bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of discharge parameters on blow-by in a coaxial plasma gun
Authors: Zhang Jun-Long  , Yang Liang  , Yan Hui-Jie  , Hua Yue  , Ren Chun-Sheng  ,   School of Physics and Optoelectronic technology, Dalian University of Technology, Dalian 116023, China
Published: December 2020

The blow-by which occurs in a coaxial plasma gun is the result of reinforcing feedback caused by the gradient of magnetic field and the component of axial current due to the canting of current sheath. The blow-by has become a serious negative effect which limits the effective use of the coaxial plasma gun, so it is necessary to study by experiment the parameters that influence the degree of blow-by. This will not only contribute to the study of the theory and mode about blow-by but also give advices to the weakening or eliminating blow-by by choosing suitable parameters in engineering field. The degree of blow-by can be observed directly by photomultiplier, and the influence of voltage of capacitance, capacitance, and the pressure of gas on blow-by have also been studied. It is shown that the blow-by would become more serious with the increase of capacitance or the voltage of capacitance while it becomes weaker with the increase of gas pressure. These phenomena can be explained based on the snowplow model. We consider that the increase of capacitance or the voltage of capacitance can make the current sheath canting more serious, however it would reduce the degree of current sheath canting with the increase of gas pressure. So the blow-by can be controlled by the parameters which influence current sheath canting.
Experimental study on laser produced tin droplet plasma extreme ultraviolet light source
Authors: Chen Hong  , Lan Hui  , Chen Zi-Qi  , Liu Lu-Ning  , Wu Tao  , Zuo Du-Luo  , Lu Pei-Xiang  , Wang Xin-Bing  ,   School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China;,   Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China;,   School of Science, Wuhan Institute of Technology, Wuhan 430073, China
Published: December 2020

Extreme ultraviolet lithography (EUVL), which uses the extreme ultraviolet radiation at a wavelength of 13.5 nm, is the leading candidate of next generation lithography addressing not only the 10 nm half-pitch nodes, but several nodes beyond that. Among all the methods for getting EUV radiation, laser-produced plasma (LPP) light source is the most promising EUV light source because of its high conversion efficiency (CE), large collect angle and low debris output. In this paper, pulsed TEA-CO2 laser and Nd:YAG laser are used to irradiate tin droplets to obtain plasma EUV emission, and the properties of EUV radiation from the plasma are studied. Results show that the EUV emission spectra induced by Nd:YAG laser have an obvious blueshift as compared with those by CO2 laser. In addition, the LPP sources are point light sources, so that the angular distribution of EUV emission from LPP can be described by Lambertian distribution.
Preparation and study of anodic alumina thin films with rainbow rings
Authors: Yang Shu-Min  , Han Wei  , Gu Jian-Jun  , Li Hai-Tao  , Qi Yun-Kai  ,   Department of Physics, Hebei Normal University for Nationalities, Chengde 067000, China
Published: December 2020

Porous anodic alumina thin films with rainbow rings were fabricated in oxalic acid electrolyte by one-step electrochemical oxidation of Al sheet. The hole depth and aperture diminish symmetrically outward from the center of the films. The relationship between the density of rainbow rings to the oxidation voltage and the time in oxalic acid solution are discussed. Theoretical study on the formation mechanism of porous anodic alumina thin films with rainbow rings indicates that the effect of carbon rod is similar to carbon dot electrode in the process of anode electrochemical reaction. Result of the theoretical study is consistent with the experimental phenomenology.
Controlling the electronic states and transport properties of single cobalt(Ⅱ)octaethylporphyrin molecule adsorbed on Au(111) surface
Authors: Li Jing-Cheng  , Zhao Ai-Di  , Wang Bing  ,   Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei 230026, China;,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

We demonstrate that the molecular ligands play important roles in controlling the electronic states and electron transport properties of single cobalt (Ⅱ) octaethylporphyrin (CoOEP) molecule adsorbed on Au(111) surface by using low-temperature scanning tunneling microscopy and spectroscopy. Single CoOEP molecule adsorbed on Au(111) surface has eight methyl groups pointing out of the surface plane. A peak located at -50 mV in dI/dV spectrum measured on the Co atom of CoOEP is identified as a d-orbital mediated resonance. We find that the methyl groups in CoOEP can be removed in a stepwise manner, and finally lead to a fully-demethylized CoOEP. The d-orbital mediated resonance gradually evolves into a sharp Kondo resonance located right at Fermi level in the demethylization process. Both experimental and theoretical results indicate that the chemical environment and magnetic moment of the central Co atom change slightly in the fully-demethylized CoOEP: the Co atom is slightly lifted by 0.15 and the magnetic moment increases from 0.5 B to 0.6 B. The emergence of Kondo effect is qualitatively explained with a simple model by consideringthe change in the tunneling parameters of the ligands upon demethylization. We also show that the transport properties of the CoOEP can be dramatically controlled by weak intramolecular van der Waals interaction. In CoOEP closely-packed dimers and trimers where CoOEP molecules are introduced close enough to each other, the ethyl groups in the neighboring area are found to be strongly lifted by 0.4 . More surprisingly, a pronounced resonance shows up at 00.8 V in the dI/dV spectra of the lifted ethyl groups. High resolution spectra show that the new resonance consists of multiple peaks with equal spacing of 137 8 mV. The spacing energy coincides with the vibrational energy of stretching mode of CC bond between ethyl group and the brim carbon atom of the porphyrin ring. Therefore the newly-emerged resonance is attributed to the vibronic states originating from the intramolecular CC bond stretching mode excited by tunneling electrons. A model considering the local formation of a barrier between the lifted part of the molecule and the substrate is employed to explain the experimental observations. Our findings show that the electron transport properties in single molecules can be intensely tuned by controlling the chemical properties of the molecular ligands.
Electron transport properties of Mg2Si under hydrostatic pressures
Authors: Zhu Yan  , Zhang Xin-Yu  , Zhang Su-Hong  , Ma Ming-Zhen  , Liu Ri-Ping  , Tian Hong-Yan  ,   State Key Laboratory of Metastable materials Science and Technology, Yanshan University, Qinhuangdao 066004, China;,   The Department of Physics, Hebei Normal University of Science & Technology, Qinhuangdao 066004, China
Published: December 2020

The electronic and thermoelectric properties of Mg2Si under hydrostatic pressures have been investigated using the first principles calculations with general potential linearized augmented plane-wave method and the semiclassical Boltzmann theory with the rigid band approach and the constant scattering time relaxation approximation. In this work, the hydrostatic pressure is simulated by applying equiaxial strain method for the cubic anti-fluorite structure of Mg2Si in space group Fm3m. The strain values ranging from -0.03 to 0.03 describe the compressive and tensile Processes under pressure. The band structure, electrical conductivity, Seebeck coefficient and power factor have been calculated and analyzed in detail.#br#From the band structure in Mg2Si one can see that the bottom of the conduction band shows significant changes under strains. Especially, when the strain is up to 0.02, there are two twofold-degeneracy states occurring at the center of the Brillouin zone. The top of the valence band shows a slight change due to the strain effect. For the unstrained structure, our calculated thermoelectric data are in accordance with other reports. Moreover, the results indicate that when the value of strain is up to 0.02, the transport properties get an optimal functioning of Mg2Si due to electron doping. At 300 K, the Seebeck coefficient improves obviously and comes up to 126%. And the power factor is up to 47% (45%) at T=300 K (700 K). Consequently, the thermoelectric properties can be improved through applying negative pressures to the Mg2Si crystal. For the case of hole doping, the transport parameters change obviously at a small strain value, and change gently at a high strain values. When the strain is up to 0.01, the Seebeck coefficient reaches the maximum value 439 μV/K-1. But, the power factor only increases 0.9%–2%. Hence, we can conclude that the hydrostatic pressures have a slight influence on the thermoelectric properties of hole-doped materials.
First-principles investigations on tetragonal distortion, electronic structure, magnetism, and phonon dispersion of Ga2XCr (X = Mn, Fe, Co, Ni, Cu) Heusler alloys
Authors: Chen Jia-Hua  , Liu En-Ke  , Li Yong  , Qi Xin  , Liu Guo-Dong  , Luo Hong-Zhi  , Wang Wen-Hong  , Wu Guang-Heng  ,   College of Science, Beijing University of Chemical Technology, Beijing 100029, China;,   State Key laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130, China
Published: December 2020

In Ga2-based Heusler alloys Ga2XCr (X = Mn, Fe, Co, Ni, Cu) the tetragonal distortion, electronic structure, magnetism and phonon dispersion have been studied by first-principles calculations based on the density functional theory. The volume-conserving tetragonal distortions of the cubic Ga2XCr show that Cr atom makes the greatest contribution to the total magnetic moment. No martensitic transformation has been found in Ga2FeCr, Ga2CoCr and Ga2CuCr. For both Ga2MnCr and Ga2NiCr, the tetragonal phase is lower in energy as compared with the cubic phase. Ga2MnCr and Ga2NiCr have the lowest total energy at c/a = 1.28 and 1.11, respectively. Correspondingly, the energy difference ΔE between the cubic and the tetragonal phase is -8.26 meV in Ga2MnCr and -6.14 meV in Ga2NiCr. For Ga2MnCr and Ga2NiCr, calculations of electronic structure and phonon dispersion reveal that a sharp peak near the Fermi level will lead to a structural instability by increasing the energy of the system, which can result in a broadening in the energy range due to hybridizations between 3d electrons as well as the potential structural transformation. With proper c/a and ΔE a potential tetragonal martensitic transformation can be expected in Ga2MnCr, the phonon dispersion of which further shows that the acoustic modes tend to be softened.
Linear magnetoresistance in topological insulator (Bi0.5Sb0.5)2Te3 thin films
Authors: Guan Tong  , Teng Jing  , Wu Ke-Hui  , Li Yong-Qing  ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Linear magnetoresistance (LMR) observed in a topological insulator {(Bi0.5Sb0.5)2Te3} thin film is systematically studied. LMR exists in very large ranges of temperature and magnetic field. It shows no trend toward saturation in the magnetic field of up to 18 T nor temperature dependence. LMR can be changed effectively by tuning the chemical potential through gate voltage. LMR shows a largest value when the chemical potential approaches to the Dirac point. These phenomena indicate that charge inhomogeneity is the origin of the LMR in this material.
Research on radiation damage in titanium oxide memristors by Monte Carlo method
Authors: Liu Hai-Jun  , Tian Xiao-Bo  , Li Qing-Jiang  , Sun Zhao-Lin  , Diao Jie-Tao  ,   School of Electronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Nano titanium oxide memristor is expected to be the basic cell of a new generation of resistive memory and applied in the control and data storage systems of spacecrafts that work in a radiation environment. The changes of radiation key factors, such as energy, intensity, direction, and duration etc. probably have an influence on the radiation damage of the titanium oxide memristor. However, there has been no relatively detailed research of it. Based on the SRIM simulation, with the Monte Carlo method used as its core, the main part of cosmic rays——proton and alpha rays and the relevance between the key factors and radiation damage in titanium oxide memristor are quantitatively studied. According to the experimental data, the relations between key factors and R_{ON}, R_{OFF}, the mobility of oxygen vacancies are analyzed. We find that the mobility of oxygen vacancies increases abruptly when the ratio between oxygen vacancies and titanium oxide molecules is greater than 0.16. Moreover, compared with proton radiation, the alpha particle radiation going into the active region in titanium oxide memristor, especially at an oblique incidence angle may cause a greater damage to the device and should be strictly avoided, and the radiation damage increases as the intensity and duration of the radiation are raised. SPICE simulations are further utilized to show the influence of radiation on the characteristics of the coexistence of dopant drift and the tunnel barrier. We also find that the titanium oxide memristor device will gradually turn into a normal resistor with a low resistance and lose its charge-memory ability after persistent radiations. This work provides support for evaluating and reducing radiation damage for titanium oxide memristors, so as to improve the reliability of the device in radiation environment.
Joint for time of arrival and direction of arrival estimation algorithm based on the subspace of extended hadamard product
Authors: Ba Bin  , Liu Guo-Chun  , Li Tao  , Lin Yu-Cheng  , Wang Yu  ,   Information Engineering University, Zhengzhou 450001, China;,   The 61539th unit of PLA, Beijing 100091, China
Published: December 2020

In the joint estimation for time of arrival (TOA) and direction of arrival (DOA) in the narrow-band orthogonal frequency division multiplexing (OFDM) system with antenna arrays, the estimation accuracy is not high in the situation of few numbers of arrays. Especially, DOA cannot be estimated if the number of multiple paths is more than that of the arrays. For these problems, a joint estimation algorithm for TOA and DOA based on the subspace of the extended hadamard product is proposed. First of all, the algorithm constructs an extended channel response in frequency domain via channel estimation for each array in the frequency domain. Then, auto-correlation matrix of extended channel response in the frequency domain is estimated by sampling many times. This estimation method of channel response in the frequency domain can use the fast Fourier transform algorithm. And the hadamard product in the extended noise subspace is obtained by eigenvalue decomposition. Finally, the pseudo-spectral function is constructed and used to search for spectrum peaks, so as to realize the joint estimation of TOA and DOA. The proposed algorithm requires no parameter paring but needs a two-dimensional searching. Monte Carlo algorithm can be used to reduce computational complexity. Simulation results show that the root mean square error of the joint TOA and DOA estimation which can be matched automatically is closer to the Cramer-Rao bound than that using present algorithms. And the proposed algorithm can be still applied when the number of multiple paths is more than number of arrays.
ECG energy distribution analysis using ensemble empirical mode decomposition energy vector
Authors: Zeng Peng  , Liu Hong-Xing  , Ning Xin-Bao  , Zhuang Jian-Jun  , Zhang Xing-Gan  ,   Institute of Biomedical Electronic Engineering, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
Published: December 2020

Ensemble empirical mode decomposition (EEMD) method eliminates mode mixing phenomenon which is an inherent problem in empirical mode decomposition (EMD), and decomposes signals according to their intrinsic characteristics. It is suitable for analyzing nonlinear and non-stationary signals. Electrocardiogram (ECG) energy distribution exhibits a certain regularity which may vary with heart diseases. Researches on ECG energy distribution change are important for heart disease clinical diagnosis. In this paper, we use EEMD method to analyze ECG and find out how ECG energy distribution varies with age and heart diseases. We decompose the ECG signal into several intrinsic mode function (IMF) components by EEMD, and find that these IMFs can reveal the fluctuation rhythm and physical significance of ECG on different time scales. After IMFs have been decomposed, we calculate their energy and obtain an energy vector. By comparing the energy vectors among healthy young subjects, healthy old subjects, and three types of patients suffering from different heart diseases, we find that there is a significant decrease of high-frequency components of energy vector in heart disease patients as compared to healthy subjects, and a slight decrease of healthy old subjects as compared to healthy young subjects. T-test is performed to compare heart disease subjects with healthy subjects. Results show that there are significant differences between certain energy vector components, especially the first component p1 which could be used as heart disease auxiliary diagnosis. Compared to traditional frequency-domain analysis methods which simply concern about the frequency of a signal and ignore its own characteristics and interactions between signal components, EEMD method depends on ECG signal itself, therefore can reflect its real characteristics, and reveals the way how age and illness influence ECG energy distribution accurately.
Magneto-hydrodynamic calculation of magnetic flux compression with explosion driven solid liners and analysis of quasi-isentropic process
Authors: Zhao Ji-Bo  , Sun Cheng-Wei  , Gu Zhuo-Wei  , Zhao Jian-Heng  , Luo Hao  ,   Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Magnetic cumulative generator (MC-1) is a kind of high energy density dynamic device. A liner is driven by a cylinderical explosive implosion to compress the magnetic flux preset in the cavity. Then the chemical energy is converted into magnetic one, which is cumulated nearby the axis to form ultra-intense magnetic field used to load sample in non-touch manner. This loading technique can bring higher pressure and relatively low elevated temperature in the sample and has a very high-degree isentropy in the course of compression. The configuration magneto-hydrodynamic code SSS/MHD is used to develop one-dimensional magneto-hydrodynamic calculation of magnetic flux compression with explosion driven solid liner. The calculation results of magnetic field in cavity and velocity of inner wall of sample tube are obtained and accord with the magnetic field measured by probe and the velocity measured by laser interference. The buckling and Bell-Plesset instabilization produced by linerly compressing magnetic field are shown through frame photography. The change laws of magnetic diffusion, eddy current and magnetic pressure in liner and sample tube are analyzed, which show that the magnetic field and pressure and eddy near to cavity in the sample tube are all higher than the ones in the liner with the same distance to cavity. The balance between the electromagnetism force and implosion action and the difference between sample tube and liner velocities are the main reasons under imploding movement. The change of isentropic increment with compression degree at the same location, whose distance is 0.05 mm to magnetic cavity in the sample tube, is discussed. The result indicates that the ratio of the maximum increment to specific heat of sample tube material is about 10%, which shows that the process of compression magnetic flux with explosion is quasi-isentropic. In general, SSS/MHD code can reveal in depth the physic images which are difficult to measure or observe in the magneto-hydrodynamics experiment.
New features of the speckle phase singularity produced in large angle scattering
Authors: Song Hong-Sheng  , Liu Gui-Yuan  , Zhang Ning-Yu  , Zhuang Qiao  , Cheng Chuan-Fu  ,   School of Science, Shandong Jianzhu University, Jinan 250101, China;,   College of Physics and Electronics, Shandong Normal University, Jinan 250014, China
Published: December 2020

Based on the interference patterns of the speckle field and the reference beam recorded by the charge-coupled device, and the digital Fourier transform technique, the complex amplitudes and phases of speckle field produced at different scattering angles are extracted. The phase distribution and the statistical properties at the singular point, such as the angle between two zero-contour lines of real part and imaginary part of the complex amplitude, the eccentricity of the intensity contours, etc. are studied. We find that there are some special properties of phase singularity when the scattering angle is large enough. With the increase of the scattering angle, great changes have taken place in the spatial distributions of the amplitude and the phase, and the probability of the angle between two zero-contour lines of real part and imaginary part is close to a smaller value, and the average eccentricity of the intensity contours around the phase singularity gradually increase. Moreover, the most interesting thing is that the eccentricity is probably greater than 1 in large anger scattering. The phase singular line as a new kind of phase singularity is found at a large scattering angle; the phase mutation rules and the vortex distribution characteristics of the phase on both sides of the phase singular line are investigated, and the hyperbolic or parabolic shape intensity contour around the phase singular line is found.
Universal function of Grneisen γ and the complete equation of state
Authors: Chen Jun-Xiang  , Yu Ji-Dong  , Li Ping  , He Hong-Liang  ,   National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621999, China
Published: December 2020

The existing Grneisen coefficient γ expressions and the experimental data fitting relations consider only the γ data fitting, rather than the change rule of γ. In this paper, the universal function of Grneisen γ is established according to the property of Grneisen γ function and the high pressure characteristics of thermodynamic γ, such as γ changing quickly at low pressure but slowly at high pressure. This universal function is substituted into the thermodynamic function γ(v, T) to obtain the isentropic temperature Ts(v), and then the Hgoniot temperature is deduced by using the relationship between isentropic temperature and Hgoniot temperature, thus Hgoniot equation becomes the complete equation of state. All the thermodynamic state variables can be calculated by the thermodynamic relations. The universal function of Grneisen γ is applied to several metals, such as Al, Ta and Cu, and the Hgoniot equation is deduced according to the isothermal equation, or the isothermal equation is calculated by the Hgoniot equation. The results are in good agreement with experimental data. There are good compatibility between the universal Grneisen γ and the heat capacity Cv. It is shown that the proposed universal function of Grneisen γ can reasonably describe the thermodynamic properties of many metals at high pressure and high temperature.
Effect of ZnO electron-transport layer on light-soaking issue in inverted polymer solar cells
Authors: Li Chang  , Xue Wei  , Han Chang-Feng  , Qian Lei  , Zhao Su-Ling  , Yu Zhi-Nong  , Zhang Ting  , Wang Ling-Xue  ,   School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China;,   Key Laboratory for Special Functional Materials Henan University, Ministry of Education, Kaifeng 475004, China;,   Institute of Optoelectronics Technology, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

A common phenomenon of polymer solar cells with metal oxide electron-transport layers (ETLs), known as “light-soaking” issue, is that the as-prepared device exhibits an anomalous S-shaped J-V characteristic, resulting in an extremely low fill factor (FF) and thus a poor power conversion efficiency. However, the S-shape disappears upon white light illumination with UV spectral components, meanwhile the performance parameters of the device recover the normal values eventually. This behavior appears to be of general validity for various metal oxide layers regardless of the synthesis and fabricating processes. Its origin is still under debate, while the ETL interface problems have generally been claimed to be the underlying reason so far. In this paper, both conventional and inverted cells with using ZnO nanoparticles (NPs) as ETL are fabricated to clarify the interface effect of the ETL on the light soaking procedure. The inverted device shows a typical light-soaking issue with an initial FF less than 20% as expected, whereas the J-V curves of the conventional cell remain regular shapes throughout the test. This result indicates that the ITO/ZnO interface is a key reason of S-shaped J-V characteristics, which is further verified via the use of Cs2CO3/ZnO ETL. The insert of Cs2CO3 layer isolates the ITO electrode from contacting with ZnO layer, and the kink disappears in the as-prepared device with this bi-layered ETL inverted structure. Our explanation for the result above is that the oxygen impurities absorbed onto the surface of ZnO NPs during fabrication process, behave as strong electron traps, and thus increasing the width of the energy barrier (EB) at the interface of ITO/ZnO. Subsequently, photogenerated electrons accumulate in the ZnO layer adjacent to the interface, resulting in extremely poor performance. Upon white light illumination, however, the trap sites are filled by photogenerated carriers within the ZnO layer, and therefore narrowing the EB. As the barrier width becomes thin enough to be freely tunneled through, a good selectivity behavior of ZnO ETL is reached, leading to a fully remarkable recovery in device performances.
For the first time fengyun3 C satellite-global navigation satellite system occultation sounder achieved spaceborne Bei Dou system radio occultation
Authors: Wang Shu-Zhi  , Zhu Guang-Wu  , Bai Wei-Hua  , Liu Cong-Liang  , Sun Yue-Qiang  , Du Qi-Fei  , Wang Xian-Yi  , Meng Xiang-Guang  , Yang Guang-Lin  , Yang Zhong-Dong  , Zhang Xiao-Xin  , Bi Yan-Meng  , Wang Dong-Wei  , Xia Jun-Ming  , Wu Di  , Cai Yue-Rong  , Han Ying  ,   Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190, China;,   National Satellite Meteorological Center, Beijing 100081, China;,   Department of Mathematics and Physics, Beijing Institute of Petrochemical Technology, Beijing 102617, China
Published: December 2020

The radio occultation (RO) technique using signals from the global navigation satellite system, is widely used to observe the atmosphere for applications such as numerical weather prediction (NWP) and global climate monitoring. Since 1995, there have been turborogue sounder on board global positioning system/meteorology, black jack sounder on board challenging minisatellite payload and gravity recovery and climate experiment, IGOR sounder on board constellation observing system for meteorology, ionosphere and climate, GRAS on board meteorological operational, which have been recieving a large number of RO data, but their observed signals come only from global positioning system (GPS). These RO data have been wildly used in NWP and climate monitoring, however they cannot meet the requirements for high accuracy and real time atmosphere observation, in this case compatible RO sounder to obtain more RO observations is significant. Global navigation satellite system occultation sounder (GNOS) on board the fengyun3 C (FY3 C) satellite, which is the first Bei Dou system (BDS)/GPS compatible RO sounder in the world, was launched on 23 September 2013. Up to now, lots of RO observations have been obtained. In this study, the components of GNOS are introduced; one-day GNOS RO events and their global distribution are analyzed; compared with the GPS RO observations, the accuracy and consistency of BDS real-time positioning results and BDS RO products are analyzed. The preliminary results show that the BDS can enhance the number of RO events by 33.3%; the average deviation and standard deviation of BDS real time positioning results are 6 m and 7 m, respectively; the BDS/GPS difference standard deviation of refrectivity, temperature, humidity, pressure and ionospheric electron density are lower than 2%, 2 K, 1.5 g/kg, 2%, and 15.6%, respectively. The BDS observations/products are consistent with those of GPS, therefore BDS RO products can bring benefit to numerical wheather prediction and global chlimate change analysis.
Theoretical model of the rotationally and tidally distorted binaries
Authors: Zhan Qiong  , Song Han-Feng  , Tai Li-Ting  , Wang Jiang-Tao  ,   Department of Physics, College of Science, Guizhou University, Guiyang 550025, China;,   Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650011, China;,   Joint Research Centre for Astronomy, National Astronomical Observatory-Guizhou University, Guiyang 550025, China
Published: December 2020

Rotation and tide are two important factors which have an influence on the stellar structure and evolution. They cannot be neglected. According to the observation data of the massive binary system V478 Cyg, we test the theoretical model including the deformation which is induced by rotation and tide (our model). We compare our model with Kähler-Eggleton (KE) model, and the distorted model is more consistent with observations than the traditional model (KE model). Besides, it is found that great deformation occurs in the outer envelope, where its density is lower than the mean density. Rotation and tide can cause the gravity at the two polar points to increase and the gravity in the equatorial plane to decrease. Therefore, the radiative flux, which depends on the local effective gravity, is not constant on the equipotentials any more. The poles which become hotter, experience a high mass loss than the equator, which becomes cooler. Furthermore, the two components in our model have bigger radii, equatorial velocities and central compactness and low H-energy production rate. The bigger mean radius of the distorted star produces a smaller temperature gradient inside the star, resulting in a lower energy transport. The lower energy generation rate inside the distorted model will widen the main sequence and increase the stellar lifetime. Stellar temperature and luminosity of the distorted model are shifted toward lower value. The tidal distortion inside the secondary star plays a most important role in the rate of the apsidal motion because of lower compactness. The apsidal motion derived from rotation is larger than the one derived from the general relativity.
Coupling dynamics for a photonic crystal fiber femtosecond laser nonlinear amplification system
Authors: Shi Jun-Kai  , Chai Lu  , Zhao Xiao-Wei  , Li Jiang  , Liu Bo-Wen  , Hu Ming-Lie  , Li Yan-Feng  , Wang Qing-Yue  ,   Ultrafast Laser Laboratory, Key Laboratory of Optoelectronics Information Technique, Ministry of Education, School of Precision Instrument and Optoelectronic Engineering, Tianjin University, Tianjin 300072, China;,   MOEMS Education Ministry Key Laboratory, Tianjin University, Tianjin 300072, China
Published: December 2020

A femtosecond laser single-stage nonlinear amplification system composed of Yb-doped large-mode-area single-polarization photonic crystal fibers is demonstrated. Effects of net cavity dispersion and pump power on oscillator output parameters and the evolution dynamics of the amplified pulse after compression are discussed for different seed pulse parameters. Under the experimental conditions in this paper, the longer and less chirped pulses are obtained with a larger negative net intracavity dispersion in the oscillator. When a nearly-transform-limited pulse is chosen as seed pulse nder the condition of oscillator pump power of 4.53 W, the shortest nearly-pedestal-free amplified pulse is achieved under the amplifier pump power of 60 W after the dispersion is compensated by a grating pair, in which the pulse duration is 45.7 fs with an average power of 28 W at a refletition frequency of 42 MHz. When the oscillator pump power is increased to 5.08 W and most nearly-transform-limited pulses under the pump condition are selected as the seed pulses, the maximum average power of 34.5 W with a duration of 53.5 fs is obtained at an amplifier pump power of 70 W.
Group velocity manipulation of far off-resonant pulse-pair in atomic system
Authors: Jiang Qi-Chang  , Liu Chao  , Liu Jin-Hong  , Zhang Jun-Xiang  ,   The State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China;,   Departments of Physics and Electronic Engineering, Yuncheng University, Yuncheng 044000, China
Published: December 2020

Based on the far off-resonant four-wave mixing process, the slow light propagations of the amplified probe and generated conjugate pulses are obtained experimentally. Simultaneous manipulations of group velocity are realized by changing the two-photon detuning between the pump light and the probe light. The dependences of gains of the injected probe and generated conjugate light on the one-photon detuning for continuous wave mode are studied at different cesium vapor temperatures and pump light powers. It is shown that the maximum of gains occurs at the proper Raman one-photon detuning. The dependence of delay time on the two-photon detuning is measured using the 6 μs and 365 ns probe pulses, respectively. For the 6 μs input probe pulse, the maximum delay times of the probe and the conjugate pulses are 2.1 μs and 1.9 μs with the fractional delays of 0.35 and 0.32, respectively, corresponding to 0.000119 c and 0.000132 c group velocity. The high fractional delays of 2.07 and 1.83 with the maximum delay times of 756 ns and 670 ns for the 365 ns input pulse are obtained.
Study of the equation of states for deuterium, helium, and their mixture
Authors: Zhang Qi-Li  , Zhang Gong-Mu  , Zhao Yan-Hong  , Liu Hai-Feng  ,   null
Published: December 2020

Equation of states for deuterium, helium, and their mixture is studied by using the quantum molecular dynamics (QMD) method. We calculate the equation of states for helium with density from 0.32 to 5 g/cm3 at temperature from 1000 to 50000 K. Results are compared with the chemical model (CM), at T less than 10000 K, and QMD is in good agreement with the CM. The shock Hugoniot curves are also calculated, and the results are in good agreement with the gas-gun experiment. The mechanism of the metal-insulator transition for helium is studied by computing its pair distribution function and density of states. The equation of states (EOS) for deuterium with density from 0.19 to 0.84 g/cm3 at temperatures from 20 to 50000 K is computed. For deuterium molecule the degree of dissociation is calculated, and the effect of the molecular vibration is accounted for using the EOS model. Theoretical Hugoniot states are also calculated and compared with the results of experiments and other theories; the maximum compressibility of hydrogen is about 4.9, and deuterium 4.4; these agree with the results of most experiments and theories. Due to the zero point motion of atoms being not taken into account, the theoretical results at low temperatures are smaller than those of experiments. The deuterium-helium mixture is studied, and its 293 points of equation of states for various xHe with densities from 0.19 to 0.84 g/cm3 at temperatures from 100 to 50000 K are calculated. The linear mixing approximation (LMA) is checked, and the maximum of the volume distinction is about 7%; the results indicate that LMA is a cursory approximation.
Universal conductance fluctuations of topological insulators
Authors: Li Zhao-Guo  , Zhang Shuai  , Song Feng-Qi  ,   National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, and Department of Physics, Nanjing University, Nanjing 210093, China
Published: December 2020

As an exotic quantum condensed matter, the topological insulator (TI) is a bulk-insulating material with a Diractype conducting surface state. Such a dissipationless transport of topological surface state (TSS) is protected by the timereversal symmetry, which leads to the potential applications in spintronics and quantum computations. Understanding the topological symplectic transport of the Dirac fermions is a key issue to the study and design of the TI-based devices. There are many transport properties about Dirac fermions. And universal conductance fluctuation (UCF) is one of the most important transport manifestations of mesoscopic electronic interference. So the UCF effect in TI is a very meaningful research field It can provide an intriguing and special perspective to reveal the quantum transport of TSSs In this review, we introduce the research progress on the UCF of TSSs in a pedagogical way We review the achievements and the existing problems in order to inspire future research work.#br#We start this review with the basic UCF theory and the experimental observation. The UCF has been observed in TI earlier, but weather it originates from TSS has not been further studied. Then a series of work is carried out to prove the topological nature of UCF in TI Firstly, the UCF phenomenon in TIs is demonstrated to be from two-dimensional (2D) interference by magnetoconductance measurements. But the residual bulk state and the 2D electron gas (2DEG) on the surface can also bring about the 2D UCF The field-tilting regulation helps us exclude the distribution from the bulk And the classic self-averaging of UCF is investigated then to obtain the intrinsic UCF amplitude. By comparing with the theoretical prediction, the possibility has been ruled out that the 2D UCF may originate from the 2DEG So its topological nature is demonstrated. Secondly, we discuss the UCF effect in TI by a macroscopic perspective, i.e. the statistical symmetry of UCF, which should be more concise and reflect its universality. For a single TSS, the applied magnetic field will drive the system from a Gaussian symplectic ensemble into a Gaussian unitary ensemble. It results in a √2 fold increase of the UCF amplitude. However, the experiment reveals that the UCF amplitude is reduced by 1/√2. This is contradictory to the theoretical prediction. Actually, there are two TSSs and they are coherently coupled to each other in TIs since the sample’s thickness is smaller than its bulk dephasing length. This leads to a Gaussian orthogonal ensemble of the intersurface coupling system without an external field. In such a case, the UCF amplitude will be reduced by 1/√2 with field increasing. It is consistent with the experimental result. Finally, the other progress on UCFs is discussed, and the general outlook is also mentioned briefly.
Multiscale theory and computational method for biomolecule simulations
Authors: Li Wen-Fei  , Zhang Jian  , Wang Jun  , Wang Wei  ,   National Laboratory of Solid State Microstructure, Department of Physics, Nanjing University, Nanjing 210093, China;,   Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
Published: December 2020

Molecular simulation is one of the most important ways of studying biomolecules. In the last two decades, by combining the molecular simulations with experiments, a number of key features of structure and dynamics of biomolecules have been reflealed. Traditional molecular simulations often use the all-atom model or some coarse grained models. In practical applications, however, these all-atom models and coarse grained models encounter the bottlenecks in accuracy and efficiency, respectively, which hinder their applications to some extent. In reflent years, the multiscale models have attracted much attention in the field of biomolecule simulations. In the multiscale model, the atomistic models and coarse grained models are combined together based on the principle of statistical physics, and thus the bottlenecks encountered in the traditional models can be overcome. The currently available multiscale models can be classified into four categories according to the coupling ways between the all-atom model and coarse gained model. They are 1) hybrid resolution multiscale model, 2) parallel coupling multiscale model, 3) one-way coupling multiscale model, and 4) self-learning multiscale model. All these multiscale strategies have achieved great success in certain aspects in the field of biomolecule simulations, including protein folding, aggregation, and functional motions of many kinds of protein machineries. In this review, we briefly introduce the above-mentioned four multiscale strategies, and the examples of their applications. We also discuss the limitations and advantages, as well as the application scopes of these multiscale methods. The directions for future work on improving these multiscale models are also suggested. Finally, a summary and some prospects are preflented.
Phase correction method based on interfacial signal in swept source optical coherence tomography
Authors: Pan Cong  , Guo Li  , Shen Yi  , Yan Xue-Guo  , Ding Zhi-Hua  , Li Peng  ,   State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

There are intrinsic phase errors in swept source optical coherence tomography (SS-OCT), which severely influences the functional imaging. To overcome this difficulty, a numerical correction method is presented in this paper to correct the phase artifacts due to wavenumber shift among the spectral interferograms, resulting from the random delay variance between the sampling trigger and the clock of the swept source laser. This correction method is based on the linear relationship of phase difference to the depth of the sample and the wavenumber shift. The detailed procedure to eliminate the phase artifacts is as follows. Firstly, we figure out the complex OCT signals through inverse Fourier transform of the initial interferograms. Then we fit the upper surface of the sample with the intensity information of the B-scan by setting a floating threshold. After that the wavenumber shifts of each A-line are determined by two steps with the phase information of the sample surface: the relative wavenumber shifts between adjacent A-lines are first obtained according to the phase difference between the adjacent A-lines, the signal depth, and the linear relationship mentioned above; then we figure out the absolute wavenumber shifts between each A-line and the first A-line of the B-scan by an iteration algorithm. With the information about the wavenumber shift, we align the initial interferograms, and obtain the corrected complex signal through re-inverse Fourier transform of the aligned interferograms. This method introduces no extra noise, realizing phase measurement limited by the signal-to-noise ratio. It is noted that we take the average phase information of several axial pixels near the sample surface to diminish the noise influence when calculating the wavenumber shifts. Besides, this corrected algorithm acquires oversampling along the scanning direction to ensure the signal correlation between adjacent A-lines.
The SS-OCT system in the paper is set up with a vertical cavity surface emitting laser with a center wavelength of 1297 nm. The system measurement range is 12 mm in lateral direction, the axial resolution is 17 m, and the lateral resolution is 24 m. And the feasibility of this method is verified by Doppler imaging of a mirror, an infra-red detection card and the cerebral cortex of a mouse.
Photonic bandgap compensation and extension for hybrid quasiperiodic heterostructures
Authors: Zou Jun-Hui  , Zhang Juan  ,   Key Laboratory of Specialty Fiber Optics and Optical Access Networks, School of Communication and Information Engineering, Shanghai University, Shanghai 200072, China
Published: December 2020

Based on the idea of multiple photonic bandgap (PBG) overlapping for a one-dimensional photonic crystal heterostructure, a novel hybrid quasiperiodic heterostructure is proposed to enlarge the omnidirectional photonic bandgap (OPBG). The heterostructure is formed by combining Fibonacci and Thue-Morse quasiperiodic structure. The results show that the OPBG of the heterostructure is enlarged obviously, which increases about three times compared with that of Fibonacci quasiperiodic structure, and twelve times compared with that of Thue-Morse quasiperiodic structure. The influences of structural parameters, such as period number and generation number, on PBGs of Fibonacci and Thue-Morse quasiperiodic structure are studied respectively. The results show that the parameters have little effects on PBG widths of the two quasiperiodic structures. The influences of the refractive indexes and thickness values of the high and low refractive index materials on OPBG of the heterostructure are also investigated. The results show that the OPBG of the heterostructure can be further broadened by increasing the refractive index ratios and thickness values of the high and low refractive index materials. The reason why the quasiperiodic structure can easily realize the multiple band gap overlapping is analyzed by comparing the bandgap properties of periodic structure. The number of PBGs of the quasiperiodic structure in the same wavelength range is more than that of the periodic structure. Moreover, with the increase of generation number of the quasiperiodic structure, due to the occurrence of PBG split, the number of PBGs increases obviously, and each PBG width is less than that of the periodic structure. Owing to this kind of PBG characteristic of the quasiperiodic structure, the heterostructure formed by cascading the two quasiperiodic structures is more prone to realizing the multiple PBG overlapping than other heterostructures, thus more easily achieving the expansion of OPBG. These results lay the design foundation for the compensation and broadening of the more complex bandgap structure.