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Chin. Phys. B  
  Chin. Phys. B--2019, Vol.28, No.3
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TOPICAL REVIEW—Fundamental research under high magnetic fields
SPECIAL TOPIC—Recent advances in thermoelectric materials and devices
GENERAL

Discrete symmetrical perturbation and variational algorithm of disturbed Lagrangian systems

Li-Li Xia, Xin-Sheng Ge, Li-Qun Chen
Chin. Phys. B 2019, 28 (3): 030201;  doi: 10.1088/1674-1056/28/3/030201
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We investigate the perturbation to discrete conformal invariance and the adiabatic invariants of Lagrangian systems. A variational algorithm is proposed for a system subjected to the perturbation quantities. The discrete determining equations of the perturbations to conformal invariance are established. For perturbed Lagrangian systems, the condition of the existence of adiabatic invariant is derived from the discrete perturbation to conformal invariance. The numerical simulations demonstrate that the variational algorithm has the higher precision and the longer time stability than the standard numerical method.

Boundary scheme for lattice Boltzmann modeling of micro-scale gas flow in organic-rich pores considering surface diffusion

Hong Zuo, Shou-Chun Deng, Hai-Bo Li
Chin. Phys. B 2019, 28 (3): 030202;  doi: 10.1088/1674-1056/28/3/030202
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We propose a boundary scheme for addressing multi-mechanism flow in a porous medium in slip and early transition flow regimes, which is frequently encountered in shale gas reservoirs. Micro-gaseous flow in organic-rich shale involves a complex flow mechanism. A self-developed boundary scheme that combines the non-equilibrium extrapolation scheme and the combined diffusive reflection and bounce-back scheme (half-way DBB) to embed the Langmuir slip boundary into the single-relaxation-time lattice Boltzmann method (SRT-LBM) enables us to describe this process, namely, the coupling effect of micro-gaseous flow and surface diffusion in organic-rich nanoscale pores. The present LBM model comes with the careful consideration of the local Knudsen number, local pressure gradient, viscosity correction model, and regularization procedure to account for the rarefied gas flows in irregular pores. Its validity and accuracy are verified by several benchmarking cases, and the calculated results by this boundary scheme accord well with our analytical solutions. This boundary scheme shows a higher accuracy than the existing studies. Additionally, a subiteration strategy is presented to tackle the coupled micro-gaseous flow and surface diffusion, which necessitates the iteration process matching of these two mechanisms. The multi-mechanism flow in the self-developed irregular pores is also numerically investigated and analyzed over a wide range of parameters. The results indicate that the present model can effectively capture the coupling effect of micro-gaseous flow and surface diffusion in a tree-like porous medium.

Dynamical control of population and entanglement for open Λ-type atoms by engineering the environment

Xiao-Lan Wang, Yu-Kun Ren, Hao-Sheng Zeng
Chin. Phys. B 2019, 28 (3): 030301;  doi: 10.1088/1674-1056/28/3/030301
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The exactly analytical solution for the dynamics of the dissipative Λ-type atom in the zero-temperature Lorentzian environment is presented. On this basis, we study the evolution of the population and entanglement. We find that the stable populations on the two lower levels of the Λ-type atom can be effectively adjusted by the combination of the relative decay rate and the environmental spectral frequency. However, for the initial Werner-like state, the stable entanglement between the two Λ-type atoms has very little tunability. Furthermore, the stable entanglement for the bilateral environment case is larger than that of the unilateral environmental case. A nonintuitive relation between the stable entanglement and stable population is found.

Statistics of states generated by quantum-scissors device

Ming-Hao Wang, Guo-An Yan
Chin. Phys. B 2019, 28 (3): 030302;  doi: 10.1088/1674-1056/28/3/030302
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Generating desired states is a prerequisite in quantum information. Some desired states can be generated by a quantum-scissors device (QSD). We present a detailed analysis of the properties of the generated states, including average photon numbers and intensity gains. The theoretical analysis shows that there is a nondeterministic amplification in terms of the average photon number under the condition that the average photon number of the input state is less than 1. In contrast to the input states, the generated states show the nonclassical property described by the negativity of the Wigner function. Furthermore, we generalize the QSD to truncate arbitrary photon number terms of the input states, which may be useful in high-dimensional quantum information processing.

Fringe visibility and distinguishability in two-path interferometer with an asymmetric beam splitter

Yanjun Liu, Jing Lu, Zhihui Peng, Lan Zhou, Dongning Zheng
Chin. Phys. B 2019, 28 (3): 030303;  doi: 10.1088/1674-1056/28/3/030303
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We study the fringe visibility and the distinguishability of a general Mach-Zehnder interferometer with an asymmetric beam splitter. Both the fringe visibility V and the distinguishability D are affected by the input state of the particle characterized by the Bloch vector S=(Sx,Sy,Sz) and the second asymmetric beam splitter characterized by the paramter β. For the total system is initially in a pure state, it is found that the fringe visibility reaches the upper bound and the distinguishability reaches the lower bound when cosβ=-Sx. The fringe visibility obtain the maximum only if Sx=0 and β=π/2 when the input particle is initially in a mixed state. The complementary relationship V2+D2 ≤ 1 is proved in a general Mach-Zehnder interferometer with an asymmetric beam splitter, and the conditions for the equality are also presented.

Plasmon mediated entanglement dynamics of distant quantum dots

Misbah Qurban, Rabia Tahira, Guo-Qin Ge, Manzoor Ikram
Chin. Phys. B 2019, 28 (3): 030304;  doi: 10.1088/1674-1056/28/3/030304
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We investigate the time evolution of entanglement between two quantum dots in an engineered vacuum environment such that a metallic nanoring having a surface plasmon is placed near the quantum dots. Such engineering in environment results in oscillations in entanglement dynamics of the quantum dots systems. With proper adjustment of the separation between the quantum dots, entanglement decay can be stabilized and preserved for longer time than its decay without the surface plasmons interactions.

Energy-optimal problem of multiple nonholonomic wheeled mobile robots via distributed event-triggered optimization algorithm

Ying-Wen Zhang, Jin-Huan Wang, Yong Xu, De-Dong Yang
Chin. Phys. B 2019, 28 (3): 030501;  doi: 10.1088/1674-1056/28/3/030501
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The distributed event-triggered optimization problem for multiple nonholonomic robots has been studied to minimize the global battery energy consumption. Each robot possesses its own cost function which depends on the state of the hand position and represents battery energy consumption. By coordinate transformation, the dynamics of the hand positions can be formulated into two groups of first-order integrators. Then the distributed event-triggered optimization algorithm is designed such that the states of robots' hand positions exponentially converge to the optimizer of the global cost function. Meanwhile, the velocity and orientation of each robot are ensured to reach zero and a certain constant, respectively. Moreover, the inter-execution time is lower bounded and the Zeno behavior is therefore naturally avoided. Numerical simulations show the effectiveness of the proposed algorithm.

Amorphous Si critical dimension structures with direct Si lattice calibration

Ziruo Wu, Yanni Cai, Xingrui Wang, Longfei Zhang, Xiao Deng, Xinbin Cheng, Tongbao Li
Chin. Phys. B 2019, 28 (3): 030601;  doi: 10.1088/1674-1056/28/3/030601
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Developing highly accurate critical dimension standards is a significant task for nanoscale metrology. In this paper, we put forward an alternative approach to fabricate amorphous Si critical dimension structures with direct Si lattice calibration in the same frame scanning transmission electron microscopy image. Based on the traceable measurement analysis, the optimized method can provide the same calibration accuracy and increase the fabrication throughput and lower the cost simultaneously, which benefits the application needs in atomic force microscopy (AFM) tip geometry characterization, benchmarking measurement tools, and conducting comparison measurements between different approaches.

Pre- and post-selected measurements with coupling-strength-dependent modulation

Zhaoxue Li, Jiangdong Qiu, Linguo Xie, Lan Luo, Xiong Liu, Zhiyou Zhang, Changliang Ren, JingLei Du
Chin. Phys. B 2019, 28 (3): 030602;  doi: 10.1088/1674-1056/28/3/030602
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Pre- and post-selected (PPS) measurement, especially the weak PPS measurement, has been proved to be a useful tool for measuring extremely tiny physical parameters. However, it is difficult to retain both the attainable highest measurement sensitivity and precision with the increase of the parameter to be measured. Here, a modulated PPS measurement scheme based on coupling-strength-dependent modulation is presented with the highest sensitivity and precision retained for an arbitrary coupling strength. This idea is demonstrated by comparing the modulated PPS measurement scheme with the standard PPS measurement scheme in the case of unbalanced input meter. By using the Fisher information metric, we derive the optimal pre- and post-selected states, as well as the optimal coupling-strength-dependent modulation without any restriction on the coupling strength. We also give the specific strategy of performing the modulated PPS measurement scheme, which may promote practical application of this scheme in precision metrology.

An improved arctangent algorithm based on phase-locked loop for heterodyne detection system

Chun-Hui Yan, Ting-Feng Wang, Yuan-Yang Li, Tao Lv, Shi-Song Wu
Chin. Phys. B 2019, 28 (3): 030701;  doi: 10.1088/1674-1056/28/3/030701
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We present an ameliorated arctangent algorithm based on phase-locked loop for digital Doppler signal processing, utilized within the heterodyne detection system. We define the error gain factor given by the approximation of Taylor expansion by means of a comparison of the measured values and true values. Exact expressions are derived for the amplitude error of two in-phase & quadrature signals and the frequency error of the acousto-optic modulator. Numerical simulation results and experimental results make it clear that the dynamic instability of the intermediate frequency signals leads to cumulative errors, which will spiral upward. An improved arctangent algorithm for the heterodyne detection is proposed to eliminate the cumulative errors and harmonic components. Depending on the narrow-band filter, our experiments were performed to realize the detectable displacement of 20 nm at a detection distance of 20 m. The aim of this paper is the demonstration of the optimized arctangent algorithm as a powerful approach to the demodulation algorithm, which will advance the signal-to-noise ratio and measurement accuracy of the heterodyne detection system.

Magnetic field analysis in a diamond anvil cell for Meissner effect measurement by using the diamond NV- center

Lin Zhao, Donghui Yue, Cailong Liu, Min Wang, Yonghao Han, Chunxiao Gao
Chin. Phys. B 2019, 28 (3): 030702;  doi: 10.1088/1674-1056/28/3/030702
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Diamond negatively charged nitrogen-vacancy (NV-) centers provide an opportunity for the measurement of the Meissner effect on extremely small samples in a diamond anvil cell (DAC) due to their high sensitivity in detecting the tiny change of magnetic field. We report on the variation of magnetic field distribution in a DAC as a sample transforms from normal to superconducting state by using finite element analysis. The results show that the magnetic flux density has the largest change on the sidewall of the sample, where NV- centers can detect the strongest signal variation of the magnetic field. In addition, we study the effect of magnetic coil placement on the magnetic field variation. It is found that the optimal position for the coil to generate the greatest change in magnetic field strength is at the place as close to the sample as possible.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Analysis of optical properties of bio-smoke materials in the 0.25-14 μm band

Xinying Zhao, Yihua Hu, Youlin Gu, Xi Chen, Xinyu Wang, Peng Wang, Xiao Dong
Chin. Phys. B 2019, 28 (3): 034201;  doi: 10.1088/1674-1056/28/3/034201
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At present, research into optical properties of bio-smoke materials mostly concentrates on single band or single germplasm. Herein, we measured the spectral reflectance of three eukaryotic bio-smoke materials and three prokaryotic bio-smoke materials in the waveband from 0.25 μm to 14 μm. Based on the Kramers-Kroning algorithm, the complex refractive index m(λ) was calculated and the Fourier-transform infrared (FTIR) spectra of materials were analyzed. The results show that n(λ) of bio-smoke materials varies between 1.1-2, and n(λ) values in the visible light to near-infrared wavebands are significantly larger than those in other wavebands. The k(λ) of bio-smoke materials varies between 0-0.4. At 6-6.5 μm, k(λ) of prokaryotic materials is 3 times that of eukaryotic materials, which is caused by C=O stretching vibration of amide I and C-N stretching vibration of amide Ⅱ in proteins. At 2.5-3 μm and 9.75 μm, k(λ) values of eukaryotic bio-smoke materials are nearly 2 times that of prokaryotic ones. The absorption peak at 2.5-3 μm is mainly triggered by C-H stretching vibration in lipid and O-H stretching vibration in bound water. The absorption peak at 9.75 μm is mainly caused by symmetric stretching vibration of PO2- in nucleic acids.

High quality 2-μm GaSb-based optically pumped semiconductor disk laser grown by molecular beam epitaxy

Jin-Ming Shang, Jian Feng, Cheng-Ao Yang, Sheng-Wen Xie, Yi Zhang, Cun-Zhu Tong, Yu Zhang, Zhi-Chuan Niu
Chin. Phys. B 2019, 28 (3): 034202;  doi: 10.1088/1674-1056/28/3/034202
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The epitaxial growth conditions and performance of a diode-pumped GaSb-based optically pumped semiconductor disk laser (SDL) emitting near 2.0 μm in an external cavity configuration are reported. The high quality epitaxial structure, grown on Te-doped (001) oriented GaSb substrate by molecular beam epitaxy, consists of a distributed Bragg reflector (DBR), a multi-quantum-well gain region, and a window layer. An intra-cavity SiC heat spreader was attached to the gain chip for effective thermal management. A continuous-wave output power of over 1 W operating at 2.03 μ wavelength operating near room temperature was achieved using a 3% output coupler.

Generation of wide-bandwidth pulse with graphene saturable absorber based on tapered fiber

Ren-Li Zhang, Jun Wang, Mei-Song Liao, Xia Li, Pei-Wen Guan, Yin-Yao Liu, Yan Zhou, Wei-Qing Gao
Chin. Phys. B 2019, 28 (3): 034203;  doi: 10.1088/1674-1056/28/3/034203
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Wide-bandwidth pulses were generated with a dispersion-managed erbium-doped passively mode-locked fiber laser based on a graphene saturable absorber. The graphene saturable absorber was composed of a tapered fiber deposited with graphene fabricated by liquid-phase exfoliation. The output pulse had a 3-dB bandwidth of 13.6 nm, which is the widest spectrum ever achieved with graphene-tapered-fiber saturable absorbers.

Aperture efficiency and mode constituent analysis for OAM vortex beam generated by digital metasurface

Di Zhang, Xiangyu Cao, Huanhuan Yang, Jun Gao, Shiqi Lv
Chin. Phys. B 2019, 28 (3): 034204;  doi: 10.1088/1674-1056/28/3/034204
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A systematic study of the aperture efficiency and mode constituent for orbital angular momentum (OAM) vortex beam generated by digital metasurface is presented. The aperture efficiency and OAM spectrum are computed for different bit numbers. It is found that the aperture efficiency declines for digital metasurface due to the phase quantization error, especially for 1-bit device. Fortunately, the OAM spectrum is barely affected by phase quantization and the designated main mode keeps dominant for different bit numbers, indicating that high purity OAM vortex beam can be generated by digital metasurface. Besides, the influence of topological charge l is also investigated. For a fixed metasurface, the radiation performance deteriorates sharply with the growing of l and the parasitic OAM mode becomes dominant at certain angle. At last, a prototype of 1-bit metasurface was simulated, fabricated and measured in anechoic chamber. The simulation and experiment results verify the correctness of the numerical analysis.

Propagation dynamics of off-axis noncanonical vortices in a collimated Gaussian beam

Cheng Yin, Xuefen Kan, Hailang Dai, Minglei Shan, Qingbang Han, Zhuangqi Cao
Chin. Phys. B 2019, 28 (3): 034205;  doi: 10.1088/1674-1056/28/3/034205
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It is widely accepted that an off-axis noncanonical vortex moves across the free-space diffracting Gaussian beam without rotation. But our analysis shows that the vortex swirls a while before it approaches infinite. By neglecting the divergence of the host beam, we focus on this rotation characteristics of the vortices in linear homogeneous media. For the symmetrical host beam, it is found that the vortex moves along an elliptical trajectory, while the topological charge and the angular momentum of the vortex core relative to the beam axis are conserved. For the asymmetrical host beam, the vortex trajectory is rather complicated, since the noncanonical parameter varies as the light propagates, resulting in topological charge inversion. But we find that the vortices are always confined in a rectangular area, and the rotation direction is determined by the topological charge.

Active hyperspectral imaging with a supercontinuum laser source in the dark

Zhongyuan Guo, Yu Liu, Xin Zheng, Ke Yin
Chin. Phys. B 2019, 28 (3): 034206;  doi: 10.1088/1674-1056/28/3/034206
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An active hyperspectral imaging (HSI) system was built with a supercontinuum (SC) laser illuminator and a visible/near-infrared hyperspectral camera, which was used for object spectrum detection in the dark. It was demonstrated that the Gaussian-like distribution of the SC illuminator can still be used for accurate reflectance spectrum measurement once the illuminator was characterized in advance. The validity of active HSI results was demonstrated by comparison with passive results. Then, the active HSI system was used to acquire reflectance spectra of different objects in just one push-broom measurement successfully. With algorithms of principal component analysis clustering and unsupervised K-means spectral classification, this active HSI system with high spectral and spatial resolutions was demonstrated to be efficient and applicable for specific spectrum detections.

Investigation and optimization of sampling characteristics of light field camera for flame temperature measurement

Yudong Liu, Md. Moinul Hossain, Jun Sun, Biao Zhang, Chuanlong Xu
Chin. Phys. B 2019, 28 (3): 034207;  doi: 10.1088/1674-1056/28/3/034207
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It is essential to investigate the light field camera parameters for the accurate flame temperature measurement because the sampling characteristics of the flame radiation can be varied with them. In this study, novel indices of the light field camera were proposed to investigate the directional and spatial sampling characteristics of the flame radiation. Effects of light field camera parameters such as focal length and magnification of the main lens, focal length and magnification of the microlens were investigated. It was observed that the sampling characteristics of the flame are varied with the different parameters of the light field camera. The optimized parameters of the light field camera were then proposed for the flame radiation sampling. The larger sampling angle (23 times larger) is achieved by the optimized parameters compared to the commercial light field camera parameters. A non-negative least square (NNLS) algorithm was used to reconstruct the flame temperature. The reconstruction accuracy was also evaluated by the optimized parameters. The results suggested that the optimized parameters can provide higher reconstruction accuracy for axisymmetric and non-symmetric flame conditions in comparison to the commercial light field camera.

Electromagnetic scattering of charged particles in a strong wind-blown sand electric field

Xingcai Li, Xuan Gao, Juan Wang
Chin. Phys. B 2019, 28 (3): 034208;  doi: 10.1088/1674-1056/28/3/034208
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Some field experimental results have shown that the moving sands or dust aerosols in nature are usually electrified, and those charged particles also produce a strong electric field in air, which is named as wind-blown sand electric field. Some scholars have pointed out that the net charge on the particle significantly enhances its electromagnetic (EM) extinction properties, but up to now, there is no conclusive research on the effect of the environmental electric field. Based on the extended Mie theory, the effect of the electric field in a sandstorm on the EM attenuation properties of the charged larger dust particle is studied. The numerical results indicate that the environmental electric field also has a great influence on the particle's optical properties, and the stronger the electric field, the bigger the effect. In addition, the charged angle, the charge density, and the particle radius all have a specific impact on the charged particle's optical properties.

Improved dielectric and electro-optical parameters of nematic liquid crystal doped with magnetic nanoparticles

Geeta Yadav, Govind Pathak, Kaushlendra Agrahari, Mahendra Kumar, Mohd Sajid Khan, V S Chandel, Rajiv Manohar
Chin. Phys. B 2019, 28 (3): 034209;  doi: 10.1088/1674-1056/28/3/034209
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This study investigates the effect of magnetic nanoparticles (NPs) on the weakly polar nematic liquid crystal (NLC). Different parameters of dielectric data were measured for both the homeotropic and planar aligned samples as a function of frequency and temperature and the substantial changes have been noticed for the doped systems. Dielectric permittivity has been increased after the dispersion of magnetic NPs in the pure NLC. Dielectric anisotropy has also been influenced by incorporating the magnetic NPs with the NLC molecules. These results were attributed to the dipole-dipole interaction between the magnetic nanoparticles and nematic liquid crystal molecules. Electro-optical study indicated the faster rise time and fall time of the doped systems as compare to pure NLC. Threshold voltage has been calculated and found to be decreased for the doped systems. Moreover, we have also calculated the rotational viscosity and the splay elastic constant for pure and the doped systems. Both the rotational viscosity and splay elastic constant of the doped systems are found to be considerably lower than those of pure NLC. Change in these properties has been explained on the basis of molecular disturbances created by the interaction between the magnetic nanoparticle and LC director. This study reveals that the inclusion of magnetic NPs in weakly polar NLC can be useful to enhance the basic properties of the weakly polar NLC and make it a promising material for many display applications.

Axial acoustic radiation force on a fluid sphere between two impedance boundaries for Gaussian beam

Yuchen Zang, Yupei Qiao, Jiehui Liu, Xiaozhou Liu
Chin. Phys. B 2019, 28 (3): 034301;  doi: 10.1088/1674-1056/28/3/034301
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The acoustic radiation force on a fluid sphere immersed in water between two boundaries given by a Gaussian beam is theoretically and numerically investigated in this work. Based on the finite series method, the Gaussian beam is expressed in terms of Bessel function and a weighting parameter. The effects of the two boundaries concerned in our study is worked out by the image theory. This work also provides a reference when considering the effects of certain factors such as the radius of the sphere and the distance between the sphere and two boundaries. The contrast with the acoustic radiation force on a fluid sphere near only one boundary is also made in this paper. Our study can offer a theoretical basis for acoustics manipulation, acoustic sensors in the field of biomedical ultrasound and material science.

Multi-bubble motion behavior of electric field based on phase field model

Chang-Sheng Zhu, Dan Han, Li Feng, Sheng Xu
Chin. Phys. B 2019, 28 (3): 034701;  doi: 10.1088/1674-1056/28/3/034701
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By coupling the phase field model with the continuity equation of incompressible fluid, Navier-Stokes equation, electric field equation, and other governing equations, a multi-field coupling model for multi-bubble coalescence in a viscous fluids is established. The phase field method is used to capture the two-phase interface. The motion and coalescence of a pair of coaxial bubbles under an external uniform electric field and the effects of different electric field strengths on the interaction and coalescence of rising bubbles are studied. The results show that the uniform electric field accelerates the collision and coalescence process of double bubbles in the fluid, and increases the rising velocity of the coalesced bubble. The electric field with an intensity of E=2 kV/mm is reduced about 2 times compared with that without electric field in coalescence time. When the electric field strength is strong (E ≥ 1 kV/mm), the coalesced bubble will rupture before it rises to the top of the calculation area, and the time of the bubble rupturing also decreases with the increase of the electric field strength. The phase field method is compared with the simulation results of Lattice Boltzmann Method (LBM), and the shape of bubble obtained by the two methods is in good agreement, which verifies the correctness of the calculation model.

A combined airfoil with secondary feather inspired by the golden eagle and its influences on the aerodynamics

Di Tang, Zhongyong Fan, Mingxia Lei, Binbin Lv, Li Yu, Hao Cui
Chin. Phys. B 2019, 28 (3): 034702;  doi: 10.1088/1674-1056/28/3/034702
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Bird flight is a remarkable adaption that has allowed thousands of species to colonize all terrestrial habitats. A golden eagle has impressive flying abilities, such as hovering, perching, preying and attacking. To reveal the flying abilities, avian geometry of a golden eagle was extracted based on noncontact surface measurements using a ROMBER three-dimensional laser scanner. Distributions of a camber line, thickness and a secondary feather line of the extracted point cloud were fitted using convenient analytical expressions. A traditional airfoil was established with the camber line and thickness, then a combined airfoil was constructed by combining the traditional airfoil with a secondary feather. Oscillations of an airfoil as well as rapid pitch up were simplified as a sine wave around the quarter chord axis. Thereafter, both steady and unsteady aerodynamic performances of the airfoil are computed, the influences of the secondary feather on the steady and unsteady aerodynamics were further studied.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Numerical study on magneto-Rayleigh-Taylor instabilities for thin liner implosions on the primary test stand facility

Xiao-Guang Wang, Shun-Kai Sun, De-Long Xiao, Guan-Qiong Wang, Yang Zhang, Shao-Tong Zhou, Xiao-Dong Ren, Qiang Xu, Xian-Bin Huang, Ning Ding, Xiao-Jian Shu
Chin. Phys. B 2019, 28 (3): 035201;  doi: 10.1088/1674-1056/28/3/035201
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The thin aluminum liners with an aspect ratio Rr<<1 have been imploded on the primary test stand (PTS) facility, where R is the outer radius of the liner and Δr is the thickness. The x-ray self-emission images present azimuthally correlated perturbations in the liner implosions. The experiments show that at -10 ns before the stagnation, the wavelengths of perturbation are about 0.93 mm and 1.67 mm for the small-radius and large-radius liners, respectively. We have utilized the resistive magnetohydrodynamic code PLUTO to study the development of magneto-Rayleigh-Taylor (MRT) instabilities under experimental conditions. The calculated perturbation amplitudes are consistent with the experimental observations very well. We have found that both mode coupling and long implosion distance are responsible for the more developed instabilities in the large-radius liner implosions.

Investigation on the drives of the poloidal flow in the ohmic and biased electrode experiments

Yi Yu, Tao Lan, Min Xu, Yizhi Wen
Chin. Phys. B 2019, 28 (3): 035202;  doi: 10.1088/1674-1056/28/3/035202
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The experimental investigation on the drives of the poloidal flow in KT-5D tokamak are presented. It is found that the poloidal flow is the main contributor to the radial electric field, and the Reynolds stress can drive significant poloidal flows in ohmic discharges. The investigation on the relationship between the radial gradient of Reynolds stress and the poloidal flow in biasing discharges indicates that not only Reynolds stress but also the Lorentz's force can drive the poloidal flow.

Influence analysis of symmetry on capsule in six-cylinder-port hohlraum Hot!

You Zou, Wudi Zheng, Xin Li
Chin. Phys. B 2019, 28 (3): 035203;  doi: 10.1088/1674-1056/28/3/035203
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We have investigated the flux symmetry on the capsule in a six-cylinder-port hohlraum for improving the design of the hohlraum. The influence factors of drive symmetry on the capsule in the hohlraum are studied, including laser power, laser beams arrangement, hohlraum geometric parameters, plasma condition, capsule convergence, etc. The x-ray radiation flux distribution on the capsule is obtained based on the three-dimensional view factor model. In the six-cylinder-port hohlraum, the main drive asymmetry is the C40 mode asymmetry. When the C40 mode asymmetry approaches zero, the drive symmetry on the capsule is optimal. Our results demonstrate that in order to have a high flux symmetry on the capsule in the laser main-pulse stage, more negative initial C40 modes are needed, which can be realized by adjusting the hohlraum geometry parameters. The hohlraum with column length LH=4.81 mm has an optimal symmetry in the laser main-pulse stage.

Transmission properties of microwave in rectangular waveguide through argon plasma

Xiaoyu Han, Dawei Li, Meie Chen, Zhan Zhang, Zheng Li, Yujian Li, Junhong Wang
Chin. Phys. B 2019, 28 (3): 035204;  doi: 10.1088/1674-1056/28/3/035204
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To study the impact of plasma generated by microwave breakdown on the propagation properties of microwave in high power microwave (HPM) devices, a three-dimensional (3-D) fluid model of argon plasma slab in rectangular waveguide is established and calculated by the finite-difference-time-domain (FDTD) method. A rectangular waveguide with a breakdown chamber filled with argon is set as the physics model, and HPM with frequency of 3-50 GHz propagates through this physics model. The time evolutions of the breakdown process are investigated, the reflection, transmission, and absorption coefficients of HPM are calculated, and the influences of some important parameters, including the thickness of the plasma slab and the microwave frequency on the propagation properties of the microwave are shown. Results of this work can offer theoretical instructions for suppressing the influence of breakdown to the performance of HPM devices, and for the use of microwave breakdown, such as the design of plasma limiter or absorber in HPM devices.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Physical properties of B4N4-I and B4N4-Ⅱ: First-principles study

Zhenyang Ma, Peng Wang, Fang Yan, Chunlei Shi, Yi Tian
Chin. Phys. B 2019, 28 (3): 036101;  doi: 10.1088/1674-1056/28/3/036101
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The structural, mechanical, electronic, mechanical anisotropy, and thermal properties of boron nitride (BN) polymorphs, such as B4N4-I and B4N4-Ⅱ, are investigated under ambient pressure utilizing first-principles generalized gradient approximation calculations using an ultrasoft pseudopotential scheme. The phonon spectra and elastic constants reveal that B4N4-I is dynamically and mechanically stable at the pressure of 0 GPa and temperature of 0 K. Anisotropic calculations indicate that both B4N4-I and B4N4-Ⅱ exhibit higher anisotropy of Young's modulus than cubic BN (c-BN). B4N4-Ⅱ and B4N4-I present indirect and wide band gaps of 5.32 eV and 4.86 eV, respectively. In addition, B4N4-I is more brittle than B4N4-Ⅱ. Moreover, the minimum thermal conductivity, κmin, of B4N4-Ⅱ at 300 K is 1.92 W/(cm·K), which is slightly higher than those of B4N4-I and c-BN (1.84 W/(cm·K) and 1.83 W/(cm·K), respectively. However, κmin of B4N4-I is slightly higher than that of c-BN.

Confinement-induced modulation of elastic properties of nano-confined fluids in slit pore

Zong-Li Sun, Yan-Shuang Kang, Yan-Mei Kang
Chin. Phys. B 2019, 28 (3): 036102;  doi: 10.1088/1674-1056/28/3/036102
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Based on statistical mechanics for classical fluids, the general expressions for the elastic moduli of inhomogeneous fluid are derived and expressed as functionals of density functions. Within the framework of classical density functional theory, the bulk modulus of confined argon in slit pore is calculated under different conditions. The effects of vapor pressure, temperature, and pore width on modulus are calculated and investigated. Obvious confinement-induced effect has been observed in the confined argon. In addition, the solvation pressure dependence of the bulk modulus is also investigated, and the results suggest that the Tait-Murnaghan equation is still valid for the confined fluids.

Phase transitions in bismuth under rapid compression Hot!

Dong-Liang Yang, Jing Liu, Chuan-Long Lin, Qiu-Min Jing, Yi Zhang, Yu Gong, Yan-Chun Li, Xiao-Dong Li
Chin. Phys. B 2019, 28 (3): 036201;  doi: 10.1088/1674-1056/28/3/036201
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The structural phase transitions of bismuth under rapid compression has been investigated in a dynamic diamond anvil cell using time-resolved synchrotron x-ray diffraction. As the pressure increases, the transformations from phase I, to phase Ⅱ, to phase Ⅲ, and then to phase V have been observed under different compression rates at 300 K. Compared with static compression results, no new phase transition sequence appears under rapid compression at compression rate from 0.20 GPa/s to 183.8 GPa/s. However, during the process across the transition from phase Ⅲ to phase V, the volume fraction of product phase as a function of pressure can be well fitted by a compression-rate-dependent sigmoidal curve. The resulting parameters indicate that the activation energy related to this phase transition, as well as the onset transition pressure, shows a compression-rate-dependent performance. A strong dependence of over-pressurization on compression rate occurs under rapid compression. A formula for over-pressure has been proposed, which can be used to quantify the over-pressurization.

Full filling of mesoporous carbon nanotubes by aqueous solution at room temperature

Xiao-Na Ren, Min Xia, Qing-Zhi Yan, Chang-Chun Ge
Chin. Phys. B 2019, 28 (3): 036801;  doi: 10.1088/1674-1056/28/3/036801
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Carbon nanotubes (CNTs) have the ideal structure to be used as templates for nanomaterials, especially for nanowires, and the tungsten nanowire is an important nanomaterial that is used as a strengthening phase. Therefore, we have proposed to apply mesoporous CNT (mCNT) as a template to prepare tungsten nanowires. However, the tungsten precursor should fill the hollow tube of mCNT firstly, and very few related studies have been reported. In this paper, we have systematically studied the filling process of ammonium metatungstate (AMT) aqueous solution. The results reveal that owing to the mesopores in the mCNT sidewall, the AMT can be encapsulated into the tube at room temperature (RT) and we can fully fill it without destroying the structure. In addition, vibration and solute concentration are also important factors. Besides, the mesoporous sidewall and hollow tubular core structure of mCNT are prerequisites to realize full filling. Furthermore, tungsten nanowires have been obtained after reduction of AMT in mCNTs.

Controllable fabrication of self-organized nano-multilayers in copper-carbon films

Wei-Qi Wang, Li Ji, Hong-Xuan Li, Xiao-Hong Liu, Hui-Di Zhou, Jian-Min Chen
Chin. Phys. B 2019, 28 (3): 036802;  doi: 10.1088/1674-1056/28/3/036802
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In order to clarify the influence of methane concentration and deposition time on self-organized nano-multilayers, three serial copper-carbon films have been prepared at various methane concentrations with different deposition times using a facile magnetron sputtering deposition system. The ratios of methane concentration (CH4/Ar+CH4) used in the experiments are 20%, 40%, and 60%, and the deposition times are 5 minutes, 20 minutes, and 40 minutes, respectively. Despite the difference in the growth conditions, self-organizing multilayered copper-carbon films are prepared at different deposition times by changing methane concentration. The film composition and microstructure are investigated by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). By comparing the composition and microstructure of three serial films, the optimal growth conditions and compositions for self-organizing nano-multilayers in copper-carbon film are acquired. The results demonstrate that the self-organized nano-multilayered structure prefers to form in two conditions during the deposition process. One is that the methane should be curbed at low concentration for long deposition time, and the other condition is that the methane should be controlled at high concentration for short deposition time. In particular, nano-multilayered structure is self-organized in the copper-carbon film with copper concentration of 10-25 at.%. Furthermore, an interesting microstructure transition phenomenon is observed in copper-carbon films, that is, the nano-multilayered structure is gradually replaced by a nano-composite structure with deposition time and finally covered by amorphous carbon.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Graphene-like Be3X2 (X=C, Si, Ge, Sn): A new family of two-dimensional topological insulators

Lingling Song, Lizhi Zhang, Yurou Guan, Jianchen Lu, Cuixia Yan, Jinming Cai
Chin. Phys. B 2019, 28 (3): 037101;  doi: 10.1088/1674-1056/28/3/037101
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Using first-principle calculations, we predict a new family of stable two-dimensional (2D) topological insulators (TI), monolayer Be3X2 (X=C, Si, Ge, Sn) with honeycomb Kagome lattice. Based on the configuration of Be3C2, which has been reported to be a 2D Dirac material, we construct the other three 2D materials and confirm their stability according to their chemical bonding properties and phonon-dispersion relationships. Because of their tiny spin-orbit coupling (SOC) gaps, Be3C2 and Be3Si2 are 2D Dirac materials with high Fermi velocity at the same order of magnitude as that of graphene. For Be3Ge2 and Be3Sn2, the SOC gaps are 1.5 meV and 11.7 meV, and their topological nontrivial properties are also confirmed by their semi-infinite Dirac edge states. Our findings not only extend the family of 2D Dirac materials, but also open an avenue to track new 2DTI.

Negative differential resistance and quantum oscillations in FeSb2 with embedded antimony

Fangdong Tang, Qianheng Du, Cedomir Petrovic, Wei Zhang, Mingquan He, Liyuan Zhang
Chin. Phys. B 2019, 28 (3): 037104;  doi: 10.1088/1674-1056/28/3/037104
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We present a systematical study on single crystalline FeSb2 using electrical transport and magnetic torque measurements at low temperatures. Nonlinear magnetic field dependence of Hall resistivity demonstrates a multi-carrier transport instinct of the electronic transport. Current-controlled negative differential resistance (CC-NDR) observed in current-voltage characteristics below~7 K is closely associated with the intrinsic transition~5 K of FeSb2, which is, however, mediated by extrinsic current-induced Joule heating effect. The antimony crystallized in a preferred orientation within the FeSb2 lattice in the high-temperature synthesis process leaves its fingerprint in the de Haas-Van Alphen (dHvA) oscillations, and results in the regular angular dependence of the oscillating frequencies. Nevertheless, possible existence of intrinsic non-trivial states cannot be completely ruled out. Our findings call for further theoretical and experimental studies to explore novel physics on flux-free grown FeSb2 crystals.

Stacked lateral double-diffused metal-oxide-semiconductor field effect transistor with enhanced depletion effect by surface substrate

Qi Li, Zhao-Yang Zhang, Hai-Ou Li, Tang-You Sun, Yong-He Chen, Yuan Zuo
Chin. Phys. B 2019, 28 (3): 037201;  doi: 10.1088/1674-1056/28/3/037201
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A stacked lateral double-diffused metal-oxide-semiconductor field-effect transistor (LDMOS) with enhanced depletion effect by surface substrate is proposed (ST-LDMOS), which is compatible with the traditional CMOS processes. The new stacked structure is characterized by double substrates and surface dielectric trenches (SDT). The drift region is separated by the P-buried layer to form two vertically parallel devices. The doping concentration of the drift region is increased benefiting from the enhanced auxiliary depletion effect of the double substrates, leading to a lower specific on-resistance (Ron,sp). Multiple electric field peaks appear at the corners of the SDT, which improves the lateral electric field distribution and the breakdown voltage (BV). Compared to a conventional LDMOS (C-LDMOS), the BV in the ST-LDMOS increases from 259 V to 459 V, an improvement of 77.22%. The Ron,sp decreases from 39.62 mΩ·cm2 to 23.24 mΩ·cm2 and the Baliga's figure of merit (FOM) of is 9.07 MW/cm2.

Magnetization-direction-dependent inverse spin Hall effect observed in IrMn/NiFe/Cu/YIG multilayer structure

Runrun Hao, Ruxue Zang, Tie Zhou, Shishou Kang, Shishen Yan, Guolei Liu, Guangbing Han, Shuyun Yu, Liangmo Mei
Chin. Phys. B 2019, 28 (3): 037202;  doi: 10.1088/1674-1056/28/3/037202
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The magnetization-direction-dependent inverse spin Hall effect (ISHE) has been observed in NiFe film during spin Seebeck measurement in IrMn/NiFe/Cu/yttrium iron garnet (YIG) multilayer structure, where the YIG and NiFe layers act as the spin injector and spin current detector, respectively. By using the NiFe/IrMn exchange bias structure, the magnetization direction of YIG (MYIG) can be rotated with respect to that of NiFe (MNiFe) with a small magnetic field, thus allowing us to observe the magnetization-direction-dependent inverse spin Hall effect voltage in NiFe layer. Compared with the situation that polarization direction of spin current (σs) is perpendicular to MNiFe, the spin Seebeck voltage is about 30% larger than that when σs and MNiFe are parallel to each other. This phenomenon may originate from either or both of stronger interface or bulk scattering to spin current when σs and MNiFe are perpendicular to each other. Our work provides a way to control the voltage induced by ISHE in ferromagnets.

Hydrogenated antimonene as quantum spin Hall insulator: A first-principles study

Xin He, Ji-Biao Li
Chin. Phys. B 2019, 28 (3): 037301;  doi: 10.1088/1674-1056/28/3/037301
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Using first-principles calculations based on density functional theory (DFT), the structural and electronic properties of hydrogenated antimonene have been systematically investigated. Phonon dispersion and molecular dynamics (MD) simulation reveal that fully hydrogenated (FH) antimonene has high dynamic stability and could be synthesized. A new σ-type Dirac cone related to Sb-px,y orbitals is found in FH antimonene, which is robust to tensile strain. Noticeably, the spin orbital coupling (SOC) opens a quantum spin Hall (QSH) gap of 425 meV at the Dirac cone, sufficiently large for practical applications at room temperature. Semi-hydrogenated antimonene is a non-magnetic metal. Our results show that FH antimonene may have great potential applications in next generation high-performance devices.

Mechanism of Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures via laser annealing

Mingchen Hou, Gang Xie, Kuang Sheng
Chin. Phys. B 2019, 28 (3): 037302;  doi: 10.1088/1674-1056/28/3/037302
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The physical mechanisms of Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures by laser annealing and rapid thermal annealing are systematically investigated. The microstructures indicate that a better surface morphology and an intact contact interface are formed after laser annealing. None of the TiN alloy spikes are formed at the interface of the laser annealing sample. The experimental results show that the current transport mechanism through the ohmic contact after laser annealing is different from the conventional spike mechanism, and it is dominated by thermionic field emission.

Antiferromagnetic interlayer coupling of (111)-oriented La0.67Sr0.33MnO3/SrRuO3 superlattices

Hui Zhang, Jing Zhang, Jin-E Zhang, Fu-Rong Han, Hai-Lin Huang, Jing-Hua Song, Bao-Gen Shen, Ji-Rong Sun
Chin. Phys. B 2019, 28 (3): 037501;  doi: 10.1088/1674-1056/28/3/037501
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We report a strong antiferromagnetic (AFM) interlayer coupling in ferromagnetic La0.67Sr0.33MnO3/SrRuO3 (LSMO/SRO) superlattices grown on (111)-oriented SrTiO3 substrate. Unlike the (001) superlattices for which the spin alignment between LSMO and SRO is antiparallel in the in-plane direction and parallel in the out-of-plane direction, the antiparallel alignment is observed along both the in-plane and out-of-plane directions in the present sample. The low temperature hysteresis loop demonstrates two-step magnetic processes, indicating the coexistence of magnetically soft and hard components. Moreover, an inverted hysteresis loop was observed. Exchange bias tuned by the temperature and cooling field was also investigated, and positive as well as negative exchange bias was observed at the same temperature with the variation of the cooling field. A very large exchange field (HEB) was observed and both magnitude and sign of the HEB depend on the cooling field, which can be attributed to an interplay of Zeeman energy and AFM coupling energy at the interfaces. The present work shows the great potential of tuning a spin texture through interfacial engineering for the complex oxides whose spin state is jointly determined by strongly competing mechanisms.

Micromagnetic simulations of reversal magnetization in cerium-containing magnets

Lei Li, Shengzhi Dong, Hongsheng Chen, Ruijiao Jiang, Dong Li, Rui Han, Dong Zhou, Minggang Zhu, Wei Li, Wei Sun
Chin. Phys. B 2019, 28 (3): 037502;  doi: 10.1088/1674-1056/28/3/037502
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Single-grain models with different cerium contents or structural parameters have been introduced to investigate the reversal magnetization behaviors in cerium-containing magnets. All the micromagnetic simulations are carried out via the object oriented micromagnetic framework (OOMMF). As for single (Nd,Ce)2Fe14B type grain, the coercivity decreases monotonously with the increase of the cerium content. Four types of grain structure have been compared:single (Nd,Ce)2Fe14B type, core ((Nd,Ce)2Fe14B)-shell (Nd2Fe14B) type with 2 nm thick shell, core (Ce2Fe14B)-shell (Nd2Fe14B) type, and core (Nd2Fe14B)-shell (Ce2Fe14B) type. It is found that core ((Nd,Ce)2Fe14B)-shell (Nd2Fe14B) type grain with 2 nm thick shell always presents the largest coercivity under the same total cerium content. Furthermore, the relationship between the coercivity and the shell thickness t in core ((Nd,Ce)2Fe14B)-shell (Nd2Fe14B) type grain has been studied. When the total cerium content is kept at 20.51 at.%, the analyzed results show that as t varies from 1 nm to 7 nm, the coercivity gradually ascends at the beginning, then quickly descends after reaching the maximum value when t=5 nm. From the perspective of the positions of nucleation points, the reasons why t affects the coercivity are discussed in detail.

Structures and local ferroelectric polarization switching properties of orthorhombic YFeO3 thin film prepared by a sol-gel method

Runlan Zhang, Shuaishuai Li, Changle Chen, Li-An Han, Shanxin Xiong
Chin. Phys. B 2019, 28 (3): 037701;  doi: 10.1088/1674-1056/28/3/037701
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Orthorhombic YFeO3 thin film was prepared on La0.67Sr0.33MnO3/LaAlO3 substrate by a sol-gel spin-coating method. The structures of the YFeO3/La0.67Sr0.33MnO3/LaAlO3 (YFO/LSMO/LAO) sample were detected by x-ray diffraction pattern, Raman spectrometer, scanning electron microscopy, and atomic force microscope. The local ferroelectric polarization switching properties of the orthorhombic YFO film were confirmed by piezoresponse force microscopy (PFM) for the first time. The results show that the YFO film deposited on LSMO/LAO possesses orthorhombic structure, with ultra-fine crystal grains and flat surface. The leakage current of the YFO film is 8.39×10-4 A·cm-2 at 2 V, with its leakage mechanism found to be an ohmic behavior. PFM measurements indicate that the YFO film reveals weak ferroelectricity at room temperature and the local switching behavior of ferroelectric domains has been identified. By local poling experiment, polarization reversal in the orthorhombic YFO film at room temperature was further observed.

Spectra properties of Yb3+, Er3+: Sc2SiO5 crystal

Yanyan Xue, Lihe Zheng, Dapeng Jiang, Qinglin Sai, Liangbi Su, Jun Xu
Chin. Phys. B 2019, 28 (3): 037802;  doi: 10.1088/1674-1056/28/3/037802
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The influence of Er3+ ions on the spectra of Yb3+, Er3+:Sc2SiO5 (SSO) single crystal, which was obtained by Czochralski (Cz) method, is discussed. The absorption coefficient at 980 nm was 13.36 cm-1 with a peak absorption cross-section of 1.46×10-20 cm2. The emission cross-sections at 1034 nm and 1062 nm were 5.5×10-21 cm2 and 4.9×10-21 cm2, respectively. The fluorescence lifetime was estimated as 1.24 ms at 1061 nm. The mechanical properties of SSO single crystal were also presented.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Effect of metal fluorides on chromium ions doped bismuth borate glasses for optical applications

L Haritha, K Chandra Sekhar, R Nagaraju, G Ramadevudu, Vasanth G Sathe, Md. Shareefuddin
Chin. Phys. B 2019, 28 (3): 038101;  doi: 10.1088/1674-1056/28/3/038101
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Fluoride based glasses with composition CaF2-ZnF2-Bi2O3-B2O3 doped with chromium ions have been investigated using physical, optical, electron paramagnetic resonance (EPR), Fourier-transform infrared spectroscopy (FTIR), and Raman studies. The amorphous nature of samples was confirmed from x-ray diffraction spectra. The density is evaluated from the Archimedes principle and the values of optical band gap and Urbach energy values were evaluated from the optical absorption spectra. Thus, molar volume, refractive index, etc., were also evaluated. The observed decrease in density and the optical band gap with CaF2 is explained using the crystalline density of metal fluorides and the ionicity of fluorine ions, respectively. The three peaks near 450 nm, 606 nm, and 720 nm, which are shown in the absorption spectra, are accredited to 4A2g4T1g, 4A2g→→4T2g, 4A2g2E transitions, respectively. Resonance signals at g≈ 4.82 and g≈ 1.99 were observed in EPR spectra which are assigned. FTIR and Raman analysis were carried out to examine the impact of metal fluorides on the structure of bismuth borate glasses.

Realizing photomultiplication-type organic photodetectors based on C60-doped bulk heterojunction structure at low bias

Wei Gong, Tao An, Xinying Liu, Gang Lu
Chin. Phys. B 2019, 28 (3): 038501;  doi: 10.1088/1674-1056/28/3/038501
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Photomultiplication (PM) structure has been widely employed to improve the optoelectronic performance of organic photodetectors (OPDs). However, most PM-type OPDs require a high negative operating voltage or complex fabrication. For obtaining high-efficiency OPDs with low voltage and easy process, here the bulk heterojunction (BHJ) structure of high exciton dissociation efficiency combined with the method of trap-assisted PM are applied to the OPDs. In this paper, we investigate the operating mechanism of OPDs based on poly(3-hexylthiophene) (P3HT):(phenyl-C61-butyric-acid-methyl-ester) (PC61BM), and poly-{[4,8-bis[(2-ethylhexyl)oxy]-benzo[1,2-b:4,5-b]dithiophene-2,6-diyl]-alt-[3-fluore-2-(octyloxy)carbonyl-thieno[3,4-b]thiophene-4,6-diyl]} (PBDT-TT-F):PC61BM doped with C60 as active layer. Furthermore, the influence of C60 concentration on the optoelectronic performances is also discussed. With 1.6 wt.% C60 added, the P3HT:PC61BM:C60 OPD exhibits a 327.5% external quantum efficiency, a 1.21 A·W-1 responsivity, and a 4.22×1012 Jones normalized detectivity at -1 V under 460 nm (0.21 mW·cm-2) illumination. The experimental results show that the effective electron traps can be formed by doping a small weight of C60 into BHJ active layer. Thus the PM-type OPDs can be realized, which benefits from the cathode hole tunneling injection assisted by the trapped electrons in C60 near the Al side. The efficiency of PM is related to the C60 concentration. The present study provides theoretical basis and method for the design of highly sensitive OPDs with low operating voltage and facile fabrication.

Double superlattice structure for improving the performance of ultraviolet light-emitting diodes

Yan-Li Wang, Pei-Xian Li, Sheng-Rui Xu, Xiao-Wei Zhou, Xin-Yu Zhang, Si-Yu Jiang, Ru-Xue Huang, Yang Liu, Ya-Li Zi, Jin-Xing Wu, Yue Hao
Chin. Phys. B 2019, 28 (3): 038502;  doi: 10.1088/1674-1056/28/3/038502
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The novel AlGaN-based ultraviolet light-emitting diodes (UV-LEDs) with double superlattice structure (DSL) are proposed and demonstrated by numerical simulation and experimental verification. The DSL consists of 30-period Mg modulation-doped p-AlGaN/u-GaN superlattice (SL) and 4-period p-AlGaN/p-GaN SL electron blocking layer, which are used to replace the p-type GaN layer and electron blocking layer of conventional UV-LEDs, respectively. Due to the special effects and interfacial stress, the AlGaN/GaN short-period superlattice can reduce the acceptor ionization energy of the p-type regions, thereby increasing the hole concentration. Meanwhile, the multi-barrier electron blocking layers are effective in suppressing electron leakage and improving hole injection. Experimental results show that the enhancements of 22.5% and 37.9% in the output power and external quantum efficiency at 120 mA appear in the device with double superlattice structure.

High quantum efficiency long-/long-wave dual-color type-Ⅱ InAs/GaSb infrared detector

Zhi Jiang, Yao-Yao Sun, Chun-Yan Guo, Yue-Xi Lv, Hong-Yue Hao, Dong-Wei Jiang, Guo-Wei Wang, Ying-Qiang Xu, Zhi-Chuan Niu
Chin. Phys. B 2019, 28 (3): 038504;  doi: 10.1088/1674-1056/28/3/038504
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A long-/long-wave dual-color detector with N-M-π-B-π-M-N structure was developed based on a type-Ⅱ InAs/GaSb superlattice. The saturated responsivity was achieved under low bias voltage for both channels. The device could be operated as a single detector for sequential detection and showed high quantum efficiencies. The peak quantum efficiencies of long-wavelength infrared band-1 (blue channel) and long-wavelength infrared band-2 (red channel) were 44% at 6.3 μm under 20 mV and 57% at 9.1 μm under -60 mV, respectively. The optical performance for each channel was achieved using a 2μm thickness absorber. Due to the high QE, the specific detectivities of the blue and red channels reached 5.0×1011 cm·Hz1/2/W at 6.8 μm and 3.1×1011 cm·Hz1/2/W at 9.1 μm, respectively, at 77 K.

Enhancing convolutional neural network scheme forrheumatoid arthritis grading with limited clinical data

Jian Tang, Zhibin Jin, Xue Zhou, Weijing Zhang, Min Wu, Qinghong Shen, Qian Cheng, Xueding Wang, Jie Yuan
Chin. Phys. B 2019, 28 (3): 038701;  doi: 10.1088/1674-1056/28/3/038701
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The gray-scale ultrasound (US) imaging method is usually used to assess synovitis in rheumatoid arthritis (RA) in clinical practice. This four-grade scoring system depends highly on the sonographer's experience and has relatively lower validity compared with quantitative indexes. However, the training of a qualified sonographer is expensive and time-consuming while few studies focused on automatic RA grading methods. The purpose of this study is to propose an automatic RA grading method using deep convolutional neural networks (DCNN) to assist clinical assessment. Gray-scale ultrasound images of finger joints are taken as inputs while the output is the corresponding RA grading results. Firstly, we performed the auto-localization of synovium in the RA image and obtained a high precision in localization. In order to make up for the lack of a large annotated training dataset, we performed data augmentation to increase the number of training samples. Motivated by the approach of transfer learning, we pre-trained the GoogLeNet on ImageNet as a feature extractor and then fine-tuned it on our own dataset. The detection results showed an average precision exceeding 90%. In the experiment of grading RA severity, the four-grade classification accuracy exceeded 90% while the binary classification accuracies exceeded 95%. The results demonstrate that our proposed method achieves performances comparable to RA experts in multi-class classification. The promising results of our proposed DCNN-based RA grading method can have the ability to provide an objective and accurate reference to assist RA diagnosis and the training of sonographers.

Exploring evolutionary features of directed weighted hazard network in the subway construction

Gong-Yu Hou, Cong Jin, Zhe-Dong Xu, Ping Yu, Yi-Yi Cao
Chin. Phys. B 2019, 28 (3): 038901;  doi: 10.1088/1674-1056/28/3/038901
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A better understanding of previous accidents is an effective way to reduce the occurrence of similar accidents in the future. In this paper, a complex network approach is adopted to construct a directed weighted hazard network (DWHN) to analyze topological features and evolution of accidents in the subway construction. The nodes are hazards and accidents, the edges are multiple relationships of these nodes and the weight of edges are occurrence times of repetitive relationships. The results indicate that the DWHN possesses the property of small-world with small average path length and large clustering coefficient, indicating that hazards have better connectivity and will spread widely and quickly in the network. Moreover, the DWHN has the property of scale-free network for the cumulative degree distribution follows a power-law distribution. It makes DWHN more vulnerable to target attacks. Controlling key nodes with higher degree, strength and betweenness centrality will destroy the connectivity of DWHN and mitigate the spreading of accidents in the network. This study is helpful for discovering inner relationships and evolutionary features of hazards and accidents in the subway construction.

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