bluuebunny/crossref_metadata_2025 huggingface dataset:
White organic light emitting devices based on ultrathin emitting layer and bipolar hybrid interlayer
Authors: Yu Hao-Jian  , Yao Fang-Nan  , Dai Xu-Dong  , Cao Jin  , Chulgyu Jhun  ,   1. Key Laboratory of Advanced Display and System Applications, Ministry of Education, Shanghai University, Shanghai 200072, China;,   2. Science and Technology Research Academy, Shanghai University, Shanghai 200072, China;,   3. School of Green Energy & Semiconductor Eng., Hoseo University, Asan City, Chungnam, 336-795, South Korea
Published: December 2020

In this paper, efficient phosphorescent white organic light-emitting diodes (WOLEDs) with stable spectra are fabricated based on doping-free ultrathin emissive layers and mixed bipolar interlayers. To achieve WOLEDs, at least three kinds of light-emitting layers, i.e. blue, green and red, are needed. The traditional method to fabricate emissive layers is by co-evaporation, which can improve electroluminescent efficiency. However, the co-evaporation rate and dopant concentration are difficult to control, which leads to a bad reproducibility and thus goes against commercialization. In order to simplify the structures of WOLEDs and improve repeatability, several doping-free ultrathin emissive layers are used in this paper with 3 nm mixed bipolar interlayers separating them. The optimal ratio of bipolar hybrid material is determined by hole-only device, electron-only device and blue phosphorescent OLED. In addition, green, orange and red monochromatic OLED have also been fabricated separately, which are used to prove that mixed bipolar material is also suitable for the three phosphorescent emitting material. The WOLED with TCTA interlayers is fabricated to confirm that mixed bipolar material is beneficial to the characteristics of WOLEDs. The energy transfer process between different emitting materials is verified by studying the transient photoluminescence lifetime. The maximum efficiency of three-color and four-color doping-free WOLED are 52 cd/A (53.5 lm/W) and 13.8 cd/A (13.6 lm/W), respectively, and the maximum external quantum efficiency of three-color and four-color doping-free WOLED are 17.1% and 11.2%, respectively. Due to the sequential energy transfer structure between different emitting layers, the Commission Internationale de L'Eclairage coordinates shows a very slight variation of (0.005, 0.001) from 465 cd/m2 to 15950 cd/m2 for three-color WOLED. The Commission Internationale de L'Eclairage coordinates shows a variation of (0.023, 0.012) from 5077 cd/m2 to 14390 cd/m2 for four-color WOLED. The four-color WOLED shows a maximum color rendering index of 92.7 at 884 cd/m2, and it reaches 88.5 at 14390 cd/m2. In addition, the lifetime of phosphorescent OLED is usually poor due to the trap formed by triplet-polaron annihilation. The exciton distribution can be broadened and the exciton concentration can be reduced by using ultrathin light emitting layers (< 1 nm) and mixed bipolar interlayers. Therefore, triplet-polaron annihilation will be reduced, and the lifetime of OLEDs will be improved.
A method of efficiently generating arbitrary vector beams
Authors: Qi Shu-Xia , Liu Sheng , Li Peng , Han Lei , Cheng Hua-Chao , Wu Dong-Jing , Zhao Jian-Lin ,   Shaanxi Key Laboratory of Optical Information Technology, School of Science, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Vector beams have been used in scientific and engineering researches due to their unique focusing properties. In recent years, many methods of generating the vector beams have been proposed, among which the spatial light modulator (SLM) is widely used based on the superposition principle with using orthogonally polarized beams. However, the energy waste is generally associated with these superposition methods. How to efficiently generate vector beams is still a hot topic. Recently, we proposed an efficient method to generate tunable vector beams by using two triangular common-path interferometers (TCPIs) as the beam splitting and combining system. However, due to the complex structure of the TCPI, the system is difficult to adjust and unstable. In addition, the optical system brings about a long optical path, and the vector beams consisting of non-eigen modes will be distorted obviously with a long distance propagation. In this paper, an improved method is proposed. We replace the TCPIs with a pair of beam displacers, which act as a beam splitter and combiner, respectively. In this setup, we can arbitrarily manipulate the polarization states and phase distributions of vector beams in real time by managing the phase diagrams load on the SLM. The whole optical system does not involve any diffractive optical elements, and has a higher conversion efficiency. The improved optical system is compact and stable, and makes the adjustment of coaxiality easier. The light energy utilization depends mainly on the reflectivity of SLM. The efficiency of generating vector beams is increased to 58% by using an SLM with a reflectivity value of 79%. Several typical vector beams with phases and tunable amplitude, including cylindrical vector beams, fractional vector beams, and vector beams with double singularities, double-mode, radially variant polarization distribution, and azimuthally and radially variant polarization distribution, are generated and verified well experimentally. This method is also expected to create high-power vector beams and play an important role in laser processing and light trapping.
Helium behavior of tungsten investigated by helium ion microscope
Authors: Ma Yu-Tian , Liu Jun-Biao , Han Li , Tian Li-Feng , Wang Xue-Cong , Meng Xiang-Min , Xiao Shan-Qu , Wang Bo ,   Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China,   Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China,   College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China,   University Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Nuclear fusion energy is a clean and safe energy resource with huge potential. Tungsten is the primary candidate for plasma facing materials (PFMs) in future nuclear reactors because of its high melting point, high thermal conductivity and high resistance to sputtering and erosion. However, the interaction between tungsten and helium plasma generated by deuterium-tritium nuclear reactions will result in the degeneration of tungsten through helium blistering in tungsten. The solubility of helium in tungsten is low, and it tends to aggregate at grain boundary, phase boundary, vacancies and dislocations, thus forming helium bubbles. These bubbles will lead to microstructure changes of surface and bulk phases, as well as a decrease in mechanical properties, which seriously affects the service life of material. Limited by experimental techniques, some basic problems for the growth of helium bubbles in tungsten are not clear, for instance, how the helium clusters migrate, and nucleation mechanisms. The study of complex helium bubble formation, evolution and its underlying mechanism in tungsten PFM necessitates advanced experimental techniques. Traditional methods such as ion implantation, scanning electron microscope and transmission electron microscope are inadequate for this task. Therefore, we propose the helium ion microscope method to investigate the aforementioned several aspects of helium in tungsten in situ and real-time. Here, a helium irradiation experiment is performed by helium ion microscope (HIM), featuring nanostructure fabrication, ion implantation and microscopic imaging. The HIM can generate an ion beam with energy in a range of 0.5−35 keV and an flux upto 1025 ions/m2/s. In the process of helium ion implantation, we observe in situ and real time the helium blistering and the morphological evolution on tungsten surface, in order to capture the helium implantation-induced microscopic damage evolution on tungsten surface and subsurface. From the results of in situ HIM experiments, it is believed that a strong orientation dependence of blistering is observed with the blister occurring preferentially on the surface of grains with normal direction close to (111), and surface blistering of tungsten is directly related to cracks immediately below the surface. The present study demonstrates that the HIM is a powerful tool for investigating the helium blistering behavior in tungsten and provides valuable experimental data and reference for designing PFMs.
Tunable mode-selective characteristics of a mode-filter petal-fiber with liquid rods
Authors: Dai Zhen-Fei , Jiang Wen-Fan , Wang Ling , Chen Ming-Yang , Gao Yong-Feng , Ren Nai-Fei ,   Institute of Opt-Electronics and Communication Technologies, Jiangsu University, Zhenjiang 212013, China,   Jiangsu Tian Xing Optoelectronics Technology Co. Ltd., Zhenjiang 212132, China
Published: December 2020

In this paper, a novel tunable mode-filter optical fiber consisting of a high-index core and petal-shaped cladding surrounded by a high-index outer ring is proposed. The cladding of the fiber is formed with periodically arranged liquid rods that support cladding modes with effective indexes. These cladding modes form a two-super-mode group. The mode-selection is realized by the coupling between the core mode and the super-mode group. With the petal-shaped cladding, cladding mode can be transmitted at high loss. With the liquid rods, the index-band of super-mode group can be adjusted by external temperature field, thereby achieving the purpose of tunable mode-selective. The super-mode group formed by the LP11 mode of the liquid rods effectively increases its operating bandwidth and temperature tuning range. The numerical simulation results show that the mode-filter fiber with a length of only 71.4 mm can achieve a particular mode loss more than 20 dB, while other modes’ losses are below 1 dB. This special fiber can be used as a mode-filter in the few-mode fiber transmission system to reduce mode crosstalk of converters, multiplexer/demultiplexer, optical switch and optical routing.
Molecular simulation of interaction between charged nanoparticles and phase-separated biomembranes containning charged lipids
Authors: Liang Yi-Ran , Liang Qing ,   Center for Statistical and Theoretical Condensed Matter Physics, Department of Physics, Zhejiang Normal University, Jinhua 321004, China
Published: December 2020

Nanoparticles have been widely used in many fields such as nanomedicine and cell imaging. Understanding the microscopic mechanism of the interaction between nanoparticles and biomembranes is very vital for the synthesis and applications of nanoparticles. In this paper, using coarse-grained molecular dynamics simulation, we study the interaction between nanoparticles coated with fully or partially charged ligands and phase-separated biomembranes containing charged lipids. The results show that the final positions or states of nanoparticles on/in the biomembranes can be readily modulated by varying the grafting density, ratio, and type of charged ligands as well as the type of charged lipids. For the nanoparticle with a highly hydrophilic surface, the nanoparticle prefers to be adsorbed on the surface of the biomembrane. In this case, the electrostatic interaction determines that the nanoparticle is adsorbed on the surface of liquid-ordered domain or the surface of liquid-disordered domain. For the nanoparticle with a (partially) hydrophobic surface, the nanoparticle tends to penetrate into the lipid bilayer from the liquid-disordered domain. In this case, the hydrophobicity of the nanoparticle plays a crucial role in the penetrating of the nanoparticle. The hydrophilicity or hydrophobicity of the nanoparticle is affected by the ratio between the charged and neutral ligands, the grafting density of the charged ligands, and the ionic concentration in the system. Furthermore, the microscopic mechanism of the interaction between charged nanoparticles and charged biomembranes is revealed by using the potential of mean force between nanoparticles and lipid domains. The potential of mean force shows that none of the (partially) charged nanoparticles can spontaneously penetrate into the liquid-ordered domain due to a high free energy barrier but they can spontaneously penetrate into the liquid-disordered domain with a certain probability. However, due to the limitation of the simulation time and the number of sampling of the simulations, only some of the partially hydrophobic nanoparticles which are not initially adsorbed onto the surface of liquid-ordered domain are found to finally penetrate into the liquid-disordered domain in this work. This work yields some theoretical insights into the application of nanoparticles in nanomedicine, cell imaging, etc.
Feedback process study in over-sized backward wave oscillator
Authors: Li Zheng-Hong , Xie Hong-Quan ,   Institute of Applied Electronics, China Academy of Engineering Physics, Mianyang 621900, China,   Science and Technology on Electronic Information Control Laboratory, Chengdu 610036, China,   Science College, Southwest University of Science and Technology, Mianyang 621010, China
Published: December 2020

Internal field emission breakdown in the electro-dynamic structures of high-power microwave devices can seriously limit the devices’ output power and pulse duration. So an over-sized backward wave oscillator (BWO) is developed to increase the diameter of the electro-dynamic structure beyond the cut-off radius, and reduce these internal fields to levels, which are below critical breakdown levels. As a typical high power microwave (HPM) device, the oversized BWO is widely used and investigated. But some interaction phenomena between the beam and the microwave field in the device are not clearly understood because the beam-loaded effect is so obvious. And the physical process for the interaction is also considered to be complicated. Here as an oscillator, the feedback process is very important in the microwave device, which includes the oversized BWO. So the interaction process between the beam and the oversized BWO is explored from the feed back process instead of the field in the device. Then the physical mechanism for the feedback process in the oversized BWO is explored both in theoretical investigation and in particle-in-cell simulation. And the equivalent circuit is established for such a purpose. The mode control mechanism is explored based on the equivalent circuit. Finally an over-sized backward wave oscillator with rectangular profile corrugations is designed to produce TM01 high power microwave radiation without mode-competition. An RF power of 7.9 GW at a frequency of 8.68 GHz is obtained in the particle in cell simulation driven by the beam with a beam voltage of 1 MW and a current of 20 kA, and the corresponding efficiency is 39.5%.
Superadiabatic scheme for fast generating Greenberger-Horne-Zeilinger state of three superconducting qubits
Authors: Yu Wan-Rang , Ji Xin ,   Department of Physics, College of Science, Yanbian University, Yanji 133002, China
Published: December 2020

With the development of quantum information processing (QIP), entangled states have been used in many important fields. One of the well-known entangled states is Greenberger-Horne-Zeilinger (GHZ) state, which provides a possibility for testing quantum mechanics against local hidden theory without using Bell’s inequality. Many schemes of generating the GHZ state have been put forward in various physical systems over the past ten years. Among these physical systems, the superconducting qubits (SQs) have the potential suitability for the integrated devices in QIP and can be controlled easily through modulating electromagnetic signals and designing level configurations. On the other hand, adiabatic passage is a typical method which is used widely to generate entanglements. However, adiabatic passage needs long evolution time to satisfy the adiabatic condition. Therefore, to speed up a slow quantum adiabatic process, a new kind of technique called " shortcuts to adiabatic passage (STAP)” has attracted much attention. The Lewis-Riesenfeld invariants and transitionless quantum driving are famous methods of STAP. But they are difficult to use in the experiment. For the Lewis-Riesenfeld invariants, the driving pulses are not smoothly turned on or off and thus lead to severe impediments in experiment. For transitionless quantum driving, a direct coupling between the initial state and the target state is needed, but is too hard to obtain experimentally. In this paper, we propose a theoretical scheme for fast generating GHZ state of three superconducting qubits via superadiabatic-based shortcuts. Firstly, with the help of quantum Zeno dynamics, we obtain the effective Hamiltonian of the system, then we choose a suitable counterdiabatic Hamiltonian in the same form as the effective Hamiltonian and add it to the effective Hamiltonian in order to construct shortcuts to adiabatic passage, which can make the system evolve along one of the superadiabatic states and thus accelerate the evolution process of the system. More importantly, the superadiabatic scheme does not need an additional coupling between the initial and finial state, which ensures its high experimental feasibility. In addition, numerical simulation results show that the proposed scheme is robust against spontaneous emission, the cavity photon leakage and the dephasing of SQs.
Charging characteristics and micromechanism of space electrons irradiated polymers
Authors: Liu Jing , Zhang Hai-Bo ,   School of Resources and Environment, University of Electronic Science and Technology of China, Chengdu 610054, China,   Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Department of Electronic Science and Technology, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

The charging characteristics and microscopic mechanism of space electrons irradiated polymers are the basis for the study and protection of spacecraft polymer charging and discharging characteristics. Monte Carlo method is used to simulate the scattering process of space electrons, and the fast secondary electron model simulates the generation of secondary electrons. The finite difference method is used to solve the charge transport process of charge continuity equation, current density equation and Poisson equation. The capture process realizes the transmission process of space electrons through the equation based on the Poole-French effect. Based on the electronic scattering/transport synchronization model and combined with the geostationary earth orbit electronic spectrum distribution theoretical formula of the French National Aeronautics and Space Research Agency (ONERA) and the ground experimental method of the agency (SIRNE), a scattering model based on the electron spectrum distribution in geosynchronous orbit is established. The numerical simulation of the charging process of space electrons irradiated polymers is carried out. The space charge density, space potential, electric field distribution and the space potential of polymer sample under the irradiation of single- and multi-energy electrons in space environment are obtained. The relationship among charging characteristics, microscopic parameters and surface potential of the sample is clarified. The surface potential characteristics of space electrons irradiated polymer are consistent with the experimental results. The single energy charge potential and strength are higher than those of multi-energy electrons. When the charging reaches a steady state, the electron mobility is smaller (less than 10–11 cm2·V–1·s–1), and the absolute value of the space potential is significantly enhanced with the decrease of the electron mobility. When the composite rate is large (greater than 10–14 cm3·s–1), the absolute value of the spatial potential increases with recombination rate increasing. The study of the charging characteristics of space electrons is not comprehensive because only the mode of single-energy electron irradiation is taken into consideration. The research results are of great scientific significance and practical value for revealing the charging characteristics and microscopic mechanism of space electrons irradiated polymer and improving the research level of spacecraft charge and discharge fault mechanism.
Properties and applications of one dimensional quasiperiodic lattices
Authors: Wang Yu-Cheng , Liu Xiong-Jun , Chen Shu ,   Shenzhen Institute for Quantum Science and Engineering, Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China,   International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China,   Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China,   Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
Published: December 2020

Quasiperiodic lattices have been widely studied in cold atoms, which make one study extended-Anderson localization transition in one-dimensional (1D) or two-dimensional (2D) systems. In 2008, Inguscio's group prepared one-dimensional quasiperiodic lattice in cold atomic system and observed Anderson localization, which promoted the theoretical and experimental studies of quasiperiodic systems. Later, Bloch's group observed the many body localization in their prepared 1D and 2D quasiperiodic lattices. Recently, they also successfully observed the mobility edge and many body localization in a system with mobility edge in quasiperiodic lattices. These cold atom experiments have promoted the researches of many body localization and mobility edge. Quasiperiodic lattices have become a platform and its effects on many physical phenomena are being extensively studied, which can be expectantly observed in cold atomic experiments. This paper is based on the authors' some related work and briefly review some recent studies on the 1D quasiperiodic lattices, including some important cold atom experiments, some important properties of the quasiperiodic lattices and their effects on some physical phenomena, such as topological states.
Fixed points and dynamic topological phenomena in quench dynamics
Authors: Deng Tian-Shu , Yi Wei ,   Key Laboratory of Quantum Information, University of Science and Technology of China, CAS, Hefei 230026, China
Published: December 2020

In this review, we discuss the recent progress on the study of dynamic topological phenomena in quench dynamics. In particular, we focus on dynamic quantum phase transition and dynamic topological invariant, both of which are hinged upon the existence of fixed points in the dynamics. Further, the existence of these fixed points are topologically protected, in the sense that their existence are closely related to static topological invariants of pre- and post-quench Hamiltonians. We also discuss under what condition these dynamic topological phenomena are robust in non-unitary quench dynamics governed by non-Hermitian Hamiltonians. So far, dynamic topological phenomena have been experimentally observed in synthetic systems such as cold atomic gases, superconducting qubits, and linear optics. These studies extend our understanding of topological matter to the non-equilibrium regime.
Phase in Rydberg electromagnetically induced transparency
Authors: Yan Dong , Wang Bin-Bin , Bai Wen-Jie , Liu Bing , Du Xiu-Guo , Ren Chun-Nian ,   Key Laboratory of Materials Design and Quantum Simulation, School of Science, Changchun University, Changchun 130022, China,   Department of Basic Courses, Changchun University of Science and Technology, Changchun 130000, China,   College of Information Science and Technology, Qingdao University of Science and Technology, Qingdao 266046, China
Published: December 2020

Transmission properties of a weak probe field traveling through a sample of interacting cold 87Rb atoms driven into the three-level ladder configuration, which is a typical Rydberg electromagnetically induced transparency (EIT) system, are investigated. Rydberg atoms are considered to be a perfect platform in the research fields of quantum optics and quantum information processing due to some exaggerated properties of Rydberg atoms with high principal quantum number, especially, the dipole-dipole interaction between Rydberg atoms leads to the so-called dipole blockade effect accommodating at most one Rydberg excitation within a mesoscopic volume. The dipole blockade effect may be mapped onto the spectrum of EIT, and the EIT exhibits the cooperative optical nonlinearity which is usually characterized by two indicators, i.e., the probe intensity and the photonic correlation. The cooperative optical nonlinearity is also found here in the phase of transmission spectrum, and the phase can be regarded as the third indicator of nonlinearity in Rydberg EIT. However, there are tremendous differences between the phase and probe transmission (photonic correlation) though they both originate from the conditional polarization. Specifically, the phase is not sensitive to neither the incident probe intensity nor the initial photonic correlation at the resonant probe frequency under the condition of the Autler-Townes (AT) splitting where two other indicators exhibit significant cooperative nonlinearity. The nonlinearity in phase spectrum occurs only in the regime between the resonant probe frequency and the AT splitting and especially is remarkable at the frequency where the probe field is classical. Finally, influence of the principal quantum number and the atomic density on the transmitted phase are examined. In the nonlinear regime, the absolute value of the phase becomes smaller and smaller as the principal quantum number and the atomic density are raised. This indicates that the nonlinearity is strengthened by increasing them. The probe phase provides an attractive supplement to study in depth the cooperative optical nonlinearity in Rydberg EIT and offers us the considerable flexibility to manipulate the propagation and evolution of a quantum light field.
Theoretical study of atomic relaxation, surface energy, electronic structure and properties of B2- and B19'-NiTi surfaces
Authors: Chen Lu , Li Ye-Fei , Zheng Qiao-Ling , Liu Qing-Kun , Gao Yi-Min , Li Bo , Zhou Chang-Meng ,   State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China,   Shandong Huifeng Casting Technology Co., Ltd., Ji'nan 250000, China
Published: December 2020

NiTi shape memory alloy has been widely used in industrial and biological fields due to its excellent mechanical properties, unique shape memory effect and superelasticity. In this paper, the atomic relaxation, thermodynamic energy, structural stability, electronic structures and other properties of all low-index surfaces of B2- and B19'-NiTi alloys are systematically studied by using the first principles calculations based on density functional theory. The calculated results show that the atomic relaxations on all low-index surfaces of both B2- and B19'-NiTi alloys are mainly concentrated in 2−3 atomic layers on the surface, which means that the surface effect is mainly confined in two or three layers on the surface configuration. In addition, the atomic relaxation of Ti-terminated surface is most remarkable, and followed by Ni-terminated surface, while the atomic relaxation of Ni&Ti-terminated surface is insignificant. Furthermore, the valence charge density decays rapidly from the surface configuration to the vacuum layer.　　The calculation results of surface energy show that surface energy is inversely related to the coordinate number, and surface stability increases with the coordination number increasing. For B2- and B19'-NiTi, the surface energy of non-dense and non-stoichiometric surface depend on the chemical potential of Ti, and the surface energy is high. Therefore, the stabilities of these surfaces change with the chemical potential of Ti increasing. However, the surface energy values of dense surface configurations with stoichiometric ratio for B2-NiTi (101) and B19'-NiTi (010) are 1.81 J/m2 and 1.93 J/m2, respectively, which are both lower than those for other non-dense surfaces in the most Ti chemical potentials range, showing excellent structural stability. Moreover, the electron density analysis indicates that the dominant bonding for B2-NiTi (101) surface is the chained Ni-Ti-Ni metallic bond, the distribution of electrons and the distance between Ni and Ti atoms on the B2-NiTi (101) surface are more uniform and smaller, respectively, than those for B19'-NiTi (010) surface. In summary, the B2-NiTi (101) surface shows the high stability.
Optimal design of large-sized sandwich transducer based on two-dimensional phononic crystal
Authors: Wang Sha , Lin Shu-Yu ,   Shaanxi Key Laboratory of Ultrasonics, Shaanxi Normal University, Xi'an 710119, China
Published: December 2020

Sandwich transducers are extremely versatile, but when the lateral dimension is too large, the displacement of the radiating surface is uneven due to the coupling vibration. Due to the unique vibrational band gap characteristics of phononic crystal, vibrations in the bandgap range can be prohibited from propagating for infinite periodic structure or suppressed for finite periodic structure, which makes it widely used in the field of vibration suppression. In this paper, a two-dimensional phononic crystal structure is formed by processing periodically aligned grooves in the front cover of a large-sized sandwich transducer. Since the periodic grooves are formed in the radial direction, the radial waves cannot propagate, and thus the lateral vibration is suppressed. Subsequently, the finite element method is used to simulate the vibration transmission characteristic, resonance frequency and emission voltage response of a large-sized sandwich transducer based on two-dimensional phononic crystal. The effects of slot height and slot width on its bandgap, resonance and anti-resonant frequency, bandwidth, and displacement profile of the radiating surface are discussed. The results show that the phonon crystal structure can be optimized by using a large-sized sandwich transducer. The large-sized sandwich transducer based on two-dimensional phononic crystal has a lateral band gap. When the operating frequency of the large-sized sandwich transducer is within the band gap range, the two-dimensional phononic crystal structure can effectively suppress the lateral vibration, and the uniformity of the displacement distribution of the radiating surface of the transducer is improved. In addition, when the slot width is constant, the bandwidth of the large-sized sandwich transducer based on the two-dimensional phononic crystal increases as the slot height increases. Similarly, when the slot height is constant, the bandwidth of the large-sized sandwich transducer based on the two-dimensional phononic crystal increases as the slot width increases. The two-dimensional phononic crystal structure is processed in the front cover of the large-sized sandwich transducer, and the working frequency band of the large-sized sandwich transducer is effectively broadened.
Transport phenomena in dilute quantum gases
Authors: Zhang Shi-Zhong ,   Department of Physics and Centre for Theoretical and Computational Physics, The University of Hong Kong, Hong Kong, SAR, China
Published: December 2020

Transport measurement is one of the most important ways to study the properties of matter. In this article, we discuss recent experiments in ultracold atomic gases where the analog of Landauer transport in mesoscopic devices is realized and spin dynamics in a strongly interacting Fermi gas is probed. In the latter case, we pay special attention to the peculiarity of spin dynamics due to identical spin rotation effect which leads to a novel form of spin diffusion current. This modifies the usual diffusion equation into a more complicated form and leads to important consequence for, in particular, transverse spin diffusion in ultracold Fermi gases.
Hydrogen soaking irradiation acceleration method: application to and damage mechanism analysis on 3DG111 transistors
Authors: Zhao Jin-Yu , Yang Jian-Qun , Dong Lei , Li Xing-Ji ,   Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

Bipolar devices are extremely sensitive to ionization effects, and their low dose rate radiation damage is more serious than their high dose rate radiation damage, which phenomenon is especially named enhanced low dose rate sensitivity. In the actual space radiation environment, the radiation dose rate of the device is extremely low. Currently, the enhanced low dose rate sensitivity effect has become a key factor of evaluating the reliability of spacecraft and its electronic systems, due to the fact that the low dose rate irradiation test needs longer time. The method to speed up the test on the ground is one of the hottest topics in this research area. In recent years, some researches have suggested that the use of hydrogen immersion irradiation for accelerating the test can simulate low dose rate radiation damage to some extent, but the damage mechanism has not been analyzed in detail. In this paper, the mechanisms of electrical properties and deep level defects for the 3DG111 transistor by 60Co gamma ray under high and low dose rates in the cases with and without hydrogen are investigated. In order to analyze the damage mechanism of bipolar junction transistor, the excess base current and deep level transient spectrum are measured by using semiconductor parameter analyzer and deep level transient spectroscopy. The experimental results show that the current gain degradation of 3DG111 transistor is more serious under low dose rate radiation than under high dose rate radiation, at the same time, the excess base current of transistor increases significantly. This shows that in the device there appears the enhanced low dose rate sensitivity. Under both high dose rate radiation and low dose rate irradiation, the radiation damage defects are the traps for both oxide positive charge and interface state. Under the low dose rate irradiation, there are two main reasons for the increase in transistor damage. First, the oxide charge concentration increases under low dose rate irradiation, and the oxide charge and interface state energy levels move toward the middle band. Eventually, the space charge region recombination of the transistor is intensified, and thus causing the excessive base current of the transistor to increase and transistor performance to degrade. The comparison shows that the number and type of defects under the high dose rate irradiation are the same as those under the low dose rate irradiation. Based on the analysis, the hydrogen treatment can be used as an effective method of accelerating the assessment of radiation damage enhancement effect at low dose rates.
Review of one-dimensional few-body systems in ultracold atomic physics
Authors: Liu Yan-Xia , Zhang Yun-Bo ,   Institute of Theoretical Physics, Shanxi University, Taiyuan 030006, China,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

We review some recent theoretical and experimental developments of one-dimensional few-body problems in ultracold atomic system. The experiments have so far realized the deterministic loading of few atoms in the ground state of a potential well, the observation of tunneling dynamics out of the metastable trap controlled by a magnetic gradient for a repulsively or attractively interacting system, the preparation of two fermionic atoms in an isolated double-well potential with a full control over the quantum state of the system, the formation of a Fermi sea by studying quasi-one-dimensional systems of ultracold atoms consisting of a single impurity interacting with an increasing number of identical fermions, and the deterministic preparation of antiferromagnetic Heisenberg spin chains consisting of up to four fermionic atoms in a one-dimensional trap. These achievements make the ultracold atoms an ideal platform to study many-body physics in a bottom-up approach, i.e., one starts from the fundamental building block of the system and observes the emergence of many-body effects by adding atoms one by one into the system. Corresponding theoretical models have been developed to explain the experimental data, to tackle the crossover boundary between few and many particles, and even explore the solvability and integrability of the models, especially the energy spectrum of interacting few atoms such as two atoms in a harmonic trap, two heteronuclear atoms of unequal mass in a ring trap, and two atoms in a \begin{document}$\delta$\end{document}-barrier split double well potential. After a brief review of Bethe-Ansatz method, a theory for the tunneling of one atom out of a trap containing two interacting cold atoms is developed based on the calculation of the quasiparticle wave function, and the tunneling dynamics of two atoms starting from the NOON state is explored from the exactly solved model of \begin{document}$\delta$\end{document}-barrier split double well based on a Bethe ansatz type hypothesis of the wave functions. It was shown that the spectroscopy and spin dynamics for strongly interacting few atoms of spin-1/2 and spin-1 can be described by effective spin chain Hamiltonians, which serves as a useful and efficient tool to study the quantum magnetism with clod atoms.
Effects of linear Zeeman splitting on the dynamics of bright solitons in spin-orbit coupled Bose-Einstein condensates
Authors: Wen Lin , Liang Yi , Zhou Jing , Yu Peng , Xia Lei , Niu Lian-Bin , Zhang Xiao-Fei ,   College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China,   Department of Science, Chongqing University of Posts and Telecommunications, Chongqing 400065, China,   Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi’an 710600, China
Published: December 2020

Solitons as self-supported solitary waves are one of the most fundamental objects in nonlinear science. With the realization of Bose-Einstein condensate, matter-wave solitons have aroused enormous interest due to their potential applications in atomic transport and atomic interferometer. In recent years, the artificial spin-orbit coupling has been realized in ultracold atoms, thus providing a new platform to study the nonlinear matter wave solitons under a gauge field, and a variety of novel soliton phenomena have been successively predicted. In this paper, we analyze the effects of linear Zeeman splitting on the dynamics of bright-bright solitons in spin-orbit coupled two-component Bose-Einstein condensate, via the variational approximation and the numerical simulation of Gross-Pitaevskii (GP) equations. For the SU(2) spin-rotational invariant attractive atomic interaction in a uniform case without external trap, we take a hyperbolic secant function as the variational Ansatz for bright soliton in variational approximation, and derive the Euler-Lagrange equations describing the evolution of the Ansatz parameters. By solving the time-independent Euler-Lagrange equations, we find two stationary solitons each with a finite momentum for a weak spin-orbit coupling due to the linear Zeeman splitting. Linearizing the Euler-Lagrange equations around these stationary solitons, we further obtain a zero-energy Goldstone mode and an oscillation mode with frequency related to linear Zeeman splitting: the former indicates that the continuous translational symmetry of the stationary solitons will be broken under a perturbation, and the later shows that the stationary solitons will oscillate under a perturbation. Furthermore, by solving the time-dependent Euler-Lagrange equations, we also obtain the exact full dynamical solutions of Ansatz parameters, and observe that the linear Zeeman splitting affects the period and velocity of soliton's oscillation and linear motion, which may provide a new method to control the dynamics of solitons. All the variational calculations are also confirmed directly by the numerical simulation of GP equations.
Modulation of orbital angular momentum in long periodchirally-coupled-cores fiber
Authors: Cui Can , Wang Zhi , Li Qiang , Wu Chong-Qing , Wang Jian ,   Institute of Optical Information, School of Science, Beijing Jiaotong University, Key Laboratory of Luminescence and Optical Information, Ministry of Education, Beijing 100044, China,   State Key Laboratory on Integrated Optoelectronics, Beijing 100083, China
Published: December 2020

A type of fiber-based orbital angular momentum (OAM) modulator is designed according to transformation relation between OAM beam and optical fiber vector mode, together with mode-coupling theory, which is based on the combination of multimode fiber structure and chirally-coupled-cores structure. Instead of applying external force or grating etching to the fiber in the system, chirally-coupled-cores fiber can realize the modulation of any optical OAM by using single fiber at 1550 nm. Therefore, the test system is relatively simple. From the equation \begin{document}${\rm{OAM}}_{ \pm l,n}^{ \pm \sigma } = {\rm{HE}}_{l + 1,n}^{{\rm{even}}} \pm {\rm{i}} \times {\rm{HE}}_{l + 1,n}^{{\rm{odd}}}$\end{document}, it can be seen that the OAM mode generated by long period chirally-coupled-cores fiber depends on the higher-order modes supported by the central fiber core. Therefore, the generation and modulation of any order OAM beam can be realized by changing the diameter of the central fiber core in theory. Through theoretical analysis and numerical simulation, the effects of different structure parameters on OAM modes are analyzed, including mode purity, mode transmission loss and effective refractive index. By keeping the propagation constants of the center core and side cores unchanged, the number of side cores has no effect on mode purity nor effective refractive index, but which is not for mode transmission loss. The loss of mode transmission increases with the increase of the number of side cores. However, it does not mean that the less number of side cores is a better case, in that the fiber symmetry and processing technology should also be considered. And the pitch calculated by the formula of phase matching condition can change in value within a certain numerical range without strongly affecting the mode purity and mode transmission loss. Pitch has a great influence on the effective refractive index of modes, therefore the pitch can be under control to change the difference in effective refractive index between OAM modes and reduce crosstalk between disparate modes. The distance between the center core and side cores of fiber has little effect on mode purity, great effect on mode transmission loss, but no effect on effective refractive index. Theoretically, the mode purity and mode transmission loss perform better with the distance between two kinds of cores increasing. But it will be limited by the fiber integration level.
Laser propagation transmission properties characteristics between airborne communication terminal and unmanned aerial vehicle target in complex atmospheric background
Authors: Wang Ming-Jun , Wei Ya-Fei , Ke Xi-Zheng ,   School of Automation and Information Engineering, Xi’an University of Technology, Xi’an 710048, China
Published: December 2020

Clouds, aerosols and atmospheric molecules are major components of the atmosphere. In the fields of atmospheric physics such as target detection, wireless optical communication and remote sensing, these atmospheric components have a strong attenuation effect on laser transmission. Based on the successive scattering method for solving the radiative transfer equation, the laser transmission model between airborne wireless optical communication terminal and ground-to-air unmanned aerial vehicle (UAV) target in complex atmospheric background is established in this paper. Considering the fact that cirrus cloud, atmospheric molecules and aerosols exist in the real atmospheric background, the variations of direct transmission power, first-order scattering transmission power of 1.55 μm laser emitted by the airborne wireless optical communication terminal with UAV target height are calculated numerically under complex atmospheric background. The effects of the aircraft located at different locations, effective radius of ice crystal particles in cirrus cloud, as well as the horizontal distance between the aircraft and UAV target on received laser transmission power are also analyzed. In the first three examples (i.e., aircraft is above, below, and inside cirrus cloud), laser direct transmission power (LDTP) is much larger than first-order scattering transmission power (FSTP); when the UAV target rises into the cloud, the FSTP is significantly enhanced as a result of the effect of diffraction light. The fourth example is for calculating the variations of LDTP and FSTP with UAV target height for different effective radii of ice crystals. The results show that the LDTP decreases with the increase of effective radius, whereas the FSTP presents an opposite scenario. The fifth example is for calculating the variations of LDTP and FSTP with UAV target height for different horizontal distances. The results show that the LDTP and FSTP decrease with the increase of the horizontal distance, which is obviously realistic. In summary, it is concluded that the laser transmitted power through cirrus clouds is strongly dependent on aircraft position: above, below, or inside cirrus cloud; the horizontal distance between the aircraft and UVA target, and effective radii of ice crystals have great influences on LDTP and FSTP. Compared with the atmosphere above the clouds, the molecules and aerosols below the clouds make the laser power have a strong attenuation. The results given in this paper provide theoretical support for further studying the laser communication experiment in ground-to-air links, UAV formation, command and networking technology in complex atmospheric background.