bluuebunny/crossref_metadata_2025 huggingface dataset:
Ab initio calculation of C—I bond dissociation of two alkyl iodide molecules
Authors: Li Rui  , Yan Bing  , Zhao Shu-Tao  , Guo Qing-Qun  , Lian Ke-Yan  , Tian Chuan-Jin  , Pan Shou-Fu  ,   吉林大学原子与分子物理研究所，长春  130012
Published: December 2020

Employing the multiconfiguration self-consistent field method and the multiconfiguration quasi-degenerate perturbation method, the adiabatic potential energy curves and vertical excitation energies of alkyl iodides CF3I and C2H2F3I are calculated for the low-lying states， respectively. It is found that the low-lying excited states of the two molecules are repulsive, and the calculated dissociation energies for their ground states are 2.473eV and 2.835eV, respectively, in which the former one agrees well with the experimental results.
Density functional theory study of the structures and properties of (Li3N)n(n=1—5) clusters
Authors: Chen Yu-Hong  , Kang Long  , Zhang Cai-Rong  , Luo Yong-Chun  , Pu Zhong-Sheng  ,   (1)兰州理工大学,甘肃省有色金属新材料省部共建国家重点实验室，兰州  730050; (2)兰州理工大学,甘肃省有色金属新材料省部共建国家重点实验室，兰州  730050；兰州理工大学物理系,兰州  730050; (3)兰州理工大学物理系,兰州  730050
Published: December 2020

Possible geometrical structures and relative stabilities of (Li3N)n(n=1—5) clusters are studied by using the hybrid density functional theory(B3LYP) with 6-31G* basis sets. For the most stable isomers of (Li3N)n(n=1—5) clusters, the electronic structure, vibrational properties, bonds properties, ionization potentials are analyzed. The calculated results showed the following tendencies: the coordination number of N are usually 4 or 5; the bond lengths for the most of the optimized (Li3N)n(n=1—5) clusters are about 0.210—0.259nm for Li—Li and 0.185—0.204nm for the bridging Li—N bonds, while the terminal Li—N bonds span 0.172—0.178nm. The outcome of population analysis suggests that the natural charge of N atoms are about -2.01e and that of Li atoms are about +0.67e; the dynamic stabilities of Li3N and (Li3N)5 clusters are higher than that of other clusters.
A general heat conduction law based on the concept of motion of thermal mass
Authors: Guo Zeng-Yuan  , Cao Bing-Yang  ,   清华大学工程力学系，北京  100084
Published: December 2020

Based on the mass-energy relation in Einstein's relativity theory, thermal energy has equivalent mass, which is referred to as thermal mass. The concepts of phonon gas mass in solids and thermon gas mass in gases are then introduced. Based on these concepts, the momentum conservation equation, including driving force, resistance and inertial force, for the thermal mass motion is established using Newtonian mechanics. Since the heat conduction is just the motion of the thermal mass (phonon gas or thermon gas) in a medium, the momentum conservation equation for thermal mass is a general heat conduction law which can unify the description of heat conduction under various conditions. The momentum conservation equation reduces to Fourier's heat conduction law when the heat flux is not very high so that the inertial force of the thermal mass can be ignored. For micro-/nano_scale heat conduction, the heat flux may be very high and the inertial force due to the spatial velocity variation can not be ignored. Therefore, the heat conduction deviates from Fourier's law, i.e. non-Fourier phenomenon takes place even under steady state conditions. In such cases, the thermal conductivity can not be calculated by the ratio of the heat flux to the temperature gradient. Under ultra fast heat conduction conditions, the inertial force of the thermal mass must be taken into consideration and the momentum conservation equation for the thermal mass motion leads to a damped wave equation. Compared with the CV model, the general heat conduction law includes the inertial force due to the spatial velocity variation. Thus the physically impossible phenomenon of negative temperatures induced by the thermal wave superposition described by CV model, is elliminated, which demonstrates that the present general law of heat conduction based on thermal mass motion is more reasonable.
Measurement and analysis of plasma antenna input impedance
Authors: Liang Zhi-Wei  , Sun Hai-Long  , Wang Zhi-Jiang  , Xu Jie  , Xu Yue-Min  ,   中国科学院空间科学与应用研究中心，北京  100080
Published: December 2020

The frequency dependence of plasma-column antenna input impedance has been measured by a vector network analyzer with different applied exciting power. The experimental results show obvious resonance behavior of the impedance. The effect of plasma parameters on the input impedance was established by means of an equivalent circuit model and the characteristics of input current. This method is useful for the research of plasma antenna dynamic reconfiguration and the realization of fast impedance matching.
Analysis of the thermal stress in infrared films
Authors: Chen Wei-Lan  , Gu Pei-Fu  , Wang Ying  , Zhang Yue-Guang  , Liu Xu  ,   浙江大学现代光学仪器国家重点实验室，杭州  310027
Published: December 2020

Films deposited at high temperature are subjected to thermal stresses in cooling down, duc to the mismatch of thermal expansion between substrate and film materials, which tends to peel off the film from the substrate. The purpose of the present work is to search the effect of thickness, Young's modulus and thermal expansion of the films on the delamination of the films. The results are helpful in reducing the possibility of the peeling of the films.
The effects of the uniaxial pressure on electronic structures of the (6, 6) single-walled carbon nanotube crystal
Authors: Xie Yan  , Luo Ying  , Liu Shao-Jun  ,   北京师范大学物理系，北京  100875
Published: December 2020

In this paper, we performed the first-principles calculations of the effects of the uniaxial pressure on electronic structures of the (6, 6) single-walled carbon nanotube crystal (SWNTC). The applied pressure is perpendicular to the axis of carbon nanotubes. The calculated results show that the (6, 6) SWNTC with tetragonal structure (t phase) is metallic, and its electrons can move along the walls of carbon nanotubes. With the increasing of the uniaxial pressure, the (6, 6) SWNTC undergoes the structural phase transitions, and transforms from the t phase to the unbonded phase, and then to the bonded phase. The uniaxial pressure mainly affects the π and π* bands of the band structure of the (6, 6) SWNTC, and these effects on the bands are not only in kxky plane but also in the direction of kz. The electronic properties of the crystal can alter from metal to semiconductor, then to metal again as the uniaxial pressure increases. The distributions of electronic charge densities show that electrons of the unbonded phase are localized near the carbon nanotubes. And electrons of the bonded phase can move not only along the walls of carbon nanotubes, but also between the two nearest nanotubes through the chemical bonds.
Study of sound speed in near-critical carbon dioxide
Authors: Luo Ben-Yi  , Lu Yi-Gang  ,   华南理工大学物理科学与技术学院，广州  510640
Published: December 2020

Based on the condensing vapor model, the expression of sound speed close to critical point is deduced,which shows the relationship between the sound speed and the density fluctuating index and thermal capacity at constant volume. Close to critical point, the sound speed of liquid carbon dioxide is inversely proportional to the density fluctuation index. The bigger the density fluctuation index, the smaller the sound speed. The sound speed is maximal at minimal density fluctuation index, where small fluctuations of density induces large fluctuations of sound speed. When the pressure increases and approaches to critical point, the rapid increase of thermal capacity induces decrease of sound speed. When the pressure increases and departs from critical point, the rapid decrease of thermal capacity at constant volume induces increase of sound speed. The calculated values of sound speed from the expression are in good agreement with the reference values from NIST.
Many-body interactions between ions in LiH crystal and its equation of state under high pressure
Authors: Jiang Li-Hua  , Liu Fu-Sheng  , Tian Chun-Ling  ,   (1)西南大学物理系，重庆  400715; (2)西南交通大学高压物理实验室，成都  610031
Published: December 2020

When the cohesive energy of LiH is calculated, the many-body correlation effect between ions and the contraction of ionic orbital are included, as two separate physical mechanisms in the total energy formula. The exchange-energy between electronic orbitals is directly computed without any adjustable parameters introduced. The results showed that many-body exchange-correlation effects markedly influence the properties at zero pressure and under high pressures. When the contributions of the nearest and next-nearest ions were taken into account, the results of the isothermal equation of state is in good agreement with experimental data in the pressure range of 0—90 GPa.
First-principles study of the effects of Sr segregated on Al grain boundary
Authors: Liu Li-Hua  , Zhang Ying  , Lü Guang-Hong  , Deng Sheng-Hua  , Wang Tian-Min  ,   北京航空航天大学理学院物理系，北京  100083
Published: December 2020

The atomic and electronic structures of an Al grain boundary with segregated Sr (substitutional) impurity atoms have been calculated by the first-principles pseudopotential method based on the local density functional theory. The results show that the boundary expands and the charge density decreases significantly over the whole boundary due to Sr segregation. This suggests grain boundary weakening, which should be responsible for the experimentally observed Sr-induced Al intergranular embrittlement.
Mechanical alloying synthesis of (Bi1-xAgx)2(Te1-ySey)3 powder and thermoelectric properties of its bulk materials prepared by spark plasma sintering
Authors: Zhang Xin  , Li Jia  , Lu Qing-Mei  , Zhang Jiu-Xing  , Liu Yan-Qin  ,   北京工业大学材料学院,新型功能材料教育部重点实验室,北京  100022
Published: December 2020

The powders of n-type (Bi1-xAgx)2(Te1-ySey)3 thermoelectric materials were synthesized by mechanical alloying and consolidated by spark plasma sintering. The milled powders were investigated by XRD and SEM, which shows that the pure Bi, Te, Ag and Se particles were alloyed after milling for 2h. With the increase of the time of mechanical alloying, the size of the powder grains decreases to about 1—0.5 μm. The effects of the doped elements on the thermoelectric properties have been studied. It was found that Ag can improve the power factor and decrease the lattice thermal conductivity, the compound (Bi0.99Ag0.01)2(Te0.96Se0.04)3 after milling for 10h possesses the highest value of the power factor and minimum thermal conductivity, which results in the highest value of ZT of 0.52 at 323K.
Study on the photovoltaic conversion of ZnO/Si heterojunction
Authors: Zhang Wei-Ying  , Wu Xiao-Peng  , Sun Li-Jie  , Lin Bi-Xia  , Fu Zhu-Xi  ,   中国科学技术大学物理系，合肥   230026
Published: December 2020

ZnO:Al films have been prepared on p-type Si substrates by DC reactive sputtering. Hall measurement showed that the ZnO:Al films exhibited apparent n type conductivity. I-V characteristics in darkness and under illumination have been performed. It was found that the illumination reverse current increased rapidly with the applied voltage and was saturated at -1 V, which was obviously different from that in darkness. This phenomenon resulted from the photovoltaic effect of heterojunction. Furthermore, in order to investigate the mechanism of photovoltaic conversion, photoconductivity and photovoltage response spectra have been studied. It was found that the photocurrent decreased sharply when the wavelength was 380 nm, and the direction of photovoltage response also changed at this point. It was presumed that this phenomenon has a close relationship with the energy band structure of the heterojunction.
Investigation on the quantum coherent transport in magnetic tunnel junctions
Authors: Yang Jun  , Wu Wen-Yuan  , Gong Yan-Chun  ,   解放军理工大学理学院，南京  211101
Published: December 2020

Using the method of scattering matrix, we investigated the quantum coherent transport in ferromagnet/insulating barrier/semiconductor/insulating barrier/ferromagnet (FM/I/SM/I/FM) magnetic double tunnel junctions. When the mean free path of the tunneling electrons(lp) is comparable to the thickness of the middle semiconductor(L), the tunneling magneto-resistance(TMR) shows quantum oscillations with the variation of the L. At the inflection point of the oscillations the cut-off vector will appear if lp is much longer than L. The analysis reveals that it is the mismatch of the electron momentum in ferromagnet and semiconductor layer that leads to the appearance of the cut-off vector. The decay of oscillation amplitude caused by phase loss restrains the occurrence of the cut-off vector. We arrive at the conclusion that the value of TMR is the square of the value of spin injection efficiency(SIE) η1 in a single junction; and the value of TMR is also the square of the value of SIE η2 in double junctions(parallel configuration)if L is much longer than lp. For this reason, the value of SIE in a single junction or double junctions can be obtained by measuring the value of TMR of double junctions. Numerical calculations indicate that the ratio TMR/η22 will also show quantum oscillations with the variation of the L if the L　is comparable to the lp.
The study of parallel pump microwave magnetic field instability threshold in metallic ferromagnetic strip under in-plane confinement
Authors: Xu Yan  , Hu Jing-Guo  ,   扬州大学物理科学与技术学院,扬州  225002
Published: December 2020

Using the Landau-Lifshitz equation, the propagating of spin wave in metallic magnetic stripe has been investigated, in which the effective boundary condition is applied for the dynamic magnetization of the metallic magnetic strip. The relationship between spin wave spectrum and width of the strip has analytically been derived. Numerical calculations show that in-plane confinement results in the obvious kinks in the threshold curves. And with the increase of strip width, the kink numbers almost rise exponentially, while the threshold jump at the first kink is nearly in inverse proportion to its width.
Study of synthesis and magnetic properties of Mn-doped ZnO diluted magnetic semiconductors
Authors: Yu Zhou  , Li Xiang  , Long Xue  , Cheng Xing-Wang  , Wang Jing-Yun  , Liu Ying  , Cao Mao-Sheng  , Wang Fu-Chi  ,   (1)北京理工大学材料科学与工程学院，北京  100081; (2)纳米器件物理与化学教育部重点实验室，北京大学电子科学与工程系，北京  100871
Published: December 2020

Co-precipitation method was employed to synthesize Mn doped ZnO dilution semiconductors Zn1-xMnxO with the nominal composition of x=0.001, 0.005, 0.007 and 0.01. The annealing temperature (Ts＝400,600,700 and 800℃)dependent structure as well as the magnetic property of the produced samples were studied. The results indicated that samples sintered in air under the temperatures of 600℃ has single wurtzite ZnO structure with prominent ferromagnetism at room temperature; while in samples with the Mn nominal content of 0.007 and 0.01 sintered in air at 800℃, a second phase, namely the ZnMnO3 was observed. The sample with x=0.007 shows largest magnetization and coercivity. Increasing the annealing temperature to 800℃ results in decreasing of both magnetization and coercively，and the paramagnetism was enhanced. Combining with the analysis of the PL spectrum, it is reasonably concluded that the ferromagnetism observed in the studied samples originates from the doping of Mn in the lattice of ZnO crystallites.
Magnetoelectric response of GMM/elastic plate/PZT laminated composite in the longitudinal vibration
Authors: Yang Wei-Wei  , Wen Yu-Mei  , Li Ping  , Bian Lei-Xiang  ,   重庆大学光电工程学院，教育部光电技术及系统重点实验室，重庆  400030
Published: December 2020

Strain in a laminated structure is transferred by the interlayer adhesive layer. However, the analysis of the adhesive layer behaviors was rarely carried out. The Hamilton's principle is used to derive the governing motion equation of the GMM/elastic plate/PZT three-layered structure. The effects of the adhesive layer resulting from the shear and longitudinal deformation are considered in the analysis. From the motion equation of the GMM/elastic plate/PZT structure and the structural boundary conditions, the equation predicting the system natural frequencies is derived. Then, using the constitutive equations of magnetostrictive and piezoelectric effects, the magneto-electric response over frequency of underlying structure is obtained. By comparing the theoretical magneto-electric response over frequency with the experimental results，it can be seen that the frequency deviation is below 9.42%，and the values of the theoretical magneto-electric voltage coefficient are in agreement with the experiment ones. The dependence of the resonance frequency of the structure on the length of the elastic plate is also discussed.
Study on the property of subwavelength imaging in a metal thin-film structure
Authors: Li Ming-Yu  , Gu Pei-Fu  , Zhang Jin-Long  , Zheng Zhen-Rong  , Liu Xu  ,   浙江大学现代光学仪器国家重点实验室，杭州  310027
Published: December 2020

The property of the near field subwavelength imaging in a metal thin-film structure is investigated using finite difference time domain method based on Drude model. Using the transfer matrix method，the transmission of this structure for the evanescent wave component is given，which illustrates the influence on the subwavelength imaging quality. In practice a Cr grating mask with 1μm period is imaged onto a photosensitive material through a silver thin film structure by utilizing the optical near-field lithography techniques.
Effect of p-GaN layer thickness on the performance of p-i-n structure GaN ultraviolet photodetectors
Authors: Zhou Mei  , Zhao De-Gang  ,   (1)中国科学院半导体研究所集成光电子学国家重点实验室，北京  100083; (2)中国农业大学理学院应用物理系，北京  100083
Published: December 2020

We investigated the influence of thickness of p-GaN layer on the performance of p-i-n structure GaN ultraviolet photodetector. Through the simulation calculation，it was found that both the quantum efficiency and dark current of device decrease when employing thicker p-GaN layer，while both the quantum efficiency and dark current increase with decreasing thickness of p-GaN layer. It is suggested that the Schottky contact junction between the metal and p-GaN may be responsible for the incompatible effect. We has to make a suitable choice of the thickness of p-GaN in the device design according to the application requirement.
Preparation and luminescence characteristics of Ca2SiO4:Dy3+ phosphor
Authors: Wang Zhi-Jun  , Li Pan-Lai  , Wang Gang  , Yang Zhi-Ping  , Guo Qing-Lin  ,   (1)河北大学国际交流与教育学院，保定  071002; (2)河北大学物理科学与技术学院，保定  071002
Published: December 2020

The Ca2SiO4:Dy3+ phosphor was synthesized by high temperature solid-state method. The emission spectrum of Ca2SiO4:Dy3+ shows bands at 486nm，575nm and 665nm under the 365nm excitation. The excitation spectrum for 575nm emission has excitation bands at 331nm，361nm，371nm，397nm，435nm，461nm and 478nm. The effect of Dy3+ concentration on the emission spectrum and luminescent intensity of Ca2SiO4:Dy3+ was investigated.The result shows that the ratio (Y/B)of yellow emission (575nm)to blue emission (486nm)increases with increasing Dy3+ concentration，and the reason was explained by Judd-Offelt theory. The luminescent intensity firstly increases with the increasing Dy3+ concentration，then decreases，and the concentration self-quenching mechanisms are the d-d interaction according to the Dexter theory. The effect of Li+，Na+ and K+ on the emission spectra of Ca2SiO4:Dy3+ phosphor was studied. The results show that the emission spectrum intensity of Ca2SiO4:Dy3+ phosphor is greatly influenced by Li+，Na+ and K+，and the evolvement trend is the same for different charge compensations，i.e.，the emission spectrum intensity firstly increases with increasing charge compensation concentration，then decreases. However, the charge compensation concentration corresponding to the maximum emission intensity is different for different charge compensations，and the concentrations are 4，4 and 3 mol% for the Li+，Na+ and K+，respectively.
Strong electron emission of antiferroelectric ceramic
Authors: Sheng Zhao-Xuan  , Feng Yu-Jun  , Huang Xuan  , Xu Zhuo  , Sun Xin-Li  ,   (1)第二炮兵工程学院103教研室，西安  710025; (2)西安交通大学电子材料研究所，西安  710049; (3)西安交通大学电子材料研究所，西安  710049；第二炮兵工程学院103教研室，西安  710025
Published: December 2020

The electron emission of a novel antiferroelectric cathode material La-doped Pb(Zr，Sn，Ti)O3(PLZST)has been studied. For driving voltage of 800V and accelerating voltage of 0V，the emission current density was 1.27A/cm2. For driving voltage of 800V and accelerating voltage of 4kV，a strong emission current density with 1700A/cm2 was obtained. The dependence of emission current on accelerating voltage was analyzed and the mechanism of antiferroelectric electron emission was discussed. It was found that strong electron emission from antiferroelectric material can be realized under lower driving voltage and the emission current was much larger than that predicted by the Child-Langmuir law. Local antiferroelectric-ferroelectric phase transition in the vicinity of the triple junction leads to initial electron emission，and these initial electrons then cause desorption of gas which had been absorbed at the ceramic surface.The desorbed gas is then ionized，which leads to plasma generation. The formation of surface plasma enhances the emission current.
Effect and mechanism of water on carbon nanotubes growth
Authors: Zhang Chun-Mei  , Bian Xin-Chao  , Chen Qiang  , Fu Ya-Bo  , Zhang Yue-Fei  ,   北京印刷学院等离子体物理与材料研究室，北京  102600
Published: December 2020

Carbon nanotubes (CNTs) were grown on 25 nm Ni coated Si substrate by dielectric barrier discharge (DBD)-type plasma enhanced chemical vapor deposition (PECVD) in downstream. The temperature was 973 K and the mixture gases were methane, hydrogen and water. The contribution of water concentration on the growth of carbon nanotubes was investigated. Scanning electron microscopy (SEM) results showed that the grown CNTs in CH4/H2 gas mixure had chain-shaped structure and the diameter was about 40—90nm. With the addition of proper amount of water, the diameter of CNTs became uniform, and the surfaces of nanotubes were fully covered with nano-sized node-like structures. When more water was added, branched carbon nanotubes were synthesized. Optical emission spectra of the plasma during synthesis of carbon nanotubes were in-situ detected for the purpose of understanding the water effect.
PIC-MCC simulations on characteristics of RBWO filled with different gases
Authors: Li Xiao-Ze  , Wang Jian-Guo  , Tong Chang-Jiang  , Zhang Hai  ,   西北核技术研究所，西安市69信箱5室，西安  710024
Published: December 2020

This paper discusses the basic theory of PIC-MCC method and its implementation in the software UNIPIC. Simulation of relativistic backward-wave oscillator (RBWO)filled with different kinds of neutral gas of different pressures is made by using UNIPIC. The effects of plasma on the propagation of electron beam and wave-beam interaction are discussed. The dependence of the output power，frequency，and the start-oscillation time of the RBWO on the kinds and pressures of the filled gases are presented. The simulation results show that the improvement of RBWO is mainly attributed to the produced ions，and that the low-energy electrons remaining in the tube is the key factor of oscillation-failure and pulse-shortening.
The detection and attribution of the abrupt change of precipitation in China based on the power-law exponent
Authors: Zhi Rong  , Gong Zhi-Qiang  ,   兰州大学大气科学学院，兰州  730000；国家气候中心，中国气象局气候研究开放实验室，北京  100081
Published: December 2020

Based on the daily precipitation observations of 740 stations in China from 1960 to 2000，the abrupt change point of power-law exponents of daily precipitationof 0—7mm in north China，northeast China and northwest China is located exactly on 1979. This indicates that the large-scale climate background of these regions has changed at that time，and it has close relation with the index MEI.This maybe one of the main reasons for the drying trend of north China.The 0—29mm daily precipitation is to some extent a stationary process，and the daily precipitation being≥30mm is obviously non-stationary，which makes the long-term prediction of heavy rainfall very difficult.
Approximate solution for a class of solitons of the Landau-Ginzburg-Higgs perturbed equation
Authors: Mo Jia-Qi  , Chen Li-Hua  ,   (1)安徽师范大学数学系,芜湖  241000; (2)福建师范大学福清分校数学与计算机科学系,福清  350300
Published: December 2020

The corresponding solution for a class of Landau-Ginzburg-Higgs equation is considered using the analytic method. From the generalized variational iteration theory, the solution of corresponding equation is obtained. And then the approximate soliton solution of the solution for the equation is obtained.
Coherent population trapping in a specific model
Authors: Bi Dong-Yan  ,   西北大学物理系，西安  710069
Published: December 2020

Coherent population trapping is shown to occur in a driven symmetric double-well potential. In the model of the ammonia molecule, for a molecule initially prepared in its lower doublet, under certain circumstances, the upper level remains unpopulated, this occurs in spite of the fact that the laser field is resonant with the |2〉→|3〉 trasition. This is a coherent population trapping phenomenon which cannot be accounted for with the convential models.
Stochastic resonance of frequency modulated signals in a linear model of single-mode laser
Authors: Zhang Liang-Ying  , Jin Guo-Xiang  , Cao Li  ,   (1)华中科技大学激光技术国家重点实验室,武汉  430074; (2)武汉工程大学计算机科学与工程学院，武汉  430073; (3)襄樊学院物理与电子信息技术系，襄樊  441053
Published: December 2020

By adding frequency modulated signal to the equation of the laser intensity of the gain-noise model of the single-mode lasers, we use the linear approximation method to calculate the power spectrum and signal-to-noise ratio (SNR) of the laser intensity, which is driven by two white noises correlated in the form of δ function. The result shows that the SNR shows typical stochastic resonance with the change of intensities of the pump noise and quantum noise. As the amplitude of a modulated signal has an effect on the SNR， it shows suppression, monotonic increase, resonance, suppression and resonance and so on， with the varing of the frequencies of the carrier signal and modulated signal.
Research on effects of current spreading and optimized contact scheme for high-power GaN-based light-emitting diodes
Authors: Shen Guang-Di  , Zhang Jian-Ming  , Zou De-Shu  , Xu Chen  , Gu Xiao-Ling  ,   北京工业大学北京市光电子技术实验室,北京  100022
Published: December 2020

GaN-based light-emitting diodes (LEDs) grown on sapphire substrate have current transport along the lateral direction due to the insulating nature of the substrate, and the anode and cathode contacts are in a side-by-side configuration. The resistance of the n-type material of the GaN and the lower confinement layer is not negligible, which causes the current to crowd near the edge of the n-contact pad. The current crowding problems will become more severe for large area and high power devices. In this paper, the current spreading effect is qualitatively analyzed. The applied current density and the effective length of the lateral current transport are found to have a considerable effect on the uniform current spreading. Based on these findings, an optimized contact scheme of high-power GaN-based LEDs is proposed to alleviate current crowding effect and reduce the series resistance of the devices. It is clearly shown that the high-power GaN-based flip-chip LEDs with optimized ring-shape interdigitated contact scheme have a relatively uniform temperature distribution by measuring the surface temperature distribution of the device with infrared thermal imaging system. It is confirmed that the current distributes more uniformly over the contact, and current densities in a localized region of the device are reduced, which can decrease the joule heat generated and improve the reliability of the GaN-based LED.
Adaptive slide mode control for a class of chaotic systems with perturbations
Authors: Li Xiu-Chun  , Xu Wei  , Xiao Yu-Zhu  ,   西北工业大学应用数学系，西安  710072
Published: December 2020

Based on the adaptive slide mode control method, we investigated the robust synchronization for a class of chaotic systems with random perturbations. This approach can be applied to may chaotic systems; and the upper bound of random perturbations is not necessarily known in advance and it is estimated through an adaptive control process. Finally, two-scroll chaotic system, Lorenz system and hyperchaotic Rssler system are taken as examples to illustrate the effectiveness of the proposed method.
Modelling of chaotic systems using wavelet kernel partial least squares regression method
Authors: Li Jun  , Dong Hai-Ying  ,   兰州交通大学自动化与电气工程学院,兰州  730070
Published: December 2020

Based on the powerful nonlinear mapping ability of kernel learning, and in combination with the partial least square (PLS) algorithm for linear regression, a wavelet kernel partial least square (WKPLS) regression method is proposed. By the method, the input-output data are firstly mapped to a nonlinear higher dimensional feature space, a linear PLS regression model is then constructed by the classic kernel transformation trick used in support vector machines. The PLS approach utilizes the covariance between input and output variables to extract latent features, and the wavelet kernel which is an admissible support vector kernel function is characterized by its local analysis and approximate orthogonality. Hence, the proposed WKPLS method combining PLS approach with wavelet kernel function shows excellent learning performance for modeling nonlinear dynamic systems. The WKPLS is then applied to modelling of several chaotic dynamical systems and compared with the kernel partial least squares(KPLS) method using Gaussian kernel function. Simulation results confirm that the WKPLS identifier is fast and can accurately approximate unknown chaotic dynamical system, and its approximation accuracy is higher than the KPLS under the same conditions.
Stability and Hopf bifurcation of the simplified Lang-Kobayashi equation
Authors: Wang Zuo-Lei  ,   江苏大学理学院，镇江  212013
Published: December 2020

Stability and Hopf bifurcation of the simplified Lang-Kobayashi equation is considered. The critical time delay associated with Hopf bifurcation of the zero equilibrium is determined by applying the bifurcation theorem. A formula for determining the direction of the Hopf bifurcation and the stability of bifurcating periodic solutions is given by using the normal form method and center manifold theorem. Finally, numerical simulations are performed to verify the analytical prediction.
Optimizing the synchronizability of generalized deactivation networks
Authors: Dai Cun-Li  , Liu Shu-E  , Tian Liang  , Shi Da-Ning  ,   (1)南京航空航天大学理学院,南京  210016; (2)南京农业大学工学院,南京  210031；南京航空航天大学理学院,南京  210016
Published: December 2020

We research the synchronizability of the generalized deactivation networks without changing its degree distribution. The synchronizability measured by the eigenratio R can be effectively optimized by adjusting the only parameter, the number of active nodes M. The eigenratio R is shown very sensitive to the M, and larger M will lead to better synchronizability. Furthermore, we find that, in a wide interval, the eigenratio R obeys a approximate power-law in the form of R～M-2.0. By introducing a perturbation, the synchronizability of network can be effectively optimized.
A network model with exponential cut-off degree distribution and local-cluster property
Authors: Yuan Shao-Qian  , Zhao Hai  , Li Chao  , Zhang Xin  ,   东北大学信息科学与工程学院,沈阳  110004
Published: December 2020

According to the character of local evolving mechanism in real network, we propose a new local-clustered network evolving model (LC model). Theoretical analysis and numerical simulations show that the LC model obeys a power-law degree distribution with an exponential cut-off, and its cluster coefficient is much bigger than the local-world model (LW model) proposed by Li and Chen and is more, close to real network. We simulate the performance of LC model against random errors and malice attacks, and discover that LC model is more fragile under attacks because of its large cluster coefficient.
Accurately calculate cross section of the n+n→2π0 reaction in the n-n renormalization chain diagram
Authors: Pan Yu  , Wang Kai-Jun  , Fang Zhen-Yun  , Wang Xian-You  , Peng Qing-Jun  ,   重庆大学理论物理研究所,重庆  400044
Published: December 2020

Adopting Lorentz-invariant coupling model of neutron n-antineutron n and neutral meson strong interaction, we made physical analysis and accurate calculation of the n-n renormalization chain diagram propagator, and obtained the theoretical results. Furthermore, in applying it to the physical process analysis and cross-section evaluation in the reaction n+n→2π0, its differential cross-section is obtained. Through the comparison between this calculation and those scenarios, namely the n-n tree diagram and renormalization chain diagram propagator contribution, some important information about radiative correction was obtained. This study would offer certain academic references to the further research on Lorentz-invariant coupling model and the nuclear physics about cross section problem of particles in nucleon antinucleon and neutral meson strong interaction in terms of theoretical calculations. In addition, it will also provide something valuable on relevant physical processes, and on the renormalization calculation orderly with different approaches in perturbation theory of quantum field theory.
Theoretical investigation of β- decays in neutron-rich nitrogen isotope
Authors: Zhang Yu-Mei  , Xu Fu-Rong  ,   (1)北京大学物理学院，核物理与核技术国家重点实验室,北京  100871; (2)北京大学物理学院，核物理与核技术国家重点实验室,北京  100871；兰州重离子加速器国家实验室原子核理论中心,兰州  730000
Published: December 2020

We have studied the low-lying level schemes of 18,19,20,21O and the β--decay branching ratios of nitrogen isotope. The shell-model calculations have been carried out in the psd shell space. The results are compared with the recent experimental data with reasonable agreement. Our calculations also predict the β--decay property of 21N and the structure of 21O.
The design of quadrapole-Ioffe configuration trap for quantum degenerate Fermi-Bose mixtures
Authors: Wang Peng-Jun  , Chen Hai-Xia  , Xiong De-Zhi  , Yu Xu-Dong  , Gao Feng  , Zhang Jing  ,   山西大学光电研究所，量子光学与光量子器件国家重点实验室，太原  030006
Published: December 2020

The quadrapole-Ioffe configuration (QUIC) trap consists of two identical quadrupole coils and one Ioffe coil, which has been applied widely to trap neutral atoms for evaporation cooling. We have designed two different structures of the QUIC trap. By the numerical calculation and experimental test, we obtained the optimized structure. In the QUIC trap, the magnetically trapped rubidium-87 atoms are cooled evaporatively to below the phase transition of Bose-Einstein condensation, at the same time, the potassium-40 atoms are cooled sympathetically to the Fermi degeneracy.
Density functional theory study of the structure and electronic properties of MgnOn(n=2—8) clusters
Authors: Ge Gui-Xian  , Luo You-Hua  ,   (1)华东理工大学物理系，上海  200237; (2)石河子大学师范学院物理系，石河子  832003
Published: December 2020

Geometric structures of MgnOn(n=2—8) clusters are optimized by using the generalized gradient approximation density functional theory. Energy, vibrational frequency and electronic properties have been calculated. The geometries of the global minima of MgnOn(n=2, 3) are ring-like. The three-dimensional structures of MgnOn(n≥4) may be built from Mg2O2 and Mg3O3 rings. The stability of clusters gained from obtuse O—Mg—O angles and much charge transfer. The transferred charge increases between Mg and O atoms with cluster size increasing, showing a tendency towards bulk charges. Mg3O3 and Mg6O6 clusters are shown to be more stable than neighboring ones by the investigations on vertical ionization potential, electron affinities and the energy gaps between the highest occupied and lowest unoccupied molecular orbitals.
Investigation on the electromagnetic characteristics of lossy metamaterial covered dielectric cylinder
Authors: Wang Hai-Long  , Wu Qun  , Meng Fan-Yi  , Li Le-Wei  , Wu Jian  ,   (1)电波环境特性及模化技术国家重点实验室，北京  102206; (2)哈尔滨工业大学电子与信息技术研究院，哈尔滨  150001; (3)哈尔滨工业大学电子与信息技术研究院，哈尔滨  150001；新加坡国立大学电气与计算机工程系，新加坡
Published: December 2020

The electromagnetic characteristics of the model with an electric line source radiating in the direction parallel to a lossy metamaterial covered infinitely long dielectric circular cylinder have been investigated. Firstly, the electromagnetic model is presented and the exact solution is derived. Secondly, this exact solution is employed in numerical calculations. The patterns of the near field under different electromagnetic parameters are obtained. The characteristics of the far field properties are also studied through the directivity and the normalized radiation resistance. Due to the effect of the negative refraction and the loss of the lossy metamaterial, in comparing the lossless metamaterial layer and the lossy conventional material layer, very different electromagnetic characteristics on the near and the far field of the lossy metamaterial covered dielectric cylinder are revealed.
Diffraction property of multi-layer dielectric gratings studied by rigorous coupled-wave analysis
Authors: Kong Wei-Jin  , Yun Mao-Jin  , Sun Xin  , Liu Jun-Hai  , Fan Zheng-Xiu  , Shao Jian-Da  ,   (1)青岛大学物理科学学院，青岛  266071; (2)中国科学院上海光学精密机械研究所，上海  201800
Published: December 2020

The rigorous coupled-wave analysis technique for describing the diffraction of multi-layer diffraction grating (MDG) is put forward. Formulations for a stable and efficient numerical implementation of diffraction efficiency are presented for MDG for TE polarization and Littrow angle. With the merit function of the -1 order diffraction efficiency higher than 96%, the parameters of MDG are optimized for HfO2 and SiO2 top layers, respectively. Numerical calculation indicates that a larger grating parameter range can be obtained with HfO2 rather than the SiO2 on the top. The manufacture tolerance and the effective incident angle for the optimized structure of MDG are discussed in the end.
A difference method to solve the laser kinetic model involving temporal-special evolution
Authors: Chen Gang  , Zhuang De-Wen  , Zhang Hang  , Xu Jun  , Cheng Cheng  ,   浙江工业大学应用物理系,杭州  310023
Published: December 2020

Based on the rate equation theory and numerical difference method, a kinetic model was developed to describe the temporal-special distribution of the particles and photon densities in a laser tube. This method improves the normal rate equation and can be used to study the laser evolution and the energy distribution.
Study on the influence of quantum state for phonon bath on the quantum behavior of mesoscopic circuit
Authors: Hu Ju-Ju  , Cai Shi-Hua  , Wang Jian-Qiu  , Ji Ying-Hua  ,   江西师范大学物理系，南昌  330022
Published: December 2020

Taking into account the interaction between electrons and phonons, we study the dynamical behavior of a mesoscopic dissipative circuit for two classes of pure initial states (grand canonical ensemble and number state) of phonon bath modes. In the long time limit t→∞: when the environment is initially at thermal equilibrium, the average values of current and charge in the circuit system will only depend on the average values of the circuit in initial quantum state, and they are not related with the environment; when the environment is initially in number state, the time evolution of the average values of current and charge are just the same as that in thermal equilibrium, which indicates that the average values of current and charge are related to certain set of occupied numbers. The quantum fluctuations of current and charge in the circuit not only depend on the initial state of the system but also depend on the quantum state and temperature of the environment. Generally, the entanglement between the circuit system and environment will lead to the reduction of the purity of the quantum state. The mesoscopic circuit will remain in a pure quantum state only when the environment is at very low temperature and at thermal equilibrium.
Experimental and theoretical study on designing of cooling device for the kilowatt-level double cladding fiber laser
Authors: Zhu Hong-Tao  , Lou Qi-Hong  , Zhou Jun  , Qi Yun-Feng  , Dong Jing-Xing  , Wei Yun-Rong  ,   (1)中国科学院上海光学精密机械研究所，上海  201800; (2)中国科学院上海光学精密机械研究所，上海  201800；中国人民解放军工程兵指挥学院，徐州  221004
Published: December 2020

Though the double cladding fiber (DCF) laser’s ability of heat dissipation is better than the traditional solid-state laser’s, the heat generation in double-cladding fiber laser is the bottleneck in the development of high power lasers. The distribution of heat deposition in the practical 400 W DCF laser is quantitatively analyzed for the first time. Based on the heat dissipation model developed in this work, in order to ensure the safe and stable operation of the kilowatt-level DCF laser, the convective coefficient near the pumping ends should be greater than 2.8×10-2W·cm-2K-1. The cooling device for high power DCF laser’s pumping ends was designed and successfully used in a laser system, and the output power of 1kW was obtained.
All optical wavelength conversion and optimum longitudinal mode selection using an injection-locked Fabry-Perot laser diode
Authors: An Yi  , Wang Yun-Cai  , Zhang Ming-Jiang  , Niu Sheng-Xiao  , Wang An-Bang  ,   太原理工大学物理系，太原  030024
Published: December 2020

Based on the cross-gain modulation effect in Fabry-Perot laser diode (FP-LD), the 2.7GHz optical pulsed signal at 1552.30nm is converted to a continuous-wave light at 1548.22nm in experiment. The variation of wavelength conversion efficiency with injection optical power and wavelength are examined in detail. Our research results indicate that there always exists a fixed longitudinal mode for a given FP-LD under certain working conditions to maximize the extinction ratio of conversion signal and conversion efficiency when the longitudinal mode is locked by the probe light. Our theoretical analysis accords with the experiment results. Moreover, there always exist an optimum signal power and a detuning range between the probe light and the longitudinal mode to improve the conversion signal further under the same longitudinal mode locked by the probe light. The optimum longitudinal mode can be determined by the FP-LD characteristics and its working conditions.
Optical beams in nonlocal nonlinear media: A variational solution of the Laguerre-Gauss form
Authors: Dai Ji-Hui  , Guo Qi  ,   华南师范大学光子信息技术实验室，广州  510631
Published: December 2020

The 1+2D nonlocal nonlinear Schrdinger equation can be transformed to the variational approach in a cylindrical coordinate system, and is applied to a model describing the propagation of optical beam in strongly nonlocal nonlinear media. By solving variational problems with expanding media response functions and assuming reasonable ansatz, the solution of the Laguerre-Gauss form is obtained. The Laguerre-Gaussian beams will form solitons or be reduced to Gaussian beams under certain conditions.
Growth and spectral properties of Tm:Y2SiO5 single crystal
Authors: Wang Xiao-Dan  , Xu Xiao-Dong  , Zhao Zhi-Wei  , Xu Wen-Wei  , Wu Feng  , Xu Jun  ,   (1)中国科学院上海光学精密机械研究所，上海  201800; (2)中国科学院上海光学精密机械研究所，上海  201800；苏州科技学院应用物理系，苏州  215009
Published: December 2020

High-quality Tm:Y2SiO5 (Tm:YSO) single crystal was grown by the Czochralski method. The lattice parameter and separation coefficient of the crystal were measured. The three polarization axis: 〈010〉, D1 and D2 of this monoclinic single crystal were determined by Laue method. Absorption spectra, fluorescence spectra and fluorescent lifetime of this single crystal were measured along the three polarization axes. Its absorption line width and absorption cross section were also calculated. A stronger absorption peak at 790nm and a fluorescence peak with enhanced emission at 2μm were observed along the D1 polarization axis compared with other two axes. Besides, this crystal exhibits bigger absorption cross section and longer fluorescence lifetime along D1 polarization axis. Therefore, Tm:YSO single crystal is suitable for AlGaAs diode-pumped laser and it possesses great potentiality in the application of 2μm solid-state laser.
The study on the rectifying properties of oxygen non-stoichiometric La0.9Ba0.1MnO3-δ/SrTiO3:Nb p-n heterojunction
Authors: Wang Chong  , Liu Zhao-Lin  , Liu Jun-Ming  , Chen Xue-Mei  , Cui Hao-Yang  , Xia Chang-Sheng  , Yang Yu  , Lu Wei  ,   (1)昆明物理研究所基础研发中心，昆明  650034; (2)南京大学固体微结构国家重点实验室，南京  210093; (3)云南大学工程技术研究院光电薄膜研究中心，昆明   650091; (4)中国科学院上海技术物理研究所红外物理国家重点实验室，上海  200083
Published: December 2020

The La0.9Ba0.1MnO3-δ/SrTiO3:Nb p-n heterojunctions have been fabricated by growing the oxygen nonstoichiometric La0.9Ba0.1MnO3-δ thin film on the Nb doped SrTiO3 substrate with pulsed laser deposition. The good rectifying curves have been demonstrated in the temperature range of 20—300K. The diffusion voltage VD exhibits a maximum near the transition temperature of La0.9Ba0.1MnO3-δ thin film, which is different to the observation in the oxygen stoichiometric La0.9Ba0.1MnO3/SrTiO3:Nb p-n heterojunction. The interesting phenomenon has been well explained with the resistance-temperature experiment of La0.9Ba0.1MnO3-δ thin film and energy band calculations.
Study on the suppression of the stimulated Brillouin scattering in high-power single-frequency multicore fiber amplifier
Authors: Wang Chun-Can  , Zhang Fan  , Tong Zhi  , Ning Ti-Gang  , Jian Shui-Sheng  ,   北京交通大学光波技术研究所,全光网络与现代通信网教育部重点实验室，北京  100044
Published: December 2020

The set of differential equations for an multicore fiber amplifier with pump, signal and the first-order Stokes, taking into account effects of thermal gradient caused by heat generation, is presented. The thermal conduction equations are solved by finite element method. The influence of pump schemes, pump power, convective coefficient, initial power of Stokes, density of the rare earth dopant and fiber length on suppression of the stimulated Brillouin scattering is studied. The results show that the backward pump scheme has advantage over the forward pump scheme in suppression of stimulated Brillouin scattering. Increasing density of the rare earth dopant can lead to higher slope efficiency and shorter optimal fiber length, which can further suppress stimulated Brillouin scattering. The stimulated Brillouin scattering gain and maximum operating temperature are compared between single core fiber amplifier and 19-core fiber amplifier with the same optimal fiber length. Compared with the single core fiber amplifier, the 19-core fiber amplifier has lower maximum operating temperature, which provides more space for further increase in output power.
A mode-locked Yb3+-doped double-clad large-mode-area fiber laser
Authors: Song You-Jian  , Hu Ming-Lie  , Liu Qing-Wen  , Li Jin-Yan  , Chen Wei  , Chai Lu  , Wang Qing-Yue  ,   (1)华中科技大学光电子科学与工程学院，武汉  430073; (2)华中科技大学光电子科学与工程学院，武汉  430073；武汉烽火通信科技股份有限公司，武汉  430074; (3)天津大学精密仪器与光电子工程学院，光电信息技术科学教育部重点实验室，天津  300072
Published: December 2020

A compact and highly stable high pulse energy passively mode-locked fiber laser is presented. A segment of Yb3+-doped double-clad large-mode-area fiber with extremely low nonlinearity is developed as the active medium. The self-starting mode-locked operation is achieved by the cooperation of nonlinear polarization evolution and semiconductor saturable-absorber mirror. The fiber laser generates laser pulses with the average power of 160mW at the repetition rate of 55.9MHz (corresponding to pulse energy of 3nJ), and the pulse duration is 10.6ps.