bluuebunny/crossref_metadata_2025 huggingface dataset:
On legislative consolidation of classification of the types of tourism
Authors: Savichev Aleksei
Published: June 2021

The successful development of tourism requires proper legal regulation. At the same time, the diversity of the types of tourism is virtually neglected by the legislator and does not receive due attention of the legal scholars. This question is being regulated fragmentary and inconsistently on the level of bylaws and legislation of the constituent entities of the Russian Federation. Occasional use of improper terminology, discrepancy in understanding of the essence of same types of tourism, disregard of their peculiarities impairs the effectiveness of state administration of tourism sector, negatively affects the quality of tourism services, and distorts the representations of Russia as a tourism friendly country. The article analyzes the grounds for classification of the types of tourism that have legal bearing: depending on the place of permanent residence of the tourist, on the purpose of tourist trips, on the way of organization of trip, on the social and age category of tourists. The conclusion is formulated that the key direction in improving sectoral tourism legislation consists in consolidation of extensive classification of the types of tourism and definition of concepts included therein in the Federal Law “On the Fundamentals of Tourism Activity”. For the purpose of unification of terminology, further development of tourism legislation, and improved quality of state administration of the tourism sector, the author proposes the original classification of tourism.
The use of eye tracking technologies in studying perception of graphic information perception
Authors: Yanchus Viktor Edmundasovich , Borevich Ekaterina Vladislavovna , Avdeeva Anastasiya Artemovna
Published: June 2021

The scientific research related to the use of eye tracking technologies are currently of particular relevance. A substantial area of scientific knowledge, in which it is feasible to use eye tracking technologies, is associated with the study of perception of visual information. One of the trends of such research is the examination of the impact of compositional construction of visual image upon its perception by the viewer. The object of this research is elements of graphic composition (stylistic and color solutions). The subject is the methods and algorithms for digital processing of graphic material. The article employs the computational methods of color correction, eye tracking technology, expert assessment, statistical processing of the obtained experimental data. The scientific novelty of this work consists in the development of methodology of preparing and conducting computational experiments for the impact of the stylistic solution of graphic composition upon its perception by the viewer. The technique developed by the authors has proven itself in carrying out the experiments for studying the effect of color solution of the frame upon its perception by the viewer. The study revealed the statistical significance of the impact of stylistic solution of graphic composition upon viewer’s perception. The hypothesis that abstract graphic compositions are difficult for viewer’s perception was statistically proven. The acquired results can be used in constructing complex graphic images, which require the speed of information perception to view them.
Building a standard system of inference rules based on the knowledge base
Authors: Kopyrin Andrey Sergeevich , Kopyrina Alina Olegovna
Published: June 2021

The authors propose to combine logical inference with the apparatus of fuzzy sets. When each solution is associated with a set of possible outcomes with known conditional probabilities, the solution is chosen based on digital information under conditions of uncertainty. Therefore, the main purpose of using fuzzy logic in expert systems is to create computing devices (or software complexes) capable of simulating human thinking and explaining decision-making methods The purpose of the work is to describe in detail a reproducible standard method of constructing rules for the output of an expert system for various economic subject areas, using a universal knowledge base scheme To make decisions in a fuzzy system, it is proposed to use the process of identifying the structure of a rule - determining the structural characteristics of a fuzzy system, such as the number of fuzzy rules, the number of linguistic terms into which incoming variables are divided. This identification is carried out using fuzzy cluster analysis, which is carried out using fuzzy decision trees. The authors present a block diagram of the inference methodology based on fuzzy logic. The method of constructing rules and the algorithm of fuzzy inference presented in the article can be used in various spheres of the economy. The novelty of the work lies in the automation and integration of the system for determining fuzzy inference rules with the stage of collecting input data in the subject area
The specifics of working with “big data” in modern media
Authors: Nerents Daria Valer'evna
Published: June 2021

As of today, Big Data is the source of information that journalists can no longer neglect. Data sets, databases, unstructured data on the official websites of the government or commercial institutions are a resource for the work of journalists. Big Data is not only the source of information, but also the evidence base. Using quantitative and statistical indicators as the arguments for their theses, the journalists increases the level of audience loyalty and trust to the publication. Data analysis, establishment of correlations, making forecasts and ratings allows creative exclusive, attractive and reliable content that attracts the audience and improves reputation of the publisher. This article is dedicated to determination of the role of “big data” in the work of information and analytical departments of the publisher, as well as in coverage of the socially relevant topics and outlining trends in further work of the journalists with such information. Over the study period (from 2017 to the present) the author employed the methods of description, comparative analysis, and generalization. In conclusion, the author notes that the collection and processing of the data requires a strong approach and utmost attention of the journalists.
The peculiarities of compositional and semantic arrangement of text in Shakir Selim’s literary-criticism article “About Shamil Alyadin, Charyks and the Pocket Knife”
Authors: Sulaimanov Mukhamed-Ali Usmanovich
Published: June 2021

This article attempts to determine the peculiarities of compositional and semantic arrangement of text of the literary-criticism article by Shakir Selim “About Shamil Alyadin, Charyks and the Pocket Knife” in the context of its genre uniqueness. The article employs the approach of methodological pluralism using the key hermeneutical and a range of auxiliary methods. In analyzing the text, the author reviews the criteria of literary work, such as fabula, plotline, chronotope, author’s modality, etc., which allow revealing the peculiarities compositional and semantic arrangement Shakir Selim’s work. The relevance of this article is defined by the lack systematic research dedicated to compositional and semantic arrangement and genre diversity of the literary-criticism texts in the Crimean Tatar literature. The subject of this research is the compositional and semantic arrangement of text on the example of the literary work “About Shamil Alyadin, Charyks and the Pocket Knife”. The author describes the genre diversity alongside the elements of time and space presented in the article, as well as explores the author’s representations  and modality. This article is first to carry out a comprehensive analysis of the peculiarities of compositional and semantic arrangement and genre diversity of the S. Selim’s work “About Shamil Alyadin, Charyks and the Pocket Knife” by means of methodological pluralism in the aspect of various structural components of the composition and content of the text.
Multicomponent terminological phrases in the veterinary terminological system of the modern German language
Authors: Khakimova Giulnara
Published: June 2021

This article is devoted to a detailed analysis of multicomponent terminological phrases in the veterinary terminological system of the modern German language. The object of the study is the German veterinary terminological system, the subject is multicomponent terminological phrases formed using the syntactic method of term formation. The paper analyzes two-, three- and more component terminological phrases in order to identify their structural, word-formation, semantic and functional features. The author examines terminological phrases in detail by the type of structural organization, by the type of internal syntactic connections, by the degree of fusion of components, by their activity within the phrases. The author reveals that substantive two-component terminological phrases with adjectives in the preposition have high productivity. Less common are uncomplicated two-component terminological phrases consisting of two nouns. The relevance of the undertaken research is due to the need to nominate new concepts, replenish and systematize the veterinary terminology of the modern German language as an integral part of the language of medicine, reflecting the professional activities of specialists in the field of veterinary medicine and related sciences aimed at preventing and treating animal diseases, protecting people from zooanthroponoses, the production of high-quality veterinary and sanitary food products, which together it has an important social significance related to the health of humanity as a whole. The analysis of linguistic features of terminological phrases in the German sublanguage of veterinary medicine undertaken by the author allowed us to conclude that the most productive model is two-component substantive terminological phrases with an adjective in the preposition as a definition. Multicomponent terminological phrases are an integral part of the term system under study and an effective means of nominating concepts in this field of science.
Initial dynamic response and reaction mechanism of cyclotrimethylenetrinitramine under shock loading
Authors: Peng Ya-Jing , Sun Shuang , Liu Wei-Na , Liu Yu-Hui ,   College of Physical Science and Technology, Bohai University, Jinzhou 121000, China
Published: June 2021

At present, the relative safety of energetic materials exposed to extreme environments is concerned widely. Understanding the initial decomposition mechanism of energetic materials under impact loading is the basis for exploring new energetic materials with high energy and low sensitivity. In this paper, we study the initial dynamic response and reaction mechanism of perfect cyclotrimethylenetrinitramine (RDX) crystal and RDX crystal with a molecular vacancy defect under shock loading by using the multiscale shock technique (MSST) combined with reactive force field (ReaxFF) molecular dynamics method. The RDX perfect supercell and supercell containing a molecular vacancy are constructed to simulate the shock process by using the generalized gradient approximation method in density functional theory and Perdew-Burke-Ernzerhof functional. Before loading the shock wave, one NVE ensemble and Berendsen thermostat are used to control the RDX equilibrium process. A multi-scale impact compression is loaded along the crystal A direction. The initial temperature is 300 K and the initial pressure is set to be an atmospheric pressure. The radial distribution functions between main atoms are calculated, and the influences of shock velocity and molecular vacancy defect on shock loading process are analyzed. The evolution of N—NO2 bond and C—N bond with time in RDX perfect crystals and vacancy crystals under shock velocity of 11 km/s are given. As a result, the possible initial decomposition path of perfect RDX crystal and vacancy RDX crystal are the first fracture of N—NO2 bond, followed by the cleavage of C—N bond at small shock velocity. The initial reaction of the RDX crystal with a molecule vacancy is earlier than that of the perfect crystal, which indicates that the vacancy crystal is more sensitive to shock and more prone to decomposition. Furthermore, the fracture of C—H bond is possible after the initial cleavage of N—NO2 bond and C—N bond, and then the H atom is transferred to oxygen atom in nitro group, forming HONO. As the shock velocity increases, the number of broken chemical bonds in the two kinds of RDX crystals increases, and the reaction becomes strong. The presence of molecular vacancy defect enhances the activity of N—NO2 bond and makes it easier to break, thus accelerating the initial reaction of the vacancy crystal. The shock velocity and the particle velocity of the RDX crystal are consistent with previous experimental results and theoretical data, which shows the validity of our calculation results.
Nonequilibrium states in quantum materials under time-period driving
Authors: Wang En , Dong Wen-Han , Zhou Hui , Liu Meng , Ji Hong-Yan , Meng Sheng , Sun Jia-Tao ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, School of Information and Electronics, Beijing Institute of Technology, Beijing 100081, China,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Published: June 2021

The topology of quantum materials is the frontier research in condensed matter physics. In contrast with the conventional classification of materials by using the local symmetry breaking criterion, the states of quantum systems are classified according to the topology of wave functions. The potential applications of topological states may lead the traditional microelectronics to break through and accelerate the significant improvement in topological electronics. Most of the recent studies focus on the topological states of quantum systems under equilibrium conditions without external perturbations. The topological states of quantum systems far from the equilibrium under time-periodic driving have attracted wide attention. Here we first introduce the framework of Floquet engineering under the frame of the Floquet theorem. The nonequilibrium topological states of massless and massive Dirac fermions are discussed including the mechanism of phase transition. Light field driven electronic transition term in the quantum material gains extra time-dependent phase. Thereby the manipulation of effective transition term of the electron is realized to regulate the non-equilibrium topological states. We also mention how the photoinduced coherent phonon affects the nonequilibrium topological states of quantum systems from the perspective of atom manufacturing. Furthermore, research outlook on the nonequilibrium topological states is given. This review provides some clues to the design of physical properties and transport behaviors of quantum materials out of equilibrium.
Dynamic analysis of bubble in liquid cavity wrapped by viscoelastic medium
Authors: Zhang Tao-Ran , Mo Run-Yang , Hu Jing , Chen Shi , Wang Cheng-Hui , Guo Jian-Zhong ,   Shaanxi Key Laboratory of Ultrasonics, Shaanxi Normal University, Xi’an 710062, China
Published: June 2021

Ultrasonic wave with higher intensity will directly cavitate in soft tissue. It is an important issue in ultrasonic therapy that the cavitation bubbles in soft tissues are driven in the ultrasonic field. It is assumed that the medium inside the bubble is gas, the cavity is filled with the incompressible viscous liquid, and the medium surrounding the cavity is viscoelastic solid. To introduce the effect of the surrounding tissue, it is assumed that the tissue is incompressible, linear and Voigt viscoelastic solid. The motion of a cavitation bubble can be affected by many factors, such as acoustic pressure, acoustic frequency, tissue elasticity and cavity size. Numerical simulation shows that the resonance frequency and amplitude of the bubbles decrease with cavity radius decreasing. It is also shown that the amplitude of the radial motion for bubbles decreases with the increase of the tissue shear modulus and the frequency, when the ratio of bubble radius to the cavity radius is constant. The effect of the elasticity is very obvious, which reduces the amplitude greatly. The effect of elasticity will be less when the driving pressure is strong. It is found that the inertial cavitation threshold of bubble is relatively low in a range of 1–5 μm. The inertial cavitation threshold of bubble increases with the increase of shear modulus and driving frequency. The smaller the cavity radius, the higher the inertial cavitation threshold of the bubble is. This report aims to provide a firm theoretical basis for the future study of bubbles in a liquid-filled cavity surrounded by a viscoelasticity tissue.
Quantitative phase microscopy imaging based on fractional spiral phase plate
Authors: Wu Di , Jiang Zi-Zhen , Yu Huan-Huan , Zhang Chen-Shuang , Zhang Jiao , Lin Dan-Ying , Yu Bin , Qu Jun-Le ,   Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
Published: June 2021

Quantitative phase imaging (QPI), which combines phase imaging with optical microscopy technology, provides a marker-free, fast, non-destructive, and high-resolution imaging method for observing transparent biological samples. It is widely used in life science, biomedicine, etc. As an emerging QPI technology, spiral phase contrast microscopy (SPCM) uses a spiral phase filter to achieve edge enhancement of amplitude or phase objects. Using the multi-step phase-shifting technology, a complex sample can be measured quantitatively, which has the advantages of high stability, high sensitivity and high precision. However, the SPCM requires at least three-step phase-shifted spiral phase filtered images to achieve the quantitative reconstruction of the amplitude and phase of a sample, and the image acquisition process and the reconstruction process are relatively complicated, which require high stability of system, and the SPCM has low temporal resolution. In order to further improve the performance of SPCM and increase the system stability, sensitivity and temporal resolution, in this paper a quantitative phase imaging method and system based on a fractional spiral phase plate is proposed. Through a sample intensity image filtered by a fractional spiral phase plate, the modified Gerchberg-Saxton iterative phase retrieval algorithm is used to quantitatively reconstruct the phase of a pure phase sample, which simplifies the experimental process and phase reconstruction steps of spiral phase contrast microsocopy. In the computer simulation experiments, the phase imaging process and the reconstruction process of spiral phase plates based on different topological charges are studied, the feasibility of which is analyzed. Finally, through imaging and phase reconstruction of the phase grating and biological cell sample, it is verified that the phase contrast microscopy method based on the fractional spiral phase plate can effectively improve the contrast of spiral phase contrast microscopy and can obtain a quantitative reconstruciton of a weak phase object. The phase information of a sample has significance in research and application for developing the spiral phase contrast microscopy.
Performance of 2-bromoterephthalic acid passivated all-inorganic perovskite cells
Authors: Lin Ming-Yue , Ju Bo , Li Yan , Chen Xue-Lian ,   School of Materials Science and Engineering, Xi’an Shiyou University, Xi’an 710065, China
Published: June 2021

All-inorganic perovskite cesium lead iodine (CsPbI3) without any volatile organic components has attracted much attention due to its superior stability, high absorption efficiency and suitable band gap. However, the power-conversion efficiencies of CsPbI3 based perovskite solar cells (PSCs) are substantially low compared with those of the organic-inorganic hybrid lead halide PSCs. The surface passivation of the CsPbI3 film by long-chain halide salts has been found to be an effective method of improving the performance. In this paper, we report the concentration effect of an inexpensive 2-bromoterephthalic acid (BBr) as passivation material on the performance of CsPbI3 perovskite solar cells. The experimental results show that the conversion efficiency of perovskite solar cells first increases and then decreases as the concentration of BBr increases from 0 to 2 mg/mL. The best conversion efficiency of CsPbI3 perovskite solar cells reaches 13.5% at 0.2 mg/mL BBr. The results from X-ray diffraction and scanning electron microscopy suggest that there is no change in the phase or microstructure of the CsPbI3 perovskite film after surface passivation by BBr. By further analyzing the photoluminescence data of the CsPbI3 film with and without capping hole transport layer, it can be found that the passivation of BBr with the concentration of 0.2 mg/mL can enhance the fluorescence excitation intensity of the CsPbI3 film and accelerate the exciton separation at the interface between CsPbI3 film and hole transport layer. Based on the electrochemical impedance spectroscopy data, we find that the electron transport ability at the interface between TiO2 and CsPbI3 can be significantly improved after surface passivation, which is induced by the acceleration of the exciton separation at the interface between CsPbI3 film and hole transport layer. The decrease of the PSCs performance when the concentration of the BBr precursor increases from 0.5 mg/mL to 2 mg/mL can be attributed to the local agglomeration of the BBr material, resulting in the block of charge transportation. This research is expected to provide basic support for the low-cost development of the passivation materials for perovskite solar cells.
Mechanism of suppressing Kelvin-Helmholtz instability by flowing magnetic field
Authors: Shi Qi-Chen , Zhao Zhi-Jie , Zhang Huan-Hao , Chen Zhi-Hua , Zheng Chun ,   National Key Laboratory of Transient Physics, Nanjing University of Science & Technology, Nanjing 210094, China,   School of Mechanical Engineering, Nanjing University of Science & Technology, Nanjing 210094, China
Published: June 2021

The evolution of the Kelvin-Helmholtz (KH) instability in the presence of classical hydrodynamics and magneto-hydro-dynamics is investigated numerically by using the magneto-hydro-dynamic (MHD) equations. The MHD equations are solved with the corner transport upwind plus constrained transport algorithm that guarantees the divergence-free constraint in the magnetic field. The numerical results are used to analyze the effects of magnetic field (\begin{document}${M_{\rm{A}}} = 3.33$\end{document}) on the vorticity and pressure evolution of mixing layer, and also compared with those in the hydrodynamics situation. Moreover, the mechanism of weakening the effect of magnetic field on the KH instability is revealed from the perspectives of the magnetic pressure and the magnetic tension. The results show that the external magnetic field has a great influence on the flow structure of the mixing layer. Specifically, the magnetic pressure has a major effect in the vorticity deposition on the interface, whereas the magnetic tension generates a torque to counter the scrolling of vortex. As a result, the large vortex structure is stretched and destroyed, and finally restrains the vortex rolling-up. In addition, with the development of mixing layer, the interface will separate at the points of maximum curvature under the joint effect of the magnetic pressure, the magnetic tension and the pressure field, and finally form a fishhook-like vortex structure.
Preparation and electrochemical performance of sodium manganese oxides as cathode materials for aqueous Mg-ion batteries
Authors: Zhang Yong-Quan , Yao An-Quan , Yang Liu , Zhu Kai , Cao Dian-Xue ,   Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China,   College of Intelligent Systems Science and Engineering, Harbin Engineering University, Harbin 150001, China,   Key Laboratory of Engineering Dielectrics and Its Application, Ministry of Education, School of Electrical and Electronic Engineering, Harbin University of Science and Technology, Harbin 150080, China,   Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen 76344, Germany
Published: June 2021

In recent years, the cathode materials of magnesium ion batteries have become a hot point of research, and the improvement of high-rate performance and cycle stability has become the main research goal. In this paper, sodium manganese oxide (Na0.55Mn2O4·1.5H2O) nanomaterial with a blended structure of nanowires and nanosheets is prepared by the hydrothermal method. The structure and morphology of the material are analyzed by X-ray diffraction and scanning electron microscopy. The variable rate charge-discharge curves and variable scan rate cyclic voltammetry curves are obtained by a battery tester and electrochemical workstation, respectively. The results show that the hydrothermal reaction time has significant effects on phase structure and morphology composition of the material. The nanosheets and nanowires in the sample form a closely blend by 72-h hydrothermal reaction (NMO-72), and the nanosheets effectively fill into the intersecting space of the nanowires. In this way, the tap density of the material is improved. More importantly, NMO-72 has higher discharge specific capacity and rate cycling performance. At a current density of 50 mA·g–1, the discharge specific capacity of NMO-72 reaches 229.1 mAh·g–1. At a current density of 1000 mA·g–1, the discharge specific capacity of the NMO-72 stabilizes at 81 mAh·g–1. When the current density returns to 50 mA·g–1 again, the discharge specific capacity remains stable at 164.7 mAh·g–1. Besides, the cyclic voltammetry test shows that the NMO-72 material has more excellent magnesium ion diffusion kinetic performance than other materials. Therefore, the NMO-72 material has more excellent reversible specific capacity, high rate performance and cycling stability.
Three-dimensional numerical simulation of physical field distribution of radio frequency thermal plasma
Authors: Zhu Hai-Long , Li Xue-Ying , Tong Hong-Hui ,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China,   Institute of Theoretical Physics of Shanxi University, Taiyuan 030006, China,   Southwestern Institute of Physics, Chengdu 610041, China
Published: June 2021

Radio frequency (RF) thermal plasma involves abundant and complex physics. The understanding of the physical field distributions of the RF thermal plasma is helpful to its applications in industrial field. In this paper, an electro-thermal-magnetic-flow strong coupling mathematical and physical model of three-dimensional RF thermal plasma is established, the actual solenoid structure of the induction coil is considered, and a C++ code is developed for calculating the complex electromagnetic field in a customized version of the computational fluid dynamics commercial code FLUENT. The physical fields of RF thermal plasma, such as temperature field, flow field and electromagnetic field are studied. The electrical conductivity, thermal conductivity and viscosity distribution of the plasma are investigated. The results show that the physical field distribution of RF thermal plasma has an important non-axisymmetric three-dimensional effect due to the actual shape of the non-axisymmetric induction coil structure. The plasma discharge presents an annular distribution with a certain deflection angle. The distribution of plasma flow field shows a non-axisymmetric electromagnetic pump effect which is different from that of the two-dimensional model. The results have great guiding significance for optimizing and controlling the RF thermal plasma in various application areas.
Telecentric in-line-and-off-axis hybrid digital holographic high-resolution reconstruction method
Authors: Zhong Zhi , Zhao Wan-Ting , Shan Ming-Guang , Liu Lei ,   College of Information and Communication Engineering, Harbin Engineering University, Harbin 150001, China,   Key Laboratory of Advanced Marine Communication and Information Technology, Ministry of Industry and Information Technology, Harbin Engineering University, Harbin 150001, China
Published: June 2021

In-line digital holography usually employs a phase retrieval algorithm to decouple the phase information but fails to eliminate the unwanted DC and twin image terms when the measured sample does not agree with the sparsity. While the off-axis digital holography can efficiently remove the unwanted image terms but can not reserve the high frequencies of the sample to realize high resolution. The in-line-and-off-axis hybrid digital holography was then developed to provide a relatively high resolution digital holographic imaging without considering the effect of the unwanted terms. In other words, the in-line-and-off-axis hybrid digital holography merges all of the best virtues of the mentioned-above methods in an efficient and elegant way. However, this state-of-the-art method requires prior knowledge about the diffraction distance, which results in time-consuming and low accuracy. In other sense, telecentric technology can realize non-diffractive imaging without the knowledge about the diffraction distance or spherical aberration or defocusing aberration. Therefore, in this paper, a novel in-line-and-off-axis hybrid digital holography is proposed by introducing telecentric imaging architecture, and the corresponding reconstruction method is further proposed by utilizing constrained iterative approach. In this method, telecentric in-line-and-off-axis hybrid digital holography is first used to acquire focused off-axis and in-line holograms, respectively. The low resolution phase information is reconstructed from the off-axis hologram by using Fourier transform method with the help of the sample-free off-axis hologram, and then multiplexed with the amplitude information obtained from the in-line hologram to act as the initial complex amplitude in the iterative recovery process. As a result, constrained iterations are carried out in the spatial domain and frequency domain to realize high resolution and high speed reconstruction. After simulations, we build an experimental setup and demonstrate the operation of the method with USAF resolution target, onion cells and bee wings. Both the simulation and experimental results show that the proposed method can require no prior knowledge to suppress the phase disturbance caused by the unwanted image terms and optical aberrations, resulting in high speed and full utilization of spatial bandwidth product of the digital camera to yield high resolution reconstruction. We hope that the proposed method will have most practical applications in the case where large resolution, high speed and good quality are needed.
Projection methods for the incompressible Navier-Stokes equations
Authors: Zhang Qing-Hai , Li Yang ,   School of Mathematical Sciences, Zhejiang University, Hangzhou 310027, China
Published: June 2021

The incompressible Navier-Stokes equations (INSE) are the basic governing equations of fluid dynamics, and their numerical solutions are of great significance. In this review paper, we first recollect some classical projection methods and their relatives in the past 50 years and then fully explain the recent fourth-order projection method called GePUP [Zhang Q 2016 J. Sci. Comput. 67 1134]. Based on a generic projection operator and the UPPE formulation of the INSE [Liu J G, Liu J, Pego R L 2007 Comm. Pure Appl. Math. 60 1443], we derive the GePUP equations, which retain the advantage of UPPE that the velocity divergence is governed by a heat equation and is thus well under control. In comparison with UPPE, the GePUP formulation is advantageous in three aspects: (1) its derivation depends on none of the properties of the Leray-Helmholtz projection; (2) the evolutionary velocity can be divergent, thus it is directly applicable to numerical calculations with nonzero velocity divergence; (3) the Leray-Helmholtz projection does appear on the right-hand sides of the governing equations, thus making it transparent to analyze the accuracy and stability issues raised by numerically approximating the Leray-Helmholtz projection. As the most appealing feature of GePUP, temporal integration and spatial discretization are completely decoupled and can be treated as black boxes, so that the user can choose his favorite methods for the two parts to form his own GePUP method. In particular, high-order accuracy in time can be easily obtained since no internal details of the ODE solver are needed. The flexibility in time makes the GePUP method applicable to both low-Reynolds-number flow and high-Reynolds-number flow. The flexibility in space makes the GePUP method applicable to both rectangular boxes and irregular domains. The numerical results and elementary analysis show that the fourth-order GePUP method may be much more accurate and efficient than classical second-order projection methods by many orders of magnitude.
First-principles study of electronic structure and optical properties of monolayer defective tellurene
Authors: Li Fa-Yun , Yang Zhi-Xiong , Cheng Xue , Zeng Li-Ying , Ouyang Fang-Ping ,   Hunan Key Laboratory for Super-Microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha 410083, China,   School of Physics and Electronic Sciences, Changsha University of Science and Technology, Changsha 410114, China,   State Key Laboratory of Powder Metallurgy, Powder Metallurgy Research Institute, Central South University, Changsha 410083, China
Published: June 2021

Monolayer tellurene is a novel two-dimensional semiconductor with excellent intrinsic properties. It is helpful in understanding doping and scattering mechanism to study the electronic structure of defective tellurene, thus it is important for the application of tellurene in electronic and photo-electronic devices. Using first-principles calculation based on the density functional theory, we investigate the effects of commonly seen point defects on the electronic structure and optical properties of monolayer β-Te. Seven kinds of point defects that may be present in β-Te are designed according to the lattice symmetry, including two single vacancies (SV-1, SV-2), two double vacancies (DV-1, DV-2) and three Stone-Wales (SW) defects (SW-1, SW-2, SW-3). It is found that the defect formation energies of these defects are 0.83–2.06 eV, which are lower than that in graphene, silicene, phosphorene and arsenene, suggesting that they are easy to introduce into monolayer β-Te. The two most stable defects are SV-2 and SW-1 where no dangling bond emerges after optimization. The calculated band structures show that all seven defects have little effect on the band gap width of monolayer β-Te, but they can introduce different numbers of impurity energy levels into the forbidden band. Among them, the SV-1, SV-2, DV-1 and SW-2 each act as deep level impurities which can be recombination centers and scattering centers of carriers, SW-1 acts as a shallow level impurity, DV-2 and SW-3 act as both deep level impurity and shallow level impurity. Besides, SW-1, SW-2 and DV-1 can change the band gap of monolayer β-Te from direct band gap to indirect band gap, which may result in the increase of the lifetime of carriers and decrease of photoluminescence of monolayer β-Te. The optical properties of monolayer β-Te, which are sensitive to the change in band structure, are also affected by the presence of defects. New peaks are found in the complex dielectric function and the absorption coefficient of defective monolayer β-Te in an energy range of 0–3 eV, of which the number and the position are dependent on the type of defect. The SV-1, DV-1, DV-2 and SW-2 can enhance the light response, polarization ability and light absorption in the low energy region of monolayer β-Te. This research can provide useful guidance for the applications of β-Te in the electronic and optoelectronic devices.
Status and prospective of high-efficiency c-Si solar cells based on tunneling oxide passivation contacts
Authors: Ren Cheng-Chao , Zhou Jia-Kai , Zhang Bo-Yu , Liu Zhang , Zhao Ying , Zhang Xiao-Dan , Hou Guo-Fu ,   Institute of Photoelectronic Thin Film Devices and Technology of Nankai University, Tianjin 300350, China,   Key Laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin, Tianjin 300350, China,   Engineering Center of Thin Film Photoelectronic Technology of Ministry of Education, Tianjin 300350, China,   Sino-Euro Joint Research Center for Photovoltaic Power Generation of Tianjin, Tianjin 300350, China
Published: June 2021

Current photovoltaic market is dominated by crystalline silicon (c-Si) solar modules and this status will last for next decades. Among all high-efficiency c-Si solar cells, the tunnel oxide passivated contact (TOPCon) solar cell has attracted much attention due to its excellent passivation and compatibility with the traditional c-Si solar cells. The so-called tunnel oxide passivated contact (TOPCon) consists of an ultra-thin silicon oxide layer less than 2 nm in thickness and a heavily doped poly-Si layer, which is used for implementing effective passivation and selective collection of carriers. This TOPCon solar cell has some advantages including no laser contact opening, no light-induced degradation and no elevated temperature-induced degradation because of N-type c-Si wafer, compatibility with high temperature sintering and technical scalability. This paper first introduces the basic structure and principles of TOPCon solar cells, then compares the existing methods of preparing ultra-thin silicon oxide layer and heavily doped poly-Si layer, and finally points out the future research direction of this cell based on the analysis of the current research status.
Luminescence spectra and energy transfer of Tm3+ and Tb3+ doped in LiMgPO4 phosphors
Authors: Xu Zhuo , Guo Jing-Yuan , Xiong Zheng-Ye , Tang Qiang , Gao Mu ,   School of Electronics and Information Engineering, Guangdong Ocean University, Zhanjiang 524088, China,   School of Physics, Sun Yat-Sen University, Guangzhou 510275, China,   Institute of intelligent manufacturing, Zhanjiang University of Science and Technology, Zhanjiang 524094, China
Published: June 2021

 LiMgPO4 (LMP) phosphor doped with rare earth is a promising radiation dosimeter material. Thermoluminescence (TL) spectroscopy is an effective method to study the carrier traps and luminescence centers in materials. To study the luminescent mechanism of rare-earth-doped LMP phosphors, LMP phosphors doped with Tm and Tb (LMP:Tm, LMP:Tb and LMP:Tm, Tb) are prepared by high temperature solid state reaction. The TL glow curve and TL spectrum of the phosphors are measured by the linear heating method, and compared with the photoluminescence (PL) spectrum.

 The shape of the TL glow curve of LMP phosphor varies with the doping active impurities, but the TL glow curves can be fitted by seven TL peaks. Double-doping Tm3+ and Tb3+ in LMP phosphor can enhance the TL intensity of the fifth peak (E ~ 1.39 eV) and weaken the seventh TL peak (E ~ 1.70 eV).

 By comparing the PL spectra with TL spectra of the phosphors, it can be seen that the TL spectra are more complex than the PL spectra excited by ultraviolet light (λ = 352 nm). In the TL process, the electrons which are excited to the conduction band release the energy to recombination centers, and the released energy can more effectively excite the rare earth ions from the ground state to excited states, resulting in the more TL emitting peaks than in the the PL process.

 Although Tm3+ and Tb3+ can be the luminescent centers in LMP phosphors when Tm3+ and Tb3+ are doped in LMP simultaneously, Tb3+ ions are likely to act as sensitizers in LMP:Tm and LMP:Tb phosphor, and Tb3+ ions transfer energy to the low-energy Tm3+ ions, which makes the luminescent centers, Tm3+ ions, excited to the high-energy state and then de-excited with emitting light. This result is also proved by the fact that the luminescence decay of Tb3+ in phosphors increases with Tm3+ concentration increasing. The energy transfer through non-radiative transition is more significant at higher temperature.
Tribological properties of suspended hexagonal boron nitride under electric field
Authors: Chen Xing-Yuan , Huang Yao , Peng Yi-Tian ,   College of Mechanical Engineering, Donghua University, Shanghai 201620, China
Published: June 2021

Hexagonal boron nitride (h-BN) has huge potential applications in micro-nano electromechanical system due to its good lubricity and insulation. In this paper, a microporous array is prepared on a SiO2/Si substrate by the substrate etching process, and then the h-BN is transferred to the microporous substrate to form a suspension structure. The effect of electric field on tribological properties of suspended h-BN is studied by atomic force microscopy. The results show that the friction of the suspended h-BN is smaller than the friction on the h-BN supported by the substrate, because the greater in-plane stretch weakens the puckering effect. The electric field increases the friction of the suspended h-BN, and the influence of positive bias is greater than that of negative bias. The application of the electric field increases the electrostatic force on the tip, thereby increasing the additional load and the interface barrier in the friction process. The electric field causes the stick-slip behavior to change from single-slip to multi-slip. Compared with the h-BN supported by the substrate, h-BN in the suspended state is strongly affected by the electric field. The reduction of the interface distance and the absence of the substrate oxide layer lead the electrostatic force to increase. This paper proposes a method to adjust h-BN’s friction by electric field, which provides theoretical guidance for studying the friction characteristics of two-dimensional materials.
Generation of focusing ring of metalens and its application in optical trapping of cold molecules
Authors: Li Jun-Yi , Ye Yu-Er , Ling Chen , Li Lin , Liu Yang , Xia Yong ,   State Key Laboratory of Precision Spectroscopy, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, China,   School of Physics and Astronomy, Sun Yat-sen University, Zhuhai 519082, China
Published: June 2021

Metasurface can precisely control degrees of freedom of the phase, polarization, and amplitude of the incident light field. It provides a new way to develop the next generation of the experimental platform of quantum-state manipulation on-chip, which has important application prospects. This paper proposes a new type of metasurface structure, that is, a metalens composed of silicon grating elements with different duty ratios that can form a focusing ring on the focal plane. The intensity distribution of the ring light field in the focal plane and the focusing characteristics of metalens with different numerical apertures are studied. An optical storage ring of magnesium fluoride (MgF) molecule is constructed by using this kind of metalens focusing ring. The optical potential and dipole force of the MgF molecule in the focused light field are calculated, and the dynamic process of MgF molecule motion in the storage ring is simulated by the Monte-Carlo method. The research results show that for the incident light of 1064-nm radially polarized light, the designed metasurface structure has good focusing characteristics, and the light field intensity of the focusing ring is 55.1 times stronger than that of the incident light. The focal length of the annular light field is 22 μm and the full width at half maximum of the light intensity distribution in the focal plane is 0.8 μm, and the numerical aperture of the hyperlens is 0.69. The maximum dipole potential of MgF molecules in the light field is 32 μK, which can realize the loading of MgF molecules and trap them in the surface storage ring.
Enhancement of two-magnon scattering in annealed nickel oxide studied by Raman spectroscopy
Authors: Song Meng-Ting , Zhang Yue , Huang Wen-Juan , Hou Hua-Yi , Chen Xiang-Bai ,   Hubei Key Laboratory of Optical Information and Pattern Recognition, Wuhan Institute of Technology, Wuhan 430205, China,   State Key Laboratory of Material Processing and Die & Mould Technology, School of Material Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Published: June 2021

Laser Raman spectroscopy is used to study the enhancement effect of two-magnon scattering in nickel oxide through annealing treatment in a temperature range from 450 ℃ to 1050 ℃, and investigate laser heating effect on two-magnon scattering. Our study shows that two-magnon scattering of nickel oxide can be tremendously enhanced with annealing temperature rising. In the temperature range from 450 ℃ to 1050 ℃, the enhancement increases with annealing temperature increasing, and with 1050 ℃ annealing the two-magnon scattering can be enhanced more than two orders of magnitude, also the enhancement of two-magnon scattering is much stronger than that of two-phonon scattering. This tremendous enhancement is correlated not only with the significant decrease of Ni-vacancy by high temperature annealing, but also with the magnetic spin ordering network of Ni ions. The variation of sensitive intensity of two-magnon scattering with the concentration of Ni-vacancy can be used to provide a simple Raman spectroscopy method of quantitatively measuring the Ni-vacancy in nickel oxide. In addition, the annealing treatment can significantly reduce the laser heating effect on two-magnon scatting in nickel oxide power samples. At low annealing temperature, the intensity of two-magnon scattering quickly quenches with increasing laser power. With 1050 ℃ annealing, the laser heating effect on two-magnon scattering is significantly reduced and two-magnon scattering can still have strong intensity at high laser power.