bluuebunny/crossref_metadata_2025 huggingface dataset:
K-shell X-ray emission from high energy pulsed C6+ ion beam impacting on Ni target
Authors: Mei Ce-Xiang  , Zhang Xiao-An  , Zhou Xian-Ming  , Zhao Yong-Tao  , Ren Jie-Ru  , Wang Xing  , Lei Yu  , Sun Yuan-Bo  , Cheng Rei  , Xu Ge  , Zeng Li-Xia  ,   Ion beam & Optical Physical Joint Laboratory of Xianyang Normal University and Institute of Modern Physics, Chinese Academy of Sciences, Xianyang 712000, China;,   School of Science, Xi'an Jiaotong University, Xi'an 710049, China;,   Institute of Modern Physics, Chinese Academy of Science, Lanzhou 730000, China
Published: December 2020

Accurate measurement of the ionization cross section of the target atom induced by collision between ions and atoms is of great significance for studying the atomic shell process and establishing a suitable theoretical model. The experimental data and the theoretical models mostly concentrate on the cases in the low energy region at present. Only a few experimental data of high energy region are reported due to the limitation of experimental conditions. Which theory is more suitable to describe the ionization cross section of the inner shell of the target atom caused by the high energy heavy ions, is necessarily studied experimentally. The C6+ ions provided by the Heavy Ion Research Facility in Lanzhou Electron Cooling Storage Ring, are used to bombard the Ni target, in which the K-shell X-ray of Ni is measured. The incident energies of C6+ ions are 165, 300, 350 and 430 MeV/u respectively. Through analyzing the intensity ratio of K/K X-ray of Ni, it is found that the influence of incident energy on the intensity ratio of K/K X-ray is not obvious. The intensity ratios of this experiment are greater than the experimental values of incident proton and the calculated values based on the Hartree-Slater theory, which may be caused by the multiple-ionization of the L shell. The production cross sections of Ni K-shell X-ray are calculated by the binary encounter approximation (BEA) model, the plane wave Born approximation (PWBA) model and the energy-loss coulomb-repulsion perturbed-stationary-state relativistic (ECPSSR) theory respectively, which are compared with the experimental results in this paper. It is found that the experimental cross section increases with the increasing incident energy, which is consistent with the trend of BEA model estimation, but the experimental value is obviously lower than the theoretical value. We think that BEA model needs to be modified when describing the ionization process in the high energy region.
Design of accelerating beams based on caustic method
Authors: Wen Yuan-Hui  , Chen Yu-Jie  , Yu Si-Yuan  ,   State Key Laboratory of Optoelectronic Materials and Technologies, School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou 510275, China;,   Photonics Group, Merchant Venturers School of Engineering, University of Bristol, Bristol BS8 1UB, United Kingdom
Published: December 2020

Self-accelerating beam is a kind of light beam capable of self-bending in free space without any external potential, of which a typical one is the well-known Airy beam. Such a beam has gained great attention for its extraordinary properties, including nondiffracting, self-accelerating and self-healing, which may have versatile applications in the delivery and guiding of energy, information and objects using light, such as particle manipulation, micro-machining, optical routing, super-resolution imaging, etc. However, since Airy beam can only propagate along parabolic trajectory, which reduces the flexibility in practical applications, thus how to design accelerating beams propagating along arbitrary trajectory is still a crucial problem in this area. One scheme is to keep on finding other analytical solutions of the wave equation besides Airy beam, such as semi-Bessel accelerating beams, Mathius beams, and Weber beams, moving along circular, elliptical, or parabolic trajectories, but it becomes increasingly difficult to find out any more solutions. A more effective solution to this problem is based on the caustic method, which associates the predesigned trajectory with an optical caustics and then obtains the necessary initial field distribution by performing a light-ray analysis of the caustics. This method has been implemented in real space and Fourier space based on Fresnel diffraction integral and angular-spectrum integral, respectively. It has been found recently that they can be unified by constructing Wigner distribution function in phase space. Based on the caustic method, accelerating beams were constructed to propagate along arbitrary convex trajectories in two-dimensional space at first. With continuous development of this method, the types of accelerating beams available have been extending from convex trajectories to nonconvex trajectories, from two-dimensional trajectories to three-dimensional trajectories, and from one main lobe to multiple main lobes, which opens up more possibilities for emerging applications based on accelerating beams. In future, previous researches and applications based on Airy beams will certainly be generalized to all these new types of accelerating beams, and owing to the great flexibility in designing accelerating beams, more application scenarios may emerge in this process with huge development potential. Thus in this paper, we review the principle and progress of the caustic method in designing accelerating beams.
Tunable unidirectional surface plasmon polariton coupler utilizing graphene-based asymmetric nanoantenna pairs
Authors: Deng Hong-Mei  , Huang Lei  , Li Jing  , Lu Ye  , Li Chuan-Qi  ,   Lab of Optoelectronics and Optical Communications, Department of Electronic Engineering, Guangxi Normal University, Guilin 541004, China
Published: December 2020

Surface plasmon polaritons (SPPs), the electromagnetic waves traveling along metal-dielectric or metal-air interface, which originate from the interactions between light and collective electron oscillations on metal surface, have received considerable attention for their promising applications in the future optical field, such as image, breaking diffraction limit, subwavelength-optics microscopy, lithography, etc. However, one of the fundamental issues in plasmonics is how to actively manipulate the propagation direction of SPPs. In this paper, we propose and numerically investigate a graphene-based unidirectional SPP coupler, which is composed of asymmetric plasmonic nanoantenna pairs with a graphene sheet separated by a SiO2 spacer from the gold substrate. The device geometry facilitates the simultaneous excitation of two localized surface plasmon resonances in the entire structure, and consequently, the asymmetric nanoantenna pairs can be considered as being composed of two oscillating magnetic dipoles or as two SPP sources. Because the resonance of the plasmonic antenna pairs depends on the bias voltage applied across graphene sheet and back-gated Au, the phase difference between radiated electromagnetic waves induced by the antenna can be tuned through varying the Fermi level of graphene. Here, approximately a n/2 phase difference between radiated electromagnetic (EM) waves can be acquired at EF 0.81 eV, which indicates that the radiated EM waves can interfere constructively along the direction of the x-axis while interfere destructively along the opposite direction. This directional propagation of EM wave leads to the unidirectional propagation of SPPs. Furthermore, electric field distribution of the cavity demonstrates that the tunability of plasmonic antenna is proportional to the electric field intensity in the vicinity of the graphene region. For our designed structure, the left cavity can provide a significantly larger tunable range than the right one. With this result, we can quantitatively analyze the tuning behavior of graphene-loaded plasmonic antenna based on equivalent circuit model, and draw the conclusions that the unidirectional SPP propagation effect originates from the interference mechanism. In addition, compared with the device reported previously, our proposed device possesses a huge extinction ratio (2600) and more broadband tunable wavelength range (6.3-7.5 m). In addition, it is possible to make up for the deficiencies of current nanofabrication technologies by utilizing its actively controlled capability. All the above results indicate that the proposed active device promises to realize a compactable, tunable, and broadband terahertz plasmonic light source. It will play an important role in future photonic integrations and optoelectronics.
Polarization control methods in structured illumination microscopy
Authors: Zhao Tian-Yu  , Zhou Xing  , Dan Dan  , Qian Jia  , Wang Zhao-Jun  , Lei Ming  , Yao Bao-Li  ,   State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710119, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Structured illumination microscopy (SIM) is one of the most promising super-resolution techniques, owing to its advantages of fast imaging speed and weak photo bleaching. The quality of the SIM image is greatly dependent on the contrast of the sinusoidal fringe illumination patterns. Low fringe contrast illumination will seriously affect the super-resolution result and lead to additional artifacts. The generation of fringe patterns with high contrast is the key requirement in hardware for the SIM technique. This can be done by the interference of two laser beams diffracted from the phase gratings addressed on a spatial light modulator. Meanwhile, for maximal interference contrast, precise polarization control to maintain s-polarization for different fringe orientations is critical. In this paper, we review several typical polarization control methods in SIM, and propose a new method by using a zero-order vortex half-wave retarder (VHR). Compared with the other methods, the presented VHR-based polarization control method is very efficient in terms of simple system configuration, ease of use, and high light energy utilization efficiency near to 100%.
Modelling and simulation of DNA hydrogel with a coarse-grained model
Authors: Wang Xi  , Li Ming  , Ye Fang-Fu  , Zhou Xin  ,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Recently supramolecular hydrogels have become a hot research point in the field of hydrogels. As promising building block for supramolecular hydrogel, DNA has received considerable attention for its designability and excellent mechanical strength, and DNA hydrogel has shown great potential applications in biological and medical areas. To better understand the structure and property of DNA hydrogel, computational simulation is a very powerful tool to complement experimental study. However, owing to the large size of DNA hydrogel system and long time scale of self-assembly process, it is practically unachievable to simulate the system directly at an all-atom level. Coarse-grained simulations should be developed. In this article, we propose a highly coarse-grained model to investigate the mesoscopic structure of well-designed pure DNA hydrogel constructed by Y-shape DNA blocks and linear DNA linkers with sticky ends. In this model, we ignore almost all the atomic details of the building blocks and only give a coarse-grained description of their shapes, and carefully design the Lennard-Jones (LJ) interaction between coarse-grained particles in order to take into account the fact that any of the three arms of a Y block can only interact with a single linker (i.e., the bond is saturated). To design a suitable interaction, here we use a combination of LJ repulsive potential between like particles and LJ attracting potential between unlike particles. Our simulation results show that the hydrogel has two states, namely, homogeneous liquid-like state at high temperature and spongy gel-like state at low temperature. State of this system is related to the degree of cross-linking which is described by average cross-linking pair number per Y-scaffold here. We find that the pair number per Y-scaffold is positively correlated with the concentration of hydrogel blocks, which is consistent with experimental results. We also investigate the distribution of local structure by using voronoi cells, then predict the hole size of the hydrogel network. By the micro-rheology method, we then determine more precisely the value of the transition temperature to be 0.06/kB-0.10/kB, which is also consistent with experimental result. The quantitative relation between transition temperature and binding energy of sticky ends can hopefully provide guidance for the optimal design of DNA hydrogels. The qualitative and even semi-quantitative agreement between our simulation results and experimental results indicates that our coarse-grained model is a suitable and effective one for this pure DNA hydrogel system. The basic ideas of our model can be generalized to more complicated DNA hydrogel systems.
Design of varying f/number of cooled infrared detectors based on spherical reflecting warm shield
Authors: Chang Song-Tao  , Tian Qi-Jie  , He Feng-Yun  , Yu Yi  , Li Zhou  ,   Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China;,   University of Chinese Academy of Sciences, Beijing 100039, China
Published: December 2020

As is well known, the f/number of a cooled infrared detector is determined by the aperture and position of the internal cold shield. Moreover, the f/number can be changed by inserting a warm shield in front of the detector. In order to reduce the stray radiation introduced by an ordinary planar warm shield, we propose a method of varying f/number of the infrared detector based on a well-designed spherical reflecting warm shield in this paper. First, an infrared radiation model is established in order to analyze the influence of the stray radiation introduced by the ordinary planar warm shield. Then the design principle of the spherical reflecting warm shield is put forward. By changing the surface shape and emission characteristics, the stray radiation introduced by the ordinary planar warm shield can be obviously reduced. Hence it is beneficial to maintain the performance of the detector effectively while the f/number is changed. To validate the proposed method, a spherical reflecting warm shield and an ordinary planar warm shield are designed to vary the f/number of a cooled infrared detector respectively. To compare the influences of the two warm shields on the cooled infrared detector, radiometric calibration experiments are conducted in a high-low-temperature test chamber. The analyses and experimental results show that the stray radiation of spherical reflecting warm shield is far less than that of the ordinary planar warm shield. Moreover, the noise equivalent temperature difference introduced by the designed spherical reflecting warm shield is lower. Therefore it is indeed better than an ordinary planar warm shield in ensuring the performance of an infrared imaging system.
2000 eV X-ray laser transparent mechanism of neon atom
Authors: Feng Lei  , Jiang Gang  ,   College of Physical Science and Technology, Sichuan University, Chengdu 610065, China;,   Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China;,   Key Laboratory of High Energy Density Physics and Technology, Sichuan University, Chengdu 610065, China
Published: December 2020

X-ray transparency occurs during the interaction of X-ray free electron laser with matter. The study of the mechanism of X-ray transparency is of great value for understanding the interaction between X-ray free electron laser and matter. In this paper, the main ionization modes from neutral neon atom till bare nucleus at different flux densities are determined based on the 2000 eV photoionization cross sections and the Auger decay rates of various neon atoms (ions), calculated by the Flexible Atomic Code program. By establishing and solving the rate equations, the formulas of the proportions of various electronic configurations of neon in the main ionization mode are obtained. The proportions of electron configurations in the main ionization modes and the atomic average photoionization cross sections at flux densities of 2000 and 10000 -2fs-1 are calculated by using the formulas. The ratios of the number of hollow atoms to that of complete valence electrons at any time under different flux density laser irradiations are calculated. It is found that both the bare nuclei and the hollow atoms cause X-ray transparency, and a relatively high ratio of the number of hollow atoms to that of complete valence electrons can be achieved by choosing appropriate flux density and pulse duration.
Generation of ultrafast broadband small angle hundreds MeV electron bunches from laser wakefield acceleration
Authors: Li Rong-Feng  , Gao Shu-Chao  , Xiao Chao-Fan  , Xu Zhi-Yi  , Xue Xing-Tai  , Liu Jian-Bo  , Zhao Yan-Ying  , Chen Jia-Er  , Lu Hai-Yang  , Yan Xue-Qing  ,   State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China;,   Center for Applied Physics and Technology, Peking University, Beijing 100871, China
Published: December 2020

Electrons can be accelerated to a GeV level in centimeters by plasma wakefield driven by laser. With the development of chirped pulse amplification technique, the accelerating field can reach 100 GV/m. The laser driven wakefield acceleration experiments with ionization injection are carried out using 68 TW (1.7 J, 25 fs) laser and a mixture gas of 99% He and 1% N2. In experiment, the output electron beam has broadband spectrum with a maximum cut-off energy of about 290 MeV and a maximum output energy is quite stable in a certain range of laser focal positions. Two-dimensional particle-in-cell simulation is carried out. It is found that the longitudinal phase space is occupied by the continuously injected electrons and the phase space distribution is quite stable after the laser has propagated several millimeters inside plasma. This acceleration process can lead to quite stable maximum output energy of electron beam. These experiments reveal the physical nature of continuous ionization injection, which is very important for improving the performance of ionization injection.
Spectral and laser properties of Nd:YSAG single crystal
Authors: Lu Wan-Cheng  , Zhang Qing-Li  , Luo Jian-Qiao  , Ding Shou-Jun  , Dou Ren-Qin  , Peng Fang  , Zhang Hui-Li  , Wang Xiao-Fei  , Sun Gui-Hua  , Sun Dun-Lu  ,   Key Laboratory of Photonic Devices and Materials of Anhui Province, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China;,   University of Science and Technology of China, Heifei 230026, China
Published: December 2020

In order to solve the problem of low segregation coefficient of Nd3+ ions in YAG crystal, Sc3+ ions are used to replace some Al3+ ions in YAG, so that the YAG cell becomes bigger, thereby the segregation coefficient of Nd3+ ion increases. In this paper, the spectra and laser characteristics of Nd:YSAG single crystal are studied. The (1.5 at.%) Nd3+:Y3Sc2Al3O12 (YSAG) laser crystal is grown by Czochralski method, and X-ray rocking curve shows that the crystal quality is good. The concentration of ions in Nd:YSAG is measured by an electronic probe. The segregation coefficient of Nd3+ ion is calculated to be 0.35, which is approximately twice as much as that of Nd3+ in YAG. The absorption and emission spectra are measured, which indicates that it can be pumped by an 808 nm-laser diode (LD). The strongest emission from the transition 4F3/24I11/2 of Nd:YSAG peaks at 1059 nm with an emission cross section of 1.0310-19 cm2, and the lifetime of 4F3/2 is about 253 s, which indicates that Nd:YSAG has roughly an efficiency equal to that of Nd:YAG, but the laser upper level lifetime is longer than that of Nd:YAG, which is more favorable for Q-switched laser operation. The 808 nm-LD is used to pump Nd:YSAG rod of 2 mm2 mm6 mm, the laser operation with a threshold of 0.85 W and a maximum output power of 1.1 W is realized:the laser slope efficiency is 21.1%, and the optical conversion efficiency is 18.3%. All of the above results show that Nd:YSAG single crystal is a good solid state laser material, which is more favorable for Q-switched laser operation.
Simulation of spontaneous emission spectrum of degenerate Ge under large injection level
Authors: Wang Jian-Yuan  , Lin Guang-Yang  , Wang Jia-Qi  , Li Cheng  ,   Department of Physics, OSED, Semiconductor Photonics Research Center, Xiamen University, Xiamen 361005, China
Published: December 2020

Germanium (Ge) is considered as a promising material for silicon (Si) based light source. Based on tensile strain and n-type heavy doping approaches, the light emitting efficiency of Ge can be improved. Nevertheless, due to the difficulty in introducing large tensile strain into Ge, the photoluminescence or electroluminescence of Ge is demonstrated under degenerated states currently. Traditional spontaneous emission (SE) theory deduced from Boltzmann approximation is inapplicable for this case. To accurately analyze the SE properties of Ge, the influences of strain, temperature and doping on quasi-Fermi level and subsequent SE spectrum of degenerated Ge are theoretically investigated based on Fermi-Dirac distribution model. Owing to large density of states (DOS) in heavy hole (hh) the valance band (VB) and L valley, it is found that compressive strain has a negligible effect on the quasi-Fermi level under carrier concentration of 1019-1020 cm-3, while tensile strain is of benefit to the improvement of carrier occupation levels, leading to dramatic increases of both peak and integrated intensities of SE spectra. Although the peak intensity of SE from -hh transition is larger than that from -1h transition regardless of strain levels in Ge, the integrated intensities of SE from -hh and -1h transitions are almost equal. With the increase of sample temperature, the carriers acquire lager kinetic energy, resulting in more dispersive distribution of electrons (holes) in valley (VB). However, more electrons (holes) are induced into conduction (valence) band at the same time. And according to Varshini's law the energy difference between and L valleys is reduced at higher temperature. Thus, both the peak and integrated intensities of the SE spectra become larger at higher temperature. It is impressive that n-type doping can greatly enhance the SE intensity compared with p-type doping irrespective of strain levels in Ge, demonstrating the significance of n-type doping in the enhancement of Ge SE. Furthermore, it is found that m factors, which can be extracted from linear fitting of log L-log n curves, diminish at heavier doping concentration. Under tensile strain condition, the variation of m factors for Ge SE with the sample temperature becomes less sensitive, implying that the tensile strain can effectively enhance the temperature stability of Ge SE. These results provide a significant guidance for analyzing the SE properties of degenerated Ge and other degenerated semiconductors.
Heterodyne polarization interference imaging spectroscopy
Authors: Cai Qi-Sheng  , Huang Min  , Han Wei  , Cong Lin-Xiao  , Lu Xiang-Ning  ,   Key Laboratory of Computational Optical Imaging Technology, Academy of Opto-Electronics, Chinese Academy of Sciences, Beijing 100094, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

A novel heterodyne polarization interference imaging spectroscopy (HPⅡS) based on a Savart polariscope is proposed in this paper. The HPⅡS is modified by introducing a pair of parallel polarization gratings into the static polarization interference imaging spectrometer. Because of the introduced parallel polarization gratings, the lateral displacements of the two beams split by the Savart polariscope vary with wavenumber. The frequency of the interferogram obtained on the detector is related to wavenumber. Like the spatial heterodyne spectrometer where the two end mirrors in a Michelson interferometer are replaced with two matched diffraction gratings, the zero frequency of the interferogram generated in HPⅡS corresponds to a heterodyne wavenumber instead of the zero wavenumber in a non-heterodyne spectrometer. Due to the heterodyne characteristics, a high spectral resolution can be achieved using a small number of sampling points. In addition, there is no slit in HPⅡS and it is an imaging Fourier transform spectrometer that records a two-dimensional image of a scene superimposed with interference curves. It is a temporally and spatially combined modulated Fourier transform spectrometer and the interferogram of one point from the scene is generated by picking up the corresponding pixels from a sequence of images which are acquired by scanning the scene. As a true imaging spectrometer, HPⅡS also has high sensitivity and high signal-to-noise ratio. In this paper, the basic principle of HPⅡS is studied. The optical path difference produced by the Savart polariscope and the parallel polarization gratings is calculated. The interferogram expression, the spectral resolution, and the spectrum reconstruction method are elaborated. As the relationship between the frequency of the interferogram and the wavenumber of the incident light is nonlinear, the input spectrum can be recovered using Fourier transform combined with the method of stationary phase. Also, the matrix inversion method can be used to recover the input spectrum. Finally, a design example of HPⅡS is given. The interferogram is simulated, and the recovered spectrum shows good agreement with the input spectrum. In the design example, the spectral range is 16667-18182 cm-1(550-600 nm), and the number of sampling points is 500. The spectral resolution of HPⅡS is 6.06 cm-1, which is 12 times smaller than that in a non-heterodyne spectrometer with the same spectral range and sampling numbers. HPⅡS has the advantages of compact structure, high optical throughput, strong stability, and high spectral resolution. It is especially suitable for hyperspectral detection with ultra-small, high stability, and high sensitivity.
Sedimentation of two non-magnetic particles in magnetic fluid
Authors: Chen Mu-Feng  , Li Xiang  , Niu Xiao-Dong  , Li You  , Adnan  , Hiroshi Yamaguchi  ,   College of Engineering, Shantou University, Shantou 515063, China;,   Energy Conversion Research Center, Doshisha University, Kyoto 630-0321, Japan
Published: December 2020

Magnetic fluid is a stable suspension of solid phase magnetic particles of diameter about 10 nm in a nonmagnetic carrier fluid like water or alcohol. Nowadays, the magnetic fluid is widely used in industry areas such as sealing, damping, lubricating, sound regulation, heat dissipation, and MHD beneficiation. Researchers have paid great attention to the behaviors of non-magnetic particles (NPs) in the magnetic field because magnetic fluid containing NPs can form different microstructures, which are easily controlled by applying a magnetic field. In order to appropriately use the properties of magnetic fluid in industry, it is necessary to study the interaction among NPs in detail. In this paper, a multi-physical numerical model is employed to investigate the sedimentation of two NPs in magnetic fluid subjected to an applied magnetic field. The magnetic fluid flow is simulated by lattice Boltzmann method, and magneto hydrodynamics is calculated with a self-correcting procedure of a Poisson equation solver, which enables the Ohm's law to satisfy its conservation law. A dipole force model is used to obtain the dipole interaction force between particles. In addition, as the permeability of the magnetic fluid is quite different from those of the NPs and magnetic fluid, correctly establishing the conjugate boundary condition of the magnetic intensity at the interface between the particles and surrounding fluid is a key because it affects the magnetic induction in the fluid-structure interaction area. A smooth transition scheme of the conjugate boundary condition for magnetic intensity at the interface between the particles and surrounding fluid is used in this work. The aim of this work is to investigate sedimentation of two NPs in magnetized magnetic fluid. By changing the ratio of magnetic permeability and the magnetic parameter, it is found that altering the ratio of magnetic permeability is more effective to change the trajectories of NPs, while changing the magnetic parameter can just give rise to a slight transform of particle trajectories. This can provide good theoretical support for the application of magnetic fluid in industry area, because the results in the present simulation can quantitatively analyze the controlling of the movement of NPs.
Research progress on photocatalytic activity of ferroelectric materials
Authors: Wu Hua-Ping  , Ling Huan  , Zhang Zheng  , Li Yan-Biao  , Liang Li-Hua  , Chai Guo-Zhong  ,   Key Laboratory of Special Purpose Equipment and Advanced Manufacturing Technology(Zhejiang University of Technology), Ministry of Education/Zhejiang Province, College of Mechanical Engineering, Hangzhou 310014, China
Published: December 2020

Photocatalytic technology is considered to be the most promising treatment technology of environmental pollution. In this technology, the electronhole pairs generated by the light-responsive materials under sunlight irradiation will produce the oxidation-reduction reactions with the outside world. At present, there are still a series of problems needed to be solved in the photocatalytic technology, among which the recombination of photogenerated electron-hole pairs is a very important limitation. In recent years, the ferroelectric materials have attracted much attention as a new type of photocatalyst because the spontaneous polarizations of ferroelectric materials are expected to solve the recombination problem of electronhole pairs in the catalytic reaction process. However, there are no systematic analyses of the specific mechanisms for ferroelectric materials. In this paper, we review the effects of ferroelectric polarization of ferroelectric materials on photocatalytic activity from three aspects. Firstly, the polarization can give rise to depolarization field and band bending, thereby affecting the separation rate of electron-hole pairs, and speeding up the transmission rate. Therefore, in the first part, the effects of depolarization field and energy band bending on catalytic activity are summarized. This can conduce to understanding the influence of polarization on catalytic activity more clearly from the intrinsic mechanism. Next, the built-in electric field induced by the polarization of ferroelectric material can increase the separation rate of photogenerated carriers and improve the catalytic activity. However, the static built-in electric field easily leads to free carrier saturation due to the electrostatic shielding, which reduces the carrier separation rate. Thus, in order to eliminate the electrostatic shielding, the effects of three external field including temperature, stress (strain) and electric field, which can regulate polarization, on the separation of electronhole pairs and photocatalytic activity are summarized in the second part. Finally, detailed discussion is presented on how to exert effective external fields, such as strain, temperature, and applied electric field, and how to study the force catalysis or temperature catalysis under the no-light condition according to the piezoelectricity effect and pyroelectric effect of ferroelectric material in the last part.
Composite electromagnetic scattering from a ship located on one-dimensional sea surface with time-domain hybrid method
Authors: Wang Qiang  , Guo Li-Xin  ,   School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710071, China;,   Department of Computer and Electronic Information, Shaanxi Xueqian Normal University, Xi'an 710100, China
Published: December 2020

With the development of broadband radar technology, transient composite scattering from a target and a randomly rough surface has aroused a great interest in oceanic remote sensing, target identification, and military applications. Time-domain integral equation (TDIE) is an effective numerical method of analyzing transient and broadband electromagnetic problems. However, the high computational complexity of numerical methods restricts its applications in analyzing the electrically large rough surfaces. To improve computational efficiency, hybrid methods have been developed by combining an analytical method with a numerical algorithm, and used to solve the electromagnetic scattering of a composite model. In these hybrid methods, numerical methods are used to calculate the scattering from a target, and analytical methods are employed to solve the scattering from a rough surface. To our knowledge, most of the hybrid methods for composite electromagnetic scattering are frequency-domain algorithms and used to investigate composite scattering from a rough surface with a target above it. Few papers have been published on the analysis of transient scattering from a rough surface with a target by using the time-domain hybrid methods. In the present paper, an efficient time-domain hybrid method that combines time-domain Kirchhoff approximation (TDKA) with TDIE is first designed to investigate the transient electromagnetic scattering from a ship located on a randomly rough sea surface. In this hybrid method, the ship and its adjacent sea surface are chosen as TDIE region and the rest of the rough surface is TDKA region. Considering the interactions between the TDIE region and the TDKA region, the hybrid TDIE-TDKA formula is derived and solved with an iterated marching-on-in-time method. Initially, the induced currents of the TDIE region are acquired by solving TDIE. Then, the currents in the TDKA region are obtained via TDKA method. The interactions between the currents in the TDKA region are neglected. The efficiency and accuracy of the hybrid TDIE-TDKA method depend on the size of the TDIE region. The minimum length of sea surface in the TDIE region is at least the size of the ship due to the strong interactions between the ship and its adjacent sea surface. Numerical results show that the hybrid TDIE-TDKA method presented in this paper is accurate and efficient compared with the full TDIE. Moreover, the influences of the ship size, the wind speed, the incident angle, and the depth of the ship immersing in sea surface on the backscattered far magnetic field are discussed in detail.
First principle study of electronic structures and optical absorption properties of O and S doped graphite phase carbon nitride (g-C3N4)6 quantum dots
Authors: Zhai Shun-Cheng  , Guo Ping  , Zheng Ji-Ming  , Zhao Pu-Ju  , Suo Bing-Bing  , Wan Yun  ,   School of Physics, Northwest University, Xi'an 710069, China;,   Institute of Photonics and Photon-Technology, Northwest University, Xi'an 710069, China;,   Institute of Modern Physics, Northwest University, Xi'an 710069, China
Published: December 2020

Graphite phase carbon nitride (g-C3N4) quantum dots have received much attention due to its good stability, water solubility, biological compatibility, non-toxicity as well as strong fluorescence characteristics. In order to enhance the light absorption and improve photocatalytic activities of the g-C3N4 quantum dots, theoretical studies are carried out on the O and S atoms doped (g-C3N4)6 quantum dots. First-principles calculations based on the density functional theory and time dependent density functional theory are performed to investigate the geometries, electronic structures and ultraviolet visible absorption spectra of O and S atoms doped (g-C3N4)6 quantum dots. The results show that the highest electron occupied molecular orbital-the lowest electron unoccupied molecular orbital (HOMO-LUMO) energy gap of doped (g-C3N4)6 quantum dots is significantly reduced though the CN bond lengths closely related to the impurities only change slightly. The calculated formation energies indicate that the O-doped (g-C3N4)6 quantum dots are more stable, and the O atom tends to substitute for N atom at the N3-site, while the S atoms prefer to substitute for N atom at the N8-site. The simulated spectra indicate that the doping of O and S in (g-C3N4)6 could improve the light absorption. Not only the absorption peaks are extended from the UV to the infrared region (e.g. 200-1600 nm), but also the corresponding absorption intensities are enhanced significantly by doping the O or S atoms with the appropriate concentration. The increase of proper impurity concentration will lead to a pronounced red shift in light absorption. The effect of doping site on the optical absorption property of (g-C3N4)6 quantum dots shows that the absorption intensity is mainly affected in the visible range, however, besides the influence on the absorption intensity, the light absorptions of some structures are also affected beyond 800 nm. Overall, the O atoms and S atoms have a substantially similar effect on the light absorption of the (g-C3N4)6 quantum dots, while the effects of these impurity atoms are different in the long wavelength region. Oxygen doping is better than sulfur doping in the absorption of (g-C3N4)6 quantum dots by comparing the doping of O and S. These first-principles studies give us a method to effectively improve the light absorption of g-C3N4 quantum dots, and could provide a theoretical reference for tuning its electronic optical properties and applications.
Acoustic field and convection pattern within liquid material during ultrasonic processing
Authors: Wu Wen-Hua  , Zhai Wei  , Hu Hai-Bao  , Wei Bing-Bo  ,   School of Natural and Applied Sciences, Northwestern Polytechnical University, Xi'an 710072, China;,   School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China}
Published: December 2020

When ultrasound propagates in a liquid alloy, nonlinear effect takes place such as cavitation effect and acoustic streaming, which accelerates the solute and thermal transportation during alloy solidification, and consequently, improves the solidification microstructures and mechanical properties of the metallic alloy. Therefore, it is significant to investigate the ultrasound propagation characteristics in liquid. Here, by choosing water as a model transparent material, the acoustic fields and flow fields induced by 20 and 490 kHz ultrasounds are investigated by numerical simulation, and the effects of frequency and ultrasonic horn radius are studied. Firstly, the simulation results demonstrate that the sound pressure under 20 kHz ultrasound decreases obviously along the ultrasonic propagation direction, and the maximum of sound pressure value is equal to the initial pressure. In this case, the cavitation effect only occurs in the region close to the ultrasonic horn. By contrast, when the ultrasonic frequency increases to 490 kHz, the sound pressure is higher than that of 20 kHz ultrasound, and displays periodical vibration characteristic along the wave propagation direction. The cavitation volume correspondingly expands to a large extent with a regular striped distribution. It can also be found that increasing the ultrasonic horn radius under 20 and 490 kHz ultrasounds can effectively promote the sound pressure level in water, and hence leads to the remarkable enlargement of cavitation volume. Secondly, the calculated results of flow field indicate that the streamlines in water are similar under the two ultrasounds with different frequencies. A jet produced by the center of horn spreads down and divergences to both sides after reaching the bottom. For both frequencies as the horn radius increases, the radius of jet increases and the average velocity in water first increases and then decreases, whose maximum value appears when the horn radius is 40 mm. Meanwhile, the average velocity under 20 kHz ultrasound is larger than that under 490 kHz ultrasound for each horn radius. Finally, particle image velocimetry method is employed to measure the velocity field in water. Both the positions of eddy and the velocity distribution are the same as the simulation results, which verifies the reliability of the present theoretical calculation model. The scenario in this work is analogous to the acoustic field and the flow field in liquid alloy, which is beneficial for the design of parameter optimization during ultrasonic processing in alloy solidification.
Passive detection of scatterer using autocorrelation of surf noise
Authors: Chi Jing  , Li Xiao-Lei  , Gao Da-Zhi  , Wang Hao-Zhong  , Wang Ning  ,   Department of Marine Technology, Ocean University of China, Qingdao 266100, China
Published: December 2020

When a scatterer is located in a diffuse noise field, time domain Green's function between two different receivers can be extracted from cross-correlation of ambient noise which is recorded by the two receivers so that target detection can be implemented. However, the method based on cross-correlation strongly depends on timing synchronization of each receiver, otherwise there will be a time drift in the cross-correlation result, which can bring error in the positioning detection. Besides, two receivers that are far from each other must communicate with each other to implement cross-correlation in real-time data processing, but big data transmission is difficult in the ocean. Compared with cross-correlation, autocorrelation means that each receiver works independently and only the final autocorrelation result is to be transmitted. Actually, the scattered wave of target is always so weak that it is submerged in the autocorrelation result of the ambient noise. In this paper, we propose a method of processing the autocorrelation of the ambient noise. When the averaging noise autocorrelation of all receivers is subtracted from the autocorrelation result of the noise recorded by each receiver, the signalnoise ratio of the scattered wave will be significantly enhanced. With the help of Kirchhoff migration algorithm, detection of a scatterer can be implemented. We have conducted a scatterer passive detection experiment in Shilaoren beach, Qingdao, and accurately detected the position of a polyviny chloride pipe (about 8 m away from the nearest receiver) using only 12 min surf noise data. The experimental result shows that the processing of autocorrelation could replace cross-correlation in passive target detection when the ambient noise is time steady and the statistical characteristics of the background noise at different receivers are the same. Unlike Green's function extracted from cross-correlation of ambient noise, each receiver can work independently without considering the problems of massive data transmission and timing synchronization, which may be suitable for target detection using multi-receivers and mobile platform.
Multi-section cellular automata model of traffic flow
Authors: Liang Jing-Yun  , Zhang Li-Li  , Luan Xi-Dao  , Guo Jin-Lin  , Lao Song-Yang  , Xie Yu-Xiang  ,   School of Information System and Management, National University of Defense Technology, Changsha 410072, China;,   School of Computer Engineering and Applied Mathematics, Changsha University, Changsha 410022, China}
Published: December 2020

It is more common for drivers to pass through multiple sections to reach destinations instead of single road section. Howerver, most of researches concentrate on improving the effect in an independent section. Based on traditional cellular automata traffic model, a multi-section model is proposed by regarding serverl road sections as a traffic system. In this model, different sections of the road might have different lengths, numbers of lanes or maximal speeds. And vehicles travel from one section to another. The main difficulty lies in dealing with the relationships among the traffic flows of different sections. Besides basic rules in NaSch model, the vehicle inflow rule, crossroad randomization brake rule and crossroad inflow rule is added in this paper to enable vehicles to flow between sections. At the beginning of section, to avoid conflicting at crossroads under open boundary condition, the concept of car pool is introduced when new vehicles enter into sections. Before arriving at the end of section, crossroad randomization brake is used to simulate the influences of crossroads. Speed decreases in probability until lower than a maximal crossroad speed. When leaving the section, vehicles go to the next section with a straight ratio. Also, new vehicles may enter according to traffic condition. Therefore, cellular automata of different sections can be connected in series.Finally, numerical simulation is demonstrated to study the influences of important parameters, including traffic inflow probability, maximal crossroad speed and crossroad randomization brake probability. Compared with traditional models, this model focuses on connecting sections. And improvements of basic models can be implanted easily, thereby increasing the accuracy of the whole model in the future. The experimental result are as follows. 1) According to space-time graphs of different inflow probabilities, there is a new kind of traffic flow called mixed flow. Traffic congestion often starts from crossroads, and spreads to the whole section. And traffic jams in previous section might relieve traffic pressure in latter section. 2) With the increase of traffic inflow probability, crossroads tends to have a greater influence on average speed as well as average traffic density. What is more, the moderate increase of vehicle numbers could cause the road capacity to drop rapidly if it exceeds the threshold value.