bluuebunny/crossref_metadata_2025 huggingface dataset:
A rapid atmospheric correction model for L-band microwave radiometer under the cloudless condition
Authors: Du Yan-Lei  , Ma Wen-Tao  , Yang Xiao-Feng  , Liu Gui-Hong  , Yu Yang  , Li Zi-Wei  ,   State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences Beijing 100101, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Atmospheric correction is very important to the accurate retrieval of geophysical parameters from spaceborne L-band radiometers. In this paper, the L-band upwelling and downwelling radiation brightness temperature and transmittance above sea surface are calculated using the atmospheric radiation transfer model based on NCEP temperature and humidity profile data. A regression model, i.e., radiation-vapor model, is established to describe the relationship between the three atmospheric radiation parameters and the atmospheric water vapor content as well as the sea surface pressure. Using this model, the atmospheric radiation parameters can be calculated and used to correct the atmospheric effects in L-band microwave radiometer observation. In order to test the proposed model, the atmospheric radiation parameters are calculated by this model and compared with the SSM/I water vapor content data and the NCEP surface pressure data. Finally, the model outputs are compared with the Aquarius satellite data. Results indicate that the radiation brightness temperature calculated by the proposed model is lower than the Aquarius data about 0.335 K and the root-mean-square error between them is about 0.086 K after correcting the systematic errors. The atmospheric transmittance calculated by the proposed model agrees well with the Aquarius data. Besides, the proposed model uses fewer input data and is faster and more stable than other existing models.
Simulation and experimental study of phase characteristics in high-gain relativistic klystron amplifier
Authors: Wu Yang  , Xu Zhou  , Xie Hong-Quan  , Li Zheng-Hong  , Ma Qiao-Sheng  ,   Institute of Applied Electronics, China Academy of Engineering Physics, Mianyang 621900, China;,   Science and Technology on High Power Microwave Laboratory, Mianyang 621900, China;,   College of Science, Southwestern University of Science and Technology, Mianyang 621010, China
Published: December 2020

In order to realize the combination of the coherent high power microwave, an S-band high gain relativistic klystron amplifier with high phase stability is presented and studied theoretically and experimentally. The phase characteristics of the output microwave are explored in particle-in-cell code and experiment. The experimental results accord well with the simulation results, which indicates that the parasitic oscillation excited by retrograde electrons is the main cause of phase variation in the development of high-gain relativistic klystron with high phase stability. When the input RF power is 10 kW, a microwave pulse with about ± 10° in relative phase difference fluctuation between output and input is obtained in experiment. And the corresponding locking duration is about 90 ns. Accordingly, the expectation of power combination efficiency of 10 high-gain relativistic klystron amplifiers can be achieved to be 99% with continuous uniform distribution of random relative phase difference.
Study of positive and negative gradient refractive index alternant surface
Authors: Liu Xiao-Bo  , Liu Ming-Li  , Chen Jian-Zhong  , Shi Hong-Yu  , Chen Bo  , Jiang Yan-Sheng  , Xu Zhuo  , Zhang An-Xue  ,   Department of Information and Communication Engineering, Xi'an Jiaotong University, Xi'an 710049, China;,   Department of Electronic Information Engineering Technology, Henan Polytechnic Institute, Nanyang 473005, China
Published: December 2020

In this paper, we design a kind of positive and negative gradient refractive index alternating surface and discuss its physical mechanism by the geometrical optics method and the numerical simulation of electromagnetic field. This structure can control the propagation of electromagnetic waves by adjusting some parameters such as refractive gradient. Under certain parameters, electromagnetic waves from space can be confined mainly in the media all the time, or are released into the space after propagating a certain distance in the media. This structure is polarization-independent and wide-band. It means that this structure can be used as a stealth surface by reducing the scattering cross section. Finally, the characteristics of the structure are verified by the numerical simulation.
Analysis on the effects of optics thermal deformation on the ion thruster operation
Authors: Chen Mao-Lin  , Xia Guang-Qing  , Xu Zong-Qi  , Mao Gen-Wang  ,   Science and Technology on Combustion, Internal Flow and Thermo-Structure Laboratory, Northwestern Polytechnical University, Xi’an 710072, China;,   State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China
Published: December 2020

Optics thermal deformation is an important factor that impacts the performance and lifetime of ion thrusters. Although some theoretical reflearch concerned with this problem was reported, its mechanism has not been fully understood. In this study, numerical investigations are performed to explain the effect of thermal deformation on the performance and lifetime of ion thrusters. The transient behavior of charged particles is calculated using a particle-in-cell simulation, while the momentum transfer collision and the charge exchange collision are calculated by means of the Monte Carlo method. Electron backstreaming restriction, perveance restriction, ions through rate, and divergence angle losses are compared and analyzed for optics deformed and undeformed. And the influence of these factors on thruster’s performance and lifetime is discussed. Results show that the ion through rate of the screen grid increases when optics begin deformed, and the thrust is slightly higher than the theoretical values predicted; the perveance threshold of the accelerator grid increases with optics haveing thermal deformation, while the crossover limit threshold is little changed, namely the thruster can be operated in conditions of a larger beam current; the electron backstreaming restriction threshold is significantly lower under a high beam current condition with optics deformed, which means that a lower accelerating gate bias is necessary to ensure thruster work. For the less obvious change of acceleratng grid current when the beam is focused, there is no moreflerosion and change of lifetime. Results provide a reflerence for the optimization design of optics and evaluation of thruster performance and lifetime.
Er-fiber femtosecond optical frequency comb covering visible light
Authors: Liu Huan  , Cao Shi-Ying  , Meng Fei  , Lin Bai-Ke  , Fang Zhan-Jun  ,   Center for Photonics and Electronics, Department of Precision Instrument, Tsinghua University, Beijing 100084, China;,   Division of Time and Frequency Metrology, National Institute of Metrology, Beijing 100029, China
Published: December 2020

Femtosecond optical frequency combs (FOFCs) with output wavelengths covering visible light have potential applications in absolute frequency measureflent of iodine-stabilized lasers and optical clock lasers. Based on optical amplification, frequency doubling and spectrum broadening, a home-made Er-fiber femtosecond optical frequency comb (Er-FOFC) with output wavelengths covering visible light is demonstrated. One path with an average power of 8 mW from Er-FOFC is used as the seed pulse for spectrum broadening to cover the visible light. This path is first amplified to 532 mW by injecting into an Er-doped femtosecond fiber amplifier with combined forward and backward pumping and then frequency doubled with a MgO: PPLN crystal with an output power of 85 mW, frequency-doubling efficiency of 32% and pulse duration of 85fs. The output power of this path can be first amplified to 532 mW through an Er-doped femtosecond fiber amplifier when the forward pumping and backward pumping both turn on. Then the frequency-doubling laser can be generated in a MgO: PPLN crystal. The frequency-doubling efficiency is 32% and the pulse duration is 85 fs; the frequency-doubling light is spectrally broadened from 500 to 1000 nm in a photonic crystal fiber (PCF), with an output power of 85 mW and coupling efficiency of 50%. To verify the performance of the broadened spectrum, the light from the Er-FOFC and a compact iodine-stabilized frequency-doubled Nd: YAG laser at 532 nm is beaten. A beat signal with a signal-to-noise ratio of 30 dB at 100 kHz RBW is obtained, which provides a useful tool for absolute frequency measureflent of visible lasers.
Influence of Gaussian function index of deformable mirror on iterative algorithm adaptive optical system
Authors: Cheng Sheng-Yi  , Chen Shan-Qiu  , Dong Li-Zhi  , Wang Shuai  , Yang Ping  , Ao Ming-Wu  , Xu Bing  ,   The Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Key Laboratory on Adaptive Optics, Chinese Academy of Chengdu, Sichuan 610209, China;,   University of Electronic Science and Technology of China, Sichuan 610054, China
Published: December 2020

Among all kinds of wavefront reconstruction algorithms in adaptive optical systems, the standard and mostly used algorithm is the direct gradient wavefront reconstruction algorithm. As the number of sub-apertures in Shack-Hartmann wavefront sensor and the actuators for deformable mirror increases, the reconstruction matrix in direct gradient wavefront reconstruction algorithm takes too much space and the number of multiplication in the algorithm increases sharply. So, the iterative algorithm is adopted in wavefront reconstruction for the high-resolution adaptive optical system. The number of multiplication and the required space of the iterative algorithm are directly related to the sparseness of both iterative matrix and slope response matrix. In an adaptive optical system, the sparseness of these two matrixes is connected with the system parameters. Therefore, it is necessary to study how to choose the proper parameters for an adaptive optical system when it uses iterative wavefront reconstruction algorithm. In this paper, the sparseness of slope response matrix and iterative matrix are analyzed based on a 613-actuator adaptive optical system. The influence of the Gaussian function index of deformable mirror on the sparsenesses of slope response matrix, iterative matrix, stability and correction qualities of the adaptive optical system are also studied under the condition of constant actuator spacing and coupling coefficient. A larger Gaussian function index results in a lower sparseness of the slope response matrix and the iterative matrix. Too large or too small a Gaussian function index will degrade the stability and the correction quality of an adaptive optical system. Finally, the optimal range of the Gaussian function index is provided by balancing the sparseness of slope response matrix, the correction quality, and the stability of the adaptive optical system.
Synthesis and optical absorption properties of LaxCe1-xB6 submicron powders
Authors: Bao Li-Hong  , Chao Lu-Meng  , Wei Wei  , O. Tegus  ,   Inner Mongolia Key Laboratory for Physics and Chemistry of Functional Materials, Inner Mongolia Normal University, Hohhot 010022, China;,   Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Published: December 2020

According to original knowledge, lanthanum hexaboride (LaB6) as an excellent thermionic electron emitter is characterized by a low work function, a high emission density, and a high brightness. Recently, much attention has been drawn to its another excellent optical properties: strong light absorption in near infrared rays (NIR), and transparency in visible light (VL), which result from the free electron plasmon resonance. However, up to now the optical properties and syntheses of ternary rareflearth hexaborides have been very rarely reported in the literature. In this paper, ternary LaxCe1-xB6 submicron crystallines are successfully synthesized using a solid-state reaction, in which La2O3 and CeO2 are used as rareflearth sources and NaBH4 as boron sources in a continuous vacuum condition. Effects of La doping content on the LaxCe1-xB6 phase composition, microstructure, and optical absorption properties are investigated by X-ray diffraction, scanning electron microscope (SEM), and transmission electron microscope (TEM). It is found that all the synthesized samples are composed of CaB6-type single-phase alloy with a space group Pm3m at the reaction temperature of 1200 ℃ held by 2 h. The SEM results indicate that the cubic-shaped ternary LaxCe1-xB6 crystals with a mean size of 200 nm are obtained and the energy dispersive spectrometer results confirm that the La atoms are randomly distributed at the lattice sites of CeB6. High resolution transmission electron microscope images refleal the single-crystalline nature, and the FFT pattern indicates the lattice fringe d=0.42 nm which agrees well with the (100) crystal plane. EDS analysis of TEM also indicates the La element has been doped into CeB6. And the optical absorption result shows that the absorption valley of CeB6 is 62 nm. With increasing La doping content to x=0.6 and 0.8, the absorption valleys of La0.6Ce0.4B6 and La0.8Ce0.2B6 decrease to 613 and 610 nm respectively indicating the blueshifts of the wavelength of absorption valley From the view point of practical application, the tunable characteristic of LaxCe1-xB6 may extend the optical applications in improving the efficiency of organic photovoltaics, replacing the expensive gold and silver nanoparticles, which may have a good usage in optical filters.
Link prediction in microblog retweet network based on maximum entropy model
Authors: Li Yong-Jun  , Yin Chao  , Yu Hui  , Liu Zun  ,   School of Computer, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Microblog is a social media platform, based on the follower-followee relationship, that enables users to share real-time information, by which the information propagation is characterized as rapid, explosive, and immediate. The research on the information propagation and retweet prediction is very important for public sentiment analysis and product promotion. A majority of existing works adopt several traditional prediction methods to predict the future information retweet based on the features extracted from existing retweet behaviors, which are hard to reconcile accuracy, complexity, robustness and feature extensiveness. To overcome the above mentioned shortcomings in existing works, we propose in this paper a link prediction algorithm based on maximum entropy model to predict retweet behavior on microblog. In our proposed approach, firstly we abstract the retweet prediction problem to a link prediction problem. Then we analyze the retweet behaviors on microblog and determine the factors influencing the retweet behavior. We extract the features from the retweet behaviors based on these factors in the next step. Now based on these features, the retweet behavior could be predicted by the proposed approach. However, information redundancy and other issues may exist among these features. These issues will cause an increase in computational complexity or a decrease in computational accuracy. To solve the above problems, we selecte the features dominating the retweet behavior with feature selection methods such as Information Gain, IG-CHI. The proposed model requires no further independent assumption in features or intrinsic constraints, and omits the processing in relation to features, which is usually the prerequisite of other prediction methods. We take the Sina Weibo retweet records in a time span from 2009 to 2012 as an example to test the effectiveness and efficiency of our link prediction algorithm. Results show that: 1) the proposed algorithm has incomparable advantages in running time; 2) as for the predicted result, the proposed algorithm is better than other algorithms in performance evaluations; 3) the proposed algorithm runs stably for different sizes of training sets and feature sets; 4) the accuracy of the predicted results remains stable based on the selected features. The proposed approach avoids the independent restriction among features and shows better accuracy than other similar methods, thus it has reference values for resolving other prediction problems in complex networks.
Quasi-particle calculations on electronic and optical properties of the peroxy linkage and neutral oxygen vacancy defects in amorphous silica
Authors: Su Rui  , Zhang Hong  , Jiang Sheng-Li  , Chen Jun  , Han Wei  ,   College of Physical Science and Technology, Sichuan University, Chengdu 610064, China;,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;,   Research Center of Laser Fusion, Mianyang 621900, China
Published: December 2020

Recently, fused silica has been used to prepare the optical windows in the inertial confinement fusion (ICF) equipment. Challenge of application of fused silica is due to the defect-related optical absorption which is considered as the main mechanism of laser-induced damage process. However, due to structural complexity, calculation of the defect-related absorption from the first principles is only limited to small clusters, and a full treatment using the state of art GW and Bathe-Salpeter equation (BSE) method is still lacking.In this work, density functional theory calculations are performed to study the defect structure of the peroxy linkage (POL) and the neutral oxygen vacancy (NOV) defects in amorphous silica. Firstly, well relaxed structure is generated by using a combination of the bond switching Monte Carlo technique and the DFT-based structure optimization. Secondly, the defect structures are generated and studied in both the ground singlet (S0) and the first excited triplet (T1) states. Finally, the electronic and optical properties of the considered structures are studied by applying the self-consistent quasi-particle GW (sc-QPGW) and the BSE methods in Tamm-Dankoff approximation.In the ground state S0, the POL defect is found to be stable and shares a similar local structure to the H2O2 molecule. However, in T1 state, the POL defect breaks into a pair of E' center ( - Si ) and peroxy oxygen radial ( O-O-Si-). For the NOV defect, the optimized Si-Si bond length in the ground state is 2.51 with a variation of 0.1 due to the structural disorder. In comparison to the ground state, the optimized Si-Si bond length in T1 state increases to 3.56 .The scGW/BSE calculation on the defect free structure predicts a quasi particle band gap of 10.1 eV and an optical band gap of 8.0 eV, which are consistent well with the available experimental results. For the POL defect, the scGW/BSE calculation reveals a weak exciton peak at 6.3 eV. Below 6.3 eV, no new exciton peak is found, implying that the experimentally suggested 3.8 eV peak could not be attributed to the POL defect. Calculations of the NOV defect gives a strong and highly polarized optical absorption peak at 7.4 eV which is close to the previous experimental result at 7.6 eV. The structural relaxation induced by NOV also contributes to another absorption peak at 7.8 eV.
Electromagnetic topology based fast algorithm for shielding effectiveness estimation of multiple enclosures with apertures
Authors: Kan Yong  , Yan Li-Ping  , Zhao Xiang  , Zhou Hai-Jing  , Liu Qiang  , Huang Ka-Ma  ,   School of Electronics and Information Engineering, Sichuan University, Chengdu 610065, China;,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
Published: December 2020

Shielding effectiveness (SE) estimation for an enclosure with apertures has been an attractive issue in electromagnetic compatibility (EMC) research area. Though many fast algorithms are developed for SE calculation, they mainly focus on the case of single cavity. Moreover, most of these methods neglect the wave coupling through apertures from enclosure to outside. A fast algorithm based on electromagnetic topology is proposed for calculating the SE of cascading multiple enclosures with apertures. In this algorithm, the wave coupling through apertures in both directions is taken into consideration. Firstly, the equivalent circuital model of cascading double enclosures and its signal flow graph of electromagnetic topology are given, followed by the derivation of scattering matrix of apertures node. Then propagation relationships at tube level and reflection relationships at node level are derived. As a result, the general BLT (Baum-Liu-Tesche) equation for voltage calculation at each node is established. Two major categories of cascading three enclosures with apertures are investigated. For serially cascading three enclosures, the general BLT equations are extended on the basis of BLT equations for cascading double enclosures, since the structures are a simple extension of them. For hybrid serially-parallelly cascading three enclosures, the common walls between the main enclosure and two sub-enclosures are considered as a topological node represented by a three-port network, whose scattering matrix is derived according to the definition of scattering parameters. Consequently, the general BLT equations for hybrid serially-parallelly cascading three enclosures are developed. Compared to the algorithms presented in the relevant literature, the topology-based algorithm proposed in this paper can not only calculate the shielding effectiveness for cascading multiple enclosures, but also lead to more accurate results in that the impedance of apertures is obtained through using diaphragms model. In order to validate the proposed method, a cascading double enclosures from a literature is chosen as an example. Calculated SE results are in good agreement with those in the literature. Then, three enclosures with different configurations and dimensions are also designed to validate the proposed method. Results from the proposed method are compared with those from the finite difference time domain (FDTD) method, and they are found to be in good agreement with each other. Experimental results also demonstrate the validation of the proposed method. Especially, the proposed method takes far less time to calculate SE than for FDTD method.
icMRCI+Q study on spectroscopic properties of twelve -S states and twenty-three states of the CF+ cation
Authors: Xing Wei  , Liu Hui  , Shi De-Heng  , Sun Jin-Feng  , Zhu Zun-Lüe  ,   College of Physics and Electronic Engineering, Xinyang Normal University, Xinyang 46400, China;,   College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China
Published: December 2020

The potential energy curves of twenty-three states generated from the twelve -S states (X1+, a3, 13+, 13, 11, 11-, 13-, 21+, 11, 23, 21 and 23+) correlating with the first dissociation channel C+(2Pu)+ F(2Pu) of the CF+ cation are obtained by using the internally contracted multireference configuration interaction approach with the Davidson modification (icMRCI+Q) on the basis of the correlation-consistent aug-cc-pV5Z and aug-cc-pV6Z basis sets for the first time. The spin-orbit coupling, core-valence correlation and relativistic corrections are taken into account, and all the potential energy curves are extrapolated to the complete basis set limit by separately extrapolating the Hartree-Fock and correlation energies scheme. Based on the calculated potential energy curves, the spectroscopic parameters of the bound and quasibound nine -S and sixteen states of the CF+ cation are obtained. And the spectroscopic parameters of X1+and a31st well-S states which are in very good agreement with experimental results are achieved. Furthermore, the vertical and adiabatic ionization potentials of ionization from the X2 state of CF radical to the bound and quasibound nine -S states of the CF+ cation are calculated, and the vertical and adiabatic ionization potentials of the CF+(X1+) CF(X2 ) and CF+(a31st well) CF(X2 ) ionizations are also in good agreement with the corresponding experimental values. Various curve crossings of -S states are revealed, and with the help of our computed spin-orbit coupling matrix elements, the predissociation mechanisms of the a31st well, 111st well and 21+ states are analyzed for the first time. The spin-orbit-induced predissociations for the a31st well, 111st well and 21+-S states could happen, and the predissociations of the a31st well, 111st well and 21 +-S states start around the vibrational levels ' = 15, ' = 1 and ' = 1, respectively. Relative energies of the twenty-three states in the dissociation limits are given, and our calculations match the experimental results very well. Finally, the Franck-Condon factors and radiative lifetimes of transitions from (2) 0+1st well (;'=05), (1) 11st well ('=05) and (2) 11st well ('=0) to X0+ states are predicted for the future laboratory research.
Mechanism of NiSi0.7Ge0.3 epitaxial growth by Al interlayer mediation at 700 ℃
Authors: Ping Yun-Xia  , Wang Man-Le  , Meng Xiao-Ran  , Hou Chun-Lei  , Yu Wen-Jie  , Xue Zhong-Ying  , Wei Xing  , Zhang Miao  , Di Zeng-Feng  , Zhang Bo  ,   Shanghai University of Engineering Science, Shanghai 201600, China;,   State Key Laboratory of Functional Material for Informatics, Shanghai Institute of Microsystem and Information Technology, CAS, Shanghai 200050, China
Published: December 2020

The formation of Nickel based germanosilicides (NiSiGe) has attracted growing interest in the state-of-the-art metal oxide semiconductor field effect transistor (MOSFET) technology, because silicon-germanium alloy (Si1-xGex) is used as embedded source/drain stressor or channel material to enhance the hole mobility in the channel region. However, a major problem of NiSiGe film is that it has a poor thermal stability after annealing at high temperature (550 ℃), which leads to its agglomeration. In this work, we study the reaction between Ni and Si0.7Ge0.3 in the presence of an Al interlayer. Pure Ni (10 nm) film and Ni (10 nm)/Al (3 nm) bi-layers are deposited respectively on Si0.7Ge0.3 substrates by electron beam evaporation. Solid-phase reactions between Ni or Ni/Al and Si0.7Ge0.3 during rapid thermal processing in N2 ambient for 30 s are studied at 700 ℃. The un-reacted metal is subsequently etched in H2SO4 solution. The NiSi0.7Ge0.3 films are characterized by Rutherford backscattering spectrometry (RBS), crosssection transmission electron microscopy (XTEM), energy dispersive X-ray spectrometer (EDX), and secondary ion mass spectroscopy (SIMS) techniques. For the Ni/Si0.7Ge0.3 sample, the segregation of Ge at grain boundaries of nickel germanosilicides during the interfacial reactions of Ni with Si0.7Ge0.3 films and the subsequent formation of Ge-rich Si1-wGew (w0.3) are confirmed by the RBS and XTEM measurements. However, in the case of Al incorporation, a very uniform and smooth NiSi0.7Ge0.3 film is obtained with atomic NiSi0.7Ge0.3/Si0.7Ge0.3 interface. The orthorhombic NiSi0.7Ge0.3 is finally epitaxial grown on cubic Si0.7Ge0.3substrate tilted at a small as demonstrated by the High resolution XTEM. Furthermore, based on the EDX and SIMS measurements, it is found that most of the Al atoms from the original interlayer diffuse towards the NiSi0.7Ge0.3 surface, and finally form an oxide mixture layer. It is proposed that the addition of Al reduce Ni diffusion, balance the Ni/Si0.7Ge0.3 reaction and mediate the NiSi0.7Ge0.3 lattice constant. In addition, the main mechanism of epitaxial growth of NiSi0.7Ge0.3 film is analyzed in detail. In summary, Al mediation is experimentally proved to induce the epitaxial growth of uniform and smooth NiSi0.7Ge0.3 layer on relaxed Si0.7Ge0.3 substrate, providing a potential method of achieving source/drain contact material for SiGe complementary metal oxide semiconductor devices.
The bond characters and phase stability effects of Cr Mo and Ni in bulk -Fe(C
Authors: Wan Ming-Jun  , Li Chun-Fu  , Wen Ping  , Zhang Feng-Chun  , Wang Yao  , Liu En-Zuo  ,   State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China;,   China Petroleum Chemical Corporation North China Company, Zhengzhou 450000, China;,   Institute of Materials Science and Engineering of Tianjin University, Tinjin 300072, China
Published: December 2020

Based on density functional theory and using the first-principle method, the electronic structures of -Fe(C) with Cr, Mo, and Ni are calculated within the generalized gradient approximation (GGA)-PW91. Meanwhile, the effects of alloys on the bonding characters and austenitic stability are studied by the overlap population, mulliken charge population, density of states, charge density difference, and cohesive energy. The results show that there coexist the metallic bond, covalent bond and weak ionic bond in each of -Fe(C)-Cr and -Fe(C)-Mo unit cell, while only metallic bond and covalent bond coexist in -Fe(C)-Ni. The bonding orbit is mainly determined by the interactions between the d orbits of alloy atoms and the orbits of Fe 3d and C 2p. Moreover, the effects of Cr, Mo, Ni solution on austenitic stability are investigated by studying the influence of alloy element on -Fe(C) electronic structure.
Surface segregation of AuCu3 by He+ and Au+ irradiation
Authors: Fa Tao  , Chen Tian-Xiang  , Han Lu-Hui  , Mo Chuan  ,   Institute of Materials, China Academy of Engineering Physics, Mianyang 621900, China;,   Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang 621900, China;,   Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Surface segregation is a significant phenomenon due to its influence on many surface processes, such as corrosion, oxidation and catalysis. Defects and vacancies produced by ion irradiation in alloys used in reactors or other radiation environments may also induce surface segregation. In this work, we deposit AuCu3 film on a Si(111) substrate by magnetic sputtering. He+ and Au+ produced by pelletron are used to simulate radiation fields in reactors, and surface segregation induced by ion irradiation is investigated. SRIM software is used to simulate ion range and displacements produced in sample. Rutherford backscattering spectrometry is used to determine concentration changes near the surface of sample before and after irradiation. The results show that two kinds of ion irradiations lead to different surface segregation trends. When irradiated by 2 MeV He+, Au elements are segregated at the surface of sample. Oppositely, when irradiated by 1 MeV Au+, Cu elements are observed at the surface of sample. After analysis and discussion, we consider that this phenomenon is induced by different vacancy distributions by He+ and Au+ irradiation. 2 MeV He+ produced Au and Cu vacancies are distributed in whole film from surface to substrate smoothly, except very near the surface the concentration of vacancies has an obvious reduction. As a result, a gradient of the vacancy concentration is formed between the surface and the interior of the film. As the concentration of vacancies on the surface is lower than in interior, it would lead to vacancy diffusion from interior to surface, equivalent to diffusions of Cu and Au atoms along the opposite directions. Because of lighter atomic mass, Cu atom has a faster diffusion rate than Au atom. As a result, the concentration of Au atoms near the surface increases. Unlike He+, Au+ produces a mass of vacancies near the surface of the film, consistent with the Bragg peak by energy deposition of Au+, but decreases rapidly inside the film. It leads to a gradient of the vacancy concentration from surface to interior of the film. When vacancies diffuse from surface to interior, Cu and Au atoms diffuse from interior to surface, the lighter Cu atom concentration increases faster than Au atom concentration. Our research results explain the different segregation trends by light ion with higher energy and heavy ion with lower energy. It may help to understand the surface segregation of alloys used in complex irradiation field.
Effects of a partially coherent beam on periodic bottle beam
Authors: Zhu Qing-Zhi  , Shen Dong-Hui  , Wu Feng-Tie  , He Xi  ,   Fujian Key Laboratory of Optical Beam Transmission and Transformation, College of Information Science and Engineering, Huaqiao University, Xiamen 361021, China
Published: December 2020

In this paper, we propose how to generate the periodic bottle beam by using a partially coherent beam. Firstly, a spatially completely coherent beam is transformed into a partially coherent beam by a rotating ground glass. Secondly, after passing through the double-axicon system, the parallel beam is converted into two Bessel beams which have the same optical frequencies but different radial wave vectors. Finally, the partially coherent periodic bottle beam can be generated by two interfering Bessel beams. Based on the interference theory, an analytical expression can be obtained for calculating the distribution of light intensity in the image and spot diagrams in spectral degree of coherence for the optical field with 0.9. By doing this calculation, the proposed optical system can be made to generate a partially coherent periodic bottle beam with the oscillation period of 2.5 mm. Before further investigating the effect of field coherence on the periodic bottle beam, we may also calculate the distribution of light intensity in the images and spot diagrams in the spectral degree at 0.83, 0.7, 0.5 and 0.2, respectively. Results show that the intensity contrast ratio between the dark focus and the surrounding periodic regions can be reduced with the decrease of the spatial coherence degree. In this case, the period of the bottle beam and the central dark focus size will not be affected. We have also designed and carried out an experimental generation of the periodic bottle beam and measured its focusing properties. In the experiment, we can control the coherence in the incident field by controlling the size of the circular aperture located behind the rotating ground-glass disk. When the size of the circular aperture is 0.1 (or 0.2) mm, the value of the coherence degree of the incident optical field is 0.9 (or 0.83). The two different coherence degrees of the partially coherent bottle beam have been measured by CCD. Experimental results show that the obtained bottle beams are of the same period of 2.5 mm. The measured diameters of the two different coherence degrees of the central spots (maximum sizes of the dark spot) are both 15 m. Experimental results also show that the spectral degree of coherence cannot affect the shape and size of the periodic bottle beam except the contrast of it. Therefore, the experimental results agree well with the theoretical results.
Design of broadband reflective 90 polarization rotator based on metamaterial
Authors: Han Jiang-Feng  , Cao Xiang-Yu  , Gao Jun  , Li Si-Jia  , Zhang Chen  ,   Information and Navigation College, Air Force Engineering University, Xi'an 710077, China
Published: December 2020

Polarization is one of the basic properties of electromagnetic waves and is valuable in communication, navigation and radar detecting. So it is important to control and manipulate polarization states of electromagnetic waves. In this paper, we design, fabricate and measure a broadband reflective metamaterial 90 polarization rotator which has a double-split-ring resonator (DSRR) structure, composed of two layers of dielectric and a metal plate ground. The explanation of the physical mechanism of the polarization rotator is presented according to the anisotropy media theory. Anisotropic metamaterials can cause a phase or amplitude difference between two crossed polarization waves, which can be used to manipulate the polarization states of the incident waves. The anisotropic polarization rotator behaves different for two orthogonal axes, and the surface current distributions of the DSRR are discussed to analyse the different characteristics of the structure along two orthogonal axes. The DSRR behaves as a dipole resonator that couples with the electric component along one axes and behaves as an LC resonance circuit that couples with the other electric component. Thus, almost an equal magnitude and a 180 phase difference can be generated between the two orthogonal electric components of the reflected waves. The polarization states of the reflected waves will be rotated by 90, when incident waves are polarized by 45 with respect to the symmetric axis of the rotator, and it will be retained when the incident waves are circularly polarized. Simulation results show that this device can work with the relative bandwidth of 90% from 5.5 to 14.5 GHz, of which the polarization conversion ratio is larger than 90%. The polarization conversion ratio will decrease as the incident angle increases, but this high polarization conversion ratio can be obtained at several frequencies. A 576-cell (2424) prototype of the polarization rotator has been fabricated using a printed circuit board method on the FR4 substrates and the experimental results agree well with that of the simulation. The polarization rotator has a simple geometry but more operating frequency bands, compared with the previous designs. It provides a route to broadband polarization rotation and has application values in polarization control, design of new antenna and stealth technology.
Measurement of standard vacuum noise at low frequencies
Authors: Xue Jia  , Qin Ji-Liang  , Zhang Yu-Chi  , Li Gang  , Zhang Peng-Fei  , Zhang Tian-Cai  , Peng Kun-Chi  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Collaborative Innovation Center of Extreme Optics, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China;,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China
Published: December 2020

Vacuum fluctuation at audio frequencies is very important and interesting in many research fields, such as the gravitational wave detection, ultra-weak magnetic field measurement, and the research of quantum metrology, etc. Since the generation of squeezed light in 1985, most of the squeezed light have been generated and measured at radio frequencies (～MHz) as there has not been much technical noise at higher frequencies. In the Michelson-interferometer-based gravitational wave detection, the detection band has frequencies from a few to tens of thousands Hz. Measuring vacuum noise at such low frequencies is a challenge since we have to stabilize and control all the audio noises and the interferences from a variety of mechanical and electronic noises, therefore a very high classical noise suppression is needed when the measurement time increases. In order to measure the squeezed light of low frequencies, the standard vacuum noise at audio frequencies must be measured. In this paper, a balanced homodyne detection system for measuring the low-frequency quantum vacuum noises is reported. It is not trivial to extend the detected frequency to very low analysis frequencies. Through a self-made self-subtraction balanced homodyne configuration, which can eliminate the DC component of each photocurrent from the photodiode and the classical common-mode technical noise, the standard vacuum noise has been detected. The linearity of the vacuum noise power has been validated by varying the local oscillator power, showing that the saturation power of light incidence is about 3.2 mW. When the incident-light power is 400 W, the standard vacuum noise is 11 dB higher than the electronic noise at 80 Hz. In the regime of about 80 Hz to 400 kHz, the linearity of the standard noise power as a function of incident laser power is verified. However, when the measurement is carried out at even lower frequencies, for example, 50 Hz, we may encounter some excess and non-stationary noises and find that the measured noise power is not proportional to the incident light power any more. These non-stationary noises are the main technical obstacle at low frequencies. The average common mode rejection ratio in the test frequency range from 10 Hz to 400 kHz is 55 dB and its maximum 63 dB at 100 Hz is obtained, implying a high suppression of the technical noise. This self-made homodyne vacuum noise detector can be widely used for precision measurement in quantum metrology and quantum optics.
Research progress of metal-insulator phase transition mechanism in VO2
Authors: Luo Ming-Hai  , Xu Ma-Ji  , Huang Qi-Wei  , Li Pai  , He Yun-Bin  ,   Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Key Laboratory of Green Preparation and Application for Functional Materials, Ministry of Education, Faculty of Materials Science & Engineering, Hubei University, Wuhan 430062, China
Published: December 2020

VO2 is a metal oxide that has a thermally-induced phase-transition. In the vicinity of 341 K, VO2 undergoes a reversible transition from the high-temperature metal phase to the low-temperature insulator phase. Associated with the metal-insulator transition (MIT), there are drastic changes in its optical, electrical and magnetic characteristics. These make VO2 an attractive material for various applications, such as optical and/or electrical switches, smart glass, storage media, etc. Thus, the reversible metal-insulator phase transition in VO2 has long been a research hotspot. However, the metal-insulator transition mechanism in VO2 has been a subject of debate for several decades, and yet there is no unified explanation. This paper first describes changes of the crystal structure and the energy band structure during VO2 phase transition. With regard to the crystal structure, VO2 transforms from the low-temperature monoclinic phase VO2(M) into the high-temperature stable rutile phase VO2(R), and in some special cases, this phase transition process may also involve a metastable monoclinic VO2(B) phase and a tetragonal VO2(A) phase. In respect of the energy band structure, VO2 undergoes a transition from the low-temperature insulator phase into a high-temperature metal phase. In the band structure of low-temperature monoclinic phase, there is a band gap of about 0.7 eV between d// and * bands, and the Fermi level falls exactly into the band gap, which makes VO2 electronically insulating. In the band structure of high-temperature rutile phase, the Fermi level falls into the overlapping portion of the * and d// bands, which makes VO2 electronically metallic. Next, this paper summarizes the current research status of the physical mechanism underlying the VO2 MIT. Three kinds of theoretical perspectives, supported by corresponding experimental results, have been proposed so far, which includes electron-correlation-driven MIT, Peierls-like structure-driven MIT, and MIT driven by the interplay of both electron-correlation and Peierls-like structural phase transition. It is noted that recent reports mostly focus on the controversywhether VO2 is a Mott insulator, and whether the structural phase transition and the MIT accurately occur simultaneously in VO2. Finally, the paper points out the near-future development direction of the VO2 research.
Mathematical algorithm model of absolute dose in radiotherapy
Authors: Xie Tian-Ci , Zhang Bin , He Bo , Li Hao-Peng , Qin Zhuang , Qian Jin-Qian , Shi Qie-Ming , Lewis Elfed , Sun Wei-Min ,   Key Laboratory of In-fiber Integrated Optics, Ministry Education of China, Harbin Engineering University, Harbin 150001, China,   Electronic Engineering College, Ministry Education of China, Heilongjiang University, Harbin 150001, China,   Optical Fiber Sensors Research Centre, University of Limerick, Limerick, Ireland
Published: December 2020

A algorithm of obtaining absolute dose at each tissue depth only by the mathematical calculation of formula is reported. The algorithm is based on integrating the energy flux of the electron generated by X-ray in the range of irradiation field, and the energy spectrum of ray and the secondary scattered ray are considered in this process. In this algorithm, the water phantom in the irradiation field is divided into several thin layers, and the energy flux of the electrons generated by interaction between the ray and thin layer reaching the calculation point is calculated. Finally, the absolute dose of the calculation point can be obtained by accumulating the energy flux contribution of all thin layers. For the X-ray with continuous energy spectrum, the expected mass attenuation coefficient is calculated for obtaining the photon flux at each depth in this process. The absolute dose calculated by this algorithm is verified by Monte Carlo simulation, and the difference between the algorithm and simulation is compensated for by a dose function about multiple scattering photons, and the function shows fast descent and then slow ascent. It is found that the ratio of the dose caused by backscatter to the surface dose, and the relationship among forward scatter, backward scatter and primary ray, and the relationship between the dose and the depth of the secondary scattered rays show a trend of first rising and then declining, and the depth of the peak value deviates from the position of the thin layer. Three-dimensional energy spectra of the secondary photon and the secondary electron are also compared with each other, and the spectrum is a function of particle flux about particle energy and particle direction. From the perspective of Compton effect, the physical meanings of different positions in the three-dimensional energy spectrum of the two particles are explained. It is found that the difference between algorithm percentage depth dose and simulation percentage depth dose is similar to the difference between small irradiation field percentage depth dose and big irradiation field percentage depth dose from simulation, and it is verified that the difference between algorithm and simulation comes from the increase of scattered rays. Finally, the algorithm is applied to the dose calculation of non-uniform phantom, which can accurately reflect the dose distribution characteristics and have less error.