bluuebunny/crossref_metadata_2025 huggingface dataset:
Hybrid parallel optimization of density matrix renormalization group method
Authors: Chen Fu-Zhou , Cheng Chen , Luo Hong-Gang ,   School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China,   Beijing Computational Science Research Center, Beijing 100084, China
Published: December 2020

Density matrix renormalization group (DMRG), as a numerical method of solving the ground state of one-dimensional strongly-correlated lattice model with very high accuracy, requires expensive computational and memory cost when applied to two- and quasi-two-dimensional problems. The number of DMRG kept states is generally very large to achieve a reliable accuracy for these applications, which results in numerous matrix and vector operations and unbearably consuming time in the absence of the proper parallelization. However, due to its sequential nature, the parallelization of DMRG algorithm is usually not straightforward. In this work, we propose a new hybrid parallelization strategy for the DMRG method. It takes advantage of the computing capability of both central processing unit (CPU) and graphics processing unit (GPU) of the computer. In order to achieve as many as DMRG kept states within a limited GPU memory, we adopt the four-block formulation of the Hamiltonian rather than the two-block formulation. The later consumes much more memories, which has been used in another pioneer work on the hybrid parallelization of the DMRG algorithm, and only a small number of DMRG kept states are available. Our parallel strategy focuses on the diagonalization of the Hamiltonian, which is the most time-consuming part of the whole DMRG procedure. A hybrid parallelization strategy of diagonalization method is implemented, in which the required data for diagonalization are distributed on both the host and GPU memory, and the data exchange between them is negligible in our data partitioning scheme. The matrix operations are also shared on both CPU and GPU when the Hamiltonian acts on a wave function, while the distribution of these operations is determined by a load balancing strategy. Taking fermionic Hubbard model for example, we examine the running performance of the hybrid parallelization strategy with different DMRG kept states and provide corresponding performance benchmark. On a 4-leg ladder, we employ the conserved quantities with U(1) symmetry of the model and a good-quantum number based task scheduling to further reduce the GPU memory cost. We manage to obtain a moderate speedup of the hybrid parallelization for a wide range of DMRG kept states. In our example, the ground state energy with high accuracy is obtained by the extrapolation of the results, with different numbers of states kept, and we show charge stripes which are usually experimentally observed in high-temperature superconductors. In this case, we keep 104 DMRG states and the GPU memory cost is less than 12 Gigabytes.
All-optical mass sensing based on ultra-strong coupling quantum dot-nanomechanical resonator system
Authors: Yang Jian-Yong , Chen Hua-Jun ,   School of Mechanics and Photoelectric Physics, Anhui University of Science and Technology, Huainan 232001, China
Published: December 2020

Nanomechanical oscillators have not only the advantages of extremely small mass and volume, but also high vibration frequency and quality factor, so they are widely used in the field of sensors. In recent years, nanomechanical oscillators comprised of graphene nanoribbons, carbon nanotubes, molybdenum disulfide and other materials have been used to make mass sensors. Great progress has been made in the application of mass sensing, but the measurement environment is limited to ultra-low temperature. Presented in this paper is a hybrid quantum dot-nanomechanical resonator (QD-NR) system which is based on semiconductor chips with quantum dots embedded at the bottom of inverted semiconductor conical nanowires. The system has the advantages of high integration level, full optical interface and low temperature compatibility. In addition, it has a coupling strength, a frequency as large as the vibration frequency of the mechanical oscillator, and a long spin life, which provides the possibility of realizing the quantum unassembled readout of a single spin at room temperature. We investigate the coherent optical properties with the optical pump-probe scheme, and an all-optical mean for determining the resonator frequency and the coupling strength of the QD and NR is presented with the absorption spectrum under different parameter regimes. We set the frequency of the pump light to be equal to the exciton frequency and scan the frequency range of the detection light, and then two sharp peaks will appear in the absorption spectrum of the probe light, and the sharp peak is for the frequency of the mechanical oscillator. Moreover, the coupling strength can be obtained from the linear relationship between the peak splitting width and the coupling strength in the absorption spectrum. Further, we put forward a room temperature mass sensing based on the hybrid QD-NR system, and the frequency shift caused by additional nanoparticles can be directly measured with the absorption spectrum, and then the mass of extra nanoparticles can be determined. Comparing with the previous nanomechanical oscillator, the exciton-phonon coupling strength is very strong in the system and can reach the ultra-strong coupling, which is advantageous for observing the coherent optical properties and reaching high precision and resolution mass sensing. In this system, the mass responsivity can reach. The scheme is expected to be applied to mass measurement of some biomolecules, isotopes and other materials, and also be widely used in other fields at a nanogram level.
Upper-laser-level lifetime measurement of rear earth dopant in active fiber
Authors: Liu Heng , Zhang Jun-Xiang , Fu Shi-Jie , Sheng Quan , Shi Wei , Yao Jian-Quan ,   Institute of Laser and Optoelectronics, Tianjin University, Tianjin 300072, China,   Key Laboratory of Optoelectronic Information Science and Technology (Ministry of Education), Tianjin University, Tianjin 300072, China,   College of Optical Science, University of Arizona, Arizona 85721, USA
Published: December 2020

The upper-laser-level lifetime (fluorescence lifetime) of the rear earth dopant in the active fiber is a key parameter which indicates the performance of the fiber, and takes an important role in designing the laser system. However, the accurate measurement of fluorescence lifetime in active fiber remains challenging, which mainly rely on the direct measurement of laser induced fluorescence lifetime of the active fiber or lifetime measurement of bulk laser glass. The former method suffers the error due to the amplified spontaneous emission and the reabsorption process, while the latter ignores the influence of high temperature and tension produced during the fiber drawing on the emission behavior of the material. Therefore, the accuracy of these measurements can become a problem. In this work, we propose a new approach to measuring the upper-laser-level lifetime of the rear earth dopant in the active fiber based on the power/energy performance of the fiber amplifier. The population inversion, i. e. the energy storage, in the active fiber of a fiber amplifier is a function of upper-laser-level lifetime. Therefore, the upper-laser-level lifetime can be derived by measuring the average power or output pulse energy of the amplifier, given that the energy storage in the active fiber is extracted adequately by a seed laser. Using the rate equations, we model the population inversion and energy storage in the active fiber each as a function of pump power and time, and the resulting relationship between the upper-laser-level lifetime and the average output power. The upper-laser-level lifetimes of several commercial Yb-doped active fibers are experimentally measured by this method through using the fibers as the gain media of the amplifier operated at 1064 nm. The convenience of experimental data processing is also discussed. The measured lifetime and evolution trend of the lifetime with dopant concentration exhibitthat they are in good agreement with those from other reports and the theoretical model, which verifies the feasibility of this method.
Grain boundary electrical characteristics for rutile TiO2 under pressure
Authors: Wang Chun-Jie , Wang Yue , Gao Chun-Xiao ,   College of Engineering, Bohai University, Jinzhou 121013, China,   College of New Energy, Bohai University, Jinzhou 121013, China,   State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
Published: December 2020

In this paper, the grain and grain boundary characteristics of pure rutile TiO2 under pressure are investigated by electrochemical impedance spectroscopy equipped with diamond anvil cell (DAC). Only one semi-circle can be detected under each pressure in a range of 1.4–11.5 GPa. With the pressure increasing, the shape of semi-circle is unchanged, while the size of semi-circle gradually decreases, which can be attributed to the decrease of bulk resistance due to the reduction of band gap under pressure. The absence of grain boundary characteristic in the impedance spectra signifying that Schottky barrier is not present at the grain boundaries. With further increasing pressure, an interesting phenomenon can be observed above 12.7 GPa. The shape of semi-circle is distorted, and exhibits two overlapping semi-circles. The first semi-circle (high frequency) originates from the contribution of bulk, and the second one (low frequency) can be ascribed to the effect of grain boundary. The occurrence of grain boundary semicircle indicates that the aggregation of space charges at the grain boundary. In this case, the phase transformation from rutile to baddeleyite structure occurs, the electric transport mechanism is changed, and new lattice defects are formed. Also, two discontinuous points (11.5 and 15.4 GPa) can be detected in the resistance curve. The remarkable change of resistance occurs at 12.7 GPa which is corresponding to the phase transition from rutile to baddeleyite phase. The occurrence of phase transition leads the new interfacial energy to occur, the total energy of system to increase, and the movement of carriers to impede. Thus, the resistance increases significantly, and the maximum value occurs at 15 GPa. Further analysis indicates that the space charge potential is modified with pressure increasing, implying that the electrical transport properties of TiO2 are related closely to phase transition. With the pressure increasing from 12.7 to 25.2 GPa, the irregular change of space charge potential can be attributed to the rutile and baddeleyite phase coexisting. When the pressure is higher than 25.2 GPa, the space charge potential is a constant (about 30 mV). According to the investigations, the TiO2 grain boundary space charge potential under pressure is mainly contributed from two parts: the electrostatic interaction and the elastic interaction.
The invariant eigen-operator method in matrix form and the eigenfrequency of several mesoscopic circuits
Authors: Wu Ze , Fan Hong-Yi ,   Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China,   Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

The Invariant Eigen-operator (IEO) method is widely used in solving the eigenfrequencies of the coulped quantum mesoscopic circuits. The previous IEO method is complicated but stylized, we always wasted much time in this boring processes. Here we extended the IEO method to the matrix form based on Lagrangian of the complex mesoscopic circuits, and express the ideas and processes of the previous calculations of the IEO method in a very simple matrix form. The mathematical methods we used is the indicator representation of the matrix, and we got a very simple and convenient matrix form of the IEO method. This form has important significance for the calculation of large-scale complex multi-loop mesoscopic circuits. Moreover, the matrix form of the IEO method is very friendly to the programming implementation of the complex quantum mesoscopic L−C circuits, it is probably a most optimal algorithm for calculating the eigenfrequencies of the quantum mesoscopic L−C circuits. In addition, with some help of computer programs, we used this method to calculate the eigenfrequencies of three L−C mesoscopic circuits, including two cases with and without mutual inductance. We revealed some relevant properties of these circuits by calculating results, indicating that the eigenfrequency is only related to the element properties of the mesoscopic circuit itself. Finally, we found that this method can also be used in other areas like atom-light coupling systems and solid state physics.
Competitive adsorption of CO and H2 on strained Fe(110) surface
Authors: Li Shou-Ying , Zhao Wei-Min , Qiao Jian-Hua , Wang Yong ,   Schools of Materials Science and Engineering, China University of Petroleum (East China), Qingdao 266580, China,   Schools of Mechanical and Electronic Engineering, Qingdao Binhai University, Qingdao 266555, China
Published: December 2020

In this work, the competitive adsorption behavior of H2 and CO on strained Fe(110) are investigated by the first-principles method based on the spin-polarized density functional theory to study the hydrogen embrittlement of steels. The results show that the most stable adsorption site for CO is top site, and the orbital of CO molecule hybridizing with Fe 3p and 4s states illustrates a strong electronic interaction between them. The adsorption energy values of CO at the four calculated adsorption sites are more negative than those of H2, which favors the binding with Fe(110) surface. The potential energy variations for CO and H2 molecules close to the surface are calculated. The attractive force of the Fe(110) surface acting on CO in 1.5–3 Å is greater than that acting on H2. The pre-adsorbed CO increases the dissociation energy barrier of H2 from 0.08 eV to 0.13 eV but reduces the force between H2 and surface. The surface tensile strain enhances the interaction between hydrogen and Fe(110), which, however, is reduced by the compressive strain. The opposite tendency is found in the adsorption of CO. The binding strength of CO is stronger than that of H2 on the strained Fe(110) surface. The difference in adsorption energy between CO and H2 decreases with tensile strain increasing. The effect of surface strain and partial pressure of CO gas phase on the surface coverage ratio of H atom are also calculated quantitatively based on thermodynamics at 298 K, with the partial pressure of H2 set to be 10 MPa. The surface ratio of the H atom decreases with partial pressure of CO increasing. The hydrogen coverage drops nearly to zero when the partial pressure of CO reaches a certain value. This result reveals that CO can inhibit hydrogen adsorption on Fe surface. In the case where the surface ratio of hydrogen decreases to 1%, the corresponding CO partial pressures are 105 Pa, 1.1 × 103 Pa, 2.4 × 105 Pa on –2%, 0, 2% strained Fe(110) surface, respectively. High CO partial pressure is needed to suppress the hydrogen adsorption since the binding strength of CO is close to that of H2 on the expanded surface.
ZrS2 quantum dots: Preparation, structure, and optical properties
Authors: Zhou Liang-Liang , Wu Hong-Bo , Li Xue-Ming , Tang Li-Bin , Guo Wei , Liang Jing ,   Key Laboratory of Advanced Technique and Preparation for Renewable Energy Materials, Ministry of Education, Yunnan Normal University, Kunming 650092, China,   Kunming Institute of Physics, Kunming 650223, China,   School of Physics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

In recent years, transition metal chalcogenides (TMDs) have attracted extensive attention of researchers due to their unique electronic structure and excellent photoelectric properties. In this paper, hexagonal structure 1T-ZrS2 quantum dots (QDs) having a monodisperse grain size of around 3.1 nm is prepared by the ultrasonic exfoliation method. The preparation includes the following steps: ZrS2 powder is ground, followed by ultrasonic exfoliation in 1-methyl-2-pyrrolidone (NMP), and 1T-ZrS2 QDs are collected after centrifugation. The structure, morphology and optical properties of the QDs are studied in detail. The structure, morphology, size distribution, and elemental composition of 1T-ZrS2 QDs are studied by using X-ray diffractometer (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The chemical bonds of 1T-ZrS2 QDs are characterized by X-ray photoelectron microscopy (XPS) and Fourier transform infrared spectrometer (FTIR). The TEM and AFM results show that the 1T-ZrS2 QDs are spherical in shape with uniform size distribution. The sizes of the 1T-ZrS2 QDs follow a Gaussian fitted distribution with an average diameter of WC = 3.1 nm and the FWHM is 1.3 nm. The XRD diffraction pattern of 1T-ZrS2 QDs show wide dispersed diffraction peaks, which is the characteristic of QDs. The diffraction peak at 2θ = 32.3° (d = 0.278 nm) corresponds to the (101) crystal plane, and the weak diffraction peak at 2θ = 56.8°(d = 0.167 nm) belongs to the (103) crystal plane. The grain size is also calculated by using the Debye-Scherrer formula, and the calculated value (2.9 nm) is consistent with the result of TEM (3.1 nm). Two Raman vibration modes (E1g and A1g) are observed. The E1g (507.3 cm–1) and A1g (520.1 cm–1) modes relate to the in-plane and out-of-plane vibration respectively. The Raman intensity of the A1g vibration mode is stronger than that of E1g. The UV-Vis and photoluminescence (PL and PLE) characterizations exhibit that the 1T-ZrS2 QDs have two UV absorption peaks at 283 nm and 336 nm, respectively. The Stokes shift is ~130 nm, the fluorescence quantum yield reaches up to 53.3%. The results show that the 1T-ZrS2 QDs have the excellent fluorescence performance and unique optical properties, which make the 1T-ZrS2 QDs an important material for developing photodetectors, multi-color luminescent devices, and other devices.
Numerical study of effect of pressure gradient on boundary-layer receptivity under localized wall blowing/suction
Authors: Lu Chang-Gen , Shen Lu-Yu , Zhu Xiao-Qing ,   School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China
Published: December 2020

Boundary-layer receptivity is the initial stage of the laminar-turbulent transition process, and plays a key role in predicting and controlling the transition. The present researches indicate that the boundary-layer receptivity is affected not only by the different sorts of free-stream disturbances or the size, shape and position of the wall localized roughness and blowing/suction, but also by the pressure gradient. Therefore, the local receptivity under the interaction between the free-stream turbulence and localized wall blowing/suction in the pressure-gradient boundary layer is studied in the present work, thus revealing the effect of the pressure gradient on the receptive process and the group speeds of the excited T-S wave packets under the interaction of the free-stream turbulence with localized wall blowing/suction in the boundary layer. High-order finite difference scheme is utilized to discretize the incompressible perturbation Navier-Stokes equation. A modified fourth-order Runge-Kutta scheme is used for time integration. The compact difference scheme based on non-uniform meshes is applied to the spatial discretization. The convective term is discretized by the fifth-order upwind compact scheme. The pressure gradient term is discretized by the sixth-order symmetric compact scheme. The viscosity term is discretized by the fifth-order symmetric compact scheme. Besides, the pressure Poisson equation is solved by the fourth-order scheme on the non-uniform meshes. The favorable or adverse pressure gradient promotes or suppresses the receptivity triggered by the interaction between free-stream turbulence and blowing/suction. And the blowing always induces a stronger receptivity than the suction in the same intensity. The initial amplitude of the T-S wave and wave packet excited in the adverse-pressure-gradient boundary layer are two orders larger than those excited in the favorable-pressure-gradient boundary layer. It is analyzed in detail that the favorable and adverse pressure gradient play a promoting or suppressing role in the growth of the excited T-S wave. Then the influences of the pressure gradient on the amplitudes, growth rates, wave numbers, phase speeds and shape functions of the excited T-S waves are investigated. The intensive research on receptivity in the pressure-gradient boundary layers provides a reference for designing the turbine machinery blades in the practical engineering.
Pricing of stochastic volatility stock index option based on Feynman path integral
Authors: Feng Ling , Ji Wan-Ni ,   School of Economics and Management, Fuzhou University, Fuzhou 350002, China
Published: December 2020

Under the background that stock index options urgently need launching in China, the research on stock option pricing model has important theoretical and practical significance. In the traditional B-S-M model it is assumed that the volatility remains unchanged, which differs tremendously from the market’s reality. When the market fluctuates drastically, it is difficult to realize the risk management function of stock index options. Although in the Heston model, as one of the traditional stochastic volatility option pricing models, the correlation risk between the volatility and underlying price is taken into consideration, its pricing accuracy is still to be improved. From the quantum finance perspective, in this paper we use the Feynman path integral method to explore a more practical stock index option pricing model.

In this paper, we construct a Feynman path integral pricing model of stock index options with stochastic volatility by taking Hang Seng index option as the research object and Heston model as the control group. It is found that the Feynman path integral pricing model is significantly superior to the Heston model either at different strike prices on the same expiration date or at different expiration dates for the same strike price. The stock index option pricing model constructed in this paper can give the numerical solution of Feynman's pricing kernel, and directly realizes the forecast of stock index option price. The pricing accuracy is significantly improved compared with the pricing accuracy given by the Heston model through using the characteristic function method.

The remarkable advantages of Feynman path integral stock index option pricing model are as follows. Firstly, the path integral has advantages in solving multivariate problems: the Feynman pricing kernel represents all the information about pricing and can be easily expanded from one-dimensional to multidimensional case, so the change of closing price of stock index and volatility of underlying index can be taken into account simultaneously. Secondly, based on the relationship between the Feynman path generation principle and the law of large number, the mean values of pricing kernel obtained by MATLAB not only optimizes the calculation process, but also significantly improves the pricing accuracy. Feynman path integral is the main method in quantum finance, and the research in this paper will provide reference for its further application in the pricing of financial derivatives.
Non-dispersion boundary conditions of micro-optical element illuminated by broadband light source
Authors: Huang Yan-Yan , Zhang Xu-Lin , Yang Wei , Wang Xiao-Bing , Lei Lei , Peng Wen-Da , Xu Ping ,   College of Physics and Optoelectronic Engineering, Institute of Micro-Nano Photoelectronic Technology, Shenzhen University, Shenzhen 518060, China
Published: December 2020

With the development of the microstructure fabrication process and the integration of micro-optical elements, diffractive micro-optical elements are widely used in broadband light sources, such as the integrated light guide plate (ILGP). And with the structural feature size of the ILGP decreasing from tens of microns to microns and even sub-microns, the diffraction dispersion phenomenon will inevitably become a prominent problem in research and design of non-dispersion elements. Nevertheless, under the broadband light source illumination, the analysis of the dispersion characteristic of diffraction spectrum of the microstructure array has not been reported in detail. Therefore a theoretical model of micro-optical element with a typical one-dimensional rectangular phase grating (RPG) and a widely used white LED source is established in this paper. The dispersion characteristic of the diffraction spectrum is studied, that is, with the increase of period of the RGP or the cone angle of incident beam, the dispersion of diffraction spectrum weakens. Dispersion parameter C and its formula are proposed, which can precisely measure the chromatic dispersion degree of the diffraction spectrum. Furthermore, the boundary criterion point of non-dispersion C = 0.3 is given explicitly. It is explored that no matter whether the cone angle of incident beam or the RPG period increases, the non-dispersion output light can be obtained only by matching the two parameters to make the dispersion parameter C less than 0.3. Then an RPG sample, of which the structural parameters are consistent with the designed ones, is fabricated by using micro-nano processing technology. By changing the cone angle of incident beam, the luminance and the chromaticity coordinates of the diffraction beam are tested. The analyses of the test results of the fabricated RPG sample show that the spectrum dispersion regularity is in accord with the theoretical analysis. The consistency verifies the correctness of dispersion parameter C, its formula and the non-dispersion boundary criterion point. The dispersion parameter C and non-dispersion boundary criterion point presented in this paper provide a guidance for analyzing the dispersion characteristics when the structural parameters of the integrated light guide plate and other broadband micro-optical element are designed.
Defocusing mechanism and focusing evaluation function of light field imaging
Authors: Liu Bin , Pan Yi-Hua , Yan Wen-Min ,   School of Information and Communication Engineering, North University of China, Taiyuan 030051, China,   Science and Technology on Transient Impact Laboratory, Beijing 102202, China
Published: December 2020

The light field imaging technology can realize the application of the full-focus image synthesis of the scene and the de-occlusion reconstruction of background target through the classification of the light field information of the scene. How to effectively evaluate the focus area in the image is a prerequisite for the above application. The dispersion characteristics of the defocusing point of a conventional imaging system are fundamentally different from those of the defocusing area in the refocusing image of the light field. Therefore, the evaluation criteria based on the diffusion characteristics of the defocusing point cannot be applied to the evaluation of the focus of the refocusing image of the light field. Aiming at the above problems, in this paper, starting from the principle of refocusing of light field imaging, we analyze the blurring characteristics of the defocused target image, and propose a new evaluation function of the focus of the refocusing image of the light field. Based on this, the refinement segmentation method of the focal region is studied to achieve the final focus area extraction. According to the indoor scene data set captured by the camera array of Stanford university, in this paper we use the traditional focus degree evaluation algorithm and the algorithm to evaluate the focusing degree of the foreground target potted plant in the scene and obtain the complete information about the foreground target, therefore we also study the refined segmentation algorithm. Then, in the process of refocusing the background object (CD box), the foreground light is screened out, and the reconstructed image of the specified focusing plane is obtained. Using the peak-signal-to-noise ratio and mean structural similarity index measure to evaluate the quality of the target in refocusing area, the results show that the proposed algorithm in this paper can effectively mark and separate the imaginary artifact information and ensure the high-quality focus reconstruction of the partially occluded target in the scene, which can effectively overcome the influence of the edge and texture information of the object in the scene on the defocusing area. The method presented in this work has better adaptability to the focus degree evaluation of the refocusing image of the light field.
Simulation on complex dynamics of hollow cathode discharge in argon
Authors: He Shou-Jie , Zhou Jia , Qu Yu-Xiao , Zhang Bao-Ming , Zhang Ya , Li Qing ,   Hebei Key Laboratory of Optic-electronic Information and Materials, College of Physics Science and Technology, Hebei University, Baoding 071002, China
Published: December 2020

In this paper, the dynamics of hollow cathode discharge in argon is simulated by fluid model. In the numerical model considered are 31 reaction processes, including direct ground state ionization, ground state excitation, stepwise ionization, Penning ionization, de-excitation, two-body collision, three-body collision, radiation transition, elastic collision, and electron-ion recombination reaction. The electron density, Ar+ density, Ar4s, Ar4p, Ar3d particle density, electric potential and electric field intensity are calculated. At the same time, the contributions of different reaction mechanisms for the generation and consumption of electron, Ar4s and Ar4p are simulated. The results indicate that hollow cathode effect exists in the discharge, and the Ar4s density is much higher than electron density. The penning ionization 2Ar4s → Ar+ + Ar+ + e and stepwise ionization involving Ar4s make important contributions to the generation of new electrons and the balance of electron energy. In particular, the penning ionization reaction 2Ar4s → Ar2+ + e, which is generally ignored in previous simulation, also has an significant influence on electron generation. The spatial distribution of excited state argon atomic density is the result of the balance between the formation and consumption of various particles during discharge. Radiation reaction Ar4p → Ar4s + hν is the main source of Ar4s generation and the main way to consume Ar4p. Ar4s + e →Ar4p + e is the main way of Ar4s consumption and Ar4p production. The simulation results also show that the Ar4p density distribution can better reflect the optical characteristics in the hollow cathode discharge.
Blue perovskite light-emitting diodes: opportunities and challenges
Authors: Duan Cong-Cong , Cheng Lu , Yin Yao , Zhu Lin ,   Institute of Advanced Materials (IAM), Nanjing Tech University (NanjingTech), Nanjing 210009, China
Published: December 2020

The great progress of light-emitting diodes (LEDs) has been made based on perovskites, and the external quantum efficiency of near infrared, red and green devices have reached > 20%, exhibiting their great potential applications in lighting and displays. However, the performance of blue perovskite LEDs is very poor, thus limiting their applications in the field of full-color displays. The blue perovskite LEDs can be achieved through mixed halides or quantum confinement effect. In this paper, we review the research progress of blue perovskite LEDs based on these two strategies, discuss the challenges to achieve high-performance perovskite LEDs and present our perspectives.
Effects of critical current density on mechanical properties of cylindrical superconductors
Authors: Cheng Peng , Yang Yu-Mei ,   Lanzhou University of Technology, School of Science, Lanzhou 730050, China
Published: December 2020

High-temperature superconductor has high critical temperature, high transport current capacity and low energy consumption, which correspondingly offer the wide applications in the field of electric power. As an important concern, the mechanical properties of superconductor carried with transport current have received extensive attention. Still, its mechanical properties in various electromagnetic environments are under study. Most of previous studies are based on the assumption of uniform distribution of critical current density, and only few researches based on the non-uniform distribution of critical current density are carried out. In this work, the mechanical flux pinning response of cylindrical superconducting structures is studied. Considering the non-uniform features of critical current density along the radial direction, the distribution law of induced magnetic field and current for the cylindrical superconducting structure is obtained based on the Bean model. Combined with the plane strain method, the analytical expression of magnetic flux pinning force, stress and magnetostriction in the superconducting structure are obtained. The results show that the uneven distribution of critical current density causes the flux pinning force to change, which further leads the superconductor`s local radial stress to vary with the critical current density. When the transport current flowing through the superconductor is increased in the ascending field, the radial stress and the hoop stress both appear compressive. The non-uniform distribution of critical current density has no significant effect on the overall trend of the internal stress, but displays an obvious influence on the stress distribution, and the superconducting structure is compressed and deformed. The results are consistent with those in the uniform case. When the transport current decreases during field descending, the critical current starts to reverse from the outermost part, then the compressive stress and tensile stress exist simultaneously. The hoop stress has a discontinuous point at the discontinuous portion of the critical current density, thus the damage probability is higher than that of the uniform distribution. In other words, the shear strength of superconductor is required to be higher for application. Also, the degree of magnetostriction is higher when the distribution of critical current density is set to be uniform, that is, the non-uniform distribution of the critical current density causes the superconducting structure to undergo greater deformation. Therefore, in engineering applications, the structural strength of the superconducting material must be enhanced to cope with the challenge from the uneven distribution of critical current density.
Enhanced third-harmonic generation in silicon metasurface
Authors: Yang Jiu-Long , Yuan Qing-Chen , Chen Run-Feng , Fang Han-Lin , Xiao Fa-Jun , Li Jun-Tao , Jiang Bi-Qiang , Zhao Jian-Lin , Gan Xue-Tao ,   MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions, and Shaanxi Key Laboratory of Optical Information Technology, School of Science, Northwestern Polytechnical University, Xi’an 710072, China,   State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics, Sun Yat-sen University, Guangzhou 510275, China
Published: December 2020

We report the enhanced third-harmonic generation (THG) from a silicon metasurface consisting of an array of L-shaped nanoresonators. The L-shaped nanoresonator is designed as a small cuboid with a notch cut from one corner. And 16 × 15 L-shaped nanoresonators are arranged into an array with a square lattice. In order to fabricate the structure, a 600-nm-thick silicon layer is first deposited on a 500-μm-thick sapphire substrate, which is then patterned into the metasurface structure by using electron beam lithography and inductively coupled plasma dry etching process. To evaluate the linear optical property of the fabricated metasurface, a continuous-wave narrow band laser with a tunable wavelength range of 1530−1560 nm is employed to measure the transmission and reflection spectrum. The measurement results show a Fano resonance at a wavelength of 1548 nm when the incident laser is linearly polarized along the long arm of the L-shaped nanoresonator. Pumping at the resonant wavelength, the metasurface shows significant polarization sensitivity for the transmitted light and the reflected light. To excite the THG signal from the metasurface, a femtosecond pulsed laser with a tunable wavelength range of 1540−1560 nm is then employed as the pump. Strong THG signal is observed when the laser wavelength is tuned on the resonant wavelength (1548 nm), indicating a conversion efficiency of ～ 3×10–7. By comparing the THG signals triggered on- and off-resonance, an enhancement factor of 220 is extracted, which is attributed to the field-enhancement of the Fano resonance. The resonance enhanced THG signal also has polarization-dependence with an extinction ratio of 15 dB. These experimental results are verified well by numerical simulations based on a finite-element technique, including the Fano resonance and the enhanced THG process. By combining the numerically calculated electrical field of the resonant mode and the calculation of nonlinear polarizations, the resonance enhanced THG as well as its polarization-dependence are confirmed numerically. The realized strongly enhanced THG from the silicon metasurface promises to extend their linear optical functionalities into nonlinear regime.
Subatomic scale study of atom-generated higher-order harmonic
Authors: Liu Yan , Guo Fu-Ming , Yang Yu-Jun ,   College of Sciences, Jilin Institute of Chemical Technology, Jilin 132022, China,   Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy, Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
Published: December 2020

The higher-order harmonics generated from an atom irradiated by ultarashort laser pulses is one of the important ways to obtain ultrashort attosecond pulses and coherent XUV sources. In order to produce a high-inntensity XUV source, one needs to study the mechanism of harmonic generation. The mechanism of the atomic high harmonic generation can be well understood by the semi-classical three-step model. First, the electron tunnels the barrier formed by the atomic potential and laser electric field, and then it propagates freely in the laser field and can be driven back to the mother ion where it recombines with the ground state of ion. Although the cutoff energy of the high harmonic can be predicted by this model, it cannot provide more information about the harmonic efficiency and the spectral structure. Recently, the generation mechanism of high harmonic has been studied by using the Bohmian trajectory scheme based on the time dependent wave packet. It is found that the harmonic structure can be reconstructed qualitatively by using a single Bohmian trajectory. The more accurate structure of harmonic spectrum needs more Bohmian trajectories. The calculation of these trajectories requires a lot of computation resources because the trajectory calculation is from the numerical solution for the time-dependent Schrödinger equation. In this work, we numerically solve the time-dependent Schrödinger equation of a model atom irradiated by ultrashort laser pulses. The time-dependent dipole moments at different spatial locations are calculated from the time-dependent wave function. The harmonic spectra are calculated from the Fourier transform of the time dipole moments. The harmonic spectra of different spatial locations show that the main emission positions of harmonic emission are near the nuclear region. One can observe the odd- and even-order harmonics at the different spatial positions. There has a larger radiation intensity for the integer-order harmonic. For the odd-order harmonics, their harmonic phases are the same on both sides of x = 0. For the even-order harmonics, their harmonic phases each have a pi difference on both side of x = 0. By using the filtering scheme, we analyze the phases of an harmonic at different spatial locations. It is found that the phase difference leads the odd-order harmonics to increase and the even-order harmonics to disappear. These findings contribute to the understanding of the physical mechanism of higher harmonic generated from an atom irradiated by strong laser pulses.
Two-dimensional phase sensitive detector and its application to demodulating amplitude modulated image
Authors: Liu Yi , Hao Si-Zhong , Tian Yu-Lin , Liu Guo-Zhong ,   College of Materials Science and Engineering, Sichuan University, Chengdu 610207, China,   No. 33 Research Institute, China Electronics Technology Group Corporation, Taiyuan 030006, China,   School of Instrumentation Science and Opto-electronics Engineering, Beijing Information Science and Technology University, Beijing 100192, China,   Institute of Precision Measuring Technology and Instruments, Beijing Information Science and Technology University, Beijing 100192, China
Published: December 2020

 Two-dimensional spatial modulation and demodulation technology can improve the weak signal detection capability of photoelectric detection system in a stronger noise background. In this paper, a two-dimensional phase-sensitive detector for the high-precision demodulation of 2D spatial amplitude-modulated signal is proposed. In this paper, we introduce the principle of extracting modulating signals from 2D amplitude modulated images by using 2D phase-sensitive detector, and simulate its ability to suppressing noise and extracting signal from the amplitude-modulated images buried in noise. In order to eliminate the influence of grid image generated by metal wire mesh sandwiched between two layers of glass on the detection of shielding glass defects, the methods of filtering in the frequency domain, rectifying plus filtering and two-dimensional phase sensitive detector are used to demodulate the mesh amplitude-modulated image, and the effects of extracting defects and suppressing noise are compared with each other.

 The principle and experimental results of defect detection of ordinary glass by using external carrier are also provided. The simulation results and the detection results show that the two-dimensional phase-sensitive detector can be used to demodulate spatial two-dimensional amplitude-modulated image produced by optical modulators to extract two-dimensional measurement signals. The 2D phase-sensitive detector can greatly improve the signal-to-noise ratio of the output image, increase detection accuracy and the ability to extract modulating signals from the amplitude-modulated image buried in noise.
Research advances in acoustic metamaterials
Authors: Tian Yuan , Ge Hao , Lu Ming-Hui , Chen Yan-Feng ,   Department of Materials Science and Engineering, College of Engineering and Applied Sciences,Nanjing University, Nanjing 210093, China,   Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
Published: December 2020

Acoustic metamaterials have opened up unprecedented possibilities for wave manipulation, and can be utilized to realize many novel and fascinating physical phenomena, such as acoustic self-collimation, cloaking, asymmetric transmission, and negative refraction. In this review, we explore the fundamental physics of acoustic metamaterials and introduce several exciting developments, including the realization of unconventional effective parameters, acoustic metasurface, total sound absorption, high-resolution imaging, parity-time-symmetric materials, and topological acoustics. Acoustic metamatetials with negative effective parameters that are not observed in nature expand acoustic properties of natural materials. Acoustic metasurfaces can exhibit wavefront-shaping capabilities, with thickness being much smaller than the wavelength. The precisely designed matematerials provide the new possibility of steering waves on a subwavelength scale, which can be used for acoustic high-resolution imaging beyond the diffraction limit. The metamaterial absorbers can achieve total sound absorption at low frequencies and exhibit broadband absorption spectrum. Moreover, structure designs guided by the topological physics further broaden the whole field of acoustic metamaterials. Phononic crystals have become aflexible platform for studying new physics and exotic phenomenarelated to topological phases. Finally, we conclude the developments of acoustic metamaterials, discuss the technical challenges, and introduce potential applications in this emerging field.
Regulation of spatial fields in wireless power transfer with artificial magnetic conductor
Authors: Shi Tai-Xia , Dong Li-Juan , Chen Yong-Qiang , Liu Yan-Hong , Liu Li-Xiang , Shi Yun-Long ,   Institute of Solid State Physics, Shanxi Datong University, Datong 037009, China,   Shanxi Provincial Key Laboratory of Electromagnetic Functional Materials for Microstructure, Datong 037009, China,   School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009, China
Published: December 2020

In order to improve the efficiency of wireless power transfer (WPT) system, the spatial fields are regulated on a two-non-resonant-coil WPT system by hexagon artificial magnetic conductors (AMC). In our configuration, the AMC is located by the side of the two-non-resonant-coil WPT system and close to the transmitter coil. The AMC structure consists of small hexagon copper patches periodically arranged on the dielectric substrate. Each patch is grounded by a via passing through its center hole. Chip capacitors are soldered in the gaps between the adjacent patches. We can design the working frequency of WPT system through the capacitance of these chip capacitors. The results show that the electromagnetic fields are changed between the transmitter coil and the receiver coil in WPT system due to the introducing of the AMC structure. There are two main reasons. First, many resonant modes are excited by near magnetic fields on the AMC structure. Second, near magnetic fields are shielded by the AMC structure. The variation of space electromagnetic field improves the transmission efficiency of WPT system. When the working frequency is 27 MHz and the transmission distance is 3 cm, the experiment verifies that the transmission efficiency increases by 22% in the WPT system with the AMC structure compared with the WPT system without the AMC structure. Simultaneously, the transmission efficiency is raised by 25% at different transmission distances. The simulation results are almost consistent with the experimental results. There is a little difference that the number of resonant modes is different between the simulation and the experiment due to the resistance loss of the chip capacitors in experiment. Therefore, we correct the simulation results under consideration of resistive loss. In addition, the excited multiple resonant modes can supply multiple and adjustable working frequencies in the WPT system with the AMC structure. In practical applications, AMC is low in cost and easy to implement.