bluuebunny/crossref_metadata_2025 huggingface dataset:
Subgroup decomposition analyses of D3h and D4h plasmonic metamolecule Fano resonance spectrum
Authors: Li Meng-Jun  , Fang Hui  , Li Xiao-Ming  , Yuan Xiao-Cong  ,   Institute of Modern Optics, College of Electronic Imformation and Optical Engineering, NanKai University, Tianjin 300071, China;,   Nanophotonics Research Centre, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
Published: December 2020

In recent decades, research about surface plasmon polariton (SPP) has earned its popularity in nanotechnology with many theoretical achievements, much progress in metal nanostructure manufacturing, spectral analyzing, biomedicine ultrasensing, etc. Group theory is an effective tool for analyzing the spectra of symmetrical organized multiparticles (dubbed as plasmonic metamolecule). Recently, SPP Fano resonance in nanostructure either from plasmonic metamolecules or from symmetry-breaking has attracted much attention. Regarding to the subgroup decomposition analysis of the D3h and D4h plasmonic metamolecule surface plasmon resonance spectra and the mechanism of forming the Fano resonance spectral dip, this paper proposes an explanation method based on group theory.By using a similar group theory approach to constructing the molecular vibration normal modes, the method to build the dipolar SPP symmetric modes of plasmonic metamolecules is established. It is confirmed that under the linear polarization excitation there exists only two dipolar SPP symmetric modes for a ring shaped Dnh plasmonic metamolecule, while adding the center particle will merely add an extra independent symmetric mode. For the D3h and D4h plasmonic metamolecule, it is found that there are two dominant eigenmodes i. e., one is composed by adding two symmetric modes and the other by subtracting two symmetric modes. The decomposition analysis further reveals that the negative coefficient of the symmetric mode for forming the short wavelength eigenmode for D3h tetramer plasmonic metamolecules is much smaller than that for D4h pentamer plasmonic metamolecules, thereby explaining that the Fano resonance dip of the pentamer is sharper than that of the tetramer. It is worth noting that the group theory can provide some guidance for building the symmetric modes and the SPP eigenmodes, but is unable to determine the coefficient of each symmetric mode.As for the origin of Fano resonance dip, so far there have existed two different perspectives: one is the traditional viewpoint, i.e., the Fano resonance dip is formed due to the coupling of the wideband superradiant bright mode with the narrowband subradiant dark mode, and the other is that the Fano resonance dip is formed by the destructive interference between two neighboring eigenmodes. The decomposition analysis described in this paper actually can unify these two perspectives.
Structural and photoluminescence characteristics of ZnCdO/ZnO single quantum well
Authors: Yi You-Gen  , Wang Yu-Ying  , Hu Qi-Feng  , Zhang Yan-Bin  , Peng Yong-Yi  , Lei Hong-Wen  , Peng Li-Ping  , Wang Xue-Min  , Wu Wei-Dong  ,   Hunan Key Laboratory for Super-Microstructure and Ultrafast Process, College of Physics and Electronics, Central South University, Changsha 410083, China;,   State Key Laboratory for High-Temperature and High-Density Plasmas Physics, Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Zn1-xCdxO/ZnO single quantum well is grown by laser molecular beam epitaxy on Al2O3(0001) substrate. Single quantum well samples respectively with the well-widths of 1.0 nm, 1.5 nm, 4 nm are obtained by controlling the epitaxial temperature and oxygen pressure in the vacuum chamber. The chemical compositions, surface morphologies, crystal structures of the samples are carefully studied, and the results show that the Zn0.98Cd0.02O single quantum wells are of high quality with very smooth surface (with the root mean square value of 0.6 nm in 20 μm×20 μm area) and good crystal structure. Quite a strong photoluminescence emission is obtained at 3.158-3.219 eV from the ZnCdO single quantum well at 4 K under a 325 nm He-Cd laser by tuning quantum well-width. The full width of half maximum of the photoluminescence emission peak of the 1.0 nm quantum well reaches 60 meV, which indicates a strong quantum confinement effect.
A novel Y2O3-Gd2O3-HfO2 impregnated W base direct-heated cathode in magnetron tube
Authors: Qi Shi-Kai  , Wang Xiao-Xia  , Luo Ji-Run  , Zhao Qing-Lan  , Li Yun  ,   Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

As the heart of a magnetron, cathode plays an important role in the device. At present, the pure W cathode is mainly used in high-power continuous wave magnetron tube. However, the pure W cathode has low thermionic emission capability and secondary electron emission yield (1.25-1.50), which result in the cathode operating at a high temperature (2450-2700 K). The higher the operating temperature of the cathode, the faster the evaporation of its surface is, which can shorten the cathode lifetime. In order to enhance the emission current, reduce the operation temperature and prolong the lifetime of the pure W cathode, a novel refractory Y2O3-Gd2O3-HfO2 impregnated W base direct-heated cathode (Y-Gd-Hf-O impregnated cathode) is developed in this paper. The present investigation mainly focuses on the thermionic emission, work function, lifetime, emission mechanism, and anti-bombing property. The direct current (dc) emission properties of the Y-Gd-Hf-O impregnated cathode are investigated, showing that it can provide more than 0.4, 1, 4.0, 7.74, 10.5 A/cm2 current density for the space charge limitation (SCL) at 1300, 1400, 1500, 1600, 1700 ℃ respectively. Absolute zero work function for the cathode is only 1.68 eV obtained by the Richardson line method. The effective work function for the cathode is in a range of 2.6-3.1 eV obtained by the Richardson-Dushman formula. The lifetime for the cathode is more than 3600 h with an initial load of 1.5 A/cm2 at 1600 ℃. The surface microstructure, element composition and content of the Y-Gd-Hf-O impregnated cathode are analyzed by the scanning electron microscope (SEM), Auger electron spectroscopy (AES), and energy disperse spectroscopy (EDS). The analysis results show that the surface of the cathode contains the Y2O3-x semiconductor layer, which causes an improvement of the electro-conductivity during the activation. The work function of the cathode can also be reduced due to the improvement of the electro-conductivity. Besides, the addition of the transition-metal oxide HfO2 changes the internal lattice energy level, which can further reduce the work function. Therefore, the Y-Gd-Hf-O impregnated cathode has good thermionic emission capability. In addition, the anti-bombing performance of the cathode is also studied, which shows that the dc emission current density decreases linearly from the initial current density of 1.5 A/cm2 to 0.4 A/cm2 after 150-h continuous electron bombing at 10 W/cm2. In the future research, we will focus on enhancing the anti-bombing property for the Y-Gd-Hf-O impregnated cathode by using Y-Gd-Hf-O doped W base direct-heated cathode.
Effects of different coil combinations on the optimal design of a 25 T superconducting magnet
Authors: Zhu Guang  , Liu Jian-Hua  , Cheng Jun-Sheng  , Feng Zhong-Kui  , Dai Yin-Min  , Wang Qiu-Liang  ,   Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

High field above 20 T is required in diverse physical programs and nuclear magnetic resonance (NMR) systems. For intended science program requirements, as a demonstration of the development in high field superconducting magnet technology, a 25 T (4.2 K) 52 mm cold-bore all-superconducting magnet consisting of a 10 T high-temperature superconducting insert magnet and a 15 T low-temperature superconducting background magnet, is being developed at the Institute of Electrical Engineering, Chinese Academy of Sciences. The development of such a magnet requires its optimization, and the choosing the number and type of coils is crucial to the final optimal design. However there are few researches focusing on the effect of coil combinations. To study the relationship between the number of coils and the magnet parameters, we first discuss the magnet optimization. The objective function of the optimization is defined as the weighted function of coil volume according to the costs of different superconductors, and the following constraint conditions are taken into considerations: center field, YBCO conductor characterization, hoop stress in Nb3Sn coils, and the critical performances of these wires. All those constraint conditions are taken in the analytical form, and the magnetic field, stress results are verified with the finite element method. To guarantee the reliability of the optimal results, in addition to consider the constraint conditions, a method of combining global optimization and local optimization is adopted. 20 different coil combinations are selected according to the investigation of superconducting wires, and their optimal results are calculated. The following conclusions are drawn from the analyses of these results. Firstly, in the design of high field magnet, the number of coils and magnet cost demonstrate a "V"-shaped relationship, that is, there exist an optimal number of coils. Secondly, when the objective function demonstrates good values, Nb3Sn coils generate fields in a range of 6-7 T, whereas NbTi coils generate fields in a range of 8-9 T. Finally, the objective functions under two different situations, i.e., Nb3Sn coils and NbTi coils are powered together and separately, are calculated. From the comparisons we find that the effect of reducing one power supply is acceptable when the number of coils is not too big.
Three wire toroidal magnetic guide based on the vertical leads and ac current modulation
Authors: Cheng Jun  , Zhang Jing-Fang  , Xu Xin-Ping  , Jiang Xiao-Jun  , Li Xiao-Lin  , Zhang Hai-Chao  , Wang Yu-Zhu  ,   Key Laboratory for Quantum Optics, Shanghai Institute of Optics and Fine Mechanics, CAS, Shanghai 201800, China;,   University of Chinese Academy of Sciences, Beijing 100080, China
Published: December 2020

A new scheme to create a closed toroidal magnetic waveguide for deBroglie wave on a single layer atom chip is proposed and there is no zero magnetic field along the guide center. The guide is a two-dimensional magnetic trap for trapping weak-field seeking states of atoms with a magnetic dipole moment. The designed wire structure on the atom chip consists of three concentric and isometric ring wires, and six vertical current leads of the three ring wires. By using the through silicon via technology, the current leads can be made perpendicular to the atom chip surface instead of being generally arranged side by side on the chip surface. Compared with the general wiring way, the vertical lead way has two advantages. One is that each ring wire gap caused by the current leads is substantially smaller than the distance between the ring wires, which permits the generation of a closed toroidal magnetic guide near the atom chip surface when dc currents are supplied to the three ring wires. The other is that the distance between two leads of each ring wire is considerably reduced, resulting in the fact that the magnetic perturbation of the leads to the whole toroidal magnetic guide is negligible. We numerically calculate the magnetic field distribution generated by our wire layout when dc currents are applied, and it is shown that a closed and tight toroidal magnetic guide is formed near the atom chip surface. However, there are zero magnetic fields existing along the center of the toroidal guide, which leads to Majorana spin flips from trapped magnetic substate to an un-trapped magnetic sub-state. According to the time-orbiting-potential principle, we propose an ac current modulation method, which is simple and stable, to reduce the atom losses and suppress the atomic decoherence in the toroidal magnetic guide. We deduce the ac current expressions for the case of three isometric infinite straight wires and apply the ac modulation current expressions directly to our three ring wire structure. The numerical calculation results show that the closed toroidal guide does no longer have zero magnetic fields near the magnetic field minimum, and that the magnetic field fluctuation of the guide is smaller. Based on the vertical leads and ac current modulation, the closed toroidal wave guide with no zero magnetic field along the guide center can be generated near the atom chip surface. This scheme has important scientific significance and engineering value for developing the cold atomic chip gyroscope.
Stochastic resonance of a linear harmonic oscillator with non-linear damping fluctuation
Authors: Tian Yan  , He Gui-Tian  , Luo Mao-Kang  ,   School of Science, Southwest Petroleum University, Chengdu 610500, China;,   College of Mathematics, Sichuan University, Chengdu 610064, China
Published: December 2020

Although non-linear noise exists far more widely in actual systems than linear noise, the study on non-linear noise is far from meeting the needs of practical situations as yet. The phenomenon of stochastic resonance (SR) is a non-linear cooperative effect which is jointly produced by signal, noise, and system, obviously, it is closely related to the nature of the noise. As a result, the non-linear nature of the non-linear noise has an inevitable impact on the dynamic behavior of a system, so it is of great significance to study the non-linear noise's influence on the dynamic behavior of the system. The linear harmonic oscillator is the most basic model to describe different phenomena in nature, and the quadratic noise is the most basic non-linear noise. In this paper, we consider a linear harmonic oscillator driven by an external periodic force and a quadratic damping fluctuation. For the proposed model, we focus on the effect of non-linear nature of quadratic fluctuation on the system's resonant behavior. Firstly, by the use of the Shapiro-Loginov formula and the Laplace transform technique, the analytical expressions of the first moment and the steady response amplitude of the output signal are obtained. Secondly, by studying the impacts of noise parameters and system intrinsic frequency, the non-monotonic behaviors of the steady response amplitude are found. Finally, numerical simulations are presented to verify the effectiveness of the analytical result. According to the research, we have the following conclusions: (1) The steady response amplitude is a non-monotonic function of coefficients of the quadratic damping fluctuation. Furthermore, the non-linear damping fluctuation is easier to contribute the system's enhancing response to the external periodic signal than the linear fluctuation. (2) The evolution of the steady response amplitude versus noise intensity presents more resonant behaviors. One-peak SR phenomenon and double-peak SR phenomenon are observed at different values of coefficients of the quadratic noise, particularly, the SR phenomenon disappears at the positive quadratic coefficient of the quadratic noise. (3) The evolution of the steady response amplitude versus the system intrinsic frequency presents true resonance, i. e. the phenomenon of resonance appears when the external signal frequency is equal to the system intrinsic frequency. True resonance is not observed in the linear harmonic oscillator driven by a linear damping fluctuation as yet. In conclusion, all the researches show that the non-linear nature of non-linear noise plays a key role in system's resonant behavior, in addition, the non-linear damping fluctuation is conductive to the detection and frequency estimation of weak periodic signal.
Research on high sensitivity detection of carbon monoxide based on quantum cascade laser and quartz-enhanced photoacoustic spectroscopy
Authors: Ma Yu-Fei  , He Ying  , Yu Xin  , Yu Guang  , Zhang Jing-Bo  , Sun Rui  ,   National Key Laboratory of Science and Technology on Tunable Laser, Harbin Institute of Technology, Harbin 150001, China;,   Post-doctoral Mobile Station of Power Engineering and Engineering Thermophysics, School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

Quartz-enhanced photoacoustic spectroscopy (QEPAS) technology was invented lately. Therefore it is an innovative method for trace gas detection compared with other existing technologies. In this paper, trace gas detection for carbon monoxide (CO) based on QEPAS technology is demonstrated. In order to realize high sensitive detection, a novel mid-infrared, state-of-art 4.6 m high power, continuous wave (CW), distributed feedback (DFB) quantum cascade laser (QCL) with single mode output is used as the laser exciting source. Therefore, the strongest absorption of fundamental frequency band of CO is achieved. Using the wavelength modulation spectroscopy and the 2nd harmonic detection, the influence of laser wavelength modulation depth on QEPAS signal level is investigated. Two important parameters of Q-factor and resonant frequency for quartz tuning fork as a function of gas pressure are measured. After optimization of the modulation depth of laser wavelength, the gas pressure of CO:N2 gas mixture and the improving speed of the V-R relaxation rate through the addition of water vapor, a minimum detection limit (MDL) of 1.95 parts per billion by volume (ppbv) for CO at gas pressure of 500 Torr and modulation depth of 0.2 cm-1 is achieved with a 1 sec acquisition time and the addition of 2.6% water vapor in the analyzed gas mixture. Finally, the influence of level lifetime of the targeted gas on QEPAS signal amplitude is investigated by comparison of CO QEPAS sensor performance using two different CO absorption lines of R(5) and R(6) located at 2165.6 cm-1 and 2169.2 cm-1respectively. The expression of the QEPAS signal amplitude is modified by adding the level lifetime parameter for a better precision.
Detection optical vortex topological charges with monocyclic multistage intensity distribution
Authors: Zhang Hao  , Chang Chen-Liang  , Xia Jun  ,   Department of Physics, Southeast University, Nanjing 211189, China;,   School of Electronic Science and Engineering, Display center, Southeast University, Nanjing 210096, China
Published: December 2020

Generation and application of the vortex beams are part of the hot topics in the optical field. In connection with the limited detection range of topological charge, we introduce a novel monocyclic multistage intensity distribution, which is generated by the coaxial superposition of two vortex beams with different topological charge numbers which have the same radius of ring in the focal plane of fraunhofer diffraction. This novel intensity distribution which is achieved by computer generated hologram is a new application of sidelobe-modulated optical vortices. The detection range of topological charge is expanded to 128 by two detection constants consisting of segments and radius in the monocyclic multistage intensity distribution method. We study the generation and distribution characteristics of monocyclic multistage intensity distribution in the focal plane of fraunhofer diffraction theoretically and experimentally to generate the qualified monocyclic multistage intensity distribution using a spatial light modulator. Excellent agreement between theoretical and experimental results is observed. The study indicates that two orbital angular momenta of vortex beams can be accurately determined by the segments and radius determined in the monocyclic multistage intensity distribution method. The method is immune to harassments from alignment and phase matching between the beams and optical elements, and has a large detection range, which is enlarged one order of magnitude compared with the previous way of detecting topological charges with sidelobe-modulated optical vortices. Our method provides a more large detection range of topological charge, which enables the vortex beams as the information carriers to carry more data in communication. Therefore, this method possesses research potential and applicability in future free-space optical communication.
Light intensity distribution of high-power laser beams on target plane under different focus system of 22 beam array
Authors: Sun Xiao-Yan  , Lei Ze-Min  , Lu Xing-Qiang  , Lü Feng-Nian  , Zhang Zhen  , Fan Dian-Yuan  ,   Key Laboratory on High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Large aperture high-power laser drivers usually focus the high power laser beams in 22 quads to the target chamber center in order to increase the light intensity on the target plane. The large aperture wedged focus lenses are the core components in the focus system of quadruplets of beams, and it is thought possible to use four two-dimensional off-axis wedged focus lenses as four sub-lenses to make up a larger aperture wedged focus lens in form to focus the four beams. Given that the large aperture two-dimensional off-axis wedged focus lenses are processed and used difficultly, the wedged focus lenses are divided into three categories: the two-dimensional off-axis wedged focus lenses, the one-dimensional off-axis wedged focus lenses, and the non-off-axis wedged focus lenses. On the basis of the three modes of the wedged focus lenses and the corresponding specific incidence angles of each sub-beam, the three focus schemes for the 22 beam array are put forward to comparatively research the light intensity distribution on the target plane. Research results show that from a perspective of the coherence among the four sub-beams, the phase factors of each sub-beam respectively introducing by the three focus systems with the two-dimensional off-axis, one-dimensional off-axis, and non-off-axis wedged focus lenses are asymmetric, asymmetric and symmetric inside each sub-beam, and symmetric, asymmetric and symmetric among the four sub-beams. Therefore, the wave front consistency of the four sub-beams decreases in the order of the focus systems with the non-off-axis, two-dimensional off-axis, and one-dimensional off-axis wedged focus lenses. The focus schemes with the non-off-axis wedged focus lenses for 22 beam array can get the narrowest main-lobe, the strongest peak-value intensity, the highest energy concentration ratio on the target plane, followed by the one-dimensional off-axis and two-dimensional off-axis wedged focus lenses. The off-axis mode of the wedged focus lenses not only increases the complexity in the course of processing and using, but also increases the main-lobe size, decreases the peak-value intensity and the energy concentration ratio, which obtains a weaker focusing characteristics than that of the non-off-axis mode of the wedged focus lenses. Research results can provide an important reference for the design of the focus system in the target area of high-power laser drivers.
Study on bending losses of few-mode optical fibers
Authors: Zheng Xing-Juan  , Ren Guo-Bin  , Huang Lin  , Zheng He-Ling  ,   Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China;,   Key Lab of All Optical Network & Advanced Telecommunication Network of EMC, Beijing Jiaotong University, Beijing 100044, China;,   State Grid Linyi Power Supply Company, Linyi 276000, China
Published: December 2020

With the rapid increase of the capacity of optical fiber transmission system, the mode division multiplexing (MDM) transmission system using few-mode fibers (FMFs) (which provides the multi-channel multiplexing, high efficiency of frequency spectrum, and low nonlinear effects) becomes a research focus to upgrade the capacity of the optical communication. In this paper, an analytical expression of bending loss for each high-order mode of parabolic-index FMFs is deduced based on the perturbation theory and verified by finite element method. Based on this expression, the influence of four key structure parameters of trench-assisted parabolic-index FMFs: i.e. the radius of fiber core, the distance between core and trench, the width of trench, and the refractive index difference of trench, on the bending loss performance are discussed in detail. It is found that, firstly, the sensitivity of the bending loss increases with the increase of mode order of FMFs. Secondly, the smaller the core radius, the smaller the bending loss of each mode-order is, since small core radius leads to a smaller effective mode area, which is beneficial for saving power leakage. Additionally, the effective mode area of LP02 mode is lower than that of LP21 mode, while the bending loss of LP02 mode is higher than that of LP21 mode, this observation is different from other mode-orders. Thirdly, an optimized distance between trench and core for each high-order mode is also investigated for obtaining minimum bending loss, which plays an important role in controlling the bending performance of FMFs. So the higher the mode-order, the smaller the optimized distance between core and trench is, and this observation could be used to optimize the bending loss of the fiber. With the increase of the distance between the core and trench, the effective mode area of high-order mode increases quickly at first, then it is approximately unaltered. The distance between the core and trench is a key factor that influences both the bending loss and the effective mode area of each mode. Finally, the bending loss of each mode decreases with the increase of the width of trench around the fiber core or the refractive index difference of trench. These results are helpful for understanding the mechanism of bending loss for FMFs and are of significance for designing and manufacturing of few-mode bend-insensitive fibers, especially for the optimization of the bending loss of specific high-order mode.
Studies on the mechanism of acoustic pulse train and full transmission
Authors: Cao Song-Hua  , Wu Jiu-Hui  , Wang Yu  , Hou Ming-Ming  , Li Jing  ,   School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an 710049, China;,   State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Critical phenomenon in a one-dimensional periodic stratified structure with time-varying elastic modulus functions is found out for acoustic waves. By using the classical separation of variables method to solve the one-dimensional wave equation, and taking the time-varying elastic modulus functions into consideration, a critical value can be found of the varying amplitude of the time-varying elastic modulus functions. Near the critical value, due to the alternation of the characteristic exponent, the reflectivity of the one-dimensional periodic stratified structure changes in essence. Below or at the critical value, the incident wave can be converted into a periodic and millisecond pulse train, particularly when the varying amplitude is at the critical value. In addition, the layer number can be up to 16. Under these circumstances, complete pulse train of 0 or 1 is generated with respect to time; in the end, when above the critical value, the reflectivity decreases rapidly to 0 within 50 milliseconds, indicating that, at one moment, the incident wave can be totally transferred through the structure as if the stratified structure becomes transparent, which means a modulational transparency. In conclusion, by altering the varying amplitude of the time-varying elastic modulus functions, three different phenomena are generated. These excellent properties could find potential applications of one-dimensional periodic stratified structure in the acoustic transducer and the control of the acoustic wave.
Study of highway lane-changing model under rain weather
Authors: Zhang Wei-Hua  , Yan Ran  , Feng Zhong-Xiang  , Wang Kun  ,   School of Transportation Engineering, Hefei University of Technology, Hefei 230009, China;,   School of Architecture and Planning, Anhui Jianzhu University, Hefei 230022, China
Published: December 2020

Rainfall decreases road adhesion coefficient and sight distance of drivers, these can easily lead to traffic accidents which affect the road traffic efficiency. To study the vehicle lane-changing behavior under rainfall conditions, the adhesion coefficient parameter and drivers' reaction delay time parameter are introduced into the safety distance model. Based on the relationship between rainfall intensity and the water film thickness as well as the relationship among the road adhesion coefficient, water film thickness, and vehicle speed, the influence of rainfall on the road adhesion coefficient is quantified. And based on the relationship between visibility distance under rainfall condition and safe distance upon stopping sight distance, the influence of rainfall on drivers' reaction delay time is quantified. Therefore, the safety distance is different under different rainfall conditions and vehicle speed, it no longer is a fixed value like in other lane-changing models by quantifying the two parameters. The improved lane-changing model is established by considering the influence of the speed difference on vehicle lane-changing behavior; the speed difference is not only existing between the research vehicle and the adjacent lane vehicle ahead, but also between the research vehicle and the adjacent lane after the car. And the safety distance model including the two parameters is embedded in the improved lane-changing model by the lane-changing rules. For the three-lane traffic, the lane-changing rules which take into consideration the safety distance and the speed difference are established respectively for each lane, and the simulation analysis is conducted using cellular automata based on the above mentioned rules. Simulation results show that in the medium density the lane-changing rates in the rain condition are significantly lower compared with sunny days, the biggest drop is about 25%. Through comparison and analysis of the space-time diagrams and the speed-time curve of one vehicle at different traffic density on rain days and sunny days, the improved model redisplays the phenomenon of free flow, free flow into dynamic blocking flow in the absence of external cause, and the phenomenon of vehicles stopping and going under blocking flow. In the medium and high densities, the rain causes more traffic congestion, and the frequency and duration of traffic congestion in space-time diagram increase accordingly; the low speed and the speed of zero state increase gradually in the speed-time curve.
Low frequency band gaps and vibration reduction properties of a multi-frequency locally resonant phononic plate
Authors: Wu Jian  , Bai Xiao-Chun  , Xiao Yong  , Geng Ming-Xin  , Yu Dian-Long  , Wen Ji-Hong  ,   State Grid Shaanxi Electric Power Research Institute, Xi'an 710054, China;,   Laboratory of Science and Technology on Integrated Logistics Support, and College of Mechatronic Engineering and Automation, National University of Defense Technology, Changsha 410073, China
Published: December 2020

A multi-frequency locally resonant (LR) phononic plate is proposed in this paper. The phononic plate consists of periodic arrays of multiple double-cantilevered thin beams attached to a thin homogeneous plate. This proposed phononic plate is simplified and modeled using a plane wave expansion method to enable the calculation of flexural wave band structures. The band gap behavior of the phononic plate is analyzed comprehensively. In addition, an experimental specimen is fabricated using a square aluminum plate with a thickness of 0.9 mm and an area of 840 mm840 mm, and attached to the specimens as periodic arrays of two types of double-cantilevered thin beams made of the same material as the host plate. And the specimen is measured by using a scanning laser Doppler vibrometer to verify the theoretical predictions of band gaps. Investigations of this paper yield the following findings and conclusions: (1) Due to the interaction of low-frequency vibrational modes of attached multiple double-cantilevered beams and flexural vibration of the host plate, the proposed multi-frequency LR phononic plate can exhibit multiple low-frequency flexural wave band gaps (stop bands). It is also found that the band gaps of a multi-frequency LR phononic plate, especially those appearing in a lower frequency range, are generally narrower than that of a single-frequency LR phononic plate with the same type of double-cantilevered beams. (2) The frequency location of band gaps moves to higher frequency range when the thickness of the double-cantilevered beams is increased, or when the length of the double-cantilevered beams is decreased. It is also shown that a very small variation of the thickness (e. g., 0.1 mm) may lead to significant changes of frequency position of the band gaps. (3) When the width of the double-cantilevered beams is enlarged or the number of the double-cantilevered beams is increased, the lower band gap edge will move to a lower frequency range, while the upper band gap edge will move to a higher frequency range. This implies that the bandwidth of the band gaps is broadened. However, at the same time, it is shown that the central frequencies of the band gaps remain almost unchanged. (4) Experimental measurements of the fabricated specimen evidence the existence of two low frequency band gaps, and confirm that the flexural plate vibrations are significantly reduced in the predicted band gaps.
Characterization of dislocation loops in hydrogen-ion irradiated vanadium
Authors: Cui Li-Juan  , Gao Jin  , Du Yu-Feng  , Zhang Gao-Wei  , Zhang Lei  , Long Yi  , Yang Shan-Wu  , Zhan Qian  , Wan Fa-Rong  ,   University of Science and Technology, Beijing 100083, China
Published: December 2020

Vanadium alloys are considered as the candidate materials for structure application in fusion reactors because of their low radiation-induced activation, high resistance to radiation damage, high thermal conduction, and low thermal expansion coefficient. Before these materials, which will be exposed to high-flux hydrogen and helium isotopes, may be safely used in fusion device much more data based on irradiation damage are required. The study of dislocation loops in vanadium is designed to indicate the mechanism of void growing under irradiation. The mechanism is that different types of dislocation loops have different bias which represent their abilities to absorb point defects. It is possible to explain the irradiation swelling performance in the material with the bias of loops. The thin disks samples used in this experiment are made of pure vanadium and vanadium alloy (V-4Cr-4Ti) by twin-jet electro-polishing. Electrolyte of H2SO4-CH3OH (1 : 6 by volume) at -20 ℃ is used in a current of 80～120 mA. To get a clear view of dislocation loops, the SRIM code is used to simulate the implantation of hydrogen ions into vanadium. The ion irradiation is carried out to a dose of 51016H+/cm2, at an energy of 30 keV. Microstructure observations are performed on a Tecnai G2 F20 (transmission electron microscope, TEM) at an accelerating voltage of 200 kV. The Burger's vectors and nature of the dislocation loops formed in pure vanadium by hydrogen implantation are confirmed by TEM. This experiment has focused on as many as 76 dislocation loops, lots of images are taken under different diffraction conditions from the same areas of interest. Results show that most of the dislocation loops have a Burger's vectors of 1/2111 (90%), and a few of 110. No loops with b= 100 loops can be found in this study. The nature of dislocation loops is determined by the inside-outside method. The number of the dislocation loops that can make sure of their nature is 29, and all of them are conformed to be interstitial type, their habit planes are from {110} to {112}. No vacancy type loops are found. The density and average size of dislocation loops in vanadium and vanadium alloy are also analysed. Compared with the pure vanadium, the loops in vanadium alloy of V-4Cr-Ti are formed in a smaller size and higher number density. As a future work the difference of the loops nature between pure vanadium and vanadium-based alloys should be investigated to illustrate their behaviour of irradiation swelling.
Heredity of icosahedrons: a kinetic parameter related to glass-forming abilities of rapidly solidified Cu56Zr44 alloys
Authors: Deng Yong-He  , Wen Da-Dong  , Peng Chao  , Wei Yan-Ding  , Zhao Rui  , Peng Ping  ,   School of Materials Science & Engineering, Hunan University, Changsha 410082, China;,   College of Science, Hunan Institute of Engineering, Xiangtan 411104, China
Published: December 2020

To explore the origin of glassy transition and glass-forming abilities (GFAs) of transition metal-transition metal (TM-TM) alloys from the microstructural point of view, a series of molecular dynamics (MD) simulation for the rapid solidification processes of liquid Cu56Zr44alloys at various cooling rates and pressures P are performed by using a LAMPS program. On the basis of Honeycutt-Andersen (H-A) bond-type index (ijkl), we propose an extended cluster-type index (Z, n/(ijkl)) method to characterize and analyze the microstructures of the alloy melts as well as their evolution in the rapid solidification. It is found that the majority of local atomic configurations in the rapidly solidified alloy are (12 12/1551) icosahedra, as well as (12 8/1551 2/1541 2/1431) and (12 2/1441 8/1551 2/1661) defective icosahedra, but no relationship can be seen between their number N(300 m K) and the glassy transition temperature Tg of rapidly solidified Cu56Zr44alloys. By an inverse tracking of atom trajectories from low temperatures to high temperatures the configuration heredity of icosahedral clusters in liquid is discovered to be an intrinsic feature of rapidly solidified alloys; the onset of heredity merely emerges in the super-cooled liquid rather than the initial alloy melt. Among these the (12 12/1551) standard icosahedra inherited from the super-cooled liquids at Tm-Tg is demonstrated to play a key role in the formation of Cu56Zr44 glassy alloys. Not only is their number N300 KTgP inherited from Tg to 300 K closely related to the GFA of rapidly solidified Cu56Zr44alloys, but a good correspondence of the onset temperatures of heredity (Tonset) with the reduced glass transition temperature (Trg= Tg/Tm) can be also observed. As for the influence of and P on the glassy transition, a continuous tracking of descendible icosahedra reveals that the high GFA of rapidly solidified Cu56Zr44 alloys caused by big and P can be attributed to their elevated inheritable fraction (fp and ftotal) above Tg.
A chaotic signal detection method based on the component permutation of the incomplete two-dimensional phase-space
Authors: Zhu Sheng-Li  , Gan Lu  ,   School of Electronic Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
Published: December 2020

Detection and identification of chaotic signal is very important in the chaotic time series analysis. It is not easy to distinguish chaotic time series from stochastic processes since they share some similar natures. The detection methods to capture and utilize the structure of state-space dynamics can be very effective. In practice, it is very hard to obtain full information about the structure, and accurate phase-space reconstruction from scalar time series data is also a real challenge. However, the chaotic signals also show fundamental dynamical structure in the incomplete two-dimensional phase-space for the reason that they are generated by the deterministic chaotic systems or maps. Based on the fact that the distribution of chaotic signals is quite different from that of the noise signals in the incomplete two-dimensional phase-space, a novel detection method, which depends on the component permutation of the incomplete two-dimensional phase-space, is proposed. The incomplete two-dimensional phase-space is first obtained through the time series. Then, the first component is sorted in the ascending order, and the second component is permutated accordingly. The permutated component shows more structure characteristics for chaotic signals because of the relation between these two components. But this phenomenon does not appear in the noise because these components are independent of each other. And then, the permutated component is segmented into several groups properly. Finally, the sample mean and sample variance of different groups are calculated to obtain the sequence of sample mean (SSM) and the sequence of sample variance (SSV). Meanwhile, by calculating the variance of the SSM and the mean of the SSV, the test statistic is obtained. Furthermore, it is proved that this test statistic follows the F distribution under the null hypothesis of Gaussian noise. The proposed method is first adopted for detecting the several chaotic signals under different data lengths in Gaussian noise conditions. The simulation results show that the proposed method can detect chaotic signals effectively under low signal-to-noise ratio and it also has a good robustness against noise compared with the permutation entropy test. The time consumptions of the proposed method under different data lengths are evaluated and also compared with the results of permutation entropy test, showing that the proposed method can detect chaotic signals quickly, and the time complexity is much lower than that of the permutation entropy test. The theoretical analysis and simulation results demonstrate that the proposed method not only outperforms the permutation entropy test with lower complexity, but also has a better robustness against noise.
Simulation of fluorescence lidar for detecting oil slick
Authors: Jing Min  , Hua Deng-Xin  , Le Jing  ,   School of Mechanical and Precision Instrument Engineering, Xi'an University of Technology, Xi'an 710048, China;,   School of Mechanical engineering, Shaanxi University of Technology, Hanzhong 723000, China
Published: December 2020

In order to measure the oil pollution on water surface, a fluorescence lidar model system based on laser induced fluorescence is put forward for detecting oil slick. The system model and fluorescence detecting principle are described in detail. According to the properties of detected material, wavelength of laser and filter of receiving system are adopted to ensure that the lidar system is operated at the peak wavelength. Following the development trend of miniaturization in the world, using single laser and intensified charge-coupled devices, a small fluorescence detecting system is designed. FTSS 350-50 laser made by CRYLAS company, with compact dimension, low weight and excellent energy efficiency, and PI-MAX4 intensified charge-couple devices made by Princeton Instruments company, with good time resolution characteristic, are selected to produce laser as a launch device and to inspect fluorescence lifetime and capture image as a receiving device, respectively. The laser excitation wavelength, the energy of laser, the center wavelength and bandwidth of filter, the received echo fluorescence signals, the detected concentration and distance are discussed in detail by means of the instance for oil on water surface. Through analyzing the relationship between the energy of laser single pulse and the detection concentration and by combining with the parameters of fluorescence lidar system and fluorescence lidar equation, the detecting ability of system model, signal-to-noise ratio, etc. are simulated particularly. A numerical simulation of the signal-to-noise ratio of the fluorescence particles is conducted particularly so that the detectable capacity of system designed could be described better. The results show that the signal-noise ratio of system which is operated during the night is superior to in daytime in the same single pulse energy case and that the detected range becomes gradually longer as the energy of laser improves with the same signal-noise ratio case. The required single pulse energy to support system is calculated, and further verifies the feasibility of the lidar system. The test results of the sample show that in the daytime, the design of fluorescence lidar model, with a Nd:YAG laser of 50 J single pulse energy and 355 nm wavelength serving as an excitation light source, with a collection device placed at a distance of 7 m, can satisfy the requirements for detecting oil pollution on the water surface in laboratory, and its signal-noise ratio can reach 10. In view of the actual surface fluorescence lidar detection requirements, the method of increasing the laser power is proposed. A real system with 50 mJ single pulse energy at a distance of 230 m has nearly the same performance as the laboratory lidar system, which could provide a valuable guidance for designing a real system.
Measurement of the magnetic dipole hyperfine constant Ahfs of cesium 7S1/2 state
Authors: Ren Ya-Na  , Yang Bao-Dong  , Wang Jie  , Yang Guang  , Wang Jun-Min  ,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China;,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China;,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Hyperfine-structure (HFS) of atoms results from the interactions between the nuclear magnetic dipole moment and the magnetic field generated by the electrons (related to the magnetic dipole hyperfine constant Ahfs), and between the nuclear electric quadrupole moment and the electric field gradient due to the distribution of charge within atoms (related to the electric quadrupole hyperfine constant Bhfs), so the accurate measurement of HFS is of interest in many fields, including atomic parity nonconservation, tests of fundamental physics, electron-nucleus interaction, and high resolution spectrum and so on. Generally, in order to obtain the atomic spectra, the frequency of laser needs to be scanned over the hyperfine transitions of atoms, so the nonlinear effect from the laser frequency scanning often limits the measurement accuracy of hyperfine splitting. In this paper, we solve this problem, and demonstrate a novel method to measure the hyperfine splitting of atoms. Taking cesium (Cs) for example, based on the Cs 6S1/2-6P3/2-7S1/2 (852.3 nm + 1469.9 nm) ladder-type atomic system, three sets of optical-optical double resonance (OODR) spectra are obtained in a room-temperature vapor cell, when the 852.3 nm laser is tuned to the 6S1/2 (F=4)-6P3/2 (F'=4) resonant transition, and the carriers of 1469.9 nm probe laser accompanied with1 sidebands from a phase-type electro-optical modulator (EOM) are scanned over the whole 6P3/2-7S1/2 hyperfine transitions. Owing to the Doppler effect, some of the hyperfine transitions in these three sets of OODR spectra overlap with the narrowest linewidth only when the frequency of the signal driving EOM equals the value of hyperfine splitting 7S1/2 state. Using this phenomenon which can effectively avoid the nonlinear influence on the measurement during the frequency scanning process of 1469.9 nm laser, we measure the hyperfine splitting of 7S1/2 state to be (2183.720.23) MHz, and the magnetic dipole hyperfine constant Ahfs to be (545.930.06) MHz, which are consistent with previously reported experimental results. This technique provides a robust and simple method of measuring hyperfine splitting with a high precision, which is significant to provide the useful information about atomic structure for developing a more accurate theoretical model describing the interaction within an atom.