Modern Physics Letters B

In this paper, we calculated the defect formation energy of oxygen vacancies with different charge states (0, +1, +2) in beryllium oxide crystal by using density functional theory (DFT). Based on defect formation energy, the positions of charge transition levels are obtained. However, there is a well-known problem that DFT will underestimate the band gap, which leads to the positions of charge transition levels are arguable. To obtain more accurate charge transition levels, we employ the hybrid functionals (HSE) to relieve the band edge problem, as well as use the finite-size corrections (FNV) to correct the defect formation energy. After obtaining the location of the charge transition level, we obtain a reliable description of the optical line shape of the F/F${}^{+}$ center containing electron–phonon coupling. The absorption spectra of the F center and F${}^{+}$ center peak at 7.1 eV and 6.3 eV, respectively. The luminescence band of the F center peaks at 4.7 eV. Furthermore, we speculate that the luminescence band near 3.7 eV is assigned to the F${}^{+}$ center.

With the popularization of 3D printing technology, micro/nanoparticles sintering technology has drawn lots of attentions all over the world. Here, molecular dynamic simulation is employed to discuss the effects of different interfacial lattice structures, different diameter of nanoparticles, and different heating rates on the coalescence of metallic Cu nanoparticles. The results showed that the diameter of nanoparticles determine the melting point of the system. Besides, the interfacial lattice structure, diameter of nanoparticles, and heating rate have an influence on the initial sintering temperature. This is because the melting point is the inherent property of material which relies on the mass of substance. However, the initial sintering temperature is sensitive to many factors, including the temperature, interfacial, and intermolecular interactions.

This paper studies the new closed form solutions to (2+1)-dimensional Bogoyavlenskii system that describes interaction of a Riemann wave propagation. The extended Fan sub-equation technique is used to investigate some new traveling wave solutions to the higher-dimensional coupled model. The obtained closed form solutions are named as shock, kink, shock and periodic soliton solutions. Clearly, the outcomes of the study confirm the strength of the current approach. Moreover, the obtained results are helpful for the understanding of non-linear wave propagation and are of great interest to present-day scientists and can be employed to deal with more complex models arising in diverse disciplines of contemporary science.

By clustering feature words, we can not only simplify the dimension of feature subsets, but also eliminate the redundancy of the feature. However, for a feature set with very large dimensions, the traditional $K$-medoids algorithm is difficult to accurately estimate the value of $k$. Moreover, the clustering results of the average linkage (AL) algorithm cannot be divided again, and the AL algorithm cannot be directly used for text classification. In order to overcome the limitations of AL and $K$-medoids, in this paper, we combine the two algorithms together so as to be mutually complementary to each other. In particular, in order to meet the purpose of text classification, we improve the AL algorithm and propose the $R^2$ testing statistics to obtain the approximate number of clusters. Finally, the central feature words are preserved, and the other feature words are deleted. The experimental results show that the new algorithm largely eliminates the redundancy of the feature. Compared with the traditional TF-IDF algorithms, the performance of the text classification of the new algorithm is improved.

In recent decades, many countries have suffered power outages and these accidents were often caused by a small disturbance, but because of the connection structure between the circuits, even a small mistake will cause the power grid cascade to fail and paralyze the network in a large area. In order to find a way to enhance the network robustness, this paper proposes three defense methods based on different ratio: the k-shell value ratio, degree ratio, and residual load ratio. We would compare the quality of the three defense methods by the relative size of the largest connected component after cascading failure. Besides, we also compare the time, the total number of crashed nodes, and the speed of cascading failure progress under three defense methods. From the experimental results, it is found that the defense methods based on the k-shell value ratio and the degree ratio have their own advantages in different situations.

The vehicle exhaust has been one of the major sources of greenhouse gas emissions. With an increase in traffic volume, it has been found that the introduced intelligent traffic control is necessary. This paper investigated a novel VSL strategy considering the dynamic control cycle to improve the traffic efficiency and environmental benefit on freeway. An extension of the cell transmission model (CTM) was used to depict the traffic characteristics under VSL control, and integrated with the microscopic emission and fuel consumption model VT-Micro to estimate the pollution emission of each cell. The VSL strategy was designed to provide multiple control cycles with different length to adjust the scope of VSL changes, furthermore, a probability formula was developed and used to determine the optimal quantity of control cycles to reduce the computational complexity of controller. An objective optimization function was formulated with the aim of minimizing total travel time and CO emission. With simulation experiments, the results showed that the proposed VSL strategy considering the dynamic control cycle outperformed uncontrolled scenario, resulting in up to 8.4% of total travel time reductions, 26.7% of delay optimization, and 14.5% reduction in CO emission, which enhanced the service level of freeway network.

The two-dimensional (2D) plane of graphene has many active sites for gas adsorption. It has broad application prospects in the field of MEMS gas sensors. At present, there are many experimental studies on graphene gas sensors, but it is difficult to accurately control various influencing factors in the experiments. Therefore, this paper applies the first principle based on density functional theory to study the adsorption and detection characteristics of graphene on CO and CO₂. The first-principles analysis method was used to study the adsorption characteristics and sensitivity of graphene. The results show that the inductive graphene has a sensitivity of 1.55% and 0.77% for CO and CO₂, respectively. The Stone–Wales defects and multi-vacancy defects have greatly improved the sensitivity of graphene to CO, which is 35.25% and 4.14%, respectively. Introduction of defects increases the sensitivity of detection of CO and CO₂, but also improves the selective gas detection material of these two gases. Thus, the control and selectively introducing defects may improve the detection accuracy of the graphene CO and CO₂.

Computational enzyme design has made great strides over the last five years. Traditional methods of enzyme design require synthesis and evaluation of many mutations. Computational enzyme design has emerged as a powerful tool to predict how specific mutations modify a protein’s activity, stability, and/or selectivity. Such computational approaches can evaluate many mutations and reduce the load of in vitro work by identifying mutations likely to accomplish design objectives. Computational approaches can explore mutational spaces inaccessible in traditional mutagenesis. Computational methods reduce cost and time compared with experimental approaches. We review the efficacy and key differences of computational enzyme design methods as published in recent studies. The included articles used computational methods to design enzymes, were published no earlier than 2015, met design objectives, and verified results in vitro.

Quantum communication plays an important role in quantum information science due to its unconditional security. In practical implementations, the users of each communication vary with the transmitted information, and hence not all users are required to participate in each communication round. Therefore, improving the flexibility and efficiency of the actual communication process is highly demanded. Here, we propose a theoretical quantum communication scheme that realizes secret key distribution for both the two-party quantum key distribution (QKD) and multi-party quantum secret sharing (QSS) modes. The sender, Alice, can freely select one or more users to share keys among all users, and nonactive users will not participate in the process of secret key sharing. Numerical simulations show the superiority of the proposed scheme in transmission distance and secure key rate. Consequently, the proposed scheme is valuable for secure quantum communication network scenarios.

The thermal efficiency of the heat exchanger is substantial in chemical and mechanical systems. The presence of the non-homogeny magnetic field considerably enhances the heat rate of nanofluid stream. In this exploration, the presence of the non-uniform magnetic intensity on the heat rate of nanofluid stream is noted inside the $180^{\circ }$ elbow pipe. FVM is used to model the flow characteristics and temperature distribution through the $180^{\circ }$ elbow pipe. Our major focus is to demonstrate the main influences of the non-uniform FHD on flow stream and heat transfer of nanofluid in various inlet velocities and magnetic intensities. Achieved outcomes display that growing the magnetic intensity from 1e + 6 to 4e + 6 enhances the average Nusselt number about 30%. Our findings show that increasing the inlet velocity to Re = 100 decreases the magnetic effects about 17% on the heat transfer growth.

The temperature and magnetic field dependence of the magnetic and electric properties of LiFeP₂O₇ (LFPO) and LiCrP₂O₇ (LCPO) are studied using a microscopic model and the Green’s function technique. We have shown that LFPO is antiferromagnetic, but shows a weak ferromagnetism along the $b$ axis which originates from the canted antiferromagnetic order. For LCPO, such a ferromagnetic order along the $b$ axis is not observed. In the temperature dependence of the electrical polarization $P_b(T)$ along the $b$ axis there is a kink at $T_N=22$ K which is an indirect evidence for the intrinsic magnetoelectric effect in LFPO. Applying an external magnetic field $H_b$, the polarization $P_b$ increases, stronger for small temperatures and the kink at $T_N$ disappears. For LCPO, we do not obtain a kink at $T_N=6$ K. LCPO is polar, but not ferroelectric. We can conclude that the missing magnetoelectric properties in LCPO could be due to the differences in the magnetic orders between LFPO and LCPO.

Through the Hirota bilinear formulation, a (2+1)-dimensional combined fourth-order nonlinear equation is proposed, which possesses lump solutions. Two classes of lump solutions are presented explicitly in terms of the coefficients in the combined nonlinear equation. A set of examples of equations is provided to show the diversity of the considered combined nonlinear equation, together with three-dimensional plots, $x$-curves and $y$-curves of two specific lump solutions in two cases of the combined equation.

This paper focuses on the self-adjointness of some Burgers-type equations based on the existing definitions. It follows that the corresponding Frobenius Burgers-type equations are constructed by taking values in a commutative subalgebra ${{𝒵}}_2^{𝜀}$. In order to investigate the self-adjointness of these Frobenius-type equations, we introduce a few additional notations and definitions. Additionally, the conservation laws are obtained of several equations studied by using symmetries.

A recently defined (3+1)-dimensional extended quantum Zakharov–Kuznetsov (QZK) equation is examined here by using the Lie symmetry approach. The Lie symmetry analysis has been used to obtain the varieties in invariant solutions of the extended Zakharov–Kuznetsov equation. Due to existence of arbitrary functions and constants, these solutions provide a rich physical structure. In this paper, the Lie point symmetries, geometric vector field, commutative table, symmetry groups of Lie algebra have been derived by using the Lie symmetry approach. The simplest equation method has been presented for obtaining the exact solution of some reduced transform equations. Finally, by invoking the new conservation theorem developed by Nail H. Ibragimov, the conservation laws of QZK equation have been derived.

Community detection is important for understanding the structure and function of networks. Resistance distance is a kind of distance function inherent in the network itself, which has important applications in many fields. In this paper, we propose a novel community detection algorithm based on resistance distance and similarity. First, we propose the node similarity, which is based on the common nodes and resistance distance. Then, we define the distance function between nodes by similarity. Furthermore, we calculate the distance between communities by using the distance between nodes. Finally, we detect the community structure in the network according to the nearest-neighbor nodes being in the same community. Experimental results on artificial networks and real-world networks show that the proposed algorithm can effectively detect the community structures in complex networks.

The finite time synchronization diffusion of uncertain networks with the switching topology is investigated in this paper. Spatiotemporal chaotic systems as nodes to construct the network, and the topology of network can jump from one construction to another to meet the actual demand. It is not like ordinary synchronization of network, our method can realize synchronization diffusion originated from boundary conditions, and the diffusion step can be determined by Taylor expand. The parameters are identified through proposed scheme against parameter uncertainties of system in practice. Numerical simulations are utilized to demonstrate the correctness and effectiveness of the finite time synchronization diffusion criteria. In the section of analysis and discussion, we have analyzed the impact of synchronization diffusion step and controller on the synchronization diffusion time.