International Journal of Modern Physics B

In this work, Fe₂N magnetic nanocomposite was synthesized via an in-situ reaction method of ball milling. In this method, Fe and h-BN were used as iron source and nitrogen source, respectively. We found that ball milling could increase the surface energy and make the sample to be amorphous, which is the key factor in synthesizing Fe₂N nanocomposite. The as-synthesized nano-sized Fe–N could disperse in the BN matrix uniformly. It is worth noting that we can obtain Fe₂N with different grain sizes by controlling the experimental conditions. The saturation magnetization of Fe₂N was measured and the value is about 0.03 emu/g. The excellent properties of Fe₂N magnetic nanocomposite suggest that Fe₂N magnetic nanocomposite could be widely used in industrial application.

We present several one-parameter families of higher-order field theory models some of which admit explicit kink solutions with an exponential tail while others admit explicit kink solutions with a power-law tail. Various properties of these families of kink solutions are examined in detail. Further, by applying the recent Manton formalism, we provide estimates for the kink–kink (KK) and antikink–kink (AK-K) acceleration and hence the ratio of the corresponding AK-K and KK forces.

Stagnation point flow of viscoelastic second grade fluid over a stretching cylinder under the thermal slip and magnetic hydrodynamics effects are studied. The mathematical model has been developed under the assumption of non-Newtonian viscoelastic fluid flow over a stretching cylinder by means of the boundary layer approximations. The developed model further reduced through the similarity transformations and constructs the model of nonlinear ordinary differential equations. The system of nonlinear differential equations is dimensionless and solved through the numerical technique bvp5c methods. The results of the physical parameters are found and interpreted in the form of tables and graphs. The velocity shows that the graph of curves enhances away from the surface when the values material parameter ${\beta }^{\ast }$ increase, which means the momentum boundary layer increases for enhancing the material parameter ${\beta }^{\ast }$. The temperature gradient reduced due enhancing the values of material parameter ${\beta }^{\ast }$ because thermal boundary layer reduced for higher values of material parameter ${\beta }^{\ast }$.

In this paper, a novel meshless numerical scheme to solve the time-fractional Oskolkov–Benjamin–Bona–Mahony–Burgers-type equation has been proposed. The proposed numerical scheme is based on finite difference and Kansa-radial basis function collocation approach. First, the finite difference scheme has been employed to discretize the time-fractional derivative and subsequently, the Kansa method is utilized to discretize the spatial derivatives. The stability and convergence analysis of the time-discretized numerical scheme are also elucidated in this paper. Moreover, the Kudryashov method has been utilized to acquire the soliton solutions for comparison with the numerical results. Finally, numerical simulations are performed to confirm the applicability and accuracy of the proposed scheme.

Accurate detection of arrhythmia signal types is of great significance for the early detection of heart disease and its subsequent treatment. The primary purpose of this study is to explore an electrocardiogram (ECG) classification system to improve its performance and achieve excellent computing performance, especially for large sample datasets. We classified ECG signals using the Hurst exponent, which is an ECG feature extracted by multifractal detrended moving average cross-correlation analysis (MF-XDMA). In addition, we used multifractal methods such as multifractal detrended fluctuation analysis (MF-DFA), multifractal detrended cross-correlation analysis (MF-DCCA) and multifractal detrended moving average (MF-DMA) to extract the features of ECG signals, and we used a support vector machine (SVM) to classify the four types of feature data. The experimental results show that MF-XDMA-SVM has the best classification performance for atrial premature beat (APB) and bigeminy signals, which indicates that MF-XDMA-SVM is the most effective for the extraction of ECG signal sequence features among the four multifractal models.

Entanglement entropy growth is studied under a form of dynamics that is based on iteration. This approach allows the investigation of the role of decoherence in producing increases of entropy. This has important consequences as far as the study of decoherence is concerned. It is indicated that results are generally independent of Hilbert space partitioning. It is seen that a deep relationship between classical dynamical entropy and the growth of entanglement entropy exists in this kind of model. The former acts to bound the latter and in the asymptotic region, they tend to a common limit.

Despite the extensive use of graphene-based materials in K-ion batteries, the effects of various edge morphologies of graphene on K atom adsorption and diffusion are unclear. In this study, the effects of K atom adsorption and diffusion on zigzag graphene nanoribbons (ZGNRs) with hydrogen (−H), ketone (=O), hydroxyl (−OH), and carboxyl (−COOH) terminal groups were investigated by density functional theory calculations. ZGNRs terminating with −H, =O and −COOH promote K atom adsorption, whereas those terminating with −OH suppress it. The −H, =O, −OH and −COOH terminations have a negligible effect on K atom diffusion in the inner region of ZGNRs. In the edge region, the diffusion barriers are nearly unchanged for −H and −OH terminations; however, they are increased for =O and −COOH terminations in the edge region compared to those in the inner region. All the terminal groups hinder K atom diffusion from the edge region toward the inner region. Our results suggest that −H termination enhances K atom adsorption and has a negligible effect on the diffusion barrier of K atom in the edge region. Therefore, the ZGNR with −H termination could be a promising candidate for K-ion batteries.

In this paper, the conformal mapping from a regular 2$n$-polygon hole with two collinear asymmetric cracks into a circle is constructed. Based on the Gurtin–Murdoch surface/ interface model and complex potential theory, two collinear asymmetric nanocracks emanating from an electrically semi-permeable regular 2$n$-polygon nanohole embedded in an infinite one-dimensional hexagonal piezoelectric quasicrystals with surface effect are investigated. The size-dependent stress intensity factors of phonon field and phason field, electric displacement intensity factor at the nanocrack tip are derived for electrically semi-permeable boundary condition. Numerical examples are illustrated to show that the size of the hole, mechanical load, electric load, cracks relative size change with stress intensity factor of phonon field and electric displacement intensity factor. Also analyzed the change of the electric displacement intensity factor with different electric permeability at the nanocrack tip and the dimensionless intensity factor with $n$.

Complex systems are usually high-dimensional with intricate interactions among internal components, and may display complicated dynamics under different conditions. While it is difficult to measure detailed dynamics of each component, proper macroscopic description of a complex system is crucial for quantitative studies. In biological systems, each cell is a complex system containing a huge number of molecular components that are interconnected with each other through intricate molecular interaction networks. Here, we consider gene regulatory networks in a cell, and introduce individual entropy as a macroscopic variable to quantify the transcriptional dynamics in response to changes in random perturbations and/or network structures. The proposed individual entropy measures the information entropy of a system at each instant with respect to a basal reference state, and may provide temporal dynamics to characterize switches of system states. Individual entropy provides a method to quantify the stationary macroscopic dynamics of a gene set that is dependent on the gene regulation connections, and can be served as an indicator for the evolution of network structure variation. Moreover, the individual entropy with reference to a preceding state enables us to characterize different dynamic patterns generated from varying network structures. Our results show that the proposed individual entropy can be a valuable macroscopic variable of complex systems in characterizing the transition processes from order to disorder dynamics, and to identify the critical events during the transition process.

In modern microwave and optical communication systems, it is urgent to develop optical components with the same performance as electronic components. In this paper, a PT-symmetric structure including electro-optical medium is designed to construct optical triode. It is found that the structure has a pole effect of amplification under certain parameters. The frequency of the incident wave at the pole is taken as the carrier frequency, and the electrical signal is modulated into an optical signal. By setting the bias electric field, the modulated optical signal can be amplified in phase and out phase, and even by doubling frequency, and a new optical triode model is obtained. The designed model will play an important role in the design of optical integrated devices.

In this paper, we investigate the spectral functions of the Higgs mode in $O(2)$ model, which can be experimentally realized in a two-dimensional Bose gas. Zero temperature limit is considered. Our calculation fully includes the 2-loop contributions. Peaks show up in the spectral functions of both the longitudinal and the scalar susceptibilities. Thus, this model cannot explain the disappearance of the response at the weak interaction limit. Neither it can explain the similarity between the longitudinal and the scalar susceptibilities in the visibility of the Higgs mode. A possible lower peak at about $2m_{\sigma }$ is also noted.