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First-principles study of Cs/O deposited Na2KSb photocathode surface
Wang Qi-Ming, Zhang Yi-Jun, Wang Xing-Chao, Wang Liang, Jin Mu-Chun, Ren Ling, Liu Xiao-Rong, Qian Yun-Sheng
Abstract +
Na2KSb photocathodes have many applications in vacuum optoelectronic devices, such as photomultiplier tubes, image intensifiers, and streak image tubes for high-speed detection and imaging in extremely weak light environments, due to their advantages of high temperature resistance, small dark current, low vacuum requirement, low fabrication cost and high fabrication flexibility. In addition, this type of photocathode has important application prospect in high brightness accelerator photoinjectors. To guide the fabrication of high-sensitivity Na2KSb photocathodes, Na2KSb surfaces with different surface orientations and atom terminations are investigated by the first-principles calculation method based on the density functional theory to obtain the most stable and most favorable surface for electron emission. From the perspectives of surface energy, adsorption energy, and work function before and after Cs adsorption, it is revealed that the Na2KSb (111) K surface exhibits superior surface stability and electron emission capability. Furthermore, the electronic structure and optical properties of Cs adsorption and Cs/O co-adsorption on the Na2KSb (111) K surface under different Cs coverages are analyzed, and the mechanism of Cs/O deposition on Na2KSb surface is studied. The adsorption energy of Cs in the Cs/O adsorption model is much larger than that in the single Cs adsorption model, indicating that the adsorption of O atoms on the Na2KSb surface can make the adsorption of Cs atoms on the surface stronger, and thus increasing the adhesion of Cs atoms on the surface. After adsorption of Cs on the Na2KSb (111)K surface, the surface work function only decreases by 0.02 eV, while the maximum work function decrease for the Cs/O adsorbed surface is 0.16 eV, with the Cs coverage of 2/4 ML and the O coverage of 1/4 ML. The adsorption of Cs/O atoms on the surface facilitates the charge transfer above the surface and results in charge accumulation, which can form the effective surface dipole moment. The magnitude of the surface dipole moment is directly related to the change of work function. Furthermore, through the analysis of the electronic band structure and density of states, it is found that the adsorbed Cs atoms have additional contribution to the band structure near the conduction band minimum. After the introduction of O atoms, the valence band moves up, also the bottom of the conduction band and the top of the valence band become flat. The Cs/O deposition is beneficial to increasing the absorption of near-infrared light on the Na2KSb surface, but it will reduce the absorption of ultraviolet light and visible light, and the refractive index will also decrease. This work has a certain reference significance for understanding the optimal emission surface of Na2KSb photocathode and the mechanism of surface Cs/O deposition.
Dielectric materials for high-performance triboelectric nanogenerators
Deng Hao-Cheng, Li Yi, Tian Shuang-Shuang, Zhang Xiao-Xing, Xiao Song
Abstract +
Triboelectric nanogenerator (TENG), as a micro-nano power source or self-powered sensor, has shown great prospects in various industries in recent years. The TENG output performance is closely related to the contact electrification characteristics of the triboelectric dielectric material. Herein, we first introduce the relevant fundamental theory and models of TENG and tribo-dielectrics. Then, we introduce the material selection, modification method (including surface modification and bulk modification) and structural design strategy of TENG dielectric material. Surface and bulk modification mainly involve surface roughness control, surface functional group regulation, and optimization of dielectric parameters. In terms of dielectric structural design, the principle of charge transport, trapping, and blocking layers as well as typical techniques to improve the dielectric properties of TENGs through multi-layer structures are highlighted. Finally, challenges and directions for future research are discussed, which is conducive to the fabricating of high-performance TENG dielectric materials.
Directional emission properties of thin film microdisk
Xu Yu-Xuan, Yao Tai-Yu, Deng Li, Chen Shi-Mei, Xu Chen-Yao, Tang Wen-Xuan
Abstract +
Based on the directional emission effect of semiconductor deformed microcavities, the fabrication of deformed microcavities in isotropic thin films will provide a new solution for multifunctional and highly integrated photonic active chips. Because the Limacon shaped microcavity has become one of the important configurations of single-mode, low threshold on-chip lasers, the directional emission properties of microdisks fabricated in thin film are investigated. Taking the TE20,1 mode existing in the Z-cut lithium niobate thin film microdisk for example, according to two-dimensional wave optics theory, the mode distribution, quality factor Q, and directional emission factor D of microdisk variations with deformation factor $\varepsilon $ are respectively analyzed through using the wave optics module of COMSOL. Adopting classical scattering theory, Poincaré surfaces of sections under different deformation factors are simulated by optimizing the Dynamical Billards.jl library in Julia. In the simulation realized by Julia, 200 particle collisions are used 200 times to simulate 200 reflections of rays and finally PSOS images are obtained. Simulation results reveal that when the azimuthal quantum number of the light wave mode remains unchanged, although the shape of the microdisk varies, the ratio of the resonant wavelength inside the microdisk to the circumference of the microdisk is approximately a constant, which can predict the microdisk size and resonant wavelength estimation of microcavities. The corresponding PSOS shows that when $\varepsilon > 0.45$, the entire region is covered by chaotic sea area, therefore $\varepsilon $ values of 0, 0.16, 0.24, 0.28, 0.45 are selected to simulate the TE20,1 mode distribution, far-field radiation flux angle distribution, and PSOS. Theoretical simulation results show that when the deformation factor is greater than 0.24, the microdisk has good unidirectional lasing property, with a Q factor greater than 105. When the deformation factor is greater than 0.4, the PSOS is almost occupied by the chaotic sea area, with a Q factor below 103. Therefore, when the deformation factor of the limacon microdisk in the thin film can be chosen between 0.24 and 0.4, under which circumstance the microdisk not only carries high quality factor (about 103-105), but also forms high laser directionality (about 6.45-8.32). The theoretical simulation results will provide a certain theoretical reference for conducting the experimental research of thin film deformation microcavities.
Aging and life control of cross-linked polyethylene as cable insulation material
Wang Jiang-Qiong, Li Wei-Kang, Zhang Wen-Ye, Wan Bao-Quan, Zha Jun-Wei
Abstract +
Cross-linked polyethylene (XLPE) has been widely used in the field of power cables because of its excellent mechanical properties and insulating properties. However, during the manufacturing of high voltage cables, XLPE will inevitably be affected by electrical aging, thermal aging and electric-thermal joint aging, which makes the performance and life of the material decline. Therefore, it is necessary to enhance the aging resistance of XLPE without affecting its mechanical properties and insulating properties, so as to extend its service life. In this work, the structural characteristics and cross-linking mechanism of XLPE are introduced, the aging process and influencing mechanism are systematically analyzed, and the life decay problems of XLPE due to aging are explored by using methods such as the temperature Arrhenius equation and the inverse-power law of voltage. The improvement strategies such as grafting, blending, and nano-particle modification can be used to enhance the thermal stability, antioxidant performance, and thermal aging resistance of XLPE, thereby extending its service life. Finally, the strategies of adjusting and controlling the service life of XLPE cable insulation materials in the future are discussed, which provides theoretical guidance for further improving long-term stable operation of XLPE cable insulation materials.
Studies of edge poloidal rotation and turbulence momentum transport during divertor detachment on HL-2A tokamak
Long Ting, Ke Rui, Wu Ting, Gao Jin-Ming, Cai Lai-Zhong, Wang Zhan-Hui, Xu Min
Abstract +
In a magnetic confinement fusion device, the plasma undergoing nuclear fusion reaction must be maintained in a high-temperature and high-density confinement state for a long enough time to release high energy, while the heat loads on the divertor target plates need to be reduced to avoid damage to wall at the same time. The latter is one of the key challenges of ITER and commercial fusion reactors in future. Divertor detachment provides an effective solution to reduce the heat load on the target plate of tokamak. However, this may result in the change of plasma states at the boundary, thus affecting the plasma confinement. In this paper, edge plasma poloidal rotation and turbulence momentum transport are studied experimentally during the divertor detachment in the L-mode discharge of HL-2A tokamak. The detachment is achieved by injecting a mixture of gas (60% nitrogen+40% deuterium) into the divertor. The gas mixture is injected by pulsed injection, with pulse length being in a range of 5—20 ms. During the divertor detached phase, both the ion saturation current density and the heat flux to the outer target plate decrease considerably. The enhanced radiation is also observed in the divertor and X-point region. It is found that in the process of attachment-to-pre-detachement, the $ \boldsymbol{E}\times \boldsymbol{B} $ poloidal flow velocity in the near scrape-off layer (SOL) changes from ion magnetic drift direction to electron magnetic drift direction. The turbulent driving force of poloidal flow, which is characterized by the negative radial gradient of momentum transfer flux (Reynolds stress), shows the same trend. In the detached phase, both the $ \boldsymbol{E}\times \boldsymbol{B} $flow and the Reynolds force become very small. Therefore, the dynamics of $ \boldsymbol{E}\times \boldsymbol{B} $ poloidal flow velocity in the SOL is consistent with the evolution of rotation driving effect induced by the turbulent momentum transport. Combined with the $ \boldsymbol{E}\times \boldsymbol{B} $ poloidal flow measured by the probe in the SOL and the beam emission spectrum inside the LCFS, the $ \boldsymbol{E}\times \boldsymbol{B} $ poloidal velocity shearing rate near the LCFS can be inferred. Compared with the attached state, when the divertor is detached, the edge poloidal flow shearing rate decreases significantly, leading to the obviously enhanced turbulence level. Under the influence of both enhanced turbulent transport and radiation, the global confinement degrades moderately. The energy confinement time decreases about 15% and the confinement factor $ {H}_{89-P} $ decreases about 10%. These results indicate that edge turbulent transport and plasma rotation dynamics play a role in the core-edge coupling process in which the divertor detachment affects the global confinement.
Influence of morphological characteristics of graphene on its field emission properties
Zheng Qin-Ren, Zhan Fu-Zhi, She Jun-Yi, Wang Jian-Yu, Shi Ruo-Li, Meng Guo-Dong
Abstract +
Graphene is one of the most potential field emission cathode materials due to its excellent electrical, thermal, and mechanical properties, as well as rich edge structures. In this paper, we study the growth parameters of graphene prepared by chemical vapor deposition, and prepare three kinds of morphologies of graphene: single-layer graphene, graphene islands, and graphene with buffer layers, and then we explore the influence of the morphological characteristics of graphene on its field emission properties, and analyze the mechanism of influence of the morphological characteristics of graphene on its field emission properties through COMSOL. Comparing with single-layer graphene, the turn-on field of graphene islands and that of graphene with buffer layers decrease to 5.55 V/μm and 5.85 V/μm, respectively. The current densities also increase to 40.3 μA/cm2 and 26.4 μA/cm2, respectively. On the other hand, the field emission currents of single-layer graphene and graphene with buffer layers are more stable. In a 5-hour test, the current densities only decrease by 2% and 4%, respectively. COMSOL simulation shows that the morphological characteristics of graphene have significant influences on the electric field distribution characteristics and heat dissipation capacity. Graphene islands and graphene with buffer layers have exposed edges, leading to local electric field concentration, and thus improving field emission properties. The graphene islands are distributed discretely on the substrate, forming no continuous graphene film and lacking transverse heat dissipation channels, so the accumulation of heat will cause damage to the graphene emitter, and affect the stability of its field emission current. This study will be of great benefit to the understanding of the influence of the morphological characteristics of graphene on its field emission properties, and improving the field emission properties of graphene materials.
Modeling of Ferroelectric Phase Transitions with Graph Convolutional Neural Networks
Ouyang Xin-Jian, Zhang Yan-Xing, Wang Zhi-Long, Zhang Feng, Chen Wei-Jia, Zhuang Yuan, Jie Xiao, Liu Lai-Jun, Wang Da-Wei
Abstract +
Ferroelectric materials are widely used in functional devices, however, achieving convenient and accurate theoretical modeling of them has been a long-standing issue. Here, we propose a noval approach for the modeling of ferroelectric materials using graph convolutional neural networks (GNN). This approach utilizes GNNs to approximate the potential energy surface of ferroelectric materials, which then serves as a calculator to enable large-scale molecular dynamics simulations. Given atomic positions, the well-trained GNN model can provide accurate predictions on the potential energy and atomic forces, reaching a level of accuracy of 1 meV, which is comparable to ab inito calculations but with much less time expense by orders of magnitude. Benefiting from the high accuracy and fast prediction of neural networks, we further combine it with molecular dynamics simulations to investigate two representative ferroelectric materials—bulk GeTe and CsSnI3, and successfully produce their temperature-dependent structural phase transitions, which are in good agreement with experimental observations.During the GNN-based MD simulation of GeTe, we obeserve an unusual negative thermal expansion around the region of its ferroelectric phase transition, which has been reported in previous experiments. For CsSnI3, we correctly obtain the octahedron tilting patterns associated with its phase transition sequence. These results demonstrate the accuracy and reliability of GNNs in the modeling of potential energy surfaces of ferroelectric materials, providing a universal approach for their theoretical investigations.
Automatic fabrication system of optical micro-/nanofiber based on deep learning*
Liu Hong-Jiang, Liu Yi-Fei, Gu Fu-Xing
Abstract +
The wide range, high precision, and dynamic real-time measurement of diameter are crucial for achieving low loss transmission and controlling dispersion in the preparation process of micro-/nanofiber. In view of the problems of small diameter regulation range, complex operation and long-time consumption of the existing preparation methods, this paper firstly realizes the automatic detection system of micro-/nanofiber based on deep learning neural network algorithm. In this paper, the image segmentation method in computer vision is used to make high-quality multi-scale micro-/nanofiber datasets, and the improved YOLOv8-FD(You Only Look Once version 8-Fiber Detection) algorithm based on small target detection is used to automatically detect the diameter of micro-/nanofiber.

Through image segmentation and identification of the target of single pixel size in the microscopic image, the diameter detection of micro-/nanofiber is finally realized. In this process, the real-time diameter of micro-/nanofiber is obtained through image information, and then the micro-/nanofiber small target is accurately segmented to achieve the precise detection of mAPIoU=50=0.995 and mAPIoU=50:95=0.765 on the micro-/nanofiber multi-scale target dataset with extremely high accuracy. The algorithm-based construction of a high-precision micro-/nanofiber automatic preparation system enables real-time accurate segmentation of fiber edges, calculation of fiber diameter, and feedback to the control system for achieving automated preparation of fibers with arbitrary diameters. Additionally, it facilitates detection of micro-/nanofiber within the range of 462 nm to 125 μm. The average response time for reasoning is 9.6 ms, while maintaining a detection error below 2.95%.

In addition, compared with other micro-/nanofiber diameter detection methods based on optical imaging and mode cutoff, this method shows advantages of high precision, high speed and arbitrary diameter preparation for diameter detection based on deep learning neural networks. The system is well-suited for high-precision real-time measurement and automated, precise preparation of micro-/nanofiber, thereby offering a novel approach for the development of low-loss transmission and adjustable dispersion micro-/nanofiber devices.

Study on binary-amplitude far-field super-resolution achromatic focusing devices
Wu Zhi-xiang, Li Xin-yu, Huang Zi-wen, Zou Yi-yang, Xiong Liang, Deng Hu, Shang Li-ping
Abstract +
The far-field super-resolution focusing devices possess characteristics such as super-resolution focusing, achromatic, small size and easy machining, making them highly promising in optical imaging, optical microscopy and lithography. In this study, we propose a binary-amplitude modulation-based method for generating far-field super-resolution achromatic focusing. By leveraging the principles of optical super-oscillation along with angular spectral diffraction theory and binary particle swarm optimization (BPSO), we optimize the binary amplitude-type far-field super-resolution focusing devices with radii of 100λ and the focal length of 25λ (λ=632.8nm) for λ1=405nm, λ2=532nm and λ3=632.8nm, respectively. Additionally, an achromatic metalens is integrated using Boolean AND operation. To assess the feasibility of our proposed approach, numerical simulations are conducted via COMSOL Multiphysics employing FEM analysis. The simulation results demonstrated that the generated spot located at 25.105λ、25.106λ, and 25.105λ, respectively. The corresponding full width at half maximum (FWHMs) are 0.441λ1(0.179μm), 0.469λ2(0.249μm) and 0.427λ3(0.270μm), which are smaller than the Abbe diffraction limit, and the far-field super-resolution achromatic focusing is realized. The sidelobe ratios are at low levels:12.5%, 12.6%, and 14.2%. The binary amplitude-type far-field super-resolution achromatic devices have the advantages of easy machining, achromatic and super-resolution, and are suitable for miniaturization and integration of optical systems.
Molecular dynamics simulation of nanodroplet impacting on high-temperature plate wall
Feng Shan-qing, Gong Lu-Yuan, Quan Sheng-Lin, Guo Ya-Li, Shen Sheng-Qiang
Abstract +
The process of droplet impacting on a high-temperature wall is a common occurrence in both daily life and industrial instruments. Most of the present researches investigated this phenomenon experimentally or in the macroscopic view. To explore the heat transfer mechanism after nanodroplet impact on hige-temperature surface, the molecular dynamics simulation was carried out to investigate droplet evolution and the influence of surface temperature on its evolution. Droplets containing 10,741 argon atoms impacted on the copper plates with temperatures of 85 K, 150 K, 200 K, 250 K, and 300 K, respectively. The number of droplet evaporation atoms was statistically obtained, the droplet barycenter displacement was analysed, the droplet density and temperature inner distributions were acquired. It is shown that the droplet presents different characteristics on the wall with different temperatures. The droplet spreads stably on the wall at 85 K as shown in Figure 1(a), while when the teperature of the wall rises to 150K, the droplet evaporates slowly and completelyas shown in Figure 1(b), and for the wall temperatures 200 K, 250 K and 300 K, the Leidenfrost phenomenon is found for the droplet is suspended above the wall as shown in Figure (c)(d)(e).. For the temperature conditions when the Leidenfrost phenomenon occurs, the higher of the wall temperature, the faster the droplet evaporating, the earlier of the detachment moment from the wall, the greater the droplet detaching velocity, and the larger the final suspending droplet volume. By analyzing the density and temperature distribution of the droplet at the moment when it detaches from the wall, it is found that the evaporation process is faster and a thicker vapor layer is generated due to the higher heat flux of the high-temperature wall, which will hinder the heat exchange, so that the average temperature of the droplet is lower and the average density is smaller.
Thermoelectric properties of Co doped TiNiCoxSn alloys fabricated by melt spinning
Junsong He, Feng Luo, Jian Wang, Shiguan Yang, Lin Cheng, Lijun Zhai, Hongxia Liu, Yan Zhang, Yanli Li, Zhigang Sun, Jifan Hu
Abstract +
Although TiNiSn-based half-Heusler thermoelectric materials obtain high power factors, their high lattice thermal conductivity greatly hinders the improvement of thermoelectric properties. In this paper, TiNiCoxSn (x=0~0.05) samples were prepared by melt spinning combined with spark plasma sintering method and their phase, microstructure and thermoelectric properties are studied. The XRD results show that the main phase of all samples is TiNiSn phase, and no other impurity phases are found, indicating that the high purity single phase can be prepared by rapid quenching process combined with SPS process. During the solidification process, the large cooling rate (105-106 K/s) is conducive to obtaining the uniform nanocrystalline structure. The grains are closely packed with a grain size of 200-600 nm. The grain size decrease to 50-400 nm for the Co-doping samples, which indicates that Co doping can reduce the grain size. For the x=0 sample, the thermal conductivity of the rapid quenching sample is significantly lower than that of bulk sample, with an average decrease of about 17.8%. Compared with the TiNiSn matrix, the thermal conductivity of the Co-doping samples are significantly reduced, and the maximum decrease is about 38.9%. The minimum value of lattice thermal conductivity of TiNiCoxSn samples is 3.19 W/mK. Therefore, Co doping can significantly reduce the кl of TiNiCoxSn (x=0.01~0.05) samples. With the increase of Co doping amount x, n/p transition is observed in the TiNiCoxSn samples, resulting in a gradually decrease of the conductivity and the power factor, and finally the deterioration of the electrical transport performance. Among them, the TiNiSn sample obtains the highest power factor of 29.56 W/mK2 at 700 K. The zT value decreases with the Co doping amount x, and the maximum zT value of TiNiSn sample at 900 K is 0.48. This work shows that the thermal conductivity of TiNiSn can be effectively reduced by using the melt spinning process and magnetic Co doping.
Micro-structural and Optical Properties of Diamond-like Carbon Films Grown by Magnetic field-assisted Laser Deposition
Lu Yimin, Wang Yujie, Xu manman, Wang Hai, Xi Lin
Abstract +
Inhomogeneous magnetic field was introduced into pulsed laser deposition process, in order to discover new properties of diamond-like carbon film grown under magnetic field, offering the theoretical and experimental basis for furtherly enhancing sp3-bond content in this film. Distribution of the magnetic strength and flux lines induced by a rectangular permanent magnet was calculated. And then, flying trace of the carbon ions in the magnetic field was also simulated by the iterative method, which indicated that the carbon ions could not expand freely and they were restrained to accumulate around the center region of the magnet source. Besides the surface interference, measurement and the fitted results of ellipsometry parameters showed that magnetic field had important influence on layer-thickness distribution and optical constant of the pulsed laser deposition-grown diamond-like carbon film. Meanwhile, it was indicated that inhomogeneity of the layer-thickness distribution and optical constant increased when the magnetic strength was higher. Micro-structure of diamond-like carbon film was affected seriously by magnetic field, which was indicated by Raman spectra. Magnetic field could enhance the local stress in the carbon matrix net, increasing the sp3-bond content. Theoretical and experimental research showed that a suitable magnetic strength could excite micro-structure of diamond-like carbon film significantly, however, the high-quality diamond-like carbon coating with practical application value would be obtained by technological adjustment.
Gas sensors based on SnS2/In2O3 for high performance NO2 detection at room temperature
Chen Jin-Long, Tao Ran, Li Chong, Zhang Jian-Lei, Fu Chen, Luo JingTing
Abstract +
NO2 is a toxic gas that reacts with other organic compounds in the air, causing air pollution and posing a significant risk to humans. Therefore, a gas sensor is needed to detect NO2. However, conventional NO2 gas sensors are difficult to operate at room temperature (25℃). In this study, NO2 gas sensing by SnS2/In2O3 at room temperature (25℃) is reported. In2O3 quantum dots and SnS2 nanosheets were prepared by the hot-injection and hydrothermal methods. By virtue of the unique two-dimensional structure of SnS2, In2O3 was decorated on it, and the composite enhanced its sensing performance. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The results demonstrate that the composites prepared by 52% In2O3 exhibit the best sensing response. The fabricated sensor shows a response of 26.6 to 1000 ppb NO2, along with fast response and recovery times, respectively, at room temperature (25℃). Moreover, this sensor demonstrates excellent reproducibility and selectivity. The heterojunction structure increases the number of active sites and accelerates the gas transport, which promotes charge transfer and gas desorption to improve NO2 gas sensing performance. This excellent sensing performance has a great application prospect in NO2 detection.
Mechanical Strengthening Property of SiC Material Covered with Multilayer Graphene From Molecular Dynamic Simulation
Chen Jing-Jing, Zhao Hong-Po, Wang Kui, Zhan Hui-Min, Luo Ze-Yu
Abstract +
A large number of practices have shown that under the coupling influence of complex working conditions and frequent reciprocating contact, the surface of semiconductor devices in micro/nano electromechanical systems often produces adhesive wear, which is the essential reason result in short durability service life and decline in contact mechanical properties for microelectronics semiconductor devices. However, graphene can significantly improve the interface properties of mechanical and electronic components due to its excellent mechanical properties, such as high carrier concentration, good thermal conductivity, and low shear. Thus, this study of mechanical strengthening properties and plastic deformation of SiC material with covered multi-layer graphene in MEMS devices will play a significant role in improving the durability service life of MEMS devices, and understanding its strengthening and toughening mechanism. Therefore, this paper studies and discusses the effects of stacking type and extreme service temperature with low and high levels on the contact mechanical properties (maximum load, hardness, Young modulus, contact stiffness), micro-structure evolution, contact mass, fold morphology, and total length of dislocation. The atomic-scale mechanism of enhanced mechanical properties of SiC material with multi-layer graphene is explained. The research shows that the damage of carbon-carbon bond during the maximum indentation depth will lead to the loss of the excellent in-plane elastic deformation ability of graphene when the graphene stacking type is AB stacking, so that the maximum load-bearing capacity of the substrate covered by three layers of graphene will drop linearly. In addition, the mechanical properties of SiC material coated with three graphene layers are twice than that pure SiC substrate, and the strengthening mechanism is mainly due to the increase of folds caused by the increase of multilayer graphene loading, which causes the contact quality between the SiC substrate and the virtual indenter to decrease, thus increasing the interface contact stiffness. The increase of the active temperature will stimulate the increase of the atomic vibration frequency, which will cause the number of interface contact atoms to increase greatly, and the interface contact stiffness will weaken, and finally lead to the increase of interface contact quality. This reason is that the mechanical properties of SiC substrate coated with multilayer graphene will decrease approximately linearly with the extreme services low temperature to high temperature. In addition, the stress concentration in the subsurface layer of SiC substrate can induce the evolution of its micro-structure, and the increase of the number of graphene layers on the substrate can effectively reduce the stress concentration distribution in the subsurface layer of the substrate.
Relationship between solar energetic particle intensity and coronal mass ejections and its associated type II radio bursts
Yan Hao, Ding Liu-Guan, Feng Li, Gu Bin
Abstract +
Based on the multiple-vantage observations of STEREO, SOHO, wind and other spacecraft, the fast and wide coronal mass ejections (CME) during the 24th solar cycle from January 2010 to September 2014 are selected in this paper. Using the outputs of Richardson’s (2014) empirical model of solar energetic particle (SEP) intensity under different conditions, the effects of its associations such as CME, pre-CME, and type II radio bursts, on SEP intensity are analyzed, and the relationship between SEP event and these characteristics is also discussed. The main conclusions are as follows. 1) The presence or absence of pre-CME within 13 h before fast CME significantly improves the model prediction effect and has a significant influence on whether fast CME produces SEP event. Compared with the events without pre-CMEs, the events with pre-CMEs have a low proportion of false alarms (FR: 47.7% vs. 70%). However, the number of pre-CMEs does not improve the model output. 2) CMEs with type-II radio bursts have significantly lower FR to generate SEP events than fast CMEs without type-II radio bursts (42% vs. 68%). And selecting type-II radio bursts as a constraint will filter out some small/weak SEP events, the relationship between model predictions and observations especially for large SEP events (e.g. Ip ≥ 0.01 pfu/MeV) will stand out. Moreover, if the type-II radio enhancement is taken into account, FR can be further reduced to 29.4%, and the proportion of hits can be further increased (HR: 48.5%), and the model prediction is significantly improved. 3) The larger the start frequency of type II radio bursts, the smaller the end frequency is, and FR decreases slightly, but at the same time, a large number of SEP events are excluded by this condition, and the results show that the constraints on the start/end frequency of type-II radio bursts do not improve the model predictions distinctly. 4) If the sub-classification of type-II radio bursts is considered as the model constraint, the CMEs associated with multi-band type-II radio bursts have better model predictions than those with single-band events. For example, m-DH-km type-II radio bursts have lower FR (35.4%) and higher HR (48%), and the accuracy of empirical model is higher. In summary, we find that in addition to the velocity and angular width of CME, the associations of pre-CME, type II radio bursts and their enhancement, and multi-band sub-classification are the favorable conditions for CME to generate SEP events. The SEP intensities obtained by the empirical model have better consistency with the observations, and better predictions can be obtained. This investigation indicates that SEP events are more likely generated by fast and wide CMEs accompanied by pre-CMEs, multi-band type II radio bursts and their enhancements, which seem to serve as discriminative signal for SEP-rich and SEP-poor CMEs.
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