bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of horizontal static magnetic field on the stability of electromagnetic levitated Cu molten droplet
Authors: Song Qi-Hui  , Shi Wan-Yuan  ,   College of Power Engineering, Chongqing University, Chongqing 400044, China;,   Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Ministry of Education, Chongqing University, Chongqing 400044, China
Published: December 2020

For an electromagnetically levitated (EML) molten droplet, there usually exist some unstable factors, such as internal fluid convection, quick spin and horizontal displacement and so on. As a result, stabilizing the droplet is very important for EML technology. In this paper, a horizontal static magnetic field is imposed on an EML Cu droplet through a U-shaped static magnetic component. The shape oscillation of a Cu droplet is recorded continuously under different magnetic field intensities using a high speed camera. The effects of static magnetic field on the oscillation frequency, amplitude and spin angle of the droplet are analyzed from the recorded data of droplet shape. The result shows that when the strength of the static magnetic field exceeds 0.3 T the solid Cu is levitated statically without any spin and horizontal movement. For molten Cu droplet, its amplitudes of the R-, A and Dmax are reduced by 25%, 76% and 60% respectively when a static magnetic field with 0.15 T is imposed. With the increase of magnetic field strength the amplitude and frequency of oscillation decease continuously. However, when the intensity of the static magnetic field is 0.3 T, its frequency is 1 Hz higher than that when the intensity of the static magnetic field is 0.2 T. Finally, the result indicates that the horizontal static magnetic field can inhibit the spin of the levitated droplets. For instance, when the strength of the magnetic field is 0.53 T the droplet spins are within a very narrow angle of 10°, which is quite smaller than in the case without static magnetic field. These results exhibit that the imposed horizontal static magnetic field can effectively improve the stability of electromagnetic levitated droplet.
A first principles study on the synergistic catalytic mechanism of anion, cation ions in TiF3, TiCl3 catalysts for LiBH4 hydrogen-storage materials
Authors: Liu Gui-Li  , Zhang Guo-Ying  , Bao Jun-Shan  , Zhang Hui  ,   College of Constructional Engineering, Shenyang University of Technology, Shenyang 110870, China;,   College of Physics Science and Technology, Shenyang Normal University, Shenyang 110034, China;,   Shenyang Siasun Robot and Automation Company Limited, Shenyang 110168, China
Published: December 2020

The synergistic catalytic mechanism of anion, cation ions in TiF3, TiCl3 catalysts for LiBH4 has been studied by first-principles method based on density functional theory. According to the results, Ti metal doping in LiBH4 is not easy realized with respect to halogen elements. Co-doping with transition metal and elements in halogen family is achieved easier than doping with Ti alone. For TiF3 catalyst, to achieve doping with one kind of element is helpful to doping with another kind of element, which accordingly results in the increase of doping concentration. Based on the analysis of the electronic structure, we find that doping with halogen element alone can reduce the stability of LiBH4; while doping with Ti alone leads to the rise of Fermi level; the introduction of defect energy level and the weakening of B-H bond; these may be responsible for improving greatly the desorption kinetics of LiBH4 by titanium halide catalysts. The improvement of the dehydrogenating kinetics of LiBH4 with titanium halide catalyst additives is mainly due to the B-H bond weakening, which makes H atom diffuse easily. For TiF3, TiCl3 catalysts, in the reversible desorption process of LiBH4, F and Ti have synergistic action for the B-H bond weakening, but the synergistic action of Cl and Ti is not obvious, this may be the reason for the advantage of TiF3 over TiCl3 in LiBH4 catalytic reaction.
Congestion control in complex network based on local routing strategy
Authors: Liu Wei-Yan  , Liu Bin  ,   Department of Information Engineering, Jiangsu Open University, Nanjing 210017, China;,   Department of Civil Engineering and Mechanics, College of Engineering and Applied Science, University of Wisconsin-Milwaukee, Milwaukee 53201, USA
Published: December 2020

In this paper, we propose a local routing strategy in a complex network, use the node contraction method to evaluate the node importance. The probability of the node transmit packet to its neighbors is adaptively adjusted based on the importance of neighbor nodes and the state of the network. The strategy can take advantage of key nodes when the network is in free flow state, ensure that packets can arrive at their destination faster, protect the key nodes by accurately identifying its importance, and fully use the capabilities of all nodes when the network is in a congestion state, and stop some key nodes from becoming the bottleneck of network. Simulation results show that the proposed local routing strategy can effectively control the network congestion, enhance the network capacity.
Macroscopic stable mechanism of autonomous cooperative system
Authors: Ru Chang-Jian  , Wei Rui-Xuan  , Qi Xiao-Ming  , Che Jun  , Guo Qing  ,   Institute of Aeronatics and Astronautics Engineering, Air Force Engineering University, Xi’an 710038, China;,   Science and Technology on Aircraft Control Laboratory, FACRI, Xi’an 710065, China
Published: December 2020

The cohesiveness of autonomous cooperative system is the basis of achieving the effective communication and cooperation among the multiple vehicles. Therefore, the biosphere mechanism of queen mandibular pheromone is used for reference in this paper, to abstract the macro motion characteristic of multiple unmanned aerial vehicles autonomous cooperative tracking system. Then, some Lyapunov functions are constructed to analyze the stability of this system, thus obtaining its judgment criterion of stability. Finally, the simulation is given to verify the effectiveness of the proposed stable mechanism. The results show that the proposed stable mechanism not only can ensure the stability of autonomous cooperative system, but also can control the scale of this system effectively by adapting some relevant control parameters.
A numerical study of effects on detection height of a radio acoustic sounding system influenced by atmospheric wind and temperature
Authors: Wang Pan-Pan  , Zhou Chen  , Song Yang  , Zhang Yuan-Nong  , Zhao Zheng-Yu  ,   Electronic Information School, Wuhan University, Wuhan 430072, China
Published: December 2020

Radio acoustic sounding system (RASS) is a detection technique using the interaction between radio wave and acoustic wave to remotely measure vertical profiles of the atmospheric temperature, and usually composed of a Doppler radar with fixed beam (monostatic or bistatic) and an acoustic source with high power. By combining acoustic propagation equation and radio wave propagation equation in a disturbance medium and using a finite-difference time-domain method, a numerical model describing the interaction between acoustic wave and electric wave is constructed, and the model is used to analyze the effects of wind and temperature on detection height of RASS. In the atmospheric temperature background, the propagations of a single frequency acoustic wave packet under different wind conditions are simulated, and the scattering propagation of electric wave packets corresponding to the acoustic scatterer are analyzed and compared. Besides, the entire physical process are described from the angle of energy density. The numerical simulation results show that the propagation trajectories of both acoustic wave and radio wave backscattering echo are changed due to the existence of wind field and temperature profile. The presence of wind field results in an offset of acoustic wave front, reducing the strength and changing the trajectory of radio wave backscattering echo, so that the detection height is limited due to the reduction of receiving data. The simulation results of the acoustic wave reveal that the temperature profile mainly affects the propagation velocity of acoustic wave, while the presence of wind field may result in shifts of propagation trajectory and acoustic wave front, and the greater the wind speed, the more the horizontal shift of acoustic wave front is. The numerical analyses of scattering propagations of radio wave with the acoustic scatterer at the same height under different background atmospheric conditions manifest that the stronger the wind speed, the more the deviation of electric wave echo from the receive antenna is, and the smaller the echo intensity is when the scattering echo propagates to the same position. The theoretical calculations with the acoustic wave scatterer at different heights under the same atmospheric wind field (strong wind) background demonstrate that if the height of scattering point is reduced, the offset of the scattering echo “bunching point” at the same altitude will be greatly improved and the intensity will be enhanced, but it also means the decline of detection height. In order to improve the detection height under the background of wind field, some methods are adopted, such as using a bistatic radar antenna or increasing the reception antenna area.
Canonical quantization of classical fields in finite volume
Authors: Liu Bo  , Wang Qing  , Li Yong-Ming  , Long Zheng-Wen  ,   Department of Physics and Electronic, School of Science, Beijing University of Chemical Technology, Beijing 100029, China;,   College of Physics Science and Technology, Xinjiang University, Urumqi 830046, China;,   School of Information Science and Engineering, Xinjiang University, Urumqi 830046, China;,   Laboratory for Photoelectric Technology and Application, Department of Physics, Guizhou University, Guiyang 550025, China
Published: December 2020

We study the problem of canonical quantization of classical scalar and Dirac field theories in the finite volumes respectively in this paper. Unlike previous studies, we work in a completely discrete version. We discretize both the space and time variables in variable steps and use the difference discrete variational principle with variable steps to obtain the equations of motion and boundary conditions as well as the conservation of energy in discrete form. For the case of classical scalar field, the quantization procedure is simpler since it does not contain any intrinsic constraint. We take the boundary conditions as primary Dirac constraints and use the Dirac theory to construct Dirac brackets directly. However, for the case of classical Dirac field in a finite volume, things are complex since, besides boundary conditions, it contains intrinsic constraints which are introduced by the singularity of the Lagrangian. Furthermore, these two kinds of constraints are entangled at the spatial boundaries. In order to simplify the process of calculation, we calculate the final Dirac brackets in two steps. We calculate the intermediate Dirac brackets by using intrinsic constraints. And then, we obtain the final Dirac brackets by bracketing the boundary conditions. Our studies show that we can not only construct well-defined Dirac brackets at each discrete space-time lattice but also keep the conservation of energy discretely at the same time.
Plasma density effect on backward Raman laser amplification
Authors: Zhang Zhi-Meng  , Zhang Bo  , Wu Feng-Juan  , Hong Wei  , Teng Jian  , He Shu-Kai  , Gu Yu-Qiu  ,   Science and Technology on Plasma Physics Laboratory, Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   School of National Defense Science and Technology, Southwest University of Science and Technology, Mianyang 621010, China;,   Center for Applied Physics and Technology, Peking University, Beijing 100088, China
Published: December 2020

Backward Raman amplification (BRA) in plasma can be used for generating ultra-powerful laser pulses. In this paper, the plasma density effect on backward Raman laser amplification is studied by using particle-in-cell method. It is found that using a low plasma density can lead to the premature Langmuir wave breaking and thus result in a small energy-transfer efficiency. On the other hand, using a high plasma density will enhance the developments of unwanted instabilities, which rapidly disturb the Raman amplification, thus limiting the interaction length and output power. Therefore, an optimal plasma density for BRA is near the threshold of Langmuir wave breaking in order to achieve both high efficiency and large energy flux. The space frequency spectrum analysis shows that the saturated intensity of amplified pulses is limited mainly by the self-phase modulation instability. By using a 1013 W·cm-2 pump pulse, our simulation results show that the initial 1013 W·cm-2 seed pulse can be well be well amplified into a pulse with an energy power of 1017 W·cm-2, a duration of 40 fs, and and an energy conversion efficiency of up to 58%.
Anisotropy of melting of Ag nanocrystal with different crystallographic planes at high temperature
Authors: Lu Min  , Huang Hui-Lian  , Yu Dong-Hai  , Liu Wei-Qing  , Wei Wang-He  ,   Faculty of Science, Jiangxi University of Science and Technology, Ganzhou 341000, China
Published: December 2020

The thermal-stability and melting mechanism of the Ag nanocrystalline in the process of high-temperature relaxation are investigated with embedded atomic method and molecular dynamics simulations. The dynamic evolution of the crystalline’s morphology is revealed based on the analyses of mean square displacement and lifetime of the stability. It is concluded that there are obviously anisotropic behaviors in the process of high-temperature relaxation in the quasi-cubic nanocrystal which is cut along the inter-perpendicular facet of {110}, {211} and {111}. The thermal-stability decreases in the sequence of facet (111), facet (110), and facet (112). The lifetimes of the first outmost and the second outmost atoms in those three different facets are extremely short and show no evidently difference from each other. However considering the facets with the same crystal plane indices, the lifetimes are longer within the third atom layer and subtly increase with the increase of the number of atom layers. However, the lifetimes are distinctly different from each other among the three different facets within the third atom layer.
Torsional mechanical properties of (n, n)-(2n, 0) carbon nanotubes heterojunction
Authors: Han Dian-Rong  , Wang Lu  , Luo Cheng-Lin  , Zhu Xing-Feng  , Dai Ya-Fei  ,   School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China;,   Jiangsu Key Laboratory on Optoelectronic Technology, Nanjing 210023, China;,   School of Physics and Electronic Engineering, Jiangsu Second Normal University, Nanjing 210013, China
Published: December 2020

A coaxial cylindrical heterojunction of carbon tubes, which consists of alternant bands of 5- and 7-membered rings, can be formed by one armchair (n, n) carbon nanotube and one zigzag (2n, 0) carbon nanotube. The torsional mechanical properties of this kind of (n, n)-(2n, 0) heterojunction constructed by the same length of armchair and zigzag nanotubes are studied by using molecular dynamics method. In order to make a comparison, the relations of the torque and axial stress to torsional angle of (n, n) and (2n, 0) carbon tubes are also systemically calculated. Moreover, the transfer process of torsional stress in the (n, n)-(2n, 0) heterojunction is analyzed. Some important conclusions are obtained. Firstly, the torsional angle corresponding to the buckling point of carbon nanotubes is closely related to their torsional stiffness. The buckling angle decreases monotonically with torsional stiffness. Secondly, as the torsion develops, the torsional stress appears from the joint position due to the fact that the junction part in the (n, n)-(2n, 0) heterojunction has the smallest torsional stiffness and then transfers from the joint position to both ends. The propagation velocity of the torsional stress in (n, n) nanotube which has smaller stiffness is faster than that in (2n, 0) nanotube with bigger stiffness. Finally, for the process of torsion within the elastic limit, no axial stress is produced in (n, n)-(2n, 0) heterojunction during the torsion. This effect is of great significance for designing the carbon nanotube-based nano-oscillator devices.
Phase-field-crystal simulation of edge dislocation climbing and gliding under shear strain
Authors: Gao Ying-Jun  , Quan Si-Long  , Deng Qian-Qian  , Luo Zhi-Rong  , Huang Chuang-Gao  , Lin Kui  ,   Guangxi Colleges and Universities Key Laboratory of Novel Energy Materials, College of Physics Science and Engineering, Guangxi University, Nanning 530004, China;,   Institute of Physics Science and Engineering Technology, Yulin Normal University, Yulin 537000, China
Published: December 2020

Structural kinetics in crystalline solids is driven heterogeneously at an atomic level by localized defects, which in turn drive mesoscopic and macroscopic phenomena such as structural phase transformation, fracture, and other forms of plastic flows. A complete description of such processes therefore requires a multiscale approach. Existing modeling methods typically operate exclusively either on an atomic scale or on a mesoscopic scale and macroscopic scale. Phase-field-crystal model, on the other hand, provides a framework that combines atomic length scale and mesoacpoic/diffusive time scale, with the potential reaching a mesoacpoic length through systemic multiscale expansion method. In order to study the dislocation movement under shear strain, the free energy density functional including the exerting shear force term is constructed and also the phase field crystal model for system of shear stain is established. The climb and glide of single dislocation in two-grain system are simulated, and the glide velocity of dislocation and the Peierls potential for dislocation gliding are calculated. The results show that the energy curve changing with time are monotonically smooth under a greater shear strain rate, which corresponds to dislocation movement at a constant speed, which is of rigorous characteristic; while under less shear strain rate, the energy change curve of system presents a periodic wave feature and the dislocation movement in the style of periodic “jerky” for gliding with the stick-slip characteristic. There is a critical potential for dislocation starting movement. The Peierls potential wall for climbing movement is many times as high as that for gliding movement. The results in these simulations are in a good agreement with the experimental ones.
Effect of electronic correlations on magnetotransport through a parallel double quantum dot
Authors: Wu Shao-Quan  , Fang Dong-Kai  , Zhao Guo-Ping  ,   College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610066, China
Published: December 2020

We theoretically investigate the effects of electronic correlations (including spin and Coulomb correlations) on the magnetotransport through a parallel double quantum dot (DQD) coupled to ferromagnetic leads. Two dots couple coherently through electron correlations, rather than tunneling directly between two dots, and each dot is coupled to two semi-infinite ferromagnetic leads. We assume that the intradot Coulomb repulsion is much larger than the interdot Coulomb repulsion U. Thus, only the zero, one and two-particle DQD states are relevant to transport. Because of interdot electron correlation, the I-V characteristics of each dot is sensitive to the change in the state of the other dot. This work focuses on the effects of electron spin correlation and electron Coulomb correlation on magnetotransport through this system. In order to determine the transport properties of the system, we use the generalized master equation method. This method is based on the reduced density operator defined by averaging the statistical operator of the total system over the states of all leads. With the framework of the generalized master equation and the sequential tunneling approximation, we calculate the current, differential conductance and tunnel magnetoresistance (TMR) in the dot 1 as a function of bias for different spin correlations and Coulomb correlations. Our results reveal that the magnetotransport through this system is more sensitive to Coulomb correlation than to spin correlation; when Coulomb correlation equals zero, the spin correlation can induce a giant tunnel magnetoresistance, which is further larger than the Jullieres value of TMR; when Coulomb correlation occurs, the giant tunnel magnetoresistance disappears; when Coulomb correlation is equal to or larger than spin correlation, Coulomb correlation can suppress spin correlation; while the coexistence of Coulomb correlation and asymmetry of the DQD system can result in dynamical channel blockade, which can lead to the occurrence of negative tunnel magetoresistance and negative differential conductance. These novel properties lead to the potential applications in nanoelectronics, and relevant underlying physics of this problem is discussed.
Electronic Tamm states of metamaterial-like semiconductor composite structures
Authors: Wu Zhi-Zheng  , Yu Kun  , Guo Zhi-Wei  , Li Yun-Hui  , Jiang Hai-Tao  ,   MOE Key Laboratory of Advanced Micro-structure Materials, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
Published: December 2020

In a semi-infinite crystal, the periodic potential is destroyed at the surface, and the electronic wave functions exponentially decay from the surface to both sides. Such localized electronic states in the vicinity of the surface are known as Tamm surface states. In analogy to the electronic Tamm states, in recent years, optical Tamm states have been found at the surface of the truncated photonic crystal composed of two kinds of dielectrics. Very recently, novel types of optical Tamm states including backward Tamm states in which the phase velocity and the group velocity of optical waves are in the opposite direction have been discovered in the photonic structures containing metamaterials. In fact, the concepts in electronic field and photonic field can inspire each other. Many unique phenomena in photonic systems can also be mapped to the electronic systems. In this paper, we study the novel types of electronic Tamm states in electronic systems, inspired by the novel types of optical Tamm states in photonic structures. #br#At first, comparing Maxwell equations with Schrodinger equations, one can see a correspondence between the parameters in electromagnetic system and the parameters in the electronic system. In particular, Hg1-xCdxTe semiconductors with special electronic band structures can realize various electronic materials in analogy to the optical metamaterials with various values of permittivity and permeability. By tuning the parameter x of Hg1-xCdxTe, we obtain a variety of metamaterial-like electronic materials, in analogy to the single-negative metamaterials, the double-negative metamaterials and the near-zero-index metamaterials in optical systems. Then, inspired by the one-dimensional heterostructures with metamaterials that generate optical Tamm states, we design a one-dimensional electronic heterostructure consisting of Hg0.847Cd0.153Te and CdTe/HgTe superlattice. When Hg0.847Cd0.153Te is analogous to the double-negative metamaterial, we find the backward electronic Tamm states in which the phase velocity and the group velocity of electronic waves are in the opposite directions. When Hg0.847Cd0.153Te is analogous to the near-zero-index metamaterial, we find a novel electronic Tamm states in which the amplitude of the electronic probability decays very slowly in Hg0.847Cd0.153Te. The discovery of these new types of electronic Tamm states enlarges our knowledge of electronic surface states.
Spin-wave band gaps created by rotating square rods in triangular lattice magnonic crystals
Authors: Hu Xiao-Ying  , Guo Xiao-Xia  , Hu Wen-Tao  , Huhe Mandula  , Zheng Xiao-Xia  , Jing Li-Li  ,   Departmentof Physics, Jining Teacher’s College, Jining 012000, China
Published: December 2020

Recently, magnonic crystals which are the magnetic counterparts of photonic crystals or phononic crystals are becoming a hot area of research. In this paper, band structure of two-dimensional magnotic crystal composed of square rods triangularly arranged are calculated by using the plane-wave expansion method. Spin-wave band structures of two-dimensional magnonic crystal composed of Fe triangularly arranged Fe in an EuO matrix. The results show that when the filling ratio f=0.4, only two absolute band gaps can be found in the case of θ=0°. The first gap appears between the first band and the second band, the second gap between the sixth band and the seventh band. However, the number of band gaps can be improved by rotating the square rods through θ=25°, there are eight absolute band gaps that can be found. The first gap appears between the first band and the second band, the fifth gap between the sixth band and the seventh band. The new band gaps can be found, the second gap appears between the third band and the fourth band, the third gap between the fourth band and the fifth band, the fourth gap between the fifth band and the sixth band, the sixth gap between the seventh band and the eighth band, the seventh gap between the eighth band and the ninth band, the eighth gap between the ninth band and the tenth band. These results show that it is possible to create spin-wave gaps by rotating square rods in a two-dimensional magnotic crystal. The numerical results of the normalized gap width ΔΩ/Ωg of the first gap between the first band and the second band always changes with filling fraction f and rotational angles θ. When f=0.6 we calculated the first normalized gap width ΔΩ/Ωg. when f=0.6 and θ=0°, the first gap width ΔΩ=0.812(μ0ω/g) and the normalized gap width ΔΩ/Ωg=0.9187. The results show that from the first normalized gap widths the largest one can be found when f=0.6 and θ=5°, the first gap width ΔΩ=0.937(μ0ω/g) and the normalized gap width ΔΩ/Ωg=0.9591. The results show that the numerical, rotating square rods can make the low frequency band gap widen in the triangular lattice of two-dimensional magnonic crystal.
Study on magnetic properties of strontium ferrite based on the technology of electron paramagnetic resonance
Authors: Li Shao-Bo  , Yin Chun-Hao  , Xu Zhen-Kun  , Li Pei-Xin  , Wu Cai-Ping  , Feng Ming-Yang  ,   Surface and Magnetism Laboratory, School of Science, China University of Mining and Technology, Xuzhou 221116, China
Published: December 2020

In order to study how the ingredient, sintering temperature, oxygen, doping and other conditions affect magnetic properties of strontium ferrite powder, a strontium ferrite powder is prepared by sol-gel method, and a new method of studying magnetic properties of strontium ferrite powder based on an electron paramagnetic resonance (EPR) is established in this paper. The sintered samples are tested by electron paramagnetic resonance spectrometer. Results show that -Fe2O3, a paramagnetic intermediate, is most compared with other ratios under calcined at 400 ℃ and the strontium iron mole ratio of 1:9; while at the other temperatures it decreases and the ferromagnetic phase increases; the optimum calcination temperature is between 800 ℃ and 900 ℃. These facts are caused by both external magnetic field and other magnetic fields, thus resulting in some new stronger magnetic moment interactions. Results also show that a large quantity of paramagnetic -Fe2O3 is found under hypoxic annealing environment, which is not conducible to generating the ferrimagnetic phase; X-ray diffraction (XRD) analysis shows that the others are paramagnetic and ferrimagnetic phase except a bit of other phases; both EPR spectra and XRD spectra show that the paramagnetic phase is least, and ferrimagnetic phase is most in the sintering sample when strontium iron mole ratio is 1:9, so the sample owns the strongest magnetism. The sample remanence experiment by milli-tesla meter also confirms these results. It is also found that paramagnetic phase can effectively decrease and ferrimagnetism is enhanced when samples are doped by lanthanum ion accounting for 20%-30% of the total number of moles of strontium lanthanum.
Luminescence properties of Eu3+ doped CaMoO4 micron phosphors
Authors: Zhao Cong  , Meng Qing-Yu  , Sun Wen-Jun  ,   Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025, China
Published: December 2020

Eu3+ doped CaMoO4 micron phosphors of different concentrations were prepared by chemical precipitation method. The photoluminescence properties were studied in detail. The X-ray diffraction measurements indicate that the samples are scheelite structure, and doping Eu3+ enlarge the lattice parameter of host material. The scanning electron microscope images show that the particle morphology is near-spherical and the size is 4-5 μm. The excitation and emission spectra of CaMoO4:Eu show that CaMoO4:Eu can be effectively excited by blue light and near UV-light, and the red light emission of high colour purity can be realized. The electron-phonon coupling properties were also studied. The results indicate that the magnitude of Huang-Rhys factor is 10-2, so the CaMoO4:Eu is a weak electron-phonon coupling material. The results also indicate that the Huang-Rhys factor increases with the increase of concentration. It is probably because that increasing the doping concentration enhances the lattice relaxation. The transition intensity parameter Ω2 of Eu3+ enlarges while the concentration is increasing. Because Ω2 and the luminescent center environment are closely related, the numerical value of Ω2 enlarges with the increase of degree of environmental disorder. But Ω4 doesn't have obvious change. It can be explained that the environmental sensitivity level of Eu3+5D0→7F2 transition is higher than that of 5D0→7F4 transition. The quantum efficiency of Eu3+ 5D0 energy level decreases with the increase of doping concentration. This can be attributed that the enhancement of Eu3+ doping concentration enlarges the energy transfer rate between luminescent centers, so the energy of excited electrons can be transferred to quenching center more easily and then the nonradiative relaxation rate of excited electrons increases. The best doping concentration of Eu3+ is 25% by drawing the concentration quenching curve. Furthermore, the energy transfer type of Eu3+ in CaMoO4 host is confirmed to be exchange interaction and the critical distance is calculated to be 8.4 Å. The chromaticity coordinate of CaMoO4:Eu phosphors is (0.654, 0.334), so the samples have high colour purity. The study indicates that CaMoO4:Eu micron phosphor prepared by chemical precipitation method is a red phosphor material with excellent property.
Multiple heat sources with multi-parameter inversion of nondestructive infrared detection
Authors: Zhang Li-Guang  , Qu Hui-Ming  ,   School of Electronic Engineering and Optoelectronics Technology, Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

This study deals with the case of multiple internal heat source inversion problem of steady-state based on nondestructive infrared detection. We construct homogeneous and heterogeneous steady heat conduction models of different shapes. Neither the number of heat sources, nor their locations, nor their sizes nor their intensities are known. We use the finite element method (FEM) based on numerical algorithm to analyze the two-dimensional model discretely. The internal heat conduction process of model is analyzed. The resultant temperature field can be decomposed into the temperature field caused by the ambient temperature and those given by internal heat sources. We simplify the finite element matrix equation according to decomposition process above. Finally, the problem boils down to solving the highly underdetermined matrix equation of Ax = b. The unknown x item corresponds to internal thermal heat source field. The piecewise polynomial spectral truncated singular value decomposition (PPTSVD) is applied for the first time to the inverse heat source problem. Its regular operator matrix is changed from the original more order differential operator matrix to regional node weighted matrix. After replacement this solution improves the effect of heat source field tending to the boundary. Results of the solution confirms a real heat source field when there are less heat sources or different heat sources are far from each other. But there also exits a serious superimposed effect between neighboring heat sources. We improve the algorithm to study this problem through using the iterative elimination process which complies with the idea of spreading heat source field and then gathering. The iteration tolerance and number of times belonging to one single PPTSVD solving process are reduced. Through iterating the multiple PPTSVD solving process and reconstructing matrixes A and b in each iteration, we obtain the scatter heat source field distribution surrounding real field. Finally, this scattered distribution solution is gathered again. According to the heat source parameter calculated by algorithm, the temperature field of whole model can be reconstructed using FEM. Comsol numerical simulation and real physical experiments are performed to verify the validity and accuracy of the algorithm in different heat conduction models. The results demonstrate that the algorithm can access each parameter of multiple heat sources. Even in the heterogeneous model, it can still obtain accurate results and reconstruct the temperature field of the two-dimensional model. The algorithm can be applied to non-destructive material detection and human infrared medical imaging fields.
Influence of length parameter on the characteristics of nanoscale titanium oxide memristor
Authors: Guo Yu-Quan  , Duan Shu-Kai  , Wang Li-Dan  ,   School of Electronic and Information Engineering, Southwest University, Chongqing 400715, China
Published: December 2020

According to the completeness theory of circuit, Chua [Chua L O 1971 IEEE Trans. Circ. Theor. 1971 18 507] put forward the fourth basic circuit element memristor besides resistor, inductor and capacitor in 1971. And memorisistance is defined as the ratio of the flux to the charge passing through it. With the emergence and development of nanoscale semiconductor technology, HP laboratoty successfully fabricated a physical memristor in 2008. The successful fabrication of memristive device caused a stir in the whole electronic field and thus a vast number of researchers were involved in the research, owing to its superior properties, i.e., nanoscale dimension, continuous input and output property, switching characteristics and unique non-volatile memory capacity. With all these extraordinary properties, memristors possess many possibilities for the development of future integrated circuits and analog computer. With the gradually in-depth study of memristor, memristor is being microsized, and its internal structure, motion law among its internal particles and influences resulting from the parameters are further explored. In recent years, the memristor has made significant achievement in the areas of non-volatile solid-state memory, intelligent storage, very-large-scale integrated circuitry, programmable analog circuits, and artificial neural networks. So far, the influence of size parameter on the memristor has been little studied, although the size parameter is one of the key factors in the memristor fabrication technology, which severely restricts the memristor development and its practical application. In the paper, we theoretically analyze the influences of size parameter on two practical memristor models (i.e., the HP memristor and spintronic memristor) in detail based on the Ohm’s law. On this basis, a series of circuit experimental simulation is carried out, and the corresponding memristor characteristic curves are thus obtained. Furthermore, we choose 4 most representative experimental results, and make specific analysis on them. Those results indicate that the optimal length of HP memristor is in a range from 8 nm to 12 nm, while the proper range of spintronic memristor is from 500 nm to 600 nm. The final results can not only contribute to memristor physical implementation and its applications, but also provide theoretical references and reliable experiment basis for the further development of the titanium oxide memristor devices and the relevant research.
Vibrational resonance and nonlinear vibrational resonance in square-lattice neural system
Authors: Sun Run-Zhi  , Wang Zhi-Zhong  , Wang Mao-Sheng  , Zhang Ji-Qian  ,   College of Physics and Electronic Information, Anhui Normal University, Wuhu 241000, China
Published: December 2020

Response characteristics of FitzHugh-Nagumo neurons to low frequency signal have been investigated by numerical simulation. Neurons are arranged on a square-lattice and are subjected to two frequency signals. Results show that, vibrational resonance of the membrane potential can be induced by varying the amplitude of the high-frequency signal, when the control parameter is selected in the excitable region. In addition, the responses of neurons to higher harmonics of low-frequency signal have been studied, and nonlinear vibrational resonances are also found. With the increase of frequency in the low-frequency signal, the response of the system to low-frequency signal can resonate. Thus, the double resonance can occur by changing the frequency in low-frequency signal and the amplitude in high-frequency signal. Moreover, effects of electrical synapses and chemical synapses on vibrational resonance and nonlinear vibrational resonance of the neurons have also been studied. Effect of the number of neurons, which are subjected to two frequency signals in the square-lattice, on the response characteristic of the system is also studied. It is found that the response characteristic of the electrical coupling neurons is quite different from that of chemical coupling neurons.
Research on X band extended cosecant squared beam synthesis of micro-strip antenna arrays using genetic algorithm
Authors: Zhang Jin-Ling  , Wan Wen-Gang  , Zheng Zhan-Qi  , Gan Xi  , Zhu Xing-Yu  ,   School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China;,   Institute of Microelectronics of Chinese Academy of Sciences, Beijing 100029, China
Published: December 2020

Synthesis of desired radiation patterns without an optimization algorithm is usually time consuming and inefficient. To achieve a desired radiation pattern such as cosecant squared beam and contoured beam, different evolutionary algorithms such as genetic algorithm (GA), particle swarm optimization algorithm, and invasive weed optimization algorithm have been used to find the excitation of radiation elements. Adaptive genetic algorithm (AGA) optimizer is a robust, stochastic search method, modeled on the principles and concepts of natural selection and evolution. As an optimizer, the powerful heuristic of the AGA is effective for solving complex and related problems. An improved AGA is proposed, in allusion to the characteristics of optimizing designs of antenna arrays which have many parameters and complicated structures. This algorithm constructs an adjustble formula to produce the crossover rate and mutation rate based on a logistic curve equation. In the way of combining roulette wheel selection and elitist strategy, this algorithm searches for the optimal solution in the global space, and is compared with the classical GA; the improved AGA has a better performance in seeking the solution. Taking the mutual coupling between the elements into account, we design the X band extended cosecant squared beam micro-strip antenna arrays based on the improved AGA. Specifications of the antenna are as follows:a -3 dB beam width in height is from 0° to 12°, a -10 dB beam width in height is from 12° to 65°, and a total height coverage is 65°; a frequency band ranges from 8.5 to 9.8 GHz and its center frequency is 9.05 GHz. Simulation results show that the fitness increases from 0.07 to 0.09, and the quality of the synthesized radiation pattern has a great improvement, which verifies the superiority of the improved AGA proposed in this paper. In addition, the prospect of the designed antenna which has an extended cosecant squared beam is promising in air-surveillance radar systems, where the radiation pattern of the antenna will compensate for the free-space loss.
An approach for calculating the optical structure based on ybar-y diagram
Authors: Lü Xiang-Bo  , Zhu Jing  , Yang Bao-Xi  , Huang Hui-Jie  ,   Laboratory of Information Optics and Optoelectronic Technology, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China;,   University of the Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The first-order quantity of the optical structure can be obtained using the ybar-y diagram and this diagram has a control point quantity. Based on the concept and quantity of the ybar-y diagram, this paper establishes a mathematical model to calculate an optical system’s first-order structure. The aberration is induced by the deflection of the transmission rays. If a first-order structure has a minimal total deflection angle of the first paraxial ray and the second paraxial ray, the higher order aberration will have a small value and the calculated first-order optical structure will be the best. According to the mathematical model, the issue of optical structure calculation is converted to a numerical optimization problem. And the objective function, i.e. the sum of the first and second paraxial ray’s deflection angles, is constructed. After comparison among etween many kinds of numerical optimization algorithms, the particle swarm optimization algorithm is used to solve the problem. Then a calculation program containing graphical user interface (GUI) is developed to calculate the first-order structure quickly and efficiently. The basic design parameters of the optical system are imported into the GUI after some treatments, then the resulting first-order structure is obtained after some clicks of the mouse. The resulting structure is thereafter converted to a practical lens system by the use of commercially available optical design software such as ZEMAX. After a lens optimization process, an actual optical system is accomplished. According to the method proposed in this paper and by the use of the calculation program, a 13 megapixel mobile phone camera lens is designed first. The F# of this lens system is 2.3 and the full field of viewing angle is 70 degree. The system has a total length of 4.5 mm and a distortion of 1.2%. Only four aspheric lenses are used and the other optical performance meets the design requirements as well. In addition, an eyepiece of helmet-mounted display system is designed, in which only two lenses are used and a visual field angle of 90 degree is achieved. The entrance pupil is 5 mm width and the image diagonal length is 65 mm. This system has a total length less than 45 mm and eye relief greater than 12 mm. Other performance of the eyepiece can also meet the requirements. These designs of the two optical systems demonstrate that the proposed method is reliable in calculating the optical structure of the optical system.
Generation of vector beams in terms of the partial light modulator of a twisted nematic liquid crystal
Authors: Xi Si-Xing  , Wang Xiao-Lei  , Huang Shuai  , Chang Sheng-Jiang  , Lin Lie  ,   Institute of Modern Optics, Key Laboratory of Optical Information Science and Technology, Ministry of Education, NanKai University, Tianjin 300071, China
Published: December 2020

We propose a vector beam generation method based on the spatial light modulator composed of twisted nematic liquid crystal. According to the relation between the rotation angle and the applied voltage on the spatial light modulator, a common optical system for generating a variety of vector beams is designed in experiments. By using this common optical system, a variety of vector beams in axisymmetric phases as well as the complex vector beams are generated, and their polarization characteristics are observed and measured experimentally, where a tight focusing field is obtained, and this may be applied in optical tweezers and lithography. In addition, the device structure is simple and easy to operate, its efficiency of producing vector beam is very high and the laser spectral characteristics are not changed in the proposed generation of vector beams. Therefore, the method we proposed can find important potential applications in strong laser of vector beams interacting with matter, and laser acceleration, etc.
Study on extending the depth of field in reconstructed image for a micro digital hologram
Authors: Yang Jing  , Wu Xue-Cheng  , Wu Ying-Chun  , Yao Long-Chao  , Chen Ling-Hong  , Qiu Kun-Zan  , Cen Ke-Fa  ,   State Key Laboratory of Clean Energy Utilization, School of Energy Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Digital micro holography offers an in-situ, non-contact and three-dimensional way to explore the microscopic world. However, as it is difficult to focalize the whole object in one single reconstructed image, the application of digital micro holography to cases with a large longitudinal object volume is limited by the microscopes depth of field. By extending the depth of field in reconstructed micro holograms in the wavelet domain, this paper fully takes advantage of numerical reconstruction algorithms to solve this problem. First, a recorded hologram is rebuilt using the wavelet transform approach by setting up an appropriate longitudinal interval to obtain a series of reconstructed hologram planes. Then each plane is decomposed with wavelet into its sub-images of both high and low frequencies. Furthermore, the local variance of the maximum intensity gradients of the high- and low-frequency coefficients is calculated and utilized as the focus criterion. Finally, the image planes are fused into a single one with the depth of field extended to a large extent. The feasibility and robustness of this reconstruction procedure for both continuum and particle fields are investigated. One of the demonstrations is made in an experiment of a tilted continuum:carbon fiber. It is different from most of the previous applications where the interrogated is the particles and where the area involved is parallel to the CCD. The carbon fiber gets successfully reconstructed in three dimensions, and the measurement errors of its diameter are presented together with the reconstruction distances. Another is an experiment of a dispersed particle field:micro transparent particles are generated by an ultrasonic atomizer, for which the reconstruction procedure achieves an extended depth of field. In addition, a numerical model based on generalized Lorenz-Mie theory is used to simulate the holograms of both opaque and transparent particles of 1-15 m in diameter. Variations of the longitudinal location errors with the Fraunhofer number are analyzed, and comparisons are made between the results of opaque and transparent particles. Both the experimental and simulation outcomes show that this reconstruction procedure is a reliable one to acquire an extended-depth-of-field hologram for both the continuum and the dispersed particle fields, and then to accurately measure the objects.