bluuebunny/crossref_metadata_2025 huggingface dataset:
An immune memory optimization algorithm based on the non-genetic information
Authors: Song Dan  , Fan Xiao-Ping  , Liu Zhong-Li  ,   School of Information Science and Engineering, Central South University, Changsha 410083, China;,   Department of Information Management, Hunan University of Finance and Economics, Changsha 410205, China
Published: December 2020

In order to improve the ability to optimize artificial immune algorithm, the memory mechanism of non-genetic information is introduced into optimization algorithm. An immune memory optimization algorithm based on the non-genetic information is proposed. Emulating human society education and experiential inheritance mechanism, the algorithm takes, stores and uses non genetic information in the evolutionary process of the population. By setting up a separate memory base, the algorithm stores non genetic information, and guides the subsequent search process. The algorithm uses the short-term memory of the prior knowledge and guides the subsequent evolution, which can increase the intelligence of search and reduce the blind search and repeat the search. The immune memory optimization algorithm based on the non-genetic information includes key operators: mutation operator, crossover operator and complement operator. The mutation operator is able to efficiently use non genetic information of grandparents to search, which can speed up the local search efficiency. In addition, the threshold to control the search depth of single dimension can avoid falling into local optimal solution making the evolutionary standstill. Through calculating comprehensive information about contemporary populations of all antibodies, complementary operator produces new antibodies containing excellent gene fragment in the global solution space. With small probability rules, crossover operator happens in an interval of multi generation, choosing the optimal antibody and a random antibody to exchange information about a single dimension. Crossover operator and complement operator can both be conducive to jumping out of optimal location. In simulation experiment, the immune memory optimization algorithm based on the non-genetic information uses four standard test functions: Ackley function, Griewank function, Rastrigin function, and transformed Rastrigin function. In order to better compare with contrast algorithm, in the case of high dimension the values of dimension are 20 and 30, and the experiment tests the four functions to make the statistical analysis of the results. On the other hand, to further test optimal performance of the algorithm in a more global massive space, multiple random experiment is carried out in the case of dimension 100. Compared with other intelligent algorithm, the simulation experiment with standard test functions of high dimension indicates that the new algorithms are superior in convergence speed, convergence precision and robustness comparison algorithm. In addition, the simulation results in the super high dimension show that the new algorithm has the global searching ability in high-dimensional solution space.
Three-dimensional optical modeling of vertical alignment mode color filter liquid-crystal-on-silicon microdisplays
Authors: Li Dan  , Zhang Bao-Long  , Kwok Hoising  ,   College of Electronic Information and Automation, Tianjin University of Science and Technology, Tianjin 300222, China;,   Center for Display Research, the Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
Published: December 2020

A three-dimensional (3D) optical model is developed for small color pixels in vertical alignment nematic (VAN) mode color filter liquid-crystal-on-silicon (CF-LCoS) microdisplays. First of all, the electromechanical characteristics of color liquid crystal (LC) cells are analyzed to achieve the orientation structure of the LC director. Then, the optical reflectance of the cell is calculated by using the extended Jones matrix. Finally, the optical reflectance on the pixel array is reduced into the displayed color image by adopting a standard RGB representation. In order to verify the accuracy of this 3D optical model, the simulation result and the observed result are compared. The simulated optical reflectance is in good agreement with the experimental result.
A new technique of full polarization hyperspectral imaging based on acousto-optic tunable filter and liquid crystal variable retarder
Authors: Li Ke-Wu  , Wang Zhi-Bin  , Yang Chang-Qing  , Zhang Rui  , Wang Yao-Li  , Song Yan-Peng  ,   Engineering and Technology Research Center of Shanxi Provincial for Optical-Electric Information and Instrument, Taiyuan 030051, China;,   School of Information and Communication Engineering, North University of China, Taiyuan 030051, China;,   Key Laboratory of Instrument Science and Dynamic Measurement, Ministry of Education, North University of China, Taiyuan 030051, China
Published: December 2020

In order to achieve all Stokes parameters of spectral image with high spectral resolution, high spatial resolution, high polarization accuracy, high signal-to-noise ratio and good stability, taking into account the orthogonal characteristic of ±1 order diffraction light which diffracts from a acousto-optic tunable filter (AOTF), a new technique of full polarization hyperspectral imaging is presented. It uses one AOTF to diffract the incident light, one liquid crystal variable retarder (LCVR) to modulate the light retardation, and two CCDs to image the ±1 order diffraction light, respectively. According to the Muller matrixes of all optical elements in the system, the basic working principle of the new technique is that LCVR sequentially provides the retardation 2π, 1.5π, π and 0.5π for each spectral channel, so the CCD obtains corresponding images. After analyzing these images, the all Stokes parameters are obtained; the precision of this system for polarization imaging is determined mainly by polarization modulation device LCVR. Considering the azimuth of LCVR fast axis and retardation precision at the same time, it is unveiled that LCVR has no effect on the accuracy of the first Stokes parameter, and the relative errors of other latter 3 Stokes parameters are less than 0.064%, 0.31% and 3.97%; then, our prototype system is used to do the outdoor experiments in a summer sunny morning, images data for 26 spectral channels with spectral bandwidth of 10 nm, which are from 450 nm to 700 nm, are acquired, the imaging quality is very fine. Firstly, LCVR are not assembled in our prototype system, and AOTF works in the sweeping frequency mode. The spectrum from each CCD proves that the diffraction efficiency of AOTF ± 1 order diffraction light is not completely the same, and the difference must be considered in polarized image processing. Then another experiment is done after LCVR has been assembled. The image data of the incident light of 600 nm are taken for example to discuss its all Stokes parameters in detail. The results show that the principle of the new technique is correct and the new scheme is feasible. This study provides a new theory and implementation scheme for the polarization spectral imaging technology.
Coarse-grain model of silicon functionalized graphene as anode material for lithium ion batteries
Authors: Hui Zhi-Xin  , He Peng-Fei  , Dai Ying  , Wu Ai-Hui  ,   School of Physics and Information Technology, Ningxia Normal University, Guyuan 756000, China;,   School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai 200091, China
Published: December 2020

The electronic transport, the storage capacity, and the service life of the anode material for lithium ion batteries will be reduced seriously in the event of the material layering or cracking, so the anode material must have strong mechanical reliability. Firstly, in view of the traditional molecular dynamics limited by the geometric scales of the model of silicon functionalized graphenen (SFG) as lithium ion battery anode material, some full atomic models of SFG are established by using Tersoff potential and Lennard-Jones potential, and used to calculate the modulus and the adhesion properties. What is more, according to the mechanical equilibrium condition and energy conservation and by combining with calculations from full atomic model through adopting the bead-spring structure, the SFG coarse-grain model and its system energy reservation equation are established. Finally, the validity of the SFG coarse-grain model is verified by comparing the tensile property of coarse-grain model with full atoms model.
Experimental study on vibration dephasing time varying with molecular surroundings
Authors: Lin Zi-Yang  , Wan Hui  , Yin Jun  , Hou Guo-Hui  , Niu Han-Ben  ,   College of Optoelectronic Engineering, Shenzhen University, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, Shenzhen 518060, China;,   d Institute of Physics, University of Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
Published: December 2020

Measuring the vibration dephasing time in molecular vibration is the free-mark method for detecting molecules harmlessly. Since molecular vibration refund processes are associated with molecular environment change, molecular vibration dephasing time also may reflect the substance's molecular environment change, which can be used to study the interaction between a certain molecule and its neighboring molecules. The molecular vibration spectrum and vibration dephasing time are obtained from the time-resolved coherent anti-stokes Raman scattering (CARS) simultaneously. Benzonitrile and methanol are used as samples for studying, the vibration dephasing time changes for the main vibration spectra when the environment changes. With benzonitrile mixed with anhydrous alcohol, its vibration dephasing time changes with environment are measured in three typical benzonitrile molecular vibrations 1017 cm-1, 2247 cm-1 and 3085 cm-1. For adjoining methanol molecular vibrations 2851 cm-1, and 2960 cm-1, vibration dephasing time changes are measured under environmental conditions. Results show that significant changes of molecular vibration dephasing time will take place in different environments. For a unidirectional molecular environment change, the molecular vibration dephasing time of benzonitrile is a one-way change, while the methanol molecule is of non-unidirectional vibration dephasing time change. But methanol molecules with vibration intensity ratios between two unidirectional changes with environment for I2851/I2960 are of a one-way change. By experimental measurement the vibration dephasing time of the main vibration mode of benzonitrile and methanol molecules varies with the changes in the environment, further understanding of differences on vibration dephasing time of molecular vibration spectra of adjacent and non-adjacent variations can explain the variation of vibration dephasing time of benzonitrile molecules. This method has the ability of detecting molecular environment change and molecular interactions, and has an important application prospect in the field of life science, molecular biology, and material science etc..
Direct measurement of the rotational constant of 0u+(6S1/2+6P1/2) long-range state via double-pass spectroscopy
Authors: Hu Chen-Yang  , Liu Wen-Liang  , Xu Run-Dong  , Wu Ji-Zhou  , Ma Jie  , Xiao Lian-Tuan  , Jia Suo-Tang  ,   Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
Published: December 2020

In this paper, we obtain the rotational constant and the distortion constant of v=187 belonging to 0u+ state below the 6S1/2+6P1/2 disassociation limit. In our experiment, we first prepare the ultra-cold cesium sample in the MOT (magneto-optical trap) by six beams of pumping laser, one beam of repumping laser, and a pair of anti-Helmholtz coils. Then we construct a high-resolution frequency reference using the double-pass photoassociation technique. The double-pass photoassociation technique is a creative and robust method. We use a polarization beam splitter to split one laser beam from the laser to two beams-Laser Ⅰ and Laser Ⅱ; Laser Ⅱ then passes twice through an acousto-optic modulator (AOM) whose central frequency is 110 MHz, using a reflecting mirror and a convex lens before illuminating the MOT. We use two shutters-S1 and S2 to control Laser Ⅰ and Laser Ⅱ. Open S1 while keep S2 close to make Laser I interact with the MOT; and after the rotational spectroscopy of J=0-6 is observed, turn off S1 and turn on S2 immediately. Let laser II interact with MOT and obtain another part of spectroscopy that is exactly the same with J=6; we define this part of spectroscopy as J'=6. The frequency interval between J=6 and J'=6 is exactly 220 MHz for the scan process is strictly linear, and that can be an accurate frequency interval in our experiment. The laser intensities of these two laser beams have to be strictly equal in case of the laser-induced frequency shift. Using the frequency interval of 220 MHz, we can calculate the frequency interval of J=0-6. The detection method we used here is the trap loss spectroscopic technology by modulating fluorescence of cold atoms in the MOT, which allows a direct spectroscopy detection at the rovibrational levels for a very weak transition probability. With the frequency intervals of each rotational quantum number, we can fit the frequency intervals to the non-rigid model to derive the rotation constant B and distortion constant D which are crucial to precisely measure the full molecule potential curves as well as deepen our understanding of molecular formation. This kind of double-pass photoassociation technique not only can direct obtain the precise value of rotation constant B and distortion constant D as compared with the traditional photoassociation method, but also can obtain a relatively accurate potential energy curve. And another great advantage is that we are able to calculate the frequency intervals easily without the wavelength meter which is rather expensive and difficult to control.
A comparison of interatomic potentials for noble gases
Authors: Sun Su-Rong  , Wang Hai-Xing  ,   School of Astronautics, Beihang University, Beijing 100191, China
Published: December 2020

Prediction of transport properties of noble gases requires the calculation of collision integrals, which depend on interatomic potentials as the input. However the accuracy of transport properties depends largely on the accuracy of interaction potentials. So different interatomic potentials of noble gases are compared in order to get the accurate transport properties. The forms and characteristics of Lennard-Jones, exponential repulsive, Hartree-Fock-Dispersion-B (HFD-B), and phenomenological model potentials that are used to describe the atomic interactions between noble gases are analyzed in this paper. Then the calculation method of transport properties is presented. Viscosities and thermal conductivities of noble gases based on these four potentials are obtained using Chapman-Enskog method in the temperature range for computation from 300 to 5000 K. It can be seen from the results that the interaction potentials have a great influence on the calculated results of transport properties. There are great differences between the results obtained using different interaction potentials. These differences of the calculated results can be explained according to the performance of interaction potentials. Results calculated with Lennard-Jones potential are always much lower in the high temperature range due to its overestimated repulsive part, and the exponential repulsive potential gives unreasonable results at low temperatures because there is no attractive well in this potential. Therefore, the accurate interatomic potentials for noble gases can be obtained only by comparing the calculated results with published experimental and theoretical data of other researchers. It can be found that the results obtained by HFD-B potential agree well with previously experimental and theoretical data. So it is apparent that the HFD-B potential in light of Hartree-Fock repulsion and dispersion theory can provide a realistic description of the trends and features of interatomic potentials, allowing accurate theoretical calculations to be made for transport properties of noble gases.
Theoretical and experimental study of the electric resonant coupling between two metamaterial resonators
Authors: Liang Hao  , Li Jian-Sheng  , Guo Yun-Sheng  ,   School of Information Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China;,   School of Mathematics, Physics and Biological Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China
Published: December 2020

In this paper, we realize the electrically coupled resonances between two metamaterial resonators based on two metal split-ring resonators gap-to-gap placed. The theoretical analysis and numerical calculation of the microwave equivalent circuit of the electrically coupled metamaterial resonators are performed. The results show that there are two resonance frequencies produced by the two coupled metamaterial resonators. For the two resonance frequencies, one gradually shifts towards the lower frequency with the coupling strength increasing, while the other is fixed at the resonance frequency of the single metamaterial resonator. The measured and simulated results of the microwave transmission spectra show that the two resonance peaks move respectively towards the lower and higher frequency with the coupling strength increasing. The analysis shows that the lower resonance frequency is mainly determined by the electrical coupling strength between the two metamaterial resonators, and the difference between the higher resonance frequency and the resonance frequency of the single resonator is mainly caused by the inevitable magnetic coupling between the two resonators. Moreover, the smaller the coupling space, the greater the influence of magnetic coupling is. The proposed dual resonance property and its tunability based on the electromagnetic coupling between the two metamaterial resonators greatly enhance the scopes of the design and application for metamaterials.
Ultrahigh-energy electron beam generated by ultra-intense circularly polarized laser pulses
Authors: Yin Chuan-Lei  , Wang Wei-Min  , Liao Guo-Qian  , Li Meng-Chao  , Li Yu-Tong  , Zhang Jie  ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190, China
Published: December 2020

The earlier research showed that circularly polarized laser pulses with peak intensities in a range of 1022-1025 W/cm2 can directly accelerate and generate GeV-TeV monoenergetic electron beams with a linear energy scaling with the laser intensity. To obtain higher energy electron beams, a scheme is proposed to use an electron beam with an initial energy E0 along the laser propagation direction. This scheme can overcome the linear energy scaling with E0=0 obtained previously and enhance the beam energy by E0 folds. This is because an electron beam with an initial energy can move with the laser pulse together and therefore obtain a longer acceleration distance. Two-dimensional particle-in-cell simulation shows that this scheme is effective only for the electron beams initially with low energy on the order of MeV. With overhigh energy, electrons will miss the optimum acceleration field because the electron acceleration distance is much longer than the Rayleigh distance and the laser intensity is significantly attenuated.
Zernike modal wavefront reconstruction algorithm based on model selection
Authors: Xie Wen-Ke  , Gao Qiong  , Ma Hao-Tong  , Wei Wen-Jian  , Jiang Wen-Jie  ,   College of Photon-electron Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

In Zernike modal wavefront reconstruction algorithm, because of a certain number of the low Zernike modes is selected subjective for making up the reconstruction model, the modes confusion and modes coupling will produced, the accuracy reduction of wavefront reconstruction is deduced. According to the minimal description length principal, a principle can balance the model error against model size so as to prevent the model from overfitting. The reconstruction model is selected by top-down method, and Levenberg-Marquardt nonlinear optimization algorithm is applied to the solution of reconstruction coefficients, then the wavefronts reconstruction is realized. Under different noise conditions, the reconstruction algorithm is validated with the numerical simulation of the wavefront reconstruction of uniform amplitude incidence beam, the results indicate: Zernike modal wavefront reconstruction algorithm based on the model selection can improve the wavefront reconstruction accuracy, and algorithm possesses the property of resistance to noise.
Fiber nonlinearity tolerance research of coherent optical orthogonal frequency division multiplexed system based on digital coherent superposition
Authors: Chen Xue-Mei  , Zhang Jing  , Yi Xing-Wen  , Zeng Deng-Ke  , Yang He-Ming  , Qiu Kun  ,   Key Laboratory of Optical Fiber Sensing and Communications, Ministry of Education, School of Communication and Information Engineering, University of Electronic science and Technology of China, Chengdu 611731, China
Published: December 2020

Fiber nonlinearity of optical orthogonal frequency division multiplexed (OFDM) system restricts the capacity improvement of optical fiber transmission. In this paper, we propose a novel digital coherent superposition (DCS) scheme to improve the tolerance to fiber nonlinearity in a coherent optical orthogonal frequency division multiplexed system. In simulation, 71.53 Gbit/s orthogonal frequency division multiplexed signal per channel with Hermitian symmetry is transmitted over 400 km standard single mode fiber in a wave division multiplexed-polarization-division multiplexed-coherent optical orthogonal frequency division multiplexed system with five channels. The 4-quadrature amplitude modulation is used for symbol mapping. For the receiver, after the conventional OFDM signal processing, we conduct DCS for OFDM subcarrier pairs, which requires only conjugation and summation in the x, y polarization direction, respectively. Firstly, the channel spacing is 25 GHz, the maximum signal-to-noise ratio improvement is 9.05 dB or 6.02 dB with or without symmetric dispersion compensation compared with a conventional orthogonal frequency division multiplexed system. The optimum launch power is increased by 2 dB. Secondly, the channel spacing is changed to 50 GHz to investigate the nonlinearity tolerance at different channel spacings in the wave division multiplexed system, the maximum signal-to-noise ratio improvement is 8.75 dB or 4.9 dB with or without symmetric dispersion compensation, respectively. Theoretical and simulation analysis show that the proposed method in this paper can effectively mitigate the first-order nonlinear distortions and hence improve the tolerance of coherent optical orthogonal frequency division multiplexed system with different channel spacings to fiber nonlinear effects.
All chirped mirrors long-term stable sub-8 fs Ti:sapphire oscillator
Authors: Fan Hai-Tao  , Wang Yan-Zhi  , Wang Zhao-Hua  , Ye Peng  , Hu Guo-Hang  , Qin Shuang  , He Hui-Jun  , Yi Kui  , Shao Jian-Da  , Wei Zhi-Yi  ,   Key Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Key Laboratory of Materials for High Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Published: December 2020

A long-term stable sub-8 fs Ti:sapphire oscillator based on domestic chirped mirrors is reported. It outputs 300 mW mode-locked pulses at 86 MHz under 4 W pump power. The second order and third order of dispersion introduced by the components of the oscillator are analyzed. Two pairs of domestically designed and fabricated chirped mirrors are utilized to compensate the dispersion introduced by the crystal and the air in cavity. By precisely controlling the dispersion of chirp mirrors, the output pulses have an ultra-broad bandwidth exceeding 150 nm (FWHM) without the insertion of wedges. With the assistance of extra-cavity dispersion compensation, a pulse duration of 7.9 fs is achieved. This is the shortest pulse duration ever reported by using domestic chirped mirrors, and the shortest pulse duration achieved without intra-cavity wedges, to the best of our knowledge. Structure design and electronic feed-back loops are employed to improve the stability of the oscillator passively and actively, respectively. With the assistance of piezoelectric ceramic, the power stability within 24 h is measured to be 0.6%, which is significantly better than that without them.
Pulsation effect on thrombus in a bifurcation pipe by the lattice Boltzmann method
Authors: Chen Jia-Min  , Jiang Yan-Hua  , Shi Juan  , Zhou Jin-Yang  , Li Hua-Bing  ,   School of Material Science and Engineering, Guilin University of Electronic Technology, Guilin 541004, China;,   School of Information and Communication Engineering, Guilin University of Electronic Technology, Guilin 541004, China
Published: December 2020

Thrombosis caused by all kinds of cardiovascular diseases, has been influencing people's health. In a blocked blood vessel, pulsation flows have a positive effect on thrombus. Because of the blood viscosity and the inertias of red blood cells and the fluid, the frequency of pulsation flow influences the effect of dredge blood clots. Under the condition of low differential pressure, conduction of the another flow pipe reducing the pressure variation causes the effect of dredging blood clots not to be ideal in the bifurcated pipe model. So we will increase the differential pressure and improve the amplitude of pulsation flow, reduce the influence of the conduction effect of expedite tube, then study the effect of dredge blood clots which is caused by the pulsation flow in the bifurcated pipe. We find that low frequency pulsation flow has a good effect on dredge blood clots for a long time. Relatively, high frequency pulsation flow needs less time, but the effect of dredge blood clots is not obvious if the frequency is higher than a certain value. The friction between cells and the walls of the tube also has an effect on dredge blood clots.
Monte Carlo simulation of the radiation transport of spherical holhraum
Authors: Li Shu  , Lan Ke  , Lai Dong-Xian  , Liu Jie  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   Center for Applied Physics and Technology, Peking University, Beijing 100871, China
Published: December 2020

To simulate the radiation transport of the spherical hohlraum with octahedral six laser entrance holes and to study the capsule radiation uniformity, a Monte Carlo method is introduced. For simple analytical models, with different hohlraumto-capsule radius ratios, the capsule radiation uniformity variation rules are studied, and the Monte Carlo calculation results can match the analytical results obtained by the “view factor” method. For more complicated models, such as the hohlraum with shields, it's difficult for an analytical method to be calculated, but is straightforward in the Monte Carlo method. Two models with different radius of the shield have been simulated. Simulated result indicates that the shield greatly influences the distribution of X-rays on the capsule surface, and an appropriate shield can increase the utilized efficiency of X-rays and improve the capsule radiation uniformity remarkably, otherwise, the uniformity might be destroyed badly. So the location and the radius of the shields must be designed carefully in a spherical hohlraum. This research supports the Monte Carlo method that is applicable in the radiation transport simulation of a complicated spherical holhraum.
Micro-mechanism of damping vibration attenuation on porous metal coating
Authors: Jiang Wen-Quan  , Du Guang-Yu  , Ba De-Chun  , Yang Fan  ,   School of Mechanical Engineering and Automation, Northeastern University, Shenyang 110819, China;,   School of Mechanical Engineering, Liaoning Shihua University, Fushun 113001, China
Published: December 2020

Based on molecular dynamics method and in-situ scanning electron microscopy (SEM) observations, the damping efficiency of the porous metal coating is discussed in this paper. Molecular dynamics simulation is performed to study the plastic deformations of Cu films with vibration. In the simulation, embedded atom method (EAM) is selected and in the method an interatomic potential function is used. And porous copper coating is carried out for calculating by using velocity-verlet algorithm. The plastic deformation is due to the dislocation nucleation near free surfaces, and the dislocation is shaped into forward emission in the crystal orientation near the defects. At the same time, the change curves of stress and strain are drawn by origin software. Damping factor (η) is calculated by using the time of strain lagging stress. The regulation of elastic potential energy attenuation is obtained by energy calculation. On the other hand, in-situ tensile/compression experiment is conducted by the FEI Quanta 200 SEM with a maximum load capacity of 2 kN at room temperature. A copper layer is deposited on the surface of the polyimide film by the electron beam evaporation deposition method. The thickness of the copper layer is 10 μm and the thickness of polyimide is 175 μm. Using the scanning electron microscope, microstructures of the coating are observed. It could be seen that the coating and the polyimide film are both better in compactness. Using in-situ testing machine at SEM, the samples with and without copper coatings are respectively tested under tensile and unloading. The rate of displacement loading is 2 mm/min, the results of load (F) and displacement (l') are printed every 0.1 s. The loading direction is horizontal. During in-situ tensile/compression test, the straining is stopped several times in order to make the observations and take micrographs. The digital SEM images are directly transferred to a computer via a direct memory access type A/D converter, which can rapidly capture clear images of the 1024×943 pixel frames. The simulations and experimental results indicate that the dislocation near defects get rid of weak pinning points and limit to the strong pinning point, the internal friction is generated due to the change of dislocation and the relative sliding near grain boundary, and the stored elastic potential energy is consumed, which causes the damping effect of the film.
N-F co-doped in titaninum dioxide nanotube of the anatase (101) surface: a first-principles study
Authors: Zhu Xue-Wen  , Xu Li-Chun  , Liu Rui-Ping  , Yang Zhi  , Li Xiu-Yan  ,   College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China
Published: December 2020

The method of co-doping is very useful to improve the photocatalytic performances of titanium dioxide nanotubes. The absorption capacity to the visible light of the titanium dioxide nanotubes can be improved significantly in experiment by doping both N and F in titanium dioxide nanotubes, but the theoretical explanations are still not clear. Doping the atom N alone, the atom F alone, and both N and F in titanium dioxide nanotubes respectively, their atomic structures, electronic properties and optical performance are studied by the first principles method based on the density functional theory. It is found that formation energies are lower in titanium-rich environment than that in oxygen-rich environment. In titanium-rich environment, the N-F co-doped TiO2 nanotube has the low formation energy and stable thermodynamic system compared with the N alone and the F alone doped TiO2 nanotube. Besides, the O3C can be replaced more easily than the O2C when doping N alone, F alone and co-doping N-F in TiO2 nanotube. By analyzing the energy band, we can find that the band gap changes little with doping N and the change of the band gap for the co-doping N-F case is the most prominent, which reduces by 0.557 eV compared with that for the un-doped TiO2 nanotube case, and this is mainly from the contributions of the impurity level near the top of the valence band. Besides, the different charges are calculated and it is indicated that the ability to gain electrons of N is stronger than that of F, and through analyzing the photocatalytic performance, it is found that though the gap of the nanotube is larger than that of the body, the reducibility of nanotube is better than that of the body. Both the reducibility and the oxidability of the nanotube are reduced but its activity is not lost when co-coping the atoms of N and F in titanium dioxide nanotubes. Moreover, the optical absorption spectrum shows that the red shift phenomenon is obvious for doped system and also for the co-doped system. Therefore, co-doping both N and F in titanium dioxide nanotubes is the most useful method to improve the photocatalytic performances of the TiO2 nanotubes.
Influences of shear deformation on electronic structure and optical properties of B, N doped carbon nanotube superlattices
Authors: Jiang Yan  , Liu Gui-Li  ,   College of Constructional Engineering, Shenyang University of Technology, Shenyang 110870, China
Published: December 2020

Carbon nanotubes, one of the most advanced nanoscale materials, have attracted much research attention since they exhibited semiconductor, metal or insulator properties depending on their geometric structures. Carbon nanotubes have great potential in various applications in electronic and optical device. Dopants to the carbon nanotubes intentionally could offer a possible route to change and tune their electronic, optical properties. Another important and effective method is to deform the carbon nanotubes structure. Superlattice structures can offer extra degrees of freedom in designing electronic, optical devices. To understand the involved mechanism, in this paper, the geometry structures, electronic structures and optical properties of the armchair carbon nanotube superlattices doped cyclic alternately with B and N under different shear deformations are investigated by the first-principles method through using the CASTEP code in MS 6.0. It is found that the structures of carbon nanotube superlattices can be dramatically changed by shear deformation. When the shear deformation is less than 9%, the optimization geometry structures of carbon nanotube superlattices are still similar to tubular structures, when the shear deformation is greater than 12%, the geometry structures of these systems have large distortions. The results about the binding energy show that the shear deformation changes the stability of the armchair doped carbon nanotube superlattice. The larger the shear deformation, the lower the stability of the doped carbon nanotube superlattices is. The analysis of charge population show that the covalent bond and ionic bond coexist in the armchair carbon nanotube superlattices doped cyclically alternately with B and N. The band gap of the carbon nanotube superlattice is affected by N, B dopants, as a result, the carbon nanotube superlattice changes from a metal to a semiconductor. Compared with the (5, 5) nanotube superlattices, the band gaps of the (7, 7), (9, 9) doped carbon nanotube superlattices increase. With increasing the shear deformation, the band gap of the doped carbon nanotube superlattices decreases gradually, when the shear deformation is greater than 12%, the band gap changes into 0 eV, the carbon nanotube superlattice changes back into a metal from a semiconductor. The analysis of density of states obtains the same conclusions as the energy band analysis. In optical properties, compared with the armchair carbon nanotube superlattices doped cyclically alternately with B and N without shear deformation, those systems under shear deformation have the peaks of the absorption coefficient and the reflectivity that are all reduced, and are all red-shifted.
Experimental study of photon correlation spectroscopy for the long-range fluctuation of polarization in ferroelectrics
Authors: Zhang Ming-Jun  , Guo Zhi  , Tai Ren-Zhong  , Zhang Xiang-Zhi  , Luo Hao-Su  ,   Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China;,   University of Chinese Academy of Sciences, Bejing 100049, China;,   Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
Published: December 2020

Based on the theory of random fluctuation of polarization clusters and the model of Wiener random process, the relaxation law of long-range fluctuation of polarization and the possible forms of light intensity autocorrelation function g2(τ) measured from photon correlation spectroscopy (PCS) experiments have been derived. The relationship between relaxation mechanisms of microscopic polarization clusters and macro relaxation laws is expounded. This research supplies a theoretical model for the application of PCS in researching the relaxation process of polarization clusters in ferroelectrics. Based on the improved He-Ne laser PCS experimental set-up, the relaxation process of long-range fluctuation of polarization clusters in BaTiO3 and 0.71Pb (Mg1/3Nb2/3) O3-0.29PbTiO3 single crystals near phase transition temperature is studied. As for BaTiO3, the dual relaxation processes of long-range fluctuation of polarization clusters are observed at temperatures above TC+4 K, which may be related to its order-disorder mechanism of phase transition. For 0.71Pb (Mg1/3Nb2/3) O3-0.29PbTiO3, the dual relaxation processes exist on both sides of the cubic-tetragonal phase transition temperature. The PCS experimental results are fitted well by the derived theoretical model, and the characteristic relaxation times of long-range fluctuation of polarization clusters are extracted. Two relaxation times, τs and τl corresponding to short and long relaxation time, respectively, are initially observed, where τs is several microseconds, and τl is tens of microseconds. The abrupt increase of relaxation times at phase transition temperature and the phenomenon of critical slowing down can be observed in the two samples.
Photonic Dirac point realized in two dimensional annular photonic crystals
Authors: Zhang Zhong-Jie  , Shen Yi-Feng  , Zhao Hao  ,   Department of Physics, China University of Mining and Technology, Xuzhou 221116, China
Published: December 2020

The Dirac cones in photonic crystals have aroused much interest in the last few years. Annular photonic crystals have also been well studied for designing and controlling the band gap because they have more parameters than usual photonic crystal. In this paper, we study a two-dimensional square lattice dielectric annular photonic crystal to explore the formation of the photonic Dirac cone by the accidental degeneracy method. The theoretical tool is the plane wave expansion method. The results show that this system can provide a Dirac point in the center of the Brillouin-zone in the photonic band if both the outer radius and the inner radius of each scatterer are chosen to be appreciate values when the dielectric refractive index of the annular rod is fixed. For example, there is a Dirac point at the photonic normalized frequency f=0.438(c/a) when n=3.4, RO=0.42a, RI=0.305a, where f is the frequency, c is the light speed in vacuum, a is the lattice constant, n is the refractive index, RO is the outer radius, and RI is the inner radius. It is also found that within a confined region of outer radius RO(0.37aROa), when a Dirac point is realized in the annular photonic crystal (n>1.4), the inner radius RI and the outer radius RO obey a relation of RI=-1.104+8.167RO+(-11.439)RO2, which is unrelated to the refractive index n of the dielectric annular rod. If n is less than 1.4, this rule is not valid. At the same time, the normalized frequency at which the Dirac point is realized, decreases with increasing both refractive index n and outer radius RO. Especially, the curves of the relation between photonic frequency f and outer radius RO almost do not change their profiles but only be shifted up and down with changing the refractive index n. Based on this, we also design and predict the annular photonic crystal which provides a Dirac point. The goal is to obtain the other relative parameters (frequency f, outer radius RO and the inner radius RI) of the photonic crystal system if the refractive index n is fixed. The values of the prediction agree very well with the values obtained by the rigid theoretical calculation within a relative error of only 4%.
Growth behaviors and forced modulation characteristics of dendritic sidebranches in directional solidification
Authors: Guo Chun-Wen  , Li Jun-Jie  , Ma Yuan  , Wang Jin-Cheng  ,   State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Growth behaviors of dendritic sidebranches under random noises and characteristics of sidebranches modulated by external forces in directional solidification are studied by using phase field simulations. Simulation results show that, under random noises no regular sidebranches appears all the time, but sidebranches can be formed within a suitable range of frequencies. Moreover, strongly correlated sidebranches are formed at a fixed frequency and in a certain period, usually called a burst, to appear. There is no correlation between different bursts, but the frequency of every sidebranch within a burst is the same as its precursor, and this fixed frequency is consistent with the peak frequency of the whole spectrum of sidebranch. By introducing a time-periodic external force with a frequency in the range of the whole spectrum, regular dendritic sidebranches can be induced, and they can be most developed if the frequency of the external force is the same with that in a burst. The simulation results can provide guidance to control dendritic morphologies in solidification.
An improved WOx memristor model with synapse characteristic analysis
Authors: Meng Fan-Yi  , Duan Shu-Kai  , Wang Li-Dan  , Hu Xiao-Fang  , Dong Zhe-Kang  ,   School of Electronics and Information Engineering, Southwest University, Chongqing 400715, China;,   Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China
Published: December 2020

Memristor is defined as the fourth basic electronic element, the studies on its models exhibit diversity. Now, the matching extent between memristor model and natural memristor has received researchers' wide attention. A new memristor model is proposed by changing the ion diffusion term of the WOx memristor, namely, adding another two internal state variables τ and μ which denote the relaxation time and retention, respectively, and the improved model can simulate natural memristor better. Firstly, the new one is able to not only describe the general characteristics of a memrsitor, but also capture the memory loss behavior. In addition, the new memristor can be considered as a neural synapse, under the action of the input pulses with different amplitudes, duration and intervals, the spike rate dependent plasticity, short-term plasticity (STP), and long-term plasticity (LTP) are analyzed, and the ''learning experience'' phenomenon which is very similar to the biological system is discovered, most of which is due to the back diffusion of the oxygen vacancies during the intervals of the input pulses which are caused by the concentration difference. Moreover, an exponential decay equation is built to describe the relaxation process of STP. Finally, taking into consideration the relationship between temperature and ion diffusion coefficient, the effect of temperature on the relaxation process of STP is discussed. Experimental results show that the new memristor model can better match the actual behavior characteristics, and more suitably acts as a synapse for being applied to neuromorphic systems.
Light-extraction enhancement of GaN-based LEDs by closely-packed nanospheres monolayer
Authors: Chen Zhan-Xu  , Wan Wei  , He Ying-Ji  , Chen Geng-Yan  , Chen Yong-Zhu  ,   School of Electronic and Information, Guangdong Polytechnic Normal University, Guangzhou 510665, China;,   College of Electromechanical Engineering, Guangdong Polytechnic Normal University, Guangzhou 510665, China
Published: December 2020

GaN based light-emitting diodes (LEDs) have been attracting a great deal of interest due to their capability in emitting a spectrum from ultraviolet to green and their applications in traffic signals, displays and solid-state lighting. However, the high efficiency of LED is still obstructed by light-extraction efficiency. In this work, we propose that light-extraction efficiency of GaN-based blue LED should be improved by a self-assembled monolayer of polystyrene spheres. The GaN-based LED grown on sapphire substrate emits the light mainly from the indium tin oxide (ITO) transparent electrode. And the hexagonal closely-packed polystyrene sphere monolayer is formed onto the ITO layer. In order to study the light-extraction efficiency affected by the size of nanosphere, nanosphere monolayers of different sizes are prepared onto the ITO layer, and the diameters of the polystyrene spheres are 250, 300, 450, 600 and 950 nm, respectively. The electroluminescence results show that using polystyrene sphere monolayer can improve the light-extraction efficiency compared with using the conventional LEDs, and the light-extraction efficiency reaches a maximum when the average size of spheres (450 nm) approximates to the wavelength (465 nm) of that light. The light output power of the LED with polystyrene sphere of the optimum size is experimentally enhanced by 1.34 and 1.25 times under the injection currents of 20 and 150 mA, respectively. In order to explain the physical mechanism of the light-extraction enhancement, we carried out the three-dimensional finite difference time-domain simulation thereby calculate the transmission spectrum of the structure. The results of simulation show that the incident light beyond the critical angle can be partly extracted when the surface of LED has a polystyrene sphere monolayer, leading to an enhanced light-extraction efficiency. So the nanosphere monolayer acts as a two-dimensional diffraction lattice which behaves as a light scattering medium for the light propagating in a waveguiding mode within the LED. Furthermore, the polystyrene nanosphere has the advantages of low-cost and high-precision, and is very suitable for large area preparation on LEDs. So this method is a simple and cost-effective method to improve the light-extraction efficiency from LED.
Ffluorescence X-ray source used for calibrating the detector of X-ray navigation
Authors: Dai Jin-Fei  , Zhao Bao-Sheng  , Sheng Li-Zhi  , Zhou Yan-Nan  , Chen Chen  , Song Juan  , Liu Yong-An  , Li Lin-Sen  ,   State Key Laboratory of Transent Optics and Photonics, Xi'an Institute of Optics and Precision Mechanicas, Chinese Academy of Sciences, Xi'an 710119, China;,   University of Chinese Academy of Science, Beijing 100084, China
Published: December 2020

Lots of research work on the X-ray pulsar navigation detector has been carried out, but the rigorous quantitative calibration results of these detectors have never been given out. In order to further promote the research process in X-ray pulsar navigation field, a kind of high-precision X-ray source which could be tunable in energy distribution and photon flux is necessary. A new method has been proposed to generate such an X-ray source, in which a conventional X-ray tube which is called the original level tube is used to excite a special fluorescence target to generate fluorescence X-ray source. Firstly, the primary experiment system is built, with which the intensity of the fluorescence X-ray source is measured in atmospheric environment. The result indicates that the fluorescence X-ray source can be implemented in vacuum system to calibrate the detectors. Then an integral fluorescence X-ray source is fabricated which can be used in vacuum system and its intensity is measured under the condition of Dx=300 cm and Ia=200 μA. The photo fluxes are obtained to be 19.57 phs/s at 4.51 keV, 25.22 phs/s at 5.41 keV, and 33.27 phs/s at 8.05 keV. These data demonstrate the correctness of our method and that this new fluorescence X-ray source can be used to calibrate the x-ray pulsar navigation detector.