Modern Physics Letters B

Researches on the human mobility have made great progress in many aspects, but the long-term and long-distance migration behavior is lack of in-depth and extensive research because of the difficulty in accessing to household data. In this paper, we use the resume data to discover the human migration behavior on the large-scale scope. It is found that the asymmetry in the flow structure which reflects the influence of population competition is caused by the difference of attractiveness among cities. This flow structure can be approximately described by the gravity model of spatial economics. Besides, the value of scaling exponent of distance function in the gravity model is less than the value of short-term travel behavior. It means that, compared with the short-term travel behavior, the long-term human migration behavior is less sensitive. Moreover, the scaling coefficients of each variable in the gravity model are investigated. The result shows that the economic level is the main factor of migration.

The undoped and magnesium (Mg)-doped Tin (IV) oxide (SnO₂) thin films were grown on glass substrate by spray pyrolysis technique. In order to observe the effect on the optical, structural, morphological, and hydrogen (H₂) gas answer properties of SnO₂ by Mg doping, X-ray diffractometer (XRD), ultraviolet–visible (UV) spectrometer, scanning electron microscope (SEM) and hydrogen (H₂) gas, measurements were taken. The absorption measurements of undoped and Mg-doped SnO₂ thin films demonstrated that band gaps varied with the changing Mg dopant ratio and this variation may be from Burstein–Moss (BM) effect. XRD measurements showed that the samples were tetragonal structures and have (110), (101), (200), (211), (220), (310) planes. The surface morphology of SnO₂ showed that samples was affected considerably by Mg dopant. The H₂ gas sensor response improves with the increase of 1%, 2% and 3% Mg doping ratio in SnO₂.

In this paper, we aim to investigate influences of an asymmetrical potential on particle transport in the presence of a periodic channel by calculating particle current and effective diffusion coefficient. First, influences of external force on transport behaviors are researched. Results reveal that with the increase of the external force, particle current increases, and the effective diffusion coefficient decreases first and then increases. That is, large external forces can promote the movement of particles. Second, influences of potential asymmetry and amplitude on particle transport are studied. These two factors have a more complex mechanism of influence on particle transport. For example, an increase of positive amplitude value leads to a decrease of particle current, while a negative value makes particle current increase first and then decreases. In other words, the effect of amplitude depends on its sign and value. For positive amplitude, the larger its value is, the greater the suppression effect on particle transport. While for negative amplitude, as its value increases, it promotes particle transport. When its value increased to a certain extent, the effect of the amplitude on the particle motion changes from promotion to suppression. For asymmetry, it can promote particle transport for positive amplitude while suppress the transport for negative amplitude. These results can provide some bases for understanding biological systems and controlling particle transport.

Deposition of Zinc sulfide (ZnS) thin films on Si (100) and glass substrates has been performed using electron beam evaporation (EBE) method without annealing. Film structure has been analyzed by XRD, while SEM and AFM have been used to explore the films morphology. Raman spectroscopy has been used to confirm film composition. The stoichiometry has been verified by EDX and XPS techniques. XRD patterns indicated that the films possess a polycrystalline cubic structure with orientations along (111) and (220) planes. The crystallinity has been better with film thickness in the 350–1700 nm range while the RMS roughness increases. Optical properties of the grown films were characterized by optical transmittance measurements (UV–Vis). The deduced energy band gap of the films shows a clear reduction from 3.45 eV to 3.36 eV with increasing film thickness. The evolution of refractive index, extinction coefficient, and dielectric constants with thickness has been investigated from transmittance spectra in the 500–1000 nm wavelength range.

In this paper, symmetry analysis is performed for the nonlinear Chen–Lee–Liu equation (NCLE) arising in temporal pulses. New forms of explicit solutions of the equation are constructed using the optimal systems by applying the power series solutions (PSS) technique and the convergence of the PSS is investigated. Finally, the conservation laws (Cls) of the model is studied using the multiplier approach.

The Heisenberg ferromagnet model has been studied theoretically using the Weiss mean-field theory and Green’s function technique. The equations for the Curie temperature, magnetization, and magnetic susceptibility were analytically derived. Moreover, we proved, that our results are useful in description of real materials. The calculated value of Curie temperature for ${\mathrm{\text{LaFe}}}_{11.0}{\mathrm{\text{Co}}}_{0.7}{\mathrm{\text{Si}}}_{1.3}$ alloy correspond well with the experimental results obtained recently on the base of the temperature dependences of magnetization.

We consider the wave equation for an electromagnetic field propagating in silicene placed in photonic crystal (PC). We study the effects observed when the depth of the nonlinearity modulation are varied, as well as the initial amplitude of the electromagnetic pulse.

Elastic steel metamaterial plates can be used for noise- and vibration-reduction due to unique physical properties related to their vibration band gap. However, obtaining a complete low-frequency vibration band gap in a thick elastic steel metamaterial plate is difficult. In this paper, we simulate a complete low-frequency vibration band gap in a thick elastic steel metamaterial plate. The structure consists of periodic, double-sided, composite stepped resonators, which were deposited on a 2D locally resonant phononic crystal plate. The phononic crystal plate consists of an array of rubber fillers embedded in a thick steel plate. The dispersion relations, power-transmission spectra, and the displacement fields of the eigenmodes are calculated using the finite-element method. The results show that, for the proposed structure, the opening of the first complete vibration band gap is reduced by a factor of 9.5 compared to a conventional thick elastic steel metamaterial plate. This causes attenuation of low-frequency elastic waves. The formation mechanisms for the vibration band gap are also explored numerically. The results indicate that the formation mechanism for the new low-frequency vibration band gap can be attributed to coupling between a local resonance mode of the composite stepped resonators and the Lamb wave mode of the thick steel-plate. The location of the vibration band gap is determined by the resonator mode of the composite stepped resonators. The vibration band gap effects of the composite stepped resonators are also investigated in this paper. We find that the location of the complete vibration band gaps can be modulated with a relatively low frequency using different composite stepped resonators. Such an elastic steel metamaterial plate with a complete low-frequency vibration band gap can be used to reduce both vibration and noise in various commercial and research applications.

The effect of high hydrostatic pressure on the relaxation of the electrical resistivity at room temperature of oxygen-nonstoichiometric ${\mathrm{\text{ReBa}}}_2{\mathrm{\text{Cu}}}_3{\mathrm{\text{O}}}_{7-x}$ (Re = Y, Ho) single crystals is investigated. The application of hydrostatic pressure has been revealed to significantly intensify the process of diffusion coalescence in the oxygen subsystem. At the same time, the intensity of the redistribution of labile oxygen is significantly changed when yttrium is replaced by holmium.

Parameter estimation of chaotic system is an important issue in nonlinear science. The meta-heuristic algorithm is one of the effective estimation approaches, and has received increasing attention. However, few people have noticed the influence of the samples on parameter estimation. In fact, when using meta-heuristic algorithm for parameter estimation, the number of samples will affect the efficiency greatly. In this paper, this problem is investigated. The relationship between sample and step size, and the factors that affect the difficulty of parameter estimation are also considered. Experimental results show that it is more efficient to set the samples to a small number, and the number of estimated parameters is the most important factor affecting the difficulty of parameter estimation. Finally, to improve the precision further, a new hybrid chaotic particle swarm optimization algorithm which combines a special inertia weight with chaotic search is proposed. Results demonstrate that the new hybrid algorithm is more effective than the other four meta-heuristic algorithms.

Carbon nanotubes (CNTs) as interconnects in integrated circuits (ICs) which are vertically aligned in growth with high tube density and long tube length are required. In this paper, we present a method to improve the height of CNTs. High-resolution transmission electron microscopic (TEM) images confirm CNTs top growth mode. By cutting and modifying the top of CNTs, the influences of different radii of apertures on interconnect resistance were studied. According to the analysis, we proposed a novel growth mechanism to improve growth height of CNTs interconnection structure and the top contact resistances of pre-cutting and post-cutting CNTs interconnection structure were forecasted. The result demonstrates that the electronic performances of the post-cutting CNTs interconnection structure with platinum (Pt)-protected layer are better than the ones of pre-cutting CNTs interconnection structure. The resistivity of the post-cutting CNTs interconnection structure with Pt-protected layer is $81.2\mathrm{\text{m}}\mathrm{\Omega }\cdot \mathrm{\text{cm}}$, which is much less than that of post-cutting CNTs interconnect structure $508.8\mathrm{\text{m}}\mathrm{\Omega }\cdot \mathrm{\text{cm}}$. In what follows, the resistance of the contacted area of pre-cutting CNTs interconnection structure is 31 $\mathrm{\Omega }$, which is much less than that of post-cutting CNTs interconnection structure 439 $\mathrm{\Omega }$. This constitutes a significant step to realize longer CNTs interconnects with complementary metal oxide semiconductor (CMOS) contact modules.

Compact microstrip antennas based on split-ring resonator (SRR) structure are proposed and fabricated in this paper. The resonant frequency of the antennas is discussed upon different geometric structures. The influencing mechanism of the antenna parameters on resonant frequency is analyzed. The analytical and experimental analyses are carried out and proved that the resonant frequency can be controlled from 13.5 GHz to 17.2 GHz by tuning some of the crucial parameters. A good agreement between the simulations and the measurement results suggests that the proposed antenna can be designed at different resonant frequencies while maintaining a small-size, low-profile structure and good performance.

The first-principles method based on density functional theory has been used to investigate the adsorption performance of NO/NO₂ molecules on intrinsic, Ag-doped, Pt-doped and Au-doped graphene. Results show that graphene doped with Ag/Pt/Au has shorter final adsorption distance, larger adsorption energy and charge transfer amount with NO/NO₂ molecules than intrinsic graphene, and the charge densities of doped graphene and NO/NO₂ molecules overlap effectively. Therefore, doping graphene with noble metals can greatly enhance the adsorption between graphene and NO/NO₂ molecules. Analysis also reveals that Au-doped graphene has the strongest adsorption effect on NO/NO₂ molecules, followed by Ag-doped graphene, while Pt-doped graphene has the weakest role on the adsorption of NO/NO₂ molecules. The work conducted in this research provides a theoretical guidance for the application of NO/NO₂ gas sensors based on graphene.

A semi-quantum secret sharing scheme using entangled states was proposed in a recent paper [Mod. Phys. Lett. B 32 (2018) 1850256. https://doi.org/10.1142/S0217984918502561]. We find a loophole of this scheme. Based on the intercept-resend attack, we propose a deterministic attack strategy and a probabilistic attack strategy. The malicious participant can escape the detection and obtains the secret. We also suggest two improvements to help increase the security of the original scheme.