bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of the terahertz spectra generated from laser induced plasma
Authors: Li Xiao-Lu , Bai Ya , Liu Peng ,   State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China,   University of Chinese Academy of Sciences, Beijing 100049, China,   Collaborative Innovation Center of IFSA (CICIFSA), Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

Broadband terahertz (THz) emission generated from laser induced gas plasma provides an effective tool for studying nonlinear spectrum, imaging and remote sensing. Recently, the contribution of plasma oscillation to the THz emission was revealed from the nitrogen molecules pumped by intense two-color laser pulses. Plasma oscillation contributes only to the THz emission at relatively low plasma density due to negligible plasma absorption. More generally, with the THz emission generated from the ionizing gaseous medium, the surrounding plasma is expected to play an important role in the generation process. For the THz radiation from laser filament, the plasma region is extended in the laser propagation direction, and the effect of surrounding plasma on the emitted THz spectrum needs studying. In this work, we investigate the relation between pump power and filament length from THz spectrum emitted by air filament driven by two-color laser pulse. The time domain spectrum of THz field is recorded by an electro-optic (EO) sampling technique. In our experiments, significant frequency shifts are observed as the pump power and the filament length increase, and we find that the center frequency of the THz radiation is shifted towards longer wavelength, which is the so called red-shift of the THz spectrum. This red-shift is independent of THz radiation angle. The observations are explained by the plasma absorption inside the air filament. Our theoretical model is based on three mechanisms: the ionization-induced photocurrent, the plasma current oscillation and the plasma absorption. We coherently add up all the local THz fields inside the air filament, and simultaneously consider the plasma absorption induced correction of the THz spectrum. The simulation well reproduces the experimental observation. The skin depth decreases as the plasma density increases, thus the plasma absorption dominates the red-shift process. If the skin depth is larger than the filament length, the plasma oscillation contributes to the THz spectrum dominantly, and thus leading to the blue-shift of THz spectrum. Our results indicate that for the extended filament length or higher plasma density, the combining effect of photocurrent, plasma oscillation and absorption, results in the observed low-frequency broadband THz spectrum. Our study offers a method of coherently controlling the broadband THz spectrum.
Magnetic field and inductance of filament conductor segment model with current continuity
Authors: Cui Xiang ,   State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China
Published: December 2020

Traditional current-carrying model of filament conductor segment is the basic model for analyzing the magnetic field in a closed conductor loop. Although it does not satisfy the law of current continuity, it is still suitable for analyzing the magnetic field in the closed conductor loop. However, for the current distribution problem of some local multi-branch parallel-connection conductor segments in a closed conductor loop, the traditional model cannot fully reflect the interaction between magnetic fields of the local multi-branch parallel-connection conductor segments. For this reason, the displacement current model proposed in the existing literature satisfies the law of current continuity and solves the above problem well. But, there remain some problems to be solved, such as incomplete theory, inconsistency and complex formulae in the existing literature. In this paper, a conductive current-carrying model of filament conductor segment is proposed, which ensures current continuity inside, outside, and on two terminals of the filament conductor segment. The differential equation of total magnetic field with more profound physical connotation and the formulae of vector magnetic potential are derived in detail. Further, the formulae for calculating magnetic field energy and inductance of the conductive current-carrying model of filament conductor segment are proposed, which greatly reduces the computational complexity and makes up for the shortcoming of model in the existing literature. An example given in this paper verifies the correctness of the above theory and formulae.
Strong coupling between metasurface based Tamm plasmon microcavity and exciton
Authors: Wu Han , Wu Jing-Yu , Chen Zhuo ,   School of Physics, Nanjing University, Nanjing 210000, China
Published: December 2020

In this paper, the Tamm plasmon and its interaction with excitons in a plasmon microcavity consisting of metasurface, dielectric spacer, distributed Bragg reflector (DBR) are studied. The reflection phase of light on the surface can be controlled by changing the structure parameters in the metasurface. When the thickness of the dielectric spacer layer of the microcavity structure keeps unchanged, the resonance position of the Tamm plasmon mode supported by the microcavity structure can be adjusted by varying the structure parameters of the metasurface, and thus providing more degrees of freedom for regulating the Tamm plasmon mode. In addition, by comparing the traditional metal thin film-dielectric spacer-DBR structure, we find that the introduction of metasurface and its regulation of reflection phase can make the metasurface-dielectric spacer-DBR structure support the Tamm plasmon mode resonance at the same wavelength under a smaller thickness of spacer. And combining the local characteristics of the super-surface field, the model volume of Tamm plasmon can be reduced effectively. On this basis, we compare the interaction of traditional and metasurface-based Tamm plasmon with single-layer tungsten disulfide (WS2), and find that metasurface-based Tamm plasmon can produce stronger photon-exciton coupling and obtain larger Rabi splitting.
High efficiency green perovskite light-emitting diodes based on exciton blocking layer
Authors: Wang Run , Jia Ya-Lan , Zhang Yue , Ma Xing-Juan , Xu Qiang , Zhu Zhi-Xin , Deng Yan-Hong , Xiong Zu-Hong , Gao Chun-Hong ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China,   Applied Basic Research Base of Optoelectronic Information Technology of Hunan Province, Hengyang Normal University, Hengyang 421002, China
Published: December 2020

In recent years, metal halide perovskite materials, owing to their excellent photoelectric properties including high photoluminescence quantum yield, high color purity, tunable band gap, etc., have been regarded as new-generation lighting sources and are widely used to fabricate perovskite light-emitting diodes (PeLEDs). Though great progresses have been made in recent years, neither the efficiency nor stability has not yet reached the requirements of commercialization. Thus, further improvement is needed. In this work, a small organic molecule material, namely 4,4'-cyclohexylidenebis[N,N-bis(p-tolyl)aniline] (TAPC) with a wide bandgap and a good hole transport ability, is used as an exciton blocking layer by utilizing the spin-coating method to improve the stability and efficiency of PeLEDs. Highly efficient and stable CsPbBr3 PeLEDs are finally realized. The physical mechanism related to the improved electroluminescence performance is investigated thoroughly. Firstly, the stepped energy level alignment is formed, since the highest occupied molecular orbital energy level (HOMO) of TAPC is located between the HOMO of (3,4-ethylenedioxythiophene):poly(p-styrene sulfonate) (PEDOT: PSS) and the valence band of CsPbBr3, which is beneficial to hole injection and transport. Meanwhile, the lowest unoccupied molecular orbital level of TAPC is high enough to prevent electrons from leaking into the anode effectively and confine electrons and excitons well in the emitting layer. Secondly, the introduction of the TAPC layer can avoid the direct contact between the perovskite light emitting layer and the strong acidic layer of PEDOT:PSS, thereby eliminating the related excitons quenching, which can further increase the radiative recombination.
Perovskite light-emitting diodes based on solution-processed metal-doped nickel oxide hole injection layer
Authors: Wu Jia-Long , Dou Yong-Jiang , Zhang Jian-Feng , Wang Hao-Ran , Yang Xu-Yong ,   Shanghai University Microelectronic R&D Center, Shanghai University, Shanghai 201900, China,   Key Laboratory of Advanced Display and System Applications, Ministry of Education, Shanghai University, Shanghai 200040, China
Published: December 2020

Formamidinium lead bromide (FAPbBr3) perovskite nanocrystals (NCs) have attracted great attention due to their remarkable performances of low cost, high color purity and tunable band gap. However, in a typical FAPbBr3 perovskite light-emitting diode(LED), PEDOT:PSS, with hygroscopic and acidic nature, serves as a hole injection layer (HIL), thus leading to the device stability to decrease seriously. Device stability is one critical issue that needs improving for future applications. Here in this study, the nickel oxide (NiO) film prepared by the solution method is adopted as the HIL of the FAPbBr3 perovskite LED to substitute detrimental PEDOT:PSS. Compared with the control device with PEDOT:PSS HIL, the resulting LED based on NiO film has the operating lifetime twice as great as that based on the PEDOT:PSS film. For further enhancing the performance of FAPbBr3 LED, two metal dopants (Cs and Li) are introduced to improve the hole injection capability of NiO film and the charge carriers’ balance of device. With Hall measurements, both NiO and Cs/Li-doped NiO demonstrate a full p-type semiconductor characteristic. Increasing the doping concentration in the film can increase the carrier concentration and reduce the carrier mobility. This decreased carrier mobility results from the increased scattering due to grain boundaries and impurity phases, seriously at high Cs/Li concentration. As a result, the device, based on the NiO film (doping 2 mol% Cs) shows the best performance with a maximum brightness value of 2970 cd/m2, current efficiency of 43 cd/A and external quantum efficiency (EQE) of 11.0%, thus its efficiency is increased nearly by twice compared with that of the PEDOT:PSS-based device. The results pave the way for making highly efficient and stability perovskite LEDs based on FAPbBr3 NCs.
Spatiotemporal evolution and spectral character of second harmonic generation in optical microresonator
Authors: Xu Xin , Jin Xue-Ying , Hu Xiao-Hong , Huang Xin-Ning ,   School of Instrument Science and Opto-electronics Engineering, Hefei University of Technology, Hefei 230009, China,   State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 710119, China
Published: December 2020

With the consideration of the second and the third order nonlinear effect, the Lugiato-Lefeve equation which describes the field evolution of the fundamental frequency wave and the second harmonic wave is introduced. Based on the Lugiato-Lefeve equation, the generation of the second harmonic wave in the SiN microresonator is analyzed, and the effect of the each parameter on the dual field is studied. Simulation results indicate that the stable field of the fundamental frequency wave is of flat top pulse, and the field of the second harmonic wave is of sinusoidal distribution. When the detuning parameter increases, the power of the dual wave inside the microresonator oscillates, and the stable power weakens, the stable light field is periodically varied. Moreover, the chaos emerges as detuning parameter becomes large. The stable field can be generated in the microresonator with the weak pump power. However, because of the high pump power, the dispersion and nonlinear effect are enhanced, resulting in the periodic light field. Furthermore, the oscillation of the dual power curve is aggravated, as the pump power increases. In addition, the turning patterns can be observed by choosing the special dimension of microresonator. Theoretical analysis results are significant for studying the generation of the second harmonic wave in the microresonator.
1.06 μm wavelength based high accuracy satellite laser ranging and space debris detection
Authors: Meng Wen-Dong , Zhang Hai-Feng , Deng Hua-Rong , Tang Kai , Wu Zhi-Bo , Wang Yu-Rong , Wu Guang , Zhang Zhong-Ping , Chen Xin-Yang ,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China,   Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China,   Key Laboratory of Space Object and Debris Observation, Chinese Academy of Sciences, Nanjing 210008, China
Published: December 2020

Classical satellite laser ranging (SLR) technology based on 532 nm wavelength usually adopts low energy laser to measure cooperative objects. However, for a very weak target, such as debris and lunar reflector arrays, laser ranging system should have much stronger detection capability than the laser ranging system for traditional application. A common way to improve system detection capability is to use high energy laser. With an additional frequency doubling crystal, it is more difficult to make a high energy laser based on 532 nm than that based on 1.06 μm, which restricts the improvement of system detection capability, and also gives rise to the short lifetime, poor system stability problems. Compared with 532 nm laser, the 1.06 μm laser has many advantages of high laser energy and power, high atmospheric transmissivity, and low background noise, thereby making it an ideal substitution for the traditional 532 nm SLR system. In this paper, we comparatively analyze the above-mentiond advantages of the 1.06 μm laser and other system’s key parameters such as detector efficiency and target reflection efficiency, calculate the echo photons one can obtain, and establish a 1.06 μm laser ranging system based on the existing 532 nm SLR at Shanghai Astronomical Observatory. Owing to the using of an InGaAs single photon detector, the system turns very compact, low cost, easy-to-be-installed and has almost no additional operation complexity than the 532 nm system. With this system, the high precision 1.06 μm laser ranging for cooperative objects based on InGaAs detector is carried out for the first time in China, and a ranging for space debris 1500 km away can also be realized. The ranging experiment shows with the same laser, SLR using 1.06 μm output reaches a detection efficiency of 7 times the detection efficiency the SLR using 532 nm output reaches, and the background noise only 1/5. This approves the advantages and feasibility of 1.06 μm system, and also shows its great potential application prospects in the high precision weak target laser detection in the day and night time. This paper provides a very easy operation, high compact and low cost method for the future high precision weak target laser ranging.
Effect analysis and magnetoelectric properties of hydrogen in Co-doped MoSe2 Co-growth
Authors: Zhang Bao-Jun , Wang Fang , Shen Jia-Qiang , Shan Xin , Di Xi-Chao , Hu Kai , Zhang Kai-Liang ,   Tianjin Key Laboratory of Film Electronic & Communication Devices, School of Electrical and Electronic Engineering, Tianjin University of Technology, Tianjin 300384, China
Published: December 2020

In this paper, Co3O4、MoO3 and Se powders were used as precursors in in-situ co-growth chemical vapor deposition method. Cobalt-doped MoSe2 nanosheets were grown on SiO2 substrate at 710 ℃. The influence of hydrogen content on its growth and regulation mechanism was discussed. Surface morphology analysis showed that the introduction of hydrogen promoted the formation of oxy-selenium metal compounds required for nucleation and the CoMoSe compound molecules required for lateral growth. AFM(atomic force microscope) results show that hydrogen is beneficial to the growth of single-layer two-dimensional cobalt-doped MoSe2. With the increase of the amount of Co3O4 precursor, the Raman and PL(photoluminescence) spectra of the sample showed red shift and blue shift, respectively, and the bandgap was modulated from 1.52 eV to 1.57 eV. The XPS(X-ray photoelectron spectroscopy) results analysis showed that the elemental composition ratio of Co was 4.4%. The magneto and electric properties of the samples were analyzed by SQUID-VSM(superconducting quantum interference device) and semiconductor parameter analyzer for electrical testing. The results show that MoSe2 changes from diamagnetic to soft magnetic after Co incorporation; the threshold voltage of back gate FETs is shifted by 5 V from pure MoSe2, and the off-state current is lower. This research provides a basis for the research and application development of ultra-thin two-dimensional materials.
The Boussinesq equation: Lax pair, Bäcklund transformation, symmetry group transformation and consistent Riccati expansion solvability
Authors: Liu Ping , Xu Heng-Rui , Yang Jian-Rong ,   School of Electronic and Information Engineering, University of Electronic Science and Technology of China, Zhongshan Institute, Zhongshan 528402, China,   School of Physics, University of Electronic Science and Technology of China, Chengdu 610054, China,   School of Physics and Electronic Information, Shangrao Normal University, Shangrao 334001, China
Published: December 2020

The Boussinesq equation is a very important equation in fluid mechanics and some other disciplines. A Lax pair of the Boussinesq equation is proposed. With the help of the truncated Painlevé expansion, auto-Bäcklund transformation of the Boussinesq equation and Bäcklund transformation between the Boussinesq equation and the Schwarzian Boussinesq equation are demonstrated. Nonlocal symmetries of the Boussinesq equation are discussed. One-parameter subgroup invariant solutions and one-parameter group transformations are obtained. The consistent Riccati expansion solvability of the Boussinesq equation is proved and some interaction structures between soliton-cnoidal waves are obtained by consistent Riccati expansion.
Comparative study of positive and negative pulsed discharge plasma characteristics of coaxial gun
Authors: Yu Xin , Qi Liang-Wen , Zhao Chong-Xiao , Ren Chun-Sheng ,   Key Laboratory of Materials Modification by Laser, Ion and Electron Beams of Ministry of Education, School of Physics, Dalian University of Technology, Dalian 116024, China
Published: December 2020

The coaxial gun plasma generated by pulsed discharge possesses the characteristics of high speed and high density, and has potential application value in the field of fusion, space propulsion and astrophysics. In this paper, the effect of positive and negative pulsed discharges on plasma characteristics are investigated and a theoretical model for analyzing the morphology of positive and negative pulsed current sheets is proposed. Positive and negative pulsed discharges are realized by changing the direction of the rectifier diode in the pulse power supply to change the direction of the recharging current. Through theoretical analysis, and measurements by using photodiode, Pearson probe, magnetic probe, HD camera, fast-framing camera and RGB image processing, the plasmas generated by positive and negative pulsed discharges are compared and investigated. Most of experimental diagnoses concentrate on investigating the plasma behavior in the coaxial gun muzzle on a microsecond-order time scale. Because radial and axial transport characteristics of plasma change little, we think, the plasma characteristics in the muzzle still depend on the characteristics of plasma in the coaxial gun. Therefore, the conclusion of the theoretical analysis of the current sheet in the coaxial gun is still valid for the plasma in the muzzle. The theoretical analysis shows that the positive pulsed current sheet presents a parabolic shape and the negative pulsed current sheet displays a convex shape, which makes the negative pulsed current sheet sweep more efficiently and a large amount of plasma is concentrated near the inner electrode, namely the cathode, so the negative pulsed plasma is denser. For the positive pulsed plasma, near the inner electrode the plasma is thin and the magnetic pressure is powerful, and near the outer electrode, the plasma is dense and the magnetic pressure is weak. Therefore, the positive pulsed plasma is faster in movement speed but easier to split, and because of its dispersion, its transport stability is not so good as that of the negative pulsed plasma. The experimental results accord with the theoretical analyses. The final conclusion shows that under the same discharge parameters, the positive pulsed discharge produced plasma is faster in movement speed but more likely to split, and the negative pulsed discharge created plasma is denser in density and more stable. Therefore, for obtaining a higher density plasma, the negative pulsed discharge is recommended, and for achieving a high-speed plasma source, the positive pulsed discharge is advised to be adopted.
Controllable growth of GeSi nanowires on trench patterned Si(001) substrate
Authors: Gao Fei , Feng Qi , Wang Ting , Zhang Jian-Jun ,   Key Laboratory of Nanophysics and Device, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Controllable growth of nanowires is a prerequisite for addressability and scalability of nanowire quantum devices. By combining top-down nanofabrication and bottom-up self-assembly, site-controlled GeSi nanowires with two (105) facets can be grown on Si (001) substrate with pre-patterned trenches. Trenches along the [100] or [010] crystallographic direction with 60 nm in width and 6 nm in height are fabricated on Si substrate by electron beam lithography and reactive ion etching. Subsequently, a 60-nm-thick Si buffer layer is grown at 330–400 ℃ on the patterned substrate to improve the surface quality. The facets at the tip of the trenches transform into (11n) after depositing the Si buffer layer. Self-organized GeSi nanowires form inside the trenches by depositing the 6-nm-thick Si67Ge33 film at 450 ℃ followed by 1 h annealing at 510 ℃. The GeSi nanowires are (105)-faceted with an average height of approximately 7 nm. Furthermore, we systematically study the influence of annealing temperature, Ge concentration and pattern period on the formation of site-controllable GeSi nanowire on a patterned Si (001) substrate. The GeSi nanowires can be formed only inside the trenches within a specific annealing temperature ranging from 500 ℃ to 520 ℃. It is also discovered that GeSi nanowires are very sensitive to Ge concentration, as they cannot form at lower Ge concentration due to a large nucleation energy barrier. In contrast, high Ge concentration will lead to the discontinuity of nanowires caused by higher atomic diffusion barrier. The generated GeSi nanowires in the trenches exhibit similar dimensions at different pattern periods, which indicates that the growth process is thermodynamically determined. Overall, we realize the controllable growth of the GeSi nanowires, while the length of nanowires can reach the millimeter even centimeter scales, replying on the patterned trench length. The above results offer a controllable growth method of the Ge nanowires, which could potentially lead to the scalability of the Ge quantum devices on Si substrates.
Optical resonance enhanced Cs activated nano-structured Ag photocathode
Authors: Peng Xin-Cun , Wang Zhi-Dong , Deng Wen-Juan , Zhu Zhi-Fu , Zou Ji-Jun , Zhang Yi-Jun ,   Engineering Research Center of Nuclear Technology Application, Ministry of Education, East China Institute of Technology, Nanchang 330013, China,   Engineering Research Center of New Energy Technology and Equipment of Jiangxi Province, East China Institute of Technology, Nanchang 330013, China,   School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

Metallic photocathodes have drawn attention due to their outstanding performances of ultrafast photoelectric response and long operational lifetime. However, due to their high work function and the large number of scattering events, metallic photocathodes typically are driven by ultraviolet laser pulses and characterized by low intrinsic quantum efficiency (QE). In this work, a new type of Mie-type silver (Ag) nano-sphere resonant structure fabricated on an Ag/ITO composite substrate is used to enhance the photocathode QE, where Mie scattering resonance is used to enhance the local density of optical state and then to improve the light absorption and electron transporting efficiency in Ag nano-spheres. The cesium (Cs) activation layer is also used to lower the electron work function and then to excite photoemission in the visible waveband for Ag photocathode. The optical characteristics of Ag nano-sphere arrays are analyzed by using finite difference time domain method. For the investigated Ag nano-sphere array, theoretical results show that Mie-type electric dipole resonance modes can be obtained over the 400–600 nm waveband by adjusting the sphere diameter, and the large resonance-enhanced absorption can be achieved in nanospheres at the resonance wavelength. The Ag nano-spheres are fabricated on the Ag/ITO substrate by magnetron sputtering and annealing process, then the Cs activation layer is deposited on surface, and finally QE is measured in an ultra-high vacuum test apparatus. Experimental results show that over 0.35% of QE is obtained for Ag nano-sphere particle (with a diameter of 150 nm) at a wavelength of 425 nm, and the wavelength positions of QE maxima are in agreement with Mie resonance for corresponding geometry predicted from the computational model. Given these unique optoelectronic properties, Ag nanophotonic resonance structured photocathodes represent a very promising alternative to photocathodes with flat surfaces that are widely used in many applications today.
Dynamics of ring dark solitons in Bose-Einstein condensates
Authors: Guo Hui , Wang Ya-Jun , Wang Lin-Xue , Zhang Xiao-Fei ,   Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi’an 710600, China,   School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China,   Department of Arts and Sciences, Shaanxi University of Science and Technology, Xi’an 710021, China
Published: December 2020

Soliton is an exotic topological excitation, and it widely exists in various nonlinear systems, such as nonlinear optics, Bose-Einstein condensates, classical and quantum fluids, plasma, magnetic materials, etc. A stable soliton can propagate with constant amplitude and velocity, and maintain its shape. Two-dimensional and three-dimensional solitons are usually hard to stabilize, and how to realize stable two-dimensional or three-dimensional solitons has aroused the great interest of the researchers. Ring dark soliton is a kind of two-dimensional soliton, which was first theoretically predicted and experimentally realized in nonlinear optical systems. Compared with the usual two-dimensional solitons, ring dark solitons have good stability and rich dynamical behaviors. Owing to their highly controllable capability, Bose-Einstein condensates provide a new platform for studying the ring dark solitons. Based on the recent progress in Bose-Einstein condensates and solitons, this paper reviews the research on the analytic solutions, stability, as well as the decay dynamics of ring dark solitons in Bose-Einstein condensates. A transform method is introduced, which generalizes the analytic solutions of ring dark solitons from a homogeneous system with time-independent nonlinearity to a harmonically trapped inhomogeneous system with time-dependent nonlinearity. The stability phase diagram of the ring dark soliton under deformation perturbations is discussed by numerically solving the Gross-Pitaevskii equations in the mean-field theory. A method of enhancing the stability of ring dark solitons by periodically modulating the nonlinear coefficients is introduced. It is also shown that the periodically modulated nonlinear coefficient can be experimentally realized by the Feshbach resonance technology. In addition, we discuss the dynamics of the decay of ring dark solitons. It is found that the ring dark soliton can decay into various vortex clusters composed of vortices and antivortices. This opens a new avenue to the investigation of vortex dynamics and quantum turbulence. It is also found that the ring dark solitons combined with periodic modulated nonlinearity can give rise to the pattern formation, which is an interesting nonlinear phenomenon widely explored in all the fields of nature. Finally, some possible research subjects about ring dark solitons in future research are also discussed.
Effect of stacking fault tetrahedron on spallation of irradiated Cu via molecular dynamics study
Authors: Zhu Qi , Wang Sheng-Tao , Zhao Fu-Qi , Pan Hao ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China,   Graduate School of China Academy of Engineering Physics, Beijing 100088, China
Published: December 2020

Stacking fault tetrahedron (SFT) is a common type of three-dimensional vacancy clustered defect in irradiated FCC metals and alloys, which has a great influence on the mechanical properties of the materials. Previous researches mostly concentrated on the effect of SFT on the mechanical response of material under quasi-static or constant strain rate loading condition, while very few studies focused on its influence on mechanical properties under the shock loading condition. Spallation is a typical failure mode of ductile metal material under shock loading, and the initial defects in the material have a great influence on the spallation behavior. In this study, molecular dynamics simulation is carried out to investigate the influence of SFT on spallation behavior of irradiated copper single crystal under different shock intensities. Copper single crystal with a perfect structural model is also investigated under the same simulation condition for comparison. The model is divided into two parts: the flyer and the target. The shock wave is generated by moving the flyer at a velocity in a range of 1.0–2.5 km/s along the [111] crystallographic orientation to achieve the desired shock-state particle velocity Up in a range of 0.5–1.25 km/s. The time evolution of pressure, free surface velocity and corresponding microstructure, are analyzed in detail to illuminate the spallation behavior of the Cu with SFT. It is revealed that the SFT collapses during shock compression and induces the generation of dislocations and stacking faults in the material. Subsequently, spallation happens when the voids nucleate and grow in the region of dislocations and stacking faults. Moreover, the materials show different spallation behaviors at different shock intensities. When Up ≤ 1.0 km/s, only elastic deformation occurs in perfect single crystal copper under shock compression, but in the copper with SFT, local defects appear and plastic deformation occurs due to the collapse of SFT under shock compression. The influence of SFT on spallation is most pronounced at a medium shock intensity. When Up = 0.75 km/s, the local defects caused by the collapse of SFT provide a wider nucleation area for the voids and promote the heterogeneous nucleation of the voids, resulting in the decreasing of the spall strength. The void nucleation of single crystal copper with SFT is found to be much later than the perfect one and the rate of spall damage evolution also decreases due to energy dissipation during SFT’s collapse and plastic deformation. When Up increases to 1.25 km/s, shock compression induces many defected atoms in both samples, so the SFT has little influence on the spall strength and spall damage of the materials.
Development and in-orbit performance evaluation of multi-layered nested grazing incidence optics
Authors: Zuo Fu-Chang , Mei Zhi-Wu , Deng Lou-Lou , Shi Yong-Qiang , He Ying-Bo , Li Lian-Sheng , Zhou Hao , Xie Jun , Zhang Hai-Li , Sun Yan ,   Beijing Institute of Control Engineering, Beijing 100190, China,   Beijing Institute of Spacecraft System Engineering, Beijing 100194, China
Published: December 2020

On November 10, 2016, China launched an X-ray pulsar navigation test satellite (XPNAV-1) to investigate the X-ray pulsar navigation technology, and a lot of scientific observation data have been obtained. The X-ray grazing incidence optics is a critical component of the focusing pulsar telescope. It plays an important role in increasing the effective area and enhancing the sensitivity of the telescope. It is also the first grazing incidence optics verified in orbit in China. According to the characteristic that the times of arrival (TOA) of X-ray photons are measured in pulsar navigation, the grazing incidence focusing optics based on single-reflection paraboloid mirror is designed, and manufacturable mirror design parameters are obtained through theoretical calculation and derivation. The theoretical effective area of the designed optics is 15.6 cm2 at 1 keV. The designed optics is then simulated to evaluate its focusing performance. It meets the focusing requirement in the full field of view. The electroforming nickel replication process used for manufacturing the mirrors for XMM-Newton and eRosita missions is investigated. A super-smooth mandrel is firstly fabricated and used for follow-up replication. An about-100 nm-thick gold layer is deposited on the mandrel, and serves as the reflection and release layer of the mirror. The nickel substrate of the mirror is electroformed on the gold layer. The mirror is finally obtained by releasing the nickel and gold layer from the mandrel. The patterns and roughness of the mandrel are then replicated onto the inner surface of the mirror. The 4-layered mirror is fabricated for the optics. The reflectivity for each layer of the 4-layered mirror is then measured with a dedicated facility on 4B7B beamline of BSRF. The effective area of the optics based on the above-measured reflectivity is 13.2 cm2 at 1 keV. Finally, according to the in-orbit observation data, the effective area of the optical system is evaluated to be a typical value of 4.22 cm2 at 1 keV, which is less than the ground-tested value. The reason for this is analyzed and it turns out to be due to the thermal deformation of mechanical structure and contamination of the mirrors. Therefore, in our future work, we will strictly control the environmental factors and implement space environmental adaptability design, while increasing the accuracy of the optics.
Structure and excitation characteristics of C5F10O under external electric field based on density functional theory
Authors: Li Ya-Sha , Sun Lin-Xiang , Zhou Xiao , Chen Kai , Wang Hui-Yao ,   College of Electrical and New Energy, Three Gorge University, Yichang 443002, China
Published: December 2020

In this paper, we use the density functional theory (B3LYP) method with 6-311g(d) basis sets to optimize the molecular structure of C5F10O and obtain the stable structure of its ground state. On this basis, the geometric characteristics, energy, frontier orbital energy levels, and infrared spectra of C5F10O under the different external electric fields (from 0 to 0.03 a.u., 1 a.u. = 5.142 × 1011 V/m) are studied by the same method. Under the same basis sets, the orbital composition and excitation characteristics of C5F10O are calculated and analyzed by the TD-DFT method. The conclusions show that as the electric field increases, the bond energy of 5C—15F and 4C=16O gradually decrease, their bond lengths increase. The charge of 13F atoms changes fastest, and it is easier to lose electrons under the action of electric field force. The potential energy of the molecule increases, and the stability gradually decreases. The energy gap EG value continuously decreases, and the molecules are more likely to be excited to participate in the chemical reaction. In the infrared spectrum, four absorption peaks are blue-shifted, and four absorption peaks are red-shifted. The excitation characteristics of the first 8 singlet excited states of the C5F10O are identified by the hole-electron analysis method. The excitation energy of the first excited state increases slightly, and the wavelength decreases, and blue shift occurs. The excitation energy values of the other excited states decrease, their wavelengths increase, and red shifts occur. Because the electrons in C5F10O become easier to excite, the stability of the system is lower.
Effects of frequency-dependent surface impedance on the vacuum electronic terahertz sources
Authors: Ren Ze-Ping , Chen Zai-Gao , Chen Jian-Nan , Qiao Hai-Liang ,   Northwest Institute of Nuclear Technology, Xi’an 710024, China
Published: December 2020

When the working frequency of vacuum electronic device reaches the terahertz frequency, the ohmic loss has a significant impact on the vacuum electronic device. To study the effect of the ohmic loss on the working characteristic of the vacuum electronic terahertz devices, this paper implements the frequency-dependent surface impedance boundary condition (SIBC) in the 3 dimensional particle in cell code UNIPIC-3D. Conformal mesh is adopted in the code to overcome the staircase error in traditional particle in cell method. By using the surface impedance boundary, we eliminate the need to study the field inside the lossy dielectric objects which require extremely small grid cells for numerical stability. In comparison with constant parameter SIBC, the dispersive SIBC is applicable over a very large frequency bandwidth and over a large range of conductivities. The correctness of the implementation is verified by simulating the lossy resonant cavity and circular waveguide, the simulated power loss is comparable with the theoretical predication. High power vacuum electronic devices of terahertz regime are attracting extensive interests due to their potential applications in science and technologies. The impulse-wave relativistic surface wave oscillator (SWO) and low-voltage continuous-wave planar grating backward wave oscillator (BWO) both made of copper are numerically studied by using UNIPIC-3D and dispersive surface impedance boundary condition. Numerical results show that the strongest field is very close to the slow wave structure where the beam-wave interaction occurs and that terahertz wave generates both in these two devices. The distributed wall loss has a considerable effect on the devices: the output power has a significant decrease and the startup time becomes longer, but the working frequencies of the two devices keep unchanged. To improve the efficiency of relativistic SWO, a resonant reflector is proposed between the diode and the slow wave structure. Numerical results show that the working frequency of the device with a resonant reflector keeps unchanged as the original one, but the output power increases to 60 MW from 41 MW of the original one when the ohmic loss is considered.
Dynamic analysis of rumor-spread-delaying model based on rumor-refuting mechanism
Authors: Zhu Lin-He , Li Ling ,   Faculty of Science, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

In this paper, we establish a susceptible-infected-removed (SIR) rumor spreading model based on the influence of rumor-refuting mechanism and time delay on internet rumor spreading. The threshold R0 of rumor spreading is obtained by using the spectral radius method of regenerative matrix; the conditions for the existence of rumor prevailing equilibrium point are given according to the quadratic function characteristics; the local stability of rumor-free equilibrium point and rumor prevailing equilibrium point are established by using eigenvalue theory and Routh-Hurwitz criterion; and the criterion for the occurrence of Hopf bifurcation is also established. The numerical simulation results show that the information about refuting rumors, released by the government and the media, can accelerate the convergence rate of rumors and reduce the maximum density of rumor-spreaders.
A method of designing binary energy degrader
Authors: Han Jin-Hua , Qin Ying-Can , Guo Gang , Zhang Yan-Wen ,   National Innovation Center of Radiation Application, Department of Nuclear Physics, China Institute of Atomic Energy, Beijing 102413, China
Published: December 2020

In order to improve the efficiency of the single event effect (SEE) experiments on the 100 MeV proton cyclotron of China Institute of Atomic Energy, a binary energy degrader that can lower the initial proton energy to other values rapidly is designed for the 100 MeV protons provided by the accelerator. The energy degrader is comprised of six aluminum plates of 0.5, 1, 2, 4, 8, 16 and 32 mm at thickness, where the thickness of the latter plate is twice that of the previous one. We introduce the concept of relative thickness, which can also represent the order of the energy of the produced protons, and the state or operation of the degrader. The energy interval of 61 protons with energy above 9.69 MeV, produced by the degrader, is between 0.84 MeV and 4.09 MeV. And their energy straggling degree is less than 10%, and full width at half maximum of the scattering angle is less than 45 mrad. So the energy degrader basically meets the requirements of the proton SEE experiments. The influence of the initial proton energy accuracy of the protons directly provided by the accelerator on the residual energy after they have passed through the degrader is discussed. It is found that the lower the residual energy, the greater the influence is. In addition, the degrader is also suitable for protons in the 70－100 MeV energy range that the accelerator can directly provide, and more continuous energy can be obtained by using more plates designed with this method. The design method of the energy reducer proposed in this paper is simple and effective, and has a strong reference value.
Effects of buoyancy and acceleration on heat transfer of supercritical CO2 flowing in tubes
Authors: Zhang Hai-Song , Zhu Xin-Jie , Zhu Bing-Guo , Xu Jin-Liang , Liu Huan ,   Beijing Key Laboratory of Multiphase Flow and Heat Transfer, School of Energy Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China
Published: December 2020

Based on the concept of single-phase fluid, the abnormal heat transfer behavior of supercritical fluid has been investigated for many years. However, there is no unified understanding of the mechanism of its flow and heat transfer. In this paper, we first review the reported effects of buoyancy and acceleration on supercritical fluids, and then study the effects of buoyancy and acceleration on the flow structure and heat transfer for the upward vertically flowing of supercritical CO2 fluid in a tube theoretically and experimentally. The results show that there is no conclusive experimental evidence that the abnormal heat transfer behavior of supercritical fluid is directly related to buoyancy and flow acceleration, and the existing criteria for estimating buoyancy and acceleration effect are based on the constant physical fluid and a lot of assumptions, as a result, different conclusions are obtained, though the same prediction method is used. Finally, we investigate the heat transfer deterioration of supercritical fluids based on the pseudo-boiling theory, and the proposed supercritical-boiling-number distinguishes the normal heat transfer deterioration from heat transfer deterioration of supercritical fluid. Our work paves a new way to understanding the supercritical fluid flow and heat transfer mechanism. The supercritical-boiling-number is important for establishing the optimum operating conditions for the supercritical fluid power cycle used in different technologies.
Fabrication and ultraviolet-visible-near infrared absorption properties of silver nano arrays based on aluminum
Authors: Liang Ling-Ling , Zhao Yan , Feng Chao ,   Institute of Laser Engineering, Beijing University of Technology, Beijing 100124, China,   Institute of Applied Mathematics and Physics, Beijing University of Technology, Beijing 100124, China,   Key Laboratory of Trans-scale Laser Manufacturing Technology, Ministry of Education, Beijing 100124, China,   Beijing Engineering Research Center of Laser Technology, Beijing 100124, China
Published: December 2020

In this paper, the highly ordered periodic silver nanosphere arrays are fabricated by vacuum evaporation based on anodic aluminum oxide (AAO) template. The diameter and spacing of silver nanosphere in the arrays are adjusted just by controlling the thickness of evaporation. Furthermore, this can effectively modulate the absorption peaks and bandwidths in ultraviolet-visible-near-infrared regions. The measurement results of absorption spectra show that the nano-arrays have obvious electromagnetic wave absorption characteristics in the ultraviolet, visible and near-infrared bands. The finite-difference time-domain theoretical simulation combined with experiments is used to analyze the physical mechanism of light absorption characteristics in different wavebands. The ultraviolet strong absorption is due to the Fano resonance induced by asymmetric dielectric environment of silver and aluminum; the visible absorption originates from local surface plasmon resonance of silver nanoparticles; the near-infrared strong absorption is attributed to the surface lattice resonance of silver nanosphere arrays.