bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of emergence of target wave and spiral wave in neuronal network induced by gradient coupling
Authors: Xu Ying  , Wang Chun-Ni  , Jin Wu-Yin  , Ma Jun  ,   Department of Physics, Lanzhou University of Technology, Lanzhou 730050, China;,   College of Mechano-Electronic Engineering, University of Technology, Lanzhou 730050, China
Published: December 2020

Distinct rhythm and self-organization in collective electric activities of neurons could be observed in a neuronal system composed of a large number of neurons. It is found that target wave can be induced in the network by imposing continuous local periodical force or introducing local heterogeneity in the network; and these target waves can regulate the wave propagation and development as pacemaker' in the network or media. A regular neuronal network is constructed in two-dimensional space, in which the local kinetics can be described by Hindmarsh-Rose neuron model, the emergence and development of ordered waves are investigated by introducing gradient coupling between neurons. For simplicity, the center area is selected by the largest coupling intensity, which is gradually decreased at certain step with increasing distance from the center area. It is found that the spiral wave and/or the target wave can be induced by appropriate selection of gradient coupling, and both waves can occupy the network, and then the collective behaviors of the network can be regulated to show ordered states. Particularly, the ordered wave can be effective to dominate the collective behavior of neuronal networks, even as the stochastic values are used for initial states. These results associated with the gradient coupling on the regulating collective behaviors could be useful to understand the self-organization behaviors in neuronal networks.
A ranking method based on self-avoiding random walk in complex networks
Authors: Duan Jie-Ming  , Shang Ming-Sheng  , Cai Shi-Min  , Zhang Yu-Xia  ,   School of Computer Scinece and Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China;,   Big Data Research Center, University of Electronic Science and Technology of China, Chengdu 611731, China;,   Physics and Photoelectricity School, South China University of Technology, Guangzhou 510640, China
Published: December 2020

Evaluation of node importance is helpful to improve the invulnerability and robustness of complex networked systems. At present, the classic ranking methods of quantitatively analyzing node importance are based on the centrality measurements of network topology, such as degree, betweenness, closeness, eigenvector, etc. Therefore, they often restrict the unknown topological information and are not convenient to use in large-scale real networked systems. In this paper, according to the idea of self-avoiding random walking, we propose a novel and simplified ranking method integrated with label propagation and local topological information, in which the number of labels that node collects from propagating process quantitatively denotes the ranking order. Moreover, the proposed method is able to characterize the structural influence and importance of node in complex networked system because it comprehensively considers both the direct neighbors of node and the topological relation of node to other ones. Through performing the experiments on three benchmark networks, we obtain interesting results derived from four common evaluating indices, i. e., the coefficient of giant component, the spectral distance, the links of node, and the fragility, which indicate that the proposed method is much more efficient and effective for ranking influential nodes than the acquaintance algorithm.
Underwater acoustic weak signal detection based on Hilbert transform and intermittent chaos
Authors: Chen Zhi-Guang  , Li Ya-An  , Chen Xiao  ,   School of Marine, Northwestern Polytechnical University, Xi'an 710012, China
Published: December 2020

In the paper, we analyse the basic dynamical model of the chaotic oscillator by using the theory of intermittent chaos to construct the column of the intermittent chaos, and present an effective method to detect the weak underwater acoustic signal with an unknown frequency. Duffing oscillator is sensitive to phase transformation from chaos to intermittent chaos, whose frequency difference is slightly different from that between the driving force signal and the signal to be detected. By employing this theory, we detect the frequency of the ship signal in ocean background noise. For the detection by using the intermittent chaos, there exists no effective way to estimate the frequency of the signal to be detected, which can only be judged by empirical methods and therefore the man-made error will exist. All of these will affect the consequence of the intermittent chaos and make the practical application difficult. To solve this problem, in this paper, we first study the basic theory of the chaotic system, then construct the simulated signal to examine the system, and finally detect the ship signal. To make the detection feasible, a chaotic oscillator column is considered to sweep through the unknown frequency of the signal. By using this method, we can obtain the frequency range. Finally Hilbert transform is used to detect the envelope of the intermittent chaos followed by measuring the frequency of the envelope through using Fourier spectrum. Thus the frequency of the signal can be calculated by using the function describing the relationship among the driving force signal, ship signal and the envelope. The simulations and the detection processing of the measured acoustic signal are carried out by using the proposed method, which can effectively detect the frequency of the ship signal embedded within strong background noise and also the frequency of the signal to be detected can be calculated, which is conducive to solving the presently existing problem about frequency estimation. Signal-to-noise ratio can be enhanced by 4.4 dB based on the method by using the Hilbert transform compared with by using the method just through using an intermittent chaotic oscillator column, which verifies the effectiveness of the method in this paper.
Dynamic response and stochastic resonance of a tri-stable system
Authors: Lai Zhi-Hui  , Leng Yong-Gang  ,   School of Mechatronics Engineering, Nanchang University, Nanchang 330031, China;,   School of Mechanical Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

Stochastic resonance (SR) describes a nonlinear phenomenon in nature, of which the essential ingredients are a nonlinear system, a weak signal, and a source of noise. Using the nonlinear system, the signal-to-noise ratio (SNR) of the output signal of the system will peak at a certain value of noise intensity under a synergistic action of input signal and noise. Besides the traditional Langevin equation, the new SR models such as monostable oscillators, chaotic systems, time-delay systems and bistable Duffing systems, can also produce SR phenomena. In this paper, a normalized symmetrical tri-stable potential function is constructed by using equilibrium parameters p and q, and a tri-stable system model simultaneously driven by weak signal and noise is further proposed. The tri-stable system model can be understood through a cantilever beam structure with three magnets, and deduced from the Brownian motion equation. We study in-depth and summarize the influences of parameters p and q on the potential barrier heights ΔU1, ΔU2 and their difference value. By analyzing the steady-state solution of the tri-stable system under invariable input, the concept of system steady-state solution curve (SSS curve) is proposed, and is used to further study the system dynamic response under low-frequency harmonic signal input. In these situations, the system response can be obtained by combining the steady-state solutions of the system following time t under a group of tempolabile inputs. Moreover, with the noise injection, the tri-stable system can realize SR under appropriate parameter condition, which can be demonstrated by the output amplitude curve and also the output SNR curve of the system against noise intensity. The mechanism of noise-induced SR of tri-stable system can be analyzed from the perspective of SSS curve. Finally, we further study the influence of tri-stable SR against system parameters. The value of damping ratio k affects the value of damping force acting on the Brownian particle, thus the tri-stable system needs noise with larger intensity to produce SR under a larger k. The values of equilibrium parameters p and q both affect the shape of the SSS curve, a larger p or a smaller q may result in larger-intensity noise for the system to produce SR.
Multifractal behaviors of the wave function for the periodically kicked free top
Authors: Zhou Jie  , Yang Shuang-Bo  ,   Jiangsu Provincial Key Laboratory for Numerical Simulation of Large Scale Complex Systems, School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

Starting from time evolution of wave function, quantum dynamics for a periodically kicked free top system is studied in this paper. For an initial spherical coherent state wave packet (localized) we find that 1) as the number of kicking is small, the speed and the direction of the diffusion for a time-evolving wave packet on a periodically kicked free top is related to the kicking strength: the stronger the kicking strength, the more chaotic for the diffusion (which means the more randomized in direction) is and the faster the speed of diffusion is, and then more quickly the full phase space is filled up; 2) as the kicking number is large, the time-evolving wave function will take on fine structure distribution in phase space, and the scope of the distribution for the fine structure will expand with the increase of the kicking strength, and the whole phase space will be filled up finally, and then the wave function will show multifractal property in phase space.#br#We study the multifractal behavior for a time-evolving wave function by partition function method: 1) for different kicking strengths and different q values, we study the scaling properties of partition function X(q), and find the power law relation between the partition function and the scaling L, i.e., X(q)-Lτ(q); 2) at different kicking strength, for a time-evolving wave function we calculate the singularity spectrum f(a)-a, and find that a maximum value of f(a) is 2.0 independent of the kicking strength, but the width of the singularity spectrum becomes narrow with the increase of the kicking strength, which means that the scope of the distribution for a is widest for regular state (localized), and is narrower for transition state from regular to chaotic, and is narrowest for chaotic state; 3) in the time-evolving process, the fluctuation for the width of the singular spectrum is smallest for chaotic state, intermediate for transition state of regular to chaotic, and the largest for regular state; 4) we calculate the generalized fractal dimension Dq-q for different kicking strengths, and find D0 = 2 independent of the kicking strength.#br#We study the mutifractal behaviors for the mean propbability amplitude distribution for a sequence of time-evolving wave functions and find that the result is similar to that of the single wave function type but has the difference: the width of the spectrum is reduced for each kicking strength.
Volterra prediction model for speech signal series
Authors: Zhang Yu-Mei  , Hu Xiao-Jun  , Wu Xiao-Jun  , Bai Shu-Lin  , Lu Gang  ,   Key Laboratory of Modern Teaching Technology, Ministry of Education, Shaanxi Normal University, Xi'an 710062, China;,   School of Computer Science, Shaanxi Normal University, Xi'an 710062, China;,   School of Automatic Control, Northwestern Polytechnical University, Xi'an 710072, China;,   School of Electronics and Information, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

The given English phonemes, words and sentences are sampled and preprocessed. For these real measured speech signal series, time delay and embedding dimension are determined by using mutual information method and Cao's method, respectively, so as to perform phase space reconstruction of the speech signal series. By using small data set method, the largest Lyapunov exponent of the speech signal series is calculated and the fact that its value is greater than zero presents chaotic characteristics of the speech signal series. This, in fact, performs the chaotic characteristic identification of the speech signal series. By introducing second-order Volterra series, in this paper we put forward a type of nonlinear prediction model with an explicit structure. To overcome some intrinsic shortcomings caused by improper parameter selection when using the least mean square (LMS) algorithm to update Volterra model efficiency, by using a variable convergence factor technology based on a posteriori error assumption on the basis of LMS algorithm, a novel Davidon-Fletcher-Powell-based second of Volterra filter (DFPSOVF) is constructed and is performed to predict speech signal series of the given English phonemes, words and sentences with chaotic characteristics. Simulation results under MATLAB 7.0 environment show that the proposed nonlinear model DFPSOVF can guarantee its stability and convergence and there are no divergence problems in using LMS algorithm; for single-frame and multi-frame of the measured speech signals, when root mean square error (RMSE) is used as an evaluation criterion the prediction accuracy of the proposed nonlinear prediction model DFPSOVF in this paper is better than that of the linear prediction (LP) that is traditionally employed. The primary results of single-frame and multi-frame predictions are given. So, the proposed DFPSOVF model can substitute linear prediction model on certain conditions. Meanwhile, it can better reflect trends and regularity of the speech signal series and fully meet requirements for speech signal prediction. The memory length of the proposed prediction model may be selected by the embedding dimension of the speech signal series. The proposed model can present a nonlinear analysis and more valuable model structure for speech signal series, and opens up a new way to speech signal reconstruction and compression coding so as to improve complexity and process effect of speech signal processing method.
First-principles study of stability and electronic structure of N2H4 adsorption on NiFe(111) alloy surface
Authors: He Yan-Bin  , Jia Jian-Feng  , Wu Hai-Shun  ,   School of Chemistry and Materials Science, Shanxi Normal University, Linfen 041004, China;,   Pharmaceutical Department, Changzhi Medical College, Changzhi 046000, China
Published: December 2020

We use the density functional theory (DFT) with dispersion correction to investigate the stability and electronic structure of hydrazine (N2H4) adsorpted on Ni8Fe8/Ni (111) alloy surface. The geometries and adsorption characteristics of the structure on the Ni8Fe8 alloy surface are presented. Results show that N2H4 bridging between two iron atoms gives the strongest adsorption with an adsorption energy of -1.578 eV/N2H4. Top modes turn out to be the local minima with adsorption energies of -1.346 eV/N2H4 (for the top site on a Fe atom) and -1.061 eV/N2H4 (for the top site on a Ni atom). It is demonstrated that the bridging mode is more favorable than the top mode on the NiFe alloy surface with a coverage of 1/16 ML, and Fe atom can provide stronger adsorption site than Ni atom. The van der Waals contribution is significant with a value of about 0.4 eV/N2H4. Meanwhile, the van der Waals contribution is larger for adsorption on Fe atom than on Ni atom, and for adsorption of the bridging mode than of the top mode. We also find that the structure of N2H4 in the anti molecule, rather than the gauche molecule, is bound on the top site of Fe atom on the NiFe alloy surface with a coverage of 1/16 ML, which demonstrates that the repulsive adsorbate-adsorbate interaction is weak on the surface with low coverage. The strong interaction between the surface atom and the adsorbate contributes to the result that the lone pair electrons of N2H4 in gauche conformer are attracted by the Fe atom. In addition, for the five adsorption structures of N2H4 on Ni8Fe8/Ni(111) alloy surface, we analyze the projected electronic density of states (DOS), induced charge density and electron localisation function (ELF) slices through the Fe-N or Ni-N bonds of the adsorbed molecule on the alloy surface. It shows that the electronic DOS presents the mixture between HOMO of N2H4 and the d orbital of the surface atom, which corresponds to charge transfer between the substrate and the adsorbate. The charges are transferred mainly from N2H4 to the surface atoms, and the extents of charge transfer are different for the bridging mode and the top one which is present in the induced charge density. Furthermore, the region of localisation in the ELF slices can be found for the adsorptions between the N atom of N2H4 and the Fe or Ni atom of surface, which gives a clear view of the coordination bonds for the interactions of N–Fe or N–Ni.
Full vibrational spectra of some electronic states of NaLi molecule using a difference converging method
Authors: Zheng Xiao-Feng  , Fan Qun-Chao  , Sun Wei-Guo  , Fan Zhi-Xiang  , Zhang Yi  , Fu Jia  , Li Bo  ,   Research Center for Advanced Computation, School of Science, Xihua University, Chengdu 610039, China;,   Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China
Published: December 2020

For most diatomic electronic states, it is very difficult to obtain the accurate vibrational spectra of the highly-excited states directly by using the modern experimental techniques and quantum theories. Based on the general expression of diatomic molecular vibrational energy, the difference converging method (DCM) is used to give a new analytical expression in this paper. By using ten known vibrational energies, the full vibrational spectra, the vibrational spectroscopic constants of the highly-excited states, and the dissociation energy can be predicted for a diatomic electronic state. In this study, the full vibrational spectra of the electronic states 31Π, 41Π and A1Σ+ of NaLi molecule are studied with the DCM and the new formula. Results show that all the vibrational levels given in the experiments can be reproduced with an error rate less than 0.02 percent in our study. In addition, By comparing with the reported experimental results, we find 26, 45 and 31 new vibrational levels for 31Π, 41Π and A1Σ+ of NaLi molecule, respectively.
Single frequency spatial power combining using sparse array based on time reversal of electromagnetic wave
Authors: Chen Qiu-Ju  , Jiang Qiu-Xi  , Zeng Fang-Ling  , Song Chang-Bao  ,   Key Laboratory of Information Processing, Electronic Engineering Institute, Hefei 230037, China
Published: December 2020

Based on time-reversal (TR) technique, the model of single frequency spatial power combining using sparse array is established. The efficiency function of spatial power combining is defined. The expression for the relationship of the statistical characteristics of combining efficiency at the time of maximum amplitude with the phase error and the number of array elements is derived. The analysis shows that when other parameters are determined, if the phase errors of the array nodes are mutually independent, and obey the uniform distribution to a certain extent, the combing efficiency's mean would not be related to the number of array elements N, but related to the statistic parameter of phase error. The combing efficiency's variance is related to not only the statistic parameter of phase errors, but also N. Once the statistic parameter of phase error is fixed, the greater the value of N, the smaller the variance is. So, in the engineering application, a large number of small power nodes could be used to reduce the phase error's effect. In addition, the influence of phase error on the combining efficiency is investigated by both theoretical analysis and the numerical simulation. The results show that when the array elements work at the same frequency, polarization and antenna type, the parameter of phase error would affect the combing result. The smaller the parameter of phase error, the larger the power of the effective point is, and the more concentrative the effective points' distribution is; the greater the parameter of phase error, the smaller the power of the effective point is, and the more dispersed the effective points' distribution is. It is also seen that even though the phase error occurs, the spatial power combining can still be realized with the time reversal technique. The determination of the phase control precision is the compromise between the requirements and the possibility. The results presented in this paper are useful for developing the microwave weapons with high power and electronic warfare.
Ultra-long cavity multi-wavelength Yb-doped fiber laser mode-locked by carbon nanotubes
Authors: Wang Yu-Bao  , Qi Xiao-Hui  , Shen Yang  , Yao Yi-Lei  , Xu Zhi-Jing  , Pan Yu-Zhai  ,   School of Science, Harbin Institute of Technology at Weihai, Weihai 264209, China;,   School of Information and Electrical Engineering, Harbin Institute of Technology at Weihai, Weihai 264209, China
Published: December 2020

We demonstrate an ultra-long cavity multi-wavelength Yb-doped fiber laser mode-locked by carbon nanotubes. The total length of the fiber laser is 1021.2 m. The different regimes of noise-like soliton and soliton rain mode-locking with the multi-wavelength operation are experimentally obtained with a repetition rate of 199.8 kHz. The higher output power and pulse energy from the soliton rain are measured to be 40.3 mW and 201.5 nJ, respectively, with a pulse width of about 102.5 ns.
Optical transparency of transparent window LiF in laser-driven quasi-isentropic compression experiment
Authors: Zhang Zhi-Yu  , Zhao Yang  , Xue Quan-Xi  , Wang Feng  , Yang Jia-Min  ,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   Department of Engineering Physics, Tsinghua University, Beijing 100084, China;,   State Key Laboratory of Laser Interaction with Matter, Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

LiF is often used as a window in laser-driven shock experiments, which can transmit and reflect visible probe laser. Researches of LiF transparency almost focus on its optical reflectivity compressed by strong shock, but there is almost no research on its optical transmissivity compressed by weak shock. In order to study the optical transmissivity of LiF, the quasi-isentropic compression experiment is carried out on the ShenGuang-III prototype laser facility, in which the velocity interferometer system for any reflector is used to diagnose the optical reflectivity of the quasi-isentropic compression sample CH/Al/LiF. The experimental results indicate that the velocity interferometer fringes are missing in the late stage of this experiment. The probe laser should penetrate LiF before it hits the rear surface of aluminum and the laser reflected by aluminum should penetrate LiF before it is collected by the velocity interferometer system for any reflector. Therefore, the reflectivity diagnosed by the velocity interferometer system for any reflector is the product of the optical reflectivity of aluminum and the optical transmissivity of LiF under the experimental condition. However, there is no research about the optical transmissivity model of thick LiF compressed by laser-driven shock. In this paper, we develop a transmissivity model for transparent window LiF and simulate the optical reflectivity of sample CH/Al/LiF. Firstly, we simulate the temperature and density of the sample by the code for one-dimensional multigroup radiation hydrodynamics (MULTI-1D). Then, based on the resulting temperature and density, we simulate the optical reflectivity of the sample by using the optical reflectivity model of aluminum and the optical transmissivity model of LiF. Without considering the transparency of LiF, the simulated result indicates that there is no signal missing in the late stage, which is different from the experimental result. By considering the transparency of LiF, the simulated result is in good agreement with the experimental result. The simulated result indicates that the formation of the strong shock, because of the later shock's catching up with the early one, obviously reduces the optical transparency of LiF and finally causes the velocity interferometer fringes to disappear. The simulated result also indicates that the energy gap of LiF calculated from density-functional theory is 1-2 eV. In this experiment, when LiF becomes opaque, its temperature is 1 eV and its pressure is 2-3 Mbar.
Effective elastic modulus of a transverse isotropy solid with aligned inhomogeneity
Authors: Xu Song  , Tang Xiao-Ming  , Su Yuan-Da  ,   School of Geosciences, China University of Petroleum, Qingdao 266580, China
Published: December 2020

The effective modulus of transversely isotropic compound material containing aligned ellipsoidal inhomogeneity is derived using the method of sphere-equivalency of effective scattering. Based on this approach, we derive the integral solution of the Eshelby tensor for the anisotropic medium, allowing for numerically evaluating the effects of anisotropy for the solution. The numerical results show that the effective modulus of the medium decreases monotonically with increasing the concentration of the inhomogeneties. The anisotropy increases if the inhomogeneity alignment direction is perpendicular to the TI symmetry axis of the background medium. By reducing the numbers of matrix elastic modulus from 5 to 2, we calculate the slowness surfaces for the three modes of propagation in an isotropic medium containing aligned ellipsoidal inhomogeneity. The results are the same as the existing ones, which validates the exactness of our theory. The modeling results can be used to evaluate elastic property of an anisotropic medium with aligned inclusions, such as earth formation shale rocks containing aligned cracks.
First-principles study on the electronic structure of Ti-doped NbSe2
Authors: Xu Jing  , Liang Jia-Qing  , Li Hong-Ping  , Li Chang-Sheng  , Liu Xiao-Juan  , Meng Jian  ,   School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China;,   Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130023, China
Published: December 2020

Layered transition metal dichalcogenides (LTMDs) have renewed interest as electronic materials, but the poor conductivities hinder their further development. Chemical doping can often significantly modify atomic structures and electronic functionalities of a wide range of materials and thus acts as one of the most effective ways to precisely tune material properties for technological application. Here, the geometries and band structures as well as the densities of states of pure NbSe2 and Ti-doped NbSe2 nanostructure are studied by employing the ab-initio plane-wave ultra-soft pseudo potential technique based on the density functional theory. We optimize the ground state of NbSe2 in the layered structure by using the generalized gradient approximation for the exchange-correlation potential. The computational structural parameters are in good agreement with experimental values within 2.5%. To investigate the stability of the doped system with changing the concentration of Ti atoms, 2×2×1 2H-NbSe2 supercells are taken into consideration. Meanwhile, we consider a total of three possible Ti-doping models: substitution, intercalation, and embedded model, and investigate the energy band diagrams, state densities and densities of partial wave state diagram before and after the doping. The results show that the energy electron density of states reaches a higher peak, and the band structure near Fermi level (EF) is changed obviously, resulting in the variations of the band gap and EF position and then the increase of electronic conductivity after doping. In addition, our calculations also predict that the electron transport properties can be enhanced by doping Ti and it can be regarded as a useful way to tailor electronic states so as to improve electron transport properties of 2H-NbSe2. Such a remarkable modification of electronic structure of 2H-NbSe2 by chemical doping offers an additional way of modulating performances of LTMDs and developing new electrical contact composite materials.
First-principles study on the elastic and thermal properties of Ca0.5Sr0.5TiO3
Authors: Shao Dong-Yuan  , Hui Qun  , Li Xiao  , Chen Jing-Jing  , Li Chun-Mei  , Cheng Nan-Pu  ,   Faculty of Materials and Energy, Southwest University, Chongqing 400715, China
Published: December 2020

In this paper, Ca/Sr atoms are confirmed to have symmetric distributions on 4c sites by using the minimum energy principle, and the stable crystal structure of Ca0.5Sr0.5TiO3 is built. The lattice parameters, elastic constants, bulk modulus, shear modulus, Young's modulus and Poisson's ratio of Ca0.5Sr0.5TiO3 (CST50) are investigated by the plane wave pseuedopotential method based on the first-principles density functional theory within the local density approximate (LDA) and generalized gradient approximation. The properties of planar acoustic velocity are studied by Christoffel equation, and the minimum thermal conductivity is investigated with Cahill and Cahill-Pohl models. The results show that the calculated lattice parameters are consistent with the corresponding experimental values. The larger calculated elastic constasnts C11, C22, and C33 suggest the incompressibility along the principle axes. The bulk modulus B is larger than the shear modulus G; G/BLDA = 0.5789 and G/BGGA = 0.5999, indicating that CST50 is a brittle material. The three-dimensional image of Young's modulus along [100], [010], and [001] crystal orientations shows the anisotropic elasticity of CST50. The planar projections of Young's modulus in (001) and (010) planes show the stronger anisotropy than in (100) plane and all the planar projections have two-fold symmetry. The Poisson's ratio exhibits the incompressbility of CST50. The universal elastic anisotropy indexes ALDAU = 0.0235 and AGGAU= 0.0341 indicate the weak anisotropy of CST50. The planar acoustic wave which has a branch of longitudinal wave and two branches of transverse wave is anisotropic along (010) and (001) planes and isotropic along (100) plane, and all the corresponding planar projections have two-fold symmetry. The minimum thermal conductivity calculated in Cahill model is isotropic in each plane, while the minimum thermal conductivity calculated in Cahill-Pohl model is proportional to the second power of T under low temperatures and reaches a constant at high temperatures. In the quasi harmonic Debye model, the molar heat capacity and thermal expansion coefficient of CST50 are close to those of calcium titanate, indicating that CST50 has the stable thermal expansion property at high temperatures. The direct band gap of CST50 is 2.19 eV and the bottom of the valence band is mainly determined by the electron orbitals of Ti-3d and O-2p. The analysis of the charge populations shows that the covalence of Ti–O is stronger than those of Sr–O and Ca–O, and the band length of Ti–O is shorter than those of Sr–O and Ca–O; (200), (110) and (002) planar contour charge densities indicate that Ti atoms interact strongly with O atoms. The charge population and contour charge density prove that CST50 has a stable Ti–O octahedral structure.
Cluster distribution for oxygen vacancy in Ti/HfO2/Pt resistive switching memory device
Authors: Jiang Ran  , Du Xiang-Hao  , Han Zu-Yin  , Sun Wei-Deng  ,   Physical School, Shandong University, Jinan 250100, China
Published: December 2020

The origin of the resistance switching behavior in HfO2 is explained in terms of filament formation/rupture under an applied voltage. In order to investigate the position and process of conductive filament in resistive switching memory, the resistive switching and chemical structure of Ti/HfO2/Pt memory device are studied. Through current-voltage measurement, typical resistive switching behavior is observed in Ti/HfO2/Pt device cells; through detecting Hf 4f with different depths by using X-ray photoelectron spectroscopy. It is observed that the Hf4+ decreases monotonically with depth increasing towards HfO2/Pt interface in low resistance state, while a fluctuation distribution of Hf4+ is shown in high resistance state and in the pristine Ti/HfO2/Pt device. The concentration of Hf4+ in high resistance state is higher than that in low resistance state, which is confirmed by measuring the electron energy loss spectrum. Additionally, the O 1s spectrum shows a similar result consistent with the Hf 4f one. The above result is explained by the existence of locally accumulated oxygen vacancies in the oxide bulk layer in high resistance state and pristine states. It is proposed that the oxygen vacancy clusters dominantly determine the resistivity by the connecting/rupture between the neighbor cluster sites in the bulk. The cluster defects are the preexisting structural distortion/injure by charge trapping defects due to the fixed charge which could confine the nucleation of oxygen vacancies and bigger distortion could be enhanced or recovered via the transportation of oxygen vacancies under the external voltage. Oxygen vacancies are driven away from the clusters under SET electrical stimulus, and then recover back to original cluster sites under RESET process.#br#The previous presumption of the ideal evenly-distributed state for oxygen vacancies in the bulk of resistance random access memories (RRAMs) device leads to an issue about where the filaments occur/form first since the oxygen vacancy defects show uniform distribution in the active oxide bulk layer. Since the conductive filament is easily formed in the cluster region of oxygen vacancies, this study could provide a deep understanding of the formation of conductive filament in RRAMs device.
Phantom experimental photoacoustic scanning imaging of prostate based on internal light irradiation using cylindrical diffusing source
Authors: Peng Dong-Qing  , Xie Wen-Ming  , Wu Shu-Lian  , Tang Jia-Ming  , Li Zhi-Fang  , Li Hui  ,   Key Laboratory of Optoelectronic Science and Technology for Medicine (Ministry of Education of China), Fujian Provincial Key Laboratory of Photonic Technology, College of Photonic and Electronic Engineering, Fujian Normal University, Fuzhou 350007, China;,   School of Science, Jimei University, Xiamen 361021, China;,   School of Information Science and Engineering, Fujian University of Technology, Fuzhou 350118, China
Published: December 2020

Photoacoustic imaging has recently emerged as a promising imaging modality for prostate cancer. As ausual light illumination model in the previous studies, the external light illumination is difficult to obtain an accurate reconstructed photoacoustic image. It suffers a great deal of light absorption attenuation by the surrounding scattering tissue and cannot colletct sufficient ultrasound signals for image reconstruction. Some particular methods are required to be considered in the photoacoustic imaging technique for examining prostate, such as a light delivery to prostate with sufficient penetrating depth and minimal invasiveness. According to the structural characteristic of prostate tissue, a photoacoustic imaging system is built by using a novel technique for prostate in this paper. In our photoacoustic imaging system, a cylindrical diffusing source with a 2-cm-long diffuser tip is used for an internal light irradiation through a urethra, and a focused transducer with a 3.5 MHz central frequency and 30.3 mm extended focal zone is located in the rectum for scanning the photoacoustic signal. Phantom experimental imaging is carried out. In the experiment, a transverse resolution of 2.21 mm and an axial resolution of 0.39 mm are obtained. The results demonstrate that the system could achieve the accurate imaging position of the absorber in the tissue sample. Because of the symmetrical emitting of the cylindrical diffusing light source and a relatively better lateral uniformity of light absorption around the light source through the internal irradiation model via urethra, light absorption of the upper side of the light source is almost the same as that of the lower side. Therefore the lengthways and lateral imaging ranges can be improved. In addition, the laser energy is allowed to be increased appropriately to obtain a further imaging result without worrying about heat damages to normal tissues, for the light absorption is less around the cylindrical diffusing light source. In conclusion, the preliminary studies show that the new technique, where the internal light irradiation is implemented by using a cylindrical diffusing source and a focused transducer with extended focal zone, has a potential application in the early noninvasive diagnosis of prostate cancer.
Preparation and characteristics of ZnO nanoflowers
Authors: Wu Xiao-Ping  , Liu Jin-Yang  , Lin Li-Mei  , Zheng Wei-Feng  , Qu Yan  , Lai Fa-Chun  ,   Fujian Provincial Key Laboratory of Quantum Manipulation and New Energy Materials, College of Physics and Energy, Fujian Normal University, Fuzhou 350117, China
Published: December 2020

Unlike the general substrates such as SiO2, ITO, and AZO, the metal foil used as a substrate is rarely studied in application in the substrate, however, it has lots of advantages including cheapness, good conductivity and excellent scalability. In this paper, an acanthosphere-like structure named ZnO nanoflowers is successfully synthesized on Cu foil by using chemical vapor deposition method. The gas flows with oxygen-argon ratios ranging from 1 : 150, 1 : 200, 1 : 250 to 1 : 400, which impacted on Cu foil, and the property of the ZnO nanoflowers are carefully studied. The SEM images shown that there are lots of ZnO nanorods grown on the sphere cores, and look like flowers. The ZnO nanoflowers contains uniformly sized ZnO nanorods and morphology with best flower structure when the oxygen/argon gas flow ratio is 1 : 250. Furthermore, the length-diameter ratio of the ZnO nanorods on the ZnO nanoflowers decreases as the oxygen-argon gas flow ratio decreases. The ZnO is of hexagonal wurtzite structure indicated by XRD pattern and there exist no other diffraction peaks existence except those from the Cu foil. In addition, the photoluminescence of ZnO nanoflower changes from a wave packet into a broad peak in the visible region when the oxygen-argon gas flow ratio between decreases. Further study of the photoluminescence by fitting the peaks in visible region with gaussian function indicates that the photoluminescence relating to the oxygen vacancy defects increases, but that relating to the zinc vacancy defects decreases. Therefore, the white light emitting device may be constructed based on the ZnO nanoflowers studied shown above. Finally, a possible model of the ZnO nanoflowers grown on Cu foil is proposed based on the experimental results.
Semiconductor Materials Genome Initiative: silicon-based light emission material
Authors: Luo Jun-Wei  , Li Shu-Shen  ,   State Key Laboratory of Superlattices and Mcrostructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

The purpose of the semiconductor Materials Genome Initiative is to discover, develop, and deploy new materials in such a way that the research and development period is reduced to a half of original period, and the cost to a fraction of the present cost, thereby speeding up the advance of clean energy sourse, state security, and human welfare, through the organic integration of experiment, computation and theory. Semiconductors play a key role in developing technologies and industries relating to economy, state security, and human welfare. The implement of the semiconductor materials genome initiative will promote the development of semiconductor science and technology into a new era. In this paper, we present a demo of the semiconductor material genome project through introducing our early work on designing silicon-based light emission materials. We first briefly review the status of development of silicon-compatible light emission and challenges facing it. We then demonstrate the power and value of semiconductor materials genome initiative by presenting our recent work on the inverse design of strongly dipole-allowed direct bandgap two-dimensional Si/Ge superlattices and one-dimensional Si/Ge core/multi-shell nanowires, respectively, from two indirect-gap materials (Si and Ge). We use a combination of genetic algorithms with an atomistic pseudopotential Hamiltonian to search through the astronomic number of variants of Sin/Gem//Sip/Geq stacking sequences. We finally give a short perspective of semiconductor materials genome initiative.
Numerical simulation of a hybrid magnetic refrigeration combined with high pressure Stirling regenerative refrigeration effect
Authors: Gao Xin-Qiang  , Shen Jun  , He Xiao-Nan  , Tang Cheng-Chun  , Dai Wei  , Li Ke  , Gong Mao-Qiong  , Wu Jian-Feng  ,   School of Material Science and Engineering, Hebei University of Technology, Tianjin 300401, China;,   Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Magnetic refrigeration is a cooling method based on the magnetocaloric effect, which uses solid magnetocaloric materials as refrigerant, and helium, water or other fluid as heat transfer fluids. Stirling refrigeration is a kind of mature gas regenerative cooling method, using helium gas as the refrigerant. These refrigerations have similar cycling characteristics, and are both safe, environmantal-friendly and high efficient cooling methods. Therefore, a hybrid magnetic refrigerator combined with Stirling gas refrigeration effect is proposed and designed. In our previous works for hybrid magnetic refrigeration, numerical simulation and experimental performance of the low-pressure hybrid magnetic refrigerator was carried out, and the cycling mechanism of hybrid magnetic refrigeration was also figured out. In this study, a numerical model for the high-pressure hybrid magnetic refrigeration cycle is established. The magnetic refrigeration materials are utilized as the regenerator matrix for both gas Stirling and active magnetic regenerative refrigeration in this model. Effects of gas Stirling and active magnetic regenerative refrigeration are combined to build a kind of high efficient refrigeration cycle. Ansys Fluent software is applied in this paper. Based on the physical model of hybrid refrigerator and the theories of magnetocaloric effect and numerical calculation of regenerator, computational fluid dynamics (CFD) model of high-pressure hybrid magnetic refrigerator is established. This paper describes the internal heat transfer mechanism of Stirling and magnetic refrigeration effect in an active regenerator. Some parameters of the model such as working frequency and utilization are analyzed and the best phase angle is figured out in order to couple these two cooling effects positively. Simulation results show that Stirling and magnetic cooling effects can be coupled positively at phase angle of 60o. Results also show that with increasing system pressure, which means to increase the utilization of the system, the system frequency can enhance the cooling performance of the system as well as improve the coefficient of performance (COP) of it. The results and analysis of the numerical model will be helpful for the construction of experimental prototype in our future work.
Phenomena of limit cycle oscillations for non-Markovian dissipative systems undergoing long-time evolution
Authors: You Bo  , Cen Li-Xiang  ,   Department of Physics, Sichuan University, Chengdu 610065, China
Published: December 2020

Understanding the non-Markovian dynamics of dissipative processes induced by memory effects of the environment is a fundamental subject of open quantum systems. Because of the complexity of open quantum systems, e.g., the multiple energy scales involving that of the system, the environment, and their mutual coupling, it is generally a challenging task to characterize the relationship among the parameters of the system dynamics and the reservoir spectra. For the two-level spontaneous emission model within structured environments, it was shown in a recent literature (Opt. Lett. 38, 3650) that a functional relation could be established between the asymptotically non-decaying population and the spectral density of the reservoir as the system undergoes a long-time evolution. It hence renders a distinct perspective to look into the character of long-lived quantum coherence in the corresponding non-Markovian process. This article is devoted to further investigate the phenomena of limit cycle oscillations possibly occurring in such non-Markovian dissipative systems in a long-time evolution. For a two-level system subjected to an environment with Ohmic class spectra, due to the presence of a unique bound-state mode of the system, the evolution trajectory of the given initial states will converge to a limit cycle in the Bloch space. The dependence of the radius and the location of the limit cycle on the spectral density function of the reservoir are manifested by virtue of the described functional relation. For the model subjected to a photonic crystal environment with multiple bands, our studies reveal that, owing to the presence of two or more bound states, the evolution trajectory of the system will converge to a toric curve of a paraboloid in the Bloch space and the phenomena of periodic or quasi-periodic oscillations could exhibit. While the equation of the parabolic curve is fully determined by the initial values of the state vector in the Bloch space, our results reveal that the scope of the evolution trajectory inside the toric curve is related to the spectral density of the reservoir and their quantified relation is distinctly characterized. Finally, the asymptotic dynamics of the correlations of a two-qubit system is discussed when it is subjected locally to the non-Markovian dissipative process.