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CN 11-1958/O4
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 Strong coupling between metasurface based Tamm plasmon microcavity and exciton Wu Han, Wu Jing-Yu, Chen Zhuo Acta Physica Sinica, 2020, 69 (1): 010201
 Achieving low frequency electromagnetic wave absorption by gyromagnetic ferrite Ye Kang-Ping, Pei Wen-Jin, Xi Xiang, Pu Yin, Wu Rui-Xin Acta Physica Sinica, 2020, 69 (1): 017801
 Perovskite light-emitting diodes based on solution-processed metal-doped nickel oxide hole injection layer Wu Jia-Long, Dou Yong-Jiang, Zhang Jian-Feng, Wang Hao-Ran, Yang Xu-Yong Acta Physica Sinica, 2020, 69 (1): 018101
 Current Issue Accepts In Press Earlier Issues Top Downloaded SCI Top Cited
 Acta Physica Sinica--2020, 69 (1)   Published: 05 January 2020
SPECIAL TOPIC—Nonlinear physics
Zhang Da-Jun
Acta Physica Sinica. 2020, 69 (1): 010202 doi: 10.7498/aps.69.20191647
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In contrast to the well-established theory of differential equations, the theory of difference equations has not quite developed so far. The most recent advances in the theory of discrete integrable systems have brought a true revolution to the study of difference equations. Multidimensional consistency is a new concept appearing in the research of discrete integrable systems. This property, as an explanation to a type of discrete integrability, plays an important role in constructing the Bäcklund transformations, Lax pairs and exact solutions for discrete integrable system. In the present paper, the multidimensional consistency and its applications in the research of discrete integrable systems are reviewed.
Liu Ping, Xu Heng-Rui, Yang Jian-Rong
Acta Physica Sinica. 2020, 69 (1): 010203 doi: 10.7498/aps.69.20191316
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The Boussinesq equation is a very important equation in fluid mechanics and some other disciplines. A Lax pair of the Boussinesq equation is proposed. With the help of the truncated Painlevé expansion, auto-Bäcklund transformation of the Boussinesq equation and Bäcklund transformation between the Boussinesq equation and the Schwarzian Boussinesq equation are demonstrated. Nonlocal symmetries of the Boussinesq equation are discussed. One-parameter subgroup invariant solutions and one-parameter group transformations are obtained. The consistent Riccati expansion solvability of the Boussinesq equation is proved and some interaction structures between soliton-cnoidal waves are obtained by consistent Riccati expansion.
Song Cai-Qin, Zhu Zuo-Nong
Acta Physica Sinica. 2020, 69 (1): 010204 doi: 10.7498/aps.69.20191887
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In this paper, we introduce an integrable reverse space-time nonlocal Sasa-Satsuma equation. The Darboux transformation and soliton solutions for this nonlocal integrable equation are constructed.
Wen Xiao-Yong, Wang Hao-Tian
Acta Physica Sinica. 2020, 69 (1): 010205 doi: 10.7498/aps.69.20191235
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It is an important research topic to study diverse local wave interaction phenomena in nonlinear evolution equations, especially for the semi-discrete nonlinear lattice equations, there is little work on their diverse local wave interaction solutions due to the complexity and difficulty of research. In this paper, a semi-discrete higher-order Ablowitz-Ladik equation is investigated via the generalized (M, N-M)-fold Darboux transformation. With the aid of symbolic computation, diverse types of localized wave solutions are obtained starting from constant and plane wave seed background. Particularly, for the case M=N, the generalized (M, N-M)-fold Darboux transformation may reduce to the N-fold Darboux transformation which can be used to derive multi-soliton solutions from constant seed background and breather solutions from plane wave seed background, respectively. For the case M=1, the generalized (M, N-M)-fold Darboux transformation reduce to the generalized (1, N-1)-fold one which can be used to obtain rogue wave solutions from plane wave seed background. For the case M=2, the generalized (M, N-M)-fold Darboux transformation reduce to the generalized (2, N-2)-fold one which can be used to give mixed interaction solutions of one-breather and first-order rogue wave from plane wave seed background. To study the propagation characteristics of such localized waves, the numerical simulations are used to explore the dynamical stability of such obtained solutions. Results obtained in the present work may be used to explain related physical phenomena in nonlinear optics and relevant fields.
Tang Na, Yang Xue-Ying, Song Lin, Zhang Juan, Li Xiao-Lin, Zhou Zhi-Kun, Shi Yu-Ren
Acta Physica Sinica. 2020, 69 (1): 010301 doi: 10.7498/aps.69.20191278
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We study the gap solitons and their stability properties in a Bose-Einstein condensation (BEC) under three-body interaction loaded in a Jacobian elliptic sine potential, which can be described by a cubic-quintic Gross-Pitaevskii equation (GPE) in the mean-field approximation. Firstly, the GPE is transformed into a stationary cubic-quintic nonlinear Schrödinger equation (NLSE) by the multi-scale method. A class of analytical solution of the NLSE is presented to describe the gap solitons. It is shown analytically that the amplitude of the gap soliton decreases as the two-body or three-body interaction strength increases. Secondly, many kinds of gap solitons, including the fundamental soliton and the sub-fundamental soliton, are obtained numerically by the Newton-Conjugate-Gradient (NCG) method. There are two families of fundamental solitons: one is the on-site soliton and the other is the off-site soliton. All of them are bifurcated from the Bloch band. Both in-phase and out-phase dipole solitons for off-site solitons do exist in such a nonlinear system. The numerical results also indicate that the amplitude of the gap soliton decreases as the nonlinear interaction strength increases, which accords well with the analytical prediction. Finally, long-time dynamical evolution for the GPE is performed by the time-splitting Fourier spectrum method to investigate the dynamical stability of gap solitons. It is shown that the on-site solitons are always dynamically stable, while the off-site solitons are always unstable. However, both stable and unstable in-phase or out-phase dipole solitons, which are not bifurcated from the Bloch band, indeed exist. For a type of out-phase soliton, there is a critical value $q_c$ when the chemical potential μ is fixed. The solitons are linearly stable as $q>q_c$, while they are linearly unstable for $q<q_c$. Therefore, the modulus q plays an important role in the stability of gap solitons. One can change the dynamical behavior of gap solitons by adjusting the modulus of external potential in experiment. We also find that there exists a kind of gap soliton, in which the soliton is dynamically unstable if only the two-body interaction is considered, but it becomes stable when the three-body interaction is taken into account. This indicates that the three-body interaction has influence on the stability of gap solitons.
Guo Hui, Wang Ya-Jun, Wang Lin-Xue, Zhang Xiao-Fei
Acta Physica Sinica. 2020, 69 (1): 010302 doi: 10.7498/aps.69.20191424
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Soliton is an exotic topological excitation, and it widely exists in various nonlinear systems, such as nonlinear optics, Bose-Einstein condensates, classical and quantum fluids, plasma, magnetic materials, etc. A stable soliton can propagate with constant amplitude and velocity, and maintain its shape. Two-dimensional and three-dimensional solitons are usually hard to stabilize, and how to realize stable two-dimensional or three-dimensional solitons has aroused the great interest of the researchers. Ring dark soliton is a kind of two-dimensional soliton, which was first theoretically predicted and experimentally realized in nonlinear optical systems. Compared with the usual two-dimensional solitons, ring dark solitons have good stability and rich dynamical behaviors. Owing to their highly controllable capability, Bose-Einstein condensates provide a new platform for studying the ring dark solitons. Based on the recent progress in Bose-Einstein condensates and solitons, this paper reviews the research on the analytic solutions, stability, as well as the decay dynamics of ring dark solitons in Bose-Einstein condensates. A transform method is introduced, which generalizes the analytic solutions of ring dark solitons from a homogeneous system with time-independent nonlinearity to a harmonically trapped inhomogeneous system with time-dependent nonlinearity. The stability phase diagram of the ring dark soliton under deformation perturbations is discussed by numerically solving the Gross-Pitaevskii equations in the mean-field theory. A method of enhancing the stability of ring dark solitons by periodically modulating the nonlinear coefficients is introduced. It is also shown that the periodically modulated nonlinear coefficient can be experimentally realized by the Feshbach resonance technology. In addition, we discuss the dynamics of the decay of ring dark solitons. It is found that the ring dark soliton can decay into various vortex clusters composed of vortices and antivortices. This opens a new avenue to the investigation of vortex dynamics and quantum turbulence. It is also found that the ring dark solitons combined with periodic modulated nonlinearity can give rise to the pattern formation, which is an interesting nonlinear phenomenon widely explored in all the fields of nature. Finally, some possible research subjects about ring dark solitons in future research are also discussed.
Wang Li, Liu Jing-Si, Li Ji, Zhou Xiao-Lin, Chen Xiang-Rong, Liu Chao-Fei, Liu Wu-Ming
Acta Physica Sinica. 2020, 69 (1): 010303 doi: 10.7498/aps.69.20191648
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Most of the atoms that realize Bose-Einstein condensation have internal spin degree of freedom. In the optical potential trap, the internal spin of the atom is thawed, and the atom can be condensed into each hyperfine quantum state to form the spinor Bose-Einstein condensate. Flexible spin degrees of freedom become dynamic variables related to the system, which can make the system appear novel topological quantum states, such as spin domain wall, vortex, magnetic monopole, skymion, and so on. In this paper, the experimental and theoretical study of spinor Bose-Einstein condensation, the types of topological defects in spinor Bose-Einstein condensate, and the research progress of topological defects in spinor two-component and three-component Bose-Einstein condensate are reviewed.
Duan Liang, Liu Chong, Zhao Li-Chen, Yang Zhan-Ying
Acta Physica Sinica. 2020, 69 (1): 010501 doi: 10.7498/aps.69.20191385
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Nonlinear waves are ubiquitous in various physical systems, and they have become one of the research hotspots in nonlinear physics. For the experimental realization, observation and application of nonlinear waves, it is very important to understand the generation mechanism, and determine the essential excitation conditions of various nonlinear waves. In this paper, we first briefly review the experimental and theoretical research progress of nonlinear waves in recent years. Based on the exact nonlinear wave solutions and linear stability analysis results, we systemically discuss how to establish the quantitative relations between fundamental nonlinear waves and modulation instability. These relations would deepen our understanding on the mechanism of nonlinear waves. To solve the excitation conditions degenerations problem for some nonlinear waves, we further introduce the perturbation energy and relative phase to determine the excitation conditions of nonlinear waves. Finally, we present a set of complete parameters that can determine the excitation conditions of nonlinear waves, and give the excitation conditions and phase diagrams of the fundamental nonlinear waves. These results can be used to realize controllable excitation of nonlinear waves, and could be extended to many other nonlinear systems.
Li Min, Wang Bo-Ting, Xu Tao, Shui Juan-Juan
Acta Physica Sinica. 2020, 69 (1): 010502 doi: 10.7498/aps.69.20191384
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In this paper, we study the generation mechanism of bright and dark solitary waves and rogue wave for the fourth-order dispersive nonlinear Schrödinger (FODNLS) equation, which can not only model the nonlinear propagation and interaction of ultrashort pulses in the high-speed optical fiber transmission system, but also govern the nonlinear spin excitations in the onedimensional isotropic biquadratic Heisenberg ferromagnetic spin with the octupole-dipole interaction. Firstly, via the phase plane analysis, we obtain both the homoclinic and heteroclinic orbits for the two-dimensional plane autonomous system reduced from the FODNLS equation. Further, we derive the bright and dark solitary wave solutions under the corresponding conditions, which reveals the relationship between the homoclinic (heteroclinic) orbit and solitary wave. Secondly, based on the exact first-order breather solution of the FODNLS equation over a nonvanishing background, we give the explicit expressions of group and phase velocities, and reveal that there exists a jump in both the velocities. Finally, in order to verify that the breather becomes a rogue wave at the jumping point, we obtain the first-order rogue wave solution by taking the limit of the breather solution at such point, which confirms the relationship of the generation of rogue wave with the velocity discontinuity.
Lou Sen-Yue
Acta Physica Sinica. 2020, 69 (1): 010503 doi: 10.7498/aps.69.20191172
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Multiple soliton solutions are fundamental excitations. There are many kinds of equivalent representations for multiple soliton solutions such as the Hirota forms, Wronskian and/or double Wronskian expressions and Phaffian representations. Recently, in the studies of multi-place nonlocal systems, we find that there are a type of novel but equivalent simple and elegant forms to describe multiple soliton solutions for various integrable systems. In this paper, we mainly review novel types of expressions of multiple soliton solutions for some kinds of nonlinear integrable systems. Meanwhile, some completely new expressions for the Sawada-Kortera equations, the asymmetric Nizhnik-Novikov-Veselov system, the modified KdV equation, the sine-Gordon equation, the Ablowitz-Kaup-Newell-Segue system and the completely discrete H1 equation are firstly given in this paper. New expressions usually possess explicit full reversal symmetries including parity, time reversal, soliton initial position reversal and charge conjugate reversal. These kinds of explicitly symmetric forms are very useful and convenient in the studies on the nonlinear physical problems such as the multi-place nonlocal systems and the resonant structures.
Pan Chang-Chang, Baronio Fabio, Chen Shi-Hua
Acta Physica Sinica. 2020, 69 (1): 010504 doi: 10.7498/aps.69.20191240
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From a microscopic perspective, the single extreme rogue wave event can be thought of as the spatiotemporally localized rational solutions of the underlying integrable model. A typical example is the fundamental Peregrine rogue wave, who in general entails a three-fold peak amplitude, while making its peak position arbitrary on a finite continuous-wave background. This kind of bizarre wave structure agrees well with the fleeting nature of realistic rogue waves and has been confirmed experimentally, first in nonlinear fibers, then in water wave tanks and plasmas, and recently in an irregular oceanic sea state. In this review, with a brief overview of the current state of the art of the concepts, methods, and research trends related to rogue wave events, we mainly discuss the fundamental Peregrine rogue wave solutions as well as their recent progress, intended for three typical integrable models, namely, the long-wave short-wave resonant equation, the three-wave resonant interaction equation, and the nonlinear Schrödinger and Maxwell-Bloch equation. Basically, while the first two models can describe the resonant interaction among optical waves, the latter governs the interaction between the optical waves and the resonant medium. For each integrable model, we present explicitly its Lax pair, Darboux transformation formulas, and fundamental Peregrine rogue wave solutions, in a self-consistent way. We confirm by convincing examples that these fundamental rogue wave solutions exhibit universality and can be applied to the multi-component or the higher-order versions of the current integrable models. By means of numerical simulations, we demonstrate as well several novel rogue wave dynamics such as coexisting rogue waves, complementary rogue waves, and Peregrine solitons of self-induced transparency.
Xu Dan-Hong, Lou Sen-Yue
Acta Physica Sinica. 2020, 69 (1): 014208 doi: 10.7498/aps.69.20191347
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The study on soliton molecules is one of the important topics in nonlinear science especially in nonlinear optics. The bright soliton molecules have been experimentally observed in optics, however, the dark soliton molecules have not yet been experimentally observed. Theoretically, the soliton molecules have been found for some coupled nonlinear systems. Nevertheless, the soliton molecules have not been obtained for non-coupled single component nonlinear models. In this paper, we first study the exact periodic waves (soliton lattices) and solitary waves for a nonlinear nonintegrable optical model with second and third order dispersions and high order nonlinear effects including self-steeping, Raman scattering and nonlinear dispersion. Two types of dark soliton lattice and three types of soliton lattice are explicitly exhibited for general nonintegrable system. Five types of bright (with and without gray background), dark and gray solitons can be obtained from the limit cases of the modules of the soliton lattices. For an integrable case, using a novel generalized bilinear form of a single component nonlinear system, the multi-soliton solutions are obtained and expressed by a completely new form which are invariant under the full reversal transformations such as the parity, the time reversal, the charge conjugate and the field reversal. To find soliton molecules, a novel mechanism, the velocity resonant, is proposed. Starting from the multi-soliton solutions and using the velocity resonance mechanism, the analytical expression of the dark soliton molecules can be readily obtained. For the model given in this paper, the integrable higher order nonlinear Schrodinger equation, one can proved that the interactions among the dark soliton molecules and the usually solitons are elastic. It is worth pointing out that soliton molecules can also exist in the case of nonintegrable systems.
Chen Zhi-Min, Duan Wen-Shan
Acta Physica Sinica. 2020, 69 (1): 014701 doi: 10.7498/aps.69.20191308
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By the reductive perturbation method, we investigate the Rogue waves in a fluid-filled elastic tube. Based on a nonlinear Schrodinger equation obtained from a fluid-filled elastic tube, the rouge wave solution in the fluid-filled elastic tube is discussed. The characteristics of a single rouge waveare studied for this system. Then, the effects of the system parameters, such as the wave number k, the parameters $\epsilon$, the density of the fluid, the thickness of the elastic tube, the Yang's modulus of the elastic tube, and the radius of the elastic tube on the rouge wave are also investigated. Finally, the model is applied to the blood vessels of both animal and the human to ascertain the effects of the rouge wave in different arteries and vessels. The results of the present study may have potential applications in medical science.
Li Zai-Dong, Guo Qi-Qi
Acta Physica Sinica. 2020, 69 (1): 017501 doi: 10.7498/aps.69.20191352
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In this paper, we introduce some new excited states of magnetization in ferromagnetic nanowires, including Akhmediev breathers, Kuznetsov-Ma soliton and rogue wave in isotropic ferromagnetic nanowires, and rogue wave in anisotropic ferromagnetic nanowires driven by spin-polarized current. The isotropic case demonstrates a spatial periodic process of a magnetic soliton forming the petal with four pieces and a localized process of the spin-wave background. In a limit case, we get rogue waves and clarify its formation mechanism. In the case of anisotropy, it is found that the generation of rogue waves mainly comes from the accumulation of energy and rapid dispersion in the center. In addition, rogue waves are unstable, the spin-polarized current can control the exchange rate of magnons between the envelope soliton and the background. These results can be useful for the exploration of nonlinear excitation in Bosonic and fermionic ferromagnet.
REVIEW
Wang Hui, Xu Meng, Zheng Ren-Kui
Acta Physica Sinica. 2020, 69 (1): 017301 doi: 10.7498/aps.69.20191486
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With the rapid development of microelectronic integration technology, the miniaturization, integration and multifunction of electronic devices are becoming a general trend. Two-dimensional materials are a class of layered material with atomic layer thickness, and have unique electrical, magnetic, optical and mechanical properties. The co-existence of the weak van der Waals force between layers and the strong covalent bonding within layers makes the two-dimensional material very suitable for the miniature design of new-generation multifunctional electronic devices. Two-dimensional materials, represented by graphene and transition metal chalcogenides, exhibit high mobility, adjustable energy band and high visible light transmittance, and thus having become the frontier hotspots in the field of micro-nanoscience in recent years. Synergy between two-dimensional materials and various functional materials such as SiO2 insulator, semiconductor, metal and organic compound may lead to new properties and device applications, thus can deepen and expand the basic research and application of two-dimensional materials. Among them, ferroelectric materials have received much attention because of their spontaneous polarizations, high dielectric constants, and high piezoelectric coefficients. The two-dimensional ferroelectric composites well have the advantages of the two, i.e. they not only contain a variety of rich phenomena such as the magnetoelectric coupling effect, ferroelectric field effect and lattice strain effect, tunneling effect, photoelectric effect, and photoluminescence effect, but also have broad applications in devices such as multi-state memories, tunneling transistors, photoelectric diodes, solar cells, super capacitors, and pyroelectric infrared detectors, which have attracted wide concern from academia and industry. To better understand the combination of two-dimensional thin films with ferroelectric substrates and provide a holistic view, we review the researches of several typical two-dimensional film/ferroelectrics heterostructures in this article. First, two-dimensional materials and ferroelectric materials are introduced. Then, the physical mechanism at the interface is briefly illustrated. After that, several typical two-dimensional film/ferroelectrics heterostructures are mainly introduced. The ferroelectric materials including Pb(Zr1-xTix)O3, (1-x)PbMg1/3Nb2/3O3-xPbTiO3, P(VDF-TrFE), are mainly summarized, and other ferroelectric materials such as P(VDF-TrFE-CFE), BaTiO3, BiFeO3, PbTiO3, CuInP2S6, HfO2 are briefly involved. The future research emphasis of the two-dimensional materials/ferroelectrics composites is also suggested at the end of the article. This review will present a significant reference to the future design of miniature and multifunctional devices.
GENERAL
Wu Han, Wu Jing-Yu, Chen Zhuo
Acta Physica Sinica. 2020, 69 (1): 010201 doi: 10.7498/aps.69.20191225
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In this paper, the Tamm plasmon and its interaction with excitons in a plasmon microcavity consisting of metasurface, dielectric spacer, distributed Bragg reflector (DBR) are studied. The reflection phase of light on the surface can be controlled by changing the structure parameters in the metasurface. When the thickness of the dielectric spacer layer of the microcavity structure keeps unchanged, the resonance position of the Tamm plasmon mode supported by the microcavity structure can be adjusted by varying the structure parameters of the metasurface, and thus providing more degrees of freedom for regulating the Tamm plasmon mode. In addition, by comparing the traditional metal thin film-dielectric spacer-DBR structure, we find that the introduction of metasurface and its regulation of reflection phase can make the metasurface-dielectric spacer-DBR structure support the Tamm plasmon mode resonance at the same wavelength under a smaller thickness of spacer. And combining the local characteristics of the super-surface field, the model volume of Tamm plasmon can be reduced effectively. On this basis, we compare the interaction of traditional and metasurface-based Tamm plasmon with single-layer tungsten disulfide (WS2), and find that metasurface-based Tamm plasmon can produce stronger photon-exciton coupling and obtain larger Rabi splitting.
ATOMIC AND MOLECULAR PHYSICS
Li Ya-Sha, Sun Lin-Xiang, Zhou Xiao, Chen Kai, Wang Hui-Yao
Acta Physica Sinica. 2020, 69 (1): 013101 doi: 10.7498/aps.69.20191455
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In this paper, we use the density functional theory (B3LYP) method with 6-311g(d) basis sets to optimize the molecular structure of C5F10O and obtain the stable structure of its ground state. On this basis, the geometric characteristics, energy, frontier orbital energy levels, and infrared spectra of C5F10O under the different external electric fields (from 0 to 0.03 a.u., 1 a.u. = 5.142×1011 V/m) are studied by the same method. Under the same basis sets, the orbital composition and excitation characteristics of C5F10O are calculated and analyzed by the TD-DFT method. The conclusions show that as the electric field increases, the bond energy of 5C—15F and 4C=16O gradually decrease, their bond lengths increase. The charge of 13F atoms changes fastest, and it is easier to lose electrons under the action of electric field force. The potential energy of the molecule increases, and the stability gradually decreases. The energy gap EG value continuously decreases, and the molecules are more likely to be excited to participate in the chemical reaction. In the infrared spectrum, four absorption peaks are blue-shifted, and four absorption peaks are red-shifted. The excitation characteristics of the first 8 singlet excited states of the C5F10O are identified by the hole-electron analysis method. The excitation energy of the first excited state increases slightly, and the wavelength decreases, and blue shift occurs. The excitation energy values of the other excited states decrease, their wavelengths increase, and red shifts occur. Because the electrons in C5F10O become easier to excite, the stability of the system is lower.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Xie Zhi-Qiang, He Yan-Liang, Wang Pei-Pei, Su Ming-Yang, Chen Xue-Yu, Yang Bo, Liu Jun-Min, Zhou Xin-Xing, Li Ying, Chen Shu-Qing, Fan Dian-Yuan
Acta Physica Sinica. 2020, 69 (1): 014101 doi: 10.7498/aps.69.20191181
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With the rapid development of metasurface and metamaterials, the image edge detection based on the optical spatial differential calculation becomes an interesting topic in recent years. There have been a certain number of studies in this region, but most of them are applicable only to one-dimensional optical spatial differential calculation. In this work, a two-dimensional optical differentiator using Pancharatnam-Berry (P-B) phase metasurface is proposed and implemented in optical image two-dimensional edge detection. Based on the principle of the spin-dependent splitting from P-B phase devices, this metasurface is capable of separating the left-handed circularly polarized light from the right-handed circularly polarized light at a certain spatial distance. After filtering out the overlapped linear polarization, the left optical information is the result of the two-dimensional optical spatial differential. Meanwhile, the resolution of the image edge information is adjustable by changing the optic axis distribution of this two-dimensional optical differentiator. These results indicate that our P-B phase metasurface can be applied to the extraction of the optical image two-dimensional edge information, and the extracted edge information is more complete than the previous one-dimensional grating metasurface. For these advantages, this two-dimensional optical differentiator shows great potential applications in ultrafast optical calculation and image processing.
Yong Kang-Le, Yan Jia-Wei, Tang Shan-Fa, Zhang Rong-Zhu
Acta Physica Sinica. 2020, 69 (1): 014201 doi: 10.7498/aps.69.20191254
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Vortex beam has potential applications in free space optical communication because of its capacity of data transmission. Therefore, it is necessary to study the propagation characteristics of vortex beams in atmospheric turbulence. When the vortex beam propagates in the atmospheric turbulence the beam drift will occur, which has a great influence on the free space optical communication. In this paper, the beam drift of vortex beams with coma and spherical aberration transmitted in atmospheric turbulence is studied by using multi-phase screen and Fourier transform method. The numerical results show that as the transmission distance increases, the effects of both coma and spherical aberration on the beam drift are enhanced. The larger the transmission zenith angle and the coma coefficients, the greater the beam drift of the vortex beam is. However, the beam drift decreases with spherical aberration coefficient increasing. When the zenith angle and the transmission distance are both unchanged, the beam drift of the both vortex beams decrease with topological charges increasing. The influence of coma aberration on beam drift is bigger than that of spherical aberration.
Sun Chen, Feng Yu-Tao, Fu Di, Zhang Ya-Fei, Li Juan, Liu Xue-Bin
Acta Physica Sinica. 2020, 69 (1): 014202 doi: 10.7498/aps.69.20191179
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Passive atmospheric wind detection technique retrieves atmospheric wind profile by measuring the Doppler shift of airglow emissions. Doppler asymmetric spatial heterodyne spectrometer (DASH), which is a Fourier transform spectrometer(FTS), retrieves the Doppler shift information of airglow emissions by detecting the phase shift of interferograms, and the measured phase accuracy directly affects the retrieved wind speed precision. The signal-to-noise (SNR) ratio is one of the significant indexes for evaluating the performance of wind-measuring interferometers in engineering applications. Studying the quantitative relationship between retrieved phase uncertainty and original interferogram SNR that is based on observations is quite essential for the DASH design, performance evaluation and wind profile applications. In this paper, the study is based on the noise propagation theory in FTS and DASH phase retrieval model. According to the Fourier transform relationship between time and frequency domain, we start from original interferogram expression, then we conduct the Fourier transforming, single frequency extracting, inverse Fourier transforming, phase calculating and first-order Taylor expanding, and finally we establish a theoretical relationship model between original interferogram SNR and retrieved phase uncertainty. In order to verify the theoretical relationship model, firstly, we generate 20 groups of interferograms (each group with 1000 frames) randomly with varying the 30-250 times SNR value. After removing the low frequency baseline, we calculate the phase of each interferogram by DASH phase retrieval model, and obtain the phase uncertainty by calculating standard deviation of the 512th sampling of each group interferogram. Another phase retrieval uncertainty is obtained by using the theoretical relationship model between SNR and retrieved phase uncertainty derived from this paper. Secondly, a total of 23 groups of experimental interferograms (each group with 100 frames) with different intensities are collected through the self-developed DASH with a center wavelength of 632.8 nm, basic optical path difference of 50 mm, spectral resolution of 0.78 cm-1. Combining physical characteristics of shot noise and DASH parameters, interferogram SNR of each frame is calculated. We calculate phase uncertainty of experimental data through the two methods mentioned above. The results from the two different calculation methods are compared with each other to determine whether the conclusion is correct. In order to improve the accuracy of phase calculation, three lines are averaged as input to reduce the random error. The average residual between the two methods is only 0.03 mrad, the high consistency of the results indicates that the theoretical relationship model between SNR and retrieved phase uncertainty for DASH is correct. The phase uncertainty can be evaluated by interferogram SNR directly in engineering, which provides a theoretical basis for optimizing the interferometer design.
Meng Ling-Jun, Wang Meng-Yu, Shen Yuan, Yang Yu, Xu Wen-Bin, Zhang Lei, Wang Ke-Yi
Acta Physica Sinica. 2020, 69 (1): 014203 doi: 10.7498/aps.69.20191265
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Optical microcavity has an important and promising application in high sensitivity sensing, but thermal drift hinders its practical use. In this study, we propose a triple-layer-coated microsphere resonator, which has a high sensitivity in refractive index sensing with low thermal drift. The refractive indexes of the three layers from the inside to the outside are high, low, and high, respectively. The two high refractive index layers can support their own whispering-gallery modes, called the inner mode (IM) and the outer mode (OM). We study the performance of IM and OM with waveguide coupling in refractive index sensing and temperature sensing. The results show that when the thickness of the middle layer is 550 nm, the refractive index sensitivity of IM and OM will be 0.0168 nm/RIU, 102.56 nm/RIU, and the temperature sensitivity will be -19.57 pm/K and -28.98 pm/K, respectively. The sensing is carried out by monitoring the difference in resonant wavelength between IM and OM and the sensing characteristics are optimized by adjusting the thickness of the middle layer. Further, when tB = 400 nm, the refractive index sensitivity can arrive at 75.219 nm/RIU, the detection limit can reach 2.2×10-4 RIU, and the thermal drift is reduced to 3.17 pm/K, thereby eliminating the effect of thermal drift to a great degree. This study provides the guidance for designing and improving the microsphere refractive index sensors.
Xia Qing-Gan, Xiao Wen-Bo, Li Jun-Hua, Jin Xin, Ye Guo-Ming, Wu Hua-Ming, Ma Guo-Hong
Acta Physica Sinica. 2020, 69 (1): 014204 doi: 10.7498/aps.69.20191093
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In the process of eliminating the residual pump light and high-order laser light, the cladding power stripper (CPS) generates abundant heat, which can affect the performance of the fiber laser system due to the photothermal conversion. Hence the efficient dissipation of thermal energy becomes a current research focus. In this paper, the five kinds of existing CPSs are simulated and compared with the results in the literature. It is found that the surface-volume ratio between the heat source and the heat transfer medium can be effectively increased by changing the shape of the polymer filling hole when the CPS is made by the high refractive index polymer method, thus reducing the temperature peak and valley value of the CPS. Besides, the heat distribution uniformity of CPS can be improved by combining the high refractive index polymer method with the acid corrosion method to prepare the two-section fiber cladding structure with uneven thickness. According to the above results, a novel CPS structure is proposed and its thermal effect is studied. The results show that when the cladding light power is 150 W, the temperature peak value of the CPS is 298 K, the temperature valley value is 293 K, and the temperature difference is 5 K. Comparing with the above five CPSs, the peak temperature is reduced by up to 11.3%, and the valley temperature is reduced by up to 8.4%, the temperature difference is reduced by up to 87.5%, which proves that the novel CPS structure can effectively suppress the temperature rising and have excellent heat distribution uniformity.
Zhu Yi-Fan, Geng Tao
Acta Physica Sinica. 2020, 69 (1): 014205 doi: 10.7498/aps.69.20191088
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A scheme for forming high-quality circular Airy beams inside the laser resonator is presented theoretically. The desired circular Airy beam can be generated when the common reflective mirror is replaced by a designed diffractive optical element. The mode generated in the proposed cavity can be stimulated by using the so-called eigenvector method. The calculated results show that the parameters of the beams can be controlled by changing the phase distribution of the diffractive optical element. The loss of the generated mode is very low, which is close to that of the fundamental Gaussian mode. The purity of the generated mode is very high, which is much better than that from the phase-only encoding method in Fourier space. The phase distribution of the diffractive optical element needs designing for a fixed resonator length. In practice, the real resonator length may not be equal to the designed resonator length. Thus, the influence of the alignment error of the resonator length is discussed in detail. The results show that the diffraction loss of the proposed system is still very small even when the error reaches up to 2 mm. Meanwhile, the purity of the generated mode decreases little. Then, the influence of etching depth errors and the decenter of the reflective mirrors are discussed in detail. Here we assume that the fluctuations are randomly distributed. The value of the maximum fluctuation is used to represent the etching depth error degree. The results show that the diffraction loss of the proposed system is more sensitive to production error, and the purity of the generated mode is more sensitive to alignment error. Thus, we estimate that the maximum etching depth error should be less than six percent of the wavelength, and the vertical distance between the centers of the two reflective mirrors should be less than 7 μm if one wants to obtain high-quality CAB with high efficiency. The requirements for precision are acceptable for existing microfabrication and operation technologies.
Meng Teng-Fei, Tian Jian-Feng, Zhou Yao-Yao
Acta Physica Sinica. 2020, 69 (1): 014206 doi: 10.7498/aps.69.20191099
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Selective reflection (SR) from the interface between transparent medium and dilute vapour is caused by the atomic vapor near the interface. The sub-Doppler structure in SR is due to the deexcitation caused by the collision between atomic vapor and the wall. Beacuse the interaction region between atomic vapor and incident light is on the order of a few hundred nanometers, SR has low optical loss and high spatial resolution. The experimental device of SR is simple. Because of the above characteristics, the SR has been widely studied and applied. The nonlinear SR spectrum of quasi lambda-type four-level system at gas-solid interface is studied theoretically in this paper. By sloving the density matrix equations, the approximate analytic solution of the matrix element associated with the probe field is obtained at normal incidence when the intensity of the probe field is very weak. The effect of the Rabi frequency, the detuning of the signal field and the detuning of the coupling field on the lineshape are analyzed by numerical simulation, respectively. Three peaks and two transparent windows appear in SR spectrum when the detuning of coupling field and signal field are both zero. The middle peak is generated due to the participation of signal field, and the other two peaks are caused by the other two fields. The linewidth and the amplitude of the middle peak can be changed by varying the Rabi frequency of signal field, and the other two peaks have little effect on the Rabi frequency of signal field. The signal generated due to the participation of signal field can be transformed from peak to transparent window when the detuning value of the signal field is equal to the Rabi frequency of coupling field. When the detuning value of the signal field is not equal to the Rabi frequency of coupling field, a dispersion-like signal between reflection peak and transparent window is generated due to the participation of signal field. The position of peak and transparent window can be manipulated by controlling the detuning value of the coupling field. When the detuning value of coupling field decreases from zero, three peaks all shift to red detuning direction. When the detuning value of coupling field is blue-detuned and increases, three peaks all shift to blue detuning direction. The numerical results can be explained by using the various electric transition pathways and dressed state theory. This study is helpful in investigating quantum coherence and dynamic process of atoms at gas-solid interface.
Zuo Guan-Hua, Yang Chen, Zhao Jun-Xiang, Tian Zhuang-Zhuang, Zhu Shi-Yao, Zhang Yu-Chi, Zhang Tian-Cai
Acta Physica Sinica. 2020, 69 (1): 014207 doi: 10.7498/aps.69.20191009
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Quantum light field is very important source in quantum optics and quantum precision measurement, and the generation of quantum state of light is significant in quantum storage, quantum metrology and studying the interaction between nonclassical light and matter. The polarization squeezed light near the atomic transition has great potential applications in the precise measurement of magnetic field as its Stokes parameter’s noise is less than the standard quantum limit (SQL). Therefore, it is very important to generate the polarization squeezed light at atomic transition. We report in this paper the experiment on generating the bright polarization squeezed light at cesium D2 line based on an optical parametric amplifier (OPA). The experimental system includes the following three parts: 1) a second harmonic generator (SHG), 2) an OPA, and 3) a detection system. The OPA has a similar structure to the SHG system with four-mirror ring cavity in which only the fundamental wave is resonant. A nonlinear type-I periodically-poled KTiOPO4 (PPKTP) crystal with a size of 1 mm×2 mm×20 mm is placed in the center of the cavity waist and its temperature is precisely controlled. The OPA is pumped by the 426 nm blue light which is generated by SHG and this OPA is operating below the threshold. The squeezed light at cesium D2 line is produced when the crystal temperature is at its optimum phase-matching temperature and the OPA cavity is stabilized based on resonance. The generated squeezed light is combined with the coherent light on a polarizing beam splitter (PBS) to obtain the polarized squeezed light for either Ŝ2 or Ŝ3 of the Stokes parameter by controlling the type of squeezed light (parametric amplification or de-amplification) and the relative phase (0 or π/2) of two beams. And for Ŝ1, the amplitude-squeezed light (corresponding to parametric de-amplification) is the Ŝ1 squeezed light. The maximum squeezing of 4.3 dB (actually 5.2 dB) is observed in a bandwidth range of 2-10 MHz. At present, the squeezing is mainly limited by the escape efficiency of OPA and the detection efficiency, and the OPA escape efficiency is mainly limited by the blue-light-induced loss of PPKTP crystal and the thermal effect of crystal. In the optical atomic magnetometer, increasing the signal-to-noise ratio (SNR) of the system can effectively improve the sensitivity of the magnetic field measurement. This bright polarization squeezed light is expected to be used in the optical cesium atomic magnetometer to improve the sensitivity of the magnetometer.
Xu Qi-Wei, Wang Pei-Pei, Zeng Zhen-Jia, Huang Ze-Bin, Zhou Xin-Xing, Liu Jun-Min, Li Ying, Chen Shu-Qing, Fan Dian-Yuan
Acta Physica Sinica. 2020, 69 (1): 014209 doi: 10.7498/aps.69.20190982
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When a light beam transmits in free space, it is easily affected by atmospheric turbulence. The effect on transmitted light is equivalent to adding a random noise phase to it, which leads its transmission quality to deteriorate. The method of improving the quality of transmitted beams is usually to compensate for the phase distortion at the receiver by adding reverse turbulence phase, and the premise of this method is to obtain the turbulence phase carried by the distorted beam. The adaptive optics system is the most common way to extract the phase information. However, it is inefficient to be applied to varying turbulence environments due to the fact that a wave-front sensor and complex optical system are usually contained. Deep convolutional neural network (CNN) that can directly capture feature information from images is widely used in computer vision, language processing, optical information processing, etc. Therefore, in this paper proposed is a turbulence phase information extraction scheme based on the CNN, which can quickly and accurately extract the turbulence phase from the intensity patterns affected by atmosphere turbulence. The CNN model in this paper consists of 17 layers, including convolutional layers, pooling layers and deconvolutional layers. The convolutional layers and pooling layers are used to extract the turbulent phase from the feature image, which is the core structure of the network. The function of the deconvolutional layers is to visualize the extracted turbulence information and output the final predicted turbulence phase. After learning a huge number of samples, the loss function value of CNN converges to about 0.02, and the average loss function value on the test set is lower than 0.03. The trained CNN model has a good generalization capability and can directly extract the turbulent phase according to the input light intensity pattern. Using an I5-8500 CPU, the average time to predict the turbulent phase is as low as s under the condition of Cn2=1×10-14 m-2/3, Cn2=5×10-14 m-2/3, and Cn2=1×10-13 m-2/3. In addition, the turbulence phase extraction capability of CNN can be further enhanced by improving computing power or optimizing model structure. These results indicate that the CNN-based turbulence phase extraction method can effectively extract the turbulence phase, which has important application value in turbulence compensation, atmospheric turbulence characteristics research and image reconstruction.
Sun Gui-Hua, Zhang Qing-Li, Luo Jian-Qiao, Sun Dun-Lu, Gu Chang-Jiang, Zheng Li-Li, Han Song, Li Wei-Min
Acta Physica Sinica. 2020, 69 (1): 014210 doi: 10.7498/aps.69.20191150
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The melting point of Ti:MgAl2O4 crystal is as high as 2130 ℃, it is a challenge to obtain a large-sized and high-quality laser crystal. By optimizing the crystal growth process, Ti:MgAl2O4 crystal with a size of 30 mm×70 mm is successfully grown by the Czochralski method under the condition of weak reducing atmosphere. The X-ray diffraction pattern is studied, and the x-ray rocking curve indicates that the grown crystal has a high crystalline quality in terms of the lower full width at half maximum(FWHM) intensity, which provides a material basis for the next laser output experiment. In a range of 100-1000 cm-1, there are four Raman vibration peaks located at 312, 410, 675 cm-1 and 771 cm-1 respectively. The grown crystal has an absorption cutoff range of 250-318 nm and two wide absorption bands of 395-495 nm and 550-1100 nm. Excited by 271 nm, the grown crystal shows a strong broadband emission ina range of 340-650 nm with a peak centered at 480 nm. After annealing in hydrogen atmosphere, shape of the transmittance spectrum and emission spectrum are both unchanged, but the fluorescent emission intensity is significantly reduced. After annealing in air atmosphere, the original two absorption bands disappear while none of the characteristics of fluorescence emission in a 340-650 nm range changes significantly. In addition, a new fluorescence emission peak near 725 nm is observed. Combining with the ESR spectrum, what we canconfirm is that the Ti:MgAl2O4 as-grown crystal contains Ti3+ and Ti4+ ions, and no ESR signal of Ti3+ is observed after annealing in air atmosphere. Moreover, excitationspectrum is also recorded. The fluorescence lifetime is 14 μs at room temperature, which is 4-5 times that of Ti:Al2O3 crystal and Ti:BeAl2O4 crystal. Furthermore, the emission cross section of the grown Ti:MgAl2O4 crystal is calculated from the Füchtbauer-Ladenburg (F-L) formula and its value is 2×10–20 cm2, large emission cross section which is beneficial for realizing laser oscillation. All the above results show that the Ti:MgAl2O4 crystal is a potential crystal material for realizing broadband tunable blue laser output.
Wang Mei-Ou, Xiao Qian, Jin Xia, Cao Yan-Yan, Xu Ya-Dong
Acta Physica Sinica. 2020, 69 (1): 014211 doi: 10.7498/aps.69.20191144
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How to effectively control the refraction, reflection, propagation and wavefront of dynamic waves or light has become one of hot research points in the field of optics. In the past few years, the concept of phase gradient metasurface has been proposed: it introduces a gradient of the phase discontinuity covering the entire angle 2π along the interface to provide an effective wave vector $\kappa$ and completely control the direction of outing wave. Therefore, the metasurface can possess many novel optical applications, such as holograms, metalenses, photonic spin Hall effect, etc. In this work, we design a simplified reflection-type optical metagrating. The results demonstrate that the metagrating can achive the function of two-channel retroreflection, that is, redirecting the incident wave back toward the source, with a nearly perfect conversion efficiency.
The metagrating designed in this paper contains only two sub-cells with π reflection phase difference in period. The working wavelength (λ) of metagrating is fixed at 3 μm. The two sub-cells are filled with an impedance matching material (their material relative refractive indexes are n1 = 1 and n2 = 1.5 respectively and their thickness is d = 1.5 μm.).The period length range is 1.5 μm ≤ p ≤ 3 μm(considering reducing the reflection order). When the incident angle is θi= ±arcsin[λ/(2p)], the absolute values of the incident angle and the reflected angle are equal, and then retroreflection occurs. When the wavelength is greater than the period (λp), the angle of retroreflection can be adjusted to any value (|θi| ≥ 30°) by adjusting the period p. In this work, COMSOL MULTIPHYSICS software is used to simulate the retroreflection reflectivity and field pattern of the designed metagrating. The results verify the two-channel retroreflection property of the metagrating. In addition,as the angle of incidence changes from 30° to 60°, the efficiency of retroreflection at any incident angle can reach to more than 95%. When the incident angle is 75.4°, the metagrating still has an efficiency of 80% retroreflection. Therefore, the metagrating also achieves the function of high-efficiency retroreflection at a large-angle. Comparing with multiple sub-cells’ metasurface, the simplified metagrating with two sub-cells enables a similar function of retroreflection, but has many potential advantages, and can play an important role in high-efficiency sensing, imaging and communication.
Lin Ze-Peng, XU Sheng-Zhuo, Bao Yun
Acta Physica Sinica. 2020, 69 (1): 014401 doi: 10.7498/aps.69.20191193
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How to improve the heat transfer efficiency of the system is always a hot issue in thermal convection research field. It is found that when the partitions are added at equal distances to the classical physical model——Rayleigh-Bénard convection system and gaps are left between the horizontal plates and partitions, the heat transfer efficiency of the system increases significantly with the number of partitions increasing. The heat transfer efficiency can reach up to 3.1 times that of the non-partition device with the specific geometric parameters. In this paper, the Direct Numerical Simulation (DNS) method is used to simulate the partitioned convection system. The mechanism of the heat transfer enhancement of the system is analyzed by studying the characteristics of the heat flow as well as the heat conduction and transport in the system. After the flow in partitioned convection system is fully developed, the fluid in each channel moves vertically in alternating direction and the upward(downward) channel has a higher(lower) temperature than the average temperature of the cell. Due to the symmetry of the system, only the bottom region of the low temperature channel, the bottom region of the high temperature channel and the gap region connecting these two channels are selected for research. By discussing the lateral and longitudinal transport processes of heat flow in the above three regions, the heat flux in the channels and gap areas of the system are studied by quantitative analysis. The results show that the low-temperature fluid in the channel impacts on the bottom plate and then moves into the gap area; the fluid is continuously heated by the bottom plate and flows out of gap area with high temperature. Finally, the fluid converges in the heat transfer channel and forms a longitudinal jet. The external input heat flux of the area that has only horizontal heat transport is large, accounting for 92% of the total heat flux which is obtained from the bottom plate. The heat flux of gap area accounts for 64% of the total heat flux, but the external input heat flux of the area that has only longitudinal heat transport is smaller. The convection system with different geometric parameters has the effect of enhancing heat transfer efficiency, and enhancement capability of the system is stronger when the height of gaps is smaller. When the number of partitions n = 11 and the height of gap d = 0.01, the value of the global Nu number is largest, Nu = 82, which is more than three times that of the system without partitions.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Zhang Na, Liu Bo, Lin Li-Wei
Acta Physica Sinica. 2020, 69 (1): 016101 doi: 10.7498/aps.69.20191344
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Graphene is a planar two-dimensional material composed of sp2-bonded carbon atoms with extraordinary electrical, optical and mechanical properties, and considered as one of the revolutionary electronic component materials in the future. Some studies have shown that the inert gas ion irradiation as a defect introducing technique can change the structure and properties of graphene without introducing additional effects. In this paper, the 5.4 keV He ion irradiation at the dose ranging from 0.7×1013 cm-2 to 2.5×1013 cm-2 has a strong effect on graphene deposited by CVD technology. The X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman) and semi-conductor parameter analysis instrument are used to study the changes in the microstructure and electrical properties of graphene before and after irradiation. Detailed analysis shows that the defect density increases gradually with the irradiation dose increasing. Raman spectrum shows that when the irradiation dose increases to 1.6×1013 cm-2, the value of ID/IG begins to decrease, and XPS shows that the irradiation changes the structure of C chemical bond in graphene which causes the bonding state of C—C sp2 to be destroyed and partly converted into the C—C sp3 bonding state. Therefore, the structure of graphene begins to transform from nano-crystalline structure into sp3 amorphous structure. Simultaneously, increasing defects causes the graphene conductivity to continuously decrease, and also gives rise to the electrical transition from defect scattering mechanism based on Boltzmann transport to the hopping transport. The positive voltage direction offset of Vdirac increases nearly in direct proportion, which is due to the enhancement of graphene’s p-type doping effect caused by defects and adsorbed impurities. This work conduces to the understanding the mechanism of He ion interaction with graphene, and also provides an effective way of controlling the electronic properties.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Ye Kang-Ping, Pei Wen-Jin, Xi Xiang, Pu Yin, Wu Rui-Xin
Acta Physica Sinica. 2020, 69 (1): 017801 doi: 10.7498/aps.69.20191229
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Under the action of static bias magnetic field, the magnetized ferrite has a permeability tensor which can be adjusted by the applied magnetic field. In this paper, the absorption properties of bulk gyromagnetic ferrites under different magnetized conditions are studied and the great potential of gyromagnetic ferrite in achieving low frequency electromagnetic wave absorption is demonstrated. Full wave electromagnetic simulations are performed based on the finite element method (FEM). A floquet port is adopted at the top boundary of the unit cell to simulate a normally incident plane wave. The unit cell boundary conditions are used in the x-y plane to simulate a periodic structure. Orthogonality magnetization in plane is utilized to solve the polarization selectivity in the condition of transverse magnetic field. The influence on absorption capacity of discrete ferrite array structure and the coupling effect of ferrite elements with different sizes are also studied in consideration of the size effect. The simulation results show that a thin bulk gyromagnetic ferrite layer whose thickness is only 4 mm can possess frequency as low as 0.48 GHz and reflectivity below -10 dB. Gyromagnetic ferrite presents different absorption properties under longitudinal magnetization and transversal magnetization, and different polarization directions in transversal magnetization as well. When longitudinal bias magnetic field H0 = 200 Oe, the bandwidth of the reflectivity below -10 dB ranges from 0.48 to 1.84 GHz. The resonant absorption frequency can be regulated by adjusting bias magnetic field and the size of ferrite element. In general, a large bias magnetic field leads to a high resonant frequency due to the ferromagnetic resonance frequency positively associated with the applied magnetic field, but a ferrite array consisting of larger size elements provides a lower resonant frequency for the size resonance negatively associated with the size. By introducing the coupling between elements with different sizes, the reflection bandwidth below -10 dB can be effectively extended to above 80% of the sum of the bandwidth possessed by single unit cell, especially 105.7% under transversal bias magnetic field 700 Oe. And the broadening effect is effective in both longitudinal and transverse magnetized state but it will be weaker when the two absorption peaks are closer. To further understand the absorption mechanism of the two-element absorber, the distribution of the electric field, magnetic field and power loss density are examined. The results prove that the two peaks at the lower frequency exactly originates from △R = 0 and the higher frequency originates from △R = 4, and therefore the widened absorption is contributed by the coupled multiple resonances provided by the elements with different sizes.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Wu Jia-Long, Dou Yong-Jiang, Zhang Jian-Feng, Wang Hao-Ran, Yang Xu-Yong
Acta Physica Sinica. 2020, 69 (1): 018101 doi: 10.7498/aps.69.20191269
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Formamidinium lead bromide (FAPbBr3) perovskite nanocrystals (NCs) have attracted great attention due to their remarkable performances of low cost, high color purity and tunable band gap. However, in a typical FAPbBr3 perovskite light-emitting diode(LED), PEDOT:PSS, with hygroscopic and acidic nature, serves as a hole injection layer (HIL), thus leading to the device stability to decrease seriously. Device stability is one critical issue that needs improving for future applications. Here in this study, the nickel oxide (NiO) film prepared by the solution method is adopted as the HIL of the FAPbBr3 perovskite LED to substitute detrimental PEDOT:PSS. Compared with the control device with PEDOT:PSS HIL, the resulting LED based on NiO film has the operating lifetime twice as great as that based on the PEDOT:PSS film. For further enhancing the performance of FAPbBr3 LED, two metal dopants (Cs and Li) are introduced to improve the hole injection capability of NiO film and the charge carriers’ balance of device. With Hall measurements, both NiO and Cs/Li-doped NiO demonstrate a full p-type semiconductor characteristic. Increasing the doping concentration in the film can increase the carrier concentration and reduce the carrier mobility. This decreased carrier mobility results from the increased scattering due to grain boundaries and impurity phases, seriously at high Cs/Li concentration. As a result, the device, based on the NiO film (doping 2 mol% Cs) shows the best performance with a maximum brightness value of 2970 cd/m2, current efficiency of 43 cd/A and external quantum efficiency (EQE) of 11.0%, thus its efficiency is increased nearly by twice compared with that of the PEDOT:PSS-based device. The results pave the way for making highly efficient and stability perovskite LEDs based on FAPbBr3 NCs.
Luo Yin-Hong, Zhang Feng-Qi, Guo Hong-Xia, Wojtek Hajdas
Acta Physica Sinica. 2020, 69 (1): 018501 doi: 10.7498/aps.69.20190878
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In order to evaluate the radiation tolerance to proton single event effect(SEE) in nanometer dual interlocked cell (DICE) hardening device accurately, single event upset (SEU) linear energy transfer (LET) threshold at heavy ion normal and tilt incidence, and the worst case SEU orientational angle are acquired based on the analysis of heavy ion SEU testing data in 65 nm dual DICE static random access memory (SRAM). It is proved that dual DICE design is effective for improving the LET threshold against SEU. Howerer, heavy ion tilt incidence at the worst orientational angle will significantly reduce the SEU threshold and increase the SEU cross section. The worst orientational angle for SEU in DICE SRAM is the large tilting angle along the well. The maximum LET value and the emission angle distribution of secondary particle induced by the nuclear reaction between protons with different energy and layers with different multiple metallization are obtained by using Monte-Carlo simulation. The maximum LET value of secondary particle from proton-copper spallation reaction is higher than 15 MeV·cm2/mg for 100 MeV and 200 MeV protons. Secondary particles with the maximum energy and longest range are emitted preferentially in the forward direction. Proton SEU sensitivity is further predicted through combining heavy ion test data with Monte-Carlo simulation. Proton SEU test data verify the effectiveness of the prediction method and the accuracy of the prediction results. The research results indicate that the tolerance of nanometer DICE hardening technique against proton SEU will be overestimated if SEE evaluation test is carried out with only 100 MeV proton accelerator or normal incidence. Proton single event upset in nanometer dual DICE SRAM has an evident dependence on tilt angle and orientational angle. By adopting the above prediction method, whether proton SEE test needs performing or not in nanometer radiation-hardening device can be judged and screened. The requirements for the maximum energy of proton accelerator can be ascertained. In order to ensure that the devices are applied to space with high reliability, SEE test should be carried out including tilt incidence at the worst orientational angle in nanometer DICE hardening device in the process of heavy ion and proton SEE test evaluation.
Dong Lei, Yang Jian-Qun, Zhen Zhao-Feng, Li Xing-Ji
Acta Physica Sinica. 2020, 69 (1): 018502 doi: 10.7498/aps.69.20191151
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During the service of the spacecraft, it will be disturbed by the energetic particles and rays, and thus induce total ionizing dose (TID), displacement damage (DD) or single event effect (SEE) to generate inside the electronic system, which can seriously affect the service lifetime of the electronic components. The difference in structure and types of electronic components are less sensitive to the radiation effects, but bipolar transistor is strongly sensitive to ionizing radiation effect. As a basic component of bipolar circuits, the in-depth study of bipolar transistor ionization radiation effect is of significance for engineering.
It has been shown that the an amount of hydrogen can inevitably introduced from an external source during the sealing process of the devices. The KOVAR alloy is widely used as a metal cap material of bipolar transistor in the process of encapsulation. The residual gas analysis (RGA) for sealed Kovar lid packages is shown to have 1%-2% of the hydrogen in the cavity. The source of the hydrogen is generally considered to be out-gassing from the gold plating on the KOVAR. So far, the researches have focused on the study of the ionization damage effect of bipolar transistors with different structures under 60Co gamma ray irradiation. There is lack of systemic study on the comparison of transistors packaged with and without cap.
In this paper, we study the influence of sealed KOVAR lid packaged on ionizing radiation damage of lateral PNP bipolar transistor (LPNP) by using 60Co gamma ray as an irradiation source. The semiconductor parameter analyzer is used to measure the electrical parameters of LPNP transistor during irradiation. The irradiation defects in LPNP transistors packaged with and without cap are characterized by deep level transient spectroscopy (DLTS). Experimental results show that the LPNP transistors packaged with and without cap have similar electrical characteristics. The base current increases with the total dose increasing, while the collector current remains almost constant. The degradation of LPNP transistor packaged with cap is more serious.
According to the excess base current varying with base-emitter voltage for the LPNP transistors packaged with and without cap, the degradation of bipolar transistor packaged with cap is more serious under the same irradiation conditions. According to the analysis of DLTS, comparing with bipolar transistor packaged without cap, the signal peak at about 300 K is shifted to the left for the bipolar transistor packaged with cap. These results indicate that the LPNP transistors packaged with cap can generate more interface states during irradiation, which is attributed to a large amount of hydrogen and water vapor out-gassing from the gold plating on the KOVAR, which is released under the thermal stress. In the sealed environment, hydrogen can only diffuse into the device cavity, and is combined with the metal material in the transistor to form metal hydride. Therefore the degradation of transistor is severe under the same irradiation condition.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Li Ang, Yu Jin-Qing, Chen Yu-Qing, Yan Xue-Qing
Acta Physica Sinica. 2020, 69 (1): 019501 doi: 10.7498/aps.69.20190729
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The creation of positron and electron pairs through photon-photon collision, named Breit-Wheeler process, has been well understood in the theories of quantum electrodynamics for nearly 100 years. The photon-photon collision, which is one of the most basic processes of matter generation in the universe, has not been observed yet. The study on photon-photon collision can promote the development of two-photon physics, quantum electrodynamics theories and high energy physics. To observe photon-photon collision in the laboratory, one needs to collimate a huge number of energetic γ-ray photons into a very small spot. Recently, the development of highly collomated source generated by 10 PW laser makes photon-photon collider much more possible than before. In photon-photon collider, the study of numerical simulation plays a critical role since no experiment has achieved such a process. In this paper, a new numerical method is developed to handle the two-photon Breit-Wheeler process. This method is based on the exact two-photon collision dynamic principle, including energy threshold condition, cross-section condition, Lorentz transformation, etc. In the method, the photons are divided into quantitative photon blocks based on the spatial coordinates. Firstly, one needs to find the collision blocks according to the spatial motion law. Secondly, the ergodic method is used to look up the photons that satisfy the energy threshold condition and the cross-section condition from the blocks. Then, one can calculate the electron yield of the photon collision, and the kinetic parameters of the positrons and electrons. This method rigorously follows the physical principle so it has high precision. On the other hand, this method determines the collision of the block in advance, which can reduce the computational requirement a lot. A series of tests is carried out to confirm the accuracy and feasibility of this numerical method by calculating the collision between mono-energetic photon beams. In the tests, the collision angle is assumed to 180° and 60° separately, the results of pair momentum distribution are discussed. We also simulate the collision of the γ-ray beams generated through the interaction between ultra-intense laser and narrow tube targets. In the simulations, the collision angle is changed from 170° to 30° to see its effect on pair production. It is found that the yield of electron-positron pairs decreases with collision angle increasing, which has also been reported in previous work. Therefore, this numerical method can be efficiently used for modeling photon-photon collider, and provide theoretical reference and suggestion to the future experimental design of γ-ray collision.
Meng Wen-Dong, Zhang Hai-Feng, Deng Hua-Rong, Tang Kai, Wu Zhi-Bo, Wang Yu-Rong, Wu Guang, Zhang Zhong-Ping, Chen Xin-Yang
Acta Physica Sinica. 2020, 69 (1): 019502 doi: 10.7498/aps.69.20191299
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Classical satellite laser ranging (SLR) technology based on 532 nm wavelength usually adopts low energy laser to measure cooperative objects. However, for a very weak target, such as debris and lunar reflector arrays, laser ranging system should have much stronger detection capability than the laser ranging system for traditional application. A common way to improve system detection capability is to use high energy laser. With an additional frequency doubling crystal, it is more difficult to make a high energy laser based on 532 nm than that based on 1.06 μm, which restricts the improvement of system detection capability, and also gives rise to the short lifetime, poor system stability problems. Compared with 532 nm laser, the 1.06 μm laser has many advantages of high laser energy and power, high atmospheric transmissivity, and low background noise, thereby making it an ideal substitution for the traditional 532 nm SLR system. In this paper, we comparatively analyze the above-mentiond advantages of the 1.06 μm laser and other system’s key parameters such as detector efficiency and target reflection efficiency, calculate the echo photons one can obtain, and establish a 1.06 μm laser ranging system based on the existing 532 nm SLR at Shanghai Astronomical Observatory. Owing to the using of an InGaAs single photon detector, the system turns very compact, low cost, easy-to-be-installed and has almost no additional operation complexity than the 532 nm system. With this system, the high precision 1.06 μm laser ranging for cooperative objects based on InGaAs detector is carried out for the first time in China, and a ranging for space debris 1500 km away can also be realized. The ranging experiment shows with the same laser, SLR using 1.06 μm output reaches a detection efficiency of 7 times the detection efficiency the SLR using 532 nm output reaches, and the background noise only 1/5. This approves the advantages and feasibility of 1.06 μm system, and also shows its great potential application prospects in the high precision weak target laser detection in the day and night time. This paper provides a very easy operation, high compact and low cost method for the future high precision weak target laser ranging.
Acta Physica Sinica
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Development of a intranuclear-cascade code CBIM applicable to the nuclear reaction with incident particle energy above 45MeV

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Accept: 2016-10-11
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The Monte Carlo intra-nuclear cascade program CBIM has been developed for describing nuclear reactions involving protons, neutrons and pions on complex nuclei. In order to describe cascade process, several simplifications have been made in the following: firstly, neither reaction, reflection, refraction, nor ionization will be taken into account before the incident particle enters the target nucleus; secondly, target nucleus is regarded as spherical and the atom number should be greater than 2; thirdly, the knocked nucleon is determined by cross section sampling; last, in the center-of-mass frame, the scattering angle is sampled based on differential cross section distribution.. The basis physics model bases on the above assumptions and Bertini intra-nuclear cascade model; meanwhile, nucleon-nucleon angle differential distributions of INCL in the center-of-mass frame have been introduced to overcome the shortage of Bertini model. The interactions between nucleon and nucleon or between nucleon and pion, for example, elastic scattering, pion production and charge exchange, are simulated in the code. In the particles collision, the nucleon density changes with the target nucleus radius; and the interaction cross sections refer to 22 kinds of experimental cross sections in Bertini model. The intra-nuclear cascades induced by 45MeV~3500MeV neutron, proton or pion below 2500MeV can be simulated by this code. Finally, comparisons with experiment on reaction cross section over the energy range 60~378MeV, and some simulation results by MCNPX, GEANT4 and PHITS over the energy range 65~3000MeV, the CBIM results are in reasonable agreement with them over the broad energy range considered.
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Nonlocal Symmetries and Interaction Solutions of the (2+1)-dimensional Higher Order Broer-Kaup System

xiangpeng xin Hanze Liu Xi-qiang LIU
Accept: 2016-10-11
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The (2+1)-dimensional higher-order Broer-Kaup (HBK) system is studied by nonlocal symmetry method and consistent tanh expansion (CTE) method. In this paper, via the localization of the residual symmetries, the nonlocal symmetries are localized to Lie point symmetries and symmetry groups are also obtained. Many types of soliton solutions and interaction solutions among different nonlinear excitations such as solitons, periodic waves etc. are constructed. In order to study their dynamic behaviors, corresponding images are explicitly given.
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Ferroelectric phase transition of perovskite SnTiO3 based on first principles

null
Accept: 2016-10-11
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Due to their spontaneous polarization, ferroelectric materials have excellent dielectric, piezoelectric, pyroelectric and other properties, which enable them to be used in many applications, such as capacitors, filters, sensors, detectors, and transducers, among others. In this paper, we employ a first-principles-based effective Hamiltonian method to investigate perovskite SnTiO$_3$, obtaining essential coefficients for the effective Hamiltonian via ab initio computations, which are used in subsequent Monte-Carlo simulations to predict the phase transition temperature of SnTiO$_3$, and different structural phases involved in such phase transition.
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The effect of linear bubble vibration on wave propagation in unsaturated porous media containing air bubbles

null
Accept: 2016-10-11
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Biot model is widely applied in geophysics, petroleum engineering, civil engineering and ocean engineering since it has been presented. This leads to a considerable development of the research on the wave propagation in saturated porous medium. However, fully saturated porous medium is rarely found in nature, almost all the rocks or soils contain two kinds of fluid, such as gas and petroleum. So many researches has been done on the wave propagation in unsaturated porous medium by domestic and abroad scholars. It is well known that the presence of a small volume of gas bubbles in a liquid can greatly alter the velocity and attenuation of acoustic waves in the liquid. Evidence is beginning to accumulate that the velocity and attenuation of acoustic waves in a saturated marine sediment can be affected by the presence of gas bubbles in the saturating liquid. To investigate the sound propagation in porous media when the pore water contains a small amount of air bubbles, this paper integrates the volume vibration of bubbles in pore water into the continuity equation of pore-fluid filtration in porous media based on Biot theory, so as to obtain the continuity equation of pore-fluid filtration with bubble volume vibration. On this basis, according to the relationship between the instantaneous radius of bubbles and the background pressure of the medium under the linear vibration of bubbles, as well as the equations of motion of the fluid medium and porous medium, a new displacement vector wave equation of porous media under the influence of bubbles is derived, which establishes the model for the sound velocity dispersion and attenuation prediction under the unsaturated porous media. The presence of air bubbles increases the compressibility of pore fluid, which leads to the decrease in the sound velocity of the bubbly saturated porous media. When the wave frequency equals to the resonance frequency of the bubbles, the bubbles in pore water will produce resonance; the medium will present to be highly dispersive and the velocity can greatly exceed the gas-free velocity, but these have not been measured in field data; and the absorption cross section of the air bubble can reach the maximum, which leads to the maximum attenuation of the porous media. It should be noted that the attenuation coefficient calculated with this model is related to the damping of bubble motion(radiation, thermal and internal friction) and the dissipation of the relative motion between the pore water and porous solid frame. The obtained numerical analysis is consistent with the above conclusions, which indicates that the volume concentration, the bubble size and the excitation frequency of sound field are important parameters affecting the sound wave propagation in the saturated porous media containing few bubbles.
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A fast particle simulation method for calculating the multipactor threshold based on the frequency domain solutions in microwave devices

null
Accept: 2016-10-11
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In order to compute the multipactor thresholds of microwave devices with high ef?ciency and precision, a novel fast particle-in-cell (PIC) method is proposed, which takes advantages of the frequency-domain (FD) electromagnetic field solver of CST Microwave Studio (MWS). At the initial stage of multipactor (when there are not many electrons in the devices), the self-consistent field generated by the electrons is much smaller than the applied electromagnetic field. Therefore it can be ignored in calculating the multipactor threshold and this will significantly reduce the computation burden. During simulations of multipactor processes, the FD fields pre-calculated by CST MWS are converted into time-domain (TD) scaling with the square root of the input power. Then the electrons are advanced by Boris algorithm. When the electrons hit the boundaries of the simulation region, where triangular facets from CST are used for discretization, the secondary electrons would be emitted. After series of simulations with variable input powers, the multipactor threshold is determined according to time evolutions of the electron number. As verifications, the multipactor thresholds in a parallel plate and a coaxial transmission line are investigated. Compared with the results of CST Particle Studio (PS), the fast method obtains almost the same thresholds, while the computational efficiency is improved more than 1 order of magnitude. Since the self-consistent field generated by the electrons is ignored in the fast method and it is considered in CST PS, the results validate that the self-consistent field can be ignored in calculating the multipactor threshold. Finally, taking a parallel plate transmission line and a stepped impedance transformer as examples, we studied the effects of the number of initial macro-particles on the calculation precision. When the initial particles are so few that it can hardly reflect the randomness of the multipactor process, it results in a higher calculated value. With the increase of the number of initial macro-particles, the calculated multipactor threshold is lower and more accurate. It is convergent when the number reaches about 2000 for the parallel plate transmission line and 4000 for the stepped impedance transformer, respectively. Taking into account other microwave devices with more complex electromagnetic field distribution, in order to ensure precision, it is recommended to select the number of initial macro-particles 8000. In addition, although CST MWS was used to obtain the electromagnetic fields and boundary information in this paper, of course, other electromagnetic software (such as HFSS) can also be adopted as an alternation.
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Penta-decomposition of instantaneous field in spanwise-rotating turbulent plane Couette flow

null
Accept: 2016-10-11
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Spanwise-rotating turbulent plane Couette flow (RPCF) is one of the fundamental prototypes for wall-bounded turbulent flows in the rotating reference frames. In this turbulent problem, there are large-scale roll cells, which are widely studied. In this paper, a penta-decomposition method is proposed to separate the instantaneous velocity and the total kinetic energy into five parts, including a mean part, a streamwise part and a cross-flow part of the secondary flow, and a streamwise part and a cross-flow part of the residual field, aimed to explore the energy balance and transfer among different shares of the turbulent kinetic energy in RPCF at Reynolds number Rew=Uwh/ν=1300 (here, Uw is the half the wall velocity difference, and h is half channel-height) and rotation number Ro=2Ωzh/Uw (Ωz is the constant angular velocity in the spanwise direction) in the range of 0≤Ro≤0.9. The results show that the energy is transferred between streamwise part (cross-flow part) of secondary flows and residual field through the correlation between the vorticity of secondary flows and shear stress of residual field. The rotation term acts as a bridge to transfer the energy between streamwise part and cross-flow part of secondary flows (residual field). Moreover, pressure-strain redistribution term also plays an important role in the energy transfer between streamwise part and cross-flow part in residual field. For the streamwise part of residual field, in certain rotate rates, the energy obtained from the streamwise part of secondary flows is larger than that got from mean flow, implying that the streamwise motions of secondary flows have a significant impact on the streamwise motions of residual field.
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The Propagation Properties of Vortex Beams in a Ring Photonic Crystal Fiber

null
Accept: 2016-10-11
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In the last decade, the vortex beams have received lots of attention for their orbital angular momentum. When they are applied to optical fiber communication field, the data channels will increase and information propagation speed will be effectively improved. Recently, researchers have shown the capability of long length stably propagation, nonlinear frequency conversion and mode division multiplexing of vortex modes in a ring fiber. Due to the photonic crystal fiber (PCF) has very flexible design degrees of freedom, it will enable a wide range of propagation properties. In this paper, A SiO2 air-holes ring PCF is proposed for separation and propagation of optical vortex modes. By using COMSOL Multiphysics software, the vortex modes(TE01, HE_21^± and TM01) are simulated and calculated. The differences of the effective refractive index between them are 4.59×〖10〗^(-4) and 3.62×〖10〗^(-4) respectively. One can analyze the propagation properties of vortex beams in the ring PCF by changing the size of first layer air holes’ radius and air hole pitch. When the incident light wavelength of TE01 mode ranges from 1650 nm to 1950 nm, this ring PCF can achieve a total dispersion variation between 44.18 to 45.83 ps?nm^(-1)?km^(-1), which is tend to be flat. When incident light wavelength is 1550 nm, the nonlinear coefficient of TE01 mode vortex light is 1.37 W^(-1)?km^(-1); Due to the long wavelength light is easier to leakage through the cladding than the short wavelength light, the confinement loss increases with the wavelength. When incident light wavelength is 2000 nm, there is still an eight-orders-of-magnitude of the low confinement loss. Theoretically, flat dispersion and low loss vortex beams in this fiber can be beneficial to propagate stably, and the vortex modes lay the foundation for long distance propagation in the optical fiber. In the future, this ring PCF will be used in optical fiber communication field and application in aspects such as continuous spectrum research, which can make it have immense advantage to traditional fibers.
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Ballistic thermal rectification in the three-terminal graphene nanojunction with asymmetric connection angles

null
Accept: 2016-10-11
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By using the nonequilibrium Green’s function method, the ballistic thermal rectification in the three-terminal graphene nanojunction is studied. The dynamics of atoms are described by the interatomic fourth-nearest neighbor force-constant model. The nanojunction has a Y-shaped structure, created by a combination of a straight graphene nanoribbon and a leaning branch as the control terminal holding a fixed temperature. No heat flux flows through the control terminal. There exists a temperature bias between the two ends of the graphene nanoribbon served as the left and right terminals, respectively. The primary goal of this paper is to demonstrate that the ballistic thermal rectification can be introduced by the asymmetric structure with different connection angles between terminals. The control terminal has a smaller connection angle with respect to the left terminal than to the right terminal. The forward direction is defined as being from the left terminal to the right terminal. The results demonstrate that, given the same control temperature and absolute temperature bias, the heat flux in the graphene nanoribbon tends to run preferentially along the forward direction. When the difference between the connection angles increases, the rectification ratio rises. Compared to the zigzag graphene nanoribbon, the rectification ratio of the armchair nanoribbon is more sensitive to the direction the control terminal. However, the greatest rectification ratio is found in the zigzag graphene nanoribbon which has a connection angle of 30 degrees with respect to the armchair branch. In addition, the direction of the control terminal can be adjusted to raise more than 50% of the rectification ratio of the graphene thermal recti?er based on the width discrepancy between the left and right terminals. The mechanism of the ballistic thermal recti?cation is also discussed. In the three-terminal graphene nanojunction, a smaller connection angle with respect to the control terminal leads to more phonon scattering. The confirmation of this conclusion comes from a comparison of phonon transmission between different couples of terminals, which shows that, in most of the frequency spectrum, the phonon transmission between the control terminal and the left terminal is smaller than that between the control terminal and the right terminal. Given the same control terminal temperature and temperature bias, the asymmetric connection angles therefore will introduce a higher average temperature of the left and right terminals, and a larger heat flux in the forward process. Moreover, the average temperature difference between in the forward process and in the reverse process is found to be proportional to the temperature bias, and the proportionality coefficient will get bigger if the asymmetry is strengthened.
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Calculation of Hamilton energy function of dynamical systems by using Helmholtz theorem

null
Accept: 2016-10-11
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The Helmholtz theorem confirmed that any vector field could be decomposed of gradient and rotational field. The supply and transmission of energy occur during the propagation of electromagnetic wave accompanied by variation of electromagnetic field, thus the dynamical oscillators and neurons can absorb and release energy in presence of complex electromagnetic condition. Indeed, the energy in nonlinear circuit is often time-varying when the capacitor is in charged or discharged, and occurrence of electromagnetic induction is available. Those nonlinear oscillating circuits can be mapped into dynamical systems by using scale transformation. Based on mean field theory, the energy exchange and transmission between electronic field and magnetic field could be estimated by appropriate nonlinear dynamical equations for oscillating circuits. In this paper, it investigates the calculation of Hamilton energy for a class of dimensionless dynamical systems based on Helmholtz’s theorem. Furthermore, scale transformation could be used to develop dynamical equations from the realistic nonlinear oscillating circuit, so the Hamilton energy function could be approached effectively. These results could be much useful for self-adaptive control of dynamical systems.
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The Effect of Collision Parameter on a Magnetized Electronegative Plasma Sheath Structure

Accept: 2016-10-11
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The structure of an electronegative plasma sheath in an oblique magnetic field is investigated. More over, the collisions between positive ions and neutral particles are taken into account. It is assumed that the system consists of hot electrons, hot negative ions and cold positive ions. Also the negative ions and the electrons are assumed to be described by the Boltzmann distributions of their own temperatures, and the accelerated positive ions are treated by means of the continuity and momentum balance equations through the sheath region. In addition, the assumption that the collision cross section has a power law dependence on the positive velocity is introduced. After theoretical derivation, an exact of sheath criterion is obtained. The numerical simulation results include the distributions of the positive ions density for different invariable ion Mach number satisfying Bohm criterion, the comparison of net space charge distributions for variable and invariable ion Mach number. Furthermore, three species of charged particles density, the net space charge and the spatial electric potential in the sheath are studied numerically for different collision parameters under the condition of the fixed ion Mach number. The results show that the ion Mach number has not only the lower limit but also the upper limit. The ion Mach number affects the sheath structure by influencing the distribution of the positive ion density, and different conclusions can be obtained because ion Mach number is adopted as variable or invariable value while discussing the effects of the other variables which can result in the variety of the ion Mach number on the sheath formation. The reason is the actual sheath structure modification brought on by the variation of a parameter can be resolved into two parts. One is the sheath formation change caused directly by the variation of the parameter, the other is the sheath formation change caused by the Bohm criterion modification which the variation of the parameter results in. Therefore, an identical ion Mach number should be adopted when researching the direct effects of a parameter variety on plasma sheath structure. In addition, it is concluded that the collisions between positive ions and neutral particles make positive ions density curve higher and electrons’ lower than the case without collisions. Negative ions density does not alter significantly whether there exists collision or not. Besides there is a peak in the profile of the net space charge while in the presence of ion-neutral collision and the net space charge peak moves toward the sheath edge. The spatial potential increases and the sheath thickness decreases on account of the presence of the collisions between ions and neutral particles.
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Omnidirectional photonic bandgap of the one-dimensional plasma photonic crystal based on a novel Fibonacci quasiperiodic structure

Accept: 2016-10-11
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Take the binary one-dimensional plasma photonic crystal based on Fibonacci quasiperiodic structure as an object, on the basis of the photonic bandgap characteristics of the structure with different initial sequence and number of period, a novel structure of one-dimensional plasma photonic crystal is proposed in this paper to enlarge the omnidirectional photonic bandgap (OPBG). Compared with previously reported structures in literatures, this structure is simpler in configuration with fewer layers and materials, and its OPBG width is wider. The influence of the parameters of the plasma material, such as the thickness, plasma frequency and collision frequency, on the OPBG characteristics of this structure is systematically discussed and compared with that of the structure in literatures. The research results can provide important theoretical guidance for the design of novel omnidirectional reflectors.
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Quantum secure direct communication protocol based on the mixture of Bell state particles and single photons

Zheng-Wen CAO
Accept: 2016-10-11
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By studying the properties of the mixture of Bell state particles and single photons, the paper designs a quantum code scheme with high coding capacity, and proposes a novel quantum secure direct communication protocol with high transmission efficiency. Alice prepares Bell state particles and single photons, and divides Bell state particles into two sequences $S_A$ and $S_B$. $S_B$ is sent to Bob for the first security check using quantum correlation properties of particles. When the check result shows that the quantum channel is safe, using designed quantum code scheme, Alice encodes her classical message on the mixed quantum state sequence of Bell sequence $S_A$ and single photon sequence $S_S$. Then, some single photons that are used for security check are re-inserted randomly into the encoded sequence, and the order of particles is rearranged to ensure to check Eve's attack. Alice sends the new sequence to Bob. Bob delays and receives it. And then, the quantum channel is conducted security check for the second time. The transmission error rate is calculated, if the error rate is lower than the tolerance threshold, the channel is safe. Bob decodes and reads Alice's message. The first security check is to determine whether quantum channel is safe. The second security check could test whether there are eavesdroppers during information transmission. Safety analysis is done by using quantum information theory to the proposed protocol. The error rate introduced by Eve and the amount of information by Eve are calculated. It is showed that this protocol can effectively resist measurement-resend attack, intercept-resend attack, auxiliary particle attack, denial of service attack and Trojan attack. Among them, auxiliary particle attack is analyzed in details. The transmission efficiency and coding capacity are also analyzed. The transmission efficiency is 2, the quantum bit rate is 1, and the coding capacity is that a quantum state can encode three bits of classical messages. We also compare the proposed protocol to many existing popular protocols in terms of efficiency, e.g., Ping-Pong protocol, Deng,F.G. et al.'s Two-step and One-pad-time quantum secure direct communication protocol, Wang,J. et al.'s quantum secure direct communication protocol based on entanglement swapping and Quan,D.X. et al.'s one-way quantum secure direct communication protocol based on single photon. It is proved that this proposed protocol has higher transmission efficiency. In addition, complex U operation and entanglement swapping are not used, and implementation process is simplified. However, this protocol is devoted to theoretical research of quantum secure direct communication. There are still some difficulties in the practical application. For example, the storage technology of quantum states is not mature at present. It is not easy to prepare and measure Bell state particles and combine them with single photons, and so on. The implementation of this protocol depends on the development of quantum technology in the future.
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The Relationship between Dielectric Properties and Nanoparticle Dispersion of Nano- SiO2/Epoxy Composites

null
Accept: 2016-10-11
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Nano-SiO2 was modified by silane coupling agent and modified nano-SiO2 powder and nano-SiO2 dispersing liquid was obtained. Unmodified and modified nano-SiO2/Epoxy composites made by “mechanical mixing method”, and modified namo-Silica/Epoxy composites made by “bubble mixing method” were prepared, respectively. The content of nano-SiO2 in the composite is 2wt%, 3wt%, 4wt%, 5wt% and 6wt%. Breakdown strength and corona-resistance characteristics of the composites were tested. The results show that, with the increase of nano-SiO2 loading, the breakdown strength and corona-resistance of nano-SiO2/Epoxy composites increase. The maximum breakdown strength of namo-Silica/Epoxy composites was appeared when the nano-Silica content is 5wt%. The SEM images of 5wt% nano-Silica loading composites were analyzed by Software Image J, and the Morisita’s Index method was used to evaluate the dispersion of nano-Silica particles in the matrix quantitatively. The best dispersion was found in the composites made by “bubble mixing method”. The relationship between dielectric properties and nano-particle dispersions of nano-Silica/Epoxy composites was discussed.
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Combined noise source identification method based on spherical microphone array with random unifrom distribution of elements

null
Accept: 2016-10-11
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As the developing of techlology, noise controlling is paied wide attention in recent years. Noise source identification is the key step for noise controlling. Spherical microphone array, which can located the noise source of arbitrary direction in three dimensional space, is widely used for noise source identification in recent years. Conventional methods for noise source localization include spherical near field acoustic holography and spherical focused beamforming. The acoustic quantities are reconstructed by using spherical near field acoustic holography method to realize the noise source identification, while the noise source can also be located by using focused beamforming based on spherical harmonic wave decomposition. However, both these methods have their own limitations while being used in noise source identification. Spherical near field acoustic holography has low resolution in high frequency with far distance from noise source to measurement array for noise source identification, whereas the spherical focused beamforming has low localization resolution in low frequency. Noise source identification is discussed here and a 64-element microphone spherical array with randomly uniform distribution of elements is designed. The combination methods of noise source identification by using spherical near field acoustic holography and mode decomposition focused beamforming are researched. The performance of the proposed combination methods is simulated, and an experiment of noise source identification is carried out based on the designed spherical microphone array to test the validity of proposed method. The dividing frequency point is when selecting noise source identification methods between near field acoustic holography of spherical wave decomposition by using the spherical array designed in this paper. Research results show that high resolution of noise source identification can be obtained by using near field acoustic holography when reconstruction frequency is with a distance from noise source to the center of spherical array, while high resolution of noise source localization can be achieved by using spherical wave decomposition beamforming when signal’s frequency is with a distance from noise source to the center of spherical array. Spherical array with random uniform distribution of elements maintains stable identification ability in all bearing. Spherical near field acoustic holography has high resolution distinguish ability in near field and low frequency, while focused beamforming method has high resolution distinguish ability in far field and high frequency. Therefore the noise source can be efficiently identified by using the proposed combined method of near field holography and focused beamforming with less elements and small aperture spherical microphone array.
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Optimization design of a Gamma-to-Electron spectrometer for high energy gammas induced by fusion

null
Accept: 2016-10-11
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Apart from neutrons, the fusion core produces gamma rays during one fusion reaction. The spectrum of gamma ray can provide very important information for fusion diagnosis. However, due to the gamma energy and yield in one fusion pulse, the gamma spectrometer used should have high detection efficiency and energy resolution. The concept of a Gamma-to-Electron magnetic spectrometer GEMS provides the idea to build up such a spectrometer to meet this requirement. Based on this concept design, four important parts of this facility are investigated. The first part is the gamma-electron converter. The main physics processes include Compton scattering of gamma ray with converter material generating electron, the electron Multiple Coulomb scattering (MCS) inside the converter and the electron attenuation. Affected by the thickness of convector, these processes gives a complex influence on the detection efficiency and angular-energy distribution of the electrons which are emitted from the downstream face of the convector. The Monte Carlo code Geant4 is employed to investigated the functions of Compton scattering, MCS and converter thick on the angular-energy distribution. The second one is the collimation. The collimation is used to select the forward direction election, the performance of cutoff angle of the collimator on the detection efficiency and resolutions, as well as the correlation between electron transportation direction and energy, are also studied using Geant4 code. The third part is the dipole magnetic field. There are several parameters of geometric and magnetic, therefore, a multi-thread parallelized Genetic algorithm is developed to get the best result. Both the irregular geometry (shape) and dipole magnetic field strength are optimized to achieve the best energy resolution and detection efficiency. The obtained magnetic field has intensity less than 100 Gauss, and its performance on gathering elections is also verified by Geant4 code. The last one is the location of electron detectors. The study shows that all the electron detectors should be located according to not a straight line but a quadratic curve. Then the optimized spectrometer is simulated by Geant4 to get the responses of gamma rays with various energies. For the gammas provided by fusion reaction, the simulation shows that when the neutron yield is about 2.5×1015 and 1.2×1016, the energy resolution reaches 0.5 MeV and 0.25 MeV, respectively, provided that different thick Be converters are employed. All in all, this optimized GEMS can be employed to measure the spectrum of gamma rays generated by the fusion reaction.
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Influnence of Nonspherical Effects on the Secondary Bjerknes Force in a Strong Acoustic Field

null
Accept: 2016-10-11
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The secondary Bjerknes force between bubbles in an acoustic field is a well-known acoustic phenomenon. The major theoretically researches of the secondary Bjerknes force were owing to two spherical bubbles. The secondary Bjerknes force between two spherical bubbles which is calculated based on the linear equations is very small and negligible, therefore these theoretically researches did not give a well explanation for the phenomenon, such as “streamer formation” and Multi-bubble sonoluminescence (MBSL). Experiments of sonoluminescence (SL) show that bubbles in a sound field are not entirely spherical bubbles. Nonspherical effects have an important influence on the secondary Bjerknes force when two bubbles come close to each other in a strong acoustic field (>1.0×〖10〗^5 Pa). How does the shape distortion of a nonspherical bubble cause the change of the secondary Bjerknes force between two bubbles, and the secondary Bjerknes force how to affect the oscillation and movement of bubbles are major problems which we wish to solve. The of the secondary Bjerknes force between a nonspherical bubble and a spherical bubble is obtained by considering the shape oscillation of a nonspherical bubble. We numerical simulate the secondary Bjerknes force between a nonspherical bubble and a spherical bubble based on the nonlinear oscillation equations of two bubbles, and compare the secondary Bjerknes force between a nonspherical bubble and a spherical bubble to the secondary Bjerknes force between two spherical bubbles in the same condition. We discuss the influence of nonspherical effects on the secondary Bjerknes force between two bubbles. The results show that when the amplitude of driving pressure is greater than the Blake threshold of a nonspherical bubble and makes the bubble oscillate stably, the secondary Bjerknes force between this nonspherical bubble and a spherical bubble is different to the secondary Bjerknes force between two spherical bubbles in direction and magnitude. The secondary Bjerknes force between a nonspherical bubble and a spherical bubble is much bigger than that of two spherical bubbles. The interactional distance of the secondary Bjerknes force between a nonspherical bubble and a spherical bubble is further than that of two spherical bubbles. The secondary Bjerknes force between a spherical bubble and a nonspherical bubble depends on the radii of two bubbles, distance between two bubbles, shape mode of the nonspherical bubble and the amplitude of driving pressure. Our research is more close to the actual bubbles in liquid. We also prove that big mutual interaction between bubbles is mainly cause for the formation of a stable structure between bubbles. For bubbles, big mutual interaction causes the cavitation become easier. These results are important to explain the phenomenon in an acoustic field, such as “streamer formation” and Multi-bubble sonoluminescence (MBSL).
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The Principle and Application of Diagonal Reducing Method in the Complex Noise Fields

null
Accept: 2016-10-11
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Acoustic environment has low signal-to-noise ratio (SNR); hence, array signal processing is always used for noise reduction and signal enhancement. Because the delay-and-sum beamforming method performs robust, so it is almost widely used, but the array gain is limited by the array aperture. The actual underwater ambient noise is complex, which includes uncorrelated noise and correlated noise. The noise power of each array element is unequal. The noise covariance matrix is not a scaled identity matrix. Consequently, the performance of array signal processing method decreases obviously. Aiming at these two problems, the diagonal reducing method of the covariance matrix in the complex noise fields is proposed. Firstly, a reducing matrix, which is defined as a diagonal matrix with unequal diagonal elements, is subtracted from the covariance matrix so as to reduce the noise, and a new matrix is obtained. Secondly, the delay-and-sum beamforming is done by using the new matrix to obtain the beaming output. The analytic solution and approximate solution of reducing matrix are obtained under the constraint condition that the output SNR attains its maximum. Thirdly, the estimation of the reducing matrix is determined by minimizing the function that is defined as the error between the covariance matrix and the estimated covariance matrix. This minimization problem is accomplished in an iterative method. Fourthly, if the noise is uniform white noise or the nonuniform white noise, this proposed method performs well. While, under the complex noise field the performance of the proposed method may be deteriorated. So the effects of the correlation of the noise field and the input SNR on the estimated error is analyzed. In fact, the weaker the correlation is, or the smaller the input SNR is, the smaller the estimated error is. Lastly, the simulation experiment and the lake trial are implemented. The simulation results show that the diagonal reducing method of the covariance matrix reduces some ambient noise, the noise output power is decreased, the output SNR is increased, and the proposed method improves performance of array signal processing. The experimental results show that the output SNR of the target using the proposed method is increased by about 14 dB. The diagonal reducing method of covariance matrix has definite value to engineering application, and is computationally attractive.
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Moving target compressive imaging based on improved row scanning measurement matrices

null
Accept: 2016-10-11
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Abstract: Moving target imaging (MTI) plays an important role in practical applications. How to capture dynamic images of the targets with high quality is a front-burner issue in the field of MTI. In order to improve the reconstruction quality, a new MTI model based on compressed sensing (CS) is proposed here, applying a sampling protocol of the row-scanning together with a motion measurement matrix constructed by our own. It is proved by the simulation and the experimental results that a relatively higher quality can be achieved through this approach. Furthermore, an evaluation criterion of reconstructed images is introduced to analyze the relationship between the imaging quality and the moving speed of the target. By contrast, the performance of our algorithm is much better than that of traditional CS algorithms under the same moving speed condition. As a result, it suggests that our imaging method may have a great application prospect in the earth observation of unmanned aerial vehicles, video monitoring in the product line and other fields.
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Spatial Correlation of Underwater Bubble clouds Based on Acoustic Scattering

null
Accept: 2016-10-11
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Using effective medium theory to describe acoustic scattering from bubble clouds, one of the underlying assumptions shows that the probability of an individual bubble being located at some position in space is independent of the locations of other bubbles. However, bubbles within naturally occurring clouds are usually influenced by the motion of the fluids which makes they become preferentially concentrated or clustered. According to Weber’s method, it is a useful way to importing spatial correlation function to describe this phenomenon in bubble clouds. The spatial correlation function is contained in acoustic scattering and it is important to notice that the spatial correlation should be dependent of the position and radius of each bubble due to the ‘‘hole correction’’ or the effect of the dynamics of the fluids. Because of these reasons, it is hard to invert the spatial distribution of bubble clouds using spatial correlation function in acoustic scattering. A method is described here in which bubble clouds are separated into many small subareas and the conception called effective spatial correlation function which is the statistic of spatial correlation function used to describe the correlation between each subarea of bubble clouds. Since the effective spatial correlation function is independent of bubbles’ radius and positions, the bubble clouds’ distribution and the trend of clustering can be inverted by using this function. The result of simulation indicates that the effective spatial correlation function can precisely track the position of the clustering center, even the clustering center covered by other bubble clouds can be detected. Using multi-bean sonar measuring the bubbly ship wake generated by a small trial vessel, the method is used to invert the spatial distribution and clustering centers of bubble field in the ship wake. The results show that effective spatial correlation function accurately inverts the distribution and clustering centers of bubbles in ship wake. Furthermore, the method presented in this paper could distinguish the bubble clouds caused by different reasons and detect upper ocean bubble clouds covered by other bubbles generated by wave breaking.
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Uncertainty Quantification in the Calculation of keff Using Sensitity and Stochastic Sampling method

null
Accept: 2016-10-11
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In the neutronics simulation of nuclear reactor, the uncertainties associated to the integral parameters due to the uncertainties in nuclear data are usually quantified using the sensitivity and uncertainty (S/U) analysis method based on the perturbation theory. S/U analysis method is only applicable to the linear model, moreover neutronics code generally can not be directly used in sensitivity analysis. Sampling approach, which evaluating the uncertainties by performing a set of stochastic simulations, is easy to implement and the uncertainties quantified is close to exact. The function of uncertainty quantification based on sampling approach have been added to uncertainty analysis code SURE. Before applying the sampling method to the uncertainty quantification in the simulation of complex problems, it is necessary to carry out a careful verification. The uncertainties of the calculated effective neutron multiplication factor keff for two selected simple critical benchmark experimental model are quantified using SU method and sampling method respectively. The keff uncertainties due to all nuclides and reaction types nuclear data quantified by two methods are in good agreement, and the correctness of the sampling function of SURE code is verified. The keffs distributions from sampling method obey normal distribution, which embodies a linear relation between input nuclear data and output keff in the range of the uncertainty range of nuclear data, and sensitivity analysis method is adaptable to quantify uncertainty of calculated keff.
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A super-resolution infrared microscopy based on a doughnut pump beam

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Accept: 2016-10-11
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This paper presents an approach to break through the diffraction limitation in infrared microscopies. In this method, instead of Gaussian pump beam, an intensive vortex beam is firstly focused on the sample, leading to saturation absorption of the peripheral molecules in the point spread function (PSF). The vortex beam is followed by a Gaussian beam with the same wavelength, which can only be absorbed by the molecules near the center, resulting in shrunken PSF which means higher resolution. Furthermore, the PSF of a system based on this approach is numerically simulated. With an 100 nJ pulse energy vortex beam and a 0.1 nJ pulse energy probe beam, the theoretical resolution (full width at half maximum, FWHM) is measured to be about 236 nm which is 14 times better than that of the traditional infrared microscopy.
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Fast Bayesian Blind Restoration for Single Defocus Image with Iterative Joint Bilateral Filters

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Accept: 2016-10-11
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It is significant to realize effective defocus image restoration for acquiring clear image in military and geological examination field. Most of existing algorithms have the problems of large computational cost, ringing and noise sensitivity, hence a novel approach by iterative joint bilateral filtering under Bayesian framework is proposed. Firstly, it utilizes defocus image depth estimation to compute the point spread function in the Bayesian framework. Then a minimum optimization problem is built to represent the blind restoration problem. After inferring the solution procedure of the minimum optimization problem, we find that the joint bilateral filters can be used to search the optimal solution, which not only simplify the searching procedure but also reduce the computational cost. Finally, an iterative joint bilateral filtering was designed to realize the image restoration. That means the original restored image obtained from the bilateral filtering is used to design the guide image for the joint bilateral filters, and the guide image will serve as the input of the optimization problem for acquiring the better optimal result. This procedure was repeated until convergence. The experiment results indicate that this method can yield the ringing, reduce the computational cost and remove the noise. Generally speaking, the average pixel error of 85% images is under 0.03, which has improved 19% comparing with the same error rang of existing algorithms. And 78% shorter than those of compared algorithms. It can be used in the engineering practice of blind restoration for single defocus image.
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First-principles study on the thermodynamic stabilities and electronic structures of long-period stacking ordered phases in the Mg-Y-Cu alloys

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Accept: 2016-10-11
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A first-principles method based on density functional theory has been used to investigate thermodynamic stability and electronic characteristics of long-period stacking ordered (LPSO) phases 14H and 18R (18R(m)，18R(t)) in Mg–Y–Cu alloys. The present calculations are performed using Vienna Ab-initio Simulation Package (VASP) with projector augmented plane wave pseudopotential, and generalized gradient approximation is used to treat with and describe the exchange-correlation interaction. The plane wave cutoff energy is set to 360 eV, the forces on all the atoms is less than 0.02 eV/?. The calculated negative enthalpies of formation show that both 14H and 18R can exist in Mg–Y–Cu system, 14H and 18R are stable with respect to the Mg, Cu and Y elements, the reaction energies indicate that 14H is more stable than 18R. The density of states (DOS) of these phases reveals that the main bonding peaks of 14H is located at energy range between -6.82 eV and 2.09 eV, those of 18R(m) at energy range between -6.82 eV and 2.02 eV, and 18R(t) at energy range between -6.82 eV and 1.98 eV. The Cu 3d orbits, Y 4d orbits, Mg 3s and Mg 2p orbits are broadly distributed in the entire region, while Cu 4s orbits, Y 4s and Y 4p orbits are very weak in whole region. For 14H,18R(m) and 18R(t) phases, the bonding originates mainly from the valence electrons of Mg 3s, Mg2p, Cu 3d and Y 4d orbits. The presence of pseudogap indicates that the bonds in 14H and 18R phases are noticeable covalent. In addition, the charge density on (0 0 0 1) plane of 14H and 18R phases are analyzed, and the results indicate that the Cu-Y bonds exhibits covalent feature in 14H and 18R, the covalent bonding of 14H phase is stronger than that of 18R phase.
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A broadband low-frequency sound insulation structure based on two-dimensionally inbuilt Helmholtz resonators

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Accept: 2016-10-11
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A man-made acoustic structure with broadband low-frequency sound insulation property is designed based on circularly inbuilt Helmholtz resonators. Beyond this structure, a two-dimensional quiet zone can be created. Being the same as the simulating model, an experimental structure is fabricated. Experiments are carried out to study its sound insulation properties. The experimental results are very coincident with the simulating one, which show that this structure has an excellent sound insulation effect in the frequency band of 680-1050Hz, and the maximum insulation sound pressure level can reach 41dB. Meanwhile, the distribution of the two-dimensional sound field above this structure is measured. The results point out that the range of the insulation area can be changed with the change of the incident frequency. In addition, the sound insulation effect is sensitive to the resonant state of the Helmholtz resonators. This work will be of help for designing new sound protection devices.
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Total Dose Dependence of Hot Carrier Injection Effect in the NMOS Devices

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Accept: 2016-10-11
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Optoelectronic properties of N/B doped graphene

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Accept: 2016-10-11
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Since its discovery in 2004, graphene has attracted great attention because of its unique chemical bonding structure, which has excellent chemical, thermal, mechanical, electrical and optical properties. Due to the zero band gap material, graphene has limited its development in the field of Nano Electronics. Only expanding the band gap of the graphene can promote the application of graphene in Nano Electronics. In this paper, we constructed three models of intrinsic graphene, N-doped graphene and B-doped graphene. The energy band structures, electronic density of states and optical properties of N/B doped graphene with intrinsic graphene and different doping concentrations were studied. The absorption spectra, the reflection spectra, the refractive index, the conductivity and the dielectric function were studied. The study shows that the electronic states near the Fermi level of N/B doped graphene are mainly composed of C-2p and N-2p/B-2p orbitals, and N/B doping can induce the change of the Fermi level and the photoelectric properties of graphene. The conclusion of this paper can provide a theoretical basis for the application of graphene in optoelectronic devices.
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A first-principles study of impurity C multiple trapped by Ni vacancy and temperature effects in NiAl intermetallics

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Accept: 2016-08-18
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By using a first- principles pseudopotential method based on the density functional theory and Vienna Ab initio Simulation Package (VASP), we investigate the multiple trapping of C by Ni vacancy (VNi) and its temperature effects in NiAl intermetallics. A single C is energetically favorable sitting at the Ni-riched octahedron interstitial site which surrounds Ni vacancy via calculating the formation energy of C in NiAl with Ni vacancy system. Single C atom prefers to interact with neighboring Ni atom and Al atom by forming a covalent bond. In NiAl intermetallics, C atoms prefer to be trapped in the Ni vacancy in the “Sequential” way, and the CnVNi (n=1, 2, 3, 4) clusters, in which the C4VNi clusters are most energetically favorable, can be easily formed. It is interesting to find that all the C atoms are coplanar with each other surrounding Ni vacancy. With the C atoms further added, both the charge density and the def-ormation charge are preferred to bind with each other despite the Ni or Al environment and the intrinsic bonding properties of C-C contain obvious covalent characteristics. Furthermore, using a first-principles calculations combined with statistical model, we quantitatively predict point defect concentrations as a function of temperature in NiAl intermetallics. It is concluded that the concentration of intrinsic VNi will obviously increase when the temperature increases. With the increase of temperature, the concentration of C atoms in the CnVNi cluster is higher than that in the intrinsic position. Besides, it is indicates that most of C atoms in NiAl intermetallics are trapped by Ni vacancy, which is due to the larger binding energy of the CnVNi clusters and most of the C atoms are trapped directly by vacancies at room temperature or high temperature to form CnVNi clusters. Since the formation of CnVNi clusters is a process of heat releasing which will further increase the temperature of the NiAl system and promote more and more Ni vacancy , we can conclude that much more vacancies are created as a result of the presence of C impurity in NiAl intermetallics. However, the Ni vacancies exist in the formation of CnVNi clusters from our calculation in a certain temperature range (less than 1000K). The existence of this kind of CnVNi clusters can effectively restrain the generation of cracks in the vacancies, which will produce some influences the mechanical properties of NiAl intermetallic compound. Consequently, our results will provide a valuable reference in order to understand the effects of C and vacancy on the mechanical properties of the NiAl intermetallics.
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Theoretical study electronic, mechanical and thermal properties of Ti3(SnxAl1-x)C2 solid solutions

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Accept: 2016-08-18
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Available experimental and theoretical studies have demonstrated that Ti3AlC2 and Ti3SnC2 compounds exhibit excellent mechanical properties at high temperatures, which render it a promising candidate as a high-temperature structural material. However, these compounds have a relatively low hardness, Young’s modulus, and poor oxidation resistance compared with other MAX phases. In order to overcome these limits, solid solutions on the M, A and/or X sites of the MAX phase compound is considered as a promising strategy to further improve the mechanical properties. Most recently the solid solutions of Ti3(SnxAl1-x)C2 have been synthesized. However, no theoretical work has focused on the Ti3(SnxAl1-x)C2 solid solutions so far. Therefore, in this work, we has performed first-principles calculation to study the microstructure, phase stability, electronic, mechanical and thermal properties of Ti3(SnxAl1-x)C2 solid solutions. Particularly, the effect of Sn concentration (x) on the properties is discussed for the Ti3(SnxAl1-x)C2 solid solutions by varying x from 0 to 1.0 in the step of 0.25. All present ab initio calculations were carried out based on density-functional theory (DFT) method, as implemented in the Cambridge Serial Total Energy Package (CASTEP) code. The electron-ion interactions were described by Vanderbilt-type ultrasoft pseudo-potentials with generalized gradient approximation (GGA-PW91) exchange-correlation function. The equilibrium crystal structures were fully optimized by independently modifying lattice parameters and internal atomic coordinates, and we employed the Broyden–Fletcher–Goldfarb–Shanno (BFGS) minimization scheme to minimize the total energy and inter-atomic forces. For the reciprocal-space integration, a Monkhorst–Pack grid of 16×16×4 was used to sample the Brillouin-zone (BZ) for Ti3AlC2, Ti3SnC2 compound and 8×8×2 for 2×2×1 supercell Ti3(SnxAl1-x)4C2 (x=0.25-0.75) compounds. Present calculated results of the enthalpy formation energy and mechanical stability criteria indicate that all the Ti3(SnxAl1-x)C2 (x=0.0~1.0) solid solutions are thermodynamic and elastically stable. Moreover, mechanical properties (including bulk modulus B and shear modulus G), the ductile and brittle behavior and the anisotropic factors of Ti3(SnxAl1-x)C2 solid solutions have been investigated, and the results indicate that all these compounds are identified as brittle materials and isotropic in nature. On the other hand, the MAX phases are good thermal materials due to their high thermal conductivity varying from 12 to 60 W/(mK) at room temperature. As for the thermal conductivity, it has become one of the most fundamental and important physical properties of the MAX phase materials, especially for applications at elevated temperatures. Therefore, the lattice thermal conductivity, the minimum thermal conductivity and temperature dependent of the lattice thermal conductivity of Ti3(SnxAl1-x)C2 solid solutions have been studied. Furthermore, Debye temperature and melting point of the Ti3(SnxAl1-x)C2 compounds are also reported. Present results predict that all Ti3(SnxAl1-x)C2 compounds have a relative high Debye temperature and melting point, indicating that all Ti3(SnxAl1-x)C2 compounds possess a rather stiff lattice and good thermal conductivity.
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Analysis for Resting State fMRI Signal complexity of Adult MDD Based on fApEn

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Accept: 2016-08-18
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In our research, we proposed a new method to measure functional magnetic resonance imaging (fMRI) signal complexity adopt fuzzy approximate entropy (fApEn) and compare it with sample entropy (SampEn). Here we collect resting state fMRI data of 22 major depressive disorder (MDD) (11 males; age: 18-65). We expect the complexity of the resting state fMRI signals measured to be consistent with the Goldberger/Lipsitz model for robustness where healthier (younger) and more robust systems exhibit more complexity in their physiological output and system complexity decrease with age. The mean whole brain fApEn demonstrated significant negative correlation (r = -0.512, p<0.001) with age. In comparison, SampEn produced a non-significant negative correlation (r = -0.102, p = 0.412). fApEn also demonstrated a significant (p < 0.05) negative correlation with age regionally (frontal, parietal, limbic, temporal and cerebellum parietal lobes). There was no significant correlation regionally between the SampEn maps and age. These results support the Goldberger/Lipsitz model for robustness and have shown that fApEn is potentially a sensitive new method for the complexity analysis of fMRI data.
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Experimental observation and study of two sets of four-wave mixing processes in a single-zero-dispersion microstructured fiber by the same pump

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Accept: 2016-08-18
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A highly nonlinear microstructured fiber with single-zero-dispersion wavelength was designed and drawn by reducing the core area in order to observe two groups of four-wave mixing by a single pump. The foundational material of the fiber was silica and its cladding was consisted of seven layer air holes. The air holes were arranged in a hexagonal lattice and the lattice pitch was Λ=2.5 μm, the radius of the air holes were r=1.03 μm. There was just one zero-dispersion wavelength in our considerable wavelength range for the microstructured fiber and the corresponding wavelength was near λ_D=0.85 μm. The basic properties of the fiber including effective refractive index, dispersion coefficient, and nonlinear coefficient were calculated by finite element method. The effective mode area was 4.4〖 μm〗^2 and the nonlinear coefficient was 0.057 m^(-1) W^(-1) for the foundation mode near the wavelength of 0.8 μm, and the nonlinear coefficient reached 0.053 m^(-1) W^(-1) near the zero dispersion wavelength of 0.85 μm. In short, the optical fiber had a stable and high nonlinear coefficient in the whole experimental band (0.80 μm~0.83 μm) which provided an important guarantee for the occurrence of four-wave mixing double parameter gain process. In addition, the phase mismatch curve was simulated by using the four-wave mixing phase mismatch formulation. Numerical simulation shown that two sets of four-wave mixing processes could occur in the designed fiber. At the normal dispersion wavelengths of 0.800 μm, 0.810 μm and 0.820 μm with different powers, the experiment result shown a significant feature of four gain wavebands located at both sides of the pump wavelength. By comparing experimental data with the phase mismatch curve, we found that the band generation meet four-wave mixing phase matching condition, thus, the simultaneous occurrence of two groups of four-wave mixing processes observed in the experiment was explained in theory. The experimental results agreed well with the theoretical predictions. This also proved the theoretical predictions that two sets of parametric gain processes and two pairs of signal and idle frequency waves can be generated in PCF. The four-wave mixing effect occurred at the normal dispersion region could be attributed to the contribution of negative fourth-order dispersion to the phase matching process. The present work can provide valuable reference to the design of microstructure fibers and the development of multi-wavelength conversion technology based on four-wave mixing effect. At the same time, this work could also supply guidance for the development of uncommon waveband lasers and broadband light sources.
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