bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of the particle on a catenoid and the quantization of the constrained system in the extended space
Authors: Xun Da-Mao  , Ouyang Tao  , Tan Rong-Ri  , Liu Hui-Xuan  ,   Faculty of Communication and Electronics, Jiangxi Science and Technology Normal University, Nanchang 330013, China;,   China Nerin Engineering Company Limited, Nanchang 330000, China
Published: December 2020

There are two approaches to investigating the quantum mechanics for a particle constrained on a curved hypersurface, namely the Schrödinger formalism and the Dirac theory.#br#The Schrödinger formalism utilizes the confining potential technique to lead to a unique form of geometric kinetic energy T that contains the geometric potential VS and the geometric momentum p,#br#T=-ħ2/(2m)▽2+VS=-ħ2/(2m)[▽2+(M2-K)],p=-iħ(▽2+Mn),#br#where ▽2 is the gradient operator on the two-dimensional surface. Both the kinetic energy and momentum are geometric invariants. The geometric potential has been experimentally confirmed in two systems.#br#The Dirac's canonical quantization procedure assumes that the fundamental quantum conditions involve only the canonical position x and momentum p, which are in general given by#br#[xi,xj]=iħÂij,[pi,pj]=iħΩij,[xi,pj]=iħΘij#br#where Âij, Ωij, and Θijare all antisymmetric tensors. It does not always produce a unique form of momentum or Hamiltonian after quantization. An evident step is to further introduce more commutation relations than the fundamental ones, and what we are going to do is to add those between Hamiltonian and positions x, and between Hamiltonian and momenta p, i.e.,#br#[x,Ĥ]=iħÔ({x,HC}c) and [p,Ĥ]=iħÔ({p,HC}c)#br#where {f,g}c denotes the Poisson or Dirac bracket in classical mechanics, and Ô({f,g}c) means a construction of operator based on the resulting {f,g}c, and in general we have [f,ĝ]≠Ô({f,g}c). The association between these two sets of relations means that the operators {x,p,H must be simultaneously quantized. This is the basic framework of the so-called enlarged canonical quantization scheme.#br#For particles constrained on the minimum surface, momentum and kinetic energy are assumed to be dependent on purely intrinsic geometric quantity. Whether the intrinsic geometry offers a proper framework for the canonical quantization scheme is then an interesting issue. In the present paper, we take the catenoid to find whether the quantum theory can be established satisfactorily. Results show that the theory is not self-consistent. In contrast, in the threedimensional Euclidean space, the geometric momentum and geometric potential are then in agreement with those given by the Schrödinger theory.
Stochastic resonance in periodic potential driven by dichotomous noise
Authors: Ma Zheng-Mu  , Jin Yan-Fei  ,   School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

Periodic potential system is widely used in a lot of areas such as biological ratchet model of motor, Josephson junction in the field of physics, engineering mechanics of the damping pendulum model, etc. Meanwhile, in the study of stochastic resonance, noise is crucial for dynamical system evolution. There are mostly colored Gaussian noises with nonzero correlation times in practical problems. Dichotomous noises belong to the color noises, and they have some simple statistical properties. In this paper, we study the motion of a Brownian particle in a periodic potential, driven by both a periodic signal and a dichotomous noise. The periodic potential system is different from the bistable system, so we use multiple indexes to explain the stochastic resonance. We calculate the average input energy of the system and the average output signal amplitude and phase difference by using stochastic energetics. Then we discuss the influences of the dichotomous noise intensity, noise correlation time and asymmetric coefficient of potential energy on the stochastic resonance. The results show that with the increase of the noise correlation time, a minimum value and a maximum value occur on the curve of the average input energy, meanwhile, the phenomenon of resonance appears in the system. With the increase of the noise intensity, the value of noise correlation time becomes greater when the phenomenon of stochastic resonance appears. Therefore, the region of stochastic resonance becomes bigger as the noise intensity or the asymmetry coefficient increases. Moreover, with the increase of the noise intensity, a mono peak is found for the signal-to-noise ratio (SNR) of the system and the stochastic resonance appears in this system. With the increase of the noise intensity, we compare the change of the SNR, the average input energy, and the average output signal amplitude. We find that the values of the amplitudes of the average output signal and SNR are basically the same, while the values of the amplitude of the average input energy of the system are a little different. This is because during the process of periodic signal doing work to the system, noise does work and passive dissipation energy of the system occures. In addition, when the curves of the amplitude of the average output signal and SNR reach their corresponding minimum values, the phase difference between the output signal and input signal is minimal.
Spectroscopic parameters and molecular constants of 75As32S+ and 75As34S+
Authors: Wang Jie-Min  , Wang Xi-Juan  , Tao Ya-Ping  ,   College of Physics and Electronic Information, Luoyang Normal College, Luoyang 471022, China
Published: December 2020

The ground state X3Σ- and low-lying excited electronic state A1Π of AsS+ ion are investigated employing the full valence complete active space self-consistent field method combined with the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach. The basis set used in the calculations is Dunning correlation-consistent basis set, aug-cc-pV5Z. To improve the quality of the potential energy curves (PECs), three kinds of corrections are considered in the present work. First, the Davidson modification is adopted to deal with the size-extensity errors from the MRCI calculations. Then, relativistic correction is calculated by the second-order Douglas-Kroll Hamiltonian approximation at the level of cc-pVQZ basis set. Finally, to eliminate the truncation errors of the basis set, the PECs of the two electronic states for each species are extrapolated to the complete basis set limit by the two-point energy extrapolation scheme. Two large basis sets, i.e., aug-cc-pVQZ and aug-cc-pV5Z, are used to perform the extrapolation calculations. With the aid of VIBROT program, all the PECs of X3Σ- and A1Π obtained here are fitted to the analytical forms, which are used to derive the spectroscopic parameters (De, D0, ωeχe, αe and Be) of 75As32S+ and 75As34S+. The effects of the Davidson modification, relativistic correction and basis set extrapolation are discussed respectively. The results indicate that the quality of almost all the spectroscopic parameters is improved by considering these corrections, which exhibit excellent agreement with the experimental data. Besides, the first 10 vibrational states for the two electronic states of 75As32S+ and 75As34S+ are determined when the rotational quantum number J equals zero. For the first 10 vibrational states, the vibrational level G(ϒ), inertial rotation constant Bv, and centrifugal distortion constant Dv are evaluated when J=0.
Theoretical study of the periodic quantum phase modulation of the dipole response in atomic He
Authors: Ding Jing-Jie  , Wang Quan-Jun  , Liu Zuo-Ye  , Hu Bi-Tao  ,   School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China
Published: December 2020

Based on the laser-induced-phase model, periodic quantum phase modulation of the dipole response in atomic He is studied theoretically. The two-level system of the transition 1s2→1s2p with a delay width of 1.8 × 109 s-1 and an energy difference of 21.2 eV between the excited state and the ground state is used in the calculation. The system is excited by attosecond laser pulse from high harmonic generator, and the spectral response of the system is of single isolated symmetric Lorentzian absorption line. After the excitation, near infrared (NIR) femtosecond laser pulse train with a repetition rate of 5 GHz, central frequency 780 nm, and pulse duration of 100 fs, is utilized to periodically modify the spontaneous decay of the excited 1s2p level. The incremental phase step Δφ depends on the intensity of the NIR laser pulse, while the initial offset phase φ can be controlled independently by partially overlapping the first NIR pulse with the excitation. Simulated results show that the Lorentzian absorption line is transformed into comb-like spectral structure with equal gap depending on the repetition rate of the NIR pulse train. The line shape of each comb tooth is symmetric Lorentzian line by setting φ = Δφ/2 = π/2, while it is Fano line by setting φ = Δφ = π. The location of the comb structure is mainly dependent on the energy difference between the excited state and the ground state, while it can be slightly tuned by controlling the incremental phase step Δφ. We develop an analytic description of the comb-like spectral structure by Fourier analysis, depending on both the atomic and the phase-control properties. The analytical expressions can be readily used to estimate the exact experimental parameters. The universality of this mechanism allows the spectral modulation in arbitrary atomic system at arbitrary frequency, including the hard X-ray regime, by using reference transitions in highly charged ions. The generalization of this approach should thus not only enable relative frequency measurement and relevant applications at extremely high frequencies, but also open the way for pulse shaping at arbitrary frequencies.
Raman coupling in atomic Bose-Einstein condensed with phase-locked laser system
Authors: Meng Zeng-Ming  , Huang Liang-Hui  , Peng Peng  , Chen Liang-Chao  , Fan Hao  , Wang Peng-Jun  , Zhang Jing  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China;,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

We present a simple, versatile and reliable phase-locked laser system. The system consists of an external cavity diode laser, Ti: Sapphire laser, fast detector, phase frequency detector (PFD) and loop filters. The beat signal of the laser is detected with a detector. From the PFD, we can obtain an error signal. The loop filter converts the output of the PFD into a control voltage and thus drives piezoelectric ceramic transducer (PZT) and current of diode laser. After locking, the bandwidth of the beat signal is reduced form MHz to Hz. So the line-width of the diode laser is almost close to that of Ti: Sapphire laser. The locking range is from sub-MHz to 10 GHz. So it is used for the ground hyperfine state transition of 87Rb. Through the use of the phase-locked loop system, we can drive the transition of 87Rb atoms between two ground hyperfine states F=2 and 1. The system is used to demonstrate Raman transition between two states through changing the detuning of the beat signal. From this, we can obtain Rabi frequency = 10 kHz. So, this system can be used to induce an effective vector gauge potential for 87Rb Bose-Einstein condensed and realize the spin-orbit coupling.
Spin-orbit interaction of light in metasuface
Authors: Yi Xu-Nong  , Li Ying  , Ling Xiao-Hui  , Zhang Zhi-You  , Fan Dian-Yuan  ,   SZU-NUS Collaborative Innovation Center for Optoelectronic Science and Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China;,   College of Physics and Electronic Information Engineering, Hubei Engineering University, Xiaogan 432000, China
Published: December 2020

Spin-orbit interaction of light in metasurface is investigated in this paper. We theoretically analyze the transfromation of circularly and linearly polarized light by metasurface with Jones matrix. The results indicate that the interaction of light with spatially inhomogeneous and anisotropic metasurface leads to a coupling of spin-orbital angular momentum. The nanostructrues of metasurfaces are arranged at a definite rate of rotation, which induces an additional space-variant geometrical phase (i.e., Pancharatnam-Berry phase). The Pancharatnam-Berry phase is dependent on the polarization handedness of the incident wave. This characteristic can result in spin-dependent split. A left/right-circular polarized beam is transfromed into a right/left-circular polarized vortex beam by the metasurfaces. In the convertion process, the sign of spin angular momentum of photons is inversed. At the same time, each photon can acquire orbital angular momentum from the inhomogeneous and anisotropic media. The case that a linearly polarized beam inputs the metasurfaces also is considered. A linearly polarized wave can be regarded as the linear superposition of left-circular and right-circular polarized wave. The two circularly plarized components are respectively converted into circularly polarized vortex beam with reverse polarization handedness. The coherent superposition of the two output components forms a cylindrical vector beam. Finally, we adopt the combination of a metasurface and spiral phase plate to verify the theoretical results. The vortex phase can be eliminated by the spiral phase plate when a left-circular polarized light is input, while topological charge of vortex phase will increase when a right-circular polarized light is input. For the case of inputting linearly polarized beam, one of the two outputing circularly polarized components can be eliminated by the helical phase through using the spiral phase plate, while the topological charge of another component increases. It results in the fact that the intensity pattern splits into two parts. The central part does not have helical phase, while the ambient ring-shaped intensity has helical phase. In order to judge the polarization handedness of output wave, the Stokes parameter S3 is measured by inserting a Glan laser polarizer and a quarter wave plate behind the spiral phase plate. The experimental results are in good agreement with theoretical analyses. These results are helpful for understanding the manipulation of light with metasurface.
Frequency doubling effect of off-axial vortex beam in the case of weak walk-off
Authors: Chen Shun-Yi  , Ding Pan-Feng  , Pu Ji-Xiong  ,   Fujian Provincial Key Laboratory of Light Propagation and Transform, College of Information Science and Engineering, Huaqiao University, Xiamen 361021, China
Published: December 2020

By using the truncated equations of the coupled wave, the expressions of the normalized electric field and the normalized intensity of the frequency doubling beam are derived in the cases with and without walk-off effect, caused by the off-axial vortex beam propagating through the negative uniaxial crystal. The influences of the off-axial magnitude, the weak walk-off angle and the crystal length on the output frequency doubling beam are mainly investigated. It is shown that while the walk-off angle is neglected, the two dark cores of the frequency doubling beam coincide with the point (0, 0); but while the weak walk-off angle is taken into account, the dark cores move along the direction where the walk-off effect is generated, and the two coincident dark cores separate in the direction perpendicular to the direction where the walk-off effect is generated on the cross-section. Especially, the distance the dark cores move is related to the off-axial magnitude, the weak walk-off angle and the crystal length. But the separation distance of the two dark cores is only related to the weak walk-off angle and the crystal length. The exact details show that when the off-axial magnitude increases, the distance the dark cores move along the direction where the off-axial magnitude is generated increases at the same time, but the separation distance has no connection with he off-axial magnitude. When the weak walk-off angle and the crystal length increase, the distance the dark cores move and the separation distance of the two dark cores increase. In addition, it can be found by comparison that when the crystal length reduces, the distance the dark cores move will decrease. And also the separation distance of the two dark cores will reduce, which is induced by the walk-off effect and the off-axial magnitude. Therefore, by reducing the crystal length, the output frequency doubling beam can be modified to a certain degree.
Formation mechanism of concentric-ring pattern in dielectric barrier discharge
Authors: Liu Wei-Bo  , Dong Li-Fang  ,   College of Physics Science and Technology, Hebei University, Baoding 071002, China;,   Aviation Engineering Institute, Binzhou University, Binzhou 256603, China
Published: December 2020

Concentric-ring pattern is observed in an Ar/air mixture dielectric barrier discharge. The discharge images within one half voltage circle are taken by an intensified-charge coupled device camera, indicating that the discharge filaments are the basic units of the concentric-ring pattern. By comparing the six instantaneous images corresponding to three successive positive and negative half voltages, it is proved that the concentric-ring pattern seen with naked eyes is formed by the numerous discharge filaments located at different positions during successive acquisition intervals. With applied voltage increasing, concentric-ring pattern can transform into spiral, and then into concentric-ring pattern again. By analyzing the features of formation and transformation of these two patterns, it is inferred that the two patterns have similar dynamic mechanisms. Discharge powers of concentric-ring pattern and spiral are calculated respectively, and the results show that the power increases linearly approximately with applied voltage increasing. The correlation coefficients of concentric-ring pattern are compared with those of spiral, and the results show that the correlation coefficient of concentric-ring pattern is relatively low and irregular, while the correlation coefficient of spiral is relatively high and has an oscillatory characteristic.
Effects of doping F and transition metal on crystal structure and properties of ZnO thin film
Authors: Zhou Pan-Fan  , Yuan Huan  , Xu Xiao-Nan  , Lu Yi-Hong  , Xu Ming  ,   Key Laboratory of Information Materials of Sichuan Province, College of Electrical and Information Engineering Southwest University for Nationalities, Chengdu 610041, China
Published: December 2020

Transition metal (TM=Cu, Ni, Mn, Fe and Co)-doped ZnO:F thin films are deposited on glass substrates by a sol-gel method through using ethanol as solvent. All the samples are checked by using X-ray diffraction (XRD), atomic force microscope (AFM), X-ray photoelectron spectroscope (XPS), photoluminescence, UV spectrophotometer, and vibrating sample magnetometer. The XRD reveals that Cu, Ni, Mn, Fe and Co occupy the Zn sites successfully without changing the wurtzite structure of ZnO at moderate doping concentration, and no evidence of any secondary phases is found. The AFM measurements show that the average values of crystallite surface roughness of the samples are in a range from about 2 to 12.7 nm. The surface of ZnO:F thin film becomes less compact and uniform when ZnO:F thin film is doped with TM ions. The TM ions are indeed substituted at the Zn2+ site into the ZnO lattice as shown in the results obtained by XPS and XRD. Further studies show that most of the ZnO films exhibit preferred (002) orientations, while the best c-axis orientation occurs in Zn0.93Co0.05F0.02O film. However, the crystalline quality and preferential orientation of ZnO film become poor in Zn0.93Mn0.05F0.02O. The optical bandgaps of all the ZnO:F films decrease after doping TM. All the samples show high transmittance values in the visible region. Strong ultraviolet emission and weak blue emission are observed in the photoluminescence spectra measured at room temperature for all the samples. The Zn0.93Mn0.05F0.02O film shows the weakest ultraviolet emission peak and strongest blue emission peak, corresponding to the strongest ferromagnetism; while for the Zn0.96Cu0.02F0.02O film, the strongest ultraviolet emission peak and weakest blue emission peak are observed, accompanied by the weakest ferromagnetism. To determine the optical bandgap (Eg) of TM-doped ZnO:F thin film, we plot the curve of (α hv)2 versus photon energy (hv). It is found that the Eg decreases from 3.16 eV to 3.01 eV with the TM ions doping. We show the variations of saturation magnetization with the Vm O concentration for TM-doped ZnO:F thin films with the different transition metal ions. In the case of Cu-doped ZnO:F thin films, the ZnO sample shows that a weaker magnetism. ZnMnFO film exhibits well-defined hysteresis with a coercive field of 7.28×10-5 emu/g. Further studies reveal that these interesting magnetic properties are correlated with the defect-related model for ferromagnetism. Our results will expand the applications of ZnO:F thin films in visible light emitting diode, photovoltaic devices, photoelectrochromic devices, etc. Meanwhile, extreme cares should be taken to control the codoping of ZnO:F thin films for tuning the magnetization.
Photoluminescence properties and energy transfer of SrZn2(PO4)2:Sn2+, Mn2+ phosphor
Authors: Xiong Xiao-Bo  , Liu Wan-Li  , Yuan Xi-Ming  , Liu Jin-Cun  , Song Jiang-Qi  , Liang Yu-Jun  ,   Engineering Research Center of Nano-Geomaterials of Ministry of Education, Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074, China;,   Hubei Key Laboratory of Forensic Science, Hubei University of Police, Wuhan 430034, China;,   Agricultural Technology Extension Center, Wuhan Agriculture Committee, Wuhan 430016, China
Published: December 2020

In this paper, SrZn2(PO4)2:Sn2+ (SZ2P:Sn2+), SrZn2(PO4)2:Mn2+ (SZ2P:Mn2+), SrZn2(PO4)2:Sn2+, and Mn2+ (SZ2P:Sn2+, Mn2+) phosphors are prepared by high temperature solid state reaction. The X-ray diffraction patterns and photoluminescence spectra of the phosphors are investigated in detail. The emission spectrum of SZ2P:Sn2+ is a wide band peaking at 461 nm due to 3P1 →1S0 transition of Sn2+, and overlaps effectively with the excitation spectrum of SZ2P:Mn2+, which shows that the absorption of SrZn2(PO4)2 host, and a series of peaks at 352, 373, 419, 431, and 466 nm, corresponding to 6A1(6S)→4E(4D), 6A1(6S)→4T2(4D), 6A1(6S)→[4A1(4G), 4E(4G)], 6A1(6S)→4T2(4G) and 6A1(6S) →4T1(4G) transition, respectively, are assigned to a wide band ranging from 200 nm to 300 nm. Therefore, luminescence intensity of Mn2+ is enhanced significantly by co-doping Sn2+ in SrZn2(PO4)2 host. According to the Dexter's energy transfer formula of multipolar interaction and Reisfeld's approximation, it is demonstrated that the energy transfer between Sn2+ and Mn2+ is due to the quadripole-quadripole interaction of the resonance transfer. The critical distance (Rc) of energy transfer is calculated to be about 1.78 nm. The tunable color is achieved by changing the doping concentrations of Sn2+ and Mn2+. The SZ2P:Sn2+, Mn2+ phosphor could emit strong blue-white light under the excitation of 254 nm ultraviolet (UV) light. The result shows that the SZ2P:Sn2+, Mn2+ is a promising phosphor for compact fluorescent lamp, and with the development of short wave UV semiconductor chip, this phosphor has potential applications in white light emitting diodes in the near future.
Electronic structure and transport properties of cathode material Li2FeSiO4 for lithium-ion battery
Authors: Ma Hao  , Liu Lei  , Lu Xue-Sen  , Liu Su-Ping  , Shi Jian-Ying  ,   College of Electronic and Information Engineering, Hebei University, Baoding 071002, China
Published: December 2020

The electronic structure and properties of silicate polyanion Li2FeSiO4 in the orthorhombic crystal structure with Pmn21 symmetry and the relevant delithiated system LiFeSiO4 are investigated by the first principles method in the framework of the density functional theory with the generalized gradient approximation. The WIEN2k software is used for the self-consistent calculation of the crystal structure to obtain the energy band, density of states, and charge density. Boltzmann transport theory is further used to obtain the values of ratio σ /τ of Li2FeSiO4 and LiFeSiO4 based on the results of the first-principles calculations. The structural stability of Li2FeSiO4 system is demonstrated by calculating and analyzing the lattice parameter and the bond length. The results indicate that Li2FeSiO4 crystal has only 2.7% volume variation in the lithiation/delithiation process and the change of the Si–O bond length is very small, which suggests that the bonding nature between silicon and oxygen atoms remains unchanged. The results of charge density analysis show that the structural stability of Li2FeSiO4 crystal during lithium deintercalation is actually a consequence of a strong covalent interaction between silicon and oxygen atoms. An analysis of density of states shows that the density in the high-energy range near the Fermi level mainly comes from Fe-3d electron states. The Fermi level moves towards the lower energy end during the deintercalation of lithium ions and the electronic conductivity decreases with the decreasing of lithium ions, indicating that the conductive properties of Li2FeSiO4 are better than those of LiFeSiO4. It suggests that Li2FeSiO4 could be modified by doping atoms to affect the electrons in orbital Fe-3d and enhance conductive properties in future research. The calculations of transport properties show that the electronic conductivity of Li2FeSiO4 is not sensitive to temperature in a range from 300 to 800 K, and Li2FeSiO4 material is a potential candidate for heat-resisting cathode material. It also indicates that Li2FeSiO4 owns a better electronic conductivity than LiFeSiO4, which is consistent with the analyses of band structure and density of states. This research reveals the microscopic mechanism such as electronic structure and electronic transport properties of Li2FeSiO4 crystal in theoretical calculations, and provides a theoretical basis for the further improvement of electrochemical properties of lithium-ion battery.
Damage-repair model for mutagenic effects of plant induced by ionizing radiation
Authors: Li Duo-Fang  , Cao Tian-Guang  , Geng Jin-Peng  , Zhan Yong  ,   Institute of Biophysics, Hebei University of Technology, Tianjin 300401, China;,   College of Electrical Engineering, Hebei University of Technology, Tianjin 300401, China
Published: December 2020

The plant mutation effects induced by ionizing radiation involve a rather complex process which is composed of physical, chemical, biochemical and biological stages. Nowadays, although ionizing radiation has been widely used in plant mutation breeding, the theoretical explanations for the mechanism of the ionizing radiation caused plant mutation effects are insufficient. Especially, a saddle shape relationship between the plant survival rate and radiation dose is found in the mutagenis effect of ionizing radiation on plants. The underlying mechanism of the saddle shape relationship remains unclear and challenges to all extant models.To explain this relationship, a damage-repair model for the plant mutation effects induced by ionizing radiation is proposed in the present work. Our model is based on the rate theory of ionizing radiation in which the cell damage and repair are taken into account simultaneously together with the micro-and macro-biological mutation effects of plant caused by ionizing radiation. The states of the radiated plant individuals are grouped into three categories: normal, damaged and lethal categories in our model. The evolution dynamics of the relative concentrations of the three categories are determined by a set of coupled equations which are mathematically the same as the Crow-Kimura equations in species evolution theories. With the numerical solution of our model in its steady state, the relative steady state concentration distributions of different categories of the radiated plants with increasing radiation dose are obtained. It is shown that without the plant repair effect, the relationship between the plant survival rate and radiation dose appears to be a conventional shoulder type one. With the plant repair effect, our model gives a saddle shape survival-dose relationship which has been observed commonly in the experiments on the radiated plants by ionizing radiation. To further test the model, the experimental data on the inbred lines of maizes radiated by heavy ion 7Li are used to determine the parameters of the model. It is shown that the theoretical results are basically consistent with the experimental ones. In addition, the mutation characteristic of the survival plants also appears to be a saddle effect-dose relationship, for which the theoretical model could also give a reasonable explanation. Our damage-repair model explains the saddle shape relationship between the plant survival rate and radiation dose, which indeed illuminates its power. And it provides a theoretical basis and reference for studying the biological effect mechanism of plants induced by ionizing radiation and conducting ionizing radiation plant breeding.
Chaos and fractal properties of solar activity phenomena at the high and low latitudes
Authors: Zhou Shuang  , Feng Yong  , Wu Wen-Yuan  ,   Chongqing Key Laboratory of Automated Reasoning and Cognition, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The solar magnetic activity is produced by a complex dynamo mechanism and exhibits nonlinear dissipation behavior in nature. The chaotic and fractal properties of solar activity phenomena are of great importance for understanding the nonlinear dynamo actions, especially nonlinear dynamo models. To study the chaotic and fractal properties of solar activity phenomena at the high-and low-latitudes, the polar faculae and sunspot numbers in the time interval from 1952 February to 1998 June are used to investigate their nonlinear dynamical behavior by the recurrence analysis method and Grassberger-Procaccia (G-P) algorithm. Firstly, the monthly average value of both polar faculae and sunspot numbers are smoothed to filter the noisy signal by the 13-point smoothing method. This procedure can keep the original dynamical information. Secondly, the correlation coefficient of these two solar activity indicators is analyzed, and the analysis results indicate that there is a negative correlation between polar faculae and sunspot numbers. To obtain more accurate results, the recurrence quantification analysis (RQA) is used to obtain the average value of the rate of DET by selecting four groups of different parameters. And then, we use the G-P algorithm to draw the correlation integral curve graphs and to obtain the correlation dimension of polar faculae and the sunspot numbers. Finally, the analysis results given by RQA and G-P algorithm are analyzed and compared by advanced statistical method. The main conclusions of this paper are as follows. 1) From a statistical point of view, the chaotic and fractal properties of high-and low-latitudes solar activity are different between in the northern hemisphere and in the southern hemisphere, owing to the fact that the temporal variation of solar activity is closely related to the magnetic field evolution. This result is in agreement with the previous results given by the polar faculae. It should be pointed out that this result is not the main goal of this article, we only reinforce this conclusion by the recurrence analysis and G-P algorithm. 2) The chaotic behaviors of solar magnetic activity at high latitude are stronger than at low latitude. Furthermore, the high-latitude solar activity in the northern hemisphere has the most complex fractal structure. Based on the solar nonlinear dynamo theory, the polar magnetic fields are the seed fields of the solar activity. That is to say, the physical meaning of polar faculae is more important than sunspot numbers. We think that our results are useful for understanding the physical nature of the systematic regularity of solar activity phenomena.
Dynamics of nonlocality in an equidistance cavity coupled by fibers
Authors: Lu Dao-Ming  ,   College of Mechanic and Electronic Engineering, Wuyi University, Wuyishan 354300, China
Published: December 2020

Entanglement and nonlocality, two most striking features of quantum mechanics, are fundamental resources for quantum information processing. They play an important role in quantum information processing. Therefore, studying the dynamics of quantum nonlocality and entanglement is of importance for both fundamental research and practical applications. In this paper we consider the case that three identical two-level atoms are trapped respectively in the three separated equidistance single-mode cavities, which are placed at the vertices of an equilateral triangle and are coupled by three fibers. Each atom resonantly interacts with cavity via a one-photon hopping. The evolution of the state vector of the system is given by solving the schrodinger equation when the total excitation number of the system equals one. The dynamics of nonlocality in the system is investigated via Mermin-Ardehali-Belinksii-Klyshko (MABK) inequality. By the numerical calculations, the MABK inequality is studied when the initial state vector of three atoms is W state or the initial state vector of three cavities is also W state. The influence of cavity-fiber coupling constant on the MABK inequality is discussed. The evolution curves of the MABK parameters Ba and Bc are plotted. The curves show that Ba and Bc both display periodic oscillations, and their oscillation frequencies all increase with the increase of cavity-fiber coupling constant. Ba and Bc are both larger than 1 when the scaling time gt takes a certain value. The results show that the quantum state of three atoms or that of three cavities displays nonlocality. On the other hand, the nonlocality of three-atom quantum state is strengthened with the increase of cavity-fiber coupling constant.
Analysis on performance optimization in measurement-device-independent quantum key distribution using weak coherent states
Authors: Wu Cheng-Feng  , Du Ya-Nan  , Wang Jin-Dong  , Wei Zheng-Jun  , Qin Xiao-Juan  , Zhao Feng  , Zhang Zhi-Ming  ,   Laboratory of Nanophotonic Functional Materials and Devices (SIPSE), and Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006, China;,   Engineering Technology Department, Guangdong Polytechnic Institute, Guangzhou 510091, China;,   School of Physics and Telecommunication Engineering, Shaanxi University of Technology, Hanzhong 723000, China
Published: December 2020

Measurement-device-independent quantum key distribution (MDI-QKD) is immune to all detection side-channel attacks, thus when combined with the decoy-state method, it can avoid the actual security loophole caused by quasisingle- photon source simultaneously. A practical weak coherent source is used as a quasi-single-photon source in the current MDI-QKD experiments; it may contain percentage of vacuum-and multi-photon pulses. Moreover, in order to study how the performance of the threshold detector affects the quantum bit error rate (QBER), we introduce the quality factor (the ratio of the dark count rate to the detection efficiency) of the threshold detector. Here, through taking into account the weak coherent source, the quality factor of the threshold detector and the reflectivity of beam splitter, we deduce and evaluate the gain, the probability for successful Bell measurement, incorrect Bell measurement when Alice and Bob send pulses with different photon numbers which have a high probability to appear in weak coherent source, and then we obtain QBER in combination with the probabilities of different photon number states, besides, we also do some simulations. The simulations show how QBER varies with the reflectivity of beam splitter and the quality factor of the threshold detector when the average photon numbers per pulse from Alice and Bob are symmetric. Furthermore, the simulations show how QBER varies with the average photon number per pulse from Alice when average photon number per pulse from Bob is 0.1. Result shows that QBER is affected by the reflectivity of beam splitter, but QBER cannot reach the minimum value in Z basis encoding scheme when the average photon numbers per pulse from Alice and Bob are both 0.1 and the reflectivity of beam splitter is 0.5, which is different from X basis encoding and phase encoding. In addition, QBER increases with the increase of the quality factor of the threshold detector, which means that better performance of the threshold detector will reduce QBER. We show that QBER in Z basis encoding reaches the minimum value when reflectivity of beam splitter is 0.5 and there is large difference between in average photon number per pulse between two sides. In conclusion, for QBER, the effect from the reflectivity of beam splitter is equal to average photon numbers from the two arms only in X basis encoding and phase encoding. Our work will provide a reference for setting up a system with better performance.
Broadband circularly polarized high-gain antenna design based on single-layer reflecting metasurface
Authors: Li Tang-Jing  , Liang Jian-Gang  , Li Hai-Peng  ,   Air and Missile Defense College, Air Force Engineering University, Xi’an 710051, China
Published: December 2020

According to the Pancharatnam-Berry phase principle, a single-layer reflecting element is proposed for steering the phase of the electromagnetic wave. The structure of the element is composed of metabolic cross wire and copper ground sheet, which are separated by an FR4 dielectric substrate with a thickness of 3 mm. When the incident wave is circularly polarized, different rotary angles of the element are used to achieve the co-polarization reflection with high efficiency in a broadband of 11-16 GHz. In the design of the focusing metasurface, the phase compensation for forming a constant aperture phase is provided by the individual reflected element with a different rotated angle. Remarkably, the size of the element is only 5 mm (0.230), and then it can be more accurate to control the phase of the array. The focusing metasurface is composed of 1515 elements with a focal length of 30 mm at 13.5 GHz. The designed sample is simulated in CST Microwave Studio. The results show that the incident circularly polarized plane wave is well transformed into a spherical wave in the band from 11 to 16 GHz, and the focal length is around 30 mm. For further application, a unidirectional Archimedean spiral antenna is located at the focal point of the metasurface. According to the reversibility principle of electromagnetic wave propagation, the spherical wave radiated by the feed antenna is converted into a plane wave by the reflecting metasurface, so that the antenna gain is remarkably enhanced. Through adjusting the distance between the feed antenna and the focusing metasurface, we find that 28 mm is the best distance. Finally, the feed antenna and the metasurface are fabricated, assembled and measured. Numerical and experimental results are in good agreement with each other, showing that the -1 dB gain bandwidth of the high-gain antenna is 12.5-16 GHz, and in this band the peak gains are all over 19 dBc and the axial ratio is better than 3 dB. In addition, the aperture efficiencies are more than 50% in the band from 12 to 15.5 GHz, especially the efficiency at 13 GHz reaches a highest value of 61%. The good performances indicate that the proposed high-gain antenna has a highly promising application in portable communication systems.
Optical precursors via spontaneously generated coherence
Authors: Ba Nuo  , Wang Lei  , Wang Hai-Hua  , Li Dong-Fei  , Wang Dan  , Yan Li-Yun  ,   Institute of Physics, Jilin Normal University, Siping 136000, China;,   Key Laboratory of Coherence Light, Atomic and Molecular Spectroscopy of the Ministry of Education, College of Physics, Jilin University, Changchun 130012, China
Published: December 2020

Optical precursors were first studied by Sommerfield and Brillouin in 1914 to resolve the apparent contradictions between fast light propagation and the theory of relativity. They showed theoretically that the front edge of a step-modulated pulse does not interact with the medium and always travels at c because the dispersive material has a finite response time to the optical pulse. The past experimental studies of precursors in classical pulse propagation were always focused on an opaque medium with single or multiple Lorentz absorption lines. In these cases, the precursor signal cannot be separated from the main pulse or otherwise the main field is absorbed. However, the electromagnetically induced transparency (EIT) technique was successfully used to separate precursors from the main pulse due to the slow-light effect in cold atoms. The EIT refers to the absorption suppression or elimination of a probe field through atomic coherence in a certain medium dressed by a strong coupling field. In this paper, a four-level double-lambda atomic system with two upper states coupled to the excited state is explored to separate optical precursors from a square-modulated laser pulse with the effect of spontaneously generated coherence (SGC). The SGC effect occurs in the process of spontaneous emission, in which the atom decays from closely placed upper levels to a single ground level. The quantum interference between the decay channels takes place, which leads to decay induced transparency, thus enhancing the Kerr nonlinearity and amplification without inversion. With the assistance of spontaneously generated coherence, an EIT window appears with steep normal dispersion when the trigger field is far from resonance. Then we can obtain the optical precursors which are separated from the main pulse due to the slow-light effects in the EIT window. In the absence of SGC, the main pulse is absorbed by an opaque medium with Lorentz absorptive lines, so the slow-light effect could not take place. In addition, we obtain the stacked optical precursors with the input probe field amplitude or phase modulated by designing a series of square pulses. For the amplitude modulation case, the peak power reaches about 4.5 times that of the input pulse. With the phase modulation we obtain a transient pulse with a peak power of 14 times that of the input, as a result of constructive interference between the stacked precursors and main field. We expect these findings to be instructive in devising optical devices for optical communication, detection and medical imaging among other applications.
Beam quality in spectral beam combination based on multi-layer dielectric grating
Authors: Jiang Man  , Ma Peng-Fei  , Zhou Pu  , Wang Xiao-Lin  ,   College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Owing to damage, thermal issues, and nonlinear optical effects, the output power of fiber laser has been proven to be limited. Beam combining techniques are the attractive solutions in order to achieve high-power high-brightness fiber laser output. Designing such a high-power laser system relies on coherent and incoherent combination of radiation from multiple laser channels into a single beam with enhanced brightness. Spectral beam combination is a promising alternative way that allows each array to be overlapped in near-and far-field without spatial interference, thus relaxing the requirements for linewidth controlling and phase locking of individual array and practically allowing power and brightness to be scaled with the potential to combine a large number of channels. Spectral beam combination implementations can be divided into two subsets: serial and parallel, based on the combining elements. For scaling high power, we pursue spectral beam combining with parallel subsets as an alternative to other beam combination implementation. In the spectral beam combining system based on multi-layer dielectric grating, the combined beam suffers the degradation in beam quality, which is caused by the optical dispersion, and also by the random error due to the misalignment of arrays or the thermal-optic effect of grating in the experimental system. In this paper, we strictly derive the equation of M2 variation caused by the optical dispersion in both single-grating structure and dual-grating structure. And also, we discuss how the laser linewidth, beam size, spectral separation of two adjacent channels, distance between two adjacent channels and the period of grating influence the desired beam quality in detail, separately, in the single-grating structure and the dual-grating structure. The results show that with the value of M2 fixed, the finite beam size gives rise to a laser bandwidth decreasing in single-grating structure combination, whereas the beam size induces a laser bandwidth to increase in dual-grating structure combination. If M2 1.2, the laser bandwidth of dual-grating system can be over several sub-nanometers, rather than several tens of pm as in the single grating design.
Theoretical study of the temperature distribution in high power gain fiber of gradient doping
Authors: Zhou Zi-Chao  , Wang Xiao-Lin  , Tao Ru-Mao  , Zhang Han-Wei  , Su Rong-Tao  , Zhou Pu  , Xu Xiao-Jun  ,   College of Optoelectric Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Thermal effect in the gain fiber is one of the main factors which restrict the power improvement of high power fiber amplifiers. Previous studies have shown that the temperature distribution is closely related to the doping concentration along the gain fiber. In order to reduce the maximum temperature of the gain fiber, we propose to use doping concentration varying along the gain fiber as a method to disperse the thermal effect of the fiber laser and improve the laser output power. Based on the rate equation model and thermal conduction model, the thermal distributions and output powers of several different gradient doping gain fibers are simulated in the cases where the output powers are approximately the same. Our study shows that compared with the conventional constant doping gain fiber, linear doping of the rare earth ion along the gain fiber can reduce the maximum temperature of the gain fiber as well as the temperature of the fusion point greatly, thus improving the stabilities of the fusion point and the fiber laser amplifier. In the case of cosinoidal doping, the gain fiber can not only reduce the temperature of the fusion point but also make the temperature have a periodic distribution along the gain fiber, which can suppress the stimulated Brillouin scattering effect effectively. The exponential doping of the gain fiber can also reduce the maximum temperature and the temperature of the fusion point, which is beneficial to the further scaling of the fiber laser output power. At the same time, it can make the gain of the signal light have a uniform distribution along the gain fiber, which suppresses the mode instability effect and improves the output beam quality of the fiber laser. These conclusions also hold true when the pump power changes. Therefore, the gradient doping of the gain fiber proposed in this paper can optimize the temperature distribution along the fiber and improve the stability of the fusion point. Besides, it can improve the beam quality of the output laser and suppress the nonlinear effect and mode instability effect. The results indicate that the gradient doping of the gain fiber is an effective and feasible way to improve the output power of fiber amplifier. Last but not the least, it is possible to produce the gradient doping gain fiber by the laser heated pedestal growth method and the direct nanoparticle deposition technique. The investigation can present a reference for designing the gain fiber in high-power fiber laser systems.