bluuebunny/crossref_metadata_2025 huggingface dataset:
Angular resolution of a neutron scatter imaging system
Authors: Zhang Mei  , Zhang Xian-Peng  , Li Kui-Nian  , Sheng Liang  , Yuan Yuan  , Song Chao-Hui  , Li Yang  ,   Northwest Institute of Nuclear Technology, Xi'an 710024, China;,   School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China;,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

Using a combination of imaging and spectroscopic capabilities, neutron scatter imaging is a novel method of detecting neutrons in an energy range from 1 to 20 MeV. The technique can be applied to measurements in a variety of areas, including solar and atmospheric physics, radiation therapy, and nuclear materials monitoring. Angular resolution is an important parameter for a neutron scatter imaging system. There are some factors causing the uncertainty in the reconstructed image due to the imperfection of the detector system and natures of neutron scattering. These factors mainly are the uncertainties of the position and the energy. In this paper, the contributions of these factors to the angular resolution are discussed. The results show that the angular resolution varies with scatter angle; the position uncertainty not only directly affects the angular resolution, but also indirectly contributes to the angular uncertainty by influencing energy uncertainty; when the detector dimension is less than 5 cm, the energy uncertainty becomes a dominating factor for angular resolution. The prototype is designed based on the above analysis results. The angular resolution of the designed prototype is tested on Cf252 source. The experimental results are basically consistent with the simulation results.
Influence of isotopic effect on the stereodynamics of reaction H+NH→N+H2
Authors: Wang Ming-Xin  , Wang Mei-Shan  , Yang Chuan-Lu  , Liu Jia  , Ma Xiao-Guang  , Wang Li-Zhi  ,   School of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, China
Published: December 2020

The stereodynamics of the H+NH reaction and its isotopic variants are investigated by the quasi-classical trajectory method at the collision energies of 8 kcal/mol and 16 kcal/mol based on the ground state potential energy surface of NH2 reported by Zhai and Han [Zhai H S, Han K L 2011 J. Chem. Phys. 135 104314]. Vector correlations of k- j' and k- k'- j', such as angular distributions of P(θr), P(φr), P(θr, φr) and the distributions of the polarization-dependent differential cross-sections are discussed in detail. The results indicate that for the two collision energies, the isotopic effect on sterodynamic property of H+NH reaction is apparent which could be attributed to the difference in mass factor in isotopy-susbstituting reaction.
A method of retrieving the constitutive parameter matrix of magnetoelectric coupling metamaterial
Authors: Xu Xin-He  , Liu Ying  , Gan Yue-Hong  , Liu Wen-Miao  ,   Nanchang Hangkong University, Nanchang 330063, China
Published: December 2020

The constitutive parameters of single negative (only electric permittivity or only permeability less than zero) metamaterials and wires-split ring resonator metamaterials can usually be retrieved by the S parameter method. Due to the cross polarization phenomenon in magnetoelectric coupling metamaterial, only two constitutive parameters of permittivity and permeability cannot accurately describe the electromagnetic characteristics of the magnetoelectric coupling metamaterial. The traditional S parameter retrieval method starts with the assumption that the metamaterial has only two constitutive parameters of permittivity and permeability, so the method to retrieve the constitutive parameters of magnetoelectric coupling metamaterials is obviously restricted. In this paper, the electric component and magnetic component in a magnetoelectric coupling metamaterial cell are treated as being equivalent to the surface current and surface magnetic flow, respectively. By deriving the relationship of the average electric flux density and the average magnetic flux density to the external electromagnetic field, we obtain a constitutive parameters matrix (2×2) of the magnetoelectric coupling metamaterial, and find analytical formulas for the relationship between these four constitutive parameters of the magnetoelectric coupling metamaterial and the parameters such as the permittivity of the electric component, permeability of magnetic element, spatial dispersion, and coupling coefficient, and then deduce the refractive index formula. We use the refractive index formula to nonlinearly fit retrieval refractive index curves, and find very good agreement between the refractive index values theoretically predicted by analytical formulas and those obtained from numerical retrievals based on full-wave simulations, thereby verifying the proposed constitutive matrix analytic formula and the refractive index expression. According to the fitting results, we obtain the frequency response curves of the four electromagnetic parameters in constitutive matrix. The proposed method of retrieving the constitutive matrix parameters will provide an important theoretical reference for the researchers engaged in analyzing and studying the coupling phenomenon between electric component and magnetic component in a magnetoelectric metamaterial cell.
New differential-mode-source cable bundle crosstalk model based on multiconductor transmission lines theory
Authors: Sun Ya-Xiu  , Zhuo Qing-Kun  , Jiang Qing-Hui  , Li Qian  ,   College of Information and Communication Engineering, Harbin Engineering University, Harbin 150001, China
Published: December 2020

The traditional cable bundle crosstalk model is established based on an intra-system common mode source, without considering the crosstalk of cable bundles stimulated by a differential-mode source between different systems. To solve the physical problem of crosstalk between independent circuit cable bundles which is stimulated by a differential-mode source, in this article we propose a new differential-mode source cable bundle crosstalk calculation method based on the multiconductor transmission line theory. According to the mechanism of the differential-mode-stimulated transmission line coupling, using this method we obtain a new three-conductor transmission line parasitic parameter circuit model and mathematic matrix model through using the transmission line propagating transverse electro magnetic mode. We deduce the parasitic parameter calculation formula by an image method and Neumann formula, and then obtain the new cable bundle crosstalk chain parameter array equations in frequency domain. By using the top and end boundary conditions of the new differential-mode cable bundle crosstalk model, we finally work out the crosstalk voltage in frequency domain. In this article, we take the crosstalk between differential-mode parallel double culprit cables and the victim cable from other independent circuit for example. By simulating the crosstalk voltage of victim cable in different position arrangements, we obtain the crosstalk physical law between cable bundles under the differential-mode source condition, that is, the crosstalk of the victim cable located between differential-mode circuits is much larger than that situated outside the differential-mode circuit. We can also verify that this model can be used to calculate the crosstalk caused by differential-mode source at different frequencies. In this article, we analytically calculate the crosstalk problems caused by differential-mode source cable bundles for the first time, which provides theoretical basis for solving some practical electromagnetic compatibility problems such as the bundling of a large quantity of wires and the predicting of cable bundle crosstalk. Therefore it perfects the application of multiconductor transmission line model to cable bundle crosstalk problem, and has strong guiding significance.
Optical bistability and optical storage based on injection locked Fabry-Perot semiconductor laser
Authors: Huang Biao  , Yu Jin-Long  , Wang Wen-Rui  , Wang Ju  , Xue Ji-Qiang  , Yu Yang  , Jia Shi  , Yang En-Ze  ,   Optical Fiber Communication Lab, School of Electronic Information Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

All-optical bistability based on injection locked Fabry-Perot semiconductor laser (FP-LD) and its application in all-optical storage are studied in this paper. Injection locking of FP-LD is experimentally studied in this paper. The output power characteristic of injection locked FP-LD is analyzed experimentally, showing that threshold width of hysteresis loop and the extinction-ratio are influenced by the difference in the injection optical-wavelength detuning. Furthermore, 2.5 GHz optical storage with 10 Gb/s input signal is realized by reasonably setting the control signal power. The feasibility of implementing high-speed all-optical storage is verified by using the injection locked FP-LD, which shows great applicability to the field of high speed optical fiber communication.
Information spreading in correlated microblog reposting network based on directed percolation theory
Authors: Wang Xiao-Juan  , Song Mei  , Guo Shi-Ze  , Yang Zi-Long  ,   Department of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China;,   The Institute of North Electronic Equipment, Beijing 100083, China
Published: December 2020

Due to the properties of rapidity, explosive, timeliness and complicated behavior for user, the research on information spreading progress and influence factors for microblog becomes a hot area of network public opinion. In this paper, firstly we use the contracting mapping principle to discuss the convergence conditions of the iterative algorithm. The numerical solution of the percolation threshold and the size of the largest out-component are proposed. Then the influence of assortativity is analyzed based on the generation model with varying parameter. The feasibility of the proposed algorithm is verified by collecting microblog reposting data. Experimental results demonstrate that four correlation characteristics are shown to have assortativity and disassortativity, but the results of message spreading are closer to that of the assortative network which is related to in-in and in-out degree correlation. It can be verified that the four types of correlation characteristics of a large part of nodes show their consistency for assortativity, through deleting a few nodes as well as extracting link scale for four degree correlations.
Numerical validation study of high power microwave soil breakdown
Authors: Tang Tao  ,   Electronic Engineering College, Chengdu University of Information Technology, Chengdu 610225, China
Published: December 2020

The nonlinear changes of soil resistivity will be caused when the high power microwave (HPM) propagates in soil, and these changes in turn counteract the propagation process so that the energy transmission efficiency of the HPM is reduced. By analyzing the dynamic ionization process of soil, a HPM soil propagation model is constructed by combining the Maxwell equations. The model is numerically validated by using a finite difference time domain method. The numerical results show the physical processes of the HPM propagation and attenuation in soil and the nonlinear change process of soil resistivity. These numerical results are verified by a theoretical analysis.
A molecular dynamics study of temperature and depth effect on helium bubble released from Ti surface
Authors: Liang Li  , Tan Xiao-Hua  , Xiang Wei  , Wang Yuan  , Cheng Yan-Lin  , Ma Ming-Wang  ,   Institute of Electronic Engineering, China Academy of Engineering Physics, Mianyang 621999, China
Published: December 2020

Using molecular dynamics simulation, the effects of temperature and depth of helium bubble on volume, pressure and releasing process of helium bubble in metal Ti are investigated. First, through studying the states of helium bubble at different depths at room temperature, the variation regularities of volume, pressure and releasing process of helium bubble with its depth are acquired. The results show that with depth augmenting, the pressure of helium bubble increases gradually, while the volume decreases, but these two parameters are kept at some level when the depth is greater than 2.6 nm. Then, the evolutions of model system with helium bubble at various temperatures are simulated. The critical temperatures of helium bubble released from Ti surface at different depths are greatly different. On the whole, the critical temperature is in direct proportion to depth. But the releasing rates at different temperatures are almost unanimous. Finally, the mechanism of helium bubble released from Ti surface is explained on the basis of statistics and analyses of pressure of helium bubble and tensile strength of the metal thin film above the bubble. It is found that helium bubble would tear the Ti film above it when the pressure in helium bubble is greater than the strength of Ti film, and then helium atoms will be released from the metal.
Dynamic stability of Zr under high pressure and high temperature
Authors: Hu Cui-E  , Zeng Zhao-Yi  , Cai Ling-Cang  ,   College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 400047, China;,   Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The phase transitions and structure stabilities of materials have always attracted much attention of the experimental and theoretical investigators. When calculating the phonon dispersion of the cubic structure of the transition metal Zr (β -Zr), the traditional methods always give the negative phonon frequencies. So the quasi-harmonic approximation cannot solve this kind of problem. We obtain the phonon dispersion of β -Zr at high pressure and high temperature by using the newly developed self-consistent ab initio lattice dynamics method, which can well consider the phonon-phonon interactions. And then the stable region of β -Zr in the high pressure and high temperature phase diagram is predicted. The full phase diagram of Zr is also predicted. We also obtain the high temperature equation of state (EOS) and thermal expansion of β -Zr, which can help to construct the EOS data base of Zr.
First-principles study of N/Cu co-doped anatase TiO2
Authors: Yang Jun  , Miao Ren-De  , Zhang Xi  ,   Institute of Sciences, PLA University of Science and Technology, Nanjing 211101, China
Published: December 2020

Using the first-principles plane-wave ultra-soft pseudo-potential method based on the density functional theory, the structures, electronic-structures and optical properties of pure anatase TiO2, N (Cu) doped TiO2, and N/Cu co-doped TiO2 crystal are studied by the local-spin density approximation plus Hubbard U method. It is shown that the lattice constants become larger because of the lattice distortion caused by doping. Impurity levels in the band gap of TiO2 are introduced by N and Cu doping, and the forbidden band width is correspondingly changed. For N doped TiO2, the reduction of the band gap is weak, while the N/Cu co-doped TiO2 band gap decreases remarkably. It leads to a red shift of visible absorption spectrum and enhances optical catalysis. The effect is useful for the practical application of photo-catalytic.
Near infrared broadband from Er-Tm codoped zinc oxide and temperature-dependent properties
Authors: Chen Dan-Dan  , Xu Fei  , Cao Ru-Nan  , Jiang Zui-Min  , Ma Zhong-Quan  , Yang Jie  , Du Hui-Wei  , Hong Feng  ,   SHU-SolarE R&D Lab, Department of Physics, College of Sciences, Instrumental Analysis and Research Center, Shanghai University, Shanghai 200444, China;,   State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structure (Ministry of Education), Advanced Materials Laboratory, Fudan University, Shanghai 200433, China
Published: December 2020

Er-Tm codoped ZnO thin film is synthesized by co-sputtering from separated Er, Tm, and ZnO targets. A flat and broad emission band is achieved in a range of 1400-2100 nm by optimizing annealing temperature, and the observed 1460, 1540, 1640 and 1740 nm emission bands are attributed to the transitions of Tm3+: 3H4 →3F4, Er3+ 4I13/2 →4I15/2, Tm3+ 1G4 → 3F2 and Tm3+ 3F4 → 3H6 transitions, respectively, which cover S, C, L, U bands. The intensity ratios of 1640 to 1535 nm and 1740 to 1535 nm below 1000 ℃ are nearly constant, while the ratios increase sharply above 1000 ℃. The temperature dependence of photoluminescence (PL) spectrum is studied under 10-300 K. With increasing the operation temperature, the bandwidth of broadband is nearly invariable (340-360 nm), and the Tm3+ PL emission intensities of 1640 nm and 1740 nm from Er-Tm co-doped ZnO thin film decrease by a factor of 1.5 and 2, respectively. Moreover, the 1535 nm emission intensity is increased by a factor of 1.2. This phenomenon is attributed to the complicated energy transfer (ET) processes involving both Er3+ and Tm3+ and the increase of phonon-assisted ET rate with temperature as well. And the cross relaxation between Tm3+ ions does not occur.
Thermoelectric properties of the Bi2Te3 nanocrystalline bulk alloy pressed by the high-pressure sintering
Authors: Wu Fang  , Wang Wei  ,   School of Physical and Electronic Engineering, Henan Institute of Education, Zhengzhou 450046, China;,   School of Information Engineering, Zhongzhou University, Zhengzhou 450044, China;,   Key Laboratory of Material Physics, Ministry of Education, School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052, China
Published: December 2020

Bi2Te3 nanowires and nanoparticles are synthesized by hydrothermal method, and the nanopowders are pressed into bulk pellets by high-pressure sintering or vacuum hot-pressed. The scanning electron microscope (SEM) results and thermal properties of such bulk samples are compared. The SEM result shows that the grain size of the high-pressure sintering sample is much smaller than that of the hot-pressed sample. The thermal properties show that the electrical resistivity, Seebeck coefficient, and thermal conductivity of the high-pressure sintering sample are all better than those of the hot-pressed sample. The ZT value of the high-pressure sintering sample prepared by nanowires reaches 0.5 at room temperature, which is much higher than that of the hot-pressed sample. Therefore the high-pressure sintering provides an effective method to press nanopowders to bulk.
Stable components in extended-range forecasting during the continuous high temperature event in August 2013 over the mid-eastern China
Authors: Zeng Yu-Xing  , Ye Tian-Shu  , Wang Kuo  , Shen Qian  ,   College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China
Published: December 2020

Based on the continuous high temperature process over the mid-eastern China in August 2013, using the NCEP/NCAR (United States National Centers for Environmental Prediction/National Center for Atmospheric Research) daily average of 500 hPa height field, the wind field reanalysis data, and the NOAA (National Oceanic and Atmospheric Administration) reconstruction sea surface temperature (SST) data, through the selection method similar to the early adoption of SST forcing, band-pass filtering and empirical orthogonal function decomposition method to extract the 10-30 days of stable components, and through a stable component of diagnostic analysis, we investigate the mechanisms for sustaining and reducing high temperature process. Results show that by selecting and using the case that is the most similar to a pre-SST forcing 30-year climatology instead of the normal 30-year climatology (1981-2010), the steady-state component extracted climate proportion is reduced, and the proportion of anomalously stable components is significantly enhanced and the described influence strength and stability are improved significantly, which can more clearly show the extended maintenance mechanism of weather processes. It suggests that early consideration SST forcing in the extraction component is very necessary. Meanwhile, the analysis of extension of stable components shows that the process of maintaining and reducing high temperature is mainly caused by the combined effect of the Arctic Oscillation, continental high latitudes zonal circulation situation in Asia and the western Pacific subtropical high intensity and location.
An integral-transformation corresponding to quantum mechanical fundamental commutative relation and its application in deriving Wigner function
Authors: Fan Hong-Yi  , Liang Zu-Feng  ,   Department of Physics, Ningbo University, Ningbo 315211, China;,   College of Science, Hangzhou Normal University, Hangzhou 310036, China
Published: December 2020

In this paper, it can be found that there is a type of integra-transformation which corresponds to a quantum mechanical fundamental commutative relation, with its integral kernel being 1/exp[2i(q-Q)(p-P)], here denotes Weyl ordering, and Q and P are the coordinate and the momentum operator, respectively. Such a transformation is responsible for the mutual-converting among three ordering rules(P-Q ordering, Q-P ordering and Weyl ordering). We also deduce the relationship between this kernel and the Wigner operator, and in this way a new approach for deriving Wigner function in quantum states is obtained.
Recommendation of important nodes in deployment optimization model of defense strategy
Authors: Yang Xiong  , Huang De-Cai  , Zhang Zi-Ke  ,   School of Computer Science and Technology, Zhejiang University of Technology, Hangzhou 310023, China;,   School of Computer &Information Engineering, Changzhou Institute of Technology, Changzhou 213002, China;,   Alibaba Research Center for Complexity Sciences, Hangzhou Normal University, Hangzhou 311121, China
Published: December 2020

Current network security defense strategy focuses on deploying to high degree nodes where there are mainly two aspects of the problem: One is that the high-degree nodes are not the backbone nodes for the network communication in many occasions; another is that these nodes are not always the most effective ones for forwarding and propagation information. With the disadvantage of current network defense strategy deployment, this paper tends to improve the traditional diffusion model of malicious program propagation and measure the importance of network nodes by using intermediate hops, then the important node for recommended deployment technology based on betweenness center control and closeness center control model is put forward. Experimental results show that the nodes with high betweenness centrality and low closeness centrality as compared with the high degree nodes can more effectively quarantine the spreading of the worms whether in scale-free network or in small world network. Meanwhile, the clustering behavior of a network will also play a certain negative impact on the spread of malicious programs.
Robust fractional-order proportional-derivative control of unified chaotic systems with parametric uncertainties
Authors: Lu Yong-Kun  ,   School of Electronic Information and Automation, Tianjin University of Science and Technology, Tianjin 300222, China
Published: December 2020

In this paper, a robust fractional-order proportional-derivative (PDμ) control is designed for controling in integer-order unified chaotic systems with parametric uncertainties. Equivalent plant is obtained by transforming the controlled dynamic system, and then the PDμ controller as an equivalent controller is applied to the equivalent plant. In the uncertain controlled unified chaotic systems, one equation is certain, and the other two equations are uncertain . The equivalent controller for the certain system is then designed based on a fractional-order proportional-derivative controller, in which three specifications for phase margin, gain crossover frequency, and robustness should be met. On the other hand, the robustness of uncertain systems is achieved by an improved Monje-Vinagre tuning method, however, the pre-specified frequency band should be replaced by the gain crossover frequency in order to reduce the complexity in determining the controllers for the uncertain systems. Specifications related to phase margin for the lower bound of the phase, gain crossover frequency for the upper bound of the gain, and robustness for the lower bound of the phase constraints are satisfied by the uncertain system. Parameters of the equivalent controller are determined based on a graphical method. Origins of the unstable equilibrium can be asymptotically stabilized by the proposed strategy for the integer-order unified chaotic systems with parametric uncertainties. Numerical simulation examples for Chen system, L system, and Lorenz system, are given to show the effectiveness of the proposed method.
Research on emission transition mechanisms of InGaN/GaN multiple quantum well light-emitting diodes using low-frequency current noise
Authors: Wang Dang-Hui  , Xu Tian-Han  , Wang Rong  , Luo She-Ji  , Yao Ting-Zhen  ,   School of Materials Science & Engineering of Xi'an ShiYou University, Xi'An 710065, China
Published: December 2020

In this paper, we measure the emission transition mechanisms in InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LED) using low-frequency current noise from 0.1 to 10 mA. According to the characteristics of the low-frequency current noise and the emission mechanisms of InGaN/GaN LEDs, we study the relationships between low-frequency current noise and current flows through the LEDs. Conclusions indicate that the low-frequency current noise is increased with the increasing current from 0.1 to 10 mA. With a lower current (I10 mA) it is the 1/f noise that dominates in LEDs, so there exists an emission transition mechanism in InGaN/GaN MQW LEDs between 0.1 and 10 mA, showing that the mechanism of the carrier recombination changes from non-radiative recombination to a stable fluctuation of carrier numbers. Conclusions of this paper provide an effective method to characterize the emission transition mechanisms, optimize the design of LED so as to improve the quantum efficiency for InGaN/GaN MQW LEDs.
Study on 0.34 THz overmoded surface wave oscillator
Authors: Wang Guang-Qiang  , Wang Jian-Guo  , Li Shuang  , Wang Xue-Feng  , Lu Xi-Cheng  , Song Zhi-Min  ,   Northwest Institute of Nuclear Technology, Xi'an 710024, China;,   Science and Technology on High Power Microwave Laboratory, Xi'an 710024, China
Published: December 2020

The simulation design and preliminary experiment on a 0.34 THz large-power overmoded surface wave oscillator are presented in this paper. For the slow wave structure (SWS) with large overmoded ratio (D/λ ≈ 6.8), a small signal theory is derived for appropriate dimensions of SWS and gap between electron beam and SWS, and makes the device oscillate near the π point of surface wave at TM01 mode. PIC (particle in cell) simulation results show that this SWO (small wave oscillation) can genetate the terahertz wave with frequency and output power of 0.34 THz and 22.8 MW, respectively. SWS with stainless steel is integrally and precisely fabricated by employing mirco-EDM technology, and the experimental setup is built based on a miniaturized pulse power driving source. Results of preliminary experiment and diagnostics show that a terahertz pulse is radiated at a frequency range of 0.319–0.349 THz, a power of no less than 250 kW, and a pulse duration of about 2 ns at beam voltage of about 420 kV and beam current of about 3.1 kA. Finally, the reason for discrepancy between the measured power and the simulation result is analyzed and discussed, laying the foundation for the performance improvement of terahertz surface wave oscillator.
Modified uniform-fission-site algorithm in Monte Carlo simulation of reactor criticality problem
Authors: Shangguan Dan-Hua  , Li Gang  , Deng Li  , Zhang Bao-Yin  , Li Rui  , Fu Yuan-Guan  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   CAEP Software Center of High Performance Numerical Simulation, Beijing 100083, China
Published: December 2020

Because of a very non-uniform power distribution in core region, a very non-uniform distribution of relative uncertainties exists for tallies in Monte Carlo criticality calculations of pin-by-pin reactor model. To make a large part of cells obtain small enough relative uncertainties with reasonable time costs, increasing the total sample scale is not a good choice. By realizing a modified uniform-fission-site algorithm on the basis of source iteration algorithm of parallel Monte Carlo transport code JMCT, we obtain higher efficiencies for tallies in the calculations of pin-by-pin model of the Dayawang reactor plant. This work supplies a useful tool for matching the goal of simulating the benchmark pin-by-pin reactor models with a pre-described standard(the so called Kord-Smith challenge).
Theoretical and applied researches on measuring line width in wavelength modulation spectroscopy
Authors: Zhang Shu-Feng  , Lan Li-Juan  , Ding Yan-Jun  , Jia Jun-Wei  , Peng Zhi-Min  ,   Beijing Orient Institute for Measurement & Test (BOIMT), Beijing 100086, China;,   Department of Thermal Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

Line width is the key parameter in tunable diode laser absorption spectroscopy (TDLAS); the dominant line widths are Doppler and collisional broadenings. Under low absorbance, the ratios of 2nd to 4th harmonics at the line center monotonously decrease and intersect at a fixed point, regardless of the changes in Doppler and collisional line widths. Based on this characteristic, a method is proposed which employs the ratios to measure the line width. To validate the reliability and accuracy of the proposed method, the transition of CO2 at 6982.0678 cm-1 is selected to measure the line width, the gas partial and total pressure. Experimental results show that the proposed method can achieve high precision in actual measurements.
Theoretical and experimental study of a controllable double-dark-hollow beam
Authors: Zhou Qi  , Lu Jun-fa  , Yin Jian-Ping  ,   College of Science, East China Institute of Technology, Jiangxi Fuzhou 344000, China;,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
Published: December 2020

A novel scheme is proposed for a double-dark-hollow beam (DDHB) based on non-full-range phase modulation with double-period. Upon illumination by a collimated He-Ni laser beam shaped by a round hole with a radius of 1.5 mm, the DDHB with an axial length of 30 mm, a width of 0.110.14 mm for each dark hollow beam and their separated distance being 57.6 m is generated in the image space of lens with a focal length of 200 mm. The proposed scheme has the advantages of simple construction and high controllability, and the separated distance between the two light pipes is only dependent on the factor of phase modulation of p. Under the given conditions, a reversible evolution process from a DDHB to a single dark hollow beam (SDHB) can be realized. Experiments for our scheme are performed, results of which are consistent with the theoretical ones. A valuable expansion of the application of DDHB in blue-detuned optical trapping is also discussed. Double and four well hollow optical traps, even the hollow optical lattices can be obtained by using various spatial combinations of our DDHB. The proposed DDHB is expected to play an important role in the study of trapping and manipulation of cold atoms or molecules.
Study on the properties of vector beams generated by a curved wave plate in the strong-focusing regime
Authors: Zhou Qiao-Qiao  , Shi Jian-Zhen  , Ji Xian-Ming  , Yin Jian-Ping  ,   Science College, Nantong University, Nantong 226019, China;,   State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062, China
Published: December 2020

We propose a new scheme to generate the axisymmetric vector beam. A curved wave plate, designed by using the birefringence properties of a crystal, can generate two different phase distributions with respect to the o-light and e-light, and it then can transform the linearly polarized light into the radial or azimuthal vector beam with the property of rotational symmetry. The above scheme has the advantage of having a simple light path and can be adjusted conveniently. According to Richards-Wolf's model of the classical vector diffraction, we calculate the distributions of the diffracted electromagnetic field that is illuminated by a hollow Gaussian beam and focused by a lens with high numerical aperture. Results show that the hollow vector beam has a very high intensity and intensity gradient and longitudinal distribution of the electric or magnetic field even if illuminated by the laser with a power of 0.5 W. In addition, real-time adjusted distributions of the photon angular momentum can be generated. This scheme has good application prospects in the manipulations of the microscopic particles.
Shape classification of single aerosol particle using near-forward optical scattering patterns calculation
Authors: Zhang Jin-Bi  , Ding Lei  , Wang Ying-Ping  , Zheng Hai-Yang  , Fang Li  ,   Laboratory of Environmental Spectroscopy, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Heifei 230031, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Particle shapes can be distinguished by the properties of near-forward optical scattering patterns of particles. The discrete dipole approximation method is used to calculate the light scattering patterns of Bacillus sphaericus, Bacillus subtilis, Burkholderia pseudomallei based on their prolate spheroid models. Shape dependence of forward angle-resolved light scattering intensity for nonspherical biological aerosol particles is discussed by simulating their light scattering response of three detectors located in different azimuthal range. Combined with sphericity index method, forward small angle (5°–20°) angle-resolved light scattering intensity has the ability to identify the elongated particles and non-elongated particles under certain orientation conditions. This study can help not only design particle morphology measurement instrument but also detect harmful biological aerosol rapidly.
Physiochemical properties and crystallization behavior of GeS2-In2S3 chalcogenide glasses
Authors: Lin Chang-Gui  , Zhai Su-Min  , Li Zhuo-Bin  , Qu Guo-Shun  , Gu Shao-Xuan  , Tao Hai-Zheng  , Dai Shi-Xun  ,   State Key Laboratory of Silicate Materials for Architecture (Wuhan University of Technology), Wuhan 430070, China;,   Laboratory of Infrared Materials and Devices, Advanced Technology Research Institute, Ningbo University, Ningbo 315211, China
Published: December 2020

Relationship among the composition, properties, and structure of glasses are one of the long standing topics in glass science. In this paper, (100-x) GeS2-xIn2S3 (x=10, 15, 20, 25 or 30 mol%) glasses and glass-ceramics are prepared by melt-quenching and subsequent heat treatments. Their composition dependence of optical bandgap, glass transition temperature, and crystallization behavior is measured by various techniques, and the effect of Ga or In element and the related structural units on their properties is discussed with the help of the previous researches on the GeS2-Ga2S3 glass system. Results show that In has a much bigger influence than Ga on the optical bandgap and glass transition temperature of chalcogenide glasses, while the crystallization behavior of the two kinds of glasses containing Ga and In is totally different, but has a close connection with the respective phase diagram. Their structural motifs can be realized by employing polarized Raman spectra. Consequently, combined with the recognition of their phase diagrams, the composition dependence of physiochemical properties and crystallization behavior, as well as the structural motifs, the correlation between chemical and structural topology is briefly discussed, which may provide a new insight into the glass topological structure.
Research on far-field enhanced imaging based on negative reflection of periodic structure
Authors: Yang Dan-Qing  , Wang Li  , Wang Xin-Long  ,   Key Laboratory of Modern Acoustics, Nanjing University, Nanjing 210093, China
Published: December 2020

Far-field high resolution imaging is one of the research focus in the field of acoustics and optics in recent years. The greatest difficulty for high resolution imaging in the far field is the evanescent waves not being able to propagate in the medium. A kind of scatterers composed of uniformly spaced steel columns is presented in this work. Negative reflection of periodic structure can change the evanescent waves to the waves that can propagate to enhance imaging. A finite element simulation has been used to study and verify the feasibility of the scheme. Results show that with the sound wave of 3.4 mm wavelength one can obtain an imaging resolution of about 0.6 wavelength in the far field of 20 cm. We further note that by reducing the lattice constant of scatterers a higher far-field resolution imaging can be hopefully reached.
Numerical study of cooling heat transfer of supercritical carbon dioxide in a horizontal helically coiled tube
Authors: Xu Xiao-Xiao  , Wu Yang-Yang  , Liu Chao  , Wang Kai-Zheng  , Ye Jian  ,   Key Laboratory of Low-grade Energy Utilization Technologies and Systems, College of Power Engineering, Chongqing University, Chongqing 400030, China
Published: December 2020

In the present study, cooling heat transfer of supercritical CO2 in a horizontal helically coiled-tube 4 mm in diameter, 2000 mm in length, a pitch of 10 mm and 0.1 in curvature is numerically investigated with RNG turbulence model. Influences of mass flow rate, heat flux and pressure on heat transfer of supercritical CO2 are studied. The characteristics of the flow and heat transfer are compared with those in a horizontal straight tube. Results show that the secondary flow and heat transfer coefficient in a helically coiled tube is obviously larger than in a horizontal straight tube. The heat transfer coefficient of supercritical CO2 increases with increasing mass flow rate, and the heat transfer coefficient increases slightly as the heat flux increases in the gas-like region, while the heat transfer coefficient is unaffected by heat flux in the liquid-like region. The peak of the heat transfer coefficient decreases and shifts to a higher temperature region as the pressure increases.
Modulational instability of a two-dimensional Bose-Einstein condensate in an optical lattice through a variational approach
Authors: Chen Hai-Jun  ,   Electrical Engineering College, Longdong University, Qingyang 745000, China
Published: December 2020

We investigate the modulational instability of a two-dimensional Bose-Einstein condensate in a two-dimensional optical lattice using a time-dependent variational approach. Within this framework, we derive the ordinary differential equations for time evolution of the amplitude and phase of modulational perturbations. Analyzing these equations and the Hamiltonian of the system, we obtain the modulational instability criterion.
Experimental and numerical studies of supersonic flow over circular protuberances on a flat plate
Authors: Gang Dun-Dian  , Yi Shi-He  , Zhao Yun-Fei  ,   College of Aesospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Although high-speed vehicles are designed to be smooth, they tend to have some protuberances on their surfaces. Thus the aerodynamic characteristics and thermal loads are changed. Meanwhile, mounting protuberances on a flat plate is an important way of flow control, and appropriate structure and location of the protuberance can improve the performance of the scramjet inlet remarkably. The nanotracer planar laser scattering (NPLS) technique is used to test the flow field of Mach 3.0 supersonic flow over circular protuberances of different heights. In total three models are tested. And the second-order scheme and fifth-order weighted compact nonlinear scheme (WCNS-E-5) is adopted to simulate the flow field. Fine structures of supersonic flow over the circular protubernaces have been obtained and the development of boundary layer in the wake flow can be observed. By comparison, it may be concluded that the protuberance lower than the local thickness will have weak disburances on its boundary layer development, and the layer after reattachment can keep its laminar state within a long distance. During the transition many clear hairpin vortices can be distinguished. When the protuberance height is larger than the thickness of the boundary layer, and the later in the region of wake flow would develop into a turbulence quickly due to intense disturbances. The transition point observed from the experimental results lies closer to the protuberance, and this might be cansed by the noise from the walls of the wind tunnel. Intermittency analysis has been done for the boundary layer in the wake flow based on the NPLS images, and the results show that the intermittency curves of the two protuberances that are larger than the local boundary layer thickness are quite similar and fluctuations are strong.
Experimental investigation on attenuation effects of electromagnetic waves in an unmagnetized plasma
Authors: Lin Min  , Xu Hao-Jun  , Wei Xiao-Long  , Liang Hua  , Zhang Yan-Hua  ,   College of Aeronautics and Astronautics Engineering, Air Force Engineering University, Xi'an 710038, China
Published: December 2020

Plasma stealth technology has many unique advantages, hence it has a promising application in the aviation and aerospace fields. The attenuation characteristics of vertical incidence of electromagnetic waves into unmagnetized plasmas with metal underlay are studied theoretically and experimentally in this paper. Regulations for the change of electromagnetic wave attenuation with plasma parameters are analyzed in theory using WKB method. A-large-area plasma slab is generated stably by inductively coupled discharge, and the reflectivity arch test system of plasma slab is set up. While the attenuation effects of electromagnetic wave in unmagnetized plasmas are studied experimentally. The electron density of plasma generated at different discharge powers is obtained by using the microwave phase and plasma spectrum diagnostic technique, ranging from 8.17× 109 to 7.61× 1010 cm-3. The plasma generated by inductively coupled plasma (ICP) has an effect on the attenuation of electromagnetic waves, and the experimental results accord well with the theoretical ones. Results show that increasing the plasma electron density and covering homogeneity can contribute to improving the attenuation effect of plasma on electromagnetic waves.
Spectral analysis of water dynamics in cement paste by quasi-elastic neutron scattering
Authors: Yi Zhou  , Zhang Li-Li  , Li Hua  ,   Department of Physics, Jinan University, Guangzhou 510632, China
Published: December 2020

Quasi-elastic neutron scattering (QENS) is a novel experimental technique for studying the translational dynamics of water in cement paste. In our work, the improved empirical diffusion model has been used to the nonlinear least square fit of the QENS experimental data of cement samples cured for 7, 14 and 30 days, where an energy resolution function R (Q, E) of four Gaussian terms instead of one Gaussian term is utilized during the fitting process. Parameters of the translational dynamics of water in cement paste have been deduced: the number density of immobile water A, the free water index FWI=B1/(A+B1+B2), the full width half maximum of Lorentzian function Γ, the average residence time τ0 between jumps and the self-diffusion coefficient Dt of mobile water. Fitted QENS spectra are more accurate and the dynamics of water in cement paste can be quantitatively explained with these deduced parameters.All this provides a practical and useful method for spectral analysis of QENS on translational dynamics of water in cement.
Theoretical investigations on the electronic modulation of diamond nanocrystals by sulfur modification
Authors: Hao Wei-Miao  , Yang Xiao-Bao  ,   Department of physics, South China University of Technology, Guangzhou 5106410, China
Published: December 2020

By stochastic search and the first-principles calculations, we have carried out a systematic investigation on the structural stabilities and electronic properties of sulfur-modified diamond nanocrystals. Among the possible catenarian, annular and cage-like candidates, we determine the stable structures as a function of hydrogen/sulfur chemical potentials according to the phase diagrams. In addition, we also study the electronic properties of sulfur-modified nanocrystals, including the gap modulation and charge distributions.
Gold nanowire tip-contact-related negative differential resistance twice and the rectification effects
Authors: Li Yong-Hui  , Yan Qiang  , Zhou Li-Ping  , Han Qin  ,   College of Physics, Optoelectronics and Energy, Soochow University, Suzhou 215006, China
Published: December 2020

Electron transport properties of molecular junctions formed by 1, 4-dithiolbenzene(DTB) coupled to [1,1,1] Au nanowires are investigated by using the method of non-equilibrium Green's functions based on first-principle density functional theory. Different S-Au contact configurations are constructed and optimized. The junction with tip-type Au electrode top binding to a thio (S) atom is illustrated by the best configuration for electron transport. Juntions with asymmetric electrode-DTB contact show excellent rectifying performance (the largest rectification ratio being 25.6). Other junctions display negative differential resistance (NDR) effect twice. Analysis shows that the rectifying effect may originate from the difference between the stabilities of S-Au contact modes at both sides. Molecular orbitals including the tip Au atoms are calculated. In low bias region, the orbitals near the Fermi energy dominate the electrons transmission; while, as the bias increases, those apart from the Fermi energy contribute to the transport, along with the DTB eigen-level. During the whole process, the locations and amplitude of transmission vary with bias voltage and I/V curves show two peaks, resulting in twice-NDR effect.
Magnetic properties of (Fe1-xCox)3BO5 nanorods
Authors: Cui Hong-Fei  , Li Kai  , Yang Chen-Guang  , He Shu-Li  ,   Department of Physics, Capital Normal University, Beijing 100048, China;,   Department of Chemistry, Capital Normal University, Beijing 100048, China
Published: December 2020

Cobalt-doped ferroferriborate ((Fe1-xCox)3BO5) nanorods (NRs) have been synthesized by using a high-temperature organic-solution-phase method, and characterized by high resolution transmission electron microscope (HRTEM) and SQUID. The aspect ratios of the NRs are tuned by reductive decomposition of Fe(acac)3 and Co(acac)2 with a predetermined ratio. HRTEM showS that the sample is polycrystalline NRs and the top view of a NR tip reveals a multiply-twined structure. Magnetization curves indicate that (Fe1-xCox)3BO5 NRs are ferromagnetic above room temperature and the antiferromagnetic component is included, the magnetic properties are dramatically modified by Co substitutional doping. The NRs are expected to be used to study the mechanical properties of biological macromolecules.