Modern Physics Letters B

Free rotating chain (FRC) is a well-known model of polymer but the knowledge to its mechanical property is yet incomplete. This work uses Monte Carlo simulation to evaluate the relation between force and extension, the specific heat, the stretching strength and the fourth-order cumulants of the order parameter of a three-dimensional (3D) FRC. We simplify some expressions to calculate the thermodynamical quantities. Our results reveal that at low force, the behavior of the mechanical property of the model is the same as that of a free jointed chain (FJC) in both two-dimensional (2D) and 3D cases. But beginning from a moderate force, the two models have different mechanical properties. Moreover, we find that a 3D FRC has essential different mechanical property from its 2D counterpart, because the extension of a stretched 2D FRC can subject to a first order transition when the bond angle is large enough, but there is no such a transition for a 3D chain despite its stretching strength exhibits a peaks at large bond angle. Our findings reveal that the space constraint on a stretched polymer favors a sharp change in its size.

A multi-functional dual-core photonic crystal fiber (PCF) polarization beam splitter with a central oval hole filled with gold is designed and described. The first layer on the circular holes around the core is filled with the nematic liquid crystal (NLC) to enhance birefringence. The full-vector finite element method is employed to study the characteristics of the polarization beam splitter and derive the optimal parameters. When the fiber length is 14.55 $\mu$m, the polarized light in the $x$- and $y$-directions can be separated at a wavelength of 1.31 $\mu$m and the bandwidths are 257 and 238 nm, respectively, for extinction ratios bigger than 10 dB. When the fiber length is 10.86 $\mu$m, the polarized light in the $x$- and $y$-directions can be separated at a wavelength of 1.55 $\mu$m and the bandwidths are 239 and 174 nm, respectively for extinction ratios larger than 10 dB. The multifunctional polarization beam splitter with an ultra-short fiber length and broad bandwidth improves the sensing performance in comparison with single-function devices and our results provide insights into the design of beam splitters with multiple functions.

Quantum dynamical properties of a general time-dependent coupled oscillator are investigated based on the theory of two-dimensional (2D) dynamical invariants. The quantum dynamical invariant of the system satisfies the Liouville–von Neumann equation and it coincides with its classical counterpart. The mathematical formula of this invariant involves a cross term which couples the two oscillators mutually. However, we show that, by introducing two pairs of annihilation and creation operators, it is possible to uncouple the original invariant operator so that it becomes the one that describes two independent subsystems. The eigenvalue problem of this decoupled quantum invariant can be solved by using a unitary transformation approach. Through this procedure, we eventually obtain the eigenfunctions of the invariant operator and the wave functions of the system in the Fock state. The wave functions that we have developed are necessary in studying the basic quantum characteristics of the system. In order to show the validity of our theory, we apply our consequences to the derivation of the fluctuations of canonical variables and the uncertainty products for a particular 2D oscillatory system whose masses are exponentially increasing.

Recently spin-tensor–momentum coupling (STMC) has been proposed to realize in the Bose–Einstein condensate (BEC). Here, we study the bright soliton in spin-1 three components BEC with STMC. The properties of the bright solitons are discussed by the analytical solutions and numerical solutions. In addition, we also study its dynamic evolution and discover the spontaneous motion, which is different from the spin-orbit-coupled solitons.

In this work, the generalized modified Korteweg–de Vries (gmKdV) equation is constructed by the first time and is solved by the Riemann–Hilbert method with the zero boundary condition. In the direct scattering transform, the analytical and asymptotic properties related to the Jost functions and the scattering matrix are given. On the basis of the above results, the appropriate Riemann–Hilbert problem (RHP) is constructed. By solving the RHP, we obtain the exact solution of the gmKdV equation in the case of no reflection potential when the scattering data $a(k)$ has simple poles and higher-order poles. Furthermore, the three special solutions under different zero points are given and the phenomenon of their spread is described, respectively.

In recent years, integrated signal processing system has been attracting increasing attention for its significant potential in future data transmission and information interaction. There is a key technical requirement for multi-pulse signal propagation that keeps the waveform shape, which contributes to the practical value of the system. Here, we investigate the effects of third-order dispersion on pulses in mid-infrared multi-pulse signal propagation via numerical simulation based on Runge–Kutta algorithm. The phenomenon of waveform distortion and reduction of conversion efficiency induced by third-order dispersion is explored and discussed in detail. To reduce the impact of nonlinear factors, we propose an on-chip signal processing system based on a lithium niobate waveguide, which achieves high-efficiency signal transmission. It opens a new way to establish a novel transmission system to process multi-pulse signal.

The atomic scale is the only relevant thermodynamic scale in our universe, since quantum properties restrict classical considerations of subatomic physics and disappear for larger scales. Then the characteristic energy that dictates the value of the unit of temperature can be the classical thermal energy defined for simplest atoms. It is shown that vibrational frequency of a classical model hydrogen atom, of the radius of its Rydberg wavelength, is in far-infrared range and from its quantum of energy one can obtain the value of Boltzmann’s constant that serves as the measure of the absolute temperature in kelvins.

The current topological edge states lack dynamical modulation and the intense field localization effect. To solve these problems, we construct a topological edge state structure based on two-dimensional photonic crystals with lattice shrink. Through the optimization of structure parameters, a nearly flat edge state dispersion curve occurs in a wide bandgap. The topological edge states with intense field localization take on some unique properties such that the transport directions can be controlled by both the source spin and the source position. The transport modes can be dynamically switched between the two opposite unidirectional channels just through moving the source position.

A nonlinear micro-polar non-Newtonian fluid model is investigated. By the complete discrimination system for polynomial method, we give the classification of the traveling wave patterns and analysis of topological stability and dynamical behaviors. We also discuss the physical realizations and the conditions of existence of these patterns. As a result, when some of parameters are not intrinsic parameters we show that in general only two stable patterns will be observed.

In reality, the types of vehicles running on the road and the driving experience of different drivers are probably different. Thus, the maximum velocity of each vehicle is usually different. Moreover, common driving experience indicates that drivers not only pay attention to the motion status of individual preceding vehicle in their view. With that in mind, an extended car-following model accounting for two preceding vehicles with mixed maximum velocity is constructed in this study. For analyzing the traffic flow’s evolution more accurately, theoretical and numerical analyses are conducted. In theoretical analysis, the model’s stability condition is inferred by using the control theory, and the mKdV equation is also derived to depict the propagation of traffic density wave by means of nonlinear analysis. Numerical experiments are performed to verify the correctness of theoretical analysis and to make a detailed analysis concerning the influences of factors considered on traffic flow. Theoretical and experimental results indicate that increasing the higher maximum velocity and the appearing probability of a car having higher maximum velocity is not conducive to traffic flow stability, and compared to only considering individual preceding vehicle’s motion status, it is obvious that the traffic flow with mixed maximum velocity is more stable when two preceding vehicles’ motion status is considered.

Soft mechanical metamaterials with hinge-like elements can undergo multi-step reconfiguration through folding and contacts, and thus exhibit highly nonlinear responses. Numerical simulation of the nonlinear behaviors is essential for the design and control of the mechanical metamaterials, but it remains a challenge due to complicated nonlinear effects. Here, we report the finite element modeling of multi-step reconfiguration of a shape-changing metamaterial, and elucidate the underlying mechanism of soft elasticity. The predicted stress–strain curve together with the folding angles of hinge elements shows excellent agreement with experimental data reported in the literature. Moreover, we explore the influence of reconfiguration and folding-induced internal stress on the bandgap distribution of the mechanical metamaterials. Our efforts provide useful guidelines for the design and application of mechanical metamaterials for both static and dynamic situations.

This paper introduces a digital control system of gyroscope. The control circuit includes amplitude control loop, phase control loop and detection circuit. The amplitude control loop realizes the stability of driving mode vibration signal amplitude. The phase control loop consists of coarse phase locking loop and precise phase locking loop. At the initial stage, coarse phase locking is used to realize the rapid start-up of the gyroscope. Then after resonance frequency settles into the lock-in range of PLL, precise phase locking is used to realize the precise phase locking. The detection circuit realizes the output of gyro angular velocity signal. The design is implemented on PCB. The test results show that the scheme can realize the stable operation of gyroscope.

By using the PIC simulation method and theoretical investigation from both the magnetohydrodynamic equations and the Vlasov equation of the dusty plasma produced by the relative streaming of the dust fluid and the background ionospheric plasma, we investigate the instability of the waves excited by this kind of the dust beam in the ionosphere. It is found that the waves are stable in both the electron and ion vibration time scales, while they are unstable in the dust grain vibration time scale. It is inferred that the wave is the high hybrid wave in the electron vibration time scale. The dispersion relations of the perturbed waves in both the electron vibration and ion vibration time scales are obtained. As the time increases until it arrives at the dust grain vibration time scale, the instability appears for the perturbed wave. Such instabilities may drive plasma irregularities that could affect radar backscatter from the clouds, when the wave satisfies the Bragg condition for backscatter. By using the dispersion relation of waves in both electron vibration and ion vibration time scales, we can infer what kind of radar backscatter can be possibly affected by the instability of the perturbed waves.

Based on the hybrid semiconductive InSb metamaterials (MMs), we investigated the tunable Fano resonances in the terahertz regime, including the effects of carrier concentrations of InSb layer, environment temperatures and operation frequencies. The results manifested that an obvious Fano resonance was observed by using the heterostructure of InSb bars, the peak value of Fano resonance reached more than 0.97 with a high $Q$-factor of larger than 50. By changing the carrier concentrations of InSb layer, the propagation properties of semiconductor MM structures can be effectively modulated, the amplitude modulation of Fano resonance can reach more than 80%. The results are helpful for designing novel tunable terahertz devices with high $Q$-factor, e.g. modulators, sensors and antenna.

This study proposes a short-term traffic flow prediction approach based on multiple traffic flow basic parameters, in which the chaos theory and support vector regression are utilized. First, a high-dimensional variable space can be obtained according to the traffic flow fundamental function. Then, a maximum conditional entropy method is proposed to determine the embedding dimension. And multiple time series are reconstructed based on the phase space reconstruction theory using the time delay obtained by mutual information method and the embedding dimension captured by the maximum conditional entropy method. Finally, the reconstructed phase space is used as the input and the support vector regression optimized by the genetic algorithm is utilized to predict the traffic flow. Numerical experiments are performed and the results show that the approach proposed has strong fitting capability and better prediction accuracy.

In this work, we report an amplified strong coupling phenomenon in a hybridized nanowire. The hybridized nanowire structure is composed of CH₃NH₃PbBr₃ perovskite nanowire coated by SiO₂ film and silver film. Due to the existence of silver film, Rabi splitting in hybrid structure can reach 303.2 meV, while the Rabi splitting in a pure perovskite nanowire is only 236.4 meV. Also, thicknesses of SiO₂ film and Ag film can control the Rabi splitting of hybridized structure: (i) the thicker the Ag film, the greater the Rabi splitting; (ii) the thinner the SiO₂ film, the greater the Rabi splitting. Finally, index of SiO₂ film shows a linear relation with Rabi splitting.