference fringes change with variations in the intensity of the applied excitation light.

In order to achieve a laser output at 1550 nm and a dynamical control, we perform an optimization design for one-dimensional PT-symmetric structure. The optimization is based on the structure parameters and the modulation of the external electric field. The optimization is performed by three steps: to achieve the defect mode, to achieve the amplification of the defect mode and to move the defect mode with a large peak value to the special wavelength 1550 nm. The maximum transmittance can reach 687.4. Through changing the electric field, the transmittance of the structure can be modulated to an arbitrary value from the cut-off state to its maximum value.