bluuebunny/crossref_metadata_2025 huggingface dataset:
Incipient spallation of high purity copper under non-one-dimensional strain shock waves
Authors: Xie Pu-Chu , Wang Xiao-Song , Hu Chang-Ming , Hu Jian-Bo , Zhang Feng-Guo , Wang Yong-Gang ,   Key Laboratory of Impact and Safety Engineering, Ministry of Education of China, Ningbo University, Ningbo 315211, China,   Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

A new spallation experimental method by using conical target is proposed. Based on the analysis of wave propagation, the basic principle of spallation experiment of conical target is discussed. Then incipient spallation of high purity (HP) copper under non-one-dimensional strain shock wave is studied experimentally by using a gas gun setup. The damage distribution characteristics and micro-mechanism of conical HP copper target are analyzed. The intrinsic relationship between the characteristics of free surface velocity profiles and damage evolution is explored. The results indicate that 1) continuous damage zones including different damage states appear in the conical HP copper target with initial spallation from the bottom of cone to the top of cone along the direction parallel to the cone surface, which is attributed to the spatial evolution of the amplitude and duration time of tensile stress in the conical target; 2) quantitative statistical analysis of damage inside conical HP copper target reveals that the nucleation and early growth of micro-voids are random, while the coalescence of micro-voids has significant localization characteristics; 3) the normal free surface particle velocity profiles with typical pull-back spallation signals at different locations of conical HP copper target are measured by multi-channel photon Doppler velocimetry. Comparing with the damage distribution characteristics, it is revealed that the spallation strength based on pull-back velocity is independent of damage, and is the critical nucleation stress of micro-voids. But the slope and amplitude of pull-back rebound velocity depend on damage evolution process, which relates to the change of damage evolution rate and stress relaxation caused by damage degree respectively.
Experimental investigation on dynamic behavior of single droplet impcating normally on dry sphere
Authors: Tang Peng-Bo , Wang Guan-Qing , Wang Lu , Shi Zhong-Yu , Li Yuan , Xu Jiang-Rong ,   Energy Institute, Hangzhou Dianzi University, Hangzhou 310018, China
Published: December 2020

The phenomenon that droplets impacting on the solid surface is ubiquitous in industrial applications such as spray cooling, spray painting, ink-jet printing, and fuel-air mixing internal combustion engines. The dynamic of droplet impacting on solid surface has been a hot topic in the area of fluid mechanics. Most of the existing experimental studies focused on the droplet impacting on flat or cylinder surface whereas the droplet impacting on a dry sphere surface, especially its effect from the sphere curvature, has been less investigated. Therefore, the dynamic behavior of a droplet impacting normally on a dry sphere is experimentally investigated at the relatively high Reynolds and Weber number in the present work. The impacting velocity of the droplet on the sphere is discussed with consideration of air resistance effect. The influences of spherical curvature and Weber number on the dynamic behavior and spreading factor are analyzed. The experimental results are compared with those of previous impacting flat researches. The results show that the drop velocity fluctuates significantly near the impacting sphere. The influence of the spherical curvature on the dynamic behavior of the droplet impact is obvious. The maximum spreading diameter of the liquid film will exceed that of the sphere with a curvature greater than 0.2 mm–1, and some segments of the liquid film rim even slide down directly. When the spherical curvature is less than 0.167 mm–1, the dynamic behaviors of the impacting droplet will undergo the spread, retraction, oscillation, and stable attachment after impacting. Then the maximum spreading factor of the droplet impacting sphere is little influenced by the curvature, and gradually tends to that of the droplet impacting plane with curvature decreasing. The Weber number has little influence on the spreading velocity of the liquid film, but obvious on the retraction. The maximum spreading factor gradually increases with Weber number increasing. A simple empirical correlation for the maximum spreading factor is obtained. This study conduces significantly to further investigating the dynamic characteristics of droplets impacting on the sphere.
Effect of pre-orientation on formation of microstructure of lamella crystal and the stress response of semicrystalline polymers: Molecular dynamics simulations
Authors: Yang Jun-Sheng , Zhu Zi-Liang , Cao Qi-Long ,   Computational Physics Key Laboratory of Sichuan Province, Yibin University, Yibin 644000, China,   Weifang University of Science and Technology, Shouguang 262700, China,   School Material Science and Engineering, Qingdao University, Qiangdao 266003, China
Published: December 2020

Molecular dynamics simulations have been used to study the effect of the pre-orientation on the microstructure of lamella crystal and the stress response of polyvinyl alcohol (PVA) semicrystalline polymer under stretching. For the different pre-oriented systems, nucleation is demonstrated to be a two-step process, however, in a different intermediate order. For the isotropic PVA polymer melt, the segment needs more time to adjust its inter-chain structure, therefore, the nucleation is assisted by local order structures, while the nucleation of the oriented PVA melt is promoted by density fluctuation. The nucleation process is the result of coupling effect of conformational and orientational ordering. The transformation from flexible chains into conformational ordered segments circumvents the entropic penalty under the shear flow, which is the most peculiar and rate-limited step in polymer crystallization. Therefore, the current work suggests that the acceleration of the nucleation rate by shear deformation is mainly attributed to the different kinetic pathway via conformational/orientational ordering-density fluctuation-nucleation. From the different pre-oriented PVA semicrystalline polymers, we know that the higher oriented degree corresponds to a higher number of Tie chains and lower Loop chains, and the higher number of Tie chains corresponds to a stronger stress-strain response. And the detailed molecular structural evolution of semicrystalline polymer under stretching is also given in this work.
Comparison of neutron induced single event upsets in 14 nm FinFET and 65 nm planar static random access memory devices
Authors: Zhang Zhan-Gang , Lei Zhi-Feng , Tong Teng , Li Xiao-Hui , Wang Song-Lin , Liang Tian-Jiao , Xi Kai , Peng Chao , He Yu-Juan , Huang Yun , En Yun-Fei ,   Science and Technology on Reliability Physics and Application of Electronic Component Laboratory, China Electronic Product Reliability and Environmental Testing Research Institute, Guangzhou 510610, China,   Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China,   Spallation Neutron Source Science Center, Dongguan 523803, China,   Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China
Published: December 2020

 Based on the wide-spectrum neutron beam (covering thermal neutrons and E > 10 MeV neutrons, with maximum energy of 1.6 GeV) provided by the China Spallation Neutron Source (CSNS), this paper focuses on the single event effect study of 14 nm FinFET large-capacity SRAM and 65 nm planar process SRAM device, using combined techniques of irradiation experiment, reverse analysis, and Monte-Carlo neutron transport simulation. The aim is to reveal the effect of integrated circuit process changing on the sensitivity of neutron induced single-bit and multiple-bit upsets (MBU), and to analyze the inner mechanisms, including the distribution of secondary particles in the sensitive volume, the characteristics of deposited charges, etc.

 The results show that compared with the 65 nm device, single event upset (SEU) cross section of the 14 nm FinFET device, induced by E > 10 MeV neutrons, is reduced by about 40 times, while the MBU ratio increases from 2.2% to 7.6%, which is due to the reduction of sensitive volume size of the 14 nm FinFET device (80 nm × 30 nm × 45 nm), pitch, and critical charge (0.05 fC). The main forms of MBU are double-bit upset, triple-bit upset and quadruple-bit upset. Unlike the phenomenon that the 65 nm device is immune to thermal neutrons, the use of the 10B element near M0 in the 14 nm FinFET device causes it to present the thermal neutron sensitivity to a certain extent. The SEU cross section induced by thermal neutrons is about 4.8 times smaller than that induced by E > 10 MeV neutrons.

 Based on the device cross-section and memory area images obtained from the reverse analysis, a device model is established and neutron transport simulation based on Geant4 toolkit is carried out. The E > 10 MeV neutrons result in abundant secondary particle distribution in the sensitive volume of the device, covering n, p into even W. The neutron energy and presence or absence of the W plug near the sensitive volume have an importantinfluence on the type and probability of secondary particles in the sensitive volume. The analysis and calculations show that a large number of high-Z secondary particles with long range and large LET values generated by high-energy neutrons in the sensitive volume of the device are the inducement of MBU, and SEUs mainly result from the contribution of light ions such as p, He, and Si.
Time domain hybrid method for coupling analysis of multi-conductor transmission lines on the lossy dielectric layer excited by ambient wave
Authors: Ye Zhi-Hong , Zhang Jie , Zhou Jian-Jian , Gou Dan ,   School of Communication and Information Engineering, Chongqing University of Posts and Communications, Chongqing 400065, China
Published: December 2020

At present, numerical methods applied to the coupling analysis of transmission lines on the lossy dielectric layer excited by ambient wave are still rare in the literature. As a temptation to fill this gap, a novel time domain hybrid method is proposed, in which the modified transmission line (TL) equations, finite-difference time-domain (FDTD) method, and some interpolation schemes are organically combined together. It can overcome the difficulty in building the coupling model of ambient wave to transmission lines on the lossy dielectric layer greatly. In this method, the modified transmission line (TL) equations suitable for the coupling analysis of multi-conductor transmission lines (MTLs) on the lossy dielectric layer are derived from the traditional TL equations firstly. Compared with the traditional TL equations, the electromagnetic fields in the lossy dielectric layer are introduced into the equivalent distribution sources of modified TL equations. Generally, the precision of TL equations is dependent on the accuracy of equivalent distribution sources, which are obtained from the incident electric fields parallel and perpendicular to the MTLs. Therefore, the FDTD method is utilized to model the structure of lossy dielectric layer to calculate the electromagnetic field distribution surrounding the MTLs and in the dielectric layer. Since the heights and distances of MTLs can be arbitrary values, the electric fields parallel and perpendicular to the MTLs cannot be obtained from the electric fields on the edges of FDTD grids directly, which should be computed via some interpolation schemes. Then the modified TL equations are established, which should be solved by the central difference scheme of FDTD method to obtain the voltages and currents on the MTLs and terminal loads. The significant feature of this proposed method is that it can realize the synchronous calculations of electromagnetic field radiation and transient responses on the MTLs. Finally, numerical simulations of single and multiconductor transmission lines on the lossy dielectric layer excited by ambient wave at different incident angles are employed to exhibit the accuracy and efficiency of the proposed method by comparing with the simulation software CST. Because the structures of MTLs do not need to be meshed, the proposed method outperforms the simulation software CST in both memory usage and computation time.
Design of second harmonic terahertz gyrotron cavity based on double confocal waveguide
Authors: Guan Xiao-Tong , Fu Wen-Jie , Lu Dun , Yang Tong-Bin , Yan Yang , Yuan Xue-Song ,   School of Physics, University of Electronic Science and Technology of China, Chengdu 610054, China,   Terahertz Research Center, School of Electronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

Quasi-optical confocal cylindrical waveguide possesses a lot of good characteristics, such as big power capacity and low mode density, which can suppress the mode competition in beam-wave interaction. So quasi-optical waveguide has a great advantage in designing high harmonic terahertz gyrotrons. For the reason that part of electron beams located in a region of weak field intensity play a limited role in beam-wave interactions, the beam-wave interaction is not efficient in confocal cavity. Motivated by enhancing the beam-wave interaction efficiency of quasi-optical gyrotron, we propose a novel terahertz harmonic gyrotron cavity with double confocal waveguide in this paper. The transverse field distribution and the mode spectrum in double confocal waveguide are analyzed and presented. A 330 GHz second harmonic gyrotron with double confocal cavity is designed, theoretically analyzed and simulated by using a particle-in-cell (PIC) code. The results obtained for double confocal cavity are compared with the results for single confocal cavity, and the physical mechanism of beam-wave interaction enhancement in double confocal cavity is discussed. Theoretical results show that the double confocal cavity is able to increase the coupling strength of beam-wave interaction, thus, to improve the output power and the interaction efficiency of quasi-optical gyrotron. The PIC simulation results suggest that a high-order waveguide mode in double confocal cavity can steadily interact with the high harmonic cyclotron mode of electron beam without mode competition. Driven by a 40 kV, 2 A electron beam with a guiding center radius of 1.65 mm and velocity ratio equal to 1.5, output power of 9.9 kW at 328.93 GHz can be generated in the designed double confocal cavity. The beam-wave interaction efficiency increases from 5.3% in single confocal cavity to 12.4% in dual confocal cavity under the same operation parameters. The double confocal cavity has great potential applications in terahertz band. Moreover, this study indicates that the eigen mode in double confocal waveguide is a kind of hybrid mode superimposed by two independent single confocal waveguide modes. This mode characteristic will be beneficial to designing a multifrequency gyrotron oscillator operated in two modes and two cyclotron harmonics, simultaneously, with a single electron beam used, which provides a new possibility to develop the novel terahertz radiation source.
Inversion of vertical rainfall field based on earth-space links
Authors: Xian Ming-Hao , Liu Xi-Chuan , Yin Min , Song Kun , Gao Tai-Chang ,   College of Meteorology and Oceanography, National University of Defense Technology, Nanjing 211101, China
Published: December 2020

The accurate measurement of rain intensity and its distribution in vertical direction can not only help to understand the process of rainfall development, but also play an important role in human life such as agriculture, weather forecasting, water resources management, and natural disaster warning. According to the analysis of the geometric structure of earth-space link and propagation model of electromagnetic wave in atmosphere, in this paper we propose a method to reconstruct two-dimensional(2D) vertical rainfall field by using earth-space links. Firstly, the measured data of micro rain radar (MRR) from Nanjing are used to generate three real vertical rainfall fields which are marked as I, II and III respectively. Secondly, based on the analysis of the earth-space link’s geometry and the effect of signal attenuation from other factors such as scintillation, atmosphere gas and cloud, the vertical rainfall field inversion model is established. According to the power-law relationship between rain intensity and rain attenuation, which is given by International Telecommunication Union (ITU), the simultaneous algebraic reconstruction technique (SART) is used to inverse the vertical rainfall field. Then, one earth station which can receive a 17 GHz signal from satellite is employed to detect the vertical rainfall field. However, the simulation results show that it is difficult for one earth station to achieve the inversion of rainfall field, and that the correlation coefficients between rainfall fields and inversed fields are 0.556, 0.504 and 0.364 respectively. Based on the result, two earth stations are jointly used. In this simulation, the result shows that after 500 iterations the correlation coefficients all increase above 0.98, and the average biases between rainfall field I, II, III and their inversed fields are 0.122, 0.159 and 0.537 mm/h, respectively. Meanwhile, the Euclidean distances decrease to 0.246, 0.235 and 0.812 mm/h, and the relative errors of entropy are both less than 2%. It can be seen from the inversion fields that the vertical distribution of rain rate is close to that of the real field, which suggests that the method proposed in this paper can basically achieve the inversion of vertical rainfall field by using earth-space links. In addition, with the combined detection of three earth stations the accuracy of the inversion results is significantly improved. The correlation coefficients are all close to 1 and the mean deviations are all on the order of 10–12 mm/h, indicating that the 2D vertical rainfall fields are accurately reconstructed. In the near future, the satellite constellation system will be globally deployed, which can promote the applications of our method in areas, such as plateaus, mountains and islands, where there exist no traditional observation data, serving as a supplement to existing precipitation measurements.
Recent developments of extreme wave events in integrable resonant systems
Authors: Pan Chang-Chang , Baronio Fabio , Chen Shi-Hua ,   School of Physics, Southeast University, Nanjing 211189, China,   Dipartimento di Ingegneria dell’Informazione, Università di Brescia, Via Branze 38, 25123 Brescia, Italy
Published: December 2020

From a microscopic perspective, the single extreme rogue wave event can be thought of as the spatiotemporally localized rational solutions of the underlying integrable model. A typical example is the fundamental Peregrine rogue wave, who in general entails a three-fold peak amplitude, while making its peak position arbitrary on a finite continuous-wave background. This kind of bizarre wave structure agrees well with the fleeting nature of realistic rogue waves and has been confirmed experimentally, first in nonlinear fibers, then in water wave tanks and plasmas, and recently in an irregular oceanic sea state. In this review, with a brief overview of the current state of the art of the concepts, methods, and research trends related to rogue wave events, we mainly discuss the fundamental Peregrine rogue wave solutions as well as their recent progress, intended for three typical integrable models, namely, the long-wave short-wave resonant equation, the three-wave resonant interaction equation, and the nonlinear Schrödinger and Maxwell–Bloch equation. Basically, while the first two models can describe the resonant interaction among optical waves, the latter governs the interaction between the optical waves and the resonant medium. For each integrable model, we present explicitly its Lax pair, Darboux transformation formulas, and fundamental Peregrine rogue wave solutions, in a self-consistent way. We confirm by convincing examples that these fundamental rogue wave solutions exhibit universality and can be applied to the multi-component or the higher-order versions of the current integrable models. By means of numerical simulations, we demonstrate as well several novel rogue wave dynamics such as coexisting rogue waves, complementary rogue waves, and Peregrine solitons of self-induced transparency.
Some recent progresses on the study of ultracold quantum gases with spin-orbit coupling
Authors: Shi Ting-Ting , Wang Liu-Jiu , Wang Jing-Kun , Zhang Wei ,   Department of Physics, Renmin University of China, Beijing 100872, China,   Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872, China
Published: December 2020

Artificial synthetic gauge field and spin-orbit coupling has been extensively studied following their experimental realization in ultracold atomic systems. Thanks for the versatile controllability, such systems not only provide possibilities to simulate and study important models in multidisciplinary fields of physics, but also work as an excellent platform to engineer novel states of matter and quantum phenomena. This paper reviews some recent progresses on the study of ultracold atomic systems with spin-orbit coupling, focusing on the effects induced by dissipation, novel interaction forms, large symmetry of spins, and long-range interactions. The investigation in these aspects is closely related to the characteristics of ultracold atomic systems, hence can bring new inspirations and perspectives on the understanding of spin-orbit coupling. In this review, we firstly investigate the appearance of a topological superradiant state in a quasi-one-dimensional Fermi gas with cavity-assisted Raman process. A cavity-assisted spin-orbit coupling and a bulk gap opening at half filling will be induced by the superradiant light generated in the transversely driven cavity mode. The topological superradiant state and the corresponding topological phase transition in the system can be driven by this mechanism. Then, symmetry-protected topological states of interacting fermions will be introduced in a quasi-one-dimensional cold gas of alkaline-earth-like atoms. Raman-assisted spin-orbit couplings in the clock states, together with the spin-exchange interactions in the clock-state manifolds will give rise to symmetry-protected topological states for interacting fermions, by taking advantage of the separation of orbital and nuclear-spin degrees of freedom in these alkaline-earth-like atoms. Furthermore, we show that an exotic topological defect, double-quantum spin vortices, which are characterized by doubly quantized circulating spin currents and unmagnetized filled cores, can exist in the ground states of SU(3) spin-orbit-coupled Bose-Einstein condensates. It is found that the combined effects of SU(3) spin-orbit coupling and spin-exchange interaction determine the ground-state phase diagram. Finally, we demonstrate that spin-orbit coupling and soft-core long-range interaction can induce an exotic supersolid phase of Bose gas, with the emergence of spontaneous circulating particle current. This implies that a finite angular momentum can be generated with neither external rotation nor synthetic magnetic field, and the direction of the angular momentum can be altered by adjusting the strength of spin-orbit coupling or interatomic interaction.
Influence of coma and spherical aberration on transmission characteristics of vortex beams in slant atmospheric turbulence
Authors: Yong Kang-Le , Yan Jia-Wei , Tang Shan-Fa , Zhang Rong-Zhu ,   College of Electronics and Information Engineering, SiChuan University, Chengdu 610065, China
Published: December 2020

Vortex beam has potential applications in free space optical communication because of its capacity of data transmission. Therefore, it is necessary to study the propagation characteristics of vortex beams in atmospheric turbulence. When the vortex beam propagates in the atmospheric turbulence the beam drift will occur, which has a great influence on the free space optical communication. In this paper, the beam drift of vortex beams with coma and spherical aberration transmitted in atmospheric turbulence is studied by using multi-phase screen and Fourier transform method. The numerical results show that as the transmission distance increases, the effects of both coma and spherical aberration on the beam drift are enhanced. The larger the transmission zenith angle and the coma coefficients, the greater the beam drift of the vortex beam is. However, the beam drift decreases with spherical aberration coefficient increasing. When the zenith angle and the transmission distance are both unchanged, the beam drift of the both vortex beams decrease with topological charges increasing. The influence of coma aberration on beam drift is bigger than that of spherical aberration.
Triple-layer-coated microspheres for refractive index sensor with internally referenced self-compensated thermal effect
Authors: Meng Ling-Jun , Wang Meng-Yu , Shen Yuan , Yang Yu , Xu Wen-Bin , Zhang Lei , Wang Ke-Yi ,   Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei 230026, China,   Science and Technology on Optical Radiation Laboratory, Beijing 100039, China
Published: December 2020

Optical microcavity has an important and promising application in high sensitivity sensing, but thermal drift hinders its practical use. In this study, we propose a triple-layer-coated microsphere resonator, which has a high sensitivity in refractive index sensing with low thermal drift. The refractive indexes of the three layers from the inside to the outside are high, low, and high, respectively. The two high refractive index layers can support their own whispering-gallery modes, called the inner mode (IM) and the outer mode (OM). We study the performance of IM and OM with waveguide coupling in refractive index sensing and temperature sensing. The results show that when the thickness of the middle layer is 550 nm, the refractive index sensitivity of IM and OM will be 0.0168 nm/RIU, 102.56 nm/RIU, and the temperature sensitivity will be –19.57 pm/K and –28.98 pm/K, respectively. The sensing is carried out by monitoring the difference in resonant wavelength between IM and OM and the sensing characteristics are optimized by adjusting the thickness of the middle layer. Further, when \begin{document}${t_B}$\end{document} = 400 nm, the refractive index sensitivity can arrive at 75.219 nm/RIU, the detection limit can reach 2.2 × 10–4 RIU, and the thermal drift is reduced to 3.17 pm/K, thereby eliminating the effect of thermal drift to a great degree. This study provides the guidance for designing and improving the microsphere refractive index sensors.
Comparison between ionospheric disturbances caused by barium and cesium
Authors: Zhu Xiao-Li , Hu Yao-Gai , Zhao Zheng-Yu , Zhang Yuan-Nong ,   Ionosphere Laboratory, School of Electronics and Information, Wuhan University, Wuhan 430079, China
Published: December 2020

After being released in the ionosphere, alkali-metal atoms will be rapidly photoionized by solar UV, producing positive ions and electrons, and forming artificial plasma cloud. Based on a three-dimensional two-species fluid model, considering both the loss of barium atoms due to photoionization and oxidation and the influence of horizontal wind field in the release region, the spatial-temporal evolution of the artificial plasma cloud is discussed. By taking into account the electromagnetic field force, pressure gradient, particle collisions and ion inertia, the ionospheric disturbance effects caused by barium and cesium are compared with each other. The simulation results show that the alkali metal rapidly expands after being released in the ionosphere, and the generated plasma cloud gradually forms an ellipsoidal structure from the inside to the outside under the constraint of magnetic field with considering no wind. Meanwhile, the expanded plasma cloud pushes away the background oxygen ions, forming an oxygen ion density hole in the release center and two symmetrical density bumps on both sides. In the absence of neutral wind, the plasma cloud is dominated by the movement along magnetic field, while considering the background neutral wind, the plasma cloud and background disturbance area will move along the direction of wind, so that the density gradient of plasma cloud becomes steepening on the upwind side. Although the movement of ion cloud across the magnetic field is constrained, the neutrals can pass through the magnetic field freely, so the ion cloud and neutral cloud will separate from each other slowly. Also, the presence of horizontal wind field will make a greater disturbance to the background oxygen ion. By comparing the simulation results of barium and cesium we can see that, qualitatively, the expansion characteristics of Cs+ and Ba+ as well as their effects on the background O+ are similar. Due to the small diffusion coefficient of cesium, the barium cloud expands more rapidly and the coverage area of Ba+ cloud is wider. Because of the large photoionization rate of cesium, the ionization yield of cesium is higher than that of barium when the same mass is released. In addition, the snowplow effect of Cs+ is stronger than that of Ba+, and the oxygen ion density holes and bumps caused by Cs+ are also larger.
A class of approximate computation method for antenna directivity
Authors: Liu Jun-Qun ,   Nanjing Research Institute of Electronics Technology, Nanjing 210039, China
Published: December 2020

Directivity is one of the core performance parameters for an antenna, and its accurate computation and measurement have been receiving attention in the past decades. While quite a number of computational methods for antenna directivity are developed, a comprehensive comparison among these methods, including their advantages and disadvantages, has not yet been reported. In the literature, most of these methods can be roughly classified as two categories, i.e. numerical methods and analytical methods. The numerical methods include those simplified numerical methods for accessing the radiation pattern. For example, some methods assume that the radiation pattern is only elevation-angle dependent, and an approximate truncation of the integral interval is often employed. The analytical methods are developed, where the electromagnetic radiation intensity and the total radiation power for a specific antenna are derived analytically. Nevertheless, so far there have been less efforts dedicated to developing general computational methods based on the antenna's planar near-field theory and associated computational schemes, although indeed quite a few of advanced mathematical approaches have been used to obtain the accurate directivity, including the series expansion based on the spherical wave scheme and the Fourier expansion scheme. In spite of these efforts, one can see that a general accurate numerical scheme for the antenna directivity is still urgently required. As an important supplement to these efforts, this paper adopts or proposes four numerical integration methods regarding planar near-field measurement of the antennas under test. Based on the planar near-field theory, microwave near-field data, and fast Fourier transform (FFT), this paper discusses the numerical integration-based algorithm schemes based on the simulated (or measured) near-field data and relevant numerical uncertainty estimation. Specifically, an antenna with accurate directivity is chosen for illustrating the accuracy assessment. First, a set of near-field data under the well-established probing condition is simulated and then used as an input for subsequent numerical calculation of the antenna directivity value. Four different numerical integration methods are employed and their possible numerical errors are discussed. Consequently, the antenna directivity values are obtained respectively from the four different numerical methods. It is revealed that the numerically evaluated directivity values from the near-field data are roughly at most 0.6 dB larger than the accurate value. This work represents a substantial step toward a reliable estimation of the antenna directivity from the near-field data of an antenna.
Experiment study of characteristics of powder pneumatic filling
Authors: Yang Jian-Gang , Hu Chun-Bo , Zhu Xiao-Fei , Li Yue , Hu Xu , Deng Zhe ,   Science and Technology on Combustion, Internal Flow and Thermal-structure Laboratory, Northwestern Polytechnical University, Xi’an 710072, China,   Xi'an Aerospace Propulsion Institute, Xi’an 710100, China,   Xi'an Modern Chemistry Research Institute, Xi’an 710065, China
Published: December 2020

Powder engine is one kind of new concept engines with multiple ignition capability and thrust modulation function. Powder filling is an important process of the powder engine tests. The powder pneumatic filling experiments were carried out to investigate the effects of the filling position of the powder collection box and the mass flow rate of fluidization gas on the stability and performance of powder pneumatic filling. It’s found that large mass flow rate of fluidization gas contributes to stability of powder pneumatic filling, but its volume efficiency of powder filling is the lowest, only 68.1%, but it’s 93.9% when the mass flow rate of fluidization gas is small. Compared with the vertical inlet of end cap, tangential inlet on the cylinder wall makes the powder uniformity better. In the pneumatic filling mode, the powder bulk density in the collection box is greater than the bulk density in the powder tank. In addition, the mass of powder calculated by position displacement is always larger than the mass of powder measured by the electronic balance. It indicates powder bulk density in tank is constantly changing during the powder pneumatic filling experiments. The actual powder bulk density in the powder tank is calculated by a model established in this paper, it’s found that when the mass flow rate of fluidization gas is low, the bulk density of the powder in the tank is increased first and then decreased, and the final bulk density is less than the initial value. While the mass flow rate of fluidization gas is high, powder bulk density in the tank is first increased, then decreased, then increased and then decreased, and the final bulk density is greater than the initial value. The compression mechanism of powder bulk density in the tank is similar to the motion law of the damper spring vibrator when it is forced to vibrate. It can be described by the damped second-order system response function. When the mass flow rate of fluidization gas is small, the damping coefficient of the system is smaller. While the mass flow rate of fluidization gas is large, the damping coefficient is larger and is variable.
Length-controllable picking method and conductivity analysis of carbon nanotubes
Authors: Wang Ya-Zhou , Ma Li , Yang Quan , Geng Song-Chao , Lin Yi-Ni , Chen Tao , Sun Li-Ning ,   School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200072, China,   Robotics and Microsystems Center, Soochow University, Suzhou 215021, China
Published: December 2020

In this paper, a length-controllable picking-up method of carbon nanotubes (CNTs) is proposed and the electrical performance data utilized for the conductivity analysis of CNT are also obtained. The micro-nano-operation system inside scanning electron microscope (SEM) is composed of 4 manipulation units each with 3 degrees of freedom, which is driven by piezoelectric ceramics and flexure hinges. In this micro manipulation system, an atomic force microscope (AFM) probe is used as the end effector to adjust the spatial pose of the CNT based on van der Waals force and two tungsten needles are used to cut the CNT from the target length and to measure the I-V characteristic data simultaneously. At first, the AFM probe is moved in the z direction to approach to the CNT until the end of the CNT is adsorbed onto the surface of the AFM probe. And then the AFM probe moves alternately in the x and z direction in order to stretch the CNT into a horizontal straight line, only in this way can the length of the CNT be measured accurately and can the cutting position be determined. Two tungsten needles cleaned by using hydrofluoric acid to remove the oxide layer are controlled to contact both sides of the cutting position on CNT and connected to the TECK 2280S power supply through the electric cabinet to apply a gradually increasing DC voltage, and the current in the circuit is measured and recorded by the TECK DMM7510 until the current abruptly changes to zero which indicates that the CNT between the tungsten needles has been cut off. The stress of the CNT in contact with the tungsten needles and the AFM probe are analyzed. The modeling of van der Waals force between AFM probe and CNT which can influence the pick-up length error caused by the deformation of CNT under the force of tungsten needles is completed. It is found that the contact length of them and the pick-up length error decrease while the van der Waals force between the AFM probe and CNT increases. The circuit models for contact between the tungsten needles and three operating objects, such as semiconducting CNT, metallic CNT and CNT bundle, are also established. In addition, the I-V characteristic equations of circuit model which can be used to fit the I-V data are derived separately. The CNT pick-up experiment is carried out and the results demonstrate that the proposed picking method can control the length of CNT effectively, but the conductivity of CNT can also be judged by fitting the I-V obtained experiment data through the derived I-V characteristic equations.
Electrical properties of an arbitrary m×n rectangular network
Authors: Tan Zhi-Zhong , Tan Zhen ,   Department of Physics, Nantong University, Nantong 226019, China,   School of Information Science and Technology, Nantong University, Nantong 226019, China
Published: December 2020

The development of natural science raises many complex new problems and requires people to find the basic method to resolve them. It was found that many problems could be resolved by building the resistor network model. In 1845, the German scientist Kirchhoff set up the node current law and the circuit voltage law.Since then the basic theory of electric circuit has been established. At present, three general theories for studying large-scale resistor networks have been developed, for example, In 2000 Cserti [Am. J. Phys. 2000, 68 , 896] set up the Green function technique to evaluate the resistance of infinite lattices. In 2004 Wu [J. Phys. A: Math. Gen. 2014, 37 , 6653] formulated a Laplacian matrix method and calculated the resistance of arbitrary finite and infinite lattices by using the eigenvalues and eigenvectors. In 2011 Tan [Resistance Network Model (Xi’an: Xidian University Press) 2011, pp16–216] proposed the recursion-transform (RT) method which depends on the one matrix along one directions and avoids the trouble of the Laplacian method that depends on two matrices along two directions. Among them, only two theories can calculate both finite and infinite networks. One is Wu's Laplacian matrix method and the other is Tan's RT method. However, there is only one way to compute a resistor network with arbitrary boundary, that is, the Tan's RT method.

Potential distribution problem in arbitrary rectangular circuit network has always been a problem of scientific research. In this paper, we develop the RT-I theory of resistor networks to calculate the arbitrary m × n circuit network model. We study the potential distribution and the equivalent resistance of a class of m × n rectangular network with an arbitrary boundary, a profound problem that has not been resolved so far, because previous research depends on the boundary conditions of rules or a zero-resistance boundary condition. Other methods, such as Green function technique and Laplacian method to calculate potential function are difficult and also impossible to study the resistor network with arbitrary boundary. Potential function problem is an important research subject in natural science and engineering technology, for example, the solution of Laplace's equation is one of research work. In this paper, we present an analytical expression of the node potential function of m × n rectangular resistor network with an arbitrary boundary, and also obtainan equivalent resistance formula between any two nodes, and the results in some special cases as well. In the comparative study of different results, a new mathematical identity and several interesting inferences are discovered.
Effects of reflection of electrons and negative ions on magnetized electronegative and collisional plasma sheath
Authors: Liu Hui-Ping , Zou Xiu ,   School of Science, Dalian Jiaotong University, Dalian 116028, China
Published: December 2020

The effects of the reflection of electrons and negative ions in magnetized electronegative and collisional plasma sheath on the Bohm criterion and the sheath structure are numerically investigated. The Bohm criterion expression of the sheath with considering the reflection of electrons and negative ions is derived theoretically. The lower limit of ion Mach number versus parameters and the distribution curve of charged particle density in sheath are obtained by numerical simulation when Boltzmannian model and reflection model are applied to electrons and negative ions. The results show that the upper limit of ion Mach number is identical to that of Boltzmannian model, but their lower limit expressions are different. The lower limit of ion Mach number in the reflection model is also related to the wall potential, and with the increase of the wall potential, ion Mach number first increases and then remains unchanged after reaching the same value as that from Boltzmannian model, and the speeds of their reaching the maximum values are different due to the difference in sheath edge negative ion concentration and temperature. In both Boltzmannian and the reflection model, the lower limit of the ion Mach number decreases with the concentration of the negative ion at the sheath edge increasing and the negative ion temperature decreasing, but the maximum value is smaller in the reflection model. The lower limit of ion Mach number for each of the two models increases with sheath edge electric field increasing, but increases faster and the final value is larger in Boltzmannian model. The lower limit of ion Mach number for each of the two models decreases with the increase of collision parameter or magnetic field angle, but decreases faster in Boltzmannian model with the increase of collision parameter or magnetic field angle. The lower limits of ion Mach number in the two models tend to be the same with the increase of magnetic field angle. When the wall potential is small, the reflection of electrons and negative ions has a great influence on the sheath structure. When the wall potential is large, the reflection of electrons and negative ions have little effect on the density distribution of charged particles in the sheath.
Rouge waves in fluid-filled elastic tube
Authors: Chen Zhi-Min , Duan Wen-Shan ,   College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China
Published: December 2020

By the reductive perturbation method, we investigate the Rogue waves in a fluid-filled elastic tube. Based on a nonlinear Schrodinger equation obtained from a fluid-filled elastic tube, the rouge wave solution in the fluid-filled elastic tube is discussed. The characteristics of a single rouge waveare studied for this system. Then, the effects of the system parameters, such as the wave number k, the parameters \begin{document}$\epsilon$\end{document}, the density of the fluid, the thickness of the elastic tube, the Yang's modulus of the elastic tube, and the radius of the elastic tube on the rouge wave are also investigated. Finally, the model is applied to the blood vessels of both animal and the human to ascertain the effects of the rouge wave in different arteries and vessels. The results of the present study may have potential applications in medical science.
Continuous-wave terahertz quantitative dual-plane ptychography
Authors: Wang Da-Yong , Li Bing , Rong Lu , Zhao Jie , Wang Yun-Xin , Zhai Chang-Chao ,   College of Applied Sciences, Beijing University of Technology, Beijing 100124, China,   Beijing Engineering Research Center of Precision Measurement Technology and Instruments, Beijing University of Technology, Beijing 100124, China
Published: December 2020

Terahertz (THz) radiation lies between the millimeter and infrared region of the electromagnetic spectrum, which is typically defined as the frequency range of 0.1–10 THz and the corresponding wavelength ranges from 30 μm to 3 mm. Terahertz radiation due to wide spectrum, high penetration, low energy, and other important features, has been a valuable tool for imaging and non-destructive testing on a submillimeter scale. Continuous-wave (CW) terahertz ptychography is a type of phase-contrast technique with advantages of simple set-up and large field-of-view. It retrieves the complex-valued transmission function of the specimen and the probe function at the same time. The extended ptychographic iterative engine (ePIE) algorithm is used as the reconstruction algorithm in the field of ptychography, because it is relatively simple, and can use computer memory efficiently. However, the problem of algorithm convergence delay makes us unable to acquire the reconstruction result very quickly. Since the ptychography is a problem of retrieving phase information, physical constraints affect the convergence speed of the algorithm strongly. In this paper, we propose a dual-plane ePIE (dp-ePIE) algorithm for CW THz ptychography. By moving detector along the axis and capturing diffraction patterns of one zone of an object at two recording planes, then, two sets of patterns used as the constraints simultaneously can increase the diversity of experimental parameter. Hence, the convergence rate can be improved. The simulation results suggest better reconstruction fidelity with a faster convergence rate by the dp-ePIE algorithm. The dual-plane terahertz ptychography experimental setup is built based on 2.52 THz optically pumped laser and Pyrocam-III pyroelectric array detector. Compared with other methods to increase the diversity of measurement, the setup of dual-plane ptychography can be compact and simple, thus reducing the terahertz wave transmission loss. A polypropylene sample is adopted and it is approximated as a pure phase object. No-reference structural sharpness (NRSS) is utilized as a quantitative evaluation index. It takes 45.086 s to achieve NRSS value of 0.9831 by using the dp-ePIE algorithm in 10 iterations, while the NRSS value and calculation time for e-PIE algorithm are 0.9531 and 57.117 s (20 loops), respectively. The experimental results show that the dp-ePIE algorithm can obtain high-quality amplitude and phase distribution with less iterations than the traditional ePIE algorithm.