Modern Physics Letters B

This paper introduces a new nanoscale slot waveguide using organic material, graphene, and silicon-based materials. The physical mechanism of additional biased voltage can improve the performance of graphene-related waveguide, the proposed waveguide exhibits tunable performance including effective refractive index and dispersion without changing its structure and geometric dimension, which contributes to the practical value in future complex signal processing system. Based on the waveguide, wavelength conversion based on four-wave mixing is theoretically investigated in the near-infrared region and the tunable wavelength conversion is realized. These research results will have potential in the fields of data transmission and optical communications and help researchers deeply understand the physical mechanisms and nonlinear effects about the optical pulse generation processes and signal processing.

The effects of semi-solid extrusion temperature change, extrusion pressure, SiC content and T5 heat treatment on the microstructure, mechanical properties, and wear resistance of SiC particle strengthened high aluminum zinc-base alloy $({\mathrm{\text{SiC}}}_P/\mathrm{\text{ZA}}27)$ composites were studied. The results show that semi-solid extrusion broke the dendrites of ${\mathrm{\text{SiC}}}_P/\mathrm{\text{ZA}}27$ composites, refined their grain structure, and improved particle aggregation. The density, hardness, yield strength, tensile strength and elongation of ${\mathrm{\text{SiC}}}_P/\mathrm{\text{ZA}}27$ composites first increased and then decreased when the extrusion temperature and SiC content increased, and also increased when the extrusion pressure rose. The optimal extrusion temperature, pressure and SiC content are 475${}^{\circ }$, 15 MPa and 10 wt.%, respectively. T5 heat treatment further refined the crystalline grains and promoted ${\mathrm{\text{Mg}}}_{32}{\mathrm{\text{Al}}}_{47}{\mathrm{\text{Cu}}}_5$ and ${\mathrm{\text{CuZn}}}_5$ to precipitate as strengthening phases, which improve the mechanical properties and wear resistance of ${\mathrm{\text{SiC}}}_P/\mathrm{\text{ZA}}27$ composites. Consequently, the hardness, yield strength, tensile strength and elongation of the heat-treated composites improved by 18.99%, 9.66%, 4.93% and 9.76%, respectively. The wear loss of the heat-treated composites reduced by 31.65% under a load of 1600 N and a rotational speed of 200 r/min compared with the as-cast composites.

The first-principle method was used to study the electronic structure of montmorillonite under high pressure. The calculated results show that the Si–O bond is more stable than the Al–O bond as the pressure was increased, while the H–O bond is almost independent of this variable. More importantly, band structure of montmorillonite changes from indirect bandgap to direct bandgap and vice-versa at 33.2 GPa and 39.2 GPa, respectively. Furthermore, density of state split phenomenon appeared in conduction band region. By calculating the montmorillonite elasticity constants under different levels of stress, the results show that C33 and C66 perpendicular to the crystal face are greatly affected by the stress. Moreover, C44 with the minimum changes during the entire stress process. The calculated results will not only help to understand the electronic structure of montmorillonite under pressure, but also provide theoretical guidance for deal with the safe problems of tunnel engineering.

A novel scheme for tunable optofluidic optical coupler is proposed by combining directional coupling waveguide structures with microfluidic channel. The normalized optical power at two output ports can be dynamically manipulated by controlling the refractive index of liquid mixture in microfluidic channel. Its optical performance is numerically investigated by employing the beam propagation method (BPM). The simulated results show that the dynamic range of over 45 dB, and optical loss of below 0.06 dB can be easily achieved, and furthermore the dependence of polarization states and operation wavelength in the range from 1500 nm to 1600 nm are very low in our designed device. In addition, the tunable optofluidic coupler has advantages including simple structure and large fabrication tolerance. Accordingly, our proposed device offers a new approach for manipulating optical power output, which has wide potential application in optofluidic systems.

In this paper, waterborne polyurethane (WPU) conductive films incorporated with reduced graphene oxide (RGO) as conductive fillers were prepared by solution blending and tape casting method. The electrical conductivity, thermal conductivity and microstructures of the composite films were systematically investigated. The experimental results demonstrate that the electrical conductivity and thermal conductivity of the RGO–WPU composite films first increased then decreased with the increase of the RGO content. The resistivity of composite film with 7% RGO reaches to the smallest that is about $0.16\mathrm{\Omega }\cdot \mathrm{\text{cm}}$, and the thermal conductivity of the composite film with 7% graphene was about 0.29 W.m.K${}^{-1}$, which an increase of 70% compared with pure WPU. The electrical conductivity of the composite film decreased with the increase of the original concentration of WPU solution and thickness of the composite film. As film heater, the composite film displayed effective and rapid heating at low input voltages owing to the good conductivity. With an input voltage was in the range of 10–24 V, the film took less than 30s to reach a steady-state temperature, demonstrating the fast response of the composite film heater and suitable for applications in the field of the fast temperature switching with low input voltages as flexible electrothermal heater.

In order to rationally formulate a customized bus route plan to improve the operation efficiency of customized buses, in view of the problem of ignoring the distance between the boarding area and the alighting area, and setting it as a fixed value when performing custom bus route optimization modeling, as well as solving the problem of multiple custom bus parking lots. This paper proposes a method based on the NSGA-II algorithm using a three-stage hybrid coding method to solve. First, according to real life, the entire operation process of customized buses is divided into four phases. Second, based on the four stages, a multi-objective optimization model of customized bus routes that satisfies multiple parking lots, multiple cars, and multiple boarding and alighting stations is constructed to pursue the minimum total travel time of passengers and minimizes the operating costs of customized bus companies. Third, the NSGA-II algorithm is employed to solve the model, including three-stage hybrid coding, segmented crossover, and segmented mutation operators. Finally, the local road network in Lanzhou City is adopted for simulation research. The results show that it is feasible to use NSGA-II algorithm to solve the problem of customizing bus routes for multiple parking lots, multiple vehicles, and multiple boarding and alighting stations. The research results are of great value for exploring the optimization methods of customized bus routes and improving the operating efficiency of custom buses.

The survival and occurrence of chaos are much dependent on the intrinsic nonlinearity and parameters region for deterministic nonlinear systems, which are often represented by ordinary differential equations and maps. When nonlinear circuits are mapped into dimensional dynamical systems for further nonlinear analysis, the physical parameters of electric components, e.g. capacitor, inductor, resistance, memristor, can also be replaced by dynamical parameters for possible adjustment. Slight change for some bifurcation parameters can induce distinct mode transition and dynamics change in the chaotic systems only when the parameter is adjustable and controllable. In this paper, a thermistor is included into the chaotic Chua circuit and the temperature effect is considered by investigating the mode transition in oscillation and the dependence of Hamilton energy on parameters setting in thermistor. Furthermore, the temperature of thermistor is adjusted for finding possible synchronization between two chaotic Chua circuits connected by a thermistor. When the coupling channel via thermistor connection is activated, two identical Chua circuits (periodical or chaotic oscillation) can reach complete synchronization. In particular, two periodical Chua circuits can be coupled to present chaotic synchronization by taming parameters in thermistor of coupling channel. However, phase synchronization is reached while complete synchronization becomes difficult when the coupling channel is activated to coupling a periodical Chua circuit and a chaotic Chua circuit. It can give guidance for further control of firing behaviors in neural circuits when the thermistor can capture the heat effectively.

An innovative structure of longitudinal grooves was designed on the volute casing of a centrifugal pump to improve the performance and internal flow characteristics. Comparisons were made between the model with grooved volute casing (GVC) and the model with original volute casing (OVC) operating in different working conditions. To get a better understanding of the influence of grooves on the centrifugal pump, some preliminary studies were performed with a simplified model. The results indicated that the application of GVC offers better pump performance under the large flow rate, also can stabilize the operating range of the centrifugal pump. In addition, the drag reduction effect of GVC is quite considerable compared with the pump with OVC. The pump with modified volute casing can suppress and eliminate the instability flow inside the impeller channels and volute casing. By using the GVC, the pressure and velocity distribution inside the impeller channel ameliorated especially for the 0.85 $R_i$ near the region of rotor–stator interaction between impeller and volute casing. Furthermore, the effects of GVC on flow passing ability may be recognized clearly for the flow area of the model with GVC increased by 5% at one impeller channel compared to the pump with OVC.

In order to further expand the application scope of 2205 duplex stainless steel (DSS), its microstructure and mechanical properties require as much attention as its corrosion properties. In this study, 2205DSSs were prepared by aluminothermic reaction and the microstructures and mechanical behavior of the rolled alloys were analyzed. The micro-nanocrystals composite structure appears in the alloys after rough rolling with deformation of 40% at $1000^{\circ }$C followed by finishing rolling with deformation of 30%, 50% and 70% at $600^{\circ }$C. With the increase of rolling deformation, the two-phase structure is gradually elongated, the average size of the two-phase grains is gradually increased, and some $\gamma$ phase will change to $\alpha$ phase, the volume fraction of $\alpha$ phase is gradually increased, and the distribution of nanocrystals is gradually uniform. Meanwhile, the fracture mode of alloy is gradually changed from ductile fracture to brittle fracture. The strength and hardness of the alloy increase gradually.

In this paper, we deduce the (2+1)-dimensional Schwarz–Korteweg–de Vries equation from two (1+1)-dimensional equations. Based on the resulting Lax pairs, we present its $N$-fold Darboux transformation. From a trivial solution, we get $2N$-soliton and $(2N+1)$-soliton solutions of the (2+1)-dimensional Schwarz–Korteweg–de Vries equation. The asymptotic analyses of the $2$-soliton, $3$-soliton and $4$-soliton solutions are presented theoretically and graphically.

We present a simple model of ionomers, namely a single polymer chain in a series of fixed attractors. In analogy to ionized bead’s claws of surrounding chains, the set of attractors can affectively slow down the diffusion motion of the target chain. The monomer mean-square displacement of ionomers is studied by using Monte Carlo algorithm, and compared with the prediction of the sticky Rouse model. The diffusion motion properties of ionomers are explored in three aspects, including the chain length of the polymer, the depth of the potential well and the number of ionic groups. The results show that a plateau appears in the monomer diffusion function due to the attraction of the attractors to the claws. However, comparative theoretical predictions and simulation results show that there exists some discrepancy between them. Therefore, the relaxation time distribution of polymer chain motion is explored. The simulation results confirm that the association lifetime is decreasing exponentially, and the expected values of the association lifetime satisfy the Boltzmann distribution as shown by the results. These results perfectly explain the deviation between the simulation data and the theoretical results.

Evolution of both low-frequency harmonic Alfvén wave train and Alfvén solitary wave is studied by using the compressible MHD fluid model. A critical point is found at which linear wave theory should be replaced by a nonlinear one. A small, but finite amplitude Alfvén solitary wave is numerically found. The head-on collision between an Alfvén wave train and an Alfvén solitary wave is also numerically investigated. An interesting result is that there is no phase shift for both colliding waves which is different from that between two KdV solitary waves.

There often exist behaviors of moving against the main direction of evacuation in order to rescue or find the important missing people in real situations. However, the traditional social force model (SFM) often lacks consideration of such “counter flow”. Motivated by this, we improve the traditional SFM to study the counter flow and its influence on evacuation out of multi-exit rooms. We call the person to be rescued “superior” and the rescuers “subordinate”. Two different rescue situations are proposed: superior waiting in place (case 1) and superior moving towards the exit (case 2). The results show that the counter flow will always reduce the evacuation efficiency to a certain extent, and the evacuation efficiency of case 1 is lower than that of case 2. At the same time, for these two cases, increasing the number of rescuers increases the evacuation time. We also find that the existence of counter flow can enlarge the effect of “faster-is-slower”, while increasing the number of exports can significantly improve the rescue efficiency. We hope that this result can help to improve the efficiency of emergency evacuation with rescue.

High-temperature superconducting (HTS) film-substrate structures have great potential applications in magnets and superconducting cables that have great potential for high temperature superconducting wires in space solar power stations. The most important issue in the successful application of those structures is the delamination of interfaces. Therefore, in this paper, the delamination induced by electromagnetic force and temperature change in the superconducting film-substrate structure is studied. Energy release rates of delamination are given. It is found that thermal effect on the energy release rate is more significant when the electromagnetic force increases. If without electromagnetic force, as the crack length reaches at its critical value, the film will be buckling and the crack becomes a mixed crack. The closed-form solution of the energy release rate of the mixed crack is provided. On the other hand, when the crack length is smaller than its critical buckling length and the crack is the mode II crack. The influence of the stress intensity factor of the mode II crack is more significant for a thicker film. This suggests that the film should be designed to be thinner. This study is useful for engineers to design HTS film-substrate structures.