bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis on the compressive sensing based narrow-band radar super resolution imaging mechanism of rapidly spinning targets
Authors: Li Shao-Dong  , Chen Yong-Bin  , Liu Run-Hua  , Ma Xiao-Yan  ,   No. Three Department, Air Force Early Warning Academy, Wuhan 430019, China
Published: December 2020

According to the characteristics of spinning targets, the narrow-band radar echoes can be directly used for imaging spinning targets. However, spurious peaks appear due to azimuth down sampling with a low pulse repetition frequency (PRF). By exploiting the sparsity of the targets, the compressed sensing (CS) theory can be adopted to obtain super resolution image under sub-sampling condition. This paper mainly focuses on analyzing the physical mechanism of the CS-based narrow-band imaging method. Firstly, the narrow-band radar's under-sampling echoes' model from rapidly spinning targets is established. The relationship between CS and the model is analyzed. Then the reasons why the CS-based narrow-band imaging method can guarantee the exact recovery of the spinning target are given from physical view. The theoretical lower limit of sub-sampling pulse numbers is provided. Finally, the simulation results verify the effectiveness of the theoretical analysis. The main results obtained in the paper are listed as follows. One is that the mechanism of the CS-based narrow-band imaging method differs from those of the conventional range Doppler imaging methods. The spurious peaks appear due to calculating the Doppler frequency directly under a low PRF. To avoid this phenomenon, the CS-based method searches the positions of the scatterers instead. The variation from calculating the Doppler frequency directly to searching the positions of the scatterers is the physical mechanism of the CS-based super resolution imaging method. The other is that the resolution and the allowable grid mismatch of the CS-based imaging method are related to the wavelength, which is 0.4 and unrelated to the bandwidth. So the performance of the CS-based imaging method is related to the sub-sampling rate, the number of the scatters and the wavelength, and unrelated to the bandwidth of the wave. However, this paper only considers the ideal point scattering model and the grid is perfectly matched with the model. In the following, three aspects can be further studied. First, due to the spinning target distribution on a continuous scene, the off-grid problem would severely affect the performance of the CS-based imaging method. The continuous compressive sensing theory can be used for solving the off-grid problem and explaining the related physical mechanism. Second, the illumination of the radar cannot reach some scatterers on the target in some observation intervals, which results in the occlusion effect and the time-varying scattering amplitude. The dynamic CS theory can be used for reference in solving this problem. Finally, if the estimated spinning frequency has error, how to correct and compensate for the error adaptively needs to be further studied.
Node importance measurement based on neighborhood similarity in complex network
Authors: Ruan Yi-Run  , Lao Song-Yang  , Wang Jun-De  , Bai Liang  , Chen Li-Dong  ,   Science and Technology on Information Systems Engineering Laboratory, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Ranking node importance is of great significance for studying the robustness and vulnerability of complex network. Over the recent years, various centrality indices such as degree, semilocal, K-shell, betweenness and closeness centrality have been employed to measure node importance in the network. Among them, some well-known global measures such as betweenness centrality and closeness centrality can achieve generally higher accuracy in ranking nodes, while their computation complexity is relatively high, and also the global information is not readily available in a large-scaled network. In this paper, we propose a new local metric which only needs to obtain the neighborhood information within two hops of the node to rank node importance. Firstly, we calculate the similarity of node neighbors by quantifying the overlap of their topological structures with Jaccard index; secondly, the similarity between pairs of neighbor nodes is calculated synthetically, and the redundancy of the local link of nodes is obtained. Finally, by reducing the influence of densely local links on ranking node importance, a new local index named LLS that considers both neighborhood similarity and node degree is proposed. To check the effectiveness of the proposed method of ranking node importance, we carry out it on six real world networks and one artificial small-world network by static attacks and dynamic attacks. In the static attack mode, the ranking value of each node is the same as that in the original network. In the dynamic attack mode, once the nodes are removed, the centrality of each node needs recalculating. The relative size of the giant component and the network efficiency are used for network connectivity assessment during the attack. A faster decrease in the size of the giant component and a faster decay of network efficiency indicate a more effective attack strategy. By comparing the decline rates of these two indices to evaluate the connectedness of all networks, we find that the proposed method is more efficient than traditional local metrics such as degree centrality, semilocal centrality, K-shell decomposition method, no matter whether it is in the static or dynamic manner. And for a certain ranking method, the results of the dynamic attack are always better than those of the static attack. This work can shed some light on how the local densely connections affect the node centrality in maintaining network robustness.
Studies of quasi one-dimensional nanostructures at high pressures
Authors: Dong Jia-Jun  , Yao Ming-Guang  , Liu Shi-Jie  , Liu Bing-Bing  ,   State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China;,   College of Physics, Jilin University, Changchun 130012, China
Published: December 2020

The ultimate goals of researches of one-dimensional (1D) nanomaterials, quasi-one-dimensional atomic/molecular chains are expected to exhibit their strong quantum effects and novel optical, electrical, magnetic properties due to their unique 1D structures. At present, synthesis and manipulation of 1D atomic/molecular chains on an atomic/molecular level in a controllable way have been the frontier subject of scientific research. The 1D atomic/molecular chains, which can be stable in ambient conditions, have been prepared successfully by using a confinement template, such as carbon nanotubes (CNTs), zeolite, etc.
High pressure can effectively tune the interatomic and intermolecular interactions over a broad range of conditions and thus to change the structures of materials. High pressure techniques have been recently adopted to investigate the 1D nanomaterials. In this paper, we briefly review some recent progress in the high pressure studies of 1D nanostructures, including iodine chains (I2)n confined in the 1D nanochannels of zeolite, multiwalled carbon nanotube (MWNT) arrays, and 1D carbon chains confined in CNTs. Particularly, polarized Raman spectroscopy combined with theoretical simulations has been used in the high pressure studies of 1D nanostructures. These studies reveal many interesting phenomena, including pressure-induced population increase and growth of 1D atomic/molecular chains. The underlying driven mechanisms have also been uncovered. Induced by pressure, the I2 molecules in zeolite 1D nanochannels rotates to the channel axial direction and the compression of the channel length in turn leads to a concomitant decrease of the intermolecular distance such that the iodine molecules come sufficiently close to the formation of longer (I2)n polymers. The novel polarized photoluminescence (PL) from the iodine chains and the pressure-induced PL enhancement due to the growth of 1D iodine chains under pressure. The depolarization effect vanishing in the polarized Raman spectra of compressed MWNT arrays. These are related to the pressure-induced enhancement of intertube interactions and inter/intratube sp3 bonding. The results obtained by polarized Raman spectroscopy overcome the difficulty:MWNTs have no obvious fingerprints for identifying the structural transformation under pressure.
Above all, the 1D nanostructures exhibit interesting and fantastic behaviors under pressure, which deserve further investigations in this research field. In addition, polarized Raman spectroscopy is an effective tool to study the structural transformations of 1D nanomaterials at high pressures, which can be extended to the studies of other analogous 1D nanostructures under pressure.
Estimating optical turbulence of atmospheric surface layer at Antarctic Taishan station from meteorological data
Authors: Wu Xiao-Qing  , Tian Qi-Guo  , Jin Xin-Miao  , Jiang Peng  , Qing Chun  , Cai Jun  , Zhou Hong-Yan  ,   Key Laboratory of Atmospheric Composition and Optical Radiation, Chinese Academy of Science, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Science, Hefei 230031, China;,   Polar Research Institute of China, Shanghai 200136, China;,   University of Science and Technology of China, Hefei 230026, China;,   Science Island Branch of Graduate School, University of Science and Technology of China, Hefei 230031, China
Published: December 2020

Turbulence intensity in the near-surface layer and its decrease rate with height are closely related to the quality of potential sites. Astronomers have been pursuing a perfect astronomical site to place the large-aperture telescopes. Compared with the best mid-latitude sites, Antarctic plateau inevitably becomes an ideal site for building the next-generation large optical and infrared telescopes, which is because of its low infrared sky emission, low atmospheric precipitable water vapour content, low aerosol and dust content of the atmosphere, and light pollution. In this paper, we establish a model of the atmospheric optical turbulence in surface layer, and use it to estimate Cn2 at Antarctic Taishan station for the first time. The meteorological parameters of the model input are the data measured by a mobile atmospheric parameter measurement system at Antarctic Taishan station from 30 December 2013 to 10 February 2014. The values of Cn2, estimated by the model and measured by a micro-thermometer, are compared. Sensitivity analysis of the estimation method is also carried out. The measurement results and analyses show that Cn2 obtained at Taishan station has obvious diurnal variation characteristics, with well-behaved peaks in the daytime and nighttime, and minima near sunrise and sunset. Cn2 obtained in the nighttime is stronger than that in daytime, more specifically, it is on the order of 210-14 m-2/3. The comparison between model predictions and experimental data demonstrates that it is feasible to estimate Cn2 in Antarctic by using this model. The biggest differences between Cn2 values obtained from the model and measurement usually emerge at sunrise and sunset, respectively. Considering the fact that Antarctic atmosphere is in a stable state most of the time, the values of Cn2 estimated by different nondimensional structure parameter functions are nearly the same. Thus, the measurement accuracy of air temperature difference from one height to another is the main factor that affects the estimated value of Cn2.
Spall behavior of copper under ultra-high strain rate loading
Authors: Xi Tao  , Fan Wei  , Chu Gen-Bai  , Shui Min  , He Wei-Hua  , Zhao Yong-Qiang  , Xin Jian-Ting  , Gu Yu-Qiu  ,   Science and Technology on Plasma Physics Laboratory, Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The spall behavior of copper at ultra-high strain rate is studied by molecular dynamics simulation combined with an experimental analysis of laser ablation of a bulk copper target by femtosecond laser pulses. In the molecular dynamics simulation, two-temperature model is used, shock wave and spallation characteristics of copper shock-loaded by femtosecond laser are analyzed in detail. It is concluded that the evolution of pressure indicates a triangular waveform of the shock wave, and the spall strength of copper is about 19 GPa at strain rates ranging from 109 s-1 to 1010 s-1, while higher pressure would melt the sample and the spall strength decreases to 14.89 GPa. Normally, the spallation is characterized by the sample free-surface undergoing alternately acceleration and deceleration, and the spallation mechanism could be explained by void nucleation, growth, coalescence that leads to the final fracture. An experiment is conducted to achieve high strain rate load on copper. The driving laser has a pulse width of 25 fs and central wavelength of 800 nm, the thickness values of the shocked copper foils are (5025) nm, fabricated by electron beam sputtering deposition onto 180 upm cover slip substrates. The driving laser beam with maximum intensity 5.51013 W/cm2, is focused on the front surface of the copper through the transparent substrate. Movements of the free rear surfaces of the copper foils are detected by chirped pulse spectral interferometry, and the theoretical time resolution is 1.3 ps. As a result, the free surface displacement and velocity evolution profile of the shocked area are obtained in a single measurement, and the results directly show that the maximum free surface velocity is 0.43 km/s and no alternately acceleration and deceleration appears. According to the shock wave relations, the maximum pressure near free-surface is 8.18 GPa. Meanwhile, derived from the velocity evolution profile, the strain rate is 7.3109 s-1. Combining with the above molecular dynamics simulation results, it is concluded that there is no spallation in the copper foil. Furthermore, we recover the sample targets and observe the microstructures by using scanning electron microscope. The copper foils are peeled off, but no spall scab is observed, indicating that the internal stress is between the copper spall strength and the bonding strength of copper foil with the transparent substrate. Ripple structure on copper surface demonstrates the femtosecond pulsed laser has ablated the copper film, and the propagation of the shock in fs regime is sensitive to microscopic defects.
Research on a six-order chaotic circuit with three memristors
Authors: Wang Wei  , Zeng Yi-Cheng  , Sun Rui-Ting  ,   School of Physics and Optoelectronic Engineering, Xiangtan University, Xiangtan 411105, China
Published: December 2020

A memristor is a nonlinear nanoscale-sized element with memory function, and it has an italic type 8 voltage-current relation curve that looks like a pinched hysteresis loop characteristic. The memristor is utilized to construct chaotic circuit, which has attracted the attention of the researchers. At present, most of studies focus on applying one or two memristors to the chaotic circuit. In order to study the multi memristor chaotic circuit, in this work we propose a six-order chaotic circuit with two flux-controlled memristors and a charge-controlled memristor. A corresponding six-order nonlinear dynamic differential equation of the circuit state variables is established. The dynamic properties of the circuit are demonstrated in detail. The analyses of equilibria and equilibrium stability show that the circuit has an equilibrium located in the three-dimensional space which is constituted by memristor internal state variables, and it is found that the equilibrium stability is determined by the circuit parameters and the initial states of three memristors. The Lyapunov exponent spectra and bifurcation diagrams of the circuit imply that it can produce two bifurcation behaviors by adjusting its parameters, which are Hopf bifurcation and anti-period doubling bifurcation. The hyperchaos, transient chaos and intermittency cycle phenomena are found in the same system. The dynamical behavior of this circuit is dependent on the initial state of memristor, showing different orbits such as chaotic oscillation, periodic oscillation and stable sink under different initial states. Finally, the simulation results indicate that some strange attractors like lotus type and superposition type are observed when voltage and electricity signal in observing chaotic attractors are generalized to power and energy signal, respectively. And the attractor production between the energy signals of the memristors are studied. Specially, when different initial conditions of three memristors are used to simulate the circuit, we can find the coexistence phenomenon of chaotic attractors with different topological structures or quasi-periodic limit cycle and chaotic attractor.
The six-order chaotic oscillating circuit is mainly composed of three parts:the parallel connection between a flux-controlled memristor and capacitor, the serial connection between a charge-controlled memristor and inductor, and another flux-controlled memristor that is alone and floating, which enriches the application of memristor in high-order chaotic circuit. Compared with most of other chaotic systems, it has many circuit parameters and very complex topological structure, which enhances the complexity of chaotic system and the randomness of the generated signal. It is more difficult to decipher the encrypted information in chaotic secure communication, and thus it has better security performance and safety performance.
The research on the illumination distribution law of the first-order scattered light in the focal plane of transmission optical system
Authors: Tan Nai-Yue  , Xu Zhong-Jie  , Wei Ke  , Zhang Yue  , Wang Rui  ,   College of Opto-Electronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

With the advantages of simple structure, low-cost, large field of view, and high image quality, the transmission optical system is widely used in detection system, microscope, telescope, etc. However, the research on the illumination distribution law in the focal plane of transmission optical system is rarely reported. In this paper, this issue is studied. During the study on the first-order scattered light distribution law in the focal plane of the transmission optical system, the limitations of the two-parameter Harvey bi-directional scatter distribution function (BSDF) scattering theory are found, namely in the condition of small scattering angle, the two-parameter Harvey BSDF theory cannot accurately describe the scattering properties of the optical surface material. So the scattering model of the transmission optical system under small scattering angle is established by introducing parameter l, and the accuracy of the new theoretical model is verified experimentally. This model complements the two-parameter Harvey BSDF scattering model and broadens the application scope of the Harvey BSDF scattering model so that it can better explain the imaging law of scattered light spot in the focal plane of transmission optical system. At a small scattering angle, the conclusions can be drawn from the new theoretical model as follows. 1) The irradiance of the final image plane increases linearly with the increase of the incident optical power. 2) In the transmission optical system, the contribution of each optical surface with the same scattering properties to scattered spot irradiance in the final image plane can be expressed by a Gaussian function. 3) The irradiance of scattered spot in the final image plane can be expressed as the superposition of n Gaussian functions, where n is the number of optical surfaces with different scattering properties in the transmission optical system.
Generation of Bessel beam by manipulating Pancharatnam-Berry phase
Authors: Chen Huan  , Ling Xiao-Hui  , He Wu-Guang  , Li Qian-Guang  , Yi Xu-Nong  ,   College of Physics and Electronic Information Engineering, Hubei Engineering University, Xiaogan 432000, China;,   College of Physics and Electronic Engineering, Hengyang Normal University, Hengyang 421002, China
Published: December 2020

Bessel beam is one of diffraction-free beams and has some peculiar properties. Varieties of its applications have been found, such as microparticle manipulating, material processing and biological studies. In this work, we propose a method of creating a Bessel beam by manipulating Pancharatnam-Berry phase. Using femtosecond laser, nano waveplatelets are written on a fused silicon glass to form a metasurface. The optical axis of waveplatelets rotating in the radial direction can produce the space-varying Pancharatnam-Berry phase. The designed metasurface acts as a planar axicon to generate Bessel beams by replacing the traditional one. A Jones calculation is employed to analyze the transformation of the metasurface. The theoretical results indicate that a left-handed circularly polarized light passing through the planar axicon is convergent, while a right-handed circularly polarized one is divergent. The intrinsic physical reason is that Pancharatnam-Berry phase is spin-dependent. Therefore, Bessel beams are generated by the planar axicon only when a left-handed circularly polarized light inputs the system. It is notable that the maximum nondiffracting distance is determined by the rate of rotation of the metasurface microstructure. By reducing the rate of rotation, we can easily obtain a longer nondiffracting distance, thus avoiding the problem that the base angle of the traditional axicon is too small to fabricate. According to the Fresnel diffraction integral, we simulate the propagation of the field emerging from the planar axicon and obtain the intensity distributions behind the planar axicon with different distances. The results show that the intensity pattern remains unchanged in the propagating process and possesses the propagation properties of Bessel beam. It implies that approximate nondiffraction Bessel beams can be achieved by employing the planar axicon with metasurface. Finally, we set up an experimental system with the Pancharatnam-Berry phase metasurface with period d=1000 upm to verify the theoretical analysis. Theoretically, the maximum nondiffraction distance is 7.9 m. In the shaded region, we measure the intensity distributions at different distances. The experimental results are in good agreement with the simulation results, so the planar axicon based on Pancharatnam-Berry phase can be an effective Bessel beam generator. We believe that these results are helpful for developing more spin-dependent photonic devices.
Optimazation of broadband third-harmonic UV generation in highly nonlinear photonic crystal fiber
Authors: Teng Huan  , Chai Lu  , Wang Qing-Yue  , Hu Ming-Lie  ,   Key Laboratory of Opto-electronic Information Science and Technology of Minstry of Education, College of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

The generation of pulse radiation with different frequency based on nonlinear optical frequency conversion technology is an effective method to produce lasers with the wavelength in the visible light or ultraviolet (UV) light range. In recent years, the developments of photonic crystal fiber (PCF) technology and ultra-short pulse technology have brought new solutions to the problems that the system needs great maintenance work, has low frequency conversion rate and much difficulty in popularizing, which the traditional frequency conversion system based on nonlinear crystal is confronting. Research on UV pulse radiation has been consistently attracting much attention of many academics. Particularly, narrowband and broadband UV pulse radiation sources are complementary, each having its own characteristics and scope of applications. The generation of narrowband UV pulse radiation of high sensitivity and high resolution through third harmonic generation (THG) in PCF has already been reported. However, the frequency conversion rate of narrowband UV pulse radiation is relatively low and the tunable ability of the spectrum is limited. These imperfections can be exactly completed by broadband UV pulse radiation. Broadband UV pulse radiation based on THG in PCF can be realized efficiently in PCF. This means that the conversion of UV light increases substantially, and simultaneously, the narrowband UV radiation of any wavelength in a certain range can be acquired more easily and the tunable ability of narrowband UV pulse radiation can be enhanced further. In this paper, the femtosecond pulse with a central wavelength of 1035 nm at a pulse repetition rate of 50 MHz is coupled into a highly nonlinear photonic crystal fiber with an appropriate length. The Raman self-frequency shift soliton produced from the ultra-short input pulse acts as a pump resource of third harmonic, transmitting through fundamental mode in PCF. Phase-matching between the fundamental mode and the high order modes is achieved and the third harmonic transmitted by specific high order modes (such as HE13) at deep UV wavelength is acquired effectively. Besides, the very high order UV mode (HOUVM) transmitting third harmonic with shorter wavelength is stimulated when intentionally inputting the ultra-short pulse into the PCF in the direction of a certain angle deviating from the axis of fiber core. Broadband deep UV (320-360 nm) pulse radiation with a UV light conversion rate of 3.6% can be acquired effectively in nonlinear PCF by stimulating a number of adjacent HOUVMs and achieving phase matching between the modes. Good agreement between theoretical results and experimental results is achieved.
Formation mechanism of water jets induced by the interaction between bubble and free surface
Authors: Zheng Jian  , Zhang Duo  , Jiang Bang-Hai  , Lu Fang-Yun  ,   College of Science, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Explosion in shallow water or small depth water will generate upward water jet, mainly because bubbles generated by explosion will interact with the surface of water. Different underwater depths can result in upward water jets with different kinds of shapes, such as water column, water plume, jet, spall dome, splash, spike, etc. To reveal the formation mechanisms of different types of water jets, a spark bubble experiment platform is set up, and the motions of bubble and free surface are studied experimentally by high-speed photography. The dynamic images for the formation process of the water jets under different initial depths of bubble are obtained. Through theoretical analysis and direct observation of the experimental data, the interaction process between the oscillating bubble and free surface are clarified, and the evolution rule of water jets is obtained. It is found that the key factor affecting the formation of different shapes of the water jets is the superposition of the disturbance of the second bubble pulse and the simple-shape jet induced by the first bubble pulse. Five types of the superpositions are summarized:1) All-fit type, with a large depth of initial bubble, the first and the second bubble impulse fit well to form a smooth and slightly arched water dome; 2) partial-fit type, with a less large depth of initial bubble, higher arched water dome is formed due to the raising effects of second bubble pulse partially fit the initial water dome shape; 3) catch-up type, with a mediate depth of initial bubble, the free-surface jet caused by first bubble pulse will be caught up from the bottom by the second pulse, and form a thin and high velocity jet; 4) run-after type, with a smaller depth of initial bubble, the free-surface jet caused by first bubble pulse will be raised from the bottom by the second pulse, and form a jet with thin head and thick pedestal, sometimes form a crown-type splash; 5) non-superposition type, the depth of initial bubble is so small that the bubble will break up, and no superposition will happen. In summary, the ratio of the initial depth to the maximum radius of bubble is found to be a decisive factor of the superposition type. The initial bubble is described by a dimensionless distance. These conclusions well explain the phenomena observed in experiment, and can provide a new vision and reference to the understanding of the formation mechanism of water jets induced by the interaction between bubble and free surface.
Effect of high power microwave injection on tropospheric freon
Authors: Ran Mao-Yi  , Hu Yao-Gai  , Zhao Zheng-Yu  , Zhang Yuan-Nong  ,   College of Electronic Information, Wuhan University, Wuhan 430072, China
Published: December 2020

High power microwave injection into the troposphere is a feasible approach to the decomposition of chlorofluorocarbon (CFC). However, in existing researches, there are only basic principles which lack quantitative tests. Hence, in this article we introduce the finite-difference time-domain method to quantitatively analyze the decomposition of CFC under high power pulses. We first investigate the principal chemical reactions of CFC decomposition induced by high power microwave injection and find that dissociation attachment is a dominant process of the microwave discharge decomposition of CFC. We use an empirical formula to calculate the decomposition efficiency of CFC. The result shows that 20% of the initial content of CFC molecules will be dissociated over 100 microseconds where we assume the electron number density to be 1013 cm-3. Then according to Maxwell's equations and the current density equation, we adopt the finite difference time domain method to simulate the generation process of a large number of free electrons induced by injecting the high power microwaves into the troposphere. The ionized electron generated by the high power microwave in troposphere is in favor of CFC decomposition since the electron affinity of CFC is larger than dissociation energy of CFC molecules. The simulation results indicate that the number density of electrons grows up to 1017 cm-3 exponentially with the injection time and will grow faster at higher height (10 km) or by the larger field intensity. During the pulse, the higher electron energy corresponds to a smaller dissociative attachment coefficient. Thus, most of the CFC molecules are decomposed during the electron-decay phase. During the relaxation period, the electron energy will return to the natural state within 0.01 ns. The number density of electrons decreases slower than the electron energy and it will take 1 ms to reach the natural state. From the results we can also see that the decay rates of the electron energy and number density decrease with the increase of the height. In this paper, two methods of calculating the CFC decomposition rate are utilized. One method is from the chemical reaction and the other method is based on an empirical formula which is mentioned before. It is shown that the results of these two methods present obvious consistency. The simulation results demonstrate that the CFC decomposition rate will increase with larger microwave intensity or higher frequency and can approach up to 6%. In conclusion, this study gives the quantitative analyses of the CFC decomposition induced by high power microwave injection in the troposphere for the first time.
Controlled production of double emulsion by microfluid technique
Authors: Chen Qiang  , Qi Xiao-Bo  , Chen Su-Fen  , Liu Mei-Fang  , Pan Da-Wei  , Li Bo  , Zhang Zhan-Wen  ,   Research Center of Laser Fusion, CAEP, Mianyang 621900, China
Published: December 2020

All planned inertial confinement fusion (ICF) capsule targets except machined beryllium require plastic mandrels with tight requirements on which the ablator is built. In this paper, the fabrication of poly(-methylstyrene) (PAMS) mandrel is studied. PAMS mandrels are produced by using microencapsulation technique. This technique involves producing a water droplet (W1) encapsulated by a flourobenzen (FB) solution of PAMS (O) with a droplet generator, and this droplet is then flushed off by external phase (W2), forming a water-in-oil-in-water (W1/O/W2) compound-emulsion droplet, which is suspended in a stirred flask filled with external phase to cure. The encapsulation process is based on a microfluid technique, which can achieve the controlled production of millimeter-scale PAMS mandrels. In this work, capillaries-based co-flowing microfluidic triple orifice generator is designed and built to fabricate W1/O/W2 droplets. Two configurations of the droplet generator:one-step device and two-step device, are employed in this experiment. In one-step device, the end of oil phase capillary is located at the same position as the end of inner water phase capillary. So the core droplet and the shell droplet break off from their capillaries ends at the same time, forming a W1/O/W2 droplet. While in the two-step device, the W1 phase capillary tip is located upstream to the W2 phase capillary tip. As a result, the core droplet and the shell droplet depart from the ends of their capillaries respectively, forming a W1/O/W2 droplet as well. Differently, the shell droplet contains only one core droplet in one-step generator, while several core droplets are contained in the shell droplet in two-step generator. In this paper, the mechanism of the droplet formation and the effect of the flow rate on the size of the droplet are studied with these two configurations. Results show that tiny difference between the two generators will lead to great differences in droplet formation mechanism and size control. In the two-step generator, the inner phase flow rate has little influence in the outer diameter of the compound-emulsion droplet. The diameters of the compound-emulsion droplets have a similar change to the diameters of the single droplets (O/W2). In one-step device, the inner phase flow rate has a significant influence on the outer diameter of the double-emulsion droplet because of the existence of W1-O interface. Finally, the compound-emulsion droplets fabricated in this experiment are cured in external phase, after which PAMS mandrels are fabricated. The diameters of the final PAMS mandrels are measured with optical microscope. The distribution of the diameters well concentrates in an area of (200010) upm, which is favorable for producing the PAMS mandrels with a diameter of 2000 upm.
Evaluation method of node importance in directed-weighted complex network based on multiple influence matrix
Authors: Wang Yu  , Guo Jin-Li  ,   Business School, University of Shanghai for Science and Technology, Shanghai 200093, China
Published: December 2020

In complex networks, the node importance evaluation is of great significance for studying the robustness of network. The existing methods of evaluating the node importance mainly focus on undirected and unweighted networks, which fail to reflect the real scenarios comprehensively and objectively. In this paper, according to the directed and weighted complex network model, by analyzing the local importance of the nodes and the dependencies among all the nodes in the whole network, a new method of evaluating the node importance based on a multiple influence matrix is proposed. Firstly, the method defines the concept of cross strength to characterize the local importance of the nodes. The index not only distinguishes between the in-strength and out-strength of the nodes, but also helps to discriminate the differences in importance among each with an in-degree of 0. In addition, to characterize the global importance of the nodes to be evaluated, we use the total important influence value of all the nodes exerted on the nodes, which makes up the deficiencies of the other evaluation methods which just depend on adjacent nodes. Emphatically, in the analysis of the influence ratio of source node on node to be evaluated, we not only take into account the distance factor between nodes, but also introduce the number of the shortest path factors. In order to make the evaluation algorithm more accurate, according to the number of the shortest paths, we present two perspectives to analyze how other factors affect the influence ratio. One is to evaluate how this source node exerts important influence on the other nodes to be evaluated. The other is to analyze how the other source nodes perform important influence on this node to be evaluated. In view of the above factors, three influence matrices are constructed, including the efficiency matrix, and the other two influence matrices from the perspectives of fixing source nodes and target nodes, respectively. Then, we use analytic hierarchy process to weight the three matrices, thereby obtaining the multiple influence matrix, which makes the global importance evaluation more comprehensive. Finally, the method is applied to typical directed weighted networks. It is found that compared with other methods, our method can effectively distinguish between nodes. Furthermore, we carry out simulation experiments of cascading failure on each method. The simulation results further verify the effectiveness of the proposed method.
Retrieval method of cirrus microphysical parameters at terahertz wave based on multiple lookup tables
Authors: Li Shu-Lei  , Liu Lei  , Gao Tai-Chang  , Hu Shuai  , Huang Wei  ,   College of Meteorology and Oceanography, PLA University of Science and Technology, Nanjing 211101, China
Published: December 2020

Cirrus is an important regulator for the flow of radiant energy in the earth-atmosphere system through the processes of scattering and absorption of radiation. In order to satisfy the urgent requirement for accurate retrieval of cirrus microphysical properties, terahertz wave is expected to be the best waveband for inverting cirrus particle size and ice water path, with terahertz wavelengths on the order of the size of typical cirrus particles. There is an urgent need for establishing stable and accurate inversion method. A new retrieval method for particle size and ice water path is developed based on multiple lookup tables for spaceborne measurements of brightness temperature spectrum of 183 GHz, 325 GHz, 462 GHz, 664 GHz, and 874 GHz channels. Five parameters are derived to quantify the effects of particle size and ice water path on terahertz radiation spectrum due to the scattering of ice clouds, manifested by brightness temperature difference, brightness temperature difference slope, etc. To retrieve cirrus microphysical parameters, a weighted least square fit that matches the modeled parameters is used. The analysis of retrieval errors are conducted by a simulated data series and the results are compared with those retrieved by the other two methods, i. e., difference method and slope method. The results retrieved by the multiple lookup table method are much closer to the simulated data series than those from the other two methods. It is indicated that the method introduced here is a stable and valid method of inverting particles between 50 and 500 m and ice water path between 10 and 500 g/m2. Compared with the errors from the difference-featured method and slope-featured method, the retrieval errors are reduced by 68.78% and 60.28% for particle size, 78.17% and 49.01% for ice water path. The analyses of retrieval uncertainties show that, in general, uncertainties of particle size and ice water path vary with particle size and ice water path. The ice water path uncertainties mainly spread in a range of 0-15 g/m2. The particle size uncertainties fluctuate within a range of 0-20 m. In other words, for small particle size range, the uncertainties are 0-5 m for thick clouds and 5-20 m for thin clouds. However, for large particle size range, the uncertainties are 0-5 m for particles larger than 300 m and 5-15 m for those smaller than 300 m. The results will be helpful for further developing the terahertz wave remote sensing of cirrus microphysical parameter technology. Moreover, it is also an important reference to the improvement of cirrus retrieval accuracy.
Experimental study on underwater supersonic gas jets in water flow
Authors: Zhang Xiao-Shi  , Xu Hao  , Wang Cong  , Lu Hong-Zhi  , Zhao Jing  ,   School of Astronautics, Harbin Institute of Technology, Harbin 150001, China;,   Research and Development Center, China Academy of Launch Vehicle Technology, Beijing 100076, China
Published: December 2020

The objective of this study is to investigate the flow structure of underwater supersonic gas jets in water flow. Supersonic gas jets submerged in a liquid flow field is experimentally studied in a water tunnel. In the experiments, a high speed camera system is used to observe the evolution of the gas jet bubble, and a dynamic pressure measurement system is used to measure the pressure fluctuation under different flow velocities simultaneously. We seek to study the mechanism of the vortex structure and the pressure fluctuation phenomenon during the gas jet evolution. The obtained results conclude that the main body formation and the pressure fluctuation of the gas jets depend heavily on the ambient flow speed. The instantaneous patterns of gas jets remarkably go upward due to the gravity effect in the still water. A shear vortex will be formed by jet-flow interaction when the ambient fluid flows. Larger vortexes are formed when the main body of the jet evolves downstream and mixes with the jet shear layer. The evolution pattern and pressure fluctuation characteristics of the gas-liquid interface are educed through a detailed analysis of the shear layer vortex structure. Backward reflection of pressure fluctuation is formed accompanying the jet bulging, necking, and back-attack. Consequently, the pressure fluctuation is transferred to the fluid at the nozzle surface and the test section. The pressure measurement system is used to confirm the pressure fluctuation phenomenon. Two measuring positions are set, i.e., pressure transducers are embedded at the nozzle surface and the test section. The pressure fluctuation with magnitude of 10 kPa is measured by the nozzle surface transducer in still water. The pressure fluctuation induced by the gas jets near the nozzle exit disappears simultaneously when the ambient fluid flows. However, the amplitude of pressure fluctuation decreases at the nozzle surface but increases at the test section with the increasing flow velocity. Power spectrum analysis is carried out and shows that the mechanical energy of the water tunnel gas jets is mainly distributed in the frequency band of 0-700 Hz. A jet induced large pressure fluctuation with a dominant frequency about 200 Hz can be captured near the nozzle surface in still water. With increasing water velocity, the dominant frequency of the unsteady pressure fluctuation decreases significantly at the nozzle surface. Conversely, the flow velocity leads to an increase in the spectral intensity of the pressure at the test section.
Ferromagnetism of undoped anatase TiO2 based on the first-principles calculations
Authors: Pan Feng-Chun  , Xu Jia-Nan  , Yang Hua  , Lin Xue-Ling  , Chen Huan-Ming  ,   School of Physics and Electronic-Electrical Engineering, Ningxia University, Yinchuan 750021, China
Published: December 2020

Compared with conventional semiconductors, the diluted magnetic semiconductors, in which the cations are substituted by transition metal ions, have attracted a great deal of attention due to their promising applications in spintronics. Recently, the unexpected room temperature ferromagnetism has been found in many undoped oxides. These findings challenge our understanding of magnetism in these systems, because neither cations nor anions have unpaired d or f electrons. Generally, the candidate defects responsible for the unexpected ferromagnetism must fulfill two conditions at the same time: (i) the defects should prefer a spin-polarized ground state with a nonzero local magnetic moments; (ii) the exchange interactions between local magnetic moments induced by defects should be ferromagnetic energetically. Among these oxides, TiO2 has recently attracted much attention because of its unique properties and potential applications in spintronics, laser diodes and biomaterials. In order to explore the origin of ferromagnetism in such an undoped TiO2 system, the electronic structures and magnetic properties of oxygen vacancy (VO) and Ti vacancy (VTi) in anatase TiO2 have been studied systematically by the first-principles calculation based on the density functional theory with the LDA+U method (UTi-3d = 5.8 eV). It is found that two electrons introduced by VO are captured by two neighbor Ti4+ ions, and thereby the Ti4+ ions are restored to Ti3+ ions with opposite spin orientation. Therefore, the single VO cannot induce local magnetic moment. The defect energy level locates near the Fermi level for VTi. Six oxygen atoms neighboring VTi constitute an octahedron, and the defect energy level is split into a single state A, a double state E and a triple state T in the octahedral crystal field. The occupation of four unpaired electrons introduced by six oxygen atoms is a+1t+3t-0e0 (subscripts + and - mean up-spin and down-spin, respectively), and the VTi can induce 4 B local moments. Furthermore, the magnetic coupling interaction between local magnetic moments induced by two VTi is ferromagnetic, and the magnetic coupling constant (JO) is 88.7 meV. It means the ferromagnetism can continue up to room-temperature. The VO cannot induce local magnetic moment, but it can enhance the coupling strength between two VTi, which can explain the origin of ferromagnetism observed experimentally in undoped anatase TiO2, i.e., the VTi induces local magnetic moment, while VO enhances the long range ferromagnetic coupling interaction between VTi. Especially, for the ferromagnetic coupling between local magnetic moments, we have proposed the second type direct exchange interaction model, which has been recommended in detail.
Theoretical study on the electronic structure and transition properties of excited state of ZnH molecule
Authors: Zhao Shu-Tao  , Liang Gui-Ying  , Li Rui  , Li Qi-Nan  , Zhang Zhi-Guo  , Yan Bing  ,   School of Physics and Electronic Science, Fuyang Normal College, Fuyang 236037, China;,   Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy(Jilin University), Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China;,   Department of Physics, College of Science, Qiqihar University, Qiqihar 161006, China
Published: December 2020

The potential energy curves (PECs) associated with the lowest four dissociation limits, i.e., Zn(1Sg)+H(2Sg), Zn(3Pu)+H(2Sg), Zn+(2Sg)+H-(1Sg) and Zn(1Pu)+H(2Sg), are calculated by using a high-level configuration interaction method. The Davidson correction, scalar relativistic effect and spin-orbit coupling effect are taken into account in calculation. On the basis of our calculated PECs of -S and states, the spectroscopic constants including Te, e, ee, Be and Re are evaluated by numerical solution of one-dimensional Schrdinger equation. The computed spectroscopic constants are reasonably consistent with previous experimental results. The dipole moment curves of the 7 -S states are presented, and the influences of the variation of electronic configuration on the dipole moment and bonding property are discussed. The computational results reveal the ionic character of the C2+ state. The variation of -S component for state near the avoided crossing point is illuminated, which is used to explain the change of transition dipole moment (TDM) around the avoided crossing point. Based on the TDMs, Franck-Condon factors and the transition energies, the radiative lifetimes of v'=0-2 vibrational levels of (2)1/2, (3)1/2, (4)1/2 and (1)3/2 states are predicted, which accord well with the available experimental values.