bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved design of quasi-optical output coupler for a W-band multicavity sheet beam klystron
Authors: Liu Guo  , Wang Jian-Xun  , Luo Yong  ,   School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

An intensive research have been done about the W-band sheet beam klystron (WSBK) for its potential value in active denial system application. The output cavity has an important influence on the output power, efficiency, bandwidth and spectrum. In this paper, multiple types of quasi-optical (QO) output couplers are designed based on the theory of equivalent dipoles and phase superimposition, and detailed study on the cold characteristics such as R/Q, M, loaded Q and mode uniformity has been all demonstrated. Compared with other tapers, QO output coupler with parabolic taper shows more excellent performance than the linear, triangle and Chebyshev tapers. We will receive benefit from improving the beam-wave efficiency and bandwidth of WSBK. Besides, a QO-output coupler with linear taper for initial experiment is fabricated.
A novel spectrum detecting algorithm for cognitive radio based on the characteristics of authorized channel
Authors: Liu Yun  , Peng Qi-Cong  , Shao Huai-Zong  , Peng Qi-Hang  , Wang Ling  ,   School of Communication and Technology Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

In a cognitive radio (CR) network, the system throughput and the probability of collision between primary users (PUs) and CR users are directly influenced by the frequency of spectrum sensing. This paper focuses on adaptively scheduling spectrum sensing such that negative impacts to the performance of the CR network are minimized. Based on an in-depth analysis into the spectral usage patterns of PUs, an adaptive spectrum detecting algorithm is proposed. By introducing a "control factor", the proposed algorithm can adaptively schedule the spectrum sensing, while maintaining the CR system stability, so as to increase spectral utilization efficiency, as well as reducing the probability of collision between PUs and CR users. Therefore, the energy consumption of the CR system is reduced. Simulations show that the proposed algorithm can effectively increase the system throughput, with minimal interference to primary users while ensuring the system stability. Meanwhile, it is shown that the proposed algorithm has low implementation complexity for practical applications.
Influences of plasma activation Se source on selenization of electrodeposited Cu-In-Ga metallic precursors
Authors: Zhang Chao  , Ao Jian-Ping  , Jiang Tao  , Sun Guo-Zhong  , Zhou Zhi-Qiang  , Sun Yun  ,   Tianjin Key Laboratory of Photo-Electronic Thin FilmDevices and Technology, Institute of Photo-Electronic Thin FilmDevices and Technique, Nankai University, Key Laboratory of Optoelectronic Information Technology, Ministry of Education (Nankai University Tianjin University), Tianjin 300071, China
Published: December 2020

In this paper, the electrodeposited Cu-In-Ga metallic precursors have been selenized by using plasma activation Se source. The power of plasma has great influence on the grain growth of Cu(In1-xGax)Se2(CIGS). The films were shown to be single phase Cu(In0.7Ga0.3)Se2 when the plasma power was 75W. And the fact that high activity Se promotes the generation of binary selenide phase at a low temperature, thus helping the growth of single phase Cu(In0.7Ga0.3)Se2, was proved by XRD analysis of the films selenized at defferent temperatures and the comparison with the films prepared by ordinary selenization. Solar cells have been prepared and found that the single phase have no influence on battery performance. The efficiency can reach 9.4% by process optimization.
Investigation on characteristics of solar cells made of MOPPV/ZnSe quantum dots composite system
Authors: Qu Jun-Rong  , Zheng Jian-Bang  , Wang Chun-Feng  , Wu Guang-Rong  , Hao Juan  ,   Shaanxi Key Laboratory of Optical Information Technology, Department of Applied Physics, School of Science, Northwestern Polytechnical University, Xi’an 710072, China
Published: December 2020

Based on some special physical properties of solar cells prepared from quantum dots polymeric materials, which have high photoelectric conversion performance, we use MOPPV solution for obtaining controllable grain sizes, good crystallinity, with a particle size of about 3.75 nm ZnSe quantum dot polymer composite materials, and different quality ratios of the composites. We also use XRD, TEM, UV-vis absorption spectra to study the characterizstics of the materials. The result shows that MOPPV and ZnSe quantum dots have effectively combined together and photoinduced charge transfer. Through the study of MOPPV, ZnSe, and MOPPV/ZnSe composite materal solar cell performance, we found that the composites exhibit an increasing trend compared with MOPPV, ZnSe monomer material photovoltaic characteristics, and the photoelectric properties of the composites showed an increase at first and then reduced with increasing quality of ZnSe quantum dots; when the ratio of MOPPV and the quality of the ZnSe is 1:1, its conversion efficiency reaches a maximum, The Voc, Isc, FF and conversion efficiency of solar cells were 0.516 V, 2.018 mA, 25.53%, and 0.167%.
An experimental method to measure W-J parameters
Authors: Chen Li-Ying  , Liu Xiu-Ru  , Li Ming-Fa  , Zhang Dou-Dou  , Wang Ming-You  , Hong Shi-Ming  ,   Laboratory of High Pressure Physics, Southwest Jiaotong University, Chengdu 610031, China;,   School of Science, Wuhan University of Technology, Wuhan 430070, China
Published: December 2020

The W-J equation of state proposed by Wu qiang and Jing fu-qian is a volume equation with pressure and temperature as the independent variables, which is mutually complementary to the Grneisen equation of state, and is extending and perfecting in theory of the equation of state. It is significant to determine the W-J parameters for the study and application of the equation. The W-J parameters can be educed from the Grneisen parameters and adiabatic bulk modulus, but it is difficult to take into account the uncertainty of these parameters. In this paper we explore a method of direct measurement of the W-J parameters. Temperature and pressure were recorded in situ during the rapid compression process, in which the rate of change in temperature was obtained, with pressure at midpoint pressure during the isentropic compression process, through correcting temperature and increasing substantially pressure combined with mean value theorem, and finally the W-J parameters were obtained according to equation R=(P/T) ( T/ P)S. No additional parameter was introduced in the whole process. In addition, as a comparison, the W-J parameters and their relationship with the pressure of sodium chloride were also calculated by using the equation of state, the empirical formula and known parameters. The results showed that the experimentally measured W-J parameters are increased with increasing pressure, and all the W-J parameters obtained by experiments are in good agreement with those by calculation. This suggests that the experimental method in rapid compression process is feasible and reliable for the direct measurement of the W-J parameters.
Canonical transform method for GPS/LEO radio occultation
Authors: Xu Xian-Sheng  , Guo Peng  , Hong Zhen-Jie  , Wu Jiang-Fei  ,   Ningbo Institute of Technology, Zhejiang University, Ningbo 315100, China;,   Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China;,   School of Mathematics & Information Science, Wenzhou University, Zhejiang 325027, China;,   Institute of Geospatial Information, Information Engineering University, Zhengzhou 450052, China
Published: December 2020

Under the atmospheric multipath conditions, both canonical transform (CT) and full spectrum inversion (FSI) method can solve the problem of calculating bending angle profiles within the multipath area. The atmospheric propagation of GPS signals under atmospheric multipath conditions is simulated using multiple phase screens (MPS) technique. Bending angle profiles computed by CT method are compared with corresponding solutions to Abel integral (taken as the true value). The results show that CT method is close to the true value in the multipath area. The retrieval accuracy of CT method is degraded to some extent when Gaussian noises are added to the phase of simulated signal. About 4500 COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) atmPhs profiles from DOY (day of year) 71 to DOY 73 in 2007 are retrieved by CT method. Statistical comparisons of the retrieved refractivity profiles, together with atmPrf data (retrieved by FSI method), with those from corresponding ECMWF (European Centre for Medium-Range Weather Forecasts) analysis show that CT method contains greater systematic negative bias than atmPrf data below 5 km. A possible reason is that the signal aperture is decreased for back-propagating the signal from LEO position to the back-propagation plane in CT method. The small aperture means low accuracy in the refractivity. The influence of signal truncation on both retrieval accuracy and occultation number is also discussed.
Melting and freezing behavior of aluminum nanoclusters with small size
Authors: Feng Dai-Li  , Feng Yan-Hui  , Zhang Xin-Xin  ,   Department of Thermal Science and Energy Engineering, University of Science and Technology Beijing, Beijing 100086, China
Published: December 2020

The melting and freezing behavior of small-sized aluminum nanoclusters with radii ranging from 0.3 nm to 1.3 nm are investigated by molecular dynamics simulation. Based on the potential-temperature curves and heat capacity-temperature curves, the size dependences of melting point and freezing point are obtained and the results are analysed by the surface energy theory and small size effect. The results show a non-monotonic size-dependence of the melting temperature when the atom number of nanoclusters is less than 80. For those clusters with atom number more than 80, the melting and freezing point drop down monotonically with size decreasing. For some special cases, such as aluminum nanoclusters with atom number 27, the melting point is nearly 40 K higher than the bulk melting point. Besides, we observe a rather strong hysterisis of the liquid-solid transition, which states that it is much easier for a cluster to go from ordered to disordered than for the opposite process.
Two-dimensional asynchronous fractional Fourier transform and propagation properties of beams in strongly nonlocal nonlinear medium with an elliptically symmetric response
Authors: Lu Da-Quan  , Hu Wei  ,   Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510631, China
Published: December 2020

Propagation of beams in strongly nonlocal nonlinear medium with an elliptically symmetric response is investigated. The result shows that the propagation of beams in this type of medium can be regarded as two-dimensional asynchronous fractional Fourier transform. With this powerful mathematical tool, the analytical solution and the propagation properties of beams can be conveniently obtained. Based on the properties of the two-dimensional asynchronous fractional Fourier transform, the general propagation properties of beams are discussed, the formation conditions of solitons and two-dimensional asynchronous breathers are analyzed, and the law for interaction among solitons and/or breathers is obtained.
Photonic band gaps of two-dimensional hexagon-lattice photonic crystals based on Taiji-shaped dielectric rods
Authors: Sheng Juan-Juan  , He Xing-Dao  , Liu Bin  , Li Shu-Jing  ,   Key Laboratory of Nondestructive Test (Ministry of Education), Nanchang Hangkong University, Nanchang 330063, China
Published: December 2020

We present a novel structure of two-dimensional (2D) hexagon-lattice photonic crystal with asymmetrical scatterers-Taiji-shaped scatterers. The properties of photonic band gap (PBG) and the influence of parameter on absolute photonic band gap are analyzed by plane wave expansion method. The calculation results demonstrate that the reduction of scatterer symmetry can produce an increase in the number of PBG and a broadening of PBG width for both TE and TM model, which is conducive to obtaining wider and more absolute PBG. By optimizing the parameters of structure, we obtain the widest absolute PBG 0.0541(ωa / 2πc) at ε = 17, R= 0.38 μm, r=0.36R, and θ = 0° and the maximum of 8 absolute PBGs at ε = 16, R=0.44, r=0.2R, and θ = 0°.
High-speed polarization controller for all-fiber quantum communication systems
Authors: Li Shen  , Ma Hai-Qiang  , Wu Ling-An  , Zhai Guang-Jie  ,   Laboratory of Space Science Experiment Technology, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190, China;,   Laboratory of Optical Physics, Institute of Physics, Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China;,   College of Physics, Beijing University of Posts and Telecommunications, Beijing 100876, China
Published: December 2020

Polarization control is of vital importance in optical communications, which can affect the stability and bit error rate of a system. We demonstrate an all-fiber high-speed polarization control scheme based on a bidirectional Sagnac ring. The polarization direction can be accurately controlled by adjusting the phase difference of an electro-optic fiber phase modulator in the ring, meanwhile it is realized that only a single beam port outputs different polarization states. The phase can be adjusted accuratly to 10-3 rad, giving an extinction ratio as high as 30 dB, and the modulation speed can reach 2 GHz. The system has excellent stability, and as the optical circuit consists of simple, low cost components which can be easily integrated, there are good prospects for its application in quantum cryptography and other optical communcations fields.
Experimental investigation on aero-optical aberration of the supersonic flow passing through an optical dome with gas injection
Authors: Zhu Yang-Zhu  , Yi Shi-He  , Chen Zhi  , Ge Yong  , Wang Xiao-Hu  , Fu Jia  ,   College of Aerospace Science and Material Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

During the flight in the atmosphere, the optical window of an optical dome needs to be cooled, and supersonic film cooling is one of the economic ways. After traversing through the complex flow field above the window, the optical wave would be distorted by fluctuations in the density field due to the expansion wave, shockwave, mixing layer, turbulent boundary layer, etc. The aero-optical aberrations induced by the flow field of an optical dome in the presence and in the absence of the gas injection at Mach 3.8 are investigated experimentally. Based on the nano-tracer planar laser scattering (NPLS) technique, the density field with high spatial-temporal resolution is first obtained by the flow image calibration, and then the optical path difference (OPD)fluctuations of the original 532 nm planar wavefront perpendicular to the window are calculated using Ray-tracing theory. Also the OPD fluctuations caused by the near-wall region flow structures are presented. In the absence of the gas injection, the flow structure is relatively simple with a long recirculation and laminar region, while in the presence of the gas injection, there appear more complex structures such as shear layer, mixing layer and turbulent boundary layer and the flow is converted into turbulence quickly. Clearly, the optical aberration in the presence of the gas injection is degraded more. For example, the values of root-mean-square OPD (OPDrms) in the absence of the gas injection are 0.038 μm and 0.0356 μm, and they are 0.0462 μm, and 0.0485 μm in the presence of the gas injection during the interval 5 μs.
Statistical feature of underwater target echo highlight
Authors: Chen Yun-Fei  , Li Gui-Juan  , Wang Zhen-Shan  , Zhang Ming-Wei  , Jia Bing  ,   Department of Ship Engineering, Dalian University of Technology, Dalian 116024, China;,   Science and Technology on Underwater Test and Control Laboratory, Dalian 116013, China
Published: December 2020

Clutter caused by reel and ocean animals is the primarily interference for active sonar. How to classify and identify underwater vehicle echo between reel and ocean animal echo is the most confusing problem that affects the performance of active sonar. Characterization and application mode of underwater target omnibearing echo characteristic are studied for the application of active sonar target identification. A method of estimating the acoustic scattering function based on highlight model is presented, through which underwater target acoustic echo characteristics could be well characterized by statistical feature, and the method is more suitable for the application in active sonar classification. Based on the method studied in this paper, statistical feature of echo highlight is extracted from lake acoustic scattering test of scalled benchmark submarine model.
Influence of growth conditions on the lateral grain size of AlN film grown by metal-organic chemical vapor deposition
Authors: Wu Liang-Liang  , Zhao De-Gang  , Li Liang  , Le Ling-Cong  , Chen Ping  , Liu Zong-Shun  , Jiang De-Sheng  ,   State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

In this paper, we investigate the effect of growth conditions on the quality of AlN film grown by metal-organic chemical vapor deposition. We test and analyze the influence of different growth conditions, such as nitridation time, growth time of AlN buffer layer and the flow rate of carrier gas, on the lateral grain size of AlN film. It is found that the redution of nitridation time, the increase of growth time of AlN buffer layer, and the reduction of the flow rate of carrier gas can enhance the lateral growth of AlN film and coalescence of islands and increase the lateral grain size of AlN film. So the quality of AlN film is improved.
Elastic and optical properties of IVB group transition-metal nitrides
Authors: Wang Jin  , Li Chun-Mei  , Ao Jing  , Li Feng  , Chen Zhi-Qian  ,   School of Materials Science and Engineering, Southwest University, Chongqing 400715, China
Published: December 2020

The elastic and optical properties of face-centered cubic IVB group transition metal nitrides such as TiN, ZrN, and HfN are calculated using the plane wave pseudopotential method based on first-principle density function theory. Electronic property is a combination of covalent, ionic, and metallic property. And band structures of these compounds show metallicities in the ground state. The obvious numerical differences between E[100] and E[111] indicate elastic anisotropy. The phenomena result in lattice distortions and microcracks in these metal nitride films. With red shift of pseudogap, the metallic properties of TiN, ZrN, and HfN are improved in turn. And the elastic and optical properties change with metallic properties improving:brittleness reduces, the degree of anisotropy increases, the critical energy between intraband and interband transitions increases, and the solar-optical selectivity decreases. So reducing the number of conduction electrons to strengthen covalency is an effective method to improve elastic isotropy and optical selectivity.
First-principles study of pressure induced phase transition, electronic structure and elastic properties of CdS
Authors: Zhou Ping  , Wang Xin-Qiang  , Zhou Mu  , Xia Chuan-Hui  , Shi Ling-Na  , Hu Cheng-Hua  ,   School of Physics, Chongqing University, Chongqing 401331, China;,   School of Science, Chongqing Jiaotong University, Chongqing 400074, China
Published: December 2020

In this work, phase stabilities, phase transitions, electronic structures and elastic properties of wurtzite structure (WZ), zinc-blende structure (ZB) and rocksalt struture (RS) phase of CdS are studied by first principles method. Results indicate that WZ and RS phases could be stable in corresponding pressure areas. However, ZB phase could not be stable. Pressure-induced metallic phase transition from WZ to RS will occur at 2.18 GPa. Electronegativity of S atom in WZ phase is much more than that of Cd atom, and the difference in electronegativity between S and Cd is less than 1.7, which induces covalent crystal of CdS. Under the condition of high pressure, radius of S is reduced sharply, which causes the increase of effective nuclear charge. Large nuclear charge will enhance the ability to attract electrons of outer shell, which will cause larger electronegativity. When pressure is higher than 2.18 GPa, the difference in electronegativity is more than 1.7. Then, CdS will be ionic crystal. C44 of WZ phase decreases with pressure, resulting in mechanical instability. And then,the WZ-to-RS phase transition occurs at 2.18 GPa. Moreover, C11 and C12 of RS phase increase with pressure. At the same time, C44 of RS is stable with pressure increasing entirely, all of which shows that RS phase has excellent stability and mechanical property under high pressure.
Time of spin-polarized tunneling through a symmetric double-barrier quantum well structure
Authors: Wang Rui-Qin  , Gong Jian  , Wu Jian-Ying  , Chen Jun  ,   School of Physics Sciences and Technology, Inner Mongolia University, Hohhot 010021, China
Published: December 2020

Tunneling time is an important factor to describe quantum electronic device. In this paper, the dynamic problem of spin-dependent tunneling is investigated by solving the time-dependent Schrödinger equation. The transmission coefficient and tunneling lifetime are discussed by use of mixing transfer-matrix and Runge-Kutta method. The k3 Dresselhaus term is considered to correct the effective Hamiltonian of the system in our calculation. The results show that the transmission peak of the electrons with different spin orientations split obviously. The building time and the tunneling lifetime through the double-barrier structure of AlxGa1-xSb material are different for the spin-down electron and spin-up electron. These time-dependent properties depend on the electronic spin orientation. It can be considered as one of reasons for spin polarization to appear. Additionally, the steady spin-polarization emerges in the well due to the k3 Dresselhaus spin-orbit coupling.
Dielectric modulus response of CaCu3Ti4O12 ceramic
Authors: Li Sheng-Tao  , Wang Hui  , Lin Chun-Jiang  , Li Jian-Ying  ,   State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

The DC conductivity of the CaCu3Ti4O12 ceramic is considerable at low frequency. The dielectric properties of the CaCu3Ti4O12 ceramics are analyzed by dielectric spectrum, and the two relaxation processes are characterized by the dielectric modulus. The two relaxation processes are considered which are dominated by the electronic relaxation of deep bulk traps at the depletion layer edge. The low-frequency and high-frequency relaxation processes are attributed to oxygen-vacancy-related defect and native defect, respectively. It is proved that the modulus response of the CaCu3Ti4O12 ceramic is equivalent to conductivity response at high temperature (low frequency), and the peak value of the M" is inversely proportional to capacitance. The activation energies calculated by conductivity and modulus are equivalent to each other. The modulus spectrum is more effective to the material which has high DC conductivity at low frequency such as CCTO ceramic.
Using scattered light to amplify the photoacoustic spectroscopic signatures of the main absorbing material in a weakly light-absorbing solid mixture
Authors: Yu Rong  , Jiang Yue-Song  , Yu Lan  , Ou Jun  ,   School of Electronic Information Engineering, Beihang University, Beijing 100191, China;,   School of Pharmaceutical, Lanzhou University, Lanzhou 730000, China
Published: December 2020

Scattered light by the sample is usually one of the main error source in conventional transmission spectroscopy and diffuse reflection spectroscopy. However, scattered light may be useful for photoacoustic spectroscopy measurement. In the present experiment, the photoacoustic spectra of an olanzapine drug tablet and its powder are studied. The olanzapine tablet is a weakly light-absorbing solid mixture and its main constituent is olanzapine. In order to eliminate the background signal produced by the photoacoustic cell wall due to absorbing the scattered light by the sample, the difference between the photoacoustic spectrum of the sample and that of its base is taken and normalized with the photoacoustic spectrum of carbon black. It is found that the photoacoustic spectroscopic signatures of olanzapine in the olanzapine table become obvious when the olanzapine table is powdered. This is the result of the internal light scattering effect in the sample. The scattered light which serves as an obstacle in conventional optical spectroscopy techniques, however, facilitates the photoacoustic spectroscopy measurement. This indicates the particular advantage of photoacoustic spectroscopy. A new method to preliminarily fast identify the main absorbing component in a weakly light-absorbing solid mixture is proposed based on the above experiment. This method can be applied to the field of solid drug and mineral and soil and so on.
Microcalcification clusters processing in mammograms based on relevance vector machine with adaptive kernel learning
Authors: Yao Chang  , Chen Hou-Jin  , Yang Yong-Yi  , Li Yan-Feng  , Han Zhen-Zhong  , Zhang Sheng-Jun  ,   School of Electronics and Information Engineering, Beijing Jiaotong University, Beijing 100044, China;,   Department of Electrical and Computer Engineering, Illinois Institute of Technology, Chicago IL 60616, USA
Published: December 2020

Using the method of adaptive kernel learning based relevance vector machine (ARVM) and combining the morphological filtering and the clustering criterion recommended by Kallergi, a new algorithm for microcalcification (MC) clusters processing in mammograms is investigated. Firstly, the detection of MC is formulated as a supervised-learning problem. Then the ARVM is used as a classifier to determine whether an MC object is present at each location in the mammogram and a morphological processing is used to remove the isolated spurious pixels. Finally, the identified MC clusters are obtained by Kallergi criterion. To improve the computational speed, a fast processing method based on ARVM is developed, in which the whole image is decomposed first into sub-image blocks for parallel operation. Experimental results indicate that the ARVM method outperforms the RVM method and, in particular, the fast processing method could greatly reduce the testing time.
Exact solutions to the nonlinear diffusion-convection equation with variable coefficients and source term
Authors: Wan Hui  ,   Center for Nonlinear Studies, Department of Mathematics, Northwest University, Xi'an 710069, China
Published: December 2020

The nonlinear diffusion-convection equation f(x)ut=(g(x)D(u)ux)x+h(x)P(u)ux+q(x)Q(u) with variable coefficients and source term has been studied. This equation is symmetrically reduced by the generalized conditional symmetry method. Some exact solutions to the resulting equations are constructed, with the diffusion terms D(u)=um (m≠-1,0,1) and D(u)=eu. These exact solutions are also the generalized functional separable solutions. Solutions to the equation with constant coefficients are covered by those exact solutions to the equation with variable coefficients.
General Hojman's method for the construction of Birkhoffian representation
Authors: Cui Jin-Chao  , Zhao Zhe  , Guo Yong-Xin  ,   School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081, China;,   School of Medical Devices, Shenyang Pharmaceutical University, Shenyang 110016, China;,   College of Physics, Liaoning University, Shenyang 110036, China
Published: December 2020

We have investigated the internal relation among the first integral, Hojman's method and Birkhoff's equations. There is a special equivalent relationship between Birkhoffian and Birkhoffian functions constructed by Hojman's method, and from this we can derive a more general form of Hojman's method. Then, combining the special equivalent relationship and Birkhoff's equations, we can derive the cyclic integral in Birkhoffian sense. An example is given to illustrate the application of the results.
Optimum valence bond scheme for its applications to the prediction of nano-structures and the study of matter properties
Authors: Gao Xiang  , Chen Xiao-Bo  , Li Jun  , Li Jia-Ming  ,   Beijing Computational Science Research Center, Beijing 100084, China;,   Department of Physics and Center for Atomic and Molecular Nanosciences, Tsinghua University, Beijing 100084, China;,   Department of Physics and Joint Center for Inertial Fusion Science and Application of China, Shanghai Jiao Tong University, Shanghai 200240, China;,   Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China
Published: December 2020

The optimum valence bond scheme is a new theoretical method in generating the initial geometric configurations in molecular dynamics simulations of cluster systems. We will present the application of such a new method to the prediction of nano-structures and the study of matter properties, especially for the low-dimensional nano-structures, such as clusters and nano wires. The optimum valence bond scheme uses the atomic geometry of structures and the space distribution of the valence electrons (mainly the molecular orbitals near the Fermi levels, i.e., the generalized frontier orbitals) to determine the possible stable geometric configurations of nano-structures. Silicon clusters are used to demonstrate the features of the optimum valence bond scheme. Metallic clusters such as those of lithium, sodium, beryllium and magnesium are used as examples to illustrate the application of the scheme to the prediction of structures and the studies of the evolution of the material properties with the sizes of clusters. We will use the adsorption process of lithium ion and MoS nano wire to illustrate the application of the optimum valence bond scheme in the studies of the ionic conduction mechanism of the energy storage materials. We will finish the paper by summarizing the direction for further development of the optimum valence bond scheme.
The development of femtosecond laser-induced periodic nanostructures and their optical properties
Authors: Peng Na-Na  , Huo Yan-Yan  , Zhou Kan  , Jia Xin  , Pan Jia  , Sun Zhen-Rong  , Jia Tian-Qing  ,   State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062, China
Published: December 2020

Micromaching by using femtosecond laser has been developing rapidly. This paper introduces the main developments in the last ten years on the formation mechanisms of periodic ripples in metals, semiconductors, and dielectrics induced by femtosecond lasers. By combining the methods of multi-beam interferences with the self-organized periodic nanostructures, two-dimensional periodic complex nanostructures can be fabricated on the surface of semiconductors. Compared with that of plane surface, the photoluminescence of nanostructures increases greatly.
Third-order aberrations of a plane symmetric optical system
Authors: Sun Jin-Xia  , Pan Guo-Qing  , Liu Ying  ,   China Airborne Missile Academy, Luoyang 471009, China;,   Aviation Key Laboratory of Science and Technology on Airborne Guided Weapons,Luoyang 471009, China;,   Opto-electricity Technology Research Center, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
Published: December 2020

The wave aberration theory of non-symmetrical optical systems is useful for understanding the misalignment in symmetrical systems and designing of off-axis mirror systems. A theory about the third-order aberrations for sub-aperture plane symmetric optical system is developed by using the aberration theory for full-aperture axially symmetric spherical systems. This paper proves the nodal aberration theory, namely, the points in the field with zero third-order aberration will deviate from the field center except for spherical aberration. It also reveals that the nodal aberrations arise from the transformation of the aberrations in full-aperture systems. This theory can be efficiently used in non-symmetric optical system designing process.
Measuring the diffusion coefficient of liquids by capillary imaging method: equivalent refractive index method
Authors: Li Qiang  , Pu Xiao-Yun  ,   Department of Physics , Yunnan University, Kunming 650091, China
Published: December 2020

A novel method for measuring the diffusion coefficient of liquids is introduced in this paper. A transparency capillary is used as both diffusive pool and imaging element, spatially resolving ability of the capillary in measuring refractive index of liquid is utilized to observe and record diffusive process directly, diffusion coefficient of liquid is calculated based on Fick second law and acquired experimental data. With the new method, the diffusive process of pure glycerol in water at 25 ℃ is investigated, the obtained diffusion coefficient is 0.898×10-5 cm2/s, which is of a relative error 4.47% compared with the literature value measured by the holographic interference. The influence of measurement accuracy of refractive index and capillary viscosity on measuring result is also analyzed. The method is characterized by micro-quantity sample required, faster measurement and better stability, which opens a new way to measure diffusion coefficient of liquid medium.
Dynamical model of non-chain pulsed DF laser
Authors: Ruan Peng  , Xie Ji-Jiang  , Pan Qi-Kun  , Zhang Lai-Ming  , Guo Jin  ,   Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, State Key Laboratory of Laser Interaction with Matter, Changchun 130033, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Based on the reaction mechanism of non-chain pulsed DF laser and taking into consideration the deactivation of the stimulated DF molecules by ground state DF molecules, D2 molecules, D atoms, F atoms, the dynamical model for non-chain pulsed DF laser is established using the rate equation theory. Through solving this model with Runge-Kutta method, the dependence of species concentration in the gain area on time is obtained. Then the effects of the working gas ratio and the reflectance of output mirror on photon number density, single pulse energy, pulse width and output power are studied in light of this model. The optimum parameters of the working gas ratio and the reflectance of output mirror are attained based on the theoretical calculation. The pulse waveform and single pulse energy of non-chain pulsed DF laser calculated by using the rate equations theory agree well with experimental data based on electric-discharge. These results would provide a theoretical support for the optimization of non-chain pulsed DF laser.
The wavelength tunable 589 nm laser output based on singly resonant sum-frequency generation and the measurement of saturate fluorescence spectrum of sodium atom
Authors: Tan Wei  , Fu Xiao-Fang  , Li Zhi-Xin  , Zhao Gang  , Yan Xiao-Juan  , Ma Wei-Guang  , Dong Lei  , Zhang Lei  , Yin Wang-Bao  , Jia Suo-Tang  ,   Laser Spectroscopy Laboratory of Shanxi University, State Key Laboratory of Quantum Optics and Quantum Optics Devices, Taiyuan Shanxi 030006, China
Published: December 2020

A wavelength-tunable laser output at 589 nm with high conversion efficiency based on sum-frequency generation by using the technique of single-wavelength extra-cavity resonance is achieved. The two fundamental wavelengths are 1583 nm and 938 nm and the nonlinear crystal is the period-poled lithium niobate. After the frequency of 1583 nm laser was locked to the cavity mode and the frequency of 938 nm laser was scanned, a 589 nm laser output with power of 4.96 mW and wavelength tuning range of 7 GHz was obtained and the stability of the output power is improved effectively with the help of servo feedback loop technique of acousto-optic-modulator. Finally, based on this laser, the saturated fluorescence spectrum of sodium D2 line in the temperature range of 348—413 K (75—140 ℃) were measured. The Doppler-free structures of D2a, D2b and crossover lines on Doppler background were observed, which can provide reference signals for the frequency locking of 589nm laser.
Investigation on the correction of the Mie scattering lidar's overlapping factor and echo signals over the total detection range
Authors: Di Hui-Ge  , Hua Deng-Xin  , Wang Yu-Feng  , Yan Qing  ,   School of Mechanical and Precision Instrument Engineering, Xi'an University of Technology, Xian 710048, China
Published: December 2020

There has been great difference between the theoretical signals of the lidar's echo and its actual signals, due to the angles between the laser beam and its receiving optical axis, and the laser intensity distribution being asymmetrical. So the correction of the echo signal is necessary. According to the mathematical derivation and the software simulation, the mathematical expression of the lidar's overlap factor is given, and the overlap factor curves with detection range are drawn which express the characters over the total detection range, then the best angle between lidar's emitting axis and the receiving axis is obtained. The overlap factors are analyzed when the laser is Gaussian with a uniform intensity distribution. The lidar distance correction signal and Klett formula are corrected by the overlap factor, and the instrument parameters of the lidor are measured. In the range where the overlap factor is not zero, its correction echo signals and extinction coefficients can be obtained by using the corrected Klett formula. While in the range of the lidar's blind zone, the signals can be derived by a slope method. Finally, the total correction curve of the extinction coefficients is gained, and it is in accordance with the actual one correction cuive.
A study of two-dimensional hexagonal phase array grating in MgO:LN based on the Talbot effect
Authors: Fan Tian-Wei  , Chen Yun-Lin  , Zhang Jin-Hong  ,   School of Science, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

In this paper, theoretical researches on the MgO:LN tunable hexagonal phase array grating based on the Talbot effect were presented. Researches revealed the effects on the intensity distribution of near-field diffraction from array grating duty cycle which is defined as D, phase difference which is defined as Δφ and the distance coefficient which is defined as β. The results obtained show that good near-field diffraction images can be achieved at D=52%, Δφ=0.75π, β=0.2. Based on the theoretical researches, the tunable hexagonal phase array grating is designed and fabricated from periodically poled MgO:LN crystal. Through experimental test, the Talbot effect diffraction imaging map is successfully obtained at different Δφ and β, which verifies the results of the theoretical researches.
Displacement damage effects on the characteristics of quantum dot lasers
Authors: Che Chi  , Liu Qing-Feng  , Ma Jing  , Zhou Yan-Ping  ,   National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

We have anelyzed the displacement damage effects on quantum dot lasers theoretically and deduced the relation between the radiation-induced threshold current change and the neutron fluence. The neutron radiation experiment for quantum dot lasers are also carried out to examine the displacement damage coefficient of the non-radioactive recombination rate. The formula fits the experimental data very well, and can describe the trend of the laser performance under electron irradiation. It can also predict the behavior of quantum dot lasers under radiation environment and is valuable for practical application.
Nonlinear interaction between ultrasound and solid rough interface
Authors: Xiao Qi  , Wang Jun  , Guo Xia-Sheng  , Zhang Dong  ,   Key Lab of Modern Acoustics (MOE), Institute of Acoustics, Nanjing University, Nanjing 210093, China
Published: December 2020

The interaction of ultrasound with an interface between two rough surfaces in contact has become a quite popular topic in many areas related to non-destructive evaluation (NDE). We proposed a theory of ultrasonic nonlinear interaction between some random rough elastic interfaces. The model of random elastic-contact interface is first described, and then the nonlinear ultrasonic interaction of interfaces with stress-strain relationship is studied, by using different models including linear simplified model, exponential model, and Gaussian model. Results of numerical simulations and experiments demonstrate that the Gaussian model is more suitable for describing the solid rough interfaces. This study provides an explanation of the ultrasonic interaction on mesoscopic level, which is a theoretical basis for practical application to detect cracks, defects and injuries in industrial ultrasonic NDE.
A coupled-mode method for sound propagation in a range-dependent penetrable waveguide
Authors: Yang Chun-Mei  , Luo Wen-Yu  , Zhang Ren-He  , Qin Ji-Xing  ,   State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The coupled-mode method based on the direct global matrix (DGMCM) approach for sound propagation in range-dependent waveguides [Luo et al., "A numerically stable coupled-mode formulation for acoustic propagation in range-dependent waveguides," Sci. China-Phys. Mech. Astron. 55, 572 (2012)] is further developed. The normal mode model KRAKEN is adopted to provide local modal solutions and their associated coupling matrices. As a result, the model DGMCM is capable of providing full two-way solutions for the two-dimensional realistic problems characterized by a penetrable bottom and a depth-varying sound speed profile. In addition, the closed-form expressions of coupling matrices for sound propagation in a range-dependent, two-layer waveguide are proposed. The numerical solutions of the coupling matrices by DGMCM agree well with the analytical solutions. Sound propagation in a penetrable wedge is solved by the updated DGMCM model. The numerical results indicate that the updated DGMCM model is numerically stable and accurate, and can provide benchmark solutions for realistic range-dependent problems.
Studies on mode feature extraction and source range and depth estimation with a single hydrophone based on the dispersion characteristic
Authors: Li Kun  , Fang Shi-Liang  , An Liang  ,   Key Laboratory of Underwater Acoustic Signal Processing of Ministry of Education, Southeast University, Nanjing 210096, China
Published: December 2020

A method of range and depth estimation was studied using a single hydrophone based on the dispersive characteristic and time-frequency analysis for low frequency underwater acoustic pulse signals in shallow water environment. First, the signal received on a single hydrophone can be decomposed into a series of modes within the frame work of normal mode theory, and then the dispersive characteristic of the propagating modes can be analyzed using the time-frequency analysis. In order to improve the time-frequency resolution, the use of the time-frequency distribution with adaptive radial-Gaussian kernel extracts the arrival time difference of propagating modes in dispersion curve, which can be used to estimate source range. Mode energy can be extracted using binary time-frequency mask filtering based on multi-mode joint matching processing; and the source depth can be estimated by comparing the differences of the mode energy of the real data and simulated replica data, yielding a contrast function. Simulation results from a shallow-water Pekeris waveguide show that the time-frequency distribution with adaptive radial-Gaussian kernel represents well the dispersion characteristics of the underwater acoustic pulse signals, provides higher time-frequency resolution and overcomes the problem of the inherent limit for the time resolution and frequency resolution in the traditional short-time Fourier transform, so that the modes can be separated and identified more easily in the time-frequency plane. From the result of the range estimation, the different mode combinations have different results of the range estimation. The range estimation result can be obtained accurately by using the mode with high energy in the time-frequency plane. The relative error in range estimation is less than 2% by using the mode with high energy. In terms of the depth estimation, the more the number of joint matching mode, the more sharp peak and low fake peaks the contrast function has, so that the depth estimation is further improved by incorporating more modes. This research has great significance for studying the extraction and separation of low frequency underwater acoustic pulse signals.
Experiments on defect mode of one-dimensional phononic crystal containing Helmholtz resonators
Authors: Gao Dong-Bao  , Zeng Xin-Wu  , Zhou Ze-Min  , Tian Zhang-Fu  ,   College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

In this paper, a local resonant phononic crystal is designed and fabricated based on Helmholtz resonators. Experiment is carried out to study the defect mode of the structure, in which a point defect is introduced. Due to the coupling of the defect cell and perfect cells, a narrow pass band appears in the local resonant forbidden band. Meanwhile, acoustic energy localization effect is observed around the defect resonator at the frequency of defect mode which changes with the defect parameter. However, the defect mode is close to the edge of the forbidden band, the localized energy is high. In addition, if the resonant frequency of the defect unit is smaller than that of the perfect unit, the localized energy is mostly distributed in the waveguide. In contrast, the energy is mostly localized in the resonators when the defect unit frequency is larger than that of the perfect unit. This work will be of help for designing new acoustic functional devices of filters and concentrators.
A testing method for assembled performances of helix slow-wave structure with a supported rod
Authors: Wei Pu  , Zhou Ming-Gan  , Zhu Lu  , Zhang Jing  , Wang Xue-Feng  , Lv Dong-Ya  , Cheng Ning  , Yang Ming-Hua  , Sun Xiao-Han  ,   Research Center for Reliability of Electronic Devices and Systems, Southeast University, Nanjing 210096, China;,   Beijing Vacuum Electronic Research Institute, Beijin 100015, China
Published: December 2020

In this paper, a novel testing method for the assembled performances of the helix slow-wave structure (SWS) with a supported rod is proposed based on heat distribution of SWS. A distributed temperature testing platform using fiber Bragg grating (FBG) and thermocouple is designed, and the influence of thermal sensors on the heat dissipation capability of the SWS is analyzed means of ANSYS. The experimental system including a distributed micro FBG sensor array is set up to test the assembled performance of SWS of the X-band TWT. The results show that the assembled performances of the SWS can be effectively obtained by the tested curve of temperature difference.