bluuebunny/crossref_metadata_2025 huggingface dataset:
Micromagnetics simulation on the microwave permeability of magnetic porous nano-flakes
Authors: Tu Kuan  , Han Man-Gui  ,   National Engineering Research Center of Electromagnetic Radiation Control Materials, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

Many modern electronic devices are operated on a frequency above 1 GHz. Frequencies of electromagnetic noises coming from these devices are usually larger than 10 GHz. High-frequency magnetic losses in the natural resonance mechanism can be used to dissipate the energy of electromagnetic noises. Ferromagnetic nanostructural materials (nano flakes or nanowires) in strong shape anisotropy fields are one of the promising anti electromagnetic interference (EMI) materials due to their large high-frequency magnetic losses. Application of EMI requires that the electromagnetic wave absorbing materials should be lightweight and have a wide absorbing bandwidth. However, most electromagnetic wave absorbing materials reported do not have these features. To meet these demands, the microwave magnetic properties of porous -Fe nano flakes (length width thickness: 300 nm 100 nm 10 nm) have been simulated based on micromagnetics theory. Compared to the nano flakes without nano pores, simulation results reveal that the demagnetization fields will be altered if a nano flake contains several pores. Effect of nano pores (diameter =15 nm) in different arrangements (rows columns: 210; 25; 22; 45) on the high-frequency magnetic properties is investigated in this paper. It is found that nano flakes can alter the configurations of magnetic domains. More domains in small sizes in an inhomogeneous localized magnetic anisotropic field have been achieved. Consequently, more high-frequency magnetic loss peaks can be found. Overlapping of magnetic loss peaks implies that it potentially enables to widen the bandwidth of electromagnetic absorption within 1030 GHz. Furthermore, simulations reveal that the quantity, magnitude and resonance frequencies of the loss peaks are strongly dependent on the quantity and the arrangement of nano pores. Besides, the existence of multi magnetic loss peaks has been studied for ellipsoid objects from the perspective of inhomogeneously localized effective magnetic fields. Results reveal that the frequently observed wide magnetic loss peaks in experimental data may be due to the inhomogeneously localized effective magnetic fields of an absorber containing a plentiful of randomly oriented particles. Clearly, compared to the nano flakes without pores, the nano flakes with pores can significantly reduce the volume density. Therefore, our simulation results show that porous nano flakes can be a good lightweight electromagnetic wave absorber candidate with wide absorbing bandwidths.
Study on charge storage characteristics of PP film electret charged by interface polarization method
Authors: Chen Gang-Jin  , Rao Cheng-Ping  , Xiao Hui-Ming  , Huang Hua  , Zhao Yan-Hai  ,   Laboratory of Electret and Its Application, Hangzhou Dianzi University, Hangzhou 310018, China
Published: December 2020

Electret attracts increasing attention nowadays because of its lasting and stable electrostatic field. To achieve the widespread use of electret material, higher density and better stability of the electret charge storage as well as well-distributed electrostatic field must be ensured at the same time. Based on the mechanism of interface polarization on double-layer media, a novel charging technology for electret is reported in this paper; and PP film is successfully charged through an auxiliary layer to form electret by this proposed method. Effect of charging temperature and charging voltage on the charge storage performance of the as-prepared PP film electret is investigated by means of surface potential measurement. Also its charge storage performance at high temperatures is explored by thermally stimulated discharge technique. Furthermore, its electrostatic field distribution in the directions of X and Y is measured. Results show that the interface polarization charging is more excellent than the corona charging. At a certain temperature, the surface potential of PP film electret increases with increasing charging voltage and both are in a good linear relationship. This is in good agreement with the theoretical analysis in terms of the equation of electret charge accumulation during the charging process. It is shown that in the case of constant charging voltage within the range of 0.53.0 kV, the effect of charging temperature is not obvious when the temperature is below 75 ℃; however, when the temperature is higher than 75 ℃, the surface potential of PP film electret increases with increasing temperature. In addition, its surface potential may change a little with time so it has an excellent charge storage stability. The distribution of its surface potential shows that it exhibits an homogeneous electrostatic field due to interface polarization charging.
Study on the absorbing properties of critically coupled resonator with graphene
Authors: Xu Jie  , Zhou Li  , Huang Zhi-Xiang  , Wu Xian-Liang  ,   Key Laboratory of Intelligent Computing and Signal Processing, Anhui University, Hefei 230039, China;,   School of Electronic and Information Engineering, Hefei Normal University, Hefei 230061, China
Published: December 2020

A critically coupled resonator (CCR) is a thin-film structure that can absorb nearly all of the incident electromagnetic radiation, leading to null scattering. In order to effectively achieve and control the critical coupling (CC) phenomena, we replace the polymer absorbing layer by a graphene-based multi-film structure. FDFD (finite difference frequency domain) method is used to solve the Maxwell equation, and the graphene's surface conductivity is calculated by using the Kubo formula. Our results demonstrate that the CC phenomenon is realized at the near-infrared frequency and the frequency of absorption peak can be engineered by the Fermi energy of the graphene sheets. With increasing Fermi energy the absorption peak moves to the longer wavelength side. The effective permittivity of a multi-film structure has a strong dependence on the thickness of the dielectric and the layer number of the grapheme sheets in the multi-film structure. It is found that the central frequency of the absorption peak shifts towards longer wavelength side with increasing layer number of the graphene sheets M and the thickness of dielectric d1. Moreover, we also demonstrate that the absorption efficiency is affected by the electron-phonon relaxation time and the incident angle. It is clear that the central frequency of the absorption peak has a slight shift and the absorption is changed with the relaxing time and incident angle. The results offer the theoretical basis to the design of graphene-based critical coupling devices and optical detectors.
Analytic models for solid state plasma of Si/Ge/Si heterogeneous and lateral SPiN diode
Authors: Kang Hai-Yan  , Hu Hui-Yong  , Wang Bin  , Xuan Rong-Xi  , Song Jian-Jun  , Zhao Chen-Dong  , Xu Xiao-Cang  ,   Key Laboratory of Ministry of Education for Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, China
Published: December 2020

Silicon-based reconfigurable antenna, which is fabricated by heterogeneous and lateral surface PiN (SPiN), is an effective technology to achieve antenna miniaturization and enhance radar and wireless communication system performance. In this paper, the heterogeneous and lateral Si/Ge/Si SPiN diode is presented, that can weaken the band gap narrowing of the P + and N + region to improve the injection ratio of PN junction. And the electrical properties of the solid state plasma within the intrinsic region are also studied. Based on the bipolar diffusion model and Fletcher boundary condition, the analytic models of the junction voltage, the current density and the solid state plasma concentration distribution are established for a large injection current, and the numerical simulation has been carried out. Results show that the junction voltage increases linearly with the increase of applied voltage and the solid state plasma concentration at the boundary; and the current density increases exponentially with increasing junction voltage and the applied voltage, respectively. And the applied voltage and the current density of heterogeneous SPiN diode is lower than that of homogeneous SPiN diode under the same condition due to the difference of barrier heights between the heterojunction and homojunction. In addition, results also show that the value of the concentration decreases with increasing length of the intrinsic region; otherwise, it increases with increasing applied voltage and the doping concentration in the P+ and N+ regions. Under the same conditions, the solid state plasma concentration of the heterogeneous SPiN diode is nearly seven times that of homogeneous diode, which is in excellent agreement with the data published, giving the evidence for the validity of our method. The proposed models provide an effective reference for the design and application of silicon-based reconfigurable antennas.
Physical mechanism of uniaxial strain in nano-scale metal oxide semiconductor transistor caused by sin film
Authors: Yang Min-Yu  , Song Jian-Jun  , Zhang Jing  , Tang Zhao-Huan  , Zhang He-Ming  , Hu Hui-Yong  ,   Key Lab of Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, China;,   National key Laboratory of Analog Integrated Circuitry, NO.24 Research Institute of CETC, Chongqing 400060, China
Published: December 2020

Performance of a nano-scale MOS (metal-oxide-semiconductor) can be significantly improved by uniaxial stress, caused by the SiN film deposited on the surface of MOS. Although this technique has been widely used in the performance improvement of CMOS and integrated circuit, the physical mechanism for instance, how is the strain in MOS channel caused by the SiN film? how about the relation between the kinds of the structure of SiN film needed to be discussed in depth. On the basis of the ISE TCAD, three typical models for stress analysis——such as the segmentation structure model, the closed-loop structure model and the integrity structure model——are proposed. And then, this paper reveals the physical mechanism about how the stress in MOS channel is caused by the SiN film and how much the magnitude of the stress in MOS channel is induced. Results shows that: 1) The “step” structure is the necessary condition for the strain in the MOS channel to be caused by the SiN film. 2) With the tendency for SiN film to shrink or expand, the film may lead to the deformation along the MOS source/drain region of the Si material, which causes the deformation of Si in the channel. 3) The whole of the channel stress in SiN film is equal to the sum of the stress in the source/drain imposed by the SiN film above the source/drain, the stress which the “closed loop structure” applies to the channel, and the stress generated in the channel by the whole SiN film. Our conclusions may provide the valuable references to the manufacture of nano-scaled MOS and the research of the novel inducing stress technique.
Effects of the surface albedo on short-wave infrared detection of atmospheric CO2
Authors: Chen Jie  , Zhang Chun-Min  , Wang Ding-Yi  , Zhang Xing-Ying  , Wang Shu-Peng  , Li Yan-Fen  , Liu Dong-Dong  , Rong Piao  ,   School of Science, Xi'an Jiaotong University, Xi'an 710049, China;,   Unit 63892 of PLA, Luoyang 471003, China;,   Physics Department, University of New Brunswick, Fredericton E3B5A3, Canada;,   Key Laboratory for Radiometric Calibration and Validation for Environmental Satellites, National Satellite Meteorological Center, Beijing 100081, China
Published: December 2020

The greenhouse gas carbon dioxide, for which short-wave infrared remote sensing detection is carried out by using satellite sensors to measure the Earth's atmosphere scattering solar radiation, and makes use of the inversion algorithm to achieve measurements. Most of the solar radiation enter the satellite sensors after surface reflection, so the surface albedo which reflects the surface features is one of the important parameters which affect the accuracy of the detection. Aiming at the great demands of high precision carbon dioxide for greenhouse gas, this study first investigate the effects of the Earth's surface albedo on the observed spectra. Simulation results show that the increase in the surface albedo will enhance the observed spectral intensity, especially larger in the O2-A band than in the 1.6 μm band. In other words, the surface albedo has a greater impact on O2-A ban. In the actual satellite inversio, the surface types of actual observation pointare uncertain, which will result in the error of surface albedo. Effect of surface albedo on the inverted XCO2 is analyzed when the surface albedo is changed by changing the type of surfac. Two observation cases are analyzed in detail. One is on April 23, 2009 for the desert surface, and another on May 21, 2013 for the grass surfac. Results show that when the O2-A band surface albedo approximates to the real surface albedo valu, the relative error of the inverted XCO2 is the smaller. If the relative changes of the O2-A band surface albedo exceed 0.25 in the grass surfac or 0.35 in the desert surface, the relative error of the inverted XCO2 will be greater than 1%, not satisfying the design requirement of the inversion system. In contrast, the changesin 1.6 μm band surface albedo have negligible effect on the inverted XCO2. This study shows the importance of surface albedo in the process of satellite remote sensin, and provides an important theoretical basis and guidance for improving the accuracy of remote sensing detectio. All these are significantly contributed to the hyperspectral satellite observation of the greenhouse gas, the investigation of global CO2 distributions, and the prediction and monitoring of the climate change.
Comparative studies of Tikhonov regularization and truncated singular value decomposition in the three-dimensional flame temperature field reconstruction
Authors: Xie Zheng-Chao  , Wang Fei  , Yan Jian-Hua  , Cen Ke-Fa  ,   State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Radiative imaging of combustion flame in furnace of power plant plays an increasingly important role in combustion diagnosis. The flame radiation image taken by a charge-coupled device (CCD) camera can reconstruct three-dimensional flame temperature distribution in the furnace. CCD cameras are used for capturing the flame images to obtain the line-of-sight radiation intensities. The temperature reconstruction matrix equation is a seriously pathological equation. Thus the temperature field reconstruction problem is an ill-posed problem. The two algorithms (Tikhonov regularization and truncated singular value decomposition (TSVD)) for solving the temperature field reconstruction are introduced. The size of the numerical simulation system is 10 m × 10 m × 10 m, which is divided into 10 × 10 × 10 volume elements in the three dimensions. Each volume element is a unit cube. Generalized cross-validation (GCV) is used to select the correct regularization parameter. The measured data are simulated by adding different random errors to the exact solution of the direct problem. The reconstructed temperature deviation is calculated by the two algorithms separately. When the measuring errors are 0.05 and 0.10, the reconstruction errors based on Tikhonov are respectively 19.3% and 7.0%, less than those based on TSVD. When the measuring errors are 0, 0.01, 0.03 and 0.07, the differences between the two kinds of errors are all less than 3%. Both the algorithms can reconstruct the correct temperature field. The times required to reconstruct the temperature field by the two algorithms are compared and their effects of the maximum temperature are also compared. When the measuring errors are 0, 0.01, 0.03, 0.05, 0.07 and 0.1, the reconstruction times based on Tikhonov are respectively-0.0917,-0.049, 0.161, 0.002, 0.135 and 0.091 s, shorter than the reconstruction times based on TSVD. There is singular value decomposition (SVD) in TSVD. And this process takes more than 2 s. If the problem is more complicated, SVD takes much more time. The errors of the maximum reconstruction temperature under Tikhonov are smaller. And the position of the maximum reconstruction temperature under Tikhonov is near the position of the exact maximum temperature in space. The maximum reconstruction temperature under TSVD is not so good as that under Tikhonov. Preliminary results indicate that the Tikhonov-based reconstruction is slightly better than the TSVD-based reconstruction, especially in reconstruction error, reconstruction time, and effects of the maximum temperature.
Correspondences between quantum and classical orbits Berry phases and Hannay angles for harmonic oscillator system
Authors: Xin Jun-Li  , Shen Jun-Xia  ,   Department of Physics and Electronic Engineering, Yuncheng College, Yuncheng 044000, China
Published: December 2020

On the basis of quantum-classical correspondence for two-dimensional anisotropic oscillator, we study quantum-classical correspondence for two-dimensional rotation and translation harmonic oscillator system from both quantum-classical orbits and geometric phases. Here, the two one-dimensional oscillators refer to a common harmonic oscillator and a rotation and translation harmonic oscillator. In terms of the generalized gauge transformation, we obtain the stationary Lissajous orbits and Hannay's angle. On the other hand, the eigenfunctions and Berry phases are derived analytically with the help of time-dependent gauge transformation. We may draw the conclusion that the nonadiabatic Berry phase in the original gauge is-n times the classical Hannay's angle, here n is the eigenfunction index. As a matter of fact, the quantum geometric phase and the classical Hannay's angle have the same nature according to Berry. Finally, by using the SU(2) coherent superposition of degenerate two-dimensional eigenfunctions for a fixed energy value, we construct the stationary wave functions and show that the spatial distribution of wave-function probability clouds is in excellent accordance with the classical orbits, indicating the exact quantum-classical correspondence. We also demonstrate the quantum-classical correspondences for the geometric phase-angle and the quantum-classical orbits in a unified form.
Protecting quantum entanglement at finite temperature by the weak measurements
Authors: Wang Mei-Jiao  , Xia Yun-Jie  ,   Shandong Provincial Key Laboratory of Laser Polarization and Information Technology, Colleg of Physics and Engineering, Qufu Normal University, Qufu 273165, China
Published: December 2020

According to the map of a qubit, a scheme for protecting entanglement of two-qubit by the weak measurements at finite temperature is proposed. Since the choices of the channel parameters and initial states are very different for different weak measurement strengths, two local unitary equivalent initial entangled states |ψ> and |φ> are chosen. Weak measurements are performed when two initial entangled states go through the generalized amplitude damping channel, and the analytical expressions of getting maximum concurrence entanglement Cr and weak measurement parameters m and n can be obtained by performing an overall optimization for four weak measurement parameters. What is more, the relationship between the weak measurement parameters and the channel parameters is further explored. Theoretical results show the entanglement protection project based on weak measurements can effectively enhance the entanglement and even prevent the sudden death of entanglement in some cases. When the channel parameter r is fixed, for different values of parameter p, the concurrence is centered at p = 0.5, and the weak measurement parameters of the maximum concurrence entanglement are the same as those for initial state |ψ>, while they are different for initial state |φ>. Under the condition of different values of r, for the fixed p and initial state |ψ> or |φ>, the weak measurement parameters remain constant as the entanglement reaches the maximum and the concurrence decreases with the increase of parameter r. Through the analysis of channel parameters, higher entanglement can be obtained by choosing appropriate channel parameters and initial state.
Propagation and inhibition of online rumor with considering rumor elimination process
Authors: Wan Yi-Ping  , Zhang Dong-Ge  , Ren Qing-Hui  ,   College of Command Information Systems, PLA University of Science and Technology, Nanjing 210007, China
Published: December 2020

As one of the most important aspects of spreading dynamics on networks, propagation of rumor, which includes the process of rumor diffusing and elimination, plays an important role in the understanding of information dissemination within social networks. However, the current understanding of rumor propagation within networks is far from clear, especially the full analysis of the process of rumor diffusing and elimination is lacking. Here, with the rumor elimination process supplemented to the susceptible-infective-refractory (SIR) rumor spreading model, a modified rumor spreading model is established and defined as spreader-ignorant-eliminater-Rstifler-Estifler (SIERsEs) model. The developed mean-field equations of SIERsEs model, with the diffussing and elimination thresholds calculated, could describe the theory of steady-state dynamics of the rumor propagation. Simulation analysis is performed to assess the interaction between the diffussing and elimination process, and estimate the influences of diffusing rate, estimation rate, and averaged degree of the network, on the rumor spreading. The results show whether low or high value of average network degree would accompany a low level of the influence of rumor propagation. In addition, the shortcomings of the traditional immunization strategies, such as targeted immunization and acquaintances immunization, are pointed out. Based on this understanding, we propose two optimized immunization strategies, defined as active immunization and passive immunization, and we further evaluate how different parameters (forgetting rate of spreader, forgetting rate of eliminater and the starting time of immunization) affect the suppression effectiveness of the newly developed active and passive immunization strategies. Importantly, some so-called rumor-inhibition strategies actually could not inhibit but enhance the rumor propagation instead. These obtained findings in the present study could not only elaborate our understandings in spreading dynamics within network, but also provide an insight into the developing effective strategies of inhibiting rumor propagation.
A method of identifying parameters of a time-varying time-delay chaotic system
Authors: Chai Qin-Qin  ,   College of Electrical Engineering and Automation, Fuzhou University, Fuzhou 350108, China
Published: December 2020

Unknown time-varying parameters, including time-delay and system parameters, commonly exist in chaotic systems. These unknown parameters increase the difficulties in controlling the chaotic systems, and make most of the existing control methods fail to be applied. However, if these parameters can be estimated, they will facilitate the controller design. Therefore, in this paper, a parameter identification problem for a general time-delay chaotic system with unknown and time-varying parameters is considered, where these unknown time-delay and parameters are slow time-varying. It is very difficult to solve this problem analytically. Thus, a unified identification method is proposed to solve the identification problem numerically. To solve this identification problem, firstly, the time horizon is divided into several subintervals evenly. Then the time-varying parameters are approximated by piecewise constant functions. The height vectors of the piecewise constant functions are unknown and to be determined. Furthermore, the heights of the piecewise constant functions keep constant between each pair of the successive partition time points but switch values at the partition time points. After the approximation, the original identification problem for finding the nonlinear functions of the unknown parameters is transformed into a problem of selecting approximate parameter vectors, where the heights of the piecewise constan functions are unknown parameter vectors to be determined. Secondly, to solve the problem of selecting approximate parameter vectors quickly, the partial gradients of the objective function with respect to the parameter vectors are derived; and they are then integrated with a gradient-based procedure to obtain the unknown heights. As the number of partitions for the piecewise function increases, the optimal results of the approximate problem will approach to the optimal results of the original parameter identification problem. Hence, the optimal piecewise functions will approach to the real nonlinear functions for the unknown parameters. Finally, parameter identification experiments on time-delayed Mackey-Class and time-delayed logistic chaotic systems are carried out. The effects of the partition number on the estimated results are discussed. Numerical results demonstrate that when some switching times of the unknown parameters do not coincide with any partition time points, small error between the estimated results and the real values are present. However, these errors can be filtered and the estimated results are consistent well with the real values. Hence, the proposed method is reasonable and effective.
A ground-based differential absorption lidar for atmospheric vertical CO2 profiling
Authors: Han Ge  , Gong Wei  , Ma Xin  , Xiang Cheng-Zhi  , Liang Ai-Lin  , Zheng Yu-Xin  ,   International School of Software, Wuhan University, Wuhan 430079, China;,   State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan University, Wuhan 430079, China;,   Collaborative Innovation Center for Geospatial Technology, Wuhan 430079, China
Published: December 2020

A differential absorption lidar (CO2-VDIAL), which is designed for vertical CO2 profile retrieving by using aerosol-scattered signals, is demonstrated in this paper. To our knowledge, it is the first time that a dye laser has been utilized to realize the wavelength modulation for a CO2-DIAL/IPDA system. Such a design scheme greatly reduces both the threshold and the cost to develop a CO2-DIAL. However, two key problems emerge in this system, i.e., wavelength stability and broad bandwidth. By adopting the CO2-VDIAL, a dual-path gas cell, and the Voigt fitting procedure, the accurate wavelength calibration of infrared pulse laser is achieved. Experimental results show that the error of wavelength calibration can be suppressed under 0.1 pm. And a wavelength stability of ～2 pm is then achieved. For tackling the error introduced by using the laser of a broad bandwidth, simulated experiments are carried out to estimate its influence. On that basis, we propose a method to calculate the correction coefficient and demonstrate the process via experiments by using a gas cell. It is demonstrated that the bandwidth of the output infrared laser is around 600-700 MHz. Hence, the broad bandwidth correction is an indispensable step for this CO2-VDIAL. Finally, horizontal, vertical and continuous detections are carried out to verify the precision and the accuracy of our CO2-VDIAL. The slope method is used to retrieve the XCO2 in the above experiments. In the horizontal detections, an R2 of 0.999 is achieved, suggesting that the precision of the system is excellent. By comparison with the in-situ measurements, a difference is found to be lower than 4 ppm. Consequently, it is concluded that the CO2-VDIAL is capable of providing retrievals with the high precision and accuracy. Moreover, the XCO2 decreases with increasing altitude according to the vertical detection experiment in the midnight on June 19m th 2015 at an urban site, demonstrating that the CO2-VDIAL is capable of providing retrievals of ranged-resolved. Finally, temporal characteristic of XCO2 can be also revealed by the CO2-VDIAL in light of continuous detections. The CO2-VDIAL has already been assembled in a container which is due to be transported to Huainai for further verifications in late 2015. Once we finish the performance optimization, the CO2-VDIAL will be installed in Tibet for long period observation.
Influence of the inclined waving wall on the surface wave evolution of liquid film
Authors: Wu Zheng-Ren  , Liu Mei  , Liu Qiu-Sheng  , Song Zhao-Xia  , Wang Si-Si  ,   School of Energy Power and Mechanical Engineering, North China Electric Power University, Baoding 071000, China;,   Department of Economic Management, North China Electric Power University, Baoding 071000, China
Published: December 2020

In this paper, the evolution of the fluid surface wave on an inclined waving wall is investigated. The waving wall is assumed to have a sinusoidal fluctuating surface, and the linear stability of the liquid film flow is analyzed. In addition, the evolutions of the disturbance wave under different tilt angles, and the variations in this wave when passing through different wall shapes are studied. It can be observed that the time evolution of the disturbance wave appears to be a near periodic variation of a larger wavelength. Further, by comparing its flow structure with that for the flat plate wall, it is found that the wave conditions are more complex. When the fluid flows through the waving wall, the disturbance wave no longer displays a regular change in space, and its amplitude increases with the tilt angle of the wall increasing. For the same tilt angle, the amplitude of the disturbance wave in the waving wall is greater than that for the flat plate wall, and the distortions in waveform are more obvious. As Re increases, the amplitude of the disturbance wave increases gradually, and the distortion of the corresponding wave increases as well. Further, with the increase of wall surface amplitude, the amplitudes of the static and disturbance waves increase, whereas the corresponding traveling-wave period remains unchanged. Finally, the influence of the wall tilt angle on flow stability is analyzed.
A method of measuring the incidence angle of intense electron beam
Authors: Hu Yang  , Yang Hai-Liang  , Sun Jian-Feng  , Sun Jiang  , Zhang Peng-Fei  ,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Xi'an 710024, China;,   Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

In recent years, a great many of effect data obtained from the high current pulsed electron beam play an important role in the studying of X-ray thermal-mechanical effects. Energy deposition profile is the criterion to measure the equivalence of thermal-mechanical effects between high-current electron beam and X-rays. To adjust the energy deposition profiles to improve the equivalence of the simulations of X-ray and thermal-mechanical effect, the intense electron beam energy deposition profile measurement should be studied. Two-dimensional distribution measurement which is an important part of the energy deposition profile is to obtain a two-dimension (r, θ) incidence angle distribution. A new method of measuring the incidence angle based on small Faraday cup array covered with aluminum films, called modified multi-layer stacking, is presented in this paper. With the help of the filtered Faraday cups, the transmission fraction of the electron beam confined at a specific position and time is stored. Two-dimension incidence angle distribution on the anode target that changes over the working time is obtained with these transmission fractions by computer calculation. The result indicates that the two-dimension incidence angle distribution has a close relationship with the pinch of the beam. The electrons tend to move vertically to the equipotential line when the diode is under Child-Langmuir flow, then they hit the target in a small angle range (E×B drift, the trajectory of the electrons becomes a slanted helix with pitch changing. The incidence angle then increases to about 60° from small angle.
A first-principle study of the effect of W-doping on physical properties of anatase TiO2
Authors: Hou Qing-Yu  , Zhao Chun-Wang  ,   School of Science, Inner Mongolia University of Technology, Hohhot 010051, China;,   College of Art and Sciences, Shanghai Maritime University, Shanghai 201306, China
Published: December 2020

The experimental studies of the effect of W-doping on conductivity of anatase TiO2 have opposite conclusions when the W-doping concentration is in a range from 0.02083 to 0.04167. To solve the conflict, two supercell models for Ti0.97917W0.02083O2 and Ti0.95833W0.04167O2 are set up for optimizing their geometries and calculating their band structures and the densities of states based on the first-principles plane-wave norm-conserving pseudopotential of the density functional theory. The electron concentration, electron effective mass, electronic mobility, and electronic conductivity are calculated as well. The calculated results show that both electronic conductivity and conductive property of the doped system increase while the electron effective mass decreases, with the increase of W-doping concentration in the presence or absence of electron spin. The conductive property of Ti0.95833W0.04167O2 system is better than that of Ti0.97917W0.02083O2 system, which is further proved by the analyses of ionization energy and Bohr radius. To analyze the stability and formation energy of W-doped anatase TiO2, two more supercell models for Ti0.96875W0.03125O2 and Ti0.9375W0.0625O2 are set up combined with the geometry optimization. The calculated results show that the total energy and the formation energy increase while the stability of the doped system decreases, with the increase of W-doping concentration in a range from 0.02083 to 0.04167 in the presence or absence of electron spin. Meanwhile the W-doping becomes more difficult. A comparison of the doped system with the pure anatase TiO2 shows that the lattice constant along the a-axis of the W-doped anatase TiO2 increases, and its lattice constant along the c-axis and volume increase as well. The calculated results agree with the experimental results. The doped system becomes a half-metal diluted magnetic semiconductor with a room temperature ferromagnetism in the presence of electron spin.
Angle dependent inverse spin Hall effect in NiFe/Pt thin film
Authors: Han Fang-Bin  , Zhang Wen-Xu  , Peng Bin  , Zhang Wan-Li  ,   State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

In NiFe/Pt bilayer, when spin current originating from the magnetization procession of NiFe is inject into the adjacent Pt layer under ferromagnetic resonance (FMR), the direct current (DC) voltage VISHE generated by inverse spin Hall effect (ISHE) will be added to the voltage VSRE generated by spin rectification effect (SRE), therefore the measured voltage in experiment is the sum of VISHE and VSRE. It is crucial to separate these contributions, which has been often overlooked before, in order to make a reasonable comparison of the ISHE among different materials. The voltages having symmetric (Lorentz type) and anti-symmetric (dispersive type) components both vary with the static magnetic field strength. However, they have different static magnetic field angle dependences according to our theoretical analysis. In order to distinguish the contribution of ISHE from that of SRE, in this paper, we employ a method, in which the voltage across the sample is measured when the static magnetic field is applied to different directions, to analyze the voltage by varying magnetic field angle in a range from 0° to 360° in steps of 10°, thereby separating the VISHE. The separation is carried out by fitting the angle dependent symmetric and anti-symmetric curves to different theoretical formulas of ISHE and SRE. The voltages of the two different contributions together with the phase angle of the microwave are obtained. At the same time, the FMR line width and the resonant field can be read out. The results show that the ferromagnetic resonance line width in NiFe(20 nm)/Pt(10 nm) sample is larger than that in NiFe(20 nm) sample due to the injection of spin current from NiFe to Pt in the bi-layer sample. We notice that in the curves of voltage vs. static magnetic field, the Lorentz symmetry components of the voltage from the bi-layer sample weight more than those from the single-layer sample. This is explained as a result of the existence of the ISHE in the bi-layer sample, where the spins are pumped from the magnetic layer to the adjacent nonmagnetic layer. The spin pumping effect does not show up in the single-layer sample. There are a large portion of symmetric components in the double layer sample, which is attributed to the ISHE. Although the voltage caused by the SRE is smaller than that by the ISHE, the SRE voltage cannot be ignored. Our work is crucial to understanding the spin-related effects in ferromagnetic/nonmagnetic metal material and provides an improved analysis method to study the spin pumping and the ISHE.
Thermoelectric transport mechanism of Mg2Si0.4Sn0.6-yBiy prepared by low-temperature microwave reaction
Authors: Zhang Hua  , Chen Shao-Ping  , Long Yang  , Fan Wen-Hao  , Wang Wen-Xian  , Meng Qing-Sen  ,   Key Laboratory of Advanced Magnesium Based Materials of Shanxi Province, Taiyuan 030024, China;,   College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China;,   College of Physics and Optoelectronic Engineering, Taiyuan University of Technology, Taiyuan 030024, China
Published: December 2020

According to Debye relaxation, the polarization of electric dipole can be accomplished in 10-10 s under the action of an alternating electromagnetic filed with a frequency of 2.45 GHz, so it is feasible to obtain nano powder by carrying out solid reaction in microwave at low temperature in a short time. In this work, the syntheses of Mg2Si0.4Sn0.6-yBiy (0 ≤ y ≤ 0.03) solid solution thermoelectric materials are successfully achieved by microwave-assisted solid state reaction at low temperature with MgH2 serving as one reactant instead of Mg, and their transportation mechanisms are studied based on the SPB (single parabolic band) model as well. The results indicate that the volatilization and oxidation of Mg can be suppressed effectively in this process. Fine stoichiometric product can be achieved with nano-lamellar structure with an interlayer spacing of about 100 nm by carrying out the reaction between MgH2 and Si, Sn in microwave at 400℃ in 15 min. The introduction of Bi dopant can increase carrier concentration and lattice distortion. With the cooperation between the nano lamellar structure and lattice distortion, the phone is scattered so effectively that the sample owns a lowest thermal conductivity, κmin of 1.36 W·m-1·K-1 at 550 K based on the fact that the phonon scattering is dominant in the heat transfer process. The calculated results show that the theoretical κmin is 0.93 W·m-1·K-1, which is lower than 1.36 W·m-1·K-1. Therefore, by further adjusting the process parameters and increasing the effective doping rate of Bi and the density of the lattice defects, it is expected to obtain lower thermal conductivity. The band convergence is also verified by increasing the density-of-state effective mass. The apparent increase in m* is due to a gradual increase in carrier concentration with increasing temperature. Despite the agreement between the data and the model, the irregular behavior between m* and temperature is a very strong indication and the electric transmission performance of the sample is likely to be influenced by the structure of the multi band structure. Owing possibly to the low reaction temperature, there are Bi precipitates at the grain boundary. In addition to the phonon scattering and the alloy scattering, the Bi segregation and the scattering of carrier by nano-lamellar structure make the carrier mobility of the sample slightly lower. The lower effective doping rate and complex band structure make the carrier concentration and density-of-state effective mass low coupled with the low carrier mobility, which leads to low material factor β with a ZT of 0.66 at 600 K consequently.
Dielectric properties and high temperature magnetic behavior on multiferroics Bi1-xCaxFeO3 ceramics
Authors: Song Gui-Lin  , Su Jian  , Zhang Na  , Chang Fang-Gao  ,   Henan Key Laboratory of Photovoltail Materials, College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China
Published: December 2020

Multiferroic Bi1-xCaxFeO3 (x=0, 0.05, 0.1, 0.15, 0.2) ceramics are prepared by sol-gel method. The effects of Ca doping on the structure, delectrical, ferromagnetism properties and high temperature magnetic behavior of BiFeO3 ceramics are studied. The structures of BiFeO3 ceramics are characterized by X-ray diffraction (XRD). The results show that all the peaks for Bi1-xFexO3 samples can be indexed according to the crystal structure of pure BiFeO3. The characteristic diffraction peaks of Bi1-xCaxFeO3 samples become gradually wider and the (104) and (110) peaks of BiFeO3 merge partially into a broadened peak (110) with Ca2+ doping increasing. XRD analysis reveals a phase transition in Ca-doped BiFeO3 from rhombohedral to orthorhombic when x is larger than 0.15. The scan electron microscope images indicate that Ca2+ doping significantly increases the grain sizes of BiFeO3 ceramic. The average grain sizes of Bi1-xCaxFeO3 samples range from 0.5 to 2 μm.#br#The dielectric behaviors of Bi1-xCaxFeO3 ceramics change with content x and frequency. The dielectric constant measured at 1 kHz reaches a maximum value of εr=4603.9 when x=0.1, seven times as big as that of pure BiFeO3. With further increasing the Ca content (x=0.15, 0.2), the value of the dielectric constant is back to the level of pure BiFeO3. The dielectric constant of Bi0.8Ca0.2FeO3 (εr=57) is less than one-tenth that of BiFeO3 (εr=629.9). The dielectric losses of Bi1-xCaxFeO3 samples become smaller than that of BiFeO3 ceramic. This dramatic change in the dielectric properties of Bi1-xCaxFeO3 samples can be understood in terms of orientational relaxation of dipoles and the space charge limited conduction associated with crystal defects at low frequency.#br#The magnetic measurements show that all samples possess strong ferromagnetism at room temperature expect BiFeO3 which is weakly ferromagnetic. The X-ray photoelectron spectroscopy spectrum indicates the coexistence of Fe2+ and Fe3+ in Bi1-xCaxFeO3 samples. The ratios of Fe2+/Fe3+ are 21/79, 23/77, 27/73, 32/68, and 32/68, respectively. The ratio of Fe2+/Fe3+ increases with doping Ca content increasing, and the magnetic preparation of BiFeO3 is enhanced.#br#It is evidenced that the ferromagnetic phase transitions of Bi1-xCaxFeO3samples occur at 878 K from M-T curve and the phase transition of BiFeO3 happens at 878 K by DSC measurement. The change in TN of Bi1-xCaxFeO3 depends mainly on the Fe-O-Fe super-exchange strength and magnetic structure of relative stability.
Electron emission from Pb(Mg1/3Nb2/3)O3-PbTiO3 ferroelectric cathode
Authors: Wang Qiu-Ping  , Feng Yu-Jun  , Xu Zhuo  , Cheng Peng-Fei  , Feng Fei-Long  ,   School of Sciences, Xi'an Polytechnic University, Xi'an 710048 China;,   Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, Institute of Electronic Materials, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

(1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 materials near the morphotropic phase boundary are selected for tentative electron emission experiments due to their excellent piezoelectric and ferroelectric properties and relatively high dielectric constants. The influences of ferroelectric and dielectric properties of ferroelectric cathode material on its threshold voltage are studied. The relationship between emission current and triggering voltage is investigated, and the relationship between emission current and extracting voltage is studied as well. The electron emission mechanism is also analyzed. The results show that emission threshold voltage of the relaxation ferroelectric 0.9Pb(Mg1/3Nb2/3) O3-0.1PbTiO3 is smaller due to its high dielectric constant at room temperature and large polarization variation. Low threshold voltage means low power consumption. This is an important factor to be considered in actual application for ferroelectric cathode and it has an important reference value. Electron emission is associated with fast polarization reversal and the formation of the plasma. The self-emission current starts on the falling edge of the triggering voltage pulse, which means that it is caused by polarization reversal. The amplitude of the self-emission current grows exponentially with the increase of triggering voltage. The amplitude of emission current shows a linear growth with the increase of extracting voltage when it is larger. It indicates that large current is determined mainly by extracting voltage. Larger current needs larger extracting voltage. The emission current starts on the rising edge of the triggering voltage pulse. It is associated with the field enhancement effect near “three interface points” and the formation of the plasma. An emission current of 210 A is obtained from the ferroelectric cathode under an extracting voltage of 2500 V, and the corresponding current density is 447 A/cm2.
Effect of nitrogen on the defect luminescence in diamond
Authors: Zhang Xiu-Zhi  , Wang Kai-Yue  , Li Zhi-Hong  , Zhu Yu-Mei  , Tian Yu-Ming  , Chai Yue-Sheng  ,   School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China;,   School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

The defect luminescences of types IIa, Ib and Ia diamond are investigated by the low-temperature micro-photoluminescence microspectroscopy. The results show that with the increase of nitrogen content, the interstitials and vacancies are trapped by the nitrogen atoms, then the luminescences of intrinsic defects such as GR1, 533.5 nm and 580 nm centers are weakened, while the emissions of nitrogen-related such as NV and 523.7 nm centers are strengthened. After high temperature annealing, the interstitials and vacancies in diamond become movable. The NV0 center is found in the IIa diamond, and the type Ib diamond presents the only strong NV luminescence. The H3 and N3 centers are observed due to the aggregation of nitrogen in Ia diamond. In addition, the nitrogen benefits the formations of the negative defects (3H center, NV- center) as the donor atom.