bluuebunny/crossref_metadata_2025 huggingface dataset:
Freezing behavior of droplet impacting on cold surfaces
Authors: Hu Hai-Bao  , He Qiang  , Yu Si-Xiao  , Zhang Zhao-Zhu  , Song Dong  ,   College of Marine, Northwestern Polytechnical University, Xi’an 710072, China;,   State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
Published: December 2020

Exploring the freezing process and its potential mechanism of the droplets impacting on a solid surface is desperately desired, owing to its anti-icing applications in aircraft, cable, radar, etc. On the controllable low temperature test equipment, the freezing dynamic behaviors of droplets impacting on three cold plates, made of copper, aluminum and silicon, are recorded by a high-speed camera in this paper, and characterized by the droplet spreading diameter, oscillation and freezing time. Here, the freezing behavior of droplets is predicated by observing the color change of the droplet. Through the experimental exploration and theoretical analysis, we reveal the effects of the impacting speed, surface temperature and thermal conductivity of material on the freezing dynamics of the droplet. We demonstrate that a cold surface shrinks the maximum spreading diameter of droplet compared with the surface at ambient temperature; the lower the surface temperature, the shorter the freezing time would be and the smaller the maximum spreading diameter would be; the maximum spreading diameter increases with increasing Weber number, whereas the oscillation and freezing time decrease. Meanwhile, the higher the material thermal conductivity, the shorter the freezing time would be, and the bigger the rising slope of the maximum spreading diameter with increasing Weber number will be. A function to predict the freezing time is derived from thermodynamic condition. The calculated values are in good agreement with the experimental data, with the maximum relative error of less than 5.3%.
Theoretical calculation of electron transport properties of atomic chains of (GaAs)n (n=1-4)
Authors: Liu Fu-Ti  , Zhang Shu-Hua  , Cheng Yan  , Chen Xiang-Rong  , Cheng Xiao-Hong  ,   College of Physics and Electronic Engineering, Yibin University, Yibin 644000, China;,   College of Chemistry and Chemical Engineering, Yibin University, Yibin 644000, China;,   College of Physical Science and Technology, Sichuan University, Chengdu 610064, China
Published: December 2020

Electron transport properties of the (GaAs)n(n=1-4) linear atomic chains, which are sandwiched between two infinite Au(100)-33 leads, are investigated with a combination of density functional theory and non-equilibrium Greens function method from first principle. We simulate the Au-(GaAs)n-Au nanoscale junctions breaking process, optimize the geometric structures of four kinds of junctions, calculate the cohesion energies and equilibrium conductances of junctions at different distances. The calculation results show that there is a stable structure for each nanoscale junction. The average bond-lengths of Ga-As in each chain at equilibrium positions for stable structure are 0.220 nm, 0.224 nm, 0.223 nm, 0.223 nm, respectively. The corresponding equilibrium conductances are 2.328G0, 1.167G0, 0.639G0, and 1.237G0, respectively. It means that each of all the junctions has a good conductivity. We calculate the transmission spectra of the all the chains. With the increase of atomic number in the (GaAs)n (n=1-4) chains, there appears no oscillation phenomenon for the equilibrium conductance. We calculate the projected densities of states of all nanoscale junctions at equilibrium positions, and the results show that electronic transport channel is mainly contributed by the px and py orbital electrons of Ga and As atoms. In the voltage range of 0-2 V, we calculate the current-voltage characteristics of junctions at equilibrium positions. With the increase of external bias, the current increases, and the I-V curves of junctions show linear characteristics for the (GaAs)n (n=1-3) atomic chains. However, there appears a negative differential resistance phenomenon in each of the voltage ranges of 0.6-0.7 V and 0.8-0.9 V for the (GaAs)4 linear atomic chain.
Measurement of single phase flow in porous media using PIV technique
Authors: Jia Yu-Peng  , Wang Jing-Fu  , Zheng Kun-Can  , Zhang Bing  , Pan Gang  , Gong Zhi-Jun  , Wu Wen-Fei  ,   Institute of Energy and Environment, Inner Mongolia University of Science and Technology, Baotou 014010, China;,   Inner Mongolia Key Laboratory for Utilization of Bayan Obo Multi-Metallic Resources: Elected State Key Laboratory, Inner Mongolia University of Science and Technology, Baotou 014010, China;,   College of Environment and Energy Engineering, Beijing University of Technology, Beijing 100124, China
Published: December 2020

Porous media are widely used in the production and living, and also in science and technology. With the development of energy, chemical industry, metallurgy, atomic energy and also with the progress of the modern industrial and agricultural production technology, a large number of heat and mass transfer problems in porous media gradually appear. Further promoting the development of the discipline about the formation and development of porous media becomes one of hot research points in the modern science and technology. It is expected that the accurate experimental picture and data can be obtained through the experiment, and the fluid flow picture and experimental data are analyzed in depth by using the corresponding software, so that the reliable data are obtained and the theory is supported intuitively, making the research of porous media more perfect. The experiment combined with particle image velocimetry technology and refractive index matching technique is conducted to test the transformation process of liquid flow in a random ball porous medium filled bed, and to extract the data. The extracted data are processed by using Tecplot software, and the transformation process of liquid flow mechanism is obtained. Experimental solid phase is a 25 mm-diameter crystal glass ball stacked bed, and liquid phase is the matching liquid prepared with the mixture of the 65% benzyl alcohol and 35% anhydrous ethanol. The refractive indexes of liquid phase and solid phase are both 1.477, which can successfully eliminate the laser light bending caused by the nismaching of refractive indexes. The flow field diagram in the pebble bed with Reynolds number Re in a range 4.7 Re 1000 is obtained experimentally. The comparisons of variations of flow field and flow lines among the different Reynolds numbers reveal that with the increase of Reynolds number, flow lines become more and more disorder: When the Reynolds number Rep exceeds 220, stable swirl flow inside the bed changes suddenly, and manifests a random feature in location and configuration, which forebodes its entrance into stable turbulence phase.
Three-color InAs/GaAs quantum dot infrared photodetector with AlGaAs inserting layer
Authors: Liu Ke  , Ma Wen-Quan  , Huang Jian-Liang  , Zhang Yan-Hua  , Cao Yu-Lian  , Huang Wen-Jun  , Zhao Cheng-Cheng  ,   Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

We report on a three-color InAs/GaAs quantum dot infrared photodetector grown by molecular beam epitaxy. The InAs quantum dots with AlGaAs inserting layers are formed on an InGaAs quantum well layer as an absorber region. The detector is an nin-type device, and three photocurret peaks at 6.3, 10.2 and 11 m are observed at 77 K, respectively. Each peak is designated and the physical mechanism is discussed. The dependences of the intensities of the three peaks on the applied bias voltage are different for the positive and the negative bias conditions due to the asymmetric structure of the absorber region. The peak arising from the transition between the quantum dot ground state and a continuum state becomes weaker when the bias voltage is larger than a certain value. The physical reason is attributed to the decrease of the wavefunction overlap between the two quantum states.
Anti-radiation of space triple-junction solar cell based on distributed Bragg reflector structure
Authors: Chang Xiao-Yang  , Yao Shun  , Zhang Qi-Ling  , Zhang Yang  , Wu Bo  , Zhan Rong  , Yang Cui-Bai  , Wang Zhi-Yong  ,   Institute of Laser Engineering, Beijing University of Technology, Beijing 100124, China;,   Redsolar New Energy Technology Co. Ltd., Zhongshan 528437, China
Published: December 2020

At present, solar cells are the main sources for spacecrafts. For a long time the bulk of the space power installations has been the solar arrays based on single junction silicon and gallium arsenide solar cells. In recent years a trend has been the active use of triple-junction GaAs solar cell with higher efficiency instead of single junction solar cells. One of the most important characteristics of solar cells used in spacecrafts is the resistance to radiation damages caused by high energy particles of the near-Earth space. According to the spectral response of triple-junction GaAs solar cell and the damage characteristics of the current under the condition of electron irradiation, the physical mechanism of cell attenuation can be determined: the current degradation originates mainly from the GaInAs subcells. These damages form additional centers of nonradiative recombination, which results in the reduction of the minority charge carrier diffusion lengths and in degradation of the solar cells photocurrent.The radiation damage caused by the electron irradiation will shorten the diffusion length of the base region and affect the collection of photo generated carriers. The ways of improving absorption of long wavelength light in GaInAs subcells with a thin base in using the distributed Bragg reflector can be investigated by the mathematical simulation method based on calculating the light propagation in a multilayer structure by means of the TFCalc software which can design optical structure. To estimate the validity of these methods for solar cells structures with distributed Bragg reflector, the spectral dependences of the photoresponse and the reflection coefficient with different base thickness values are calculated and compared with experimental results. Based on the physical mechanism of the degradation, the thickness of middle subcell base layer is reduced, and an appropriate structure of the distributed Bragg reflector is simulated by the TFCalc software. As a result, the new structure solar cells are that the thickness of the base layer is 1.5 m compared with the different middle subcell thickness values, and the distributed Bragg reflector structure with 15 paris of the Al0.1Ga0.9As/Al0.9Ga0.1As with 850 nm central wavelength is embedded in the middle subcell of the base layer, the distributed Bragg reflector has a highest reflectivity of more than 97% in the actual test, and a bandwidth of 94 nm, which can satisfy design requirement. After irradiating the new structure of solar cells, the decay of its short-circuited current is reduced by 50% compared with that of the original structure, and the remaining efficiency factor is increased by 2.3%.
Excitation processes in experimental photoionized plasmas
Authors: Han Bo  , Wang Fei-Lu  , Liang Gui-Yun  , Zhao Gang  ,   Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Photoionized plasmas widely exist nearby strong radiative sources in the universe. With the development of the high energy density facilities, photoionized plasmas related to astrophysical objects are generated in laboratories accordingly. RCF (radiative collisional code based on the flexible atomic code) is a theoretical model applied to steady-state photoionized plasmas. Its rate equation includes five groups of mutually inverse atomic processes, which are spontaneous decay and photoexcitation, electron impact excitation and deexcitation, photoionization and radiative recombination, electron impact ionization and three body recombination, autoionization and dielectronic capture. All of the atomic data are calculated by FAC (the flexible atomic code), and with four input parameters, RCF can calculate the charge distribution and emission spectrum of the plasma. RCF has well simulated the charge state distribution of a photoionizing Fe experiment on Z-facility and the measured spectrum of photoionizing Si experiment on GEKKO-XII laser facility. According to the simulation results, the importance of photoexcitation and electron impact excitation processes in the two photoionization experiments is discussed. In the photoionizing Fe experiment condition, high energy photons not only ionize the ions by photoionization directly, but also excite the ions to autoionizing levels, ionizing the ions indirectly. What is more, far from ionizing the ions, electrons even suppress the ionization of the plasma by exciting the ions to levels with small ionization cross sections. In the photoionizing Si experiment condition, because of high photoexcitation rate, strong resonance line of He-like ion and some Li-like ion lines, which have similar spontaneous decay rates as the resonance line, are emitted. Although the intercombination line of He-like ion has lower spontaneous decay rate than the resonance lines, strong recombination makes them have comparable strengthes. Electron impact excitation can influence the line ratio of He-like ion lines by affecting the distribution of 1s2l (l=s,p) levels.
Frequency control of the broadband ultrashort terahertz source generated from the laser induced plasma by two-color pluses
Authors: Li Na  , 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
Published: December 2020

The terahertz (THz) radiation becomes an attractive light source utilized in molecular dynamic spectroscopy, remote sensing, medicine, communication and fundamental research. The controlling of the THz spectrum is necessary for the applications. In this paper, a method is proposed for controlling the terahertz spectra generated from the laser induced plasma by two-color pluses based on the contribution of plasma oscillation. The plasma current oscillation can shift the THz spectrum when the length of medium is less than plasma skin depth. Experimentally we use a short length of molecules by means of the molecular beam method. We investigate the changing spectrum of broadband ultrashort terahertz THz generated from a jet of nitrogen (N2) molecules pumped with the two-color laser pulses following the varying plasma density and plasma length. With the increase of plasma density and the decrease of the plasma length, we observe the increase of THz central frequency (0.8-1.4 THz) and the broadening of the THz spectral width (0.78-1.53 THz). The analysis and the calculation show that the THz spectrum changes due to the frequency and the width of the plasma resonance. This scheme of controlling the THz spectrum by changing the plasma density and length is easier to implement and do not need to use complex shaped optical pulses. The discovery provides a new way of controlling the low-frequency broadband THz spectrum.
Theoretical study on thermal and acoustic surface wave properties of Ga3PO7 crystal at high temperature
Authors: Hao Juan  , Zhou Guang-Gang  , Ma Yue  , Huang Wen-Qi  , Zhang Peng  , Lu Gui-Wu  ,   China University of Petroleum, College of Science, Beijing 102249, China;,   Beijing University of Science and Technology Information, College of Science, Beijing 100081, China
Published: December 2020

The high-temperature piezoelectric crystal Ga3PO7is a versatile functional material widely used in many electromechanical devices. As the Curie temperature of this crystal is as high as 1346 ℃, it can break through the current temperature limitations(1200 ℃) and then be used in extremely high-temperature condition. However, it is very difficult to explore its properties in such a high-temperature environment. Moreover, the relevant theoretical research has not been reported to date. Aiming at this problem, the density function theory combined with quasi harmonic approximation theory is used to investigate the structural, thermal and surface acoustic wave (SAW) properties of Ga3PO7. Firstly, the Gibbs energies of Ga3PO7 crystal with different stains are calculated, and the equilibrium structures of Ga3PO7 crystal at different temperatures (from 0 ℃ to 1200 ℃) are found according to minimal energy principle. Secondly, based on the result above, we optimize Ga3PO7 crystal at different temperatures, and then, the thermal and elastic properties of Ga3PO7 crystal within 0-1200 ℃ are calculated using CASTEP package based on the density functional theory in the generalized gradient approximation. The results show that its lattice constants increase almost linearly as temperature increases while its density decreases. Owing to anisotropy, its lattice constant along the c axis increases much more greatly than along the a axis. The coefficients of thermal expansion along the a and c axis are evaluated to be 1.6710-6 K-1 and 3.5810-6 K-1, respectively, and the volumetric heat capacity is evaluated to be 2.067 J/gK. These values all agree well with the experimental values. Finally, the elastic constants, bulk modulus and SAW properties of Ga3PO7 crystal at different temperatures (from 0 ℃ to 1200 ℃) are calculated. The results show that the bulk modulus can reach 175 GPa, and it changes very little as temperature increases. The fluctuation of elastic constants has slight influences on SAW velocity and the electric-mechanical coupling factor. When the propagation angle is 151, it possesses the stablest SAW properties and the largest electric-mechanical coupling factor which can reach 0.7%. The comprehensive analyses of the thermal, mechanical and SAW properties show that Y-cut Ga3PO7 possesses a greater potential application in high temperature environment.
Identifying the mobility edges in a one-dimensional incommensurate model with p-wave superfluid
Authors: Liu Tong  , Gao Xian-Long  ,   Department of Physics, Zhejiang Normal University, Jinhua 321004, China
Published: December 2020

The mobility edges which separate the localized energy eigenstates from the extended ones exist normally only in three dimensional systems. For one-dimensional systems with random on-site potentials, one never encounters mobility edges, where all the eigenstates are localized. However, there are two kinds of 1D systems such as correlated disordered models, and the systems of exponentially decaying hopping kinetics, features of mobility edges at some specific values become possible. We study in this paper the properties of the mobility edges in a one-dimensional p-wave superfluid on an incommensurate lattice with exponentially decaying hopping kinetics. Without the p-wave superluid, the system displays a single mobility edge, which separates the extended regime from the localized one at a certain energy. Without the exponentially decaying hopping term, the system displays a phase transition from a topological superconductor to an Anderson localization at a certain disorder strength, where no mobility edge exists. We are interested in the influence of the p-wave superfluid on the mobility edge. By solving the Bogoliubov-de Gennes equation, the eigenvalues and the eigenfunctions are obtained. In order to identify the extending or the localized properties of the eigenvectors, we define an inverse participation ratio IPR. For an extended state, IPRn～1/L which goes to zero at a large L, and for a localized one, IPRn being constant. Therefore, the IPR can be taken as a criterion to distinguish the extended state from the localized one, while the mobility edge is defined as the boundary between two different states. We find that, with a p-wave superfluid, the system changes from a single mobility edge to a multiple one, and the number of mobility edges increases with the increased superfluid pairing order parameter. To further obtain the energy or the location of the mobility edge, we investigate the scaling behavior of wave functions by using a multifractal analysis, which is calculated through the scaling index . The minimum value of the index, with the values min= 1, 0min1, and min= 0, mean the extended, critical, and localized states, respectively. For the two consecutive states, the minima of the scaling index min when extrapolating to the large size limit between 0 and 1 signal the mobility edge. By exploring the corresponding Bogoliubov quasi-particle wave functions for the system under open boundary conditions together with the multifractal analysis for the system under periodic boundary conditions, we identify two mobility edges for the system of the p-wave superfluid pairing. Furthermore, we will investigate how the existence of the mobility edges influences the p-wave superfluid, and identify the phase diagram at the given parameters. We will in the future try to understand the relationship between the topological superfluid and the mobility edges.
Effects of in-situ surface modification by pulsed laser on InAs/GaAs (001) quantum dot growth
Authors: Zhang Wei  , Shi Zhen-Wu  , Huo Da-Yun  , Guo Xiao-Xiang  , Peng Chang-Si  ,   School of Optoelectronics Information Science and Engineering, Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215123, China
Published: December 2020

InAs/GaAs quantum dots (QDs) have been extensively applied to high-performance optoelectronic devices due to their unique physical properties. In order to exploit the potential advantages of these QD-devices, it is necessary to control the QDs in density, uniformity and nucleation sites. In this work, a novel research of in-situ pulsed laser modifying InAs wetting layer is carried out to explore a new controllable method of growing InAs/GaAs(001) QDs based on a specially designed molecular beam epitaxy (MBE) system equipped with laser viewports. Firstly, a 300 nm GaAs buffer layer is grown on GaAs (001) substrate at 580 ℃ and the temperature decreases to 480 ℃ to deposit InAs. As soon as the amount of InAs deposition reaches 0.9 ML, a single laser pulse ( =355 nm, pulse duration ～ 10 ns) with an energy intensity of ～ 40.5 mJ/cm2 is in-situ introduced to irradiate the surface. Then, the sample is taken out and then its surface modification is immediately evaluated by atomic force microscope measurement. Atomic layer removal nano-holes elongated in the direction, and a surface density of ～2.0109 cm-2 are observed on the wetting layer. We attribute the morphology change to being due to laser-induced atom desorption. Because indium atoms should be easily desorbed away at substrate temperature of 480 ℃ during the laser irradiation, some vacancy defects are created. Then atoms adjacent to those defects would become weakly bounded, resulting in preferential desorption around the defect sites in sequence. Therefore, atomic layer removal is intensified by such a kind of chain effect and finally nano-holes are developed on the surface. In order to make clear how these nano holes of special kind influence the InAs/GaAs (001) QD growth, we perform another study by continuously depositing the InAs after the irradiation at the same thickness of 0.9 ML. It is found that when 1.7 ML InAs is deposited, QDs start to nucleate into some nano-holes and then are further deposited with an InAs coverage of 1.9 MLs, all the nano holes would be completely nucleated by QDs with a good uniformity, and there are no QDs in the remaining area. Such an effect of QD preferential nucleation in nano-holes could be explained by the following two causes. Firstly, adsorbed indium atoms tend to immigrate into nano-holes for lower surface energy induced by the concave surface curvature. The enhanced accumulation of Indium is in favor of the preferential nucleation of QDs in nano-holes. On the other hand, QD growth in areas outside the nano holes is depressed for indium desorption in pulsed laser irradiation process. In conclusion, our studies of in-situ laser-induced surface modification reported here provide a potential solution of controllable InAs/GaAs (001) QD growth.
On-chip fabrication of lateral growth ZnO nanowire array UV sensor
Authors: Li Jiang-Jiang  , Gao Zhi-Yuan  , Xue Xiao-Wei  , Li Hui-Min  , Deng Jun  , Cui Bi-Feng  , Zou De-Shu  ,   Institute of Opto-Electronics, Peking University, Beijing 100124, China
Published: December 2020

In this paper, we integrate nano technology into traditional microelectronic processing, and develop an on-chip UV sensor based on lateral growth ZnO nanowire arrays. Traditional procedures are used to fabricate the interdigital electrodes, and ZnO nanowires are self-organized and grown between electrodes laterally by hydrothermal method. Additional inclined nanowires are removed during the post-processing procedures, such as ultrasound cleansing and electrode reinforcement. Two kinds of electrode structures are applied, i.e., Cr and Au. For the Cr electrode device structure, because Cr will restrain nanowires from growing vertically on its top, the laterally grown nanowire is long enough to reach the other side of the electrode. The corresponding photoelectric response mechanism is photoconduction controlled by surface oxide ion adsorption. Although the photocurrent is large, the gain is low, and the response speed is slow. Under the UV radiations of 20 mW/cm2 and of 365 nm in wavelength, the dark current is 2.210-4 A with 1 V bias voltage, the gain is up to 64, the photocurrent cannot reach saturation after 25 s, and the recovery time is 51.9 s. A secondary electrode can be fabricated after growing the nanowire arrays to reinforce the connection between the electrode and the ends of the nanowires. However, the direct contact between metal and semiconductor will form a Schottky contact. The photoelectric response mechanism is then changed to photovoltaic effect, which can greatly improve the gain and response speed. Under UV radiations of 20 mW/cm2 and of 365 nm in wavelength, the dark current is 4.310-8 A with 1 V bias voltage, the gain is up to 1300, the respond time is 3.8 s, and the recovery time is 5.7 s. For the Au electrode device structure, because Au is catalysis for ZnO nanowire growth, nanowires grown in lateral direction will compete with those grown in vertical direction, and hence the laterally grown nanowires are not long enough to reach the other side of the electrode. Nanowires grown from two sides of the electrodes will meet each other and form a bridging junction, however, this will turn the photoconduction mechanism from surface ion controlled into a bridging junction controlled, which yields the best device performance. Before removing the inclined nanowires by ultrasound cleansing, under UV radiations of 20 mW/cm2 and of 365 nm in wavelength, the dark current is 8.310-3 A with 1 V bias voltage, the gain is up to 1350, the respond time is 3.3 s, and the recovery time is 3.4 s. After removing the inclined nanowires, under UV radiations of 20 mW/cm2 and of 365 nm in wavelength, the dark current is 10-9 A with 1 V bias voltage, the gain is up to 8105, the respond time is 1.1 s, and the recovery time is 1.3 s.
Functional coupling analyses of electroencephalogram and electromyogram based on variational mode decomposition-transfer entropy
Authors: Xie Ping  , Yang Fang-Mei  , Li Xin-Xin  , Yang Yong  , Chen Xiao-Ling  , Zhang Li-Tai  ,   Key Laboratory of Measurement Technology and Instrumentation of Hebei Province, Institute of Electric Engineering, Yanshan University, Qinhuangdao 066004, China;,   Department of Rehabilitation Medicine, the No. 281 Hospital of Chinese People's Liberation Army, Qinhuangdao 066100, China
Published: December 2020

The functional corticomuscular coupling (FCMC) is defined as the interaction, coherence and time synchronism between cerebral cortex and muscle tissue, which could be revealed by the synchronization analyses of electroencephalogram (EEG) and electromyogram (EMG) firing in a target muscle. The FCMC analysis is an effective method to describe the information transfer and interaction in neuromuscular pathways. Forthermore, the multiscaled coherence analyses of EEG and EMG signals recorded simultaneously could describe the multiple spatial and temporal functional connection characteristics of FCMC, which could be helpful for understanding the multiple spatial and temporal coupling mechanism of neuromuscular system. In this paper, based on the adaptively decomposing signal into frequency band characteristis of variational mode decomposition (VMD) and the quantitatively detecting the directed exchange of information between two systems of transfer entropy (TE), a new methodvariational mode decomposition-transfer entropy (VMD-TE) is proposed. The VMD-TE method could quantitatively analyze the nonlinear functional connection characteristic on multiple time-frequency scales between EEG over brain scalp and surface EMG signals from flexor digitorum surerficialis, which are recorded simultaneously during grip task with steady-state force output.In this paper, application of VMD-TE method consists of two steps. Firstly, the EEG and EMG signals are adaptively decomposed into multi intrinsic mode functions based on variational mode decomposition method, respectively, to describe the information on different time-frequency scales. Then the transfer entropies between the different timefrequency scales of EEG and EMG are calculated to describe the nonlinear corticomuscular coupling characteristic in different pathways (EEGEMG and EMGEEG), to show the functional coupling strength (namely VMD-TE values). finally, the maximum VMD-TE values between the different time-frequency scales of EEG and EMG signals among the eight subjects are selected, to describe the discrepancies of FCMC interaction strength between all time-frequency scales. The results show that functional corticomuscular coupling is significant in both descending (EEGEMG) and ascending (EMGEEG) directions in the beta-band (15-35 Hz) in the static force output stage. Meanwhile, the interaction strength between EEG signal and the gamma band (50-72 Hz) of EMG signal in descending direction is higher than in ascending direction. Our study confirms that the beta oscillations of EEG travel bidirectionally between sensorimotor
Iterative learning control of a class of discrete-time singular system
Authors: Cao Wei  , Guo Yuan  , Sun Ming  ,   College of Computer and Control Engineering, Qiqihar University, Qiqihar 161006, China
Published: December 2020

Singular systems are also called descriptor systems. Compared with normal systems, singular systems have become one of effective tools which can describe and characterize varieties of real systems, because they can better describe physical properties of the systems. Up to now, the analyses and syntheses of singular systems have been widespread applied to linear matrix inequality (LMI) method. The method requires known systems to have accurate mathematical model information, however, real systems have difficulties in obtaining their accurate mathematical models, owing to the fact that real systems are frequently subjected to all kinds of interferences, uncertainties, and nonlinear factors. Specially, in the case of singular systems, obtained LMI conditions often have a constraint equation or LMI is semi-definite, which makes it more difficult to solve LMI. Therefore, in order to avoid the above two problems occurring in settling state tracking issue for singular systems, in the meantime, for convenience of computating control algorithm and information storage, in this paper we propose a discrete-time iterative learning control algorithm for a class of discrete-time singular system with repetitive running characteristics in finite time interval. The specific process is divided into two steps. First, the class of discrete-time singular system is decomposed into normal discrete-time state equation and algebraic equation form by nonsingular transformation. Accordingly, the singular system state is also decomposed into two parts. Among them, the dimension of the first part state is equal to singular matrix rank and another is equal to system dimension minus singular matrix rank. In addition, the control law of last iterative learning is modified by using two tracking errors at two different times: one error is real-time tracking error generated from the comparison between the first part state and its desired state and another is tracking error at a previous time generated from comparison between the second part state and its desired state. And thus a new control law of next iterative learning is obtained, such that, as for any given real singular system, its state may completely track the desired state as long as selected learning gain can satisfy the convergence condition of the algorithm. Further, the convergence of the control algorithm is theoretically proved by compression mapping method, and thus its sufficient convergence condition is given in the sense of -norm. The results indicate that the proposed iterative learning control algorithm can make system state realize the perfect tracking of desired state as iteration number gradually increases in finite time interval, and the convergence of the algorithm only depends on system parameters and learning gain rather than initial value of control variable. The simulation example finally verifies the effectiveness of the proposed algorithm.
Tripartite entanglement of {Cu3} single molecular magnet with magnetic field in thermal equilibrium
Authors: Zheng Yi-Dan  , Zhou Bin  ,   Faculty of Physics and Electronic Science, Hubei University, Wuhan 430062, China
Published: December 2020

Quantum entanglement is one of the most fundamental properties of quantum mechanics. Because of the nonlocality, quantum entanglement is widely used in quantum computation and quantum information. Considering the fact that thermal fluctuation suppresses quantum effects, the concept of thermal entanglement is introduced to refer to the idea that the effect of temperature should be viewed as external control in the preparation of entangled state. It has been found that nanoscale single molecular magnet has a novel quantum effect at low temperature. Furthermore, single-molecular magnet is viewed as a promising candidate for realizing encoding and manipulation of quantum information. Na9[Cu3Na3(H2O)9(-AsW9O33)2]26H2O (denoted as {Cu3} for convenience) is one of the typical representatives of nanoscale single molecular magnets. In this paper, we will theoretically analyze the properties of tripartite entanglement in {Cu3} with an external magnetic field in thermal equilibrium. The tripartite negativity is used to characterize the tripartite entanglement. The tripartite negativity of {Cu3} single molecular magnet is calculated numerically by using the equivalent spin model and experimental fitting parameters. We consider the magnetic fields along the vertical and the parallel directions of triangular spin ring, respectively, and the case with a tilted magnetic field is also discussed in this paper. It is shown that the magnitude and direction of magnetic field, and temperature have importance effects on the tripartite negativity of the system. It is found that the larger extra strong magnetic field will inhibit the generation of the quantum state of tripartite entanglement at higher temperature. In addition, compared with the magnetic field along the parallel direction of triangular spin ring and the tilted magnetic field, the magnetic field along the vertical direction of triangular spin ring obtains larger values of tripartite negativity under the same temperature and magnetic field. We also plot the variations of the critical temperature with the magnetic field along different directions, and from the critical temperature-magnetic field phase diagrams one can obtain the range of parameters in which the tripartite entanglement of the system exists. We also find that entanglement revival behaviors may occur in the specific range of parameters. Therefore, the properties of the tripartite entanglement in the {Cu3} triangular spin ring can be controlled and enhanced by choosing appropriate magnitude and direction of the magnetic field and temperature.
Incoherent ptychography in Fresnel domain with simultaneous multi-wavelength illumination
Authors: Pan An  , Wang Dong  , Shi Yi-Shi  , Yao Bao-Li  , Ma Zhen  , Han Yang  ,   State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710119, China;,   Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Academy of Optoelectronics, Chinese Academy of Sciences, Beijing 100094, China
Published: December 2020

Single wavelength illumination is used in the traditional ptychography. Even though using multi-wavelength to improve image quality, it takes the scheme of illuminating in turn due to the requirement of coherence. So far, the addition of incoherent modes has been regarded as a nuisance in diffractive imaging. Here we propose a scheme of incoherent ptychography and an algorithm of information multiplexing that uses the multi-wavelength illumination simultaneously, which are demonstrated in experiment and simulation. Compared with the scheme of traditional ptychography, it can recover not only the object well, but also the spectral response of the object, probes of complex value and spectral weight of each wavelength respectively. This method obtains much information about the object and owns the multichannel and multispectral merits. Meanwhile, by means of color image coding, this method can retrieve true color images and enhance the image quality. The proposed algorithm has strong robustness. Besides, we also investigate how many modes can be recovered by this method. The work may open up possibilities for information multiplexing in ptychography and multispectral microscopy imaging over various applications.
Gyrator transform of four-petal Gaussian beam and generation of rectangular hollow beam
Authors: Gong Ning  , Zhu Kai-Cheng  , Xia Hui  ,   School of Physics and Electronics, Central South University, Changsha 410083, China
Published: December 2020

Four-petal Gaussian beam is a special type of Gaussian beam, and its propagation properties are widely used in micro optics, optical communication and splitting technology. Recently, the generations and the properties of different types of hollow beams have become a hot research topic, such as research on hollow optical vortex beams. The Gyrator transform can be used to fulfill the mode conversion of laser beam. In this paper, based on the Gyrator transform, the analytical expression of four-petal Gaussian beam passing through such a transform system is derived, and the intensity distribution and the corresponding phase distribution associated with the transforming four-petal Gaussian beam are analyzed by numerical simulations. It is found that the four-petal Gaussian beam can be transformed into rectangular hollow beam by Gyrator transform, under the appropriate conditions of the beam order, the beam parameter, the transform angle of Gyrator transform, and the waist width. For the beam order n=m=3, the transform angle of Gyrator transform = 0.4133, the beam parameter K=30, and the waist width = 0.9, the rectangular hollow optical vortex beams can be obtained. Under such conditions, the maximum intensities appear in the four corners, and they are almost uniform on the four sides. The effects of the beam parameters, the transform angle, and the beam order on the distributions of intensity and phase of the rectangular hollow beam are analyzed in detail. The numerical results show that for the beam parameter K10, the rectangular hollow beam always is obtained, and for a lager beam parameter, the intensity distribution of the rectangular hollow beam is more uniform. Different beam order generates different type of hollow beam. For example, for n=m = 2, = 1.2, K = 30, and = 0.5409, a new strange circular hollow beam with solid circular nucleus can be obtained. The transform angle of Gyrator transform has a significant effect on the energy distribution of the hollow beam. When the transform angle changes in a small range, the uniformity of the intensity distribution of the rectangular hollow beam is lost. The bigger the transform angle change, the more serious the loss of uniformity of the hollow beam intensity is. The size of the hollow beam bright ring is determined by the waist width of the four-petal Gaussian beam: the larger the waist width, the smaller the bright ring is. The results further enriches the applications of Gyrator transform system and the four-petal Gaussian beam in the beam shaping.
Investigation on Ge-As-Se-Te chalcogenide glasses for far-infrared fiber
Authors: Zhao Zhe-Ming  , Wu Bo  , Liu Ya-Jie  , Jiang Ling  , Mi Nan  , Wang Xun-Si  , Liu Zi-Jun  , Liu Shuo  , Pan Zhang-Hao  , Nie Qiu-Hua  , Dai Shi-Xun  ,   Laboratory of Infrared Material and Devices, The Research Institute of Advanced Technologies, College of Information Science and Engineering, Ningbo University, Ningbo 315211, China;,   Nanhu College, Jiaxing University, Jiaxing 314001, China;,   Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province, Ningbo 315211, China
Published: December 2020

With the development of infrared optics, low-loss waveguide materials are required. Especially, low-loss optical fiber development for far-infrared application has become a focus. Chalcogenide Ge-As-Se-Te(GAST) glasses and fibers for far-infrared light are prepared and investigated in this paper. The thermal properties and the infrared transmissions are reported. The influences of oxygen and hydrogen on the glass transmission and fiber attenuation are discussed. Low-loss GAST fiber with a structure of fine core/cladding is reported by a novel extrusion method (0.46 dB/m at 8.7 m, 1.31 dB/m at 10.6 m, base loss being under 1 dB/m from 7.2 to 10.3 m). Here, the glasses are prepared by traditional vacuum melt-quenching and vapor distillation method. Structure and physical properties of GAST glass system are studied with X ray diffractions and thermal expansion instrument. Optical spectra of GAST glass system are obtained by spectrophotometer and infrared spectrometer. Main purification processes with different oxygen-getters (magnesium and aluminum) are disclosed. The fiber attenuation is measured by the cut-back method with an Fourier transform infrared spectroscopy spectrometer. The lowest loss of this fiber can be reduced to 1.32 dB/m at 10.6 m, as it has a structure of Ge20As20Se15Te45 core and Ge20As20Se17Te43 cladding. The results show that these glasses are well transparent in a wide infrared window from 1.1 to 22 m, and these glass fibers can transmit far-infrared light up to 12 m, thus the GAST glass system is one of good candidates for far-infrared transparent materials. The fiber attenuation can be reduced effectively by the reasonable purification and novel extruded-processing. These fibers are suited for the power delivery of CO2 laser.
Theoretical model and simulation of ship underwater radiated noise
Authors: Sun Jun-Ping  , Yang Jun  , Lin Jian-Heng  , Jiang Guo-Jian  , Yi Xue-Juan  , Jiang Peng-Fei  ,   Qingdao Branch, Institute of Acoustics, Chinese Academy of Sciences, Qingdao 266023, China;,   Key Laboratory of Noise and Vibration Research, Chinese Academy of Sciences, Beijing 100190, China;,   Key Laboratory of Underwater Acoustic Environment, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences (Institute of Information Engineering), Beijing 100049, China
Published: December 2020

Ship underwater radiated noise is one of the most important ocean ambient noise sources, and building a reasonable model for the ship underwater radiated noise is helpful for understanding the physical mechanism and reducing research cost of ship underwater radiated noise. The quasi-periodic random sound pulse sequence signals act well in explaining the rhythm and the power spectrum variation of the ship underwater radiated noise, and reveal that there are not any real sinusoidal components in ship radiated noise signals, which come from the non-linear transformation of the signals, and the analysis of some representative experimental data of ship radiated noise also supports this idea. Based on this, the explosion-type cosine pulses are used as the units of quasi-periodic random sound pulse sequences. This model can generate the power spectrum with a peak, and the peak location can change with ship velocity or ship type. The power spectrum variation characteristics of quasi-periodic random sound pulse sequences consisting of the explosion-type cosine pulses are in good agreement with the measured ship underwater radiated noise data, which shows that this model is of important practical value.
Measurement of shear elasticity of granular solid
Authors: Yan Xi-Ping  , Peng Zheng  , He Fei-Fei  , Jiang Yi-Min  ,   School of Physics and Electronics, Central South University, Changsha 410083, China
Published: December 2020

Using a direct shear-box capable of very low shearing rate, we measure the force-displacement curve of cyclic, large-amplitude shear, and also the total plastic displacement residual after each cycle, for samples of glass beads. As the shear rate decreases, we observe a transition from normal, elastoplastic behavior to pure elastic behavior, with reducing residual, or total plastic, displacement after each cycle. Remarkably, this transition is also observed for large amplitude of the cyclic shear, up to 90% of the failure value. The force-displacement relation is necessarily rate-dependent during this transition. These experimental results demonstrate that granular solids may respond in a purely elastic manner, both for low amplitude force oscillations of high frequencies (such as sound) and for large amplitude ones of low frequencies, implying that the granular matter has a purely elastic regime, in which the theory of elasticity holds fully true. This regime has been overlooked in the literature, probably because its deformation rate is nearly two orders of magnitude lower than those typically used. Theoretically, the present measurements support granular solid hydrodynamics, or the fact that strong deviation from elastoplastic dynamics and rate independence take place in the low frequency limit, with a rate-dependent transition to the classic theory of elasticity.