bluuebunny/crossref_metadata_2025 huggingface dataset:
Electroluminescence from silicon-based light-emitting device with erbium-doped TiO2 films: Enhancement effect of ytterbium codoping
Authors: Zhu Wei-Jun , Chen Jin-Xin , Gao Yu-Han , Yang De-Ren , Ma Xiang-Yang ,   State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

In the past years, light-emitting devices (LEDs) based on erbium (Er)-doped insulators or wide-bandgap semiconductors have received intensive attention because the intra-4f transition (4I13/2→4I15/2) of Er3+ ions at ～ 1540 nm has potential applications in the optical interconnection for silicon-based circuits. The LEDs with rare-earth (RE)-doped SiOx (x ≤ 2) or SiNx (x ≤ 4/3) films have been well investigated as the silicon-compatible emitters. However, they suffer difficulty in injecting current and easing fatigue. In this context, the LEDs with RE-doped oxide semiconductors have been extensively investigated out of research interest in recent years. Among the oxide semiconductors, TiO2 is a desirable host for RE-doping because it is transparent for visible and infrared light, and cost-effective, and has considerably high RE solubility. In our previous work (Zhu C, Lü C Y, Gao Z F, Wang C X, Li D S, Ma X Y, Yang D R 2015 Appl. Phys. Lett. 107 131103), we have realized erbium (Er)-related visible and near-infrared (～ 1540 nm) electroluminescence (EL) from the LED with a structure of ITO/TiO2:Er/SiO2/n+-Si, in which TiO2:Er refers to the Er-doped TiO2 film as the light-emitting layer. In this work, we co-dope ytterbium (Yb) into the TiO2:Er film in the aforementioned LED to significantly enhance the Er-related visible and near-infrared EL. It is revealed that a certain amount of Yb co-doping enables the TiO2:Er film to transform its crystal phase from anatase to rutile. Such a phase transformation reduces the symmetry of crystal field surrounding the Er3+ ions incorporated into the TiO2 host. Moreover, the substitution of over-sized Yb3+ ions for Ti4+ ions in the TiO2 host leads to the distortion of the crystal field around the Er3+ ions. The aforementioned symmetry-reduction and distortion of the crystal field increase the probabilities of the intra-4f transitions of Er3+ ions. Due to the aforementioned reason, the Yb co-doping into the TiO2:Er film remarkably enhances the EL from the corresponding LED. It is believed that the strategy of Yb-codoping can be adopted to enhance the EL from the LEDs with other RE-doped TiO2 films.
Two-dimensional crystallization in finite-sized colloidal systems
Authors: Bei Bang-Kun , Wang Hua-Guang , Zhang Ze-Xin ,   Centre for Soft Condensed Matter Physics and Interdisciplinary Research, Soochow University, Suzhou 215006, China,   College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
Published: December 2020

The nature of crystallization is considered to be one of the most fundamental research problems in condensed matter physics. With single particle resolution offered by video microscopy, colloidal suspensions provide a novel model system for studying crystallization, melting and other phase transitions, where the structures and dynamics of the particles during the transitions can be quantitatively probed. Traditional systems for studying the crystallization typically focus on the infinitely large systems in order to obtain the equilibrium state. However, studies of the crystallization in finite-sized systems such as crystallization in thin films and porous media, are rare despite the fact that they are the common phenomena in natural world. In this paper, we experimentally investigate the crystallization in a finite-sized colloidal system with attractive interactions. The colloidal suspension is composed of polystyrene microspheres dispersed in a mixture of water and 2, 6-lutidine, in which the interaction between the particles can be tuned by adjusting the temperature. We increase the temperature to 34 °C to induce attractions between the particles and thus producing a cluster, and then reduce the temperature to 33 °C to tune off the attractions. Thus we obtain a finite-sized liquid cluster of the colloidal particles. Crystallization is triggered by increasing the temperature to 34 °C. The crystallization process is recorded by video microscopy and the video data are analyzed by a standard particle tracking algorithm. Through the analysis of radial distribution function, Voronoi diagram, and local order parameter, we find that the crystallization of the finite colloidal system starts from the central dense region of the liquid cluster. This leads to a crystalline phase in the center and a liquid phase on the edge of the cluster. As time elapses, the central crystalline region grows while outer liquid region shrinks. The crystallization process exhibits a two-step scenario: a fast crystallization initially and a slow crystallization at the later stage. At the initial stage, the center of the system forms a dense metastable liquid phase, which lowers the free-energy barrier of crystallization and results in a fast crystallization. As the crystalline region grows, the metastable phase disappears, and thus the crystallization rate decreases. Moreover, a bimodal distribution of the orientational order parameter is observed during the crystallization in our finite-sized colloidal system, which is consistent with that in a large system. This indicates that the bimodal distribution is a common feature of the two-dimensional crystallization.
Applications of organic additives in metal halide perovskite light-emitting diodes
Authors: Li Zhen-Chao , Chen Zi-Ming , Zou Guang-Rui-Xing , Yip Hin-Lap , Cao Yong ,   State Key Laboratory of Luminescent Materials and Devices, School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China
Published: December 2020

In recent years, metal halide perovskites have received extensive attention due to their superior optoelectronic properties and solution processability, which also become a research hotspot in the field of optoelectronics. Among all the perovskite optoelectronics applications, perovskite light-emitting diode (LED) becomes one of the important research topics because it is likely to be used in the next-generation display technique. Based on the high photoluminescence quantum yield (PLQY), facilely tunable bandgaps, and sharp emission of perovskite material, the external quantum efficiency of perovskite LED has increased from less than 1% to over 20% within only five years, showing the most rapid development speed in the LED field. During the 5-year exploration of perovskite LEDs, researchers have focused their efforts on how to realize the crystal-growth control in the perovskite film formation process, enhance PLQY of the perovskite films, and improve the performance of perovskite LEDs. Among all the approaches, the utilization of organic additives including small molecules and polymers proves to be an effective strategy. Here, in this article, we review the recent advances in metal halide perovskite LEDs based on the strategy of organic-additive treatment. We also analyze and discuss the interaction between organic additive and perovskite crystal as well as its influence on the performance of perovskite LED. In the end, we discuss the challenges remaining in perovskite LEDs and the prospects for perovskite LEDs.
Optimizing synchronizability of multiplecoupled star networks
Authors: Shu Rui , Chen Wei , Xiao Jing-Hua ,   School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China
Published: December 2020

In this paper, we discuss the optimization problem of the synchronization for Kuramoto oscillators in coupled star networks. In previous studies of star networks, the natural frequencies of leaf nodes are usually equal or only adjusted within a small parameter range, but this assumption is not satisfied in most of cases. Considering the random distribution of the frequency of the leaf nodes in a single star network and multiple coupled star networks, the critical coupling strength required for system synchronization is obtained according to the boundedness of the sinusoidal function. In a single star network, the piecewise linear relationship between the critical coupling strength of the system and the frequency of the central oscillator is found. In the coupled system of two star networks, we consider that they are coupled through the central node. The parameter plane of the natural frequency of the central node will be divided into different regions. In each region, the critical coupling strength is determined by the coupling strength within the respective star networks or the coupling strength between the two central nodes. Considering the coupling of multiple star networks, we introduce a central connection node through which the central nodes of multiple star networks are coupled. In the above two models of multiple coupled star networks, the piecewise linear relationship between the critical coupling strength of the system and the sum of frequencies of the center oscillators is found. The critical coupling strength of the two types of networks is smallest at the piecewise point. According to the optimization results, we find that with the increase of coupling strength, when there is only one cluster in the system, the critical coupling strength becomes small. So we can reduce the critical coupling strength of the system by adjusting the frequency of the central oscillator for achieving the effect of synchronous optimization. When multiple clusters are generated in the system, the critical coupling strength turns large. Because of the similarity between star network and scale-free network and the application of Kuramoto model in power grid, this paper can provide a good theoretical reference for the further study on synchronization optimization of scale-free network and power grid.
Effect of capacitance on positive and negative symmetric pulse with fast rising edge based on GaAsphotoconductive semiconductor switch
Authors: Gui Huai-Meng , Shi Wei ,   College Information Engineering, Shaanxi Polytechnic Institute, Xianyang 712000, China,   Department of Applied Physics, Xi’an University of Technology, Xi’an 710048, China
Published: December 2020

Femtosecond streak camera is currently the only diagnostic device with a femtosecond time resolution. Scanning circuit with bilateral symmetrical output is an important part of femtosecond streak camera. To achieve better performance of the streak camera, high requirements are placed on the output of scanning circuit. Owing to the excellent feature of litter time jitter and fast response speed, a GaAs photoconductive semiconductor switch (PCSS) has become a core device in the scanning circuit. Investigating the positive and negative symmetric pulses with fast rising edgeof GaAs PCSS is of great significance to improving the time resolution of femtosecond streak camera. In this paper, a laser with a pulse width of 60 fs was used to trigger a GaAs PCSS with an electrode gap of 3.5 mm. Under different storage capacitors and bias voltages, the positive and negative symmetric pulses withthe fastest rise time of 149 ps and the highest voltage transmission efficiency of 92.9% were obtained. The test results meet the design requirements of streak camera to realize femtosecond time resolution. Through the comparative analysis of the experimental values, it is concluded that the storage capacitor can affect the efficiency and rise time of the output electrical pulse in the same trigger laser pulse. By calculating the multiplication rate of carriers in combination with the output electrical pulse waveform, it is concluded that the GaAs PCSS operates in linear mode. According to the working characteristics of the linear mode and the energy storage characteristics of the capacitor, the analysis indicates that, when the characteristics of the trigger laser pulse are the same, the transmission efficiency and rise time of the output electric pulse voltage increase with the increase in storage capacitor, which is consistent with the experimental results. This study has a certain guiding significance for the better application of GaAs PCSS in femtosecond streak camera, which also has a certain propelling effect on improving the time resolution of femtosecond streak camera.
Domain decomposition based integral equation modeling of 3-dimensional topography in frequency domain for well electromagnetic field
Authors: Li Jing-He , He Zhan-Xiang , Meng Shu-Jun , Yang Jun , Li Wen-Jie , Liao Xiao-Qian ,   College of Earth Sciences, Guilin University of Technology, Guilin 541004, China,   Department of Earth and Space Sciences, Southern University of Science and Technology, Shenzhen 518055, China
Published: December 2020

As an efficient geophysical exploration technology, well electromagnetic method is particularly applicable to oil and gas exploration in China's complex terrain areas (deserts, mountains, etc.). A serious influence of topographic relief area on the electromagnetic response of well is inevitable but challenging. To the best of our knowledge, there is no literature on modeling the electromagnetic response of three-dimensional (3D) topography with well electromagnetic method. Based on the domain decomposition, an integral equation method is presented to simulate the electromagnetic response of 3D topography in frequency domain via the well electromagnetic method. Compared with the finite difference and finite element method based on partial differential equation, this method is very efficient in simulating topographic response without huge computation or truncation boundary error accumulation or special boundary condition requirements. Firstly, an induction coefficient is defined according to the topographic relief situation. Then the computational domain consisting of the target body, background medium and 3D topography is divided into reference model, background medium and the distribution of target body medium area. According to the characteristics of each sub-region, Anderson algorithm is an analytic solution based on Gaussian filtering, which is used to provide the primary field from the excited sources in surface. And then, the stable double conjugate gradient-fast Fourier transform is incorporated into integral equation algorithm to obtain the fast 3D terrain shaft frequency domain electromagnetic responses. By comparing the calculation results using the new algorithm presented in this paper with the analytical solutions of Anderson algorithm for half-space model with surface electromagnetic method, the precision and the efficiency of this new algorithm are demonstrated. And the ability to model the electromagnetic responses of 3D topography is shown by comparing with the published results of 3D boundary integral equation. Thus, the high accuracy and high efficiency of the new algorithm presented in this paper are validated. Finally, the influence of 3D valley topography on electromagnetic field response of surface to borehole electromagnetic (SBEM) observation system is presented and analyzed. It is observed that the response of SBEM is seriously disturbed by the field of 3D valley topography which is necessarily removed. The research results presented in this paper are of significance for guiding the identification and correction of electromagnetic topographic effect from 3D SBEM.
All-electron calculation of ground state vibration-rotation energy levels of 7Li2(0, ±1) molecular systems
Authors: Wang Qiao-Xia , Wang Yu-Min , Ma Ri , Yan Bing ,   Key Laboratory of Applied Atomic and Molecular Spectroscopy, Jilin Province, Institution of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
Published: December 2020

The investigation of spectroscopic information is important for understanding the mechanisms of molecular photochemical and photophysical reactions. As a prototype to study the electronic structures and spectra of diatomic molecular systems, the vibration-rotational spectra of alkali dimer and its ions have aroused considerable research interest in the last two decades. Single-reference and multi-reference coupled cluster theory in combination with correlation consistent Gaussian basis set are adopted to study the ground-state potential energy curves of 7Li2(0,± 1) molecular systems. The correlation effect and relativistic effect of all the electrons are taken into account in the calculation. And the spectroscopic constants, including the equilibrium internuclear distance Re, the harmonic vibrational frequency ωe, the anharmonic constant ωexe, the equilibrium rotational constant Be, and the dissociation energy De of the molecular system and vibration-rotational energy level information of the ground states are obtained by solving the radial Schrödinger equations. The calculated spectroscopic constants of the neutral and positive ion system accord well with the experimental values; however for the negative ion system, the calculation of equilibrium internuclear distance needs further improving, and other spectroscopic constants are consistent well with the experimental values. The present computational results indicate that the ground state wave functions of neutral and positive ion systems have obvious single reference configuration characteristics, while the ground state of negative ion molecule system should be described with multireference configuration wave functions. The vibration-rotational energy levels of ground state with different theoretical methods are in good agreement with the experimental values. The vibrational-rotational energy levels and spectroscopic constants of neutral and positive ion systems are well reproduced, and some experimental information about spectrum is still lacking. Although the difference among the equilibrium internuclear distances for the ground state of the negative ion, obtained from different theoretical methods are still existent, the results of the vibrational level interval accord well with each other. This study provides useful information about spectrum for accurately investigating the electronic structures and spectra of the ground state of Li2 molecular system and its two isotopic molecules, especially for the negative ion system with little information about spectrum.
Coupled resonance of bubbles in spherical cavitation clouds
Authors: Zhang Peng-Li , Lin Shu-Yu , Zhu Hua-Ze , Zhang Tao ,   Institute of Applied Acoustics Shaanxi Normal University, Xi’an 710062, China,   College of Science, Xi’an University of Science and Technology, Xi’an 710054, China
Published: December 2020

The interaction between bubbles in bubble group mainly acts on the other bubble through radiation sound pressure between the bubbles. In this paper, based on the bubble dynamics equation in bubble clouds, the equation of bubble wall motion is linearly reduced, the expression of bubble resonance frequency in spherical bubble group is obtained and the correction coefficient of bubble resonance frequency and single bubble are given. Furthermore, the effects of the initial radius, the number of bubbles and the distance between bubbles on the resonance frequency are discussed. The results show that the phase of bubbles is taken into account. Considering the interaction between bubbles, the resonance frequency of bubbles in spherical bubble group is obviously less than that of single bubble. With the decrease of the number of bubbles in bubble group, the distance between bubbles increases, the interaction between bubbles in bubble group decreases, and the resonance frequency of bubbles returns to the resonance frequency of Minnaert single bubble. At the same time, the resonance frequency of bubbles in bubble group changes gradient with the increase of the distance between bubbles and the number of bubbles. However, when the number of bubbles increases a certain value, the resonant frequency of the bubble is almost constant. When the bubble group has a certain radius, the more the number of bubbles, the smaller the resonance frequency of the bubble is, but there exists a critical value. It is also found that a smaller correction coefficient is held by the bubble group with larger initial radius, which indicates the same number of bubble groups. Under the same bubble spacing, the interaction of small bubbles with smaller bubbles is more significant, and the resonance frequency of the bubble is obviously affected. Because the frequency and amplitude of driving sound pressure can only be given values in ultrasonic cavitation, the resonant frequency of cavitation bubbles will be reduced by properly injecting air bubbles into liquid, which makes most of cavitation bubbles undergo intense non-linear oscillating steady-state cavitation. Therefore, the occurrence of cavitation can be effectively suppressed.
Magnetization reversal and coercivity in rare-earth permanent magnets and composite magnets
Authors: Li Zhu-Bai , Li Yun , Qin Yuan , Zhang Xue-Feng , Shen Bao-Gen ,   Key Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Inner Mongolia University of Science and Technology, Baotou 014010, China,   School of Science, Inner Mongolia University of Science and Technology, Baotou 014010, China,   State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

The coercivities in rare earth permanent magnets even with the same intrinsic properties may differ largely. In this paper, what determines the coercivity is discussed via the investigation of thermal activation in Pr-Fe-B ribbons prepared by melt-spinning method. The thermal activation, resulting from thermal fluctuation overcoming the energy barrier under the applied field, is the critical behavior of magnetization reversal. The activation size is comparable to the theoretical domain wall size, implying that the magnetization reversal undergoes the nucleation of revered domain wall at grain outer-layer in Pr-Fe-B ribbons, and the defects near the grain boundary are critical for the magnetization reversal and coercivity. The exchange coupling between the defect region at grain outer-layer and the perfect region in the inside of grain promotes the nucleation of reversed domain and the depinning of domain wall motion. The reduced anisotropy of the defect region also contributes to the overcoming of energy barrier of magneto crystallie anisotropy in the inside of Pr-Fe-B grains by the coupling effect, so the nucleation field of reversed domain and coercivity decrease largely, and the domain wall size is a little larger than the theoretical value due to the coupling between the defect region at grain outer-layer and the perfect region in the inside of grain in the critical magnetization reversal. In Pr2Fe14B/α-Fe composite magnets, the exchange coupling between the soft and hard magnetic phase leads the domain wall size to increase in the critical magnetization reversal of thermal activation, and so the exchange energy plays a role in overcoming the energy barrier, resulting in the further decrease of coercivity. Via the addition of Ti and Nb element, the coercivity increases significantly. Based on the investigation of thermal activation, the size of defect region involved in the domain wall decreases, and the contribution of the anisotropy in the defect region and interface to the overcoming of energy barrier is weakened, so the applied magnetic field should be increased in the magnetization reversal. The coercivity can be enhanced by reducing the size of defect region at grain outer-layer and by making the anisotropy change abruptly at the interface between the hard and soft magnetic phase.
Transmission characteristics of vortex beams in a sixfold photonic quasi-crystal fiber
Authors: Wei Wei , Zhang Zhi-Ming , Tang Li-Qin , Ding Lei , Fan Wan-De , Li Yi-Gang ,   School of Physics, Nankai University, Tianjin 300071, China
Published: December 2020

In an optical fiber communication system, vortex beams have aroused great interest in the last several decades. Vortex beams possess many intriguing properties. For example, they have the ability to carry orbital angular momentum (OAM) which is mutually orthogonal. The OAM is a fundamental physical quantity of light which can be used as information carriers for transmission channel of optical fiber. Combined with the existing multiplexing techniques such as wavelength division multiplexing technique, advanced multilevel amplitude modulation formats, etc., the vortex beams provide an alternative to the increase of the transmission capacity and spectral efficiency of the optical fiber transmission system. Recently, long-length transmission of vortex-beam in optical fiber has been realized and there have also occurred some new designs of optical fiber on vortex beams, such as air-core ring shaped fiber, graded index vortex fiber, multi-ring fiber, and supermode fiber. Photonic crystal fiber (PCF) is flexible in design. Therefore, it is easy to regulate the transmission performance of PCF by adjusting the radius and the pitch of the air holes and so on. In this paper, we propose a newly designed sixfold photonic quasi-crystal fiber (SPQCF) to transmit vortex beams stably. Transmission characteristics of this newly designed fiber are simulated and calculated by using COMSOL multiphysics software. When the wavelength of the incident light is 1550 nm, the effective index difference between the vortex modes in a group is more than 10–4 which is large enough to preclude the LP modes from being formed, and to transmit 7 vector modes (10 OAM modes). Changing the radius and pitch of the air holes, we can regulate the dispersion characteristic and confinement loss of the SPQCF flexibly. At 1550 nm, the confinement loss of the SPQCF maintains 10–8−10–7 which is low enough to confine the vortex beams in the fiber core. When the incident light wavelength of HE21 ranges from 1500 nm to 1800 nm (r0 = 1.9 μm), the dispersion coefficient of the SPQCF is between 63.51−65.42 ps·nm–1·km–1 which tends to be flat. By changing r0, the flat trend is adjusted to different wavelength range. This dispersion characteristic possesses great potential for the transmission of optical solitons. The effective mode area (HE21) is about 40 μm2 and the nonlinear coefficient (HE21) is maintained on the order of 10–3 between 1500−1600 nm. These features suppress the generation of nonlinear effect in the fiber and benefit the transmission of vortex beams. The stable transmission distance is longer than 1 km. In summary, we design a new type of PCF featuring quasi-crystal structure which has a ring shaped fiber core and supports the transmission of vortex beams stably.
Control of maximum evolution speed of quantum states by two-mode entangled light field
Authors: Tian Cong , Lu Xiang , Zhang Ying-Jie , Xia Yun-Jie ,   School of Physics and Physical Engineering, Qufu Normal University, Qufu 273165, China,   Shandong Provincial Key Laboratory of Laser Polarization and Information Technology, Department of Physics, Qufu Normal University, Qufu 273165, China
Published: December 2020

We consider a two-mode entangled coherent light field, in which one mode of the light field is injected into the cavity and interacts with a two-level atom. According to the theory of cavity electrodynamics, the evolution state of atomic system is deduced. Aiming at the dynamic process from the initial state of an atomic system to the target evolution state, the quantum speed limit time is used to characterize the maximum evolution rate of the quantum state of an atomic system. The maximum evolution rate of an atomic system can be controlled by adjusting the coherent parameters of the two-mode entangled coherent light field. But up to now, which kind of quantum speed limit time can be better, universal and strict applicable to the quantum dynamics process of any system is still an unresolved important issue. Based on different methods of measuring the distance between two quantum states and different dynamic evolution channels, many definitions of the quantum speed limit time have been given. The quantum speed limit time proposed by Deffner and Lutz (Deffner S, Lutz E 2013 Phys. Rev. Lett. 111 010402) and the other deduced by Campaioli et al. (Campaioli F, Pollock F A, Binder F C, Modi K 2018 Phys. Rev. Lett. 120 060409; Campaioli F, Pollock F A, Modi K 2018 arXiv:1806.08742) have attracted extensive attention. In this paper, we first compare the advantages of two quantum speed limit times to characterize the maximum evolution rate of quantum states. We find that the quantum speed limit time expression given by Campaioli et al. (Campaioli F, Pollock F A, Modi K 2018 arXiv:1806.08742) in 2018 is a tighter bound when describing the boundary of the shortest time required for the quantum state evolution of a two-level atomic system. Therefore, this paper is mainly based on the quantum speed limit time given by Campaioli et al. to analyze how to achieve the maximum evolution rate of the quantum state of the atomic system by manipulating the parameters of a two-level entangled coherent light field. The results show that the maximum evolution speed of the quantum state of the atomic system can be significantly affected by the coherent parameters of the light field interacting with the atom under certain conditions. Furthermore, when the interacting light field parameters cannot well control the maximum evolution speed of the quantum state, the quantum correlation with the two-mode entangled coherent light field can realize the remote control of the maximum evolution speed of quantum state of atomic system by the light field parameters that are not involved in the atom-light interaction.
Numerical simulation of mixture gas arc of Ar-O2
Authors: Wang Xin-Xin , Chi Lu-Xin , Wu Guang-Feng , Li Chun-Tian , Fan Ding ,   School of Materials Science and Engineering, Chongqing University of Technology, Chongqing 400054, China,   Chongqing Municipal Engineering Research Center of Higher Education Institutions for Special Welding Materials and Technology, Chongqing 400054, China,   School of Materials Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, China,   State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals, Lanzhou 730050, China
Published: December 2020

Mixture gas arcs are used extensively in welding manufacturing. A two-dimensional steady mathematical model for Ar-O2 mixture gas arc is developed to understand further the heat and mass transfer of the mixture gas arc. The model is based on the assumption of local thermodynamic equilibrium, and the thermodynamic parameters and transport coefficients are dependent on both the temperature and the oxygen content. In the present model, the diffusion between the argon species and oxygen species is depicted by the approach of the combined diffusion coefficient, i. e. the mixture gas arc is simplified into two different species, and the diffusion between them is formulated by combined ordinary diffusion coefficient and combined temperature diffusion coefficient; the oxygen distribution and its influence on the temperature and flow field of the arc are investigated for two different current conditions. It is shown that the oxygen species presents significant non-uniform distribution for argon gas mixed with 5% oxygen; the oxygen content is higher than that in mixed shielding gas in the regions close to the electrodes and arc axis, while its content is lower than that of the mixed shielding gas in other regions. For high current, oxygen concentrates more to the flat anode, while it concentrates more to tungsten cathode for low current. For both cases, oxygen content is inhomogeneous in the region 0.1 mm above the anode. The 5% oxygen mixed in argon constricts the arc plasma to some extent and thus raises the arc temperature as well as the plasma flow velocity.
Effects of oxidation on silicon vacancy photoluminescence and microstructure of separated domain formed nanodiamond films
Authors: Chen Long , Chen Cheng-Ke , Li Xiao , Hu Xiao-Jun ,   College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou 310014, China
Published: December 2020

In order to increase the oxidation sites for enhancing the Si-V photoluminescence intensity of nanocrytalline diamond films, we prepare nanocrystalline diamond films; these films each are comprised of separated domains and oxidized for different times. Each single domain consists of nanodiamond grains with a size of larger than 100 nm and amorphous carbon. In the gaps between domains of separated domain there is formed a film that allows more sites to contact air to ensure the efficient oxidation of the film. As a result, silicon vacancy photoluminescence intensity of the separated domain forming the film is largely enhanced by about 22.7 times after oxidation. The SEM images and Raman spectra of oxidized samples show that the film contains flower-shaped diamond aggregates, each of which is comprised of radially arranged diamond grains. The mixture of nanodiamond grains and amorphous carbon fills the gaps between diamond petals. These fillers disappear after long-term oxidation, but the diamond petals stay stable. Raman spectra show that the amount of amorphous carbon largely decreases after oxidation, while diamond content apparently rises. Hydrogen is desorbed from the film after short-time oxidation according to Raman spectra, thus the quenching effect on silicon vacancy photoluminescence caused by hydrogen termination of diamond surface state is removed. Diamond petals of large size and nanodiamond grains in the fillers are both silicon vacancy photoluminescence sources of the film; the exposed diamond flats on the surface of unoxidized domains provide limited silicon vacancy photoluminescence for the film. The sufficient exposure of diamond grains after the removal of amorphous carbon leads to the significant enhancement of film’s silicon vacancy photoluminescence. With longer-time oxidation, the photoluminescence of film will slightly decrease due to the disappearance of small-sized nanodiamond grains, but the film photoluminescence almost remains stable in both intensity and property due to the stability of large-sized diamond grains. The film after 140-min oxidation remains photoluminescence enhancement, 8.3 times the photoluminescence of the unoxidized sample. The full width at half maximum of photoluminescence peak declines to merely 5.6－6.0 nm because of diamond petals’ high degree of order, which is advantageous for diamond silicon vacancy photoluminescence.
Design and output performance of vibration energy harvesting triboelectric nanogenerator
Authors: Wu Ye-Sheng , Liu Qi , Cao Jie , Li Kai , Cheng Guang-Gui , Zhang Zhong-Qiang , Ding Jian-Ning , Jiang Shi-Yu ,   Institute of Intelligent Flexible Mechatronics, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

With the advent of global warming and energy crisis, the search for renewable energy to reduce carbon emissions has become one of the most urgent challenges. Ithas become a research hotspot to collect or harvest various mechanical energy in nature and convert it into electric energy. Vibration is a common form of mechanical movement in our daily life. It is visible both on most working machines and in nature and is a type of potential energy. There are several methods that can convert such mechanical energy into electric energy. Triboelectric nanogenerator (TENG) based on the principle of contact electrification and electrostatic induction which first appeared in 2012 by Zhonglin Wang provides a feasible method of efficiently collecting the vibrational energy with different vibrating frequencies. In this paper, a contact-separation mode of TENG is designed and implemented. The voltage- quantity of charge- distance(V-Q-x)relation of TENG is calculated. During the experiment, the factors such as load resistance, vibration frequency, etc. which affect the output performance, are considered and analyzed. An electrically driven crank-connecting rod mechanism is employed to provide the vibration source with adjustable frequency in a range of 1-6 Hz. The result shows that the amount of charge transfer in each working cycle remains almost unchanged, while the voltage and current increase with frequency increasing. When the frequency is 5 Hz, the best power matching resistance of the TENG is about 33 MΩ and the maximum output power reaches 0.5 mW. For a further study, a COMSOL software is used to simulate the distribution rule and variation rule of the electric potential in the contact-separation process, then the theoretical charge density and the experimental charge density on the polymer surface are compared and analyzed in order to provide theoretical and practical support for the design of TENG with collected vibration energy and self-powered vibration sensor. The result shows that the electric potential is proportional to the distance between two friction layers. While as the distance between two friction layers increases, the electric potential and the charge density both show a tendency to concentrate in the middle of the friction layer. The huge difference between experimental result and the simulation predicts thatmuch work should be done continually to improve the output of the TENG. Finally, the obtained results conduce to understanding the contact electrification and electrostatic induction mechanism and also provide a new method of harvesting the vibration energy.
Progress of ARPES study on topological semimetals
Authors: Deng Tao , Yang Hai-Feng , Zhang Jing , Li Yi-Wei , Yang Le-Xian , Liu Zhong-Kai , Chen Yu-Lin ,   CAS Center for Excellence in Superconducting Electronics (CENSE), State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences, Shanghai 200050, China,   University of Chinese Academy of Sciences, Beijing 100049, China,   School of Physical Science and Technology, ShanghaiTech University, ShanghaiTech Laboratory for Topological Physics, Shanghai 201210, China,   Department of Physics, University of Oxford, Oxford OX1 3PU, United Kingdom,   Department of Physics, Tsinghua University, Beijing 100084, China
Published: December 2020

Topological semimetal, known as a type of topological quantum materials without energy gap, has attracted lots of research interests due to its unique physical properties such as novel quasiparticles, giant magnetoresistance and large carrier mobility. Topological semimetal can be further classified into topological Dirac semimetal, topological Weyl semimetal, topological nodal-line semimetal and topological semimetals with " new fermions”. The high-resolution angle-resolved photoemission spectroscopy (ARPES) has emerged as a powerful experimental technique to directly visualize the electronic structure and identify the characteristic topological electronic states in topological semimetals. Here we would briefly introduce the ARPES technique and review some of the recent progress of ARPES study on the electronic structures of typical topological semimetals. We would focus mostly on the physics origin and ARPES signature of topological electronic structures and hope the readers would find it interesting and useful in the understanding of this material class which both is important in physics and has promising application potentials.
A modified HLLEM scheme and shock stability analysis
Authors: Hu Li-Jun , Yuan Hai-Zhuan , Du Yu-Long ,   School of Mathematics and Statistics, Hengyang Normal University, Hengyang 421002, China,   School of Mathematics and Computational Science, Xiangtan University, Xiangtan 411105, China,   School of Mathematical Sciences, Beihang University, Beijing 100191, China
Published: December 2020

Reliable numerical simulations for hypersonic flows require an accurate, robust and efficient numerical scheme. The low-dissipation shock-capturing methods often suffer various forms of shock wave instabilities when used to simulate hypersonic flow problems numerically. For the two-dimensional(2D) inviscid compressible Euler equations, the stability analysis of the low-dissipation HLLEM scheme is conducted. The odd and even perturbations are added to the initial state in the streamwise direction and the transverse direction respectively, and the evolution equations of perturbations are deduced to explore the mechanism of instability inherent in the HLLEM scheme. The results of stability analysis show that the perturbations of density and shear velocity in the flux transverse to the shock wave front are undamped. Due to the symmetry, the 2D Sedov blast wave problem is computed to prove the multidimensionality of the shock instability. In the one-dimensional case which is free from the instability, the undamped property of density perturbation is also existent but no shear velocity is found. The conclusion can be drawn as follows: the shock instability of HLLEM scheme is triggered by the perturbation growth of shear velocity in the flux transverse to the shock wave front. Based on the conclusion of stability analysis, the instability of HLLEM scheme is cured by adding the shear viscosity to the transverse flux. In order to avoid affecting the resolution of the shear layer due to the introduction of too high shear viscosity, two functions to detect the shock wave and the subsonic regimes are defined, so that the shear viscosity is only added to the transverse flux in the subsonic regime of the shock layer, while the rest of numerical fluxes are still computed by the original HLLEM scheme. The results of stability analysis and some challenging numerical test problems show that the modified HLLEM scheme not only retains the merits of the original HLLEM, such as, resolving contact discontinuity and shear wave accurately, but also has greatly improved its robustness, inhibiting the unstable phenomena from occurring effectively when computing the strong shock wave problems.
Molecule-like structural units in silicate-glass-forming oxides
Authors: Wan Fa-Qi , Ma Yan-Ping , Dong Dan-Dan , Ding Wan-Yu , Jiang Hong , Dong Chuang , He Jian-Xiong ,   Key Laboratory of Special Glass of Hainan Province and State Key Laboratory of South China Sea Resources Utilization, Hainan University, Haikou 570228, China,   College of Physical Science and Technology, Dalian University, Dalian 116622, China,   School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028, China,   Key Laboratory for Materials Modification by Laser, Ion and Electron Beam, Dalian University of Technology, Dalian 116024, China,   Hainan Zhonghang Special Glass Technology Co., Ltd. & State Key Laboratory of Special Glass, Haikou 579124, China
Published: December 2020

Silica glasses are composed of multi-oxides, apart from the major component silica. Though it is a general practice in the industries to prepare glasses at specific oxide ratios, the composition rule is largely missing, complicated by the implication of multi-oxides. Necessarily, their interpretation is rooted in chemical units, on which the specific compositions depend. However, in silica glasses the inter-atomic bonding network is continuous and there is no weak bonds, like the inter-molecular ones in molecular compounds, to define molecular entities that carry the chemical information of the materials. As the first stage towards understanding the composition rule, the present paper introduces a new method, so-called the cluster-plus-glue-atom model, to unveil the molecule-like structural units of the glass-relevant oxides. It is pointed out that their respective contributions to the construction of glass networks originate from their characteristic cluster structures, and from which molecule-like structural units are proposed that represent the smallest structural units of these oxides. Oxides participating in the glass network formation mainly present triangular or tetrahedral clusters which are required for a three-dimensional glassy network. For example, the basic network former SiO2 is formulated as [Si-O4]Si and contains 32 valence electrons. The intermediate oxides are characterized by the simultaneous formation of both octahedra and tetrahedra. The network modifiers present mainly cubes and octahedra. It is confirmed that the molecule-like structural units of the glass-formation oxides all meet octet rule (that is, the total number of valence electrons contained in each structural unit is an integer multiple of 8), just like common molecules. The proposed concept of molecular structural units sheds a new light on understanding the composition rule of silicate glasses and can eventually solve the long-standing problem of composition design of silica glasses.
Investigation of NO content varaitaion in the lymphatic vessels under different outlet pressures by a lattice Boltzmann method
Authors: He Yi-Nan , Zhang Qian-Yi , Wei Hua-Jian , Shi Juan ,   School of Material Science and Engineering, Guilin University of Electronic Technology, Guilin 541004, China,   School of Information and Communication, Guilin University of Electronic Technology, Guilin 541004, China
Published: December 2020

The lymphatic system is an important defense function system in the human body. It is also critical to humoral homeostasis. Local dysfunction will cause edema, immune deficiency, and a high incidence. There are intraluminal valves in the lymphatic system, which allows the lymph fluid to flow to the large veins and heart. It has three major immune functions. First, it can resist bacterial viruses and protect the human body from disease attacks. Secondly, it is supplemented by lymphocytes to remove the products produced by metabolism. In the end, The damaged organs and tissues are repaired by lymphocytes to restore normal physiological functions. The lymphatic system does not have the same pump as the heart of the blood circulatory system. The driving of lymph is mainly done by the spontaneous contraction of the lymphatics (the lung lymphatic system is compressed by the alveoli). The autonomic contraction cycle of lymphatic vessels is caused by the increase of Ca2+ in lymphocytes, and the contraction drives the fluid to produce shearing force. The shearing force produces nitric oxide synthase (eNOS) in lymphatic endothelial cells, and eNOS increases NO and increases NO. Decreasing Ca2+ relaxes lymphatic vessels, fluid shear rate decreases after lymphatic vessel relaxation, eNOS decreases, NO decreases, Ca2+ increases, lymphocytes contract, and a new cycle begins. It can be seen that the concentration of NO and its distribution play a key role in the contraction of lymphatic vessels. Obviously, export pressure affects the shear rate of fluid in the lymphatics, which in turn affects the concentration of NO and the contraction of lymphatic vessels. To investigate the effect of lymphatic outlet pressure on lymphatic vessel contraction, we established a lattice Boltzmann model to simulate the initial lymphatic vessels embedded in porous tissue and the collecting lymphatic vessels with two pairs of valves. The valve is the main source of NO. Once contraction begins, the contraction is spontaneous, self-sustaining, and the system exhibits non-linear dynamics. This model can reproduce NO and The interaction of Ca2+ and the spontaneous contraction of lymphatic vessels, and the distribution of NO under different outlet pressures and their average values were studied.