International Journal of Modern Physics B

In recent years, noncollinear topological textures have long gained increasing research attentions for their high values of both fundamental researches and potential applications. The recent discovery of intrinsic orders in magnetic and polar two-dimensional (2D) van der Waals materials provides a new ideal platform for the investigation of noncollinear topological textures. Here, we review the theoretical and experimental progresses on noncollinear topological textures in 2D van der Waals materials in very recent years. During these years, magnetic skyrmions of both Bloch and Néel types have been observed experimentally in a few 2D van der Waals materials and related heterostructures. Concurrently, more theoretic predictions basing on various mechanisms have been reported about different noncollinear topological textures in 2D van der Waals materials, such as skyrmions, bimerons, anti-biskyrmions and skyrmionium, which are still waiting to be confirmed in experiments. Besides, noncollinear topological electric dipole orders have also been predicted in 2D van der Waals materials. Taking advantage of the intrinsic 2D nature and high integratability, the 2D van der Waals materials will play an important role in the investigation on noncollinear topological textures in both magnetic and polar systems.

The neutron capture processes in the AlN nanoparticles were investigated by computer modeling. Neutrons absorption were separately investigated for aluminum (Al) and nitrogen (N) atoms in the AlN nanoparticles. The modeling was performed separately for each stable Al and N isotopes, because the effective absorption cross-section of different types of isotopes of Al and N atoms is different. Moreover, effective cross-section spectra of neutron capture for aluminum and nitrogen atoms were comparatively investigated.

Silicon–carbon nanofibers-carbonized yeast powder composite (SCNFs/CYP) was fabricated using the electrostatic spinning and hydrothermal processes. Experimental results show that the carbon nanofibers can restrain the volume expansion of silicon in the electrochemical process and the microporous structure of carbonized yeast powder can increase the specific surface area and promote the penetration of electrolyte. The compound was cyclically tested at charge–discharge rate of $0.5^{\circ }$C, and the first charge/discharge capacity was 1725 and 1732 mAh/g. Although it is lower than the capacity of single structure silicon–carbon nanofibers (SCNFs), with the increase of the number of cycles, the capacity of charging and discharging has been greatly improved, and it can be maintained at 1656 mAh/g after 180 cycles. The $R_{\mathrm{\text{CT}}}$ after 1 cycle, 10 cycles and 100 cycles were 486, 286.5 and 231 $\mathrm{\Omega }$, from which we can see that the SCNFs–CYP has lower overall impedance values as the cycle increases. This indicated that the addition of carbon nanofibers and carbonized yeast powder inhibited the volume expansion and increased the specific surface area, providing more electrical contact sites.

This paper pays attention to the piecewise continuous time modeling of a hydro-turbine governing system in the process of shutdown transient. As a pioneering work, the piecewise nonlinear dynamic transfer coefficients are introduced into the system. Moreover, for different hydrographs of shutdown transient process, the effect of different shutdown laws on the quality of shutdown transient process has been analyzed by numerical simulations. The nonlinear dynamic behaviors of the hydro-turbine governing system are illustrated by bifurcation diagrams, Poincaré maps, time waveforms and phase orbits. More importantly, these methods and analytic results are useful for the safe and stable operation of a hydropower station in the process of shutdown transient.

In this study, analytical solutions and physical interpretations are presented for the Riemann wave equation (RWE), which has an important physical property in fluid dynamics. The solutions of the RWE, which models the formation, interaction and breaking of the waves that occur as a result of any external effect on the ocean surface, are examined using the generalized exponential rational function method (GERFM). Bright (nontopological) soliton, singular soliton and solitary wave solutions are produced with advantages of GERFM over other traditional exponential methods. The factors in which solitary wave solutions cause breaking of wave are examined. The effects of parameters on wavefunctions and the physical interpretations of these effects are discussed and supported by graphics and simulations.

Complex networks depict the individual relationship in a population, which can help to deeply mine the characteristics of complex networks and predict the potential collaboration between individuals by analyzing their interaction within different groups or clusters. However, the existing algorithms are with high complexity, which cost much computational time. In this paper, an efficient graph clustering algorithm based on spectral coarsening is proposed, to deal with the large time complexity of the traditional spectral algorithm. We first find the subset most possibly belonged to the same cluster in the original network, and merge them into a single node. The scale of the network will decrease with the network being coarsened. Then, the spectral clustering algorithm is performed on the coarsened network with the maintained advantages and the improved time efficiency. Finally, the experimental results on the multiple datasets demonstrate that the proposed algorithm, compared with the current state-of-the-art methods, has superior performance.

The main focus of this research is to explore the consequences of motile gyrotactic microorganisms for unsteady Williamson nanofluid induced by bidirectional periodically accelerated surface. The combined features of magnetic and buoyancy forces with association of nanoparticles and swimming microorganisms developed the nanofluid bioconvection. Thermal radiation and heat generation aspects are considered to analyze the heat transportation phenomenon. The consequences of activation energy and chemical reaction are further explored for physical relevance. Appropriate transformations have been employed to transmute the formulated nonlinear equations into dimensionless form, and then analytically elucidated by homotopic technique. The effect of diverse dominant parameters on velocities, concentration, temperature, motile microorganisms as well as skin friction coefficients are deliberated through various graphs while the deviation in local Sherwood, Nusselt and motile density numbers have been deliberated by numerical data in tabular form. It is noticed that both velocity components periodically drop for augmentation in Williamson parameter. Current investigation accentuated that higher reaction rate leads to decay in concentration distribution, but impact of activation energy parameter is rather conflicting. Furthermore, the profile of motile microorganism leads to be intensified for higher magnetic parameter, while opposite trend is perceived for bioconvected Peclet and Lewis numbers.

This paper analyzed motion that randomly switches between the persistent motion runs and pause periods. A two-state continuous-time Markov chain is used to model the motion, which led to a system with coupled differential equations. Using a combined Fourier–Laplace transform, an analytical expression for calculating the mean-squared displacement is derived. The overall motion is investigated and identified from the obtained mean-squared displacement. The mean-squared displacement is a nonlinear function in time that is dependent on the phase transition rate, the direction switching rate, the average speed, and the initial state. It decays and grows with increasing the direction switching and average speed, respectively. The effective diffusivity descents exponentially in short times and remains constant in long times. The waiting time in each phase decayed exponentially. The probability density function for the position of a particle at a given time tends to be Gaussian in long times. The motion can be interpreted as a super-diffusion in short times and a standard diffusion in long times with a diffusion coefficient dependent on the phase transition rates, the direction switching rate and the average speed. Persistence influences the dynamical behavior for short times while for long times diffusive behavior is exhibited.

The aim of this research is study the effect of polishing factors to the reduction ratio rate in surface roughness (%$\mathrm{\Delta }Ṙ)$ during the Magnetic Abrasive Finishing (MAF) process using Response Surface Methodology (RSM). The parameters studied were machining gap, rotational speed, abrasive size and magnetic abrasive particle (MAP) size. Quadratic models were developed by applying Box–Behnken Design (BBD). Also, experiments were carried out on the silicon wafer and results of surface roughness data were analyzed by using analysis of variance (ANOVA) and significant factors were identified. According to our findings, the maximum %$\mathrm{\Delta }Ṙ$ value and the best surface roughness of silicon wafer achieved 3.70 and 51 nm, respectively.

In this work, an in-situ XPS analysis test combined self-designed high precision fretting wear tester was carried out to study the fretting wear behavior and the resulting tribo-oxidation of thermal-oxidation film on Ti6Al4V titanium alloy under the varied working atmosphere. The fretting-induced tribo-oxidation under the air and vacuum ($4\times 10^{-3}$ Pa) environment was analyzed and its response on the resulting fretting wear resistance and damage mechanism was discussed. Results show that the working environment plays a significant role in the formation of tribo-oxidation and then determining the fretting wear resistance. Thermal-oxidation film in the vacuum atmosphere shows a better fretting wear resistance than that in the air atmosphere for all fretting regimes, except for partial slip regime (PSR) where there is an equivalent fretting wear resistance. Compared with the substrate Ti6Al4V titanium alloy, the thermal-oxidation film in the vacuum atmosphere performs a good protection for titanium alloy, especially for slip regime (SR), but not applied for air atmosphere.