bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical studies on the radiative electron capture and subsequent radiative decay in the collision of Xe53+ ions with neutral Xe
Authors: Liang Teng  , Ma Kun  , Wu Zhong-Wen  , Zhang Deng-Hong  , Dong Chen-Zhong  , Shi Ying-Long  ,   Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China;,   School of Information Engineering, Huangshan University, Huangshan 245041, China;,   Department of Physics, Tianshui Normal University, Tianshui 741000, China
Published: December 2020

The radiative electron capture (REC) and subsequent radiative decay of initial hydrogen-like Xe52+ ions are studied in the collision of Xe53+ with Xe atom at a projectile energy of 197 MeV/u within the framework of the multiconfiguration Dirac-Fock method and the density matrix theory. We calculate the differential and total cross sections as well as the REC photon energies for REC to the 1snp1/2, 3/2 Jf=1 (n=2-5) levels of finally helium-like Xe53+ ions. Moreover, the transition energies and rates of the subsequent 1snp3/2 Jf=1 1s2 Jd = 0 decay as well as the angular distribution and linear polarization of the associated characteristic photons are also calculated. It is found that the REC photons are remarkably anisotropic. Through the analysis of the REC angular distribution characteristics, we find that the different configurations of the REC angular distribution are similar in quality, and they all have a peak at the 90. That is to say, the REC process can more easily occur in the direction perpendicular to the incident direction of the projectile ions. In addition, while the characteristic photons from the subsequent 1snp3/2 Jf=11s2 Jd= 0 radiative decay of Xe52+ ions exhibit an anisotropic angular distribution and strong linear polarization, their counterparts from the 1snp1/2 Jf = 1 1s2 Jd = 0 decay are almost isotropic and linearly unpolarized. The angular distribution and linear polarization of the radiation photon decay from the (1s np1/2,3/2 Jf = 0) states to the ground state（1s2 Jd = 0）both reach a maximum value at the 90, their characteristics are similar to those of the REC photons, that is to say, the deexcited process can more easily occur in the direction perpendicular to the incident direction of the projectile ions, and in this direction the decay photons have much larger polarization degree.
Theoretical investigation on a kind of time-dependent Bessel beam
Authors: Yue Yang-Yang  , Zhang Xing-Yu  , Yang Bo  , Lu Rong-Er  , Hong Xu-Hao  , Zhang Chao  , Qin Yi-Qiang  , Zhu Yong-Yuan  ,   National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, Key Laboratory of Modern Acoustics, Nanjing University, Nanjing 210093, China;,   College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China;,   School of Physics, Nanjing University, Nanjing 210093, China
Published: December 2020

Non-diffracting beams have been a hot topic since the Airy wave packet was introduced to optics domain from quantum mechanics. Great efforts have been made to study this theme in recent years. The researches have ranged from paraxial regime to non-paraxial regime, and a series of new non-diffracting beams have been discovered. However, most of these beams are obtained under the time harmonic condition. To break this limitation, we propose a concept of time-dependent Bessel beam in this paper, which generalizes the non-diffracting beams to non-time-harmonic regime.We start from Maxwell's equations in vacuum under non-paraxial condition using the method borrowed from the half-Bessel beam. To obtain the non-time-harmonic solution, the fourth dimensional imaginary coordinate is introduced, which refers to the covariance in the theory of special relativity. By solving the wave equation without the time harmonic condition, we obtain the analytical expression for a time-dependent beam in the form of Bessel functions. Thus we call it time-dependent Bessel beam.The diffraction properties and space-time characteristics of the time-dependent Bessel beam are investigated theoretically. The transverse intensity and the intensity distribution of the beam are calculated and discussed in detail. The wave function of the time-dependent Bessel beam is in the same form as the normal Bessel beam so that it can exhibit non-diffraction in the four dimensional space-time. When propagating along a space-time hyperbolic trajectory, the intensity of the time-dependent Bessel beam remains constant and the width of the beam decreases with propagating distance and time increasing. Besides, we deduce the critical condition of the spatiotemporal characteristics of the beam, and the result agrees well with the concept of the light cone in the theory of special relativity.The method to deduce the time-dependent Bessel beam used in this paper is universal, and it will provide a valuable access to other solutions for the wave equations under different conditions. We extend the study of non-diffracting beams from time harmonic regime to non-time-harmonic regime. Furthermore, our work demonstrates the relation between the non-diffracting accelerating beams and the theory of special relativity. We believe this work will open up a new vista and give a new insight into the research of non-diffracting accelerating beams or other relevant research fields.
Analysis of the symmetry of the ambient noise and study of the noise reduction
Authors: Xia Hui-Jun  , Ma Yuan-Liang  , Liu Ya-Xiong  ,   School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China;,   Key Laboratory of Ocean Acoustics and Sensing of Ministry of Industry and Information Technology, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Acoustic environment has a low signal-to-noise ratio (SNR); hence, array signal processing is widely used for noise reduction and signal enhancement. The actual ambient noise includes uncorrelated noise and correlated noise. The received noises of the two arbitrary array elements are correlated. Consequently, the performance of array signal processing method decreases obviously. Aiming at this problem, the real-part elimination of covariance matrix method is proposed. Firstly, from a physical point of view, the noise signals can be generated by using a number of uncorrelated noise sources: the more the noise sources, the less the error between the noise from the model and the actual noise will be. Theoretically, the noise field is decomposed into the symmetrical noise field and the asymmetrical noise field. A number of noise sources generate the symmetrical noise fields; the directions of these noise sources are symmetric, and the powers of two arbitrary symmetric sources are the same. Secondly, the symmetry of the ambient noise is analyzed, as a result, the symmetrical noise can only affect the real part of the covariance matrix. Thirdly, the real part of covariance matrix is eliminated in order to reduce the noise, and then the delay-and-sum beamforming is achieved by using only the imaginary part. The advantages are that the output signal-to-noise ratio is increased and the noise output power is reduced obviously; the disadvantage is that it produces a false target. The azimuth of the actual target differs from that of the false target by 180, and the false target cannot be distinguished. Finally, to eliminate the false target, the real part of the signal covariance matrix is reconstructed by establishing a constrained optimization problem, which is solved by using the particle swarm algorithm. Then, the reconstructed covariance matrix composed of the imaginary part and the reconstruction of real part is applied to delay-and-sum beamforming, as a result, the false target is eliminated. The simulation results show that the real-part elimination of covariance matrix method reduces the symmetrical ambient noise, the noise output power is reduced, the output signal-to-noise ratio is increased, and this method improves the performance of array signal processing. The experimental results show that the output SNRs of two targets with using the imaginary part of covariance matrix are increased by 3.57 dB and 3.149 dB, respectively, and the output SNRs of two targets with using the reconstructed covariance matrix are increased by 7.027 dB and 6.985 dB, respectively. The real-part elimination of covariance matrix method is easy to implemente, and has a definite value for engineering application.
Array gain of conventional beamformer affected by structure of acoustic field in continental slope area
Authors: Xie Lei  , Sun Chao  , Liu Xiong-Hou  , Jiang Guang-Yu  ,   School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Conventional beamforming (CBF) is an important processing step in underwater array signal processing. Previous researches have shown that the sound field structure as manifested by amplitude nonhomogeneity and wave-front corrugation can reduce the array gain of CBF. The acoustic environment of the continental shelf slope area is very complex. For an underwater acoustic array in this area, the amplitude and phase of the received signals will be distortional seriously. Recently, the acoustic field correlation has been the focus of research on the array gain relations with the underwater acoustic filed. However, the attenuation of acoustic field correlation is not the only factor that induces the array gain to decline, and the analyses of the array gain in the shallow water based on normal-mode model are not applicable to the continental slope area. In this paper, the array gain relations with the structure of acoustic field in continental slop area are investigated based on the theory of underwater acoustic signal propagation. The effects of acoustic field on the signal and noise gains are considered respectively. The analytic expressions of the array gain of CBF in an isotropic noise field are derived from the primal definition of array gain, which indicates that acoustic field correlation and transmission loss in continental slope are the intrinsic factors that affect the array gain of CBF. A horizontal uniform linear array (ULA) with a wide aperture receiving signals from a source in the deep water region is considered in the upslope propagation condition. The RAM program is utilized in the numerical simulations to generate the sound field of this specific environment with given parameters. The array gains, the ATLs and the horizontal longitudinal correlation coefficients of the acoustic field corresponding to three different locations are compared. Conclusions can be drawn as follows. 1) The array gain of CBF is determined by acoustic field correlation and the acoustic average transmission loss (ATL), and its maximum is less than 10lg M as the signal waveform distortion. 2) when the ATLs corresponding to hydrophones at two different receiving locations are similar, the correlation of acoustic filed is higher, and the array gain of CBF is larger. 3) When the ATLs corresponding to hydrophones at two different receiving locations are greatly different, the relation between the array gain of CBF and the acoustic filed correlation is no longer positive. The simulation results verify the array gain of CBF relations with the acoustic filed correlation and the transmission loss in the continental slope area.
Site preference in isoelectronic Heusler alloy Fe2RuSi
Authors: Xin Yue-Peng  , Ma Yue-Xing  , Hao Hong-Yue  , Meng Fan-Bin  , Liu He-Yan  , Luo Hong-Zhi  ,   School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130, China
Published: December 2020

The site preference, electronic structure, and magnetism of Heusler alloy Fe2RuSi are investigated theoretically and experimentally. The magnetic and electronic properties of Heusler alloys are strongly related to the atomic ordering and site preference in them. Usually, the site preference of the transition metal elements is determined by the number of their valence electrons. However, the recent results suggest that some new possible factors such as atomic radius should also be considered. Here we compare the phase stabilities of several different atomic orderings like XA, L21, DO3, L21B in Fe2RuSi, in which Fe and Ru atom have 8 valence electrons each, thus the influence of number of their valence electrons can be omitted. First-principles calculations suggest that Ru atom prefers entering sites A and C in the lattice. In ground state, the most stable structure is of XA type, in which Fe and Ru atoms occupy A and C sites, respectively and the second stable structure is L21B type, in which Fe and Ru atoms occupy A and C sites randomly. With Ru atom entering into the B site, the total energy increases rapidly. Thus there is still a strongly preferable occupation of Ru though Fe and Ru atom are isoelectronic. This confirms that the valence electrons rule may be not enough to determine the site preference of the transition metal element in Heusler alloy. The preferable occupation of Ru atom in Fe2RuSi can be explained from the electronic structure. It is found that in the XA DOS, there is strong hybridization between the electrons of the nearest Ru and Si or Fe (B) atom. However, in the high energy L21 structure the hybridization between Ru and the nearest Fe (A, C) is weak, which reduces its phase stability. This is confirmed further by the charge density difference calculation. Single phase Fe2RuSi with a lattice parameter of 5.79 is synthesized successfully. Comparing the superlattice reflections (111) and (200) in the experimental XRD pattern with those in the simulated patterns for different structures, we find that Fe2RuSi crystallizes in L21B structure rather than the most stable XA one at room temperature, which mainly originates from the contribution of mixed entropy to the free energy, and its caused atomic disorder at high temperatures. This disorder can be retained during the cooling procedure, while it does not influence the conclusion that Ru atom prefers the (A, C) sites in Fe2RuSi strongly. Finally, the saturation magnetization Ms at 5 K is 4.87 B/f.u., which agrees well with the theoretical result. The large total magnetic moment mainly comes from the contributions of Fe, especially Fe magnetic moments on B sites.
Oscillatory frequencies in spatiotemporal system with local inhomogeneity
Authors: Gao Ji-Hua  , Shi Wen-Mao  , Tang Yan-Feng  , Xiao Qi  , Yang Hai-Tao  ,   Key Laboratory of Special Functional Materials of Shenzhen, College of Materials, Shenzhen University, Shenzhen 518060, China
Published: December 2020

Target waves usually emit concentric circular waves, whereas spiral waves rotate around a central core (topological defect) region, the two forms of waves are closely related due to the similarity of their spatial structures. Spiral waves can be generated spontaneously in a homogeneous system, while target waves usually cannot be self-sustained in the same system. Therefore, spiral waves can be found in diverse natural systems, and target waves can be produced from the spirals with special boundary configurations or central pacemakers. The pacemaker of target wave is an oscillatory source or medium inhomogeneity. To model the inhomogeneity in some realistic situations, we introduce local parameter shifts and simulate the transition from spiral waves to target waves. In this research, the evolution of the spiral waves in the complex Ginzburg-Landau equation is investigated by numerical simulations, and the multi-spiral patterns can be transformed into stable target waves with local inhomogeneous parameter shifts in a two-dimensional (2D) spatiotemporal system. The detailed study shows that the initial multi-spiral waves can be influenced by introducing inhomogeneity in the local area of the system space, and the oscillatory frequency of the system plays an important role in changing the pattern. A successful transition from inwardly propagating spirals to target waves can be observed when the oscillatory frequencies of non-controlled and local inhomogeneous region, which have equal values, are both less than the inherent frequency of system. When we inspect the relationship between oscillatory frequencies and the characteristics of the inhomogeneous region, an intriguing V-shaped line is found in parameter-frequency diagram, and the V-shaped area presents three features. Firstly, the left and right sides of the V-shaped area are symmetrical. Secondly, the propagating directions of target waves from the left and right sides are opposite. An inwardly propagating target wave is formed on the left side of the V-shaped area, and an outwardly propagating target wave stably exists on the right side of the line. Thirdly, as local inhomogeneous parameter 2 increases, the V-shaped area moves towards the local inhomogeneous parameter 2 and decreases simultaneously, and the width of the V-shaped area remains approximately the same. To our knowledge, this V-shaped line is a novel observation, hence the changes of the system frequencies are thought to be provoking. This work presents the numerical experiments and theoretical analyses for the stable conditions of target waves, and therefore provides the ideas in the applications of signal propagation and mode competition.
High repetition rate and high beam quality joule level Nd: YAG nanosecond laser for Thomson scattering diagnosis
Authors: Qiu Ji-Si  , Tang Xiong-Xin  , Fan Zhong-Wei  , Chen Yan-Zhong  , Ge Wen-Qi  , Wang Hao-Cheng  , Liu Hao  ,   Academy of Opto-Electronics, Chinese Academy of Sciences, Beijing 100094, China;,   Zhong Ke He Guang (Tianjin) Research Institute of Applied Laser Technology Co., Ltd. Tianjin 300304, China
Published: December 2020

A joule-level Nd: YAG nanosecond laser of high repetition frequency and high beam quality is developed for Thomson scattering diagnosis. The laser is designed as a master oscillator power-amplifier system mainly including single longitudinal mode seed, pre-amplifier unit and energy extraction unit. The single-longitudinal-mode Q-switched laser of a high stability is taken as the seed laser of output pulse at J level. The pre-amplifier unit amplifies the J-level pulse laser beam into hundreds of mJ level. In order to obtain the high-quality laser beam output, phase conjugation is adopted to compensate for the laser beam distortion. The ultra-filtered FC-770 is taken as an SBS gain medium of 0.0011 cm-1 absorption coefficient, 197.9 GW/cm2 optical breakdown threshold and 3.5 cm/GW gain coefficient. The double-pass amplification of SBS phase conjugation could realize a real-time repair towards the non-uniformity, deformation and wavefront aberration caused by thermal distortion of the optical components and the laser amplifier to achieve the uniform amplified beam output of high quality close to the diffraction limit. In the energy extraction unit, the amplifier of large-diameter slab is used for energy amplification. The size of the slab is 7 mm 35 mm138.2 mm of 56 cutting angle and 0.6% Nd3+ doping concentration. The slab is plated by a layer of SiO2 against light leak. Horizontal pumping mode is adopted. And the slow axis of the laser diode is almost the same as the length of the slat and the direction of laser transmission. The single-plane array is composed of 8 groups of vertical stacks and each group consists of 12 laser diode bars of power 200 W. At 200 Hz repetition frequency, 250 s pump pulse width and 140 A pump current, the up to 2.3 J stored energy can be achieved The energy extraction unit achieves high gain amplification and finally outputs high-quality laser beam. Under the condition of 200 Hz high repetition frequency and 8.23 J single pulse energy injected by the single longitudinal mode seed, 1.85 J output energy is gained. The energy extract efficiency of the laser system is 52.46%. The output laser possesses a pulse width of 5.36 ns, a far field beam spot 1.72 times the diffraction-limited value, and 1.3% energy stability (RMS).
Goos-Hnchen shift based on nearzero-refractive-index materials
Authors: Lu Zhi-Ren  , Liang Bin-Ming  , Ding Jun-Wei  , Chen Jia-Bi  , Zhuang Song-Lin  ,   College of Optical and Electronic Information Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
Published: December 2020

Goos-Hnchen shift is a special optical phenomenon. With the development of the nano-optics, Goos-Hnchen shift has become one of the most valuable and hottest issues in optical field. Meanwhile, due to the unique feature of the near-zero-refractive-index material, it has been used in many fields, but the effect of Goos-Hnchen shift has little studied and received less attention. As a result, the purpose of this paper is to analyze the Goos-Hnchen shift based on near-zero-refractive-index material. In the paper, the photonic crystal with specific parameter is used to simulate the near-zero-refractive-index material, and the measurement in the simulation is based on finite difference time domain. We approach the issue by studying whether and how the wavelength and temperature will affect the Goos-Hnchen shift based on near-zero-refractive-index material. After the simulation at different wavelengths and temperatures based on the incidence angle which gives rise to total reflection, the results of the simulation reveal that when wavelength is between 1.648a and 1.848a (not including 1.848a), the Goos-Hnchen shift is positive and increases gradually, and the total reflection angle decreases. When wavelength is between 1.848a and 2.048a, the total reflection angle increases. When the wavelength is in a range between 1.848a and 1.858a, the Goos-Hnchen shift is negative. When the wavelength is above 1.858a, the Goos-Hnchen shift is negative and increases gradually. When the temperature increases from 0 ℃ to 100 ℃, the Goose-Hnchen shift is unsimilar to the situation of different wavelengths, and fluctuates in the interval at wavelengths ranging from 1.648a to 1.848a, and the total reflection angle increases gradually. Goose-Hnchen shift decreases at a wavelength of 2.048, and the total reflection angle decreases gradually, but a little. Based on the simulation result, it is concluded that the variations of the wavelength and temperature will affect the Goos-Hnchen shift based on near-zero-refractive-index material, and the effective value is in a range from about 1a to 4a, which is not a small value to the shift especially in some precision instruments. As a result, the changes of wavelength and temperature should be taken into consideration, when Goos-Hnchen shift based on near-zero-refractive-index materials is measured or used in research. These findings are expected to be instructive for device design and nano-optics.
Rapid solidification mechanism and magnetic property of ternary equiatomic Fe33.3Cu33.3Sn33.3 alloy
Authors: Xia Zhen-Chao  , Wang Wei-Li  , Luo Sheng-Bao  , Wei Bing-Bo  ,   Department of Applied Physics, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Rapid solidification is a typical non-equilibrium phase transition process, and the crystallization rate of liquid metal is larger than 1 cms-1. If the alloy is solidified in this case, the solute segregation is reduced or even eliminated and the solid solubility can be improved significantly. Rapid solidification technique can be used to refine the microstructures of alloys, which provides an effective method to prepare the novel metastable materials and improve their strengths, plasticities magnetic properties, etc. In this work, the rapid solidification mechanism and magnetic property of ternary equiatomic Fe33.3Cu33.3Sn33.3 alloy are investigated by drop tube and melt spinning techniques. It is known that Fe-Cu-Sn ternary alloy forms a typical immiscible system. However, the experimental results reveal that the liquid phase separation does not take place during the rapid solidification of ternary equiatomic Fe33.3Cu33.3Sn33.3 alloy. The solidification microstructures are all composed of primary Fe dendrites together with Cu3Sn and Cu6Sn5 phases. Under the free fall condition, as the drop tube technique provides microgravity and containerless states, the maximum surface cooling rate and maximum undercooling of alloy droplets are 1.3105 Ks-1and 283 K (0.19 TL), respectively. When the surface cooling rate reaches 1.9103 Ks-1, the primary Fe phase appears as coarse dendrites, and its maximum dendrite length is 41 m. Meanwhile, the Cu3Sn and Cu6Sn5 phases are distributed in the Fe interdendritic spacings. Once the surface cooling rate increases up to 3.3103 Ks-1, the morphology of the primary Fe phase transforms from coarse dendrites into broken dendrites. It is found that the cooling rate and undercooling greatly affect the solidification microstructure of alloy droplets. During the melt spinning experiments, since the large temperature gradient exists between the wheel surface and free surface, the solidification microstructure is subdivided into two crystal zones according to the different microstructure morphologies of Fe phase: fine grain (zone I) and coarse grain (zone II), where zone I is characterized by granular grains while zone II has some dendrites with secondary branch. Under the rapid cooling condition, the microstructures of ternary equiatomic Fe33.3Cu33.3Sn33.3 alloy ribbons are refined significantly and show soft magnetic characteristics. As the surface cooling rate increases from 8.9106 to 2.7107 Ks-1, the lattice constant of Fe solid solution rises rapidly and the coercivity increases from 93.7 to 255.6 Oe. Furthermore, the results indicate that the grain size of Fe phase is the main factor influencing the coercivity of alloy ribbons.
Carlson iterating and rational approximation of arbitrary order fractional calculus operator
Authors: He Qiu-Yan  , Yuan Xiao  ,   College of Electronics and Information Engineering, Sichuan University, Chengdu 610065, China
Published: December 2020

With the development of factional calculus theory and applications in different fields in recent years, the rational approximation problem of fractional calculus operator has become a hot spot of research. In the early 1950s and 1960s, Carlson and Halijak proposed regular Newton iterating method to implement rational approximation of the one-nth calculus operator. Carlson regular Newton iterating method has a great sense of innovation for the rational approximation of fractional calculus operator, however, it has been used only for certain calculus operators. The aim of this paper is to achieve rational approximation of arbitrary order fractional calculus operator. The realization is achieved via the generalization of Carlson regular Newton iterating method. To construct a rational function sequence which is convergent to irrational fractional calculus operator function, the rational approximation problem of fractional calculus operator is transformed into the algebra iterating solution of arithmetic root of binomial equation. To speed up the convergence, the pre-distortion function is introduced. And the Newton iterating formula is used to solve arithmetic root. Then the approximated rational impedance function of arbitrary order fractional calculus operator is obtained. For nine different operational orders with n changing from 2 to 5, the impedance functions are calculated respectively through choosing eight different initial impedances for a certain operational order. Considering fractional order operation characteristics of the impedance function and the physical realization of network synthesis, the impedance function should satisfy these basic properties simultaneously: computational rationality, positive reality principle and operational validity. In other words, there exists only rational computation of operational variable s in the expression of impedance function. All the zeros and poles of impedance function are located on the negative real axis of s complex plane or the left-half plane of s complex plane in conjugate pairs. The frequency-domain characteristics of impedance function approximate to those of ideal fractional calculus operator over a certain frequency range. Given suitable initial impedance and for an arbitrary operational order, it is proved that the impedance function could meet all properties above by studying the zero-pole distribution and analyzing frequency-domain characteristics of the impedance function. Therefore, the impedance function could take on operational performance of the ideal fractional calculus operator and achieve the physical realization. It is of great effectiveness in the generalization of this kind of method in both theory and experiment. The results educed in this paper are the basis for further theoretic research and engineering application in constructing the arbitrary order fractional circuits and systems.
Broadband and low-loss left-handed materials based on multi-opening cross shape structures
Authors: Wu Liang-Wei  , Zhang Zheng-Ping  ,   College of Big Data and Information Engineering, Guizhou University, Guiyang 550025, China;,   Guizhou Aerospace Measurement and Testing Technology Research Institute, Guiyang 550000, China
Published: December 2020

The unique electromagnetic properties of left-handed materials have received much attention due to their applications in microwave devices, radar antenna and electromagnetic stealth and so on. However, the double side etching of dielectric substrate for most traditional left-handed materials will lead to the complexity of manufacture, narrow left-handed bandwidth and higher loss. In order to overcome the shortages of traditional left-handed materials, a new broadband and low-loss left-handed material with multi-opening cross shape structure is presented in this paper. The structure is fabricated on a single side of a dielectric substrate by integrating an electric resonator with a magnetic resonator to form a left-handed unit. Through theoretical analysis, software simulation and effective electromagnetic parameters extraction, the results show that the structure has a double negative characteristics (ε μ <0) in the 12.7-21.1 GHz range, which is basically in the Ku band. The absolute bandwidth of left-handed character is up to 8.4 GHz and the loss of unit cell is less than 0.3 dB. The structure realizes a wider left-handed bandwidth with smaller cell size and lower loss than the conventional left-handed materials, and it provides an important reference for the application and design of the broadband and low-loss microwave left-handed materials.
Research progress of electrochromic performances of WO3
Authors: Fang Cheng  , Wang Hong  , Shi Si-Qi  ,   China Building Materials Academy, Beijing 100024, China;,   School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China
Published: December 2020

From the aspects of both experimental studies and first-principles calculation, we review the research progress of improving the electrochromic performances of WO3, and analyze the transformation tendency in applied field, performance requirement and research focus. Due to the low color-switching, the application field of WO3 shifts from display devices to smart windows or other energy-saving devices. According to the requirement for electrochromic performance, the concerned WO3 morphology changes from amorphous form to nanostructure. For the high desire of smart windows in large-area curtain walls, the solid state inorganic electrochromic materials with lithium ion conductors are used as substitutes for the organic electrochromic films in hydrogen ion electrolytic solution. Correspondingly, response time and cycle life are regarded as the most important performance indices. Doping and synthesizing nanostructure are considered to be the main methods to improve electrochromic performance by introducing the pores into the crystals as the ion diffusion path. Especially, the nano-crystalline WO3 attracts much attention, due to its high stability and quick color switching. In the respect of the first-principles calculation, the simple cubic WO3 is a widely used model for calculation, because of its simple structure and high symmetry. However, there always occur the underestimation of band gap and the incorrect relationship between the cell sizes of WO3 and LiWO3. In response to the problem, by analyzing the Li-intercalated WO3 configuration, it is found that the lattice parameter is closely associated with the interaction between lithium and oxygen. The large discrepancy between the experimental and calculated band gaps is primarily due to the omission of the structural distortion in the calculation, including tilting of WO6 octahedra, as well as the off-centering of W in octahedral caused by the second-order Jahn-Teller effect. According to this, we propose a distorted cubic WO3 model (Im3 space group) to better explain the relevant experimental results. In light of the achieved results and the encountered problems in recent researches, it is generally received that the industrialization of nano-crystalline WO3 and systematic calculation on the lithium diffusion in WO3 deserve the serious consideration. In addition, possessing the function of blocking near-infrared and visible light selectively is the trend for the next generation electrochromic materials. Therefore, the noteworthy development directions on the aspect of both experimental studies and first-principles calculation are pointed out to provide some valuable references for the further researches.
Distribution characteristic of p-channel metal-oxide-semiconductor negative bias temperature instability effect under process variations
Authors: Tang Hua-Lian  , Xu Bei-Lei  , Zhuang Yi-Qi  , Zhang Li  , Li Cong  ,   Key Laboratory of Wide Band-Gap Semiconductor, School of Microelectronics, Xidian University, Xi’an 710071, China
Published: December 2020

Negative bias temperature instability (NBTI) is a p-channel metal-oxide-semiconductor (PMOS) degradation mechanism, which becomes one of the important reliability concerns. The NBTI drastically influences device performance and circuit lifetime. On the other hand, the circuit performance is also affected by the fabrication-induced process variation when the transistor size shrinks to a nanometer-scale. In the presence of the fabrication-induced random variations, the NBTI aging process and its influence on PMOS device become a random process. In this paper, the joint effects of NBTI and process variations on PMOS device are investigated. Firstly, the influence of process variation on NBTI aging is analyzed based on the reaction-diffusion (R-D) mechanism. The NBTI-induced PMOS threshold voltage degradation depends not only on stress time but also on fabrication-determined process parameters, such as the initial threshold voltage and oxide thickness. Then the statistical model is proposed to model NBTI-induced aging under process variation, which captures the threshold voltage variation and oxide thickness variation as random vectors with normal distributions. For 100-times Monte-Carlo simulation based on 65 nm technology, the voltage error and oxide thickness error of the PMOS device are obtained. Applying these process errors to the statistical model, the results show that mean value of threshold voltages is increased along the negative direction with the stress time going on under the process variation and NBTI effect interaction. Meanwhile the standard deviation of threshold voltage is reduced, which represents that the matching between those PMOS devices becomes better. The proposed statistical model accuracy is verified by R-D model theoretical solutions. The maximum relative error of the mean value and of the standard deviations for the threshold voltages degradation of the PMOS device are only 0.058% and 0.91% respectively in 104 s. The distribution characteristic of PMOS NBTI effect is more serious to analog circuit, because analog circuit is more sensitive to device mismatch. For current steering digital-to-analog converter (DAC), PMOS device is always adopted as current source due to its good isolating properties. The PMOS current source requires good matching, and mismatch error could cause circuit failure. To realize aging simulation on DAC circuit in Spectre environment, the above statistical NBTI model is realized by Verilog-ASM language as the subcircuit module to PMOS device. Finally, this module is applied to the current steering DAC. Considering the NBTI effect under process variations, the simulation results show that the DAC gain error is increased with the stress time going on, while its linearity error is gradually reduced.
Bonding nature of the amorphous structure studied by a combination of cutoff and electronic localization function
Authors: Wang Xin-Yang  , Chen Nian-Ke  , Wang Xue-Peng  , Zhang Bin  , Chen Zhi-Hong  , Li Xian-Bin  , Liu Xian-Qiang  ,   Institute of Microstructure and Properties of Advanced Materials, Beijing University of Technology, Beijing 100124, China;,   College of Electronic Science & Engineering, Jilin University, Changchun 132000, China
Published: December 2020

The analysis of the local structure of covalent glass is one of the major challenges for analyzing the amorphous structure. Usually, people use a cutoff distance to determine the coordinated atoms and relevant structural information, such as coordination number and bond angles. Recently, the electron localization function (ELF) has been used to analyze the local structure of amorphous Ge2Sb2Te5. But how to determine the EFL threshold and cutoff distance has not been reported. Here, according to the ab-initio calculations, we systematically investigate the relationship between the bond number and the ELF threshold, and also the cutoff distance in amorphous GeTe. The reasonable value of the ELF threshold and the cutoff distance are determined according to the inflection point and slope change of the bond number with ELF value respectively. Furthermore, the minimal ELF value distributions of Ge-Ge, Ge-Te and Te-Te bonds are presented. The comparison shows that the majority of removed bonds in structural analysis are weak Ge-Te bonds due to the low localization degree of electron. In contrast, the stronger Ge-Ge bonds are almost unchanged when changing the ELF threshold value from 0.58 to 0.63 because of the high localization degree of electron. The average minimal ELF value of Ge-Te bonds in crystalline GeTe is calculated, and it is close to the ELF threshold that is determined by the inflection point. t is easy to find that the Ge-Te bonds which are removed by increasing the ELF threshold are relatively weak. Therefore, these weaker bonds should be removed in structure analysis, which also means that the ELF threshold determined by the inflection point are reasonable value. Finally, based on the EFL threshold value, the coordination number and bond angle distribution of Ge in amorphous GeTe are obtained. The analysis of the coordination number of the Ge atoms shows that as the ELF threshold increases from 0.58 to 0.63, the 5- fold Ge atoms almost disappear because they are against the (8-N) rule. Furthermore, when the ELF threshold value is 0.58, the bond angle distribution analysis of Ge atoms shows that the local structure is a configuration that is mainly defectively octahedral (3-fold Ge) and distorted tetrahedral (4-fold Ge), but it remains unchanged when the threshold value increases to 0.63. It further demonstrates that all the removed chemical bonds are weaker ones as the ELF threshold increases. This approach is useful to improve the accuracy of amorphous structure analysis by obtaining the more reasonable inter-atomic bonding information. And it should be applied to the structural analyses of other systems generally.
Research on coordinate transformation design of a cylinderical acoustic cloak with pentamode materials
Authors: Lu Zhi-Miao  , Cai Li  , Wen Ji-Hong  , Wen Xi-Sen  ,   Science and Technology on Integrated Logistics Support Laboratory, College of Mechatronic Engineering and Automation, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The pentamode material, similar to fluid in physical properties, serves as a useful way for the physical implementation of the anisotropic fluid. Based on the similarity, a method to design cloak with the pentamode materials has been put forward by Norris. To analyze the effect factors and rules of the stealth performance of the cloak, the present article is focused on the studying of the coordinate transformation equation of the pentamode cloak design of Norris. Cloaks with different materials parameters distribution can be achieved by adjusting coordinate transformation equations. There are four kinds of the distribution of pentamode cloak material parameters: the density equation being constant, the modulus equation being constant, the density equation being, power equation and the modulus equation being power equation. The average visibility is considered as the standard of stealth effect and is calculated with different coordinate transformation equations by using the software COMSOL. The average visibility is used to analyze the relationship between stealth effect and coordinate transformation equations. The relationship between the coordinate transformation equation and the route of acoustic wave transmission, the relationship between the materials of obstacle and the stealth effect, and the relationship between the route of acoustic wave transmission and the stealth effect are studied. Two results are achieved by comparing these relationships mentioned above. The first is that the stealth effect of a cloak with aluminum obstacle is worse than one with water obstacle. The reason lies in the impedance mismatch between the aluminum and the cloak material. The second result shows that the coordinate transformation equation is related to the distribution of material parameters and the route of acoustic wave transmission and it can affect the scattering property of the cloak. When the route of acoustic wave transmission is close to inner surface of cloak, the stealth effect is relatively poor, while when the route of acoustic wave transmission is close to outer surface of cloak, the stealth effect is relatively well. The reason is that when the route of acoustic wave transmission is close to inner surface of cloak, the acoustic wave affects the obstacle which leads to the enhancement of the scattering of obstacle. So when designing the cloak, not only the physical realization of the cloak material but also the distributed situation of the route of acoustic wave transmission should be considered. And the route of acoustic wave transmission is decided by the coordinate transformation equation. Therefore the stealth performance can be improved by applying proper coordinate transformation equation.
Experimental investigation on the starting vortex induced by symmetrical dielectric barrier discharge plasma actuator
Authors: Zhang Xin  , Huang Yong  , Wang Wan-Bo  , Tang Kun  , Li Hua-Xing  ,   School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China;,   China Aerodynamics Research and Development Center, Mianyang 621000, China
Published: December 2020

Flow control using plasma actuator is a promising research field of aeronautical applications. Due to its low energy consumption, rapid response and simple construction, this actuator has been investigated in various aerodynamics problems, such as boundary layer flow control, drag reduction, lift enhancement, noise reduction, and flow separation control. In order to understand the controlling mechanism of plasma actuator, many researchers have been carried out some experiments on the plasma actuator characterization in quiescent air and obtained the evolution process of starting vortex induced by plasma actuator. But the plasma actuator always works under flow condition. Therefore, understanding the interaction process between the starting vortex and incoming flow is a key to promote this technology development. In this paper, the starting vortex induced by symmetrical Dielectric Barrier Discharge (DBD) plasma actuator in quiescent air or under flow condition was investigated using Particle Image Velocimetry (PIV). Compared with the asymmetrical DBD plasma actuator, the symmetrical plasma actuator adopted the whole metal plate model as the insulated electrode. Three layers of kapton film as dielectric material covered the testing model and the thickness of each layer was 0.05 mm. The copper foil which was 2 mm in width and 0.05 mm in thickness was mounted on the trailing edge of the plate and oriented along the spanwise direction to induce a wall jet in the streamwise direction. The input AC voltage was 8 kV p-p and the frequency of the power source was 3 kHz. The wind speed was 1 m/s. The results suggested that the symmetrical actuator produced one pair of counter-rotating starting vortexes on each side of upper electrode and the trajectory of the starting vortex core was shown to scale with t0.7 in quiescent air. Compared to the evolution law of starting vortex in still air, the development evolution and life time of starting vortex under flow condition was different due to the interaction influence between incoming flow and starting vortex. The breakdown time of downstream starting vortex was earlier and the location of the starting vortex core scaled with t0.45 under flow condition. Conversely, the life time of upstream starting vortex which was in the opposite direction of incoming flow was delayed. The incoming flow enhanced the upstream starting vortex's capability of promoting mixing and entraining high-momentum fluid into boundary layer, therefore the boundary layer became more energetic and capable of withstanding adverse pressure gradient. The jet effect and mixing function could be achieved by the symmetrical plasma actuator. These investigations laid the groundwork for flow control using DBD plasma actuator at high wind speed or high Reynolds number.