bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and properties of non-balance electric bridge gas sensor based on a single Sb doped ZnO microwire
Authors: Feng Qiu-Ju , Shi Bo , Li Yun-Zheng , Wang De-Yu , Gao Chong , Dong Zeng-Jie , Xie Jin-Zhu , Liang Hong-Wei ,   School of Physics and Electronic Technology, Liaoning Normal University, Dalian 116029, China,   School of Microelectronics, Dalian University of Technology, Dalian 116024, China
Published: December 2020

Zinc oxide (ZnO) is a wide direct band gap (3.37 eV) II-VI semiconductor material with a wide range of applications in light emitting devices, solar cells, field emission devices, gas sensors, etc. Over the past decades, metal oxide semiconductors have been investigated extensively for sensing various types of vapors and toxic gases. Among the various metal oxides for gas sensing applications, ZnO is one of the potential materials for high response, stability and sensitivity to volatile organic gases. At present, the ZnO-based gas sensor has a relatively high operating temperature. However, the stability and lifetime of gas sensors operating under high temperature conditions with a long term will be greatly reduced. In addition, the power consumption of gas sensors is also significantly increased. Furthermore, there can exist the potential of explosion when gas sensors are used to detect the flammable gases at high temperature. Therefore, it is necessary to improve the sensing properties and reduce the operating temperature of gas sensors. In this paper, ultra-long, large-sized Sb doped ZnO microwires are successfully prepared by using chemical vapor deposition. The gas sensor is based on the principle of non-balance electric bridge, and a single Sb doped ZnO microwire is used as a bridge arm R4 of non-balance electric bridge to produce a gas sensor that can work at room temperature. The results show that the response-recovery curves of sensors at the acetone and ethanol concentrations of 20 ppm, 50 ppm, 100 ppm and 200 ppm (1 ppm = 10–6) are rectangular at room temperature, and have stable current values in air and measured gas, and the response value of the device gradually increases with gas concentration increasing. Furthermore, the detection of acetone and ethanol gas reveal that the device has better selectivity for acetone gas. The response of the gas sensor to 200 ppm acetone is about 243%, with response and recovery time of 0.2 s and 0.3 s, respectively. Compared with the traditional resistive gas sensor, this non-balanced electric bridge sensor has high response, fast response and recovery time. In addition, the sensing mechanism of the device is also studied.
Effect of ambient gas pressure on characteristics of air plasma induced by nanosecond laser
Authors: Liu Jia-He , Lu Jia-Zhe , Lei Jun-Jie , Gao Xun , Lin Jing-Quan ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China,   Xi’an Institute of Applied Optics, Xi’an 710065, China
Published: December 2020

The ambient gas pressure has an important influence on the laser induced plasma characteristics. The effects of gas pressure on the characteristics of air plasma induced by nanosecond laser are studied by using the optical emission spectroscopy, and the relationship between the gas pressure and the spectral intensity, and between electron temperature and electron density of air plasma are discussed. The air gas pressure in chamber is continuously changed in a range from 10 to 100 kPa by using a mechanical pump and measured by using a barometer. The ns laser energy in experiment is fixed at 100 mJ in the whole experiment. The digital delay trigger (Stanford DG535/645) is used to trigger the laser and ICCD synchronously, and the delay and gate time of ICCD are set to be 0 and 5 μs, respectively. The experimental results show that air plasma emission spectrum consists of the line and continuous spectrum, and the spectral intensity of air plasma emission spectrum is dependent on gas pressure in a range from 10 to 100 kPa, and the evolution of atomic spectrum intensity with gas pressure is different from that of ion spectrum intensity. The air density in the region of laser breakdown increases with air pressure increasing, which leads the breakdown probability of air gas to increase, thus resulting in the air plasma spectral intensity increasing. Under the confinement action of the ambient air gas in the expanding region of air plasma, the collision probability and energy exchange probability among particles in the air plasma are both increased, and the trisomic recombination probability of ion-electron-atom is also increased. As a result, the atomic spectral intensity of O Ι 777.2 nm and N Ι 821.6 nm both increase with the air gas pressure increasing, and the spectral intensity is highest at 80 kPa, and then slowly decreases. But the spectral intensity of N II 500.5 nm reaches its maximum value at 40 kPa, and decreases as the pressure becomes greater than 40 kPa. The electron density of the air plasma increases with the air pressure increasing, and the growth rate becomes slow after 80 kPa. The electron temperature of the air plasma reaches a maximum value at 30 kPa. The plasma electron temperature gradually decreases as the pressure becomes greater than 30 kPa. The research results can provide an important experimental basis for studying the laser-induced air plasma characteristics at different altitudes, and also give important technical support for laser atmospheric transmission and atmospheric composition analysis in the future.
Transient characteristics of electron beam induced current in dielectric and semiconductor sample
Authors: Li Wei-Qin , Huo Zhi-Sheng , Pu Hong-Bin ,   School of Automation & Information Engineering, Xi’an University of Technology, Xi’an 710048, China,   Department of Electronic Science and Technology, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

The electron beam induced current (EBIC) characteristics of dielectric/semiconductor thin films under the electron beam (e-beam) irradiation is the important means of implementing the electron microscopic detection. The transient EBIC characteristics of the SiO2/Si thin film irradiated by a high-energy e-beam are investigated by combining the numerical simulation and the experimental measurement. The scattering process of electrons is simulated by the Rutherford scattering model and the fast secondary electron model, and the charge transport, trapping and the recombination process are calculated by the current continuity equation and the Poisson equation. The transient charge distribution, EBIC and the transmission current are obtained, and influence of the beam current and the beam energy on them are analyzed. The results show that due to the electron scattering effect, the free electron density decreases gradually along the incident direction. The net charge density near the surface is positive and negative along the incident direction because of secondary electrons (SEs) emitted from the surface, and therefore the electric field intensity is positive near the surface and negative inside sample, which causes some electrons to be transported to the substrate and some SEs return to the surface. The negative charge density at the SiO2/Si interface is higher than that in the nearby region because some electrons are trapped by the interface trap. With the decrease of the net charge density with e-beam irradiation, the charging intensity decreases gradually. Meanwhile, electrons are gradually transported to the substrate, and consequently EBIC and the sample current increase and the electric field intensity decreases with e-beam irradiation. However, due to the weak charging intensity, the surface emission current and the transmission current remain almost invariant with e-beam irradiation. The EBIC, the transmission current and the surface emission current are approximately proportional to the beam current. For the SiO2/Si thin film in this work, the transmission current increases gradually to the beam current value with the increase of the beam energy, and the EBIC presents a maximum value at the beam energy of about 15 keV.
Phase transformation, magnetic properties, and exchange bias of Heusler alloy Mn50–xCrxNi42Sn8
Authors: Algethami Obaidallah A  , Li Ge-Tian , Liu Zhu-Hong , Ma Xing-Qiao ,   Department of Physics, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

In this paper, phase transformations, magnetic properties and exchange bias of Mn50–xCrxNi42Sn8 (x = 0, 0.4, 0.6, 0.8) polycrystalline samples are investigated. It is found that each of all the alloys has a tetragonal martensite structure at room temperature. The transformation temperature decreases with the increase of Cr content. The maximum magnetization difference between martensite and austenite phase is ∆M = 7.61 emu/g. The change of magnetic properties is mainly related to the change of Mn-Mn distance and the hybridization strength between Ni(A)-Mn(D). The ferromagnetism of martensite can be enhanced by Cr doping. The exchange bias field is observed to reach up to as high as 2624 Oe in Mn50Ni42Sn8 alloy after cooling from room temperature to 5 K in 500 Oe magnetic field, which decreases gradually with the increase of Cr content. Furthermore, the exchange bias field increases first and then followed by a decrease with the increase of the cooling field in Mn49.2Cr0.8Ni42Sn8. This is mainly attributed to the change of the interface exchange coupling between the spin glass state and antiferromagnetic region.
Ionizing radiation damage mechanism and biases correlation of AlGaN/GaN high electron mobility transistor devices
Authors: Dong Shi-Jian , Guo Hong-Xia , Ma Wu-Ying , Lv Ling , Pan Xiao-Yu , Lei Zhi-Feng , Yue Shao-Zhong , Hao Rui-Jing , Ju An-An , Zhong Xiang-Li , Ouyang Xiao-Ping ,   School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, China,   State Key Laboratory of Science and Technology on Reliability Physics and Application of Electronic Component, CEPREI, Guangzhou 510610, China,   Northwest Institute of Nuclear Technology, Xi’an 710024, China,   Key Laboratory of Wide Bandgap Semiconductor Materials and Devices, Ministry of Education, School of Microelectronics, Xidian University, Xi’an 710071, China
Published: December 2020

In this paper, the total dose effect on AlGaN/GaN high-electron-mobility transistor (HEMT) devices after 60Co γ-ray irradiation with a total dose of 1 Mrad(Si) was investigated at different biases (VGS = –3 V, VDS = 0.5 V; VGS = –1.9 V, VDS = 0.5 V; VGS = 0 V, VDS = 0 V). The experimental results were analyzed using 1/f low-frequency noise and direct current electrical characteristics. The electrical parameters degraded mostly under zero bias condition because of the radiation-induced defect charge of the oxide layer and the interface state. Wherein, the saturation drain current was reduced by 36.28%, and the maximum transconductance was reduced by 52.94%. The reason was that the oxide dielectric layer of AlGaN/GaN HEMT devices generated electron-hole pairs under γ-ray irradiation, and most of the electrons were quickly swept out of the oxide region corresponding to the gate-source and gate-drain spacer regions, and most of the holes remained in the oxide. Under the action of the built-in electric field, holes slowly moved towards the interface between the oxide and AlGaN, which depleted the two-dimensional electron gas of the channel.According to the McWhorter model, the low-frequency noise in the AlGaN/GaN HEMT devices results from random fluctuations of carriers, which are caused by the capture and release processes of carriers by traps and defect states in the barrier layer. The extracted defect densities in AlGaN/GaN HEMT devices increased from 4.080 × 1017 cm–3·eV–1 to 6.621 × 1017 cm–3·eV–1 under the condition of zero bias, and the result was in good agreement with test results of the direct currentelectrical characteristics. The damage mechanism was the radiation-induced defect charge in the oxide layer and the interface state, which increased the flat-band voltage noise power spectral density of the AlGaN/GaN HEMT devices. According to the charge tunneling mechanism, the spatial distribution of defect in the barrier layer was extracted, and the result also proved that the densities of radiation-induced defect charges under zero bias were more than the other biases. The experimental results showed that zero bias was the worst bias for AlGaN/GaN HEMT devices irradiation.
First-principles investigation on electronic structure and solar radiation shielding performance of Tl0.33WO3
Authors: Qin Jing-Yun , Shu Qun-Wei , Yuan Yi , Qiu Wei , Xiao Li-Hua , Peng Ping , Lu Guo-Song ,   Guizhou Institute of Technology, Guiyang 550003, China,   College of Materials Science and Engineering, Hunan University, Changsha 410082, China
Published: December 2020

With energy-saving and emission-reduction have become the theme of today's social development, the theoretical design and research of novel transparent heat insulation materials for windows, which can save energy and improve the comprehensive utilization efficiency of solar energy, are particularly crucial.

In this paper, a calculation method based on DFT(density functional theory) is used to study the lattice parameters (the geometric structure of h-WO3 crystal was optimized by calculation) electronic band structure, formation energy, and optical properties of pure hexagonal phase tungsten trioxide(h-WO3) before and after doping with Tl. The calculated results indicate that the lattice volume increases and the total system energy decreases to a negative value after Tl-doped h-WO3, while the system has better stability; The electron band structure changes greatly after doping, but the material still maintains n-type conductivity. In the meantime, the optical properties of the material also changed, h-WO3 had no near-infrared absorption performance before Tl-doping, and Tl0.33WO3 after Tl-doped had strong near-infrared absorption performance. On this basis, the solar radiation shielding performance of h-WO3 before and after Tl doping has been studied. The results show that pure h-WO3 has no solar radiation shielding performance, while Tl0.33WO3 thin films after Tl-doped h-WO3 have high transparency in visible light region and strong absorption in near infrared radiation. The calculation results provide a theoretical basis for the application of transparent thermal insulating material for windows of Tl-doped h-WO3.
Comparison of performance of rank aggregation algorithms in aggregating a small number of long rank lists
Authors: Chen Wen-Yu , Zhu Zhang-Qian , Wang Xiao-Meng , Jia Tao ,   College of Computer & Information Science, Southwest University, Chongqing 400715, China,   Department of National Defense Economy, Army Logistics University of Chinese People’s Liberation Army, Chongqing 500106, China
Published: December 2020

Rank aggregation aims to combine multiple rank lists into a single one, which has wide applications in recommender systems, link prediction, metasearch, proposal selection, and so on. Some existing studies have summarized and compared different rank aggregation algorithms. However, most of them cover only a few algorithms, the data used to test algorithms do not have a clear statistical property, and the metric used to quantify the aggregated results has certain limitations. Moreover, different algorithms all claim to be superior to existing ones when proposed, the baseline algorithms, the testing samples, and the application scenario are all different from case to case. Therefore, it is still unclear which algorithm is better for a particular task. Here we review nine rank aggregation algorithms and compare their performances in aggregating a small number of long rank lists. We assume an algorithm to generate different types of rank lists with known statistical properties and cause a more reliable metric to quantify the aggregation results. We find that despite the simplicity of heuristic algorithms, they work pretty well when the rank lists are full and have high similarities. In some cases, they can reach or even surpass the optimization-based algorithms in performance. The number of ties in the list will reduce the quality of the consensus rank and increase fluctuations. The quality of aggregated rank changes non-monotonically with the number of rank lists that need to be combined. Overall, the algorithm FAST outperforms all others in three different rank types, which can sufficiently complete the task of aggregating a small number of long rank lists.
A new method for selecting arbitrary Poincare section
Authors: Zhang Shi , Wang Pan , Zhang Rui-Hao , Chen Hong ,   Electronic Engineer College, Heilongjiang University, Harbin 150080, China
Published: December 2020

Poincare section is an important method for analyzing nonlinear systems. Choosing a suitable plane as the Poincare section is the key to using the Poincare section to analyze a nonlinear system. At present, it is still a difficult problem to select a suitable Poincare section when analyzing a nonlinear system. This is caused by two reasons. On the one hand, the classical method for selecting a partial Poincare section only applies to analyze a part of the nonlinear system orbit, whether the selected plane is a suitable Poincare section is affected by the different initial points. On the other hand, according to the actual situation, different researchers have different needs for Poincare section. In order to solve this problem, a new method named Projection Time Domain method is put forward in this paper. This method can help us not only directly reflect the intersection between the nonlinear system orbit and the selected plane, but also accurately adjust the direction and position of the selected plane in real time. It can be used to quickly find a plane which fully intersects the nonlinear system orbit or an arbitrary plane as a Poincare section. In this paper, the complete definition of Projection Time Domain method is given firstly. Then, the principle of Projection Time Domain method is theoretically analyzed in detail. At the same time, the rules for determining whether the selected plane is a suitable Poincare section in the time domain are also studied. Finally, it is introduced how to quantify the direction and position of the selected plane in the phase space. The simulation experiments are conducted with three typical three-dimensional and four-dimensional nonlinear systems by using this new method. The experimental results consistent with the theoretical analysis, which demonstrate the effectiveness and practicability of this method.
Effect of out-of-plane driving flow on formation of plasmoids in current sheet system
Authors: Wang Lin , Wei Lai , Wang Zheng-Xiong ,   School of Physics, Dalian University of Technology, Dalian 116024, China
Published: December 2020

In the last two decades, a wide variety of plasmoids events have been observed, ranging from space and astrophysical phenomenon to magnetically confined laboratory plasmas, in which there are a lot of evidence of observational plasmoid-like features supported by direct large-scaled computer simulations. A super-Alfvénic instability, named plasmoid instability, occurs in an extended current sheet, when the Lundquist number exceeds a critical value. The large-aspect-ratio current sheet is fragmented by generating, growing, coalescing and ejecting of plasmoids so that this phenomenon has been proposed as a possible mechanism for fast reconnection scenario. This super-Alfvénic plasmoid instability has been usedin the significant new development of reconnection theory, and thus can provide alternative and more convincing mechanism for fast reconnection. In this work, a “driving” kind of shear flow in the out-of-plane direction is imposed on a two-dimensional, three-component magnetohydrodynamic model with a current sheet system to study the dynamic process of the plasmoids in a current sheet system. The effect of the width and strength of the driving flow on the reconnection rate of plasmoids are numerically analyzed in detail. It is found that the plasmoids are easily formed in the case of strong and wide out-of-plane driving flow. The reconnection rate and the number of the plasmoids increase with the driving flow width and/or driving flow strength increasing. In the presence of guiding field, it is found that the symmetry of the plasmoids is broken in the reconnection plane. In addition, for the fixed guiding field, the growth rate of plasmoids increases much faster when the strength of driving flow increases.
Spin noise spectroscopy of cesium vapor in micron-scale cell
Authors: Guo Zhi-Chao , Zhang Tong-Yao , Zhang Jing ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

In this paper, the spin dynamics and broadening mechanism of cesium vapor in cells without buffer gas is investigated by means of spin noise spectroscopy. In a macro atomic vapor cell, the lineshape of detuning frequency spectrum of spin relaxation rate is of Gaussian distribution. For a micron-scaled vapor cell with strong spatial locality, the lineshape of detuning frequency spectrum of spin relaxation rate is of Lorentzian distribution. The parameter dependence of detuning frequency spectrum of spin relaxation rate, such as temperature, is studied quantitatively. The detuning frequency spectrum of the spin relaxation rate is measured experimentally to be broadened by \begin{document}$ \sim $\end{document}4 GHz, which is obviously larger than the unhomogeneous Doppler broadening of \begin{document}$ \sim $\end{document}500 MHz for a macro atomic vapor cell. At the same time, the detuning frequency spectrum of total noise in the two atomic vapor cells is studied. In the macro atomic vapor cell, the total noise intensity strongly relies on the detuning frequency of the laser with respect to the atomic resonance transition. In the micron-scaled vapor cell, due to the strong homogeneous broadening, the center of the detuning frequency spectrum of the total noise is observed to dip. Finally, a simplified physical model is established to compute the broadening of the micron-scaled vapor cell. The homogeneous broadening of atoms is explained experimentally and theoretically in the micron-scaled vapor cell.
Surface enhanced Raman scattering characteristics of three-dimensional pyramid stereo composite substrate
Authors: Wu Mei-Mei , Zhang Chao , Zhang Can , Sun Qian-Qian , Liu Mei ,   School of Physics and Electronics, Shandong Normal University, Jinan 250014, China
Published: December 2020

Surface enhanced Raman scattering (SERS) is a highly sensitive spectroscopy technique, which is widely used in chemical reaction detecting, medical diagnostics, and food analysis. The construction of the substrate structure has a very important influence on enhancing the SERS signal of the probe molecule. In this paper, a three-dimensional (3D) pyramid stereo composite SERS substrate is prepared by using polymethyl methacrylate (PMMA) to encapsulate silver nanoparticles, which achieves high sensitivity detection of Rhodamine 6G (R6G) molecules. By adjusting the dispersion density of silver nanoparticles in the PMMA acetone solution, the effective oscillation of light in the pyramid valley is realized, which not only ensures the high-density "hot spot" effect of the 3D structure, but also avoids deforming the adsorption probe molecules caused by the metal-molecule interaction. It also effectively prevents the silver nanoparticles from being oxidized and provides a larger range of electromagnetic enhancement for probe molecules, resulting in a stable output of the enhanced Raman signal. This research result provides an effective strategy for designing a high performance and reusable SERS substrate, meanwhile, it has important guiding significance for further designing an SERS substrate with improved 3D structure in the future study.
Review of the research on nano-structure used as light harvesting in perovskite solar cells
Authors: Pan Heng , Chen Pei-Run , Shi Biao , Li Yu-Cheng , Gao Qing-Yun , Zhang Li , Zhao Ying , Huang Qian , Zhang Xiao-Dan ,   Tianjin Key Laboratory of Optoelectronic Thin Film Devices and Technology, Institute of Optoelectronic Thin Film Devices and Technology, Nankai University, Tianjin 300071,  China
Published: December 2020

In recent years, nano-structures used as light harvesting have been widely used in perovskite cells to enhance the photon absorption of cells. The introduction of trapping structures in perovskite cells can change the photon propagation in the cell and the photon energy absorbed by the cell. The nano-structure used in different interfaces of perovskite cells can increase the absorption of light by the device to different degrees, and ultimately improve the efficiency of the solar cell. Therefore, the effective light trapping structure has become trending in the application of perovskite cells. How to effectively apply the such nano-structure is the key to improve the power conversion efficiency(PCE) of perovskite cells. So far, there is three ways including surface antireflection nanostructure, texture structure and plasmon nanostructure to apply to perovskite solar cell. The first one is ordered and disordered antireflection nanostructure that enhance the absorption of light on the surface of perovskite cells and makes visible light scatter at the interface of the nanostructure to reflection probability, the second one is texture structure that can not only improve the light absorption but avoid the formation of short-circuit channel inside the cell, the third one is plasmon nanostructure that can further improve the absorption of the thin film absorption material in the long band, so as to achieve the effect of improving the light utilization and cell efficiency. The trap structure is expected to achieve good photon absorption performance in wide spectral range and wide incidence angle range under the condition of reducing the thickness of active layer. At the same time, it has the advantages of good repeatability, easy to simulate and easy to change the structure. Therefore, using various trap technologies to design efficient trap structure has become a research hotspot in the field of solar cells. So far, most of the reports on the trapping structure have been applied to the silicon-based thin film solar cells, but few of them have been reported on the perovskite cells. This paper starts from the description of the perovskite cell with different nano-structures, comparing and summarizing the different structures, and analyzes the advantages and Disadvantage.
Exploring the roots of social gravity law
Authors: Yan Xiao-Yong ,   Institute of Transportation System Science and Engineering, Beijing Jiaotong University, Beijing 100044, China,   Complex Labortary, University of Electronic Science and Technology of China, Chengdu 611731, China
Published: December 2020

Many spatial mobility of people, goods and information, such as human travel, population migration, commodity trade, information communication, social interaction and scientific cooperation, follow a law similar to Newton’s law of universal gravitation. This law, named social gravity law, is that the flow between two locations is directly proportional to the product of the vitality of these two locations, and inversely proportional to a power function of their distance. The gravity model established by analogy with the gravity law has also been widely used to predict trip distribution, population migration, interregional trade flows, etc. But why do many complex social systems have such a simple law? It is an interesting and valuable issue. This paper reviews the research on exploring the roots of the social gravity law from various perspectives, including statistical physics, microeconomics, and game theory.
Discrete modulation continuous-variable quantum key distribution based on quantum catalysis
Authors: Ye Wei , Guo Ying , Xia Ying , Zhong Hai , Zhang Huan , Ding Jian-Zhi , Hu Li-Yun ,   School of Computer Science and Engineering, Central South University, Changsha 410083, China,   Center for Quantum Science and Technology, Jiangxi Normal University, Nanchang 330022, China
Published: December 2020

Compared with discrete variable quantum key distribution (DVQKD), continuous variable (CV) QKD has high security bit rate and other advantages, which, however, are slightly insufficient in secure transmission distance. In addition, the application of quantum catalysis has significantly improved the performance of Gaussian modulated (GM) CVQKD, especially in secure transmission distance. Recently, the application of quantum catalysis has significantly improved the performance of GM-CVQKD. However, whether it can be used to improve the performance of discrete modulated (DM) CVQKD protocol is still ambiguous. Therefore, a scheme of DM CVQKD protocol based on quantum catalysis is proposed in this paper to further improve the performance of the proposed protocol in terms of secure key rate, secure transmission distance and maximum tolerable noise. Our results show that under the same parameters, when the transmittance T introduced by quantum catalysis is optimized, the proposed scheme can effectively further improve the performance of QKD system compared with the original four-state modulation CVQKD scheme. In particular, when the tolerable excess noise is 0.002, the use of quantum catalysis can break the safe communication distance of 300 km with a key rate of 10–8 bits/pulse. However, if this noise is too large, the improvement in the effect of quantum catalysis on protocol performance will be restrained. In addition, in order to highlight the advantages of the use of quantum catalysis, the ultimate limit PLOB (Pirandola-Laurenza-Ottaviani-Banchi) bound of point-to-point quantum communication is given in this paper. The simulation results indicate that although neither the original scheme nor the proposed scheme can break the bound, compared with the former, the latter can be close to the boundary in long-distance transmission. These results provide theoretical basis for achieving the ultimate goal of global quantum security communication.
Application of electrical action to design and analysis of magnetically driven solid liner implosion
Authors: Zhang Zheng-Wei , Wang Gui-Lin , Zhang Shao-Long , Sun Qi-Zhi , Liu Wei , Zhao Xiao-Ming , Jia Yue-Song , Xie Wei-Ping ,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621999, China
Published: December 2020

As a typical cylindrical-convergent drive technique, magnetically driven solid liner implosion could compress interior substance with a shock or quasi-isentropic manner, which has been widely used to investigate the hydrodynamic behavior, the dynamic characteristics of material and fusion energy and so on. For aspecific facility, the implosion parameters depend on material, radius and thickness of the liner, and the ablation of liner restrict the optional parameters. The concept of electrical action is introduced via thin shell model, which not only is the representation of states for conductive metal, but also indicates the change of liner velocity under the condition of thin shell hypothesis. The result shows that the outer velocity of liner increases linearly with electrical action and is directly proportional to liner thickness but inversely proportional to liner density. The incompressible zero-dimensional model is used to calculate the dynamic parameters of thin shell liner, including the implosion time, the outer interface velocity, the implosion kinetic energy, and the electrical action under the condition of low linear current density. There exist optimal radius and thickness which can achieve the maximum velocity, momentum, and kinetic energy. The aluminum is suitable for reaching higher velocity and the copper can obtain higher pressure according to a proportionality coefficient Qb/ρ which is an intrinsic quality of metal. A one-dimensional (1D) elastic plastic magnetic hydrodynamic code which is called SOL1D is developed to simulate liner implosion behavior. The modified relationship between resistivity and electrical action is introduced to SOL1D, which can adapt higher hydrodynamic pressure. According to current waves, the 1D code can be used to simulate liner implosion behavior for all kinds of current densities. The 1D simulation liner velocity is in agreement with both the experimental results and the electrical action model for liner implosion experiment on FP-1 facility. The simulation of isentropic compression experiment at ZR facility shows that the magnetic diffusion process is suppressed at extra high current density and hydrodynamic pressure, and the electrical action is larger than the experimental value of wire electrical explosion. The zero-dimensional (0D) and 1D simulation show that estimating the liner velocity and liner phase changing via the electrical action are suitable when thin shell hypothesis and low current density assumption are satisfied.
Theoretical study of angle-cut collimator based design in high-energy proton radiography
Authors: Chen Feng , Xu Hai-Bo , Zheng Na , Jia Qing-Gang , She Ruo-Gu , Li Xing-E ,   Graduate school of China Academy Of Engineering Physics, Beijing 100088, China,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

The angle-cut collimator plays an important role in high-energy proton radiography. By using the collimator, the image contrast can be improved, and the material diagnosis and density reconstruction can be realized through secondary imaging. As all these techniques depend on the flux value, it is of great significance to reduce the error of the detected flux value. The ideal collimator is a much thin surface, but thick enough to block protons outside the collimation region. It is designed by stretching the aperture of the collimation plane. The shape is cylindrical, and it will increase the error of the flux value with the angle truncation. The initial bunch is defined and the phase diagram of the bunch within the angle-cut is ideal in the theoretical model. The equation of designing the collimator is given by theoretical analysis. It is given by the transfer matrix, the radius of the object and the angle-cut. The pore structure is oval-shaped by calculating and simulating. The proton imaging system of 1.6 GeV is established by Geant4 program, and the detector is ideal. The round copper plate and the concentric spheres are chosen as objects respectively. The parameters of the designed collimator is given by this method. The ideal collimator, tensile collimator and designed collimator are used in simulation, the radius of object is 5 cm and the angle-cut is 2 mrad and 3.5 mrad. The results show that when using the ideal and the designed angle-cut collimator, the flux distributions are in good agreement, while when using the tensile collimator, the result is quite different from that obtained by using the ideal collimator. Therefore, the collimator designed by this method can effectively reduce the error of the detected flux value.
Coupling mechanism of mass transport and electrochemical reaction within patterned anode of solid oxide fuel cell
Authors: Xu Han , Zhang Lu , Dang Zheng ,   Department of Building Environment and Energy Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

Patterned electrodes are widely used in the development of novel electrodes of solid oxide fuel cells (SOFCs) because of their well-controlled geometries, distinguishable catalytically active sites and simple transport paths. In the existing studies the patterned electrodes are usually adopted to reveal relevant reaction mechanisms and to investigate the electrochemical characteristics of new materials of SOFCs, however, the effects of electrode geometry are not taken into consideration. In the present paper, a lattice Boltzmann model for simulating the charge transport and electrochemical reaction in an SOFC patterned anode is established, and the key dimensionless parameters governing the above electrode process are deduced. This model is then used to investigate the effects of the key dimensionless parameters on the electrochemical performance of a patterned anode. More importantly, the influences of the patterned anode geometry on the coupling of the charge transport and electrochemical reaction are unraveled. According to the sensitivity of the electrode performance to the dimensionless parameters, a dimensionless phase map, which is divided into maximum area, transition area and minimum area, is built. It is concluded that the transition area, in which the electrode performance varies dramatically with the parameters of design and operation, is regarded as the optimal range for studying the relevant reaction mechanism. Meanwhile, it is found that although the electron transport does not restrict the electrode performance, the moderate decrease of the height-to-width ratio of electronic conductor is capable of enlarging the transition area, which is beneficial to revealing the relevant reaction mechanism. Conversely, the ion transport is the rate-limiting step, however, the transition area remains unchanged under different ionic conductor geometries. The present numerical method and conclusions could offer guidance for rationally designing and operating the patterned electrodes.
Impact of charge carrier recombination and energy disorder on the open-circuit voltage of polymer solar cells
Authors: Zhou Qing-Zhong , Guo Feng , Zhang Ming-Rui , You Qing-Liang , Xiao Biao , Liu Ji-Yan , Liu Cui , Liu Xue-Qing , Wang Liang ,   Key Laboratory of Optoelectronic Chemical Materials and Devices, Ministry of Education, Flexible Display Material and Technology Co-Innovation Center of Hubei, School of Chemical and Environmental Engineering, Jianghan University, Wuhan 430056, China
Published: December 2020

Charge carrier recombination and energy disorder in organic solar cells both have a profound impact on the open-circuit voltage of the device. In this paper, both traditional fullerene-(PC71BM) and nonfullerene-(O-IDTBR) based solar cells were fabricated using the same electron donor material (PTB7-Th). The room-temperature current density–voltage characteristics showed that despite the values of their power conversion efficiencies were very close, there was a huge open circuit voltage (Voc) difference between the PC71BM and O-IDTBR devices. To understand the sources of the Voc variation, characterization techniques such as impedance spectra, low temperature electrical characterization method, transient photovoltage, and electroluminescent spectra were carried out. Temperature-dependent Voc of the devices were measured in a large temperature range between 120 K and 300 K. The charge transfer state energy (ECT) of the fullerene and the nonfullerene cells were determined to be 1.13 V and 1.34 V, respectively. Furthermore, the Mott-Schottky equation was applied to analyze the capacitance- voltage curves of the fabricated devices. Results showed that the built-in voltage (Vbi) of the O-IDTBR based cell (1.38 V) was much higher than that of the PC71BM cell (1.15 V). By analyzing the above data, it was easy to speculate that charge carrier recombination loss in the PC71BM device was more serious since the net electric field was relatively weak. Impedance spectra were used to measure the charge carrier recombination process in both devices. Fitting results through the equivalent circuit stated clearly that values of the recombination resistance in the O-IDTBR device were much higher in the test range, indicating that the charge carrier was less easy to recombine in the nonfullerene device. This speculation could be verified by the transient photovoltage (TPV) measurements since the carrier lifetime in the O-IDTBR device was much longer. The excited states in the devices were investigated by the electroluminescence spectra. Since the full width at half maximum (FWHM) of the O-IDTBR emission spectrum was narrower, the excited state energy distribution in the O-IDTBR device was more uniform. Based on the above analyses, the higher Voc in the O-IDTBR device was attributed to the mild charge carrier recombination and low energy disorder.
Numerical simulation of flows around single and multiple flexible hydrofoils in array arrangement by a Cartesian grid method
Authors: Xin Jian-Jian , Chen Zhen-Lei , Shi Fan , Shi Fu-Long ,   Faculty of Maritime and Transportation, Ningbo University, Ningbo 315211, China,   School of Hydraulic Engineering, Changsha University of Science and Technology, Changsha 410114, China
Published: December 2020

Studies on hydrodynamic characteristics of viscous incompressible flows around flexible hydrofoils are of practical importance for the design and performance optimization of marine structures such as ship rudders and stabilizing fins. The aim of this paper is to extend a radial basis function based ghost cell method to simulate flows around single or multiple flexible moving hydrofoils in array arrangement. The numerical model is based on a ghost cell finite difference method for considering the influence of the immersed boundaries on the flow. Also, a compact supported radial basis function (CSRBF) is introduced to track the complex flexible boundary with some controlling points of the body surface. Based on the present method, the uniform flow around a flexible hydrofoil swimming like a fish is simulated. Good grid convergence of drag and lift coefficients demonstrates the accuracy and reliability of the present method. Also, the hydrodynamics patterns of the flexible hydrofoil under different oscillation frequencies are studied. Further, the thrust generation mechanism of the hydrofoil is explained. Afterwards, flows around the undulating hydrofoils in array arrangement are simulated. The force coefficients and wake patterns under different distances and oscillation frequencies are investigated. It is observed that the thrust coefficients of the hydrofoils under narrow arrangement and high oscillation frequencies have significant amplification effects. In addition, the critical frequency at zero thrust reduces.
The electron transfer properties of an open double quantum dot based on a quantum point contact
Authors: Lan Kang , Du Qian , Kang Li-Sha , Jiang Lu-Jing , Lin Zhen-Yu , Zhang Yan-Hui ,   School of Physics and Electronics, Shandong Normal University, Jinan 250014, China
Published: December 2020

We theoretically study the electron transfer properties of a double quantum dot system in dissipative and pure dephasing environments based on a quantum dot contact detector. Theoretical results show that in the dissipative environment, the decoherence caused by the detector would increase the stable value of the average current and Fano factor as functions of time. Meanwhile, we find the existence of the quantum Zeno effect during the process of dynamical evolution. In the case of symmetric DQD, the relaxation caused by the dissipative environment would decrease the amplitude of the average current with time evolution and increase the value of the Fano factor in the long time limit. In the case of asymmetric DQD, the relaxation reduces the peak value of Fano factor over time. In the pure dephasing environment, we find that the frequent measurement would hinder the switch between different current channels during the cotunneling process. This results in a high value of Fano factor. In the case of symmetric DQD, increasing the pure dephasing rate would improve the value of Fano factor. In the case of asymmetric DQD, the dynamical evolution with time is not sensitive to the pure dephasing rate. In addition, it is indicated that the transfer probability of electron in the detector is only affected by the coupling between QPC and DQD. The environments have no effect on the transfer of a single electron in the detector. Our theoretical results provide theoretical references for experimental researchers to study the electron transport properties.
Theoretical analysis of wide-angle metamaterial absorbers based on equivalent medium theory
Authors: Wu Yu-Ming , Ding Xiao , Wang Ren , Wang Bing-Zhong ,   Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

In the past decade, most of researchers have been devoted to broadening the bandwidth of absorber. There are few researches on how to achieve wide-angle absorbing materials by detailed theoretical analysis and design guidance. It is still difficult to design wide-angle absorbers. In this paper, based on the equivalent medium theory, the reflectivity of the metamaterial absorber with a single-layered medium backed with metal reflector is analyzed in detail. Starting from the basic electromagnetic theory, the reflection coefficient of the absorber under transverse electric(TE) plane wave and transverse magnetic (TM) plan wave irradiation are derived. And the equivalent electromagnetic parameters of realizing the wide-angle absorbing effect are analyzed, which provide a theoretical basis for designing the wide-angle metamaterial absorber. The theoretical analysis results show that the equivalent electromagnetic parameters required for the medium to achieve low-profile and wide-angle absorbing effect are mainly related to the equivalent permeability and have little relationship with the equivalent permittivity. Moreover, the equivalent electromagnetic parameter value for achieving ultra-wide-angle absorber under TE wave and that under TM wave irradiation are different from each other. In other words, the anisotropic metamaterial with appropriate equivalent permeability has the potential to be used to design the ultra-wide-angle absorbers which are not sensitive to TE waves nor TM waves. In addition, in order to find the theoretically achievable widest absorbing angle value under TE wave and TM wave irradiation, the reflection coefficients at all angles must be less than or equal to –10 dB to obtain the relationship among the equivalent electromagnetic parameters, thickness and angle. The results show that the theoretically achievable widest absorbing angle value is 86.56° under TE wave and TM wave irradiation. The designer can choose the corresponding thickness and permeability from the data obtained from the analysis according to the design requirements. The narrow-band absorbers have limited applications. Therefore, in this paper we also theoretically analyze the values of the equivalent electromagnetic parameters for ahcieving wide-band and wide-angle absorbing materials, and make theoretical verification. The results show that the wide-band and wide-angle absorber can be achieved theoretically, while the equivalent electromagnetic parameters of the medium vary with frequency as some special curves indicate. Although this method is based on the equivalent medium theory and has no direct relationship with the actual structure, it does provide theoretical guidance for designing the wide-angle absorbers.