bluuebunny/crossref_metadata_2025 huggingface dataset:
Structures and properties of functional transition metal borides
Authors: Tao Qiang  , Ma Shuai-Ling  , Cui Tian  , Zhu Pin-Wen  ,   State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
Published: December 2020

Transition metal borides (TMBs) are hard or potential superhard materials due to abrasion resistant, corrosion preventive, oxidation resistance and high hardness. However, few TMBs are superhard materials, so, discussing the strength of TMBs to understand hardness mechanism is necessary. Moreover, there are superconductors, magnetic materials, and catalysts in TMBs. But uncovering more functions in TMBs is important for finding a new kind of functional hard or superhard material. While, high energy is necessary to synthesize TMBs due to strong BB covalent bonds and high melting of transition metal. Thus high temperature or extreme condition is necessary for synthesizing single crystal or bulk sample with high density, which is important for testing physical properties. Various ways of hybridizing boron atoms and high content of valence electron of transition metal are used to induce a large number of structures and potential new properties in TMBs. Boron atoms can form different substructures with different content of boron in TMBs, such as one-dimensional, two-dimensional and three-dimensional (3D) structures. These different boron atom substructures can affect the stability of structure and physical properties, especially hardness, because of the strong covalent bonds between boron atoms. Thus the structure and hardness of TMBs have always received much attention. The multiple electron transfer between transition metal and boron induces diverse chemical bonds in TMBs. All of covalent bonds, ionic bonds, and metal bonds in TMBs determine the mechanic performances, electricitic and magnetic properties, and chemical activity of TMBs. In this work, synthesis method, stability of structure, hardness, and functional properties of TMBs are discussed. The using of high pressure and high temperature is an effective method to prepare TMBs, because under high pressure and high temperature the electrons can transfer between transition-metal atoms and boron atoms in TMBs. There are not only stable TMBs which are even under very high pressure, but also many metastable structures in TMBs. Hardness values of TMBs are discussed by different content of boron, the high boron content or even 3D boron structure is not superhard material. Because insufficient electron transfer can form the distorted BB covalent bond which is weaker than directional covalent bonds like CC in diamond. Thus electron transfer is significant in TMBs for designing hard or even superhard materials. Besides high hardness, there are superconductor, magnetic material, and catalyzers in TMBs, but there are many potential properties of TMBs which are unknown. Further study to uncover the new properties of TMBs is significant for finding a new kind of functional hard material.
Design of ultra-hard multifunctional transition metal compounds
Authors: Bao Kuo  , Ma Shuai-Ling  , Xu Chun-Hong  , Cui Tian  ,   State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
Published: December 2020

Transition metals have special characteristics, such as a large number of valence electrons, multi valence states, high electron density, etc. Introducing a light element, such as boron, carbon, nitrogen, oxygen, etc. into a transition metal is an important means for searching the new multifunctional hard materials. With the development of ab intio calculation, advance in computer and the more in-depth understanding of the nature of hardness, it is possible to design new multifunctional ultra-hard transitional metal with using the advanced structure searching software, which could now serve as the experimental syntheses of these materials. In the present article, we introduce the design of ultra hard multi functional transition metal materials. We first introduce some basic ideas of hardness and material design, then conduct some studies, afterwards we discuss some difficulties in this kind of research. Hopefully these results in the present study could be helpful for designing and synthesizing the ultra-hard multifunctional materials.
High pressure synthesis of nanotwinned ultrahard materials
Authors: Xu Bo  , Tian Yong-Jun  ,   State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China
Published: December 2020

In this review, we present our recent research progress in superhard materials, with specially focusing on two topics. One topic is to understand hardness microscopically and establish the quantitative relationship between hardness and atomic parameters of crystal, which can be used to guide the design of novel superhard crystals. The other topic is to identify the fundamental principle and technological method to enhance the comprehensive performances (i.e., hardness, fracture toughness, and thermal stability) of superhard materials, and to synthesize high-performance superhard materials. Starting from the chemical bonds associated with crystal hardness and electronic structure, we propose a microscopic understanding of the indentation hardness as the combined resistance of chemical bonds in a material to indentation. Under this assumption, we establish the microscopic hardness model of covalent single crystals and further generalize it to polycrystalline materials. According to the polycrystalline hardness model, we successfully synthesize nanotwinned cubic boron nitride and diamond bulks under high pressure and high temperature. These materials exhibit simultaneous improvements in hardness, fracture toughness, and thermal stability. We also clarify a long-standing controversy about the criterion for performing a reliable indentation hardness measurement. Our research points out a new direction for developing the high-performance superhard materials, and promises innovations in both machinery processing industry and high pressure science.
In-situ magnetic measurements of substances under extreme conditions
Authors: Huang Xiao-Li  , Wang Xin  , Liu Ming-Kun  , Liang Yong-Fu  , Liu Bing-Bing  , Cui Tian  ,   State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
Published: December 2020

Temperature and pressure are the two most important thermodynamic elements, which determine the existent state of substance. Low temperature and high pressure are significant and key extreme conditions in the modern experimental science, providing new routes for many subjects such as physics, chemistry, materials and biology, and playing an important role in finding new phenomena. The magnetic research under extreme conditions is an important branch of the study of the extreme conditions, which not only presents the magnetic changes of the material under extreme conditions, but also is an important means to explore the high temperature superconductors. In this article, we elaborate the principle and method of measuring the magnetic susceptibility and superconducting transition temperature under high pressure. The in-situ magnetic measurement system under high pressure and low temperature is also briefly introduced, designed and installed by ourselves. Using the in-situ magnetic measurement system, the magnetic transition of iron and the superconducting transition temperature of the yttrium barium copper oxide sample under high pressure are measured.
A method to calculate the electron sheath profile of the nonaxisymmetrical magnetic insulation
Authors: Wei Hao  , Sun Feng-Ju  , Hu Yi-Xiang  , Liang Tian-Xue  , Cong Pei-Tian  , Qiu Ai-Ci  ,   State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049, China;,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

The nonaxisymmetrical magnetic insulation would occur due to the disalignment of inner electrodes in long magnetically insulated transmission lines, or the nonuniform distributions of injected currents in induction cavities of magnetically insulated induction voltage adders (MIVA). The electron sheath profile is a very important parameter to characterize the nonaxisymmetrical magnetic insulation. In the past, the three-dimensional particle in cell simulation was usually used to determine the electron sheath profile, which is extremely time-consuming and inefficient. In this paper, a fast and efficient calculation method is proposed. The classical one-dimensional Creedon theory of the magnetic insulation equilibrium is generalized to a two-dimensional plane of (r, ) via introducing a parameter defined as the azimuthal mode number. Two-dimensional Creedon is developed to model the asymmetric magnetic insulation of the MIVA. Provided the azimuthal distributions of magnetic flux density on the cathode, which is in proportion to the cathode current, the two-dimensional Creedon model is numerically solved. A numerical solution method to calculate the electron sheath profile is proposed, and then the calculation error is also given. As the azimuthal distribution of magnetic flux density on the cathode meets a cosine function, the profile of the electron sheath is approximate to the Gauss function. As the nonuniform portion of cathode current increases, the electron sheath becomes more eccentric, and the calculation error is also much larger.
A jet acceleration mechanism for the black hole disk system
Authors: Xu Jia-Di  , Jiang Zhi-Xiong  , Gong Xiao-Long  ,   School of Physical and Optoelectronic, Yangtze University, Jingzhou 434023, China;,   Department of Astronomy, Beijing Normal University, Beijing 100875, China
Published: December 2020

A jet acceleration mechanism of extracting energy from the disk-corona surrounding a rotating black hole is proposed. In this disk-corona scenario, the central object is a rotating Kerr black hole, and a geometrically thin and optically thick disk is sandwiched by a slab corona. The large-scaled magnetic field plays an important role in jet acceleration mechanism. So we obtain the value of the magnetic field in such a disk-corona system by solving the disk dynamic equations in the context of general relativity. The results show that the value of magnetic field decreases with the increase of disk radius, while increases with the increase of black hole spin parameter a*. Then the analytical expression of the jet power is derived based on the electronic circuit theory of the magnetosphere. It is found that the jet power increases obviously with increasing black hole spin parameter a* and magnetic stress parameter . Furthermore, the calculation results also show that the jet power is mainly from the inner region of the disk-corona system, which is consistent with the observations of the jet. Finally, a sample composed of the 23 Fermi blazars with high jet power is used to explore our jet production mechanism. The conclusion suggests that our jet acceleration mechanism can simulate all sources with high power jet. By comparing with the observational data, we find that these high jet power sources cannot be explained by the Blandford-Znajek mechanism, even if the central object is extreme Kerr black hole.
Influence of periodic volatility on the stability of financial market
Authors: Zhou Ruo-Wei  , Li Jiang-Cheng  , Dong Zhi-Wei  , Li Yun-Xian  , Qian Zhen-Wei  ,   Catastrophic Risk Management Research Center, School of Finance, Yunnan University of Finance and Economics, Kunming 650221, China;,   Department of Statistics, Yunnan University, Kunming 650091, China
Published: December 2020

Various stochastic volatility models have been designed to model the variance of the asset price. Among these various models, the Heston model, as one-factor stochastic volatility mode, is the most popular and easiest to implement. Unfortunately, recent findings indicate that existing Heston modelis not able to characterize all aspects of asset returns, such as persistence, mean reverting, and clustering. Therefore, a modified Heston model is proposed in this paper. Compared with the original Heston model, the mean-reverting Cox Ingersoll and Ross process is modified to include a cosine term with the intention of capturing the periodicity of volatility. The phenomenon that high-volatile period is interchanged with low-volatile periods can thus be better described by adding such a period term to the volatility process. In addition, the geometric Brownian motion is replaced by a random walk in the presence of a cubic nonlinearity proposed by Bonanno et al. By doing so, a financial market with two different dynamical regimes (normal activity and extreme days) can be modeled. Closed-form solution for the modified Heston model is not derived in this paper. Instead, Monte-Carlo simulation is used to generate the probability density function of log-return which is then compared with the historical probability density function of stock return. Parameters are adjusted and estimated so that the square errors can be minimized. Daily returns of all the component stocks of Dow-Jones industrial index for the period from 3 September 2007 to 31 December 2008 are used to test the proposed model, and the experimental results demonstrate that the proposed model works very well. The mean escape time and mean periodic escape rate of the proposed modified Heston model with periodic stochastic volatility are studied in this paper with two different dynamical regimes like financial markets in normal activity and extreme days. Also the theoretical results of mean escape time and mean periodic escape rate can be calculated by numerical simulation. The experimental results demonstrate that 1) larger value of rate of return, smaller long run average of variance and smaller magnitude of periodic volatility will reduce the mean periodic escape rate, and thus stabilize the market; 2) by analyzing the mean escape time, an optimal value can be identified for the magnitude of periodic volatility which will maximize the mean escape time and again stabilize the market. In addition, an optimal rate of relaxation to long-time variance, smaller frequency of the periodic volatility, larger rate of return, and stronger correlation between noises will furtherreduce the mean escape time and enhance the market stability.
Reconstruction algorithm of chaotic signal based on generalized likelihood ratio threshold-decision
Authors: Ren Zi-Liang  , Qin Yong  , Huang Jin-Wang  , Zhao Zhi  , Feng Jiu-Chao  ,   School of Electronic and Information Engineering, South China University of Technology, Guangzhou 510641, China;,   School of Computer Science and Network Security, Dongguan University of Technology, Dongguan 523808, China
Published: December 2020

Blind signal reconstruction in sensor arrays is usually a highly nonlinear and non-Gaussian problem, and nonlinear filtering is an effective way to realize state estimation from available observations. Developing the processing problem of blind signal in wireless sensor networks (WSNs) will greatly extend the application scope. Meanwhile, it also meets great challenges such as energy and bandwidth constrained. For solving the constrained problem in WSNs, the observed signals must be quantified before sending to the fusion center, which makes the overall noise unable to be modeled accurately by simple probabilistic model. To study the reconstruction issue of chaotic signal with unknown statistics in WSNs, a reconstructed method of chaotic signal based on a cost reference particle filter (CRPF) is proposed in this paper. The cost recerence cubature particle filter (CRCPF) algorithm adopts cubature-point transformation to enhance the accuracy of prediction particles, and cost-risk functions are defined to complete particle propagation. The effectiveness of proposed CRCPF algorithm is verified in the sensor network with a fusion center. Moreover, a generalized likelihood ratio functionis obtained by the cost increment of local reconstructed signals in the cluster-based sensor network topology model, which is used to reduce the network energy consumption by selecting working nodes. Simulation results show that compared with CPF and CRPF, the proposed algorithm CRCPF attains good performance in a WSN with unknown noise statistics. Meanwhile, the CRCPF algorithm realizes the compromise between energy consumption and reconstruction accuracy simultaneously, which indicates that the proposed CRCPF algorithm has the potential to extend other application scope.
A new technique for measuring single-shot ultrashort laser pulse
Authors: Xia Yan-Wen  , Shen Miao  , Sun Zhi-Hong  , Peng Zhi-Tao  , Lu Zong-Gui  ,  Zhou Song  , Zhang Bo  , Su Jing-Qin  ,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   Graduate School of Chinese Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

A new triple correlation technique for measuring intensity profile of single-shot ultrashort laser pulse is described. The technique uses two consecutive second-order nonlinear interactions of replicas of the pulse for generating a two-coordinate output intensity distribution that corresponds to a third-order correlation function and offers advantages over the previously techniques such as frequency-resolved optical gating, self-referencing spectral phase interferometry for direct field reconstruction because it requires no additional spectral information to profile the pulses. This intensity distribution is recorded, and the pulse profile can be obtained by analytical calculation. Combining the reconstructed intensity profile with its corresponding optical spectrum, the exact phase variation in time can be recovered with Gerchberg-Saxton algorithm through an iterative calculation.
Simulating scattering properties of nonspherical aerosol particles using multiresolution timedomain method
Authors: Hu Shuai  , Gao Tai-Chang  , Li Hao  , Yang Bo  , Jiang Zhi-Dong  , Chen Ming  , Li Shu-Lei  ,   College of Meteorology and Oceanography, PLA University of Science and Technology, Nanjing 211101, China;,   National Key Laboratory on Electromagnetic Environment and Electro-optical Engineering, PLA University of Science and Technology, Nanjing 210007, China;,   Navy Aeronautical and Astroautical University, Qingdao 266041, China
Published: December 2020

Scattering process of aerosol particles plays an important role in atmospheric radiative transfer since it can modify the transmission, reflection and absorption ability of atmospheric system. Owning to the uncertainty of aerosol particles' scattering properties, which results from their complicated geometries and inhomogeneous compositions, there still exists a considerable uncertainty in the radiative transfer numerical simulation, and simulating the scattering properties of aerosol with irregular shapes has become a hotspot in meteorological study. To this end, a new aerosol scattering model is developed based on multi-resolution time-domain (MRTD), by which the scattering processes of nonspherical and inhomogeneous particles can be simulated. In this model, the near electromagnetic field is calculated by MRTD technique. Considering the particularity of aerosol medium, a transformation technique from near field to far field is derived based on volume integration method, and then the scattering amplitude matrix and Meller matrix can be calculated by the obtained far electric field as well. The models for particle extinction and absorption cross section are derived from Maxwell's curl equations in the frequency domain, by which the integration scattering properties can be simulated accurately. The MRTD scattering model is validated by comparing with Mie theory and T matrix method for spherical particle, ellipsoidal particle and cylindrical particle, and the influence of grid size on the simulation accuracy is analyzed subsequently. In the last part, the efficiency of the MRTD scattering model is quantitatively discussed. The simulation results show that the relative errors of scattering phase function simulated by our model are less than 8%, and the errors in forward scattering direction are much smaller, which are less than 4%. The precisions for extinction and absorption efficiency are much higher than the results from the scattering phase function, and the relative errors can reduce to 0.1% for particles with their radii comparable to the wavelength of incident light. The gird size has a significant influence on model precision; to achieve the same accuracy, the grid size first increases with increasing particle radius, and then decreases as a function of particle size for particles with size parameter less than 20. In the next step, we will try to establish the scattering property database of nonspherical particles based on the MRTD scattering model developed here.
Application of cone-cylinder combined fiber probe to surface enhanced Raman scattering
Authors: Guo Xu-Dong  , Tang Jun  , Liu Wen-Yao  , Guo Hao  , Fang Guo-Cheng  , Zhao Miao-Miao  , Wang Lei  , Xia Mei-Jing  , Liu Jun  ,   North University of China, Key Laboratory of Instrumentation Science and Dynamic Measurement, Ministry of Education; Science and Technology on Electronic Test and Measurement Laboratory, Taiyuan 030051, China
Published: December 2020

Owing to increasingly severe environmental pollution, food safety and other problems, higher and higher requirements for the detecting technique of poisonous and harmful biochemical molecules have been put forward. The conventional biochemical detector has the disadvantages of large size, high cost and inability to realize far-end and in-situ detection functions. Based on the requirements of the biochemical molecular detection technology for high sensitivity, miniaturization, far-end detection, insitu detection, real-time analysis and the like, a detection method using a fiber surface-enhanced Raman scattering (SERS) probe to carry out Raman signal detection has been put forward in recent years. The detection method not only realizes far-end and insitu detection functions, but also has a relatively high sensitivity. In this paper, a taper and cylinder combination type fiber probe is made by adopting a simple tube corrosion method, Under the situation of fixed temperature, cone-cylinder combined fiber probes with different diameters are obtained by controlling the corrosion time, and silver nanoparticles are bound to the surface of a silanized silicon dioxide fiber probe through electrostatic forces. Then, the sizes and morphologies of silver nanoparticles on the surface of the fiber probe are observed under a scanning electron microscope. Besides, the detection limit of a rhodamine 6G (R6G) solution is used to manifest both the activity and the sensitivity of the fiber probe, and the self-assembly time of the silver nanoparticles are further optimized to be 30 min and the diameter of the fiber probe to be 62 upm. When the concentration of a silver sol solution is constant, a high-sensitivity fiber SERS probe can be prepared. Through far-end detection, the detection limit of the R6G can reach 10-14 mol/L, and the enhancement factor is 1.36104. This work can serve as an experimental basis for a novel fiber surface-enhanced Raman scattering sensor in such aspects as high sensitivity and low cost. The studies of this paper are expected to provide an appropriate detection technique for rapid quantitative detection of biochemical molecules, and further provide a reference for various application fields of environmental monitoring and food safety analysis in future in terms of realizing rapid and accurate in-situ detection. Therefore, the fiber SERS probe has large application foreground in molecular detection.
Effect of standing wave on the uniformity of a low magnetic field helicon plasma
Authors: Niu Chen  , Liu Zhong-Wei  , Yang Li-Zhen  , Chen Qiang  ,   Lab of plasma physics and materials, Beijing Institute of graphic communication, Beijing 102600, China
Published: December 2020

Helicon wave discharge has higher coupling efficiency than capactively coupled and inductively coupled discharge in low static magnetic field. In the wave sustained mode, a large volume and large area plasma can be produced at lower pressure by using comparable discharge power, and thus it expands the helicon wave plasma applications in material surface modification, thin film deposition, dry etching and thruster usage. However, the application of helicon wave source still faces challenges, such as the controversial power coupling mechanism, operation stability and the plasma distribution uniformity in the experiment. The wave mode existing in bounded helicon wave plasma column generally consists of helicon and Trivelpiece-Gould (TG) components, and their mode transitions and different transverse wave field distribution regions, and the propagating characteristic of the helicon wave are directly related to the power coupling and plasma density distribution in the source region, then affect the uniformity of material processing and film deposition in the diffusion chamber. In this paper, the plasma azimuthal non-uniformity, with using Doubble Saddle antenna, 100 G static magnetic field in helicon wave plasma source, is studied by electrical characteristic (power-current) curve, intensified charge coupled device (ICCD) image and magnetic probe measurements. The electrical characteristic curve indicates two discharge stages with different effective resistances. Meanwhile, in the second stage, the higher effective resistance would result in higher coupling efficiency and higher plasma density. But the ICCD image demonstrates the azimuthal non-uniformity of plasma, indicating that the main heating points at the diagonal edge are linked to the stationary transverse electrical field line pattern of azimuthal mode number m=+1 helicon wave, and the magnetic probe is used to measure the helicon wave magnetic field Bz component along the quartz source tube axially. The magnetic probe results show that the standing wave appearing below the antenna even though in the upper region of the antenna is characteristic of the traveling wave. Furthermore, at the plasma boundary, the standing wave can be coupled to the TG wave, and not like travelling wave it has no angular rotation of the electric field and may cause the non-uniform coupling between the helicon and TG components. The TG wave then has azimuthal non-uniform electron heating. Therefore, the standing helicon wave below the antenna is the key factor to the plasma non-uniformity problem. Changing the propagating characteristics of the helicon wave further in the plasma column will be of positive significance for optimizing the discharge efficiency of the plasma source and controlling the plasma distribution uniformity, stability and other operations as well.
Using quaternions to analyze the trapping force of an ellipsoidal bead
Authors: Zhang Shu-He  , Liang Zhen  , Zhou Jin-Hua  ,   Department of Biomedical Engineering, Anhui Medical University, Hefei 230032, China
Published: December 2020

In the ray-optics (RO) model of optical tweezers, tracing refractive and reflected rays with vectors play important roles in calculating the trapping forces. Traditional ray-tracing method with solid geometry, to some extent, is complicated in determining the orientations of those refractive and reflected rays according to spatial incident rays. It is difficult to calculate the trapping forces for irregular particles. In this paper, quaternion is proposed to rotate ray vectors for simplifying the traces of all kinds of spatial rays. Then, it is appropriate to calculate the trapping force of an ellipsoid bead. Based on the algorithm of quaternion and the convention between the interface normal and angular directions, the direction of normal always points from optically denser medium to thinner medium. The rotation axis is the cross product of the incident ray and the interface normal. And the positive angular direction can be determined by right-hand rule based on the orientation of the rotation axis. According to Snell' law, the rotation angle between the incident ray and refractive/reflected ray can be determined. The quaternion for rotation consists of rotation axis and angle. So the refractive and reflected rays are both determined by quaternions of incident ray and rotation based on rotation rules. Furthermore, the force on interface can also be calculated according to momentum changes of the photon before and after the interface refraction and reflection. The quaternion method is used to analyze the effects of coverslip position and deformation ratio on the trapping efficiency of ellipsoid particles. Our simulative results show that the lateral and axial trapping efficiencies are obviously affected by the deformation of the ellipsoid itself. No matter whether the bead deforms transversely or axially, the transverse and axial trapping efficiencies both become larger at a specific deformation. Meantime, the increase of the spherical aberration reduces the maximum axial trapping efficiency, and the equilibrium position of the bead becomes farther away from the center. Using quaternion method, the calculation of refractive lightvector can be simplified in comparison with by using the method of Euclidean geometry or transformation matrix. Theoretically, this quaternion can be used to trace rays on any irregular geometric surfaces. In conclusion, the method of quaternion can make ray tracing easier and extend the applications of RO model.
Analyses of the effect of mismatch on the performance of inverted GaInP/InxGa1-xAs/InyGa1-yAs triple-junction solar cells
Authors: Ma Da-Yan  , Chen Nuo-Fu  , Fu Rui  , Liu Hu  , Bai Yi-Ming  , Mi Zhe  , Chen Ji-Kun  ,   School of Renewable Energy Sources, North China Electric Power University, Beijing 102206, China;,   Department of Mathematics and Physics, Shijiazhuang Tiedao University, Shijiazhuang 050041, China;,   School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

The traditional lattice matched GaInP/(In) GaAs/Ge triple-junction (3J) solar cell has no much room to enhance its practical achievable conversion efficiency because of its inappropriate ensemble of bandgap energies. According to the P-N junction formation mechanism and the close equilibrium condition, we explore a series of computational codes in the framework of MATLAB to simulate and optimize the inverted structure of series-connected 3J solar cells with a fixed top bandgap of 1.90 eV on GaAs substrate. In this paper, structural optimization is conducted in the real device design, because the realistic (QE) is closely related to a set of material parameters in the subcell, i.e., the absorbtion coefficient of material, subcell thickness, minority carrier diffusion length, surface recombination velocity, etc.
The results indicate improved inverted 3J solar cells with nearly optimized bandgaps of 1.90, 1.38, and 0.94 eV, by utilizing two independently lattice-mismatches (0.17% and 2.36% misfit respectively) to the GaAs substrate. A theoretical efficiency of 51.25% at 500 suns is demonstrated with this inverted design with the optimal thickness (4 m GaInP top and 3.1 m InGaAs middle). By contrast, the efficiency with the infinite thickness of subcells is reduced by 1%, which is mainly attributed to the effect of minority carrier recombination on Jsc. Exactly speaking, if photo-generated carriers make a contribution to Jsc, they must be collected effectively by the P-N junction before recombining. A new model is proposed based on the effect of dislocation on the metamorphic structure properties by regarding dislocation as minority-carrier recombination center. Our calculation indicates that threading dislocations density in the middle junction is approximate to 1.70105 cm-2 when dislocations in the gradient buffer layer are neglected. The theoretical efficiency is increased by 0.3% compared with the inverted design containing a single metamorphic junction.
As a result, based on the two metamorphic combinations, a solar cell with an area of 30.25 mm2 is prepared. The efficiency of the designed cell with two lattice-mismatched junctions reaches 40.01% at 500 suns (AM1.5D, 38.4 W/cm2, 25℃), which is 0.4% higher than that of the single metamorphic junction 3J solar cell.
Hybrid algorithm for composite electromagnetic scattering from the multi-target on and above rough sea surface
Authors: Li Bing  , Ma Meng-Chen  , Lei Ming-Zhu  ,   College of Automation, Harbin Engineering University, Harbin 150001, China
Published: December 2020

In the study of electromagnetic scattering of multi-target composite on and above the rough sea surface, the common algorithm such as the method of moment analyzes the relationship between the target and the rough sea surface point by point, so the common algorithm usually requires massive computation and a lot of time. In this paper, the rough sea surface is described by Pierson-Moscowitz (PM) spectrum and Monte Carlo method, and the composite electromagnetic scattering from multiple conductor flying targets above the rough sea surface is investigated by using the hybrid algorithm-the method of moment in the Kirchhoff approximation. The composite scattering region is divided into target region and rough sea surface region. The target region and the rough sea surface region are investigated by using the method of moment, and the Kirchhoff approximation, respectively. The formulas of the hybrid algorithm in different polarizations are derived in detail, and the scattering coefficients in different incident angles, target heights, target sizes, target distances and wind velocities are calculated in detail. The characteristics of the composite scattering coefficient from the multiple conductor flying target above the rough sea surface are also obtained. Results show that the hybrid algorithm, i. e., the combination of method of moment and the Kirchhoff approximation, can obtain higher accuracy, and reduce the computation time efficiently. The computation time used by the hybrid algorithm is 19% of that by using the method of moment. Moreover, the performance becomes more favorable with the increase of size of rough sea surface.
Intelligent particle filter based on bat algorithm
Authors: Chen Zhi-Min  , Tian Meng-Chu  , Wu Pan-Long  , Bo Yu-Ming  , Gu Fu-Fei  , Yue Cong  ,   China Satellite Maritime Tracking and Controlling Department, Jiangyin 214431, China;,   School of Automation, Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

Particle filer is apt to have particle impoverishment with unstable filtering precision, and a large number of granules are required to estimate the nonlinear system accurately, which reduces the comprehensive performance of the algorithm. To solve this problem, a new particle filter based on bat algorithm is presented in this paper, where particles are used to represent individual bat so as to imitate the search process of bats for preys. In traditional resampling process, particles are directly discarded, the improved algorithm adopts another approach and solves the problem of particle impoverishment. It combines the advantages of particle swarm optimization algorithm and harmonic algorithm perfectly. New particle filter has capacity of global and local search and is superior in computation accuracy and efficiency. By adjusting frequency, loudness, and impulse emissivity of particle swarm, the optimal particle at that time is followed by particle swarm to search in the solution space. The global search and local search can be switched dynamically to improve the overall quality of the particles swarm as well as the distribution rationality. In addition, the improved particle filter uses Lvy flight strategy to avoid being attracted by harmful local optimal solution, it expands the space of research and further promotes the optimization effect of particle distribution. Using the useful information about particle swarm, improved particle filter can make particles get rid of local optimum and reduce the waste of iterations in insignificant status change. Based on the number of valid particle samples, it can improve quality of particle samples by expanding their diversity. In information interaction mechanism of improved particle filter, the method in this paper sets scoreboard of particle target function to compare the value of particle target function at each iteration sub-moment with the value of target function on scoreboard to gain global optimum of all particles at current filtering moment. Taking information interaction between global optimum and particle swarm, the guiding function of global optimum is realized. The process of particle optimization is ended prematurely through setting a maximum iteration or termination threshold. There is a tendency for the whole particle swarm closing to high likehood area without global convergence so that the advantages of improved particle filter in accuracy and speed will not be damaged. In addition, convergence analysis and computational complexity analysis are given in this paper. Experiment indicates that this method can improve the particle diversity and prediction accuracy of particle filter, and meanwhile reduce the particle quantity obviously which is required by the state value prediction for nonlinear system.
High-resolution reconstruction of Fresnel zone plate coded imaging
Authors: Wang Xin-Yi  , Fan Quan-Ping  , Wei Lai  , Yang Zu-Hua  , Zhang Qiang-Qiang  , Chen Yong  , Peng Qian  , Yan Zhuo-Yang  , Xiao Sha-Li  , Cao Lei-Feng  ,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   Key Laboratory of Optoelectronic Technology and Systems of the Education Ministry of China, Chongqing University, Chongqing 400030, China
Published: December 2020

Zone plate coded imaging is an experimental technique for particle and strong X-ray imaging, which is widely applied to astronomy, nuclear medicine, and laser inertial confinement fusion researches. From conventional perspective, spatial resolution of zone plate depends on the encoding zone plate width of outermost ring r with a size greater than 1.22r. In X-ray region, however, the outermost ring width of Fresnel zone plate is limited by processing technology. Such a limitation makes it impossible to fabricate a sufficiently small zone plate, thus restricting the applications of Fresnel zone plate coded imaging. In this paper, we present a new reconstruction method of zone plate coded imaging by using a higher-order order Gabor zone plate. With the proposed method, higher spatial resolution can be achieved than with the regular methods, thus the spatial resolution is improved by 1/m times the width of outermost ring (where m is a positive integer). Consequently such a breakthrough goes beyond the limits of Rayleigh criterion in general.
Measurements of line strengths for some lines of ammonia in 6611-6618 cm-1
Authors: Nie Wei  , Kan Rui-Feng  , Xu Zhen-Yu  , Yang Chen-Guang  , Chen Bing  , Xia Hui-Hui  , Wei Min  , Chen Xiang  , Yao Lu  , Li Hang  , Fan Xue-Li  , Hu Jia-Yi  ,   Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China;,   University of Science and Technology of China, Hefei 230026, China
Published: December 2020

The target gas molecular absorption spectrum parameters especially line strengths are very important for measuring temperature and concentration with tunable diode laser absorption spectroscopy (TDLAS) technique. Usually, researchers use line strengths which come from spectrum database, like HITRAN and GEISA and HITEMP spectra database, but those database include values from the theoretical computation, as is well known, there is a big error between the theoretical value and the actual value. In order to modify the line strengths of the database, 20 ammonia spectrum absorption lines in a wavenumber range between 6611 and 6618 cm-1 are measured at different pressures by using direct tunable diode laser absorption spectroscopy (dTDLAS) technique. The measurement procedure is repeated at least 10 times at each pressure, and then average value is calculated. Voigt fitting is used to obtain all line integral area, and then the line integral area is obtained by linear fitting. The slope of the fitting straight line equals line strength. Uncertainty analysis is given for the measurements. The measured linestrength is a function of integrated area, temperature, pressure, species mole fraction and effective path length. So, the calculated linestrength uncertainties based on those parameters uncertainties, and the uncertainties of pressure, species mole fraction and effective path length are similar for all transitions with P =0.25%, =0.2%, and L =0.4%. The uncertainties of the integrated area and temperature are related to different lines, and their values come from the actual measurement. In the end, uncertainty propagation formula is used to calculate linestrength uncetainty. Uncertainties of our measured line strengths are in a 0.81%-3.33% range. Our measured line strength values are different from line strengths in the HITRAN 2012 database, and the deviations are in 0.51%-17.28% range.
Propagating properties of spatial solitons in the competing nonlocal cubic-quintic nonlinear media
Authors: Huang Guang-Qiao  , Lin Ji  ,   Department of Physics, Zhejiang Normal University, Jinhua 321004, China
Published: December 2020

We study the new spatial optical solitons and their propagating properties in the one-dimensional nonlocal cubic-quintic (C-Q) nonlinear model by the numerical method. We obtain multi-bright solitons and multipole soliton solutions in the one-dimensional nonlocal C-Q nonlinear model. The propagation of bright solitons is stable in the competing nonlocal cubic self-defocusing and quintic self-focusing nonlinear media when these nonlocal and nonlinear parameters are in the appropriate value domain. Considering the different nonlinear cubic effects, the interaction between two optical solitons with the same phase in the general nonlocal media displays the attraction or the repulsion for different nonlocal and nonlinear parameters. We find that the interval of two solitons affects the interaction between them. The refractive index is changed with the propagating constant when the nonlocal constant d3 is 10. Moreover, the triplepole, quadrupole and pentapole solitons can propagate steadily when the nonlocal parameters are appropriate, but hexa-pole (or above) solitons propagate unsteadily for any nonlocal parameter. Furthermore, we investigate the multi-pole solitons and their propagation stabilities by the Newton difference method and the Fourier split step method, obtain the stable propagation conditions for dipole, triplepole and quadrupole solitons, and find that the propagation of the pentapole and higher-order pole solitons is unstable. We also discuss the interactions of multi-pole solitons when they propagate along the axis z. The interactions are attraction or repulsion when the nonlocal and the nonlinear parameters are different. Meanwhile, we simulate the evolution of the refractive index along the axis z when the spatial optical solitons are multi-pole solitons. Finally, we study the relation between the power of soliton and the propagation constant under different degree of nonlocality. The power of the single bright soliton does not monotonically increase with the increasing propagation constant when the degree of nonlocality d3 is 10. We also derive the relation between the power of dipole bright solitons with the cubic nonlinearity parameter and the propagation constant under different degree of nonlocality. The power decreases monotonically with the increasing propagation constant when the cubic nonlinearity is a certain value or with the increasing cubic nonlinearity when the propagation constant is a certain value.
Investigation of Hall effect on the performance of magnetohydrodynamic heat shield system based on variable uniform Hall parameter model
Authors: Li Kai  , Liu Jun  , Liu Wei-Qiang  ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

There has been a resurgence in the field of magnetohydrodynamic (MHD) flow control in the past 20 years. An increasing demand for sustained hypersonic flight and rapid access to space, along with numerous mechanical and material advances in flight-weight MHD technologies, has aroused renewed interest in this subject area. As a novel application of MHD flow control in the thermal protection field, MHD heat shield system has been proved to be of great intrinsic value by lots of researchers in recent years. Although its theoretical feasibility has been validated, there are many problems that remain to be further investigated. Among those problems, the Hall effect is a remarkable one that may affect the effectiveness of MHD flow control. Considering the fact that it is not sufficient to evaluate the Hall effect by merely using the chemical reaction model implemented in the nonequilibrium flow simulation to calculate the Hall parameter, a parametric study is conducted under the assumption of simplified uniform Hall parameter. First, coupling numerical methods are constructed and validated to solve the thermochemical nonequilibrium flow field and the electro-magnetic field. Second, a series of numerical simulations of the MHD head shield system is conducted with different magnitudes of Hall parameter under two magnetic induction intensities (B0=0.2 T, 0.5 T). Finally, the influence of Hall effect on the performance of MHD heat shield system is analyzed. Results indicate that Hall effect is closely related to the wall conductivity. If the vehicle surface is regarded as an insulating wall, the heat flux variation is co-determined by varying the Lorentz forces within the boundary layer and the shock-control effect. Compared with the one neglecting the Hall effect, the heat flux with Hall effect is slightly mitigated as the increase of Lorentz forces in the boundary layer dominates when the stagnation magnetic induction intensity B0 equals 0.2 T. However, the heat flux is increased when B0 equals 0.5 T, because the decrease of shock stand-off distance dominates which increases the gas temperature outside the boundary layer. Moreover, in this case the larger the Hall parameter, the higher the heat flux will be. As for the conductive wall, the performance of MHD heat shield system becomes worse with the increase of Hall parameter, and while it is equal to or higher than 5.0, this system loses its effectiveness.