Modern Physics Letters B

This work presents a general framework of finite-difference hybrid scheme which contains a linear central scheme and a nonl-inear WENO scheme. A new optimal-designed shock sensor is used to distinguish the smoothness of flowfield and a binary-type weighting function is used to switch sub-schemes rationally. Based on the above improvements, the effects of different combinations of each component within the hybrid scheme are characterized in linear advection equation and Euler equations. The maximum reference threshold values are provided. Extensive test cases indicate the hybrid scheme’s numerical robustness, low-dissipation, and superior computational efficiency. Specifically, benefited from the high-resolution shock sensor which can accurately perceive shocks without excessive misidentifications, the hybrid scheme can achieve non-oscillatory solutions, and resolve more vortices in smooth regions compared to the original shock-capturing scheme. Meanwhile, the superiority of the hybrid scheme is further confirmed in the Reynolds-averaged Navier–Stokes equations/Lager Eddy Simulations (RANS/LES) for the DLR scramjet combustor case with viscous terms and/or sub-grid scale models are used. The present hybrid framework can be easily implemented within the existing numerical simulation code framework.

The layered Bi₃O₄Br nanoplates were synthesized through a simple calcination process, which can simultaneously harvest visible light and ultrasonic vibration to realize the effective piezo-photocatalysis. The piezo-photocatalysis over the Bi₃O₄Br leads to a great enhancement in catalytic efficiency with respect to the pure photocatalysis or piezocatalysis. The apparent rate constant of piezo-photocatalysis for the degradation of MO achieves to be 0.008 min${}^{-1}$, which is 5.20 and 1.51 times as high as the individual piezocatalysis and photocatalysis, respectively. This enhancement would be attributed to the built-in piezoelectric field induced by ultrasonic vibration facilitating the separation of charge carriers in photoexcited Bi₃O₄Br.

For gauging the drowsiness, various algorithms have been proposed, but the maximum of approaches tries to gauge the facial expression and even change in the skin. In this paper, gauging the landmarks that have been discovered precisely enough to reliably predict the drowsiness was tried using the degree of eye-opening. The suggested algorithm within the paper finds that using the landmarks and eye aspect ratio (EAR) characterizes a person’s eye-opening in each frame. A simple mathematical expression i.e. Euclidean distance finds eye blinks being a blueprint for EAR. Thus, these values help us detect drowsiness. Once the detection happens, other problems arise as to how to send the data to a larger place, as a person may be critical and there is no internet at that place. Then messages cannot be received to a family member. To avoid this situation, nRF is used to facilitate multi-hop communication. Second, this paper focuses on the sleep pattern of an elderly, which is indeed an important aspect of gauging drowsiness. The lack of sleep is very common in the old person. Thus, this aspect helped us to accurately predict the physical condition of the elderly and indeed act as a piece of very useful information in restricting the fall of the elderly. So, for predicting the health of the elderly, we have applied the machine learning model and able to predict the condition of the elderly. The model on real-world scenarios was tested and the results are indeed accurate.

Both the linear and the nonlinear magnetosonic wave in a multi-component dusty plasma are studied in the present paper. The dependence of the dispersion relation of the linear waves on the dust size distribution are given. It seems that the larger the difference between the maximum and the minimum radius of the dust grains, the lower the wave frequency for all cases of the dust size distribution. Furthermore, it is noted that the width, the amplitude and the propagation velocity of the KdV solitary wave depend on the dust size distribution, especially it depend on whether the number density of the larger sized dust grain is larger or smaller than that of the smaller sized dust grain. For the power law dust size distribution, the width and the propagation velocity of the KdV solitary wave between the maximum and the minimum radius of the dust grains is larger than that of mono-sized dusty plasma.

The effects of Fe–NM (NM=B, C, N) co-doping on the stability, electronic structures, magnetic and optical properties of 2H-WSe₂ monolayer are investigated in detail by spin-polarized density functional theory (DFT) calculations. The results show that the Fe-doped WSe₂ monolayer exhibits magnetic half-metallicity (HM) with a 100% spin polarization due to the electrons partially occupied Fe $e_1$ and $a_1$ bonding states at the Femi level $(E_F)$, and eventually induces a magnetic moment of 2 ${\mu }_B$. The Fe–B and Fe–N co-doped WSe₂ monolayers show obvious spin-polarization and retain semiconductor character with an indirect bandgap of 0.034 eV and 0.220 eV, respectively, which can be attributed to the strong hybridization between the Fe $d_{xy}$, $d_z^2$ states and $B$, $Np$ orbitals at the $E_F$. Interestingly, the Fe–C co-doped WSe₂ monolayer exhibits a typical non-magnetic semiconductor due to the effective charge compensation between Fe and C atoms, leading to completely symmetrical spin-up and spin-down channel of $a_1$, $a_2$, $a_3$ and $a_4$ states near $E_F$. Moreover, the optical properties of WSe₂ monolayer can be effectively tuned by Fe–NM co-doping, which can attribute to the introduction of impurity state. The excellent magnetic HM, tunable magnetic, optical properties of Fe–NM co-doped WSe₂ monolayers are of great significance for further application in the fields of spintronics, opto-electronics and magneto-optics devices.

Dynamic characteristics and sensitivity analysis of a tubular pump unit during starting process are proposed in this paper. A dynamic model of the pump unit, suitable for describing its transient characteristics during starting process, is established by using rigid body dynamics, fluid dynamics and hydraulic theory. The extended Fourier amplitude sensitivity test (EFAST) analysis method is used to investigate the influence of unit parameters on system outputs. Simulation of the pump unit is carried out for the starting process to verify the sensitivity analysis and explore the dynamic characteristics of the pump unit. The dynamic responses of the system parameter (rotating speed, flow and head) are revealed by the start-up simulation. Research results provide theoretical guidance for the rational design and safe operation of tubular pump stations.

The structural and temperature reliance manner of the thermodynamic parameters of Ni–Al intermetallic compounds with different pressures is comprehensively studied by executing first-principles calculation using the density functional theory (DFT). The calculated optimized volume and bulk modulus are in good agreement with the experimental and theoretical results at zero pressure. Quasi-harmonic Debye model is adopted to find out the bulk modulus, volumetric thermal expansion coefficient, Debye temperature, Gibbs free energy and enthalpy of Ni–Al intermetallic compounds in different pressure ranges from 0 MPa to 600 MPa and temperature ranges from 0 K to 1200 K. Additionally, special attention is paid to calculate the mutual relationships between the thermodynamic parameters with different pressures and temperatures.

The crystal structure and atomic dynamics of Fe₃O₄ nanoparticles have been studied. The crystal structure of iron oxide nanoparticles was determined by X-ray diffraction. The analysis showed that the crystal structure of $d\approx$ 50–100 nm dimensional iron oxide corresponds to a high symmetry cubic crystal structure. Calculations have shown that there are four infrared active, five Raman active and seven hyper-Raman active modes in the space group Fd-3m with cubic symmetry. Four of these modes have been observed using Raman spectroscopy: 213, 271, 380 and 591 cm${}^{-1}$. The vibrational modes are interpreted by Gaussian function. It was found that these vibration modes correspond to the vibration of O–Fe–O bonds and iron-oxygen polyhedra.

To reduce the calculation cost and improve the accuracy of flow field prediction, an adaptive proper orthogonal decomposition (APOD) surrogate model based on K-means clustering algorithm was proposed to reconstruct the flow field of impeller. The experiment samples were designed by introducing the perturbation of the blade control parameters such as blade wrap angle and blade angle of outlet. K-means clustering algorithm was used to classify the sample blade shapes, and find out the cluster of the objective blade. The snapshot set, which consisted of the blade shape and the flow field data of impeller, can be described as a linear combination of orthogonal basis by POD method. The radial basis function (RBF) was used to fit the orthogonal basis coefficients of the objective blade, and then the flow field of objective impeller was reconstructed. The traditional fixed sample POD (FPOD) method and the proposed APOD method were used to reconstruct the flow field in impeller, respectively, and the prediction results of the two methods were compared and analyzed. The results show that the proposed APOD method could quickly and accurately reconstruct the objective flow field. The flow field prediction accuracy of the APOD method is significantly higher than the FPOD method, and the calculation time for the flow field prediction is less than 1/360 of the CFD.

Based on the Gurtin–Murdoch surface/interface model and complex potential theory, by constructing a new conformal mapping, the anti-plane fracture problem of three nano-cracks emanating from a magnetoelectrically permeable triangle nano-hole in magnetoelectroelastic materials with surface effect is studied. The exact solutions of the stress intensity factor, the electric displacement intensity factor, the magnetic induction intensity factor, and the energy release rate are obtained under the boundary conditions of magnetoelectrically permeable and impermeable. The numerical examples show the influence of surface effect on the stress intensity factor, the electric displacement intensity factor, the magnetic induction intensity factor, and the energy release rate under two different boundary conditions. It can be seen that the surface effect leads to the coupling of stress, electric and magnetic field, and with the increase of cavity size, the influence of surface effect begins to decrease until it tends to classical elasticity theory.

We analyzed the role of the inclusion of anti-dots on the vortex state and some calorimetric properties of a mesoscopic superconducting square immersed in an external applied magnetic field. We calculated the magnetization, entropy, Gibbs free energy, density of Cooper pairs and specific heat for this system in a zero field cooling process, solving the time-dependent Ginzburg–Landau equations. We found that the critical temperature is non-dependent on the number of anti-dots and dependent slightly on the size of the defects. Oscillations in the entropy and specific heat are found due the temperature dependence of the superconducting characteristics length.

In non-linear optics, it is well known that the non-linear Schrödinger (NLS) equation was always used to model the slowly varying wave trains. However, when the width of optical pulses is in the order of femtosecond ($10^{-15}$ s), the NLS equation becomes less accurate. Schäfer and Wayne proposed the so-called short pulse (SP) equation which provided an increasingly better approximation to the corresponding solution of the Maxwell equations. Note that the one-soliton solution (loop soliton) to the SP equation has no physical interpretation as it is a real-valued function. Recently, an improvement for the SP equation, the so-called complex short pulse (CSP) equation, was proposed in Ref. 9. In contrast with the real-valued function in SP equation, $u(x,t)$ is a complex-valued function. Since the complex-valued function can contain the information of both amplitude and phase, it is more appropriate for the description of the optical waves. In this paper, the new types of solutions — double-pole solutions — which correspond to double-pole of the reflection coefficient are obtained explicitly, for the CSP equation with the negative order Wadati–Konno–Ichikawa (WKI) type Lax pair by Riemann–Hilbert problem method. Furthermore, we find that the double-pole solutions can be viewed as some proper limits of the soliton solutions with two simple poles.

In this paper, finite-time synchronization for a class of complex-valued coupled chaotic systems with bounded non-identical perturbations and discontinuous activations is investigated. State feedback controller and Lyapunov function are designed to deal with time delay of the coupled systems. By separating the state variables into real and imaginary parts and using chain rule, sufficient conditions are obtained to realize finite-time synchronization. Moreover, the setting time can be estimated for chaotic systems. Those results can be applied to the continuous and real-valued chaotic systems. Finally, numerical simulations are given to demonstrate the effectiveness of the theoretical results.

This paper presents a sigma-delta interface for fluxgate sensor based on a single-loop high-order modulation. A feedforward summation loop structure can reduce the linearity overload in integrators and the swing of integration signals. A Local feedback branch is proposed to realize the zero of noise transfer function (NTF) optimization and enhance noise shaping performance within signal band. The interface is fabricated in a standard 0.5 $\mu$m CMOS process and the active circuit area is about 13 mm². The chip consumes 120 mW from a 10 V supply with a sampling clock of 250 k Hz. The average noise floor of the digital fluxgate is about −115 dBV/Hz${}^{1/2}$ over a 100 Hz bandwidth.

The aim of this work is to investigate new exact solutions of Tzitzéica type equations. We utilize the Painlevé transformation to transform the aforesaid non-linear evolution equations into ordinary differential equations. Then, the simplest equation method is employed for securing some real and complex solutions of the Tzitzéica equation, the Tzitzéica–Dodd–Bullough equation and the Dodd–Bullough–Mikhailov equation. After the execution of the simplest equation method, we obtain many new results more simply and reliably than the other approaches executed on these equations. The solutions are obtained and verified through soft computations. Also, the dynamics of some solutions are presented via three types of graphs including 2D, 3D and contour graphs.

The evaporation of fluid on solid surface is an important process in nature and industry. The high-efficiency heat transport between the working fluid and the solid surface can enhance the energy conversion and utilization. Thus, it is of great significance to study the mechanism of the evaporation phenomenon at the liquid–solid interface. In this study, the evaporation of refrigerant R32 on Pt surface is investigated by molecular dynamics (MD) method. The effects of the substrate temperature on the evaporation behavior of R32 are discussed in detail. It is found that R32 molecules mainly enter the vapor region by evaporation when the substrate temperature is no larger than 300 K. The evaporation rate increases with the increase of substrate temperature. The nucleate boiling and film boiling clearly occur when the substrate temperature is 350 K. The nanobubble formation, growth and coalesce is observed in the simulation. The heat flux changes rapidly when the system is boiling. As time goes on, a vapor film forms and then it leads to the heat transfer deterioration.