bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental investigation of ejecta on melted Sn sample under shock loading
Authors: Chen Yong-Tao  , Hong Ren-Kai  , Chen Hao-Yu  , Ren Guo-Wu  ,   Laboratory for Shock Wave and Detonation Physical Research, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Ejecta production from the metal surface under shock-loading is currently a focused issue both at home and abroad. However, the traditional experimental techniques, such as piezoelectric pin, only diagnose the ejected data for low-density ejecta but not for high-density ones, giving a poor understanding of this process. Particularly, when ejecta production increases significantly as the loaded metal melts on release or shock, the measurement carried out by the traditional piezoelectric pin becomes worse, and brings further missing knowledge in the ejecta evolution.In this paper, an Asay-F window designed earlier by the authors based on the traditional Asay-window, is employed to investigate the formation process of the ejecta from the melted Sn metal. As indicated by previous experimental findings on shocked Pb sample, the Asay-F window is a reliable and effective tool for measuring the high-density ejecta by comparing the result with those of the piezoelectric pin. The interface velocity within the Asay-F window measured by Doppler pin system, is obtained. On the basis of momentum conservation condition, the physical quantities of ejecta, such as accumulative areal mass, volume density and velocity, are derived from the interface velocity. By analyzing the experimental data diagnosed by the Asay-F window, which is placed at different offsets from the free surface of Sn sample, the expansion evolution of the ejecta is obtained. Through transforming the dynamic volume density to the static one, the picture of the ejecta density distribution changes with the spatial distance at a specific moment, which is explicitly displayed. It is found that the ejecta density distributions gained from the different offsets at the uniform moment are consistent. As a consequence, the self-similar expansion evolution of the ejecta is experimentally confirmed, which successfully avoids the unclear understanding of this process if only examined by the piezoelectric pin. This experiment may lay the foundation of the formation of the ejecta production for the metal sample subjected to high pressure loading.
Influence of thermal treatment on the ionic valence and the magnetic structure of perovskite manganites La0.95Sr0.05MnO3
Authors: Wu Li-Qian  , Qi Wei-Hua  , Li Yu-Chen  , Li Shi-Qiang  , Li Zhuang-Zhi  , Xue Li-Chao  , Ge Xing-Shuo  , Ding Li-Li  ,   Hebei Advanced Thin Film Laboratory, Department of Physics, Hebei Normal University, Shijiazhuang 050024, China;,   No.46 Research Institute of China Electronics Technology Group Corporation, Tianjin 300220, China
Published: December 2020

In traditional views, the magnetic ordering of oxides may be explained using magnetic superexchange (SE) or double exchange (DE) interaction models. Both models are based on an assumption that the valences of all oxygen ions be -2. For example, both La and Mn in LaMnO3 are assumed to be trivalent, in which antiferromagnetic spin structure is explained using the SE interaction between Mn3+ cations mediated by oxygen anions. In La1-xSrxMnO3, there exists a part of Mn4+ cations with the content ratio of Mn4+/Mn3+ being x/(1-x), in which spin structure and electronic transport properties are explained by DE interaction. However, there is a part of monovalent oxygen ions existing in oxides. Cohen [Nature 358 136] has calculated the densities of states for valence electrons in the perovskite oxide BaTiO3 using density functional theory. Results indicate that the average valence of Ba is +2, being the same as that in the traditional one, but the average valences of Ti and O are +2.89 and -1.63 respectively, agreeing with the results obtained using ionicity investigation [Rev. Mod. Phys. 42 317] and X-ray photoelectron spectra (XPS) analysis, but different from the conventional results +4 and -2. In this paper, three samples with the nominal composition La0.95Sr0.05MnO3 are prepared by different thermal-treatments. Likewise, there are only Mn2+ and Mn3+ cations, but no Mn4+ cations in La0.95Sr0.05MnO3, a result obtained by XPS analysis, and the average valence of Mn in La0.95Sr0.05MnO3 samples increases with increaseing thermal-treatment. Although the crystal structures of the samples are the same, the magnetic moments per formula are obviously different. This magnetic structure cannot be explained using the conventional SE and DE interaction models. Using the O 2p itinerant electron model for spinel ferrites proposed recently by our group, we can explain this magnetic structure. The variation trend of the average valences of Mn cations calculated using the magnetic moments per formula of the samples at 10 K, is in accordance with the experiment results of XPS. The O 2p itinerant electron model is based on an assumption that there is a part of monovalent oxygen ions in the oxides, which is the fundamental difference from SE and DE interaction models.
Effect of variable network clustering on the accuracy of node centrality
Authors: Song Yu-Ping  , Ni Jing  ,   Business School, University of Shanghai for Science and Technology, Shanghai 200093, China
Published: December 2020

Measurements of node centrality are based on characterizing the network topology structure in a certain perspective. Changing the network topology structure would affect the accuracy of the measurements. In this paper, we employ the Holme-Kim model to construct scale-free networks with tunable clustering, and consider the four measurements of classical centrality, including degree centrality, closeness centrality, betweenness centrality and the eigenvector centrality. For comparing the accuracy of the four centrality measurements, we simulate the susceptible-infected-recovered (SIR) spreading of the tunable clustering scale free networks. Experimental results show that the degree centrality and the betweenness centrality are more accurate in networks with lower clustering, while the eigenvector centrality performs well in high clustering networks, and the accuracy of the closeness centrality keeps stable in networks with variable clustering. In addition, the accuracy of the degree centrality and the betweenness centrality are more reliable in the spreading process at the high infectious rates than that of the eigenvector centrality and the closeness centrality. Furthermore, we also use the reconnected autonomous system networks to validate the performance of the four classical centrality measurements with varying cluster. Results show that the accuracy of the degree centrality declines slowly when the clustering of real reconnected networks increases from 0.3 to 0.6, and the accuracy of the closeness centrality has a tiny fluctuation when the clustering of real reconnected networks varies. The betweenness centrality is more accurate in networks with lower clustering, while the eigenvector centrality performs well in high clustering networks, which is the same as in the tunable clustering scale free networks. According to the spreading experiments in the artificial and real networks, we conclude that the network clustering structure affects the accuracy of the node centrality, and suggest that when evaluating the node influence, we can choose the degree centrality in the low clustering networks, while the eigenvector centrality and the closeness centrality are still in the high clustering networks. When considering the spreading dynamics, the accuracy of the eigenvector centrality and the closeness centrality is high, but the accuracy of the degree centrality and the betweenness centrality is more reliable in the spreading process at high infectious rates. This work would be helpful for deeply understanding of the node centrality measurements in complex networks.
Synchronizability and eigenvalues of two-layer star networks
Authors: Xu Ming-Ming  , Lu Jun-An  , Zhou Jin  ,   School of Mathematics and Statistics, Wuhan University, Wuhan 430072, China
Published: December 2020

From the study of multilayer networks, scientists have found that the properties of the multilayer networks show great difference from those of the traditional complex networks. In this paper, we derive strictly the spectrum of the super-Laplacian matrix and the synchronizability of two-layer star networks by applying the master stabi- lity method. Through mathematical analysis of the eigenvalues of the super-Laplacian matrix, we study how the node number, the inter-layer and the intra-layer coupling strengths influence the synchronizability of a two-layer star net-work. We find that when the synchronous region is unbounded, the synchronizability of a two-layer star network is only related to the intra-layer coupling strength between the leaf nodes or the inter-layer coupling strength of the entire network. If the synchronous region of a two-layer star network is bounded, not only the inter-layer coupling strength of the network and the intra-layer coupling strength between the leaf nodes, but also the intra-layer coupling strength between the hub nodes and the network size have influence on the synchronizability of the networks. Provided that the same inter-layer and intra-layer coupling strengths are concerned, we would further discuss the opti-mal ways of strengthening the synchronizability of a two-layer star network. If the inter-layer and intra-layer coupling strengths are far less than unity, changing the intra-layer coupling strength is the best way to enhance the synchronizability no matter what the synchronous region is. While if the coupling strengths are the same as, less than or more than unity, there will be different scenarios for the network with bounded and unbounded synchronous regions. Besides, we also discuss the synchronizability of the multilayer network with more than two layers. And then, we carry out numerical simulations and theoretical analysis of the two-layer BA scale-free networks coupled with 200 nodes and obtain very similar conclusions to that of the two-layer star networks. Finally, conclusion and discussion are given to summarize the main results and our future research interests.
Evolutions of two-qubit entangled system in different noisy environments and channels
Authors: Cao Lian-Zhen  , Liu Xia  , Zhao Jia-Qiang  , Yang Yang  , Li Ying-De  , Wang Xiao-Qin  , Lu Huai-Xin  ,   Shandong Provincial Key Laboratory of Multi-Photon Entanglement and Manipulation, Department of Physics and Optoelectronic Engineering, Weifang University, Weifang 261061, China
Published: December 2020

Quantum information technology is mainly based on quantum entanglement. As an important coherent superposition state, the coherence of quantum entanglement source is easily affected by environment and becomes fragile, which will lead to the failure of the quantum information processing. Thus, it is critical to reveal the evolutions of quantum entanglement source under different noisy environments and different noisy channels. Firstly, we experimentally prepare a high-fidelity two-bit entangled state by several technical methods. The fidelity observed for the state prepared in our experiment is 0.993 and the signal-to-noise ratio can reach up to 299. Then, we simulate the bit-flip noise and phase-shift noise (collective and non-collective) using the all-optical experimental setup. Finally, based on the entanglement qubit state, we experimentally study the evolutions of entanglement characteristic under different noisy environments and the single, double and mixed noisy channels. The experimental results show that for the same type of noise, the entanglement properties disappear fast when entangled qubit passes through dual channel noisy environment. The upper bounds of noise intensity to destroy the entanglement property are 0.25 and 0.26 for the single bit-flip noise and phase-shift noisy channels, respectively. The comparison between the two different kinds of noisy environments shows that the entanglement properties disappear fast when entangled bit passes through non-collective environment. The upper bounds of noise intensity are 0.08 and 0.14 for non-collective bit-flip and phase-shift noise to destroy the entanglement property, while the noise intensities are 0.14 and 0.23 for collective bit-flip and phase-shift noise, respectively. For different kinds of noises, the results show that bit-flip noise is more likely to destroy the entanglement properties than the phase-shift. Our results have great significance for the theoretical and experimental studies of entanglement decoherence and have important application value for quantum information processing technology based on the nonlinear optical system.
Effect of local coordination environment on molecule vibration in N2-molecule solid
Authors: Cao Shan  , Li Jun  , Liu Yuan-Qiong  , Wang Kai  , Lin Wei  , Lei Hai-Le  ,   Research Centre of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   Department of Material Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China
Published: December 2020

The vibration feature in a molecule solid is an important character of its structure. The different vibration frequencies of isolated nitrogen molecule (N2) and nitrogen molecule in the solid state are explored. Five solid-cluster models with the different numbers of nitrogen molecules (N46, N60, N76, N100, and N126) are constructed on the basis of -N2 crystal structures. The density functional theory is used to calculate the vibration frequencies of nitrogen molecules. The calculated infrared spectra and average vibration frequencies (AVFs) of the optimized structures for the five models are compared with each other. The results indicate that the AVF of nitrogen molecule in solid model is higher than that of isolated nitrogen molecule due to the collective effect. It is found that the AVF increases with increasing the number of molecules. The AVF of the inner molecules is always higher than that of surface molecules in the solid. On a whole, the vibration frequencies are ordered as vinner vsurface visolated for each case. The local coordination environment is believed to be mainly responsible for the differences in frequency among the isolated, surface and inner molecules. The bond length of molecule in solid is shorter than that in an isolated molecule, thus resulting in a stronger bond force and a higher vibration frequency. Similarly, due to a smaller number of molecules interacting with surface molecules, the bond force between molecules in the solid surface is weaker, thus resulting in a lower vibration frequency than in the inner region of solid.
How to eliminate unwanted elasto-optical birefringence from optical devices
Authors: Li Chang-Sheng  , Chen Jia  ,   School of Instrumentation Science & Opto-Electronics Engineering, Beihang University, Beijing 100191, China
Published: December 2020

There often appears unwanted elasto-optical birefringence in optical devices such as electro-optical, magneto-optical modulators and sensors when they are manufactured and used. This kind of elasto-optical birefringence causes unwanted effect for optical device and needs to be removed. Based on the method of index ellipsoid analysis, we theoretically analyze elasto-optical effects in various point groups of optical crystals and glasses, and accordingly propose some methods to eliminate unwanted elasto-optical birefringences in optical crystals and glasses. Main conclusions show that for orthorhombic biaxial crystal and the light wave propagating along any one crystalline axis of the crystal, if there is no shearing stress and the two external normal stresses applied to the other two crystalline axes can keep a constant ratio related to crystal parameters including refractive index and photoelastic constants, then unwanted elasto-optical birefringence can be eliminated from relevant optical devices, typical crystals include potassium titanium oxide phosphate (KTiOPO4, KTP) crystal and rubidium titanium oxide phosphate (RbTiOPO4, RTP) crystal, which are usually used as electrooptic Q-switchers in laser systems. For all the uniaxial crystyals such as potassium dihydron phosphate (KH2PO4, KDP), beta-barium borate ( -BaB2O4, BBO) and lithiun niobate (LiNbO3, LN) crystals, cubic crystals of 43 m, 432, m3 m point groups such as bismuth germanate (Bi4Ge3O12, BGO) crystal, and optical glasses, if the two normal stresses applied to the x1- and x2- crystalline axes of the crystal are equal to each other and there is no shearing stress, or there exists only one normal stress applied to the x3- crystalline axis of the crystal, then for the light wave propagating along the x3- crystalline axis, unwanted elasto-optical birefringence in relevant optical devices can also be eliminated. The above-proposed method to remove unwanted elasto-optical birefringence is benificial to design, manufacture, and usage of related optical devices.
A fast two dimensional joint linearized bregman iteration algorithm for super-resolution inverse synthetic aperture radar imaging at low signal-to-noise ratios
Authors: Li Shao-Dong  , Chen Wen-Feng  , Yang Jun  , Ma Xiao-Yan  ,   No. three department, Air Force Early Warning Academy, Wuhan 430019, China
Published: December 2020

In practical inverse synthetic aperture radar (ISAR), the traditional imaging algorithms have low range and low cross-range resolutions while the echoes have limited bandwidth and sparse azimuth aperture in small coherent processing interval. To obtain super-resolution ISAR imaging at low signal-to-noise (SNR) ratios, this paper puts forward a novel fast two-dimensional joint linearized Bregman iteration (2D-JLBI) algorithm based on compressive sensing theory. Firstly, the radar echoes are established as a two-dimensional joint sparse representation model in the range frequency-azimuth Doppler domain. Consequently, the original two-dimensional super resolution imaging problem is converted into a two-dimensional jointly compressive reconstruction problem. Secondly, to avoid the reconstruction complexity from the vectorization of the echoes, the two-dimensional joint linearized Bregman iterative algorithm is proposed. Meanwhile, three strategies, namely the weighted residual iteration, estimation of the stagnation step, and optimizing the condition numbers of sensing matrices, are combined to improve the convergence speed. Both the ISAR imaging ability at low SNR and its speed are improved obviously. Finally, simulation experiments show that the proposed algorithm can shorten the imaging time and have better noise robustness under the condition of sub-Nyquist sampling rate and low SNR.
Damage effects and mechanism of the GaN high electron mobility transistor caused by high electromagnetic pulse
Authors: Liu Yang  , Chai Chang-Chun  , Yu Xin-Hai  , Fan Qing-Yang  , Yang Yin-Tang  , Xi Xiao-Wen  , Liu Sheng-Bei  ,   Ministry of Education Key Lab. of Wide Band-Gap Semiconductor Materials and Devices, Xidian University, Xi'an 710071, China;,   Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

As electromagnetic environment of semiconductor device and integrated circuit deteriorates increasingly, electromagnetic pulse (EMP) of device and damage phenomenon have received more and more attention. In this paper, the damage effect and mechanism of the GaN high electron mobility field effect transistor(HEMT) under EMP are investigated. A two-dimensional electro-thermal theoretical model of GaN HEMT under EMP is proposed, which includes GaN polarization effect, mobility degradation in large electric field, avalanche generation effect, and self-heating effect. The internal transient response of AlGaN/ GaN HEMT is analyzed under the EMP injected into the gate electrode, and the damage mechanism is studied. The results show that the temperature of device keeps increasing, and the rate is divided into three stages, which present a tendency of rapid-slow-sharp till burn-out. The first rapid increasing of temperature is caused by the avalanche breakdown, and then rate becomes smaller due to the decrease of electric field. As the temperature is more than 2000 K, a positive feedback is formed between the hot electron emission and temperature of device, which causes temperature to sharply increase till burn-out. The maximum values of electric field and current density are located at the cylinder surface beneath the gate around the source, which is damage prone because of heat accumulation. Finally, the dependences of the EMP damage power, P, and the absorbed energy, E, on pulse width are obtained in a nanosecond range by adopting the data analysis software. It is demonstrated that the damage power threshold decreases but the energy threshold increases slightly with the increasing of pulse-width. The proposed formulas P = 38-0.052 and E = 1.1 0.062 can estimate the HPM pulse-width dependent damage power threshold and energy threshold of AlGaN/GaN HEMT, which can provide a good prediction of device damage and a guiding significance for electromagnetic pulse resistance destruction.
Automatic seizure detection of electroencephalogram signals based on frequency slice wavelet transform and SVM
Authors: Zhang Tao  , Chen Wan-Zhong  , Li Ming-Yang  ,   Department of Communication Engineerings, Jilin University, Changchun 130012, China
Published: December 2020

Over 50 million people all over the world are suffering from epilepsy It is of great significance to achieve automatic seizure detection in electroencephalogram (EEG) signal for clinical diagnosis and treatment. In order to achieve automatic diagnosis of epilepsy, a multitude of automated computer aided diagnostic techniques have been proposed. However, only a few of studies lay emphasis on the effects of different rhythm signals. To explore the influence of rhythm signals on classification accuracy, a newly-developed time-frequency analysis method called frequency slice wavelet transform (FSWT), which is able to locate arbitrary time-frequency range with the use of frequency slice function and whose inverse transformation only relies on fast Fourier transform, is employed to extract five different rhythm signals, namely (0.5-4 Hz), (4-8 Hz), (8-13 Hz), (13-30 Hz) and (30-50 Hz) from original EEG signal. Subsequently, for extracting the nonlinear and linear features, the approximate entropy of each rhythm signal and fluctuation index of adjacent rhythm signals are calculated to reflect the variation characteristics of rhythm signals and they are flocked together to form the nine-dimensional feature vectors. Finally, the extracted vectors are fed into a support vector machine (SVM) which is optimized by genetic algorithms (GA) for classification. Specifically, since the parameters of SVM are associated with the final classification accuracy and appropriate parameters could lead to a remarkable result, GA is applied to parameter optimization, half of the obtained vectors are randomly selected as a training set for training, and the remaining vectors constitute a testing set to test the established model. Experimental results of the proposed approach, which is employed in a public epileptic EEG dataset obtained from department of epitology at Bonn University for validation indicate that the proposed method in this study can carry out the task of classifying normal, inter-ictal and epileptic seizure EEG signals with a high classification accuracy (98.33%), a sensitivity of 99%, a specificity of 99%, and a positive predictive value of 99.5%. The presented approach provides an outstanding scheme for the automatic diagnosis of epilepsy, and the directions of our further research may include the application of the proposed method to the diagnosis of other disorders.
Imaging through dynamic scattering media with compressed sensing
Authors: Zhuang Jia-Yan  , Chen Qian  , He Wei-Ji  , Mao Tian-Yi  ,   School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China;,   Jiangsu Key Laboratory of Spectral Imaging and Intelligence Sense, Nanjing 210094, China
Published: December 2020

Imaging through scattering media has been a focus in research because of its meaningful applications in many fields. Recently, it has been proposed that high quality images can be recovered after passing through stationary scattering media by using the single-pixel imaging system based on compressed sensing. No doubt, it is a very interesting discovery about compressed sensing. However, it is also reported that high quality image can be recovered only with stationary scattering media. Mostly, the scattering media will not remain stationary, for example, the properties of the fog will be dynamically changed when their is wind. Thus, in a dynamic case, the transmittance of the scattering media will be nonlinear over the time, which will make the measured data nonlinear and the reconstructed image quality decrease. In this paper, a novel algorithm of linear transformation for measured data (LTMD) is proposed to make the nonlinear attenuation factor gain a linear transformation after passing through the dynamic scattering media. The factor is proposed from the theoretical calculus based on compressed sensing, and this correction factor can help to eliminate the nonlinear errors caused by dynamic scattering media and make the measured data linear. So the transformed data will greatly upgrade the reconstructed image quality. Simulation results show that high peak singnal to noise ratio images can still be recovered even when the dynamic frequency reaches 300 times in the 900 times of sampling. In experiments, plastic films are used as scattering media, and the number of films can be changed during the sampling to simulate the dynamic state of scattering media. With LTMD, high quality image with a resolution of 64 48 is recovered after passing through dynamic plastic films while the recovered result without LTMD is still hard to be distinguished. The traditional reconstructed algorithms orthogonal matching pursuit, Tval3 and L1-magic are also used in the experiments, and the image is still hard to recover with any of the three traditional algorithms. In a word, the proposed LTMD algorithm uses the correction factor to make the affected nonlinear-measured data linear, so as to increase the reconstructed quality of the imaging system based on the compressed sensing even when passing through scattering media with highly dynamic frequency.
An optoelectronic oscillator based on series resonance cavity
Authors: Huang Gang-Bin  , Wang Ju  , Wang Wen-Rui  , Jia Shi  , Yu Jin-Long  ,   School of Electronic Information Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

Commercial and military applications of microwave and millimeter-wave sources in aerospace, radar, navigation, and communication system require high spectrum purity and low phase-noise oscillators. The optoelectronic oscillator (OEO) emerges as an excellent low noise source that has attracted great attention in recent years. In this paper, a novel technique is proposed for single-mode selection in an optoelectronic oscillator, which uses a microwave cavity as the mode selector. It consists of a pump laser and a feedback circuit including an intensity modulator, an optical fiber delay lines, a photodetector, an amplifier, a filter and two drilling cables. The drilling cable is fabricated by drilling open holes on a coaxial cable using a drilling machine. By changing the radius of the drilling holes, the designed reflection coefficient can be obtained. By simulation, the constructed microwave resonator that consists of a filter and two drilling cables has a higher Q value and only the modes that satisfy the oscillation conditions of the loop will be selected. The basic principle is analyzed theoretically and experimentally. By comparing with traditional structure of OEO, it is shown that the novel structure can effectively improve the side-mode suppression ratio. In addition, the stability of the oscillation frequency is easier to control than the parallel structure. In this experiment, the output of a 10 GHz single-mode signal with a side-mode suppression ratio of 72 dB and a phase noise of -122 dBc/Hz@10 kHz from the carrier is obtained. Meanwhile, phase-lock techniques are used to compensate the drift of cavity length. Then the radio frequency (RF) stability of the oscillation frequency is measured using an RF spectrum analyzer, and the RF stability over 3 hours for the OEO is less than 4 Hz. This scheme has the advantages of traditional OEO with low noise since no extra active devices are needed, and it suppresses the side-mode noise also effectively. In addition, this system is promising for the development of compact, high frequency, low cost and low noise OEOs.
A controllable circular ring acoustic focused field
Authors: Zheng Li  , Guo Jian-Zhong  ,   Institute of Applied Acoustics, School of Physics and Information Technology, Shaanxi Normal University, Xi'an 710062, China
Published: December 2020

Based on Huygens principle about the aspect of phased array, this paper presents a structure of cylindrical acoustic transducer consisting of circular ring piezoelectric transducer elements in radial vibration mode, which can be used to achieve the ultrasonic nondestructive test for the cylindrical scanning acoustic field in three-dimensional space. By analyzing the acoustic field of a single ring line source and a single element, the sound field distribution of the phased array is obtained for constructing circular ring acoustic focused field. By means of the phased array incentive mode, the phase difference of driving signals is generated and forms a regular time delay; with the accomplishment of sound field scanning in cylindrical three-dimensional space, the circular ring acoustic focused field can be controlled in real time.Theoretical analysis and finite element simulation results demonstrate that the size of the circular ring acoustic focused field can be controlled by the numbers of the excited array elements, which are 4, 8, 16 and 32 respectively in our work. We find that with more array element numbers, the circular ring acoustic field has better focused features. The radius size of the circular ring acoustic focused field can be controlled by the different locations of the focus positions which are 30 and 50 mm respectively in our work. And we find that as the distance between the focus positions and the center of piezoelectric wafer becomes longer, the radius of the circular ring acoustic focused field becomes bigger, and the position of the focus is equivalent to the radius of the circular ring acoustic focused field. The movement along the axial direction of circular ring acoustic focused field can be controlled by the angle of deflection, which are set as 0, 10 respectively in our work. And we find that the circular ring acoustic focused field is deflected in a corresponding deflection angle along the Z-axis, and the moving distance is FZ = F/sin . With the theoretical analysis and the experimental simulation, it can be shown that the structure of cylindrical acoustic transducer array presented in this paper could create an adjustable circular ring acoustic focused field and can potentially provide an acoustic field scan method in detection ultrasound, medical ultrasound and other areas of a cylindrical space.
Impurity concentration effects on the structures, ductile and electronic properties of Zr-doped gamma-TiAl alloys
Authors: Song Qing-Gong  , Qin Guo-Shun  , Yang Bao-Bao  , Jiang Qing-Jie  , Hu Xue-Lan  ,   Institute of Low Dimension Material and Technology, College of Science, Civil Aviation University of China, Tianjin 300300, China;,   Sino-European Institute of Aviation Engineering, Civil Aviation University of China, Tianjin 300300, China
Published: December 2020

This investigation aims at the Zr-doping in -TiAl alloy systems in which Ti (or Al) atoms are partly replaced and the impurity concentrations are 1/54, 1/36, 1/24 and 1/16 (molar ratio), respectively. The structural, energy, plastic and electronic properties of the alloys are calculated and studied by using the first-principles method based on the density functional theory and other physical theory. From geometry optimization results it is shown that doping with Zr can change the structural symmetry of the -TiAl systems. These results also suggest that the cubic degree of Zr-doped -TiAl alloys can be increased due to the Zr-substitution. For instance, the cubic degrees of Ti12Al11Zr and Ti18Al17Zr systems are enhanced distinctly, which are positive for improving the mechanical properties of the alloys. The average formation energies obtained indicate that the Ti atom replaced by Zr can slightly decrease the formation energy of the system (0.003 eV/atom); while Zr substituting the Al atom can increase the formation energies of the systems (0.07 eV/atom). Accordingly, when Zr atoms are introduced in the -TiAl system, they tend to substitute Ti atoms, and can also substitute Al atoms with a certain possibility. Thus, various Zr-doped -TiAl regions can be produced in the system. The integral effects are of significance for improving the performance of the -TiAl based alloys by means of Zr-doping method. Comparing the axial ratios of Zr-doped -TiAl systems with that of pure -TiAl system, we find that Zr substituting Al atom can reduce the axial ratio of the Zr-doped alloys, which is responsible for the ductility of the materials. It should be mentioned that when the impurity concentration is in the range of 1.85 at%-6.25 at%, the doping effect will be most distinct and the axial ratio of the alloys is close to unity. It is expected that the Ti12Al11Zr system has a good ductility for its axial ratio equals to 1.007. The band structures of Zr-doped -TiAl systems show that they all have metallic conductivities. After Zr atom substitutes the Al atom in the -TiAl system, the intensity of covalent bond between Zr atom and its nearest neighbour Ti atoms in Ti12Al11Zr system reduces evidently and the bond length increases (0.032 ), which is indicated by the obtained overlap population (decrease by 0.21) and the densities of states in the Zr-doped and pure -TiAl systems. These results in the decrease of average intensity of Ti-Al(Zr) bonds and the increase of metallic bonds in Ti12Al11Zr system, which is an important factor for improving the ductility of -TiAl based alloys.
Research on surface potential decay characteristics of epoxy resin charged by direct current corona
Authors: Ru Jia-Sheng  , Min Dao-Min  , Zhang Chong  , Li Sheng-Tao  , Xing Zhao-Liang  , Li Guo-Chang  ,   State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049, China;,   State Grid Smart Grid Research Institute, Beijing 102209, China
Published: December 2020

Surface charge accumulation and decay behaviors of dielectric materials are the key factors restricting the development of high voltage direct current power equipment. For flat samples, the density of surface charges deposited by corona can be regarded as a linear change with the surface potential. For this reason, the behavior of surface charge decay can be directly related to that of surface potential. According to the corona charging process, the surface charge deposition and detrapping process, as well as the charge transport process in the bulk, we may establish a physical model dynamic response to the surface potential. Influences of grid voltage, relative permittivity, and bulk conductivity on the surface potential decay process can be obtained through calculating the surface potential decay behaviors of epoxy resin. The higher the grid voltage, the faster the surface potential decays. At the typical parameter value of epoxy resin (relative permittivity 3.93, bulk conductivity 10-14 S m-1), the normalized decay rate can be fitted by two straight lines in a log-log plot; moreover, the calculated results show a linear variation of power factors with the grid voltage, while the power function shows a relationship between the characteristic time and the grid voltage. The bigger the relative permittivity, the slower the surface potential decays. In the typical parameter area of epoxy resin (relative permittivity 3-4), the surface potential decay time constant increases from 1720 s to 2540 s, showing a linear variation. Also the bigger the bulk conductivity, the faster the surface potential decays. In the typical parameter area of epoxy resin (bulk conductivity 10-15-10-13 S m-1), the surface potential decay time constant decreases from 24760 s to 260 s, showing a power function relationship.
Global threshold analysis of multicarrier multipactor based on the critical density of electrons
Authors: Wang Xin-Bo  , Li Yong-Dong  , Cui Wan-Zhao  , Li Yun  , Zhang Hong-Tai  , Zhang Xiao-Ning  , Liu Chun-Liang  ,   Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China;,   National Key Laboratory of Science and Technology on Space Microwave, Xi'an Institute of Space Radio Technology, Xi'an 710100, China
Published: December 2020

Multicarrier multipactor, which is found in the wideband high power vacuum microwave passive components, potentially threatens the reliability of microwave systems in space and accelerator applications. The global threshold analysis of multicarrier multipactor is of vital importance for the risk assessment of high power vacuum devices. Till now, however, no effective solutions for the global threshold analysis of multicarrier multipactor have been proposed for practical microwave components with complex structures. In this paper, an efficient approach capable of evaluating the global threshold of multicarrier multipactor based on detectable level of multipactor test system is presented. Electromagnetic characteristics of the microwave device are theoretically related to the electron density by equivalently considering the distribution zone of electrons as a plasma medium. In order to obtain the global threshold using the optimization algorithm, such as the Monte Carlo method, we further propose an efficient approach capable of rapidly computing the fluctuation of number of electrons in the evolving process of a multicarrier multipactor based on the equivalency of half-sine-like segments for the acceleration of electrons. Analytical results comply with the tested thresholds. Different from the conventional equivalent power using the empirical rule, the proposed approach is based on the criterion of critical density of electrons and rapidly computing the fluctuation of number of electrons, providing an efficient method for the accurate global threshold analysis of multicarrier multipactor.
Detail investigation of the inclined pressure structure and gravity darkening in critical rotating star Achernar
Authors: Tai Li-Ting  , Song Han-Feng  , Wang Jiang-Tao  ,   Department of Physics, College of Science, Guizhou University, Guiyang 550025, China;,   Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650011, China;,   Joint Research Centre for Astronomy, National Astronomical Observatory-Guizhou University, Guiyang 550025, China
Published: December 2020

Rotation and tide are two important factors that have very important impacts on the stellar structure and evolution. Based on the observational data of Achernar, we have derived the inclined pressure structure in a single rotating star or as a member in the binaries. We have given the distributions of the physical quantities on the isobaric surface and these distributions are derived from the Legendre series of expansions. We have also found the relationship between all levels of perturbation potential functions (including rotational and tidal distortions) and the distributions of density and pressure under the condition of inclined pressure structure. In particular, the gravitational darkening with the models including the effects of rotation and tide is investigated. We have found that the critical ratio of equatorial radius to the polar radius is consistent with the observations in rotating binaries better than that in single rotating model. The reason is that the tidal force can make the polar radius shortened because the tidal force exerts an inward force to the two polar points. However, the theoretical angular velocity in binaries is smaller than that observed. It is also shown that the positive shear enhances the centrifugal force and decreases the mean effective gravitational acceleration and effective temperatures whereas the negative shear plays a role to strengthen the effective gravitational acceleration. Moreover, the solid body rotation has not been supported inside Achernar because magnetic fields have not been detected through observations. Furthermore, the theoretical angular velocity in rigid rotation is higher than the angular velocity observed. Achernar has a periodic variation of light curves due to mass outburst, which also supports differential rotation. A positive shear indicates that the mass in accretion disks is falling to Achernar and the Achernar is spun up to critical rotation according to current observations. By comparing the theoretical results with observations, it can be seen that when the theoretical spin angular velocity of Achernar is 4.65 10-5 s-1 and the positive shears / s are 0.7851, the temperature of the polar points is 16041 K and that of equatorial sphere is 12073 K. Relative errors between the theoretical values and observations are less than 3% and are listed in the text. This model is the best and is the most possible one for Achernar.
Control of nonautonomous matter rogue waves
Authors: Zhang Jie-Fang  , Dai Chao-Qing  ,   School of Electronical and Information Engineering, Zhejiang University of Media and Communications, Hangzhou 310018, China;,   School of Sciences, Zhejiang A&F University, Lin'an 311300, China
Published: December 2020

We study a (1+1)-dimensional variable-coefficient Gross-Pitaevskii equation with parabolic potential. A similarity transformation connecting the variable-coefficient Gross-Pitaevskii equation with the standard nonlinear Schrödinger equation is constructed. According to this transformation and solutions of the standard nonlinear Schrodinger equation, we obtain exact rogue wave solutions of variable-coefficient Gross-Pitaevskii equation with parabolic potential. In this solution, a Galilean transformation is used such that the center of optical pulse is Xc = v(T-T0) while the Galilean transformation was not used in previous analysis. By the Galilean transformation, the parameter T0 is added into the solution. It is found that the parameter T0 is important to control the excitations of rogue waves. Moreover, the parameters a1 and a2 in solution are complex parameters which can modulate the behaviors of rogue waves. If they are restricted to real numbers, we can obtain some well-known rogue wave solutions. If the parameter a2 =-1/12, we can have a second-order rogue wave solution. If the parameter a2 is a complex number, the solution can describe rogue wave triplets. Here two kinds of rogue wave triplets, namely, rogue wave triplets I and II are presented. For rogue wave triplet I, at first, two first-order rogue waves on each side are excited, and then a first-order rogue wave in the middle is excited with the increase of time. On the contrary, for rogue wave triplet II, a first-order rogue wave in the middle is initially excited, and then two first-order rogue waves on each side are excited with the increase of time.#br#From these solutions, the controls for the excitations of rogue waves, such as the restraint, maintenance and postponement, are investigated in a system with an exponential-profile interaction. In this system, by modulating the relation between the maximum of accumulated time Tmax and the peak time T0 (or TI,TII), we realize the controls of rogue waves. When Tmax > T0 (or TI,TII), rogue wave is excited quickly, and the atom number of condensates increases; when Tmax = T0 (or TI,TII), rogue wave is excited to the maximum amplitude, then maintains this magnitude for a long time, and the atom number of condensates also increases; when Tmax T0 (or TI,TII), the threshold of exciting rogue wave is never reached, thus the complete excitation is restrained, and the atom number of condensates reduces. These results can be used to understand rogue waves better, that is, besides their "appearing from nowhere and disappearing without a trace", rogue waves can be controlled as discussed by a similar way in this paper. These manipulations for rogue waves give edification on theory and practical application.
Syntheses of B2O3-doped gem-diamond single crystals
Authors: Xiao Hong-Yu  , Liu Li-Na  , Qin Yu-Kun  , Zhang Dong-Mei  , Zhang Yong-Sheng  , Sui Yong-Ming  , Liang Zhong-Zhu  ,   Department of Mathematics and Physics, Luoyang Institute of Science and Technology, Luoyang 471023, China;,   National Lab oratory of Superhard Materials, Jilin University, Changchun 130012, China;,   State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
Published: December 2020

In the present paper, by the temperature gradient method, the gem-diamond single crystals with B2O3-added in the synthetic system of the FeNiMnCo-C are synthesized under 5.3-5.7 GPa and 1200-1600℃. The P-T phase diagram of diamond single crystal growing in the synthesis system of the FeNiMnCo-C-B2O3, is obtained. By B2O3-added in synthesis system, the V-shape section for the diamond growth, which is the region between the solvent/carbon eutectic melting line and diamond/graphite equilibrium line under pressure and temperature, is moved upwards. We find that the minimum pressure of diamond growing increases from 5.3 GPa to 5.4 GPa and the synthesis range of the low temperature hexahedron diamond growth becomes wider, which can be due to the chemical energy increase of the carbon depositing in the diamond surface by the additive of the B2O3. The synthetic diamond single crystal exhibits a perfect hexahedral shape or cubo-octahedral shape or octahedral shape. In the system of the FeNiMnCo-C-B2O3, we think that the catalyst activity decreases with the generation of CO2, so high-quality diamond single crystal can hardly be synthesized when the content of the B2O3 is more than 3 wt‰ and synthesis time is more than 20 h, However, when the content of the B2O3 is no more than 1 wt‰, the rate of finished products of the low temperature hexahedron diamond will increase significantly. Because the amount of the B2O3 additive is so small, in the syntheses of B2O3-added diamond single crystals, the black areas which appear when B element enters into diamond crystal lattice are not observed. The growth rate of diamond single crystal will be reduced obviously by B2O3-added in synthetic system. Under our system synthesis, when the growth time is 10 h, the growth rate of the diamond will reduce 0.22 mg/h by 2 wt‰ B2O3 added in synthetic system. When the growth time extends to 20 h, the growth rate increases to 0.47 mg/h. Moreover, with the extension of growth time, the catalyst activity decreases continuously with the product of the CO2 increasing in the reaction chamber, so the effect of additive on the growth of diamond strengthens gradually. The results of the scanning electron microscope images indicate that the surface defects of the diamond crystal increases by the addition of B2O3.