bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamical modeling and analysis of buck converter operating in pseudo-continuous conduction mode
Authors: Li Zhen-Hua  , Zhou Guo-Hua  , Liu Xiao-Tian  , Leng Min-Rui  ,   School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, China
Published: December 2020

Taking buck converter operating in pseudo-continuous conduction mode (PCCM) for example, through a detailed description of the switch state of the switching converter, its accurate discrete-time model is established in this paper. On the basis of the model, bifurcation diagrams of the PCCM buck converter with the variations of circuit parameters are obtained, including load resistance, equivalent series resistance (ESR) of inductor, inductance, capacitance, reference current, and input voltage. And the complex dynamical behaviors existing in PCCM buck converter, such as subharmonic oscillation, period-double bifurcation and chaos, are revealed. Under different load resistances, time-domain simulation waveforms and phase portraits of PCCM buck converter are obtained by Runge-Kutta algorithm based on the piecewise smooth switch model. The working states of PCCM buck converter, reflected by the time-domain waveforms and phase portraits, are consistent well with those described by the bifurcation diagrams. It is shown that the time-domain simulation results verify the validation of the discrete-time model.#br#From theoretical analysis and simulation results, some conclusions can be obtained below. 1) When the load resistance gradually decreases, PCCM buck converter has a unique bifurcation route, i. e. , from PCCM period-1 state, PCCM multi-period oscillation via period-double bifurcation, chaos, CCM-PCCM multi-period oscillation, to CCM period-1 state via inverse period-double bifurcation. What is more, the bifurcation analysis with the load resistance serving as parameter indicates that the PCCM buck converter is more suitable for light load conditions, and its stable state will be lost and operation mode can be shifted (from PCCM to CCM) with increasing the load. 2) The ESR of inductor is closely related to the power loss and will affect the stability of the PCCM converter. The larger the ESR, the more the power loss will be. However, the PCCM converter is more stable if the ESR is larger. 3) Period-double bifurcation or inverse period-double bifurcation exists in the PCCM buck converter with the other circuit parameters varied in a wide range except for the load resistance, and there are three working states of buck operating in PCCM, i.e., stable period-1 state, multi-period sub-harmonic oscillation, and chaos. The research results in this paper are useful for designing and controlling PCCM switching converter.
Transportation of Gaussian light beam in two-layer clouds by Monte Carlo simulation
Authors: Sun Xian-Ming  , Xiao Sai  , Wang Hai-Hua  , Wan Long  , Shen Jin  ,   School of electrical and electronic engineering, Shandong University of Technology, Zibo 255049, China
Published: December 2020

Based on the radiative transfer theory, the backscattering characteristics of water clouds and ice-water two layers clouds irradiated by infinite narrow collimated light beam are studied by using the Monte Carlo method. The incident wavelength is 0.532 μupm, and the cloud particle shape is assumed to be of sphere or plate. The single scattering characteristics of the clouds are computed based on the Mie theory, and the scattering angle sampling is based on the Mie phase function. The photon step adjustment is considered when the step is large enough to cross the cloud layer. The variations of reflection functions of the water clouds and ice-water two layers clouds with the radial length r and zenith angle are given, and the interior light intensity distribution of clouds are given in two dimensions. From the computed results, we find that the reflection characteristics of the two layer clouds are greatly different from those of the pure water clouds. The reflection intensity of ice clouds covered with water clouds is bigger than that of ice clouds covered with water clouds. This reason is that the sizes of ice clouds are larger than those of the water clouds, so more photons will be scattered into the interior of the clouds.#br#The cloud layer is assumed to be linear and invariant, so the response to an infinitely narrow photon beam will be described by a Green's function of the clouds, and the response to the Gaussian beam can be computed from the convolution of the Green's function according to the profile of the Gaussian photon beam. The multiple scattering characteristics of the Gaussian photon beam are computed from the convolution of the impulse response, i.e., the response to an infinitely narrow photon beam, according to the profile of the Gaussian light photon beam. From the computed results, we find that the reflection function of clouds for Gaussian incidence has a great difference from that for the infinite narrow beam incidence. The reflected light intensity is inversely proportional to the size of the Gaussian beam at the location near r=0. So the laser spot must be considered when detecting the clouds by using of the lidar, and the method presented in this paper can give theoretical support.
The -type four-particle entangled state generated by using superconducting artificial atoms with broken symmetry
Authors: Leng Chun-Ling  , Zhang Ying-Qiao  , Ji Xin  ,   Department of Physics, College of Science, Yianbian University, Yanji 133002, China
Published: December 2020

We propose a scheme for generating a genuine -type four-particle entangled state of superconducting artificial atoms with broken symmetry by using one-dimensional transmission line resonator as a data bus. With the help of the Circuit quantum electrodynamics system composed of -type three-level artificial atoms and transmission line resonator, our scheme also has long coherence time and storage time. Meanwhile, the -type three-level artificial atom used in the scheme is different from natural atom and has cyclic transitions. Furthermore, our scheme is easy to control and flexible. Through a suitable choice of the Rabi frequencies and detunings of the classical fields, we can use this system to implement the selective coupling between two arbitrary qubits. After suitable interaction time and simple operations, the desired entangled state can be obtained. Since artificial atomic excited states and photonic states are adiabatically eliminated, our scheme is robust against the spontaneous emissions of artificial atoms and the decays of transmission line resonator. We also analyze the performance and the experimental feasibility of the scheme, and show that our scheme is feasible under existing experimental conditions.
Raman effect on dark soliton trapping in high birefringence fiber
Authors: Yan Qing  , Jia Wei-Guo  , Yu Yu  , Zhang Jun-Ping  , Menke Neimule  ,   School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China
Published: December 2020

Not only the interaction between optical pulse and orbital electron but also the interaction between optical pulse and optical phonon needs to be considered when input pulse energy is large. The latter induces the simulated Raman scattering, thus generating the Raman gain. We analyze the effect of Raman gain, especially parallel Raman gain, on dark soliton trapping in high birefringence fiber by analytical method and numerical method. In the first part, we introduce some research results of soliton trapping obtained in recent years. In the second part, the coupled nonlinear Schrödinger equation including Raman gain is utilized for high birefringence fiber. The trapping threshold of dark soliton with considering the Raman gain is deduced by the Lagrangian approach when input pulse is the dark soliton pulse that the amplitude of two polarized components of the dark soliton are the same (see formula (26)). Fig. 1. shows the relation between threshold and parallel Raman gain according to formula (26) when group velocity mismatching coefficient values are 0.15, 0.3, and 0.5 (vertical Raman gains are all 0.1). In the third part, the propagation of the two orthogonal polarization components of dark soliton is simulated by the fractional Fourier transform method. Figures 2-4 show respectively dark soliton trapping with group velocity mismatching coefficient values of 0.15, 0.3 and 0.5. We consider three situations in which Raman gain is not included and the parallel Raman gains are 0.4 and 0.6 when vertical Raman gains are both 0.1 in different group velocity mismatching coefficient values. We obtain the threshold of dark soliton by numerical method under different conditions and analyze the figures. At the same time, we compare the analytical solution with the numerical solution and discuss the effect of Raman gain on dark soliton trapping. The last part focuses on our conclusion. It is found that the threshold which is obtained by analytical method is smaller than that from the numerical solution. The difference between the analytical and numerical dependences decreases with group velocity mismatching coefficient decreases. As a result, formula (26) is in good agreement with numerical data for small group velocity mismatching. The larger the group velocity mismatching, the larger the amplitude threshold of dark soliton is. It also shows that the amplitude threshold of dark soliton can be reduced due to Raman gain and the threshold is reduced faster with the increasing of Raman gain.
Liquid crystal lens with large-range electrically controllable variable focal length
Authors: Yin Xiang-Bao  , Liu Yong-Jun  , Zhang Ling-Li  , Lü Yue-Lan  , Huo Bo-Fan  , Sun Wei-Min  ,   Key Laboratory of In-fiber Integrated Optics, Ministry Education of China, Harbin Engineering University, Harbin 150001, China;,   College of Science, Heilongjiang University of Science and Technology, Harbin 150022, China;,   College of Science, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

A novel structure model with different disc-ring radii of liquid crystal lens is proposed, in which liquid crystal director could be controlled by changing the electric field intensity dependence. Then the theory of liquid crystal and the geometric optics are analyzed. By using the finite element method, under the same constant voltage, we obtain the distributions of the electric field intensity at different positions of the liquid crystal layer. Then, the simulation results provide a theoretical guideline for the experimental fabrication. Due to the fact that the electric field intensity at the electrode edges is stronger than that at the circular hole, a shorter focal convergence could be realized by controlling the voltage between the upper and the lower substrates. In this paper, the influences of the electrode size and spacer thickness on the focal length of liquid crystal lens are also discussed experimentally and theoretically. Through optimizing various parameters, a prototype liquid crystal lens with a large zoom range and simple structure is obtained. Its focal length can be controlled to be 75-230 mm in a range of 25 VRMS-250 VRMS.
Modification of geometrical attenuation factor of bidirectional reflection distribution function based on random surface microfacet theory
Authors: Liu Hong  , Zhu Jing-Ping  , Wang Kai  ,   Shanxi Key Laboratory of Information Photonic Technique, School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China;,   The State Key Laboratory of Astronautic Dynamics, Xi'an Satellite Control Center, Xi'an 710043, China
Published: December 2020

The reflection attenuation factor given by Blinn has been widely used as an important factor in the bidirectional reflectance distribution function (BRDF) model based on geometrical optics theory for nearly half a century. However, Blinn's attenuation factor is based on microfacet theory and geometry of equicrural V-grooves caused sharp turning points and obvious error in its function curves. In this paper, a modified geometry attenuation factor based on random surface microfacet theory is presented. We assume that the surface is composed of a large number of microfacets, and the slope of each microfacet is independent of each other and follows Gaussian distribution. The attenuation effect is caused by the masking and shadowing factors in adjacent microfacets. Depending on the slope angles of microfacets, reflection falls in three submodels, i.e., passing model, semi-passing model, and masking/shadowing model when discussing masking/shadowing factor. The modified attenuation factor is given in an integral expression. The modified geometry attenuation factor is simulated and compared with Blinn's geometry attenuation factor. The sharp turning point in Blinn's attenuation factor curve is eliminated and the error of the BRDF curve is reduced. The result shows that the modified geometry attenuation factor reaches better physical rationality and significantly improves the accuracy of BRDF model. Compared with Blinn's geometry attenuation factor, the modification reduces the standard error between BRDF model and existing data from 0.0636 to 0.0084. The cause of the error in Blinn's geometry attenuation factor is analyzed, the equicrural V-grooves assumption of Blinn's geometry attenuation model considers too much reflection attenuation in the condition of small incident angle and large reflect angle. The modification in this paper is based on random surface microfacet theory, in which the angular dependence of adjacent microfacet is eliminated, for this reason the accuracies of geometry attenuation model and BRDF model are improved.
Estimation of steady loss factor with decay rate method
Authors: Gu Jin-Tao  , Sheng Mei-Ping  ,   Department of Environmental Engineering, School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Steady loss factor is derived according to its definition, and a conclusion is obtained that steady loss factor is not always among modal loss factors but related to contributions of each modal response to vibration response. To obtain the conclusions about the range of steady loss factor, four cases are discussed according to positions of the two natural frequencies related to the central frequency. 1) Both natural frequencies are lower than the central frequency. 2) Both natural frequencies are higher than the central frequency. 3) One natural frequency, whose modal loss factor is smaller, is higher than the central frequency and the other natural frequency is lower than the central frequency. 4) One natural frequency, whose modal loss factor is larger, is higher than the central frequency and the other natural frequency is lower than the central frequency. Steady loss factor ranges between modal loss factors only if the frequency, whose value of multiplying modal loss factor is largest, is lower than central frequency of frequency band and at the same time, the frequency, whose value of multiplying modal loss factor is the smallest, is higher than the central frequency. Process loss factor which is a time-dependent function is proposed for the description of loss factor of decay process. Meanwhile, the way to calculate process loss factor with modal frequency, loss factor and amplitude is presented. Process loss factor tends to steady loss factor contributed by the mode with smallest loss factor over time. The accuracy is good enough for traditional decay rate method to estimate steady loss factor when there is only one mode or lots of modes in the frequency band. It is difficult for traditional decay rate method to be used to evaluate steady loss factor in the mid-frequency band where frequency density is not enough. A new method is proposed to estimate steady loss factor through separating the smallest modal loss factor components in the frequency band with time decay curve step by step according to the different decay characteristics. Simulation and experimental results indicate that the proposed method can cover the shortage of traditional decay rate method of estimating the steady loss factor in mid-frequency band.
Generalized Birkhoff system and a kind of combined gradient system
Authors: Mei Feng-Xiang  , Wu Hui-Bin  ,   School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081, China;,   School of Mathematics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

A combined gradient system which is obtained by adding a gradient system to a skew-gradient system is proposed. The property of the system is studied. Three results on its solution are obtained. Moreover, a criterion on the stability of the system is presented. The generalized Birkhoff system is a more extensive constrained mechanical system than Lagrange system, Hamilton system and Birkhoff system. The conditions under which a generalized Birkhoff system can be considered as a combined gradient system are given. When a generalized Birkhoff system is transformed into a combined gradient system, its integration and stability can be discussed by using the property. Finally, some examples are given to illustrate the application of our results.
Bending phenomenon of temperature calibration curve in junction temperature measurement by the high transient current
Authors: Guo Chun-Sheng  , Wang Lin  , Zhai Yu-Wei  , Li Rui  , Feng Shi-Wei  , Zhu Hui  ,   College of Electronic Information and Control Engineering, Beijing University of Technology, Beijing 100124, China;,   The 13th Research Institute Of China Electronics Technology Group Corporation, Shijiazhuang 050051, China
Published: December 2020

To measure the junction temperature of diodes under operating conditions, the temperature calibration curve is studied under large current conditions. To avoid the self heating by the large current conditions, pulsed currents are used in the paper. The temperature calibration curve of TO-247-2L fast recovery diode is investigated in this paper. The 0-1.5 A pulse current, of which the pulse width is 250 μs and the duty cycle is 5%, is chosen to study the temperature calibration curves under 50, 70, 90, 110, 130 ℃ respectively.#br#The results show that under the large current condition, the temperature calibration curve bends. The main reason for the bending phenomenon is that the series resistance changes with temperature increasing, which is affected by the mobilities of electrons and holes in semiconductor material. With the temperature rising, the mobility decreases, which results in the increasing of series resistance. Due to the series resistance increasing The voltage on p-n junction will be reduced. For this reason, a higher voltage is needed to obtain the same current, and the temperature calibration curve will bend.#br#There are two reasons which will lead to the temperature rising. The first reason is self-heating of devices by the power dissipation, and the second reason is that the temperature of device is heated by ambient temperature. Under the same temperature, self-heating behaviors of device by different currents will result in different series resistances. But in the paper, the results show that the series resistances under different currents are the same, which illustrates that self-heating is not the key reason for the change of series resistance. So, the temperature changing of the diode is caused by the ambient temperature rising, which verifies that the bending phenomenon of the temperature calibration curve of TO-247-2L fast recovery diode is caused by the ambient temperature rising.#br#Then, through experimental measurements and theoretical calculations, the accurate nonlinear temperature calibration curve is acquired, which can reduce the measurement errors of high current transient junction temperature.
Introduction to first-principles simulation package ABACUS based on systematically improvable atomic orbitals
Authors: Liu Xiao-Hui  , Chen Mo-Han  , Li Peng-Fei  , Shen Yu  , Ren Xin-Guo  , Guo Guang-Can  , He Li-Xin  ,   Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China;,   Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China;,   Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, USA;,   Network Information Center, Supercomputing Center, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

With the rapid development of supercomputers and the advances of numerical algorithms, nowadays it is possible to study the electronic, structural and dynamical properties of complicated physical systems containing thousands of atoms using density functional theory (DFT). The numerical atomic orbitals are ideal basis sets for large-scale DFT calculations in terms of their small base size and localized characteristic, and can be mostly easily combined with linear scaling methods. Here we introduce a first-principles simulation package “Atomic-orbital Based Ab-initio Computation at UStc (ABACUS)”, developed at the Key Laboratory of Quantum Information, University of Science and Technology of China. This package provides a useful tool to study the electronic, structural and molecular dynamic properties of systems containing up to 1000 atoms. In this paper, we introduce briefly the main algorithms used in the package, including construction of the atomic orbital bases, construction of the Kohn-Sham Hamiltonian in the atomic basis sets, and some details of solving Kohn-Sham equations, including charge mixing, charge extrapolation, smearing etc. We then give some examples calculated using ABACUS: 1) the energy orders of B20 clusters; 2) the structure of bulk Ti with vacancies; 3) the density of states of a model protein; 4) the structure of a piece of DNA containing 12 base pairs, 788 atoms. All results show that the results obtained by ABACUS are in good agreement with either experimental results or results calculated using plane wave basis.
Novel properties of 5d transition metal oxides
Authors: Du Yong-Ping  , Liu Hui-Mei  , Wan Xian-Gang  ,   National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China;,   Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
Published: December 2020

The spin-orbit coupling (SOC) in the 5d transition metal element is expected to be strong due to the large atomic number and ability to modify the electronic structure drastically. On the other hand, the Coulomb interaction in 5d transition is non-negligible. Hence, the interplay of electron correlations and strong spin-orbit interactions make the 5d transition metal oxides (TMOs) specially interesting for possible novel properties. In this paper, we briefly summarize our theoretical studies on the 5d TMO. In section 2, we systematically discuss pyrochlore iridates. We find that magnetic moments at Ir sites form a non-colinear pattern with moment on a tetrahedron pointing to all-in or all-out from the center. We propose that pyrochlore iridates be Weyl Semimetal (WSM), thus providing a condensed-matter realization of Weyl fermion that obeys a two-component Dirac equation. We find that Weyl points are robust against perturbation and further reveal that WSM exhibits remarkable topological properties manifested by surface states in the form of Fermi arcs, which is impossible to realize in purely two-dimensional band structures. In section 3, based on density functional calculation, we predict that spinel osmates (AOs2O4,A=m Ca,Sr) show a large magnetoelectric coupling characteristic of axion electrodynamics. They show ferromagnetic order in a reasonable range of the on-site Coulomb correlation U and exotic electronic properties, in particular, a large magnetoelectric coupling characteristic of axion electrodynamics. Depending on U, other electronic phases including a 3D WSM and Mott insulator are also shown to occur. In section 4, we comprehensively discuss the electronic and magnetic properties of Slater insulator NaOsO3, and successfully predict the magnetic ground state configuration of this compound. Its ground state is of a G-type antiferromagnet, and it is the combined effect of U and magnetic configuration that results in the insulating behavior of NaOsO3 We also discuss the novel properties of LiOsO3, and suggest that the highly anisotropic screening and the local dipole-dipole interactions are the two most important keys to forming LiOsO3-type metallic ferroelectricity in section 5. Using density-functional calculations, we systematically study the origin of the metallic ferroelectricity in LiOsO3. We confirm that the ferroelectric transition in this compound is order-disorder-like. By doing electron screening analysis, we unambiguously demonstrate that the long-range ferroelectric order in LiOsO3 results from the incomplete screening of the dipole-dipole interaction along the nearest-neighboring Li-Li chain direction.
Electron spin resonance study on charge ordering and spin ordering in nanocrystalline Bi0.2Ca0.8MnO3
Authors: Wang Qiang  ,   Shaanxi Xueqian Normal University, Department of Computer and Electronic Information, Xi'an 710061, China
Published: December 2020

Bi-based manganites Bi0.2Ca0.8MnO3 samples with different paiticle sizes were prepared by the sol-gel technique. The effect of paiticle size on the charge ordering (CO) and spin correlations of Bi0.2Ca0.8MnO3 was investigated by electron spin resonance (ESR). The variation in ESR intensity with temperature shows that the long-range CO transition is suppressed by the size reduction, and completely disappears as the paiticle size is reduced to 40 nm. In the paramagnetic (PM) region, the ESR intensity is fitted by the Arrhnius formula. The result shows that the activation energy is significantly enhanced with decreasing of paiticle size, especially in the 40 nm sample, indicating the enhancement of ferromagnetic (FM) correlations. However, the temperature dependence of ESR line width displays a typical CO characteristics for all samples. Thus, it is suggested that there is the short-range CO state in the 40 nm sample, while the long-range CO transition is completely suppressed. It is found that the onset temperatures of CO states are almost the same in all samples, indicating that the strength of CO correlations is not influenced by size reduction in this compound. A positive Curie-Weiss (CW) temperature is obtained from the line width in high-temperature PM regime, which confirms the existence of FM correlations in this system. Moreover, the value of CW temperature shows a significant decrease with particle size reduction, which indicates that the FM interactions can be weakened by size reduction in this system. Based on the research of ESR intensity and line width, it is concluded that the suppressed CO cannot be attributed to the enhancement of double-exchange FM interactions in Bi0.2Ca0.8MnO3 nanoparticles. To explain these behaviors, a core-shell model based on surface effect is proposed. In nanosized CO manganites, the disordered surface spins destroy the collinear antiferromagneitc (AFM) configuration, and favor FM surface layer coupled with the inner AFM core. With the reduction of paiticle size, the weakening of long-range AFM CO is more significant than that of short-range FM ordering due to the increase of surface spin disorders. With the reduction of paiticle size, the FM ordering will gradually dominate in the competition between FM ordering and AFM ordering, which results in the disappearance of CO transition peak in the ESR intensity curve.
Recent progress in controllability of complex network
Authors: Hou Lü-Lin  , Lao Song-Yang  , Xiao Yan-Dong  , Bai Liang  ,   Science and Technology on Information Systems Enginering Laboratory, National University of Defense Technology, Changsha 410073, China;,   School of Mathematics and Statistics, The University of Western Australia, Crawley, WA 6009, Australia
Published: December 2020

The model, structure and dynamics of complex systems and networks are studied to control complex systems, which reflects the ability to understanding complex systems. Recently, the research on controllability of complex networks by using control theory and complexity science has attracted much attention. It has been investigated extensively by many scientists from various fields, and many meaningful achievements have been obtained in the past few years. In this paper, the process of controllability of complex networks is discussed, the framework of structural controllability based on maximum matching is introduced in detail, and the relevant research status since 2011 is summarized. Controllabilities of complex networks are introduced in the following aspects: different types of controllabilities, relationship between controllability and network statistical characteristics, classification and measures based on controllability, robustness of controllability, and optimization methods of controllability. Finally, the questions urgent to solve in controllability are discussed, so as to give a help to the the study in this respect.#br#There are five sections in this paper, which involve with different aspects of controllability. In the introduction section, the research work of controllability since 2011 is briefly mentioned, and the difference between controllability and previous pinning controllability is clarified. In the second section, the concept of controllability and different types of controllabilities are discussed in detail, including structural controllability, exact controllability, controllability with edge dynamics and controllability with nodal dynamics. In the third section, the relationship between controllability and network structure is investigated, especially the effects of common statistical characteristics and low-degree nodes on controllability. In the fourth section, the measures based on controllability are introduced, which includes control profiles, control range, control centrality, control capacity and control modality. In the fifth section, the research work about control robustness is discussed from robustness measures to optimization methods. In the fifth section, the optimization methods of controllability are introduced, which are classified into two different strategies: topology and edge direction.
Study of plant fluorescence properties based on laser-induced chlorophyll fluorescence lifetime imaging technology
Authors: Wan Wen-Bo  , Hua Deng-Xin  , Le Jing  , Yan Zhe  , Zhou Chun-Yan  ,   School of Mechanical and Precision Instrument Engineering, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

Plant fluorescence is a susceptible signal in plant fluorescence remote sensing detection. In order to solve this problem, a technique for plant chlorophyll fluorescence lifetime imaging is presented to evaluate living status for plant growth and environmental monitoring. A concave lens is used to expand laser beam at a wavelength of 355 nm, and the living plant is exposed in this laser light source to excite chlorophyll fluorescence. And the chlorophyll fluorescence signals are detected by an intensification charge coupled device. Time resolved measurement method is used in this article, so that every time the same fluorescence signals can be excited by the same laser pulse. Meanwhile, the delay time needed for triggering intensification charge coupled device should be changed consecutively, and the whole discrete fluorescence signal can be obtained. The discrete fluorescence signals from the particular location points of the plant are fitted. An improved method of forward iterative deconvolution is used to retrieve the corresponding fluorescence lifetime, and the high-precision fluorescence lifetime can be obtained. Furthermore, the fluorescence lifetime values at all the location points are retrieved to obtain the distribution map of chlorophyll fluorescence lifetime. This method can give the chlorophyll fluorescence image efficiently. The distribution map of fluorescence lifetime can more effectively reflect the plant chlorophyll concentration than the fluorescence intensity image does. The physical property of chlorophyll fluorescence lifetime from living plants has been studied preliminarily, indicating that the plant physiological status is related to its fluorescence lifetime to a certain extent; and the chlorophyll fluorescence lifetime and plant environment have a subtle and complex correlation. In the future, the relationship between chlorophyll fluorescence lifetime and plant environment will be expected to study with the cooperation of biophysicist.
Simulation and experimental investigation of tooth tissue in photothermal radiometry dynamic response induced by modluated laser
Authors: Liu Jun-Yan  , Wang Fei  , Wang Xiao-Chun  , Ma Ying  , Wang Yang  ,   State Key Laboratory of Robotics and System (HIT), Harbin Institute of Technology, Harbin 150001, China;,   School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China;,   Department of Stomatology, Fourth Affiliated Hospital of Harbin Medical University, Harbin 150001, China
Published: December 2020

The photon-density wave is generated in tooth tissue due to the scattering induced by modulated laser beams, and furthermore, thermal-wave will form because of photothermal effect. A one-dimensional thermal-wave model for three-layer tooth tissue using modulated laser stimulation is developed based on 1D diffusion approximation of the radiative transfer theory in combination with 1D heat conduction equation. Effects of photothermal properties (i.e. light absorption coefficient, scattering coefficient and thermal diffusivity coefficient), enamel depth and caries depth on the photothermal radiometry (PTR) dynamic responses are investigated based on the 1D thermal wave model coupling with photon-density wave. The PTR amplitude and phase delay (the phase difference between the PTR signal and reference signal) are strongly dependent on the photothermal parameters of the dental enamel caries layers (DECLs). PTR amplitude and phase delay increase with increasing DECL absorption coefficient, scattering coefficient and thermal diffusivity. Additionally, PTR amplitude may also increase due to the larger thickness of caries layer, and the PTR phase peak value is generated at low frequencies. The inhomogeneous photothermal properties of dental enamel healthy layer (DEHL) also have obviously influenced PTR amplitude and phase. Increasing DEHL scattering coefficient leads to the increase of PTR amplitude, but has no apparent effect on the PTR phase. While the PTR phase delay increases with increasing DEHL absorption coefficient. The delay of PTR amplitude and phase is enlarged at the high value of DEHL thermal diffusivity. However, the DEHL layer thickness has no apparent effect on the PTR amplitude and phase.The PTR signal of tooth tissue induced by the 808 nm diode laser is monitored using an infrared detector (HgCdTe, spectral width 2.012.0 m), and the PTR amplitude and phase response are obtained using lock-in amplifier (SR830). Through frequency-scanning experiments of dental tissue, PTR dynamic responses can be measured and employed to characterize the inhomogeneity and caries of the tooth tissue. The photothermal parameters and caries characteristic of the tooth issue can be simultaneously obtained by multi-parameters statistic best-fit.Simulation and experimental results show that the PTR dynamic response has the advantages of high sensitivity and high contrast for inhomogeneity and caries of the tooth tissue.
Influence of spatial geometrical curvature on nonlocal electron heat transport in expanding plasmas
Authors: Zheng Wei-Zhen  , Zhao Bin  , Hu Guang-Yue  , Zheng Jian  ,   Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China;,   Department of Mathematics and Physics, Nanjing Institute of Technology, Nanjing 211167, China
Published: December 2020

The electron thermal transport in fluid theory would be inaccurate when the collisionality is not enough, and the Fokker-Planck (FP) simulations are usually employed to resolve the inadequacies. In this paper, the one-dimensional Fokker-Planck code is extended to handle the cylindrical and spherical geometries in which the electron distribution functions are solved in the reference frame of the ion fluid. The FP code is validated in the fluid limit by comparing with fluid (MULTI) simulations. Then, the expansions of plasmas in different spatial geometries are simulated with the FP and fluid codes. As the main characters of nonlocal transport, the electron thermal transport inhibition and preheating are investigated in expanding plasmas. The spherical nonlocal theory can give the thermal transport inhibition and preheating phenomenon, which is exploited to fit the heat flux with variation of fitting parameter . The spherical nonlocal theory will reproduce Spizer-Hrm expression as = 0. Then we analyze the heat flux after the plasma expanding 200 ps with a uniform initial temperature T = 100 eV and density ne= 1 1021 /cm3. By comparing the heat flux computed by spherical nonlocal thermal transport theory and FP simulation, it is found that (n-1)/r term in Eq. (3a) cannot be neglected when the radius is small and the geometrical curvature effect will decrease the nonlocality of transport in outer expanding plasmas. The geometrical curvature effect leads to a smaller thermal transport inhibition and preheating in the expanding plasmas as comparing the spherical case with the planar one. The expansions of plasmas in different spatial geometries are also simulated with the FP and fluid codes under the initial conditions which are similar to the inertial confinement fusion. The same influence of geometrical curvature on nonlocal electron thermal transport are also obtained.
Effect of existence form of La3+ on the properties of the Bayan Obo Mine tailing glass ceramics
Authors: Chen Hua  , Li Bao-Wei  , Zhao Ming  , Zhang Xue-Feng  , Jia Xiao-Lin  , Du Yong-Sheng  ,   Key Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Inner Mongolia University of Science &Technology, Baotou 014010, China;,   School of Materials Science & Engineering, Inner Mongolia University of Technology, Hohhot 010051, China;,   School of Mathematics, Physics and Biological Engineering, Inner Mongolia University of Science &Technology, Baotou 014010, China;,   School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450001, China
Published: December 2020

Clarifying the effect of rare earth (RE) elements on the microstructure and properties of glass ceramics is technically and theoretically important for the further development. Thus the glass ceramics of the CaO-Al2O3-MgO-SiO2 with 04 wt% La2O3 are fabricated from Bayan Obo Mine tailing and fly ash by means of the conventional melting method. Effect of the existence form and the concentration variation of La3+ ions on the crystallization behavior, microstructure and properties, such as bending strength, chemical resistance and density of the glass ceramics, are investigated by DTA, XRD, SEM, TEM and EDS. Results show that both the glass transition and crystallization peak temperature of the samples shift to high temperatures with increasing La2O3 content. Augite [Ca(Mg, Al, Fe)(Si, Al)2O6] is the only crystalline phase in all the five samples. Augite crystals in the form of column are distributed uniformly within the residual glass, and their average size is below 100 nm. The crystallinity of augite has been effectively enhanced by the addition of 1 wt% of La2O3. Owing to the similar ion radius of La3+ and Ca2+, Ca2+ ions within augite have been partially substituted by La3+. Such a substitution can serve as one of the key factors to the enhancement of bending strength of the investigated material with 1 wt% of La2O3 because of the stronger bonding energy of La-O than Ca-O. With further increase of La2O3 from 1 to 4 wt%, the Ca3La6 (SiO4)6 secondary phase forms on the boundary between augite grains and residual glass phase in the form of irregular-shaped particles and this in turn hinders the growth of augite crystals. The crystallinity of augite will be decreased gradually since then. Meanwhile, the formation of this La-riched phase (Ca3La6(SiO4)6) may also prevent augite grains from growing through consuming Ca2+ and Si4+ ions which are two key constituent elements of augite grains. Therefore, there are two forms of La3+ ions in the glass ceramics developed from Bayan Obo Mine tailing: one is the substitution of Ca2+ ion by La3+ in augite crystalline phase, and the other is the forming of secondary crystalline phase La-riched Ca3La6 (SiO4)6. The glass ceramic sample with 1 wt% of La2O3 shows the optimum properties. Its density is 3.18 g/cm3, the bending strength is 198 MPa, and the weight loss in 20 wt% NaOH of this sample is lower than 1 wt%.
Transmission mode of a single layer graphene and its performance in the detection of the vibration spectrum of gas molecular
Authors: Yang Jing-Jing  , Li Jun-Jie  , Deng Wei  , Cheng Cheng  , Huang Ming  ,   Wireless Innovation Lab of Yunnan University, School of Information Science and Engineering, Kunming 650091, china;,   School of Chemical Science and Technology, Kunming 650091, China;,   Radio Monitoring Center of Yunnan Province, Kunming 650228, China
Published: December 2020

Since its successful preparation in 2004, graphene has attracted a great deal of attention, and the sensing application is an important research field. But nearly all the researches about graphene sensors focus on low frequency band, of which the mechanism is mainly dependent on the detection of charge carrier concentration and conductivity variation induced by the absorption of molecules. However, due to the fact that most of the molecules absorbed on the surface of graphene will induce the change of conductivity, this method is incapable of distinguishing different molecules. Transmission mode of a single molecular layer is studied based on Kubo formula and combined with a numerical method. The relation between transmission properties and effective mode index is analyzed, and the broadband localization capability of the waveguide mode is demonstrated. Meanwhile, the variation of the transmission intensity which is due to the interaction between the first order waveguide mode and the gas is adopted to retrieve the vibration spectrum of molecules. Taking the sensing of SO2, CO and C7H8 as examples, the effectiveness of this method is verified based on eigenmode analysis. Results show that the transmission spectrum is consistent with the variation spectrum of gas molecules; besides, in the transmission direction, the larger the interaction range, the greater the attenuation of mode transmission intensity will be. This study has provided a theoretical foundation for the realization of the detection and identification of gas moleculan fingerprints.
Photoconductive UV detector based on high-resistance ZnO thin film
Authors: Qi Xiao-Meng  , Peng Wen-Bo  , Zhao Xiao-Long  , He Yong-Ning  ,   The School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

As a wide bandgap semiconductor material, ZnO has huge potential in applications such as light emitting devices and sensors. Compared with GaN and SiC, ZnO has a bandgap of 3.37 eV and exciton binding energy of 60 meV at room temperature, indicating it is a promising candidate of UV detector. ZnO based metal-semiconductor-metal photoconductive ultraviolet detector has the advantages of high optical gain and strong responsivity. However, due to the photoconductive relaxation and surface effect of the ZnO material, a ZnO-based photoconductive UV detector has a slow response which is defective for practical application. The intrinsic defects typically generated during the synthesis of ZnO, e.g. oxygen vacancy, should be responsible for the slow response. Therefore, we have fabricated the high-resistive ZnO thin film based UV detector and studied its UV response characteristic. High resistance ZnO thin film is fabricated on glass by RF magnetron sputtering and followed by lift-off photolithography to form Al interdigital electrodes. SEM and XRD images show that the as-fabricated ZnO thin film grows with preferential orientation along c-axis. A linear I-V curve under UV illumination indicates the ohmic contact between Al and ZnO. From these results, we can calculate the resistivities to be 3.71×109 Ω · cm and 7.20×106 Ω · cm respectively when in the dark and under 365 nm UV light of 303 μW/cm2. The light-to-dark current ratio is up to 516 with bias of 40 V. Besides, the ZnO thin film detector shows a stable, rapid, repeatible and reproducible response with a rise time of 199 ms and a fall time of 217 ms when exposed to periodically switched UV light illumination at a bias voltage of 40 V. Moreover, the detector has a high selectivity for 365 nm UV light and the responsivity is 0.15 mA/W with the intensity of 303 μW/cm2. Furthermore, the transient response process is analyzed using the theory of surface recombination and bulk recombination of ZnO semiconductor. For a high resistance ZnO thin film based UV detector, the surface recombination process is weakened ascribed to the decrease of intrinsic defects and the bulk recombination process plays a leading role, resulting in the fast response. Results show that high resistivity ZnO thin film based UV detectors have outstanding UV photoresponse characteristics for potential applications in UV/radiation detection.
Effect of the intrinsic in-plane shape anisotropy on the oscillation characteristics of zero-field spin torque oscillator
Authors: Guo Yuan-Yuan  , Hao Jian-Long  , Xue Hai-Bin  , Liu Zhe-Jie  ,   Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China;,   Department of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China;,   Department of electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
Published: December 2020

The spin-torque oscillator, which can generate an AC voltage oscillation with the same frequency, have attracted considerable attention due to its potential applications in the frequency-tunable transmitters and receivers for wireless communication and the recording heads of high-density hard disk drives. However, from the energy-balance equation's point of view, in the absence of in-plane shape anisotropy of spin torque oscillator, the energy supplied by the spin torque is always larger than the energy dissipation due to the Gilbert damping, thus, a finite magnetic field applied perpendicular to the plane is required for a steady-state precession. This feature has limited its potential applications. In this paper, the influence of the intrinsic in-plane shape anisotropy on the magnetization dynamics of spin torque oscillator consisting of an in-plane polarizer and an out-of-plane free layer is studied numerically in terms of the Landau-Lifshitz-Gilbert-Slonczewski equation. It is demonstrated that the additional in-plane shape anisotropy plays a significant role in the energy balance between the energy accumulation due to the spin torque and the energy dissipation due to Gilbert damping, which can stabilize a steady-state precession. Therefore, a stable self-oscillation in the absence of the applied magnetic field can be excited by introducing additional in-plane shape anisotropy. In particular, a relatively large current region with zero-field self-oscillation, in which the corresponding microwave frequency is increased while the threshold current still maintains an almost constant value, can be obtained by introducing a relatively large intrinsic in-plane shape anisotropy. Our results suggest that a tunable spin transfer oscillator without an applied magnetic field can be realized by adjusting the intrinsic in-plane shape anisotropy, and it may be a promising configuration in the future wireless communications.