bluuebunny/crossref_metadata_2025 huggingface dataset:
Opinion formation model with co-evolution of individual behavior and social environment
Authors: Liu Xiao-Hang , Wang Yi-Ning , Qu Zi-Min , Di Zeng-Ru ,   School of Governance, Beijing Normal University, Beijing 100875, China,   School of Systems Science, Beijing Normal University, Beijing 100875, China
Published: December 2020

Entering the information era, the formation of public opinion is largely associated with the complex system constructed by the Internet, thereby possessing new characteristics. The formation of public opinion is the result of the interaction of individual behavior with social environment. In reality, the environmental factor and the individual behavior are usually related to each other and co-evolve with time. Based on the Ising model, in this paper established is an opinion formation model that includes the process of the accumulation and digestion of the social tension. In the model, a parameter named effective dissolving factor c is designed to represent the extent of the interaction between the system and the social environment. A two-dimensional dynamical system is involved in the model to describe the dynamics of individual behavior and social tension. The co-evolution behavior of the system is studied. Based on the Landau mean field theory, the stationary states of the dynamical system under different parameter values, i.e. the value of effective dissolving factor c, their stability and bifurcation of the system, are analyzed. Finally, the computer simulation method is used to verify the results. The research shows that with the co-evolution mechanism of the system, our model exhibits certain self-organization characteristics. When the effective dissolving factor c is smaller than the threshold value, the system will reach final consensus opinion, resulting in a macroscopically ordered state. Otherwise, when the dissolving factor c exceeds a threshold value, the system is stable in the disordered state. It is interesting to find that there is such a critical value of the parameter that it leads the system to be self-organized into a critical state from any initial state. The future detailed investigation on the criticality of the co-evolving system is also suggested, such as testing whether the system has evolved into the critical state according to the finite-sized scaling theory and calculating the critical exponent of the system. In addition, in this paper provided is a new perspective to tackle practical problems in public opinion. Based on the mechanism of the formation of public opinion revealed by our model, researchers are encouraged to conduct studies on how to monitor the state of public opinion more precisely and to predict the tipping point of the system evolution.
Experimental study on influence of fiber numerical aperture on mode instability threshold of ytterbium fiber oscillator
Authors: Chen Yi-Sha , Liao Lei , Li Jin-Yan ,   Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

The phenomenon mode instability is the most limiting factor for further scaling the output power and beam quality in high power fiber lasers. Thus, it is meaningful and necessary to study the influencing factor of mode instability and finally find the approaches to mitigating its influence. Theoretical calculations reveal that the fiber V-parameter has a negative effect on fiber amplifier mode instability threshold. Nevertheless, the influence of fiber core numerical aperture (NA) on fiber oscillator mode instability threshold has rarely been investigated compared with that on the fiber amplifier. In this paper, we build a high-power all-fiber laser oscillator pumped by 976nm laser diodes and measure its laser efficiency and mode instability threshold of 20/400 step-index ytterbium doped fiber with different fiber core NA. Experimental result reveals that at the same 976 nm pump power, the fiber with relatively low core NA (~0.059) has a higher mode instability threshold power than that with relatively high core NA (~0.064), and that even a higher core NA (~0.064) fiber has a higher laser efficiency than lower core NA (~0.059) fiber. The fact shows that the fiber core NA has a significant influence on mode instability threshold, and a relatively high core NA results in a lower mode instability threshold. Also, numerical simulations explain the reason why the fiber core NA has a negative effect on mode instability threshold in fiber oscillator. First of all, the higher fiber core NA will support more propagating modes in fiber, and the lower fiber core NA will result in higher order mode (HOM) content leaking into fiber cladding and the overlap of HOM content and gain area is reduced, thus the gain of HOM is relatively reduced. Also, the bending loss of HOM is very sensitive to fiber core NA variation, and the increase of fiber core NA will reduce the bending loss of HOM dramatically. In conclusion, the fiber core NA has a significant negative effect on fiber oscillator mode instability threshold, and numerical simulationscan explain the physical origin of the negative effect of fiber core NA on laser oscillator mode instability threshold. Thus, for the mode instability mitigation in high power laser oscillator, optimizing the NA of active fiber conduces to the increase of mode instability threshold, which is helpful and necessary for further scaling the output power and beam quality.
First-principles study of five isomers of two-dimensional GeSe under in-plane strain
Authors: Zuo Bo-Min , Yuan Jian-Mei , Feng Zhi , Mao Yu-Liang ,   School of Physics and Optoelectronic, Xiangtan University, Xiangtan 411105, China,   School of Mathematics and Computational Science, Xiangtan University, Xiangtan 411105, China
Published: December 2020

Using first-principles calculations, we investigate the stability and electronic properties of five isomers of two-dimensional (2D) GeSe monolayer under in-plane strain. Our calculated results show that the five isomers of GeSe monolayer are all stable. It is found that the α-GeSe has a direct band gap, while each of the β-GeSe, γ-GeSe, δ-GeSe and ε-GeSe possesses an indirect band gap. By applying compressive or tensile uniaxial and biaxial strain to the five GeSe isomers, the indirect-to-direct transition in band gap is found. In the α-GeSe, the changes from indirect-to-direct and semiconducting-to-metallic are both found under an applied strain. In the 2D β-GeSe and γ-GeSe, an adjustable range of indirect band gap under strain is found. Moreover, a direct band gap in the δ-GeSe is found separately under the biaxial compression strain of σxy = –2% and σxy = –4%. By applying a tensile strain of 10% along the armchair direction in ε-GeSe, a transition from an indirect to direct band gap occurs. When the tensile strain is continuously increased to 20%, the band structure of ε-GeSe maintains direct character. This direct band gap can be tuned from 1.21 eV to 1.44 eV. When 10% tensile strain is applied along the biaxial direction, the transition in band gap from indirect-to-direct also occurs. Our results indicate that the direct band gap can be tuned from 0.61 eV to 1.19 eV when the tensile strain is increased from 10% to 19% in ε-GeSe.
High-voltage flexible solid state supercapacitor based on neutral hydrogel/carbon nanotube arrays
Authors: Wu Meng-Dan , Zhou Sheng-Lin , Ye An-Na , Wang Min , Zhang Xiao-Hua , Yang Zhao-Hui ,   Center for Soft Condensed Matter Physics and Interdisciplinary Research, Jiangsu Key Laboratory of Thin Films, Soochow University, Suzhou 215006, China
Published: December 2020

As a new energy storage device, supercapacitor (or electrochemical capacitor) has an ultra-long cycle life, extremely high power density and enhanced energy density. It fills the gap in the energy-power spectrum between traditional capacitor and battery. In general, the traditional energy storage and conversion device cannot have a perfect trade-off between high energy density and high power density. With the rapid development of modern society, developing light, portable, safe and environmentally friendly high-performance energy storage devices has become increasingly vital. Therefore, there are numerous researches of flexible solid supercapacitors emerging at this historic moment. The selection of flexible electrode materials and that of electrolytes are crucial factors in designing the flexible solid state supercapacitors, which have been the research hotspots in recent years. Carbon nanotube array has been widely used in electrode material of super capacitors due to its excellent electrical conductivity, large specific surface area and super high chemical stability. But in assembly process, carbon nanotube array easily collapses and breaks its neat orientation because of its poor mechanical strength. In consideration of environmental contamination and practical demands, in this paper the neutral gel electrolyte is adopted to embed carbon nanotube array to form flexible composite film electrode. Besides the fact that we use hydrophilic flexible carbon cloth as current collector and neutral gel electrolyte as separator to prepare flexible devices, we compare the electrochemical properties among different devices by changing the electrolyte salt added in gel electrolyte. Meanwhile, after continuous bending and folding, the properties of flexible devices have not been significantly damaged, indicating good flexibility and mechanical stability. The specific capacity of the whole device with PVA-NaCl used as gel electrolyte increases up to 104.5 mF·cm–3, which is much higher than the specific capacity of the composite device formed by organic ionic gels with carbon nanotube array and that of the composite device formed by commercial short carbon nanotubes with hydrogels. A maximum energy density of 0.034 mW·h·cm–3 is obtained at the same time. In addition, it has good rate performance, cycling stability, suppressing self-discharge property, and good chemical stability at a high voltage of 1.6 V. Neutral gel/carbon nanotube array composite devices not only meet the needs of the era of green safety, flexible and portable folding, but also open up the future application prospects of medical implants.
Internal friction characteristics of compacted billet of metal powder in sintering process
Authors: Hao Gang-Ling , Xu Qiao-Ping , Li Xian-Yu , Wang Wei-Guo ,   College of Physics and Electronic Information, Yan’an University, Yan’an 716000
Published: December 2020

Sintering plays a decisive role to determine final product quality in the powder metallurgy process. Understanding the law of structure and defects as well as determining the initial sintering temperature and crystallization temperature will prove clear information to determine favorable sintering technology for the powder compacted billet. In this paper, the internal friction characteristics in the sintering process for powder compact billet, pure Al, Mg, Cu, Fe are systematically studied in terms of internal friction technology. Two internal friction peaks, named heating peak and cooling peak are respectively found in the first run. The cooling peak is a stable relaxational internal friction peak. It is concluded that the peak is associated with the viscous sliding of grain boundary based on the activation energy and peak temperature location. The heating peak is an unstable internal friction peak corresponding to the decline of resistance and relative dynamic modulus, the peak temperature being considered as an initial sintering temperature due to the great change of material performance. Furthermore, the heating peak is dependent on powder particle size and compressing pressure, which increases with the decrease of particle size or compressing pressure. The dependence can be understood according to the increase of weak bonding interface and activated slipping distance between powder particles. The internal friction of the powder compacted billet in the heating process gradually increases with the temperature increasing, which is mainly due to the micro sliding of the weak bonding interface, but the enhancing trend stops and internal friction rapidly declines when the temperature approaches to the peak location due to the transition of weak bonding interface to grain boundary, as a result, leading to the formation of the heating peak. The occurrence of therising temperature peak indicates the formation of grain boundary between powder particles in the sintering process of powder compacted billet. Correspondingly, the peak temperature can be used as a crystallization temperature.
Preparation, optical, and electrical properties of rubrene∶MoO3 films
Authors: Li Rui-Dong , Deng Jin-Xiang , Zhang Hao , Xu Zhi-Yang , Pan Zhi-Wei , Sun Jun-Jie , Wang Gui-Sheng ,   College of Applied Science, Beijing University of Technology, Beijing 100124, China
Published: December 2020

In this paper, the mixed films with different rubrene-to-MoO3 ratios are deposited on the substrates of Si, indium tin oxide and quartz glass by using the thermal evaporation technique. First, these films are characterized by atomic force microscopy and X-ray diffraction in order to identify their surface morphology and their structure properties. The results show that all the films are amorphous and the film has the best flatness when the rubrene-to-MoO3 ratio is 2∶1. Second, the optical properties of the mixed films are investigated by both photoluminescence (PL) spectra and absorption spectra. The optical band gap of rubrene and MoO3 are 2.2 eV and 3.49 eV respectively and there is almost no absorption about rubrene and MoO3 in the near-infrared (NIR) region. However the PL spectrum shows a peak in NIR region and it indicates that the interface between rubrene and MoO3 possesses an abrupt discontinuity at the vacuum level, resulting in electron wave functions overlapping and charge-transfer complex (CTC) forming. The intermediate state within the original band gap of rubrene with energy of 1.25 eV is induced by the CTC, which suggests the possibility of charge transfer exciton generated upon NIR excitation. The absorption spectra of the mixed films show that there is an obvious absorption. All the films have the same absorption peak except the film with a rubrene-to-MoO3 ratio of 4∶1 and it indicates that the concentration of MoO3 has almost no influence on the absorption of the mixed films. The optical band gaps of the mixed thin films are calculated in a spectral range of 345－1035 nm according to the Tauc equation, and the results show that the optical band gap of the film with a rubrene-to-MoO3 ratio of 2∶1 is narrowest (~2.23 eV).

In order to study the electrical characteristics of the mixed films, an Al/rubrene:MoO3/ITO device is fabricated. The current density-voltage (J-V) characteristic is also investigated. The analysis of the J-V measurement for the device indicates that the current conduction in the Al/rubrene:MoO3/ITO device is Ohmic type when the rubrene-to-MoO3 ratios are 4∶1 and 2∶1, and it is Schottky type when the ratio is other value. The current for rubrene-to-MoO3 ratio of 1∶1 is larger than that for 1∶2, which indicates that the contact is better when the surface is more smooth. These properties of the mixed films can result in the applications in the near-infrared region.
Design and experiment of re-injection off-axis integrated cavity output spectroscopy technology in 2 μm band
Authors: Zhou Zi-Xin , Huang Yin-Bo , Lu Xing-Ji , Yuan Zi-Hao , Cao Zhen-Song ,   Key Laboratory of Atmospheric Optics, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China,   Science Island Branch of Graduate School, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Off-axis integrated cavity output spectroscopy (OA-ICOS) is a highly sensitive laser spectroscopy technique. However, due to the use of dense high-order modes for detection, OA-ICOS signal power is low, thus making the detection sensitivity highly dependent on the laser power. To this problem, we introduce an optical re-injection method to re-inject the laser back into the optical cavity again, improving the utilization of laser energy and the power of signal. In this paper, we use optical tracking software to design a re-injection structure, and study several factors affecting the signal gain. Then, we build a re-injection OA-ICOS device in the 2 μm band and also conduct a series of experimental researches. Our results show that the re-injection method enhances the OA-ICOS signal power 8 times and signal-to-noise ratio 4.6 times, which effectively improves the detection sensitivity and the absorption depth of the spectral signal, and alleviates the problem of low signal power in OA-ICOS detection.
Enhancement of photoluminescence from zinc oxide by aluminum nanoparticle surface plasmon
Authors: Liu Zi , Zhang Heng , Wu Hao , Liu Chang ,   Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, Hubei Nuclear Solid Physics Key Laboratory, School of Physics and Technology, Wuhan University, Wuhan 430072, China
Published: December 2020

During the past few decades, surface plasmons (SPs) have become a research hotspot. The SPs are the collective oscillations of free electrons at the interface between metal and dielectric surrounding. Localized surface plasmon resonance (LSPR) for metal nanoparticles (NPs) has a wide application in the light emission enhancement by the selective photon absorption and by increasing local electromagnetic field. Nowadays, many achievements of SP-enhanced-emissions are applied to light emitting diodes. With the advantages of the direct wide band gap (3.37 eV) and large exciton binding energy (60 meV), zinc oxide (ZnO), which is considered as a potential material, has a wide range of applications, especially in ultraviolet (UV) optoelectronic devices. However, the low photoluminescence efficiency of ZnO limits the commercial applications of ZnO-devices. The relevant research shows that the selection of different metal NPs, such as platinum (Pt), aluminum (Al), argentum (Ag), aurum (Au), is one of the approaches to improving the UV emission from ZnO. In this study, two-dimensional arrays of Al NPs are used to improve the LSPR photoluminescence efficiency from ZnO grown by the atomic layer deposition (ALD). The two-dimensional arrays of Al NPs are fabricated on the surfaces of p-type Gallium nitride (GaN) substrates by colloid lithography. With the air-liquid interface self-assembly, the monolayer masks for colloid lithography are obtained on the substrates of p-type GaN. Then, after a 50-nm Al layer is deposited by thermal evaporation, the Al NPs’ arrays are gained by being dipped into toluene and extra sonication to remove the masks. Finally, 15 nm Al2O3 and 200 nm ZnO films are deposited in sequence by ALD at a temperature of 125 ℃. The extinction spectra of Al NPs’ arrays are acquired by an ultraviolet-visible spectrophotometer. The results of the extinction spectra suggest that the radiative recombination rate is increased by the resonance coupling between the localized surface plasmons (LSP) of the Al NPs arrays and the excitons of the ZnO. A 1.91-fold enhancement of photoluminescence integral intensity in band-edge emission is measured because of the Al NP arrays coupled with ZnO. The result means that the LSP of the Al NPs’ arrays can increase the UV-emission of the ZnO. Therefore, this cost-effective and facile approach can be used in high-performance optoelectronic devices.
Theoretical study of interface thermodynamic properties of 1,3,5-triamino-2,4,6-trinitrobenzene based polymer bonded explosives
Authors: Fan Hang , He Guan-Song , Yang Zhi-Jian , Nie Fu-De , Chen Peng-Wan ,   School of Mechatronical Engineering, Beijing Institute of Technology, Beijing 100081, China,   Institute of Chemical Materials, CAEP, Mianyang 621900, China
Published: December 2020

The thermodynamic properties of insensitive high explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) based polymer bonded explosives (PBXs) are investigated by using first principle calculation and molecular dynamics simulation. The results include the phonon dispersion relations, interface thermal conductances, and thermal conductivities of TATB based PBXs. Both TATB and PVDF structures are optimized, in which the optimized lattice constants accord with previous results. The phonon dispersion relation of TATB and PVDF are calculated based on lattice dynamics. All interatomic force constants are calculated by the finite displacement method (numerical derivatives from perturbed supercells). The calculated phonon dispersion relation of TATB and heat capacity are in general agreement with experimental and theoretical results. The imaginary frequencies are observed in both TATB and PVDF dispersion relation. The imaginary frequencies are mainly due to the smaller calculated supercell size and temperature effect. The phonon mode of TATB and PVDF are assigned at Γ point. Based on the calculated phonon dispersion, some information including heat capacity, phonon density of states and phonon mode assignment is derived. The TATB possesses 144 phonon modes including 3 acoustic-phonon modes and 141 optical phonon modes. The anylized phonon mode of TATB shows that -NO2 dominates the phonon DOS in low frequency zone, phenyl rings dominate in middle frequency zone and -NH2 dominates in high frequency zone. By analyzing the phonon density of states and capacity, both TATB and PVDF imply that low-frequency vibration dominates the thermal conductivity. The thermal conductivity is determined for TATB by using the equlibrium molecular dynamics method and an established TATB force field. The TATB model is built with 2880 atoms. The structure of TATB is optimized by using molecular mechanics, then this system is relaxed by using a Nose-Hoover thermostat and barostat with a damping factor of 50 fs cin time steps of 0.1 fs. The calcultated thermal conductivity at room temperature shows good agreement with experimental result. The interface thermal conductance of TATB-PVDF is calculated by using a diffusive mismatch model. The interface thermal transport still follows Fourier’s law of heat conduction, and ballistic thermal transport mechanism is not involved. By using the above results, the thermal conductivity of mixture TATB-PVDF system is analized with a simple series model. The particle size smaller than 100 nm significantly suppresses the mixture system thermal conductivity.
Squeezed property of optical transistor based on cavity optomechanical system
Authors: Li Sen , Li Hao-Zhen , Xu Jing-Ping , Zhu Cheng-Jie , Yang Ya-Ping ,   Key Laboratory of Advanced Micro-Structured Materials of Ministry of Education, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
Published: December 2020

All-optical diodes and all-optical transistors are the basis of all-optical logic devices. We study the quantum statistical properties of all-optical diodes based on cavity quantum electrodynamics (QED)[1], and discuss the squeezed properties of the output light after passing through the diode when coherent light and squeezed light are incident. Here we extend our research to all-optical transistor, and take all-optical transistor based on cavity optomechanical system as the research object. By changing the intensity of classical pump light, the all-optical transistor can effectively control the output of the probe light and realize optical amplification. We discuss the squeezed properties of the output light of the all-optical transistor with squeezed light and coherent light as the probe light. Our results show that when the probe light is coherent, the output light remains coherent no matter whether it works in the amplified region, and is not squeezed. When the input probe light is amplitude squeezed light, the output light is still squeezed light in the light amplification region of all-optical transistor, but the squeezed properties are modulated by the input light squeezed properties and system parameters. When the squeezed angle of the input probe squeezed light is 0°, the minimum squeezed parameter S1 of the output squeezed light decreases with the increase of the squeezed coefficient r of the input probe light, and the minimum value approaches to the squeezed limit of –0.25. But the change of squeezed angle of the input probe squeezed light changes has a great influence on the squeezed parameter S1,2 of the output light, and the squeezed properties will disappear. Only when the squeezed angle is an integer multiple of π, will the squeezed properties of the output light be best. This result has a potential application value in quantum measurement, weak signal detection, and other fields.
Topological edge states with skin effect in a trimerized non-Hermitian lattice
Authors: Xu Nan , Zhang Yan ,   School of Physics, Northeast Normal University, Changchun 130024, China
Published: December 2020

In recent years, exploring new topological quantum model structures and in depth analyzing the novel physical properties in various multimerized topological lattices have become a hot topic in the field of quantum optics. Among the different model structures, the multimerized non-Hermitian lattice controlled by different parameters in the future research of topological quantum materials, we believe, can exhibit more meaningful novel topological properties. As one of the most classic topological models, the one-dimensional Aubry-André-Harper (AAH) model has received more and more attention in the study of multimerized lattices. In this paper, we focus on the novel topological properties of a trimerized non-Hermitian lattice, and extend the trimer model structure from a one-dimensional chain to a quasi-one-dimensional zigzag structure. The results show that firstly, if the nearest-neighbor forward coupling coefficient in the unit cell is not equal to the backward coupling coefficient, the chiral inversion symmetry of the system is destroyed. It can be observed that the bulk states and the edge states in the trimerization model will be localized on the same edge of the lattice, and the skin effect will appear in the system. With the increase of the nearest-neighbor coupling coefficient, the width of the edge state changes in which the lower edge state of the imaginary part of the spectrum is narrowed until it disappears. The degree of degeneracy of the system changes, and the number of edge states is reduced from four to two. Remarkably, the generalized bulk-boundary correspondence is shown in certain non-Hermitian topological systems. Secondly, when the trimerization model considers the influence of the next-nearest-neighbor coupling, the numerical results show that the upper and lower energy gaps in the energy spectrum and the edge states in the energy spectrum are asymmetrical as the next-nearest-neighbor coupling coefficient is modulated in an appropriate range. The upper energy gaps and the edge states are narrowed, and the edge states of the lower energy gaps are widened. At the same time, the novel topology features of the system can also be used to achieve the quantitative control of the energy spectrum edge states, and other interesting directions are worth exploring.
Singularly perturbed solutions of a class of non-Fourier temperature field distribution
Authors: Bao Li-Ping , Li Wen-Yan , Wu Li-Qun ,   School of Science, Hangzhou Dianzi University, Hangzhou 310018, China,   School of Science, Hangzhou Dianzi University, Hangzhou 310018, China
Published: December 2020

Thermoelastic coupling model excited by laser is of great significance in engineering. To study the thermoelastic coupling model, the distribution of temperature field must be determined firstly. Because the laser excitation time is short (usually femtosecond), the traditional Fourier heat conduction law is no longer suitable. Therefore, it is necessary to establish the distribution of temperature field by using the non-Fourier heat conduction law. Previous studies on the temperature field model mostly use numerical analysis and computer simulation to discuss its numerical solution, but few can directly solve the analytical solution of the model. Up to now, there are few reports about using singularly perturbed analysis method to solve the asymptotic solution of temperature field model and determine the jumping position of heat conductivity coefficient. In this paper, a temperature field model is constructed by using the non-Fourier heat conduction law, i.e. a class of singularly perturbed hyperbolic equations with small parameters in an unbounded domain. The nonlinear singularly perturbed two-parameter hyperbolic equations with discontinuous coefficients are obtained when the heat conduction coefficients jump due to sharp temperature changes. By using the singularly perturbed biparametric expansion method, the asymptotic solution of the problem is obtained. First, the expansion of the problem is obtained by using singularly perturbed method. The existence and uniqueness of the internal and external solutions are obtained by estimating the maximum modulus of the internal and external solutions and the maximum modulus estimates of the time derivatives, and the formal asymptotic expansion of the solutions is obtained. Secondly, the singularly perturbed hyperbolic equation is corrected by the singular perturbation theory, and the derivative of the solution is estimated. The position expression of the jump of the thermal conductivity coefficient is determined by the Fourier transform, and the seam method is used to connect the seams of the two sides of the jump position of the thermal conductivity coefficient, thus the form asymptotic expansion of the solution is obtained. Finally, the uniform validity of the asymptotic solution is obtained by estimating the residual term, and the distribution of the temperature field with discontinuous heat conduction coefficient is obtained. In this paper, we have synthetically applied the knowledge of ordinary differential equations, partial differential equations, mathematical and physical equations, nonlinear acoustics, mathematical analysis, singular perturbation theory and so on, which enriched the study of non-Fourier temperature field model.
Tunable unconventional phonon blockade in Fabry-Perot cavity and optical parametric amplifier composite system
Authors: Li Hong , Zhang Si-Qi , Guo Ming , Li Mei-Xuan , Song Li-Jun ,   Institute for Interdisciplinary Quantum Information Technology, Jilin Engineering Normal University, Changchun 130052, China,   Jilin Engineering Laboratory for Quantum Information Technology, Changchun 130052, China
Published: December 2020

In this paper, we present a scheme to realize an unconventional photon blockade effect in a Fabry-Perot cavity and optical parametric amplifier (OPA) composite system. The system includes a tunable phase of complex driving strength, the second-order correlation function is used to describe the photon statistical properties. The numerical simulation of the photon blockade effect is conducted with different parameters. Our calculations show that the unconventional photon blockade effect can be controlled by the tunable phase of complex driving strength. Under the weak driving condition, the exact optimal conditions for strong photon anti-bunching are analytically derived (i.e. the optimal nonlinear gain of optical parametric amplifier and the phase of the field driving for the strong photon anti-bunching are obtained), and obtain the analytic calculations of the second-order correlation function. Under the optimal conditions, we perform a numerical simulation with different parameters. The optimal conditions for strong photon anti-bunching are found by analytic calculations, which are in good agreement with the numerical results. The results provide a platform for coherently operating the photon blockade and have potential applications in quantum information processing and quantum optical devices.
Global analysis of crises in shape memory thin plate system
Authors: Yue Xiao-Le , Xiang Yi-Lin , Zhang Ying ,   Department of Applied Mathematics, Northwestern Polytechnical University, Xi’an 710072, China
Published: December 2020

The unique global properties of shape memory alloy are mainly derived from the martensite phase transition and its inverse, which result from the change of temperature and external load. In this paper, the global characteristics of shape memory alloy thin plate system are analyzed with the temperature and harmonic excitation amplitude as control parameters. Based on the method of Poincare map, the complex crisis phenomenon of the system including the sudden change in number, size and type of attractors can be observed through the global multivalued bifurcation diagram. However, the specific crisis type is not clear, it is necessary to be analyzed from the global viewpoint. By computing the global diagram with the composite cell coordinate system method which constructs a composite cell state space by multistage division of the continuous phase space, the attractors, saddles and basins of attraction of the system can be obtained more accurately. The vivid evolutionary processes of the crisis phenomena of the system are illustrated, and it can be found that the system presents a complex global structure with amplitude and temperature changing. There exist two kinds of crises: one is the boundary crisis resulting from the collision between a chaotic/periodic attractor and a chaotic saddle within the basin boundary, which causes the attractor to vanish, and the other is the merging crisis caused by the collision of two or more attractors with the chaotic saddle within the basin boundary where a new chaotic attractor appears. When multiple attractors coexist in the system, the basin boundary may be smooth or fractal, and for any point at boundary, its small open neighborhood always has a nonempty intersection with three or more basins, which is known as Wada basin boundary. It is difficult to predict the dynamic behavior of the system accurately due to the fractal, the Wada-Wada, Wada-fractal and fractal-Wada basin boundary metamorphoses which can be observed along with the variation of temperature and amplitude through the composite cell coordinate system method, which owns a unique advantage in depicting basin boundary. Furthermore, the Wada property is displayed more clearly by refining specified region. The results of this paper provide a theoretical analysis tool for adjusting the dynamic response of shape memory alloy thin plate system and optimizing the deformation and vibration control of mechanical equipment through controlling temperature and excitation intensity.
Moving target detection algorithm based on spatiotemporal correlation multi-channel clustering
Authors: Xu Yan , Wang Pei-Guang , Yang Qing , Dong Jiang-Tao ,   College of Electronic Information Engineering, Hebei University, Baoding 071002, China,   Department of Electronic and Optical Engineering, Army Engineering University Shijiazhuang Campus, Shijiazhuang 050000, China,   College of Electronic Information Engineering, Hebei University of Technology, Tianjin 300401, China,   The 54th Research Institute of China Electronics Science and Technology Corporation, Shijiazhuang 050000, China
Published: December 2020

In the process of tracking target, certain multi-modal background scenes are not suitable for the off-line training model, and moving target detection is affected as background in the current video environment is mostly multi-modal scene with much noise, and the characters of moving targets irregularly change, which,therefore, requires a more stable and robust moving target detection algorithm. To solve this problem, taking advantage of spatiotemporal relationship learning, the mixed Gaussian model (GMM) is improved in three aspects.

First, the initialization method combining five-frame difference and intra-frame neighborhood average is proposed to obtain the initial parameters of the mixed Gaussian model. The five-frame difference method is introduced to obtain the initial parameters of the model, so that the background model is closer to the real scene. The intra-frame neighborhood average value is introduced, and an accumulation matrix CA is proposed to record the number of neighboring pixel points, then to enhance the information relevant to the neighborhood. This process can reduce the discontinuity of the target.

Second, the calculation method of the neighborhood correlation is introduced to update the parameter of Gaussian model. Since the single pixel feature is related to the neighborhood random correlation, the random subsampling technology and neighborhood spatial propagation theory are combined together, and the execution efficiency is taken into account to simplify the process of updating model. To speed up the model convergence, an observation vector is built in the time dimension to optimize the model parameters, and the weight ω is gained based on the posterior probability.

Then, the color-gradient method incooperated with the color HSI space and gradient information is adopted in this paper to complete the multi-channel Gaussian mixture model. The initial and the updated parameters of the Gaussian model in each channel can be acquired via the above steps. To simplify the computation of three channels, the random sampling of background pixels is introduced. Finally the detection of moving targets in complex environments is realized.

The experiments show that the proposed algorithm has a great improvement in suppressing the influence of complex background and detecting target integrity, and the influence of the moving target in the initial stage is eliminated.
Sound transmission in two-dimensional periodic poroelastic structures
Authors: Qiao Hou , He Zeng , Zhang Heng-Kun , Peng Wei-Cai , Jiang Wen ,   Department of Mechanics, Huazhong University of Science and Technology, Wuhan 430074, China,   National Key Laboratory on Ship Vibration and Noise, China Ship Development and Design Center, Wuhan 430064, China
Published: December 2020

To obtain excellent sound reduction performance, in this paper we introduce a novel periodic poroelastic composite structure, which combines poroelastic material and periodic structure and aims at using the remarkable acoustic performance of these two. This periodic composite structure comprises three parts, i.e. the poroelastic domain, the elastic domain (thin plate), and the periodic resonators, which can be simple single-degree-of-freedom resonators (SRs) or composite two-degree-of-freedom resonators (CRs). A theoretical model is established by using Biot theory for the poroelastic domain, and by using the effective medium method for the resonator-plate coupling system, which is considered as an isotropic plate with an equivalent dynamic density. This method is validated with degenerated model in the literature; the results obtained by this method are in excellent consistence with the results in the literature. Parameter analyses are performed to test the influences of poroelastic addition and periodic resonator on the sound transmission loss (STL) of this periodic composite structure under two kinds of boundary conditions. The poroelastic addition is found to increase the STL while the influences of resonators are complicated. The STL increases notably in the frequency range bounded by the characteristic frequencies of these resonators, however, a decrease just follows when it exceeds these frequencies, which can be observed in both SR case and CR case under the two boundary conditions. In the meantime, when multiple SR is placed in a periodic lattice, it is found that different resonators with ascending mass and characteristic frequencies have superior STL to those with ascending characteristic frequencies but have equal mass. The case with CR, which is more complicated as expected, shows less STL decrease than the case with SR, but wider frequency range where the STL increases than a poroelastic composite structure without resonators. This results from the fact that the frequency band of vibration suppression in the CR case is wider than in the SR case. As a result, to achieve the desired STL performance in a frequency range, the proposed composite structure using SR with tuned characteristic frequencies is enough; however, if a wider frequency band is expected even if there is a slight STL tradeoff, the CR case is a better option. Though the method proposed is only valid in the low-to-medium frequency range, the results obtained can benefit theoretical development of low-to-medium sound modulation applications, they are also valuable and illuminating for investigating the broadband sound modulation.
Fiber gratings matching and output characteristics of fiber laser
Authors: Liu Jia-Xing , Liu Xia , Zhong Shou-Dong , Wang Jian-Qiang , Zhang Da-Peng , Wang Xing-Long ,   School of Precision Instruments and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China,   Advanced Fiber Resources (Zhuhai), Ltd., Zhuhai 519080, China
Published: December 2020

In order to improve the output power and processing quality in industrial applications, it is important to optimize the output characteristics of the high-power fiber lasers. The slope efficiency, backward leaking power and stimulated Raman scattering are key issues in high-power fiber laser design. The parameters matching the fiber gratings, which are the critical components, have a direct influence on the whole fiber laser system. In this paper, the parameters matching the fiber gratings in fiber lasers are investigated. Firstly, the origin of slope efficiency, backward leaking power and stimulated Raman scattering are analyzed in theory. Then the influences on output characteristics of fiber lasers comprised of the output coupler gratings, which have different bandwidths and reflectivities, are experimentally studied. Finally, the optimized parameters and matching principle of fiber gratings in high-power fiber laser are obtained , thus providing an alternative method to improve the output characteristics of high-power continuous wave fiber laser.
Intraband relaxation process in PbSe quantum dot studied by lattice relaxation method
Authors: Liang Yu-Hong , Li Hong-Juan , Yin Ji-Wen ,   School of Physical and Electronic Information Engineering, Chifeng University, Chifeng 024000, China
Published: December 2020

Within the frame of lattice relaxation model, several intraband relaxation processes between the three lowest excited states and ground state in a PbSe quantum dot are studied based on the electron-longitudinal optical phonon coupling via Fröhlich mechanism. We find that Huang-Rhys factors decrease with the radius of quantum dot increasing in different relaxation processes. More important is the fact that the obtained values of Huang-Rhys factors satisfy the experimental measurements in the strong coupling limit. These intraband relaxation processes follow the asymmetrical Gaussian distribution with respect to the radius, in which the probabilities with which these intraband relaxation transitions occur are different. Among these relaxation processes, two intraband transitions from the third excited state to ground state and to second excited states dominate the relaxation processes on a several nanometer scale of radius. Moreover, the temperature dependence for each of these relaxation processes can be modulated by the radius of quantum dot. These theoretical results are consistent with the experimental measurements and provide an important insight into the intraband relaxation in quantum dots in experiments.
Low-frequency generation-recombination noise behaviors of blue/violet-light-emitting diode
Authors: Wang Dang-Hui , Xu Tian-Han ,   School of Materials Science and Engineering, Xi’an Shiyou University, Xi’an 710065, China
Published: December 2020

During the past two decades, GaN-based light-emitting diode has been used as a high-quality light-source. Low-frequency noise as a diagnostic tool for quality control and reliability estimation has been widely accepted and used for semiconductor devices. Understanding the origin of efficiency-droop effect is key to developing the ultimate solid-state light source. Various mechanisms that may cause this effect have been suggested, including carriers’ escape, loses due to dislocations, and the Auger effect. In this study, we investigate the low-frequency noise behaviors of GaN-based blue light-emitting diode with InGaN/GaN multiple quantum wells. The measured currents range from 0.1 mA to 180 mA. According to the characteristics of power spectral density of current noise and the generation-combination mechanism between electrons and holes in the active region of light-emitting diode (LED), we adopt the well-known model of low-frequency noise to fit the relationship between power spectral density of current and frequency, and find that there exists a transition between generation-combination and 1/f noise when the light-emitting diode begins to work. In other words, it can be derived that the low-frequency noise behaviors are dominated by generation-combination noise when the currents are between 0.1 mA and 27 mA; with the current gradually increasing, the origin source of low-frequency noise in blue/violet-light LED will transit to the 1/f noise. Through the analysis of the transport and recombination mechanism of the carriers, and combination with the model of low-frequency noise, we analyze the corner frequency of the generation-recombination noise. The results of this paper provide an effective tool and method to study the conversion of light-emitting diodes.
High-pressure structure prediction and high-temperature structural stability of periclase
Authors: Song Ting , Sun Xiao-Wei , Wei Xiao-Ping , Ouyang Yu-Hua , Zhang Chun-Lin , Guo Peng , Zhao Wei ,   School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070, China
Published: December 2020

Periclase is the terminal component of the ferropericlase, and its chemical composition is MgO. It is well known that there exists a huge difference between the melting curves of MgO determined experimentally and theoretically. A feasible way to clarify the nature of the melting temperature is to investigate the possible new phase of MgO. Meanwhile, it is very important to study the new phase and the influence of temperature on structural stability of MgO in high-pressure condensed matter physics and geophysics. In the present work, we study in detail the phase stability and the possible existing structures of MgO, which include the structure predicted by particle swarm optimization algorithm through using the first-principles pseudopotential density functional method. We find that MgO crystallizes into a rocksalt structure in a pressure range from 0 to 580 GPa and that the CsCl-type structure is of a high-pressure phase at up to 800 GPa. Although an NiAs-type hexagonal phase perhaps explains the volume discontinuity at (170 ± 10) GPa along the MgO Hugoniot in a shock-compression experiment (Zhang L, Fei Y W 2008 Geophys. Res. Lett. 35 L13302) and a wurtzite phase perhaps explains the huge difference between the melting curves of MgO determined experimentally and theoretically (Aguado A, Madden P A 2005 Phys. Rev. Lett. 94 068501), neither of them is existent in the entire range of pressures studied, according to the thermodynamic stability calculations. The calculations of phonon spectra indicate that the B3, B4, B81, B82, and P3m1 phases of MgO are dynamically stable at zero pressure. That is to say, all of the predicted structures are the metastable structures of MgO. In addition, the high-temperature structural stability of MgO is investigated by using very similar Lewis-Catlow and Stoneham-Sangster shell model potential based on the classical molecular dynamics (MD) simulations. In order to take into account the non-central force in crystal, the breathing shell model is also introduced in simulation. The thermodynamic melting curves are estimated on the basis of the thermal instability MD simulations and compared with the available experimental data and other theoretical results in the pressure range of 0－150 GPa.