bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of ternary polymer solar cells based on P3HT: PTB7-Th: PCBM
Authors: Deng Li-Juan  , Zhao Su-Ling  , Xu Zheng  , Zhao Ling  , Wang Lin  ,   Key Laboratory of Luminescence and Optical Information, Ministry of Education, Beijing Jiaotong University, Beijing 100044, China;,   Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

Recently, ternary bulk-heterojunction (BHJ) polymer solar cells (PSCs) occur as an attractive strategy with simple fabrication technology to extend the spectrum of wide bandgap polymers into the near infrared region by adding a narrow bandgap sensitizer. In this paper, a series of cells including binary BHJ-PSCs with P3HT:PCBM as the active layer (control cell) and ternary BHJ-PSCs with different PTB7-Th doping concentrations are fabricated to investigate the effect of PTB7-Th on the performance of PSC. The short-circuit current density (Jsc) and fill factor (FF) of the ternary PSCs are simultaneously improved by adding a small amount of PTB7-Th into P3HT:PCBM. The champion photoelectric conversion efficient of ternary PSCs (with 15 wt% PTB7-Th) is 3.71%, which is larger than 2.71% of the control cell. In a ternary device, the absorption region shows a distinct red-shift and the relative absorption intensity from 650 nm to 800 nm is gradually enhanced with the incrtease of PTB7-Th doping concentration. The increased photon harvesting in the solar spectral range results in an increased short-circuit current density. However, despite the fact that the photoluminescence (PL) spectrum of P3HT has a large overlap with the absorption spectra of PTB7-Th, which makes it possible for Frster resonance energy to transfer between P3HT and PTB7-Th, the PL intensity of P3HT at 650 nm is quenched with the increase of PTB7-Th doping concentration while the photoluminescence remains almost the same in the long wavelength region, which suggests that the main mechanism between PTB7-Th and P3HT is photo-induced electron transfer from P3HT to PTB7-Th (hole transfer from PTB7-Th to P3HT), not energy transfer. The PSCs with P3HT:PTB7-Th (1:1) as an active layer display a large Jsc compared with the P3HT-based one. When the concentration of PTB7-Th decreases and the concentration of P3HT is unchanged (P3HT:PTB7-Th 1 : 0.5), the Jsc can be further enhanced. The increased Jsc value of P3HT: PTB7-Th (1:0.5) PSCs confirms that the photo-generated excitons can be dissociated into free charge carriers at the P3HT:PTB7-Th interface and reinforce the charge transfer between P3HT and PTB7-Th. In P3HT:PCBM binary organic solar cell, the photo-generated excitons only can be directly dissociated into free charge carriers at the P3HT:PCBM interface and then transported to the respective electrodes, while incorporating PTB7-Th, the interaction between P3HT and PTB7-Th also makes the photo-generated excitons dissociated at the interface of P3HT:PTB7-Th, and at the interface of PTB7-Th:PCBM. The increasing of excitons dissociated leads to a higher FF. The present study is the first report on utilizing PTB7-Th in P3HT:PCBM PSC.
First-principle study of the oxygen adsorption on Zr surface with Nb or Ge
Authors: Zhang Hai-Hui  , Li Xiao-Di  , Xie Yao-Ping  , Hu Li-Juan  , Yao Mei-Yi  ,   Key Laboratory for Microstructures, School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China
Published: December 2020

It is observed that the addition of Nb or Ge to Zr alloy can improve its corrosion resistance. Because of the extreme importance of the mechanism of oxidation to corrosion properties of Zr alloy, we systematically investigate the O adsorption properties on pure Zr surface and Zr surface with Nb or Ge using first-principle calculations based on density functional theory. Firstly, we present the absorption energies to reveal the influences of Nb and Ge on the O absorption capacity of Zr surfaces, resepctively. According to the calculated absorption energies, we find that Nb and Ge reduce the oxygen absorption capacities of most of surfaces, and the only exception is that Nb enhances the oxygen absorption capacity of Zr(1120) surface. Moreover, the absorption energy of O at favorable site on Zr(0001) surface is much lower than on Zr(1010) or (1120) surface. Therefore, the initial oxidation of polycrystalline Zr should occur at Zr(0001) surface and the absorption capacity of this surface takes a predominant role in the initial oxidation of polycrystalline surface. Secondly, the segregation of Nb or Ge in Zr alloy is anisotropic. We find that the segregation of Ge to surface is exothermic, while the segregation of Nb to surface is endothermic. Nb and Ge migrate to Zr(0001) surface more easily than to Zr(1120) and Zr(1010) surfaces. Therefore, the influence of Nb or Ge on absorption property of Zr(0001) is much larger than that of Zr(1010) or (1120) surface. Based on the adsorption and segregation properties of Nb and Ge on Zr surfaces, both Nb and Ge can reduce the oxygen absorption capacity of Zr surface and inhibit the initial oxidation of Zr alloy surface, which can be used to understand the experimental observation that Nb and Ge can improve the corrosion resistance of Zr alloy. Finally, the electronic structure analysis shows that the influences of Nb and Ge on oxygen adsorption capacity of Zr surface are exerted by changing the d-band distribution. According to Hammer-Norskov d-band center theory, the absorption energy of absorpate on transition metal surface is mainly determined by d-band center. The addition of Nb or Ge to the Zr surface changes the location of d-band of the surface, which results in the variation of absorption energy of O atom on the Zr surface. For absorption at top site on each surface, it is found that the absorption energy of O only depends on the d-band center of the surface atom below the O atoms. However, for absorption at favorable sites on each surface, the absorption energy of O atom is influenced not only by the d-band center of surface atom, but also by atomic structural properties of the surface.
Observation of particle manipulation with axial plane optical microscopy
Authors: An Sha  , Peng Tong  , Zhou Xing  , Han Guo-Xia  , Huang Zhang-Xiang  , Yu Xiang-Hua  , Cai Ya-Nan  , Yao Bao-Li  , Zhang Peng  ,   State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710119, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Optical micromanipulation of particles based on the optical trapping effect induced by the interaction between light and particles has been successfully applied to many interdisciplinary fields including biomedicine and material sciences. When particles are trapped in three dimensions, the conventional wide-field optical microscopy can only monitor the movement of the trapped particles in a certain transverse plane. The ability to observe the particle movement along light trajectories is limited. Recently, a novel method named axial plane optical microscopy(APOM) has been developed to directly image the axial plane that is parallel to the optical axis of an objective lens. The APOM observes the axial plane by converting the axial information of a sample into that of a transverse plane by using a 45°-tilted mirror. In this paper, we propose and demonstrate that the APOM serves as an effective tool for observing the axial movement of particles in optical tweezers. By combining with a conventional wide-field optical microscopy, we show that both transverse and axial information can be acquired simultaneously for the optical micromanipulation. As in our first experimental demonstration, we observe two particles which are trapped and aligned along the optical axis. From the transverse image, only one particle is observable, and it is difficult to obtain the information along the axial direction. However, in the axial plane imaging, the longitudinal dipolar structure formed by the two particles is clearly visible. This clearly demonstrates the APOM imaging capability along the axial axis. The numerically simulations on the trapping focal spot against the position of a collimating lens agree well with our experimental APOM results. Furthermore, we directly observe the dynamic capture process of a single trapped particle in transverse plane by conventional wide-field optical microscopy as well in axial plane by the APOM, and can obtain the 3D information rapidly and simultaneously. We point out that the observable axial dynamic range is about 30 μm. Taking advantages of no requirement of scanning and data reconstruction, the APOM has potential applications in many fields, including optical trapping with novel beams and 3D imaging of thick biological specimens.
Propagation properties of vortex beams in a ring photonic crystal fiber
Authors: Zhang Ling-Xiang  , Wei Wei  , Zhang Zhi-Ming  , Liao Wen-Ying  , Yang Zhen-Guo  , Fan Wan-De  , Li Yi-Gang  ,   School of Physics, Nankai University, Tianjin 300071, China
Published: December 2020

In the last decade, the vortex beams have received lots of attention for their orbital angular momentum.When they are applied to optical fiber communication field,the data channels will increase and information propagation speed will be effectively improved. Recently, researchers have shown the capabilities of long length stably propagation, nonlinear frequency conversion and mode division multiplexing of vortex modes in a ring fiber. Due to the photonic crystal fiber(PCF) having very flexible design degrees of freedom, it will enable a wide range of propagation properties. In this paper, a SiO2 air-hole ring PCF is proposed for separation and propagation of optical vortex modes.By using COMSOL Multiphysics software,the vortex modes(TE01, HE21± and TM01) are simulated and calculated. The differences in effective refractive index between them are 4.59×10-4 and 3.62×10-4 respectively. One can analyze the propagation properties of vortex beams in the ring PCF by changing the size of first layer air hole radius and air hole pitch. When the incident light wavelength of TE01 mode ranges from 1650 nm to 1950 nm, this ring PCF can achieve a total dispersion variation between 44.18 to 45.83 ps·nm-1·km-1, which is tend to be flat. When incident light wavelength is 1550 nm, the nonlinear coefficient of TE01 mode vortex light is 1.37 W-1·km-1. Due to the fact that long wavelength light is easier to leakage through the cladding than the short wavelength light, the confinement loss increases with the wavelength. When incident light wavelength is 2000 nm, there is still an eight-orders-of-magnitude of the low confinement loss. Theoretically, flat dispersion and low loss vortex beams in this fiber can be beneficial to propagating stably, and the vortex modes lay the foundation for long distance propagation in the optical fiber. In the future, this ring PCF will be used in optical fiber communication field and applications in aspects such as continuous spectrum research, which can make it have immense advantage over traditional fibers.
Spatial correlation of underwater bubble clouds based on acoustic scattering
Authors: Fan Yu-Zhe  , Li Hai-Sen  , Xu Chao  , Chen Bao-Wei  , Du Wei-Dong  ,   Acoustic Science and Technology Laboratory, College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin 150001, China
Published: December 2020

With using the effective medium theory to describe acoustic scattering from bubble clouds, one of the underlying assumptions shows that the probability of an individual bubble located at some position in space is independent of the locations of other bubbles. However, bubbles within the clouds that naturally occur are usually influenced by the motion of the fluid, which makes them preferentially concentrated or clustered. According to Weber's method, it is a useful way of introducing the spatial correlation function to describe this phenomenon in bubble cloud. The spatial correlation function is involved in acoustic scattering and it is important to notice that the spatial correlation should be dependent on the position and radius of each bubble due to the “hole correction” or the effect of the dynamics of the fluid. Because of these reasons, it is hard to invert the spatial distribution of bubble clouds by using the spatial correlation function in acoustic scattering. A method is described here in which bubble clouds are separated into many small subareas and the conception, called effective spatial correlation function which is the statistic of spatial correlation function, is used to describe the correlation between subareas of bubble clouds. Since the effective spatial correlation function is independent of bubble radius and positions, the bubble clouddistribution and the trend of clustering can be inverted by using this function. The simulation indicates that the effective spatial correlation function can precisely trace the position of the clustering center, even the clustering center covered by other bubble clouds can be detected. With using the multi-bean sonar for measuring the bubbly ship wake generated by a small trial vessel, the method is used to invert the spatial distribution and clustering centers of bubble field in the ship wake. The results show that the effective spatial correlation function accurately inverts the distribution and clustering centers of bubbles in ship wake. Furthermore, the method presented in this paper could distinguish between the bubble clouds caused by different reasons and detect upper ocean bubble clouds covered by other bubbles generated by wave breaking as well.
A broadband low-frequency sound insulation structure based on two-dimensionally inbuilt Helmholtz resonator
Authors: Gao Dong-Bao  , Liu Xuan-Jun  , Tian Zhang-Fu  , Zhou Ze-Min  , Zeng Xin-Wu  , Han Kai-Feng  ,   Academy of Ocean Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Helmholtz resonator(HR) has already been demonstrated both theoretically and experimentally to be a metamaterial with negative mass density and negative bulk modulus simultaneously. The HR can resonate at a frequency corresponding to a wavelength much longer than its geometrical parameters. At this time, the incident acoustic energy can be located. Therefore, the HR structures are considered to be good choices for controlling low-frequency sound waves. Furthermore, existing results indicate that the wide forbidden band could be formed by a one-dimensional structure shunted with detuned HRs. Based on these aforementioned theories, a man-made acoustical structure with broadband low-frequency sound insulation effect is designed by circularly inbuilt HRs. Beyond this structure's surface, a two-dimensional quiet zone can be created. With the same simulated model, an experimental structure is fabricated based on PVC plastic material. The structure consists of five layerd circular plates. In the top four plates, two kinds of holes are drilled. The smaller holes in the top plate act as shot necks of the HR, while the bigger holes in the middle three plates serve as the cavities of the HR. They can construct 60 resonators with different resonant frequencies. Experiments are carried out to study its sound insulation properties. In the experiments, three kinds of HRs with resonant frequencies 785, 840 and 890 Hz from inner loop to outer loop, respectively, are formed. The experimental results are very coincident with the simulation results from the software of COMSOL Multiphysics based on finite element method, which shows that this structure has an excellent sound insulation effect in a frequency band of 680-1050 Hz, and the maximum insulation sound pressure level can reach 41 dB. Meanwhile, the distribution of the two-dimensional sound field is measured. The results point out that the range of the insulation area can be changed with the incident frequency. In addition, the sound insulation effect is sensitive to the resonant state of the HRs. When all of the resonators at the same loop resonate simultaneously, the insulation sound pressure level will be higher. On the contrary, the insulation sound pressure level will be lower because of the energy leaking through the positions where the HRs do not resonate with the others. This work will be of help for designing new sound protection devices for low-frequency sound waves.
Diffusion of diblock copolymer in periodical channels:a Monte Carlo simulation study
Authors: Wang Chao  , Chen Ying-Cai  , Zhou Yan-Li  , Luo Meng-Bo  ,   Department of Physics, Taizhou University, Taizhou 318000, China;,   Department of Physics, Zhejiang University, Hangzhou 310027, China
Published: December 2020

In recent years, the static and the dynamical properties of polymer confined in nano-channels have become a hot topic due to its potential applications in technology, such as genome mapping, DNA controlling and sequencing, DNA separation, etc. From the viewpoint of polymer physics, the properties of polymer confined in nano-channels are affected by many factors, such as the channel size, the channel geometry, the polymer-channel interaction, etc. Consequently, many researches have been extensively performed to uncover the underlying physical mechanisms of the static and the dynamical properties of polymer confined in nano-channels. Although many conformations are forbidden as polymer is confined in channels, the static properties of polymer are found to be still complicated. For the simplest case, i.e., homo-polymer confined in homogeneous solid channels, there are several scaling regimes, in which polymer adopts different conformation modes and the extension of polymer shows different scaling relations with the channel diameter, the polymer length, the persistence length, etc. In addition, the dynamical properties of polymer, such as the diffusivity and the relaxation, have also been extensively studied. Though the properties of polymer confined in homogeneous channels have been well studied, we know little about those of polymer inside compound channels. It is found that the dynamics of polymer in compound channels is quite different from that of polymer in homogeneous channels, and compound channel could be useful for DNA separation and DNA controlled movement.In this work, the diffusion of diblock copolymer(ANABNB) in periodical channels patterned alternately by part and part with the same length lp/2 is studied by using Monte Carlo simulation. The interaction between monomer A and channel is attractive, while all other interactions are purely repulsive. Results show that the diffusion of polymer is remarkably affected by the length of block A(NA), and the diffusion constant D changes periodically with NA. Near the peaks of D, the projected length of block A along the channel is an even multiple of lp/2, and the diffusion is in consistence with that of homo-polymer in homogenous channels. While near the valleys of D, the projected length of block A is an odd multiple of lp/2, and polymer is in a state with long time trapping and rapid jumping to other trapped regions in the diffusion process. The physical mechanisms are discussed from the view of polymer-channel interaction energy landscape.
Influence of collision energy on the stereodynamics of the H+CH+→C++H2 reaction
Authors: Tang Xiao-Ping  , Zhou Can-Hua  , He Xiao-Hu  , Yu Dong-Qi  , Yang Yang  ,   School of Physics and Electronic Technology, Liaoning Normal University, Dalian 116029, China;,   State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Dalian 116023, China;,   Key Laboratory of Chemical Lasers, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
Published: December 2020

The reactive cross section and stereodynamics at selected collision energies for the H(2S)+CH+(X1Σ+)→C+(2P)+H2(X1Σg+) reaction on a globally smooth ab initio potential surface of the 2A' state are calculated in detail by the quasi-classical trajectory(QCT) method. The calculated cross section decreases with the increase of the collision energy, which is found to be in overall good agreement with the previous time-dependent quantum results in the high collision energy regime (Ec>20 meV). The discrepancy between the QCT and previous quantum cross section below 20 meV can be attributed to the limitations of the classical trajectory method, because the QCT method cannot handle the effect of zero point energy. In general, QCT results show qualitative agreement with the quantum results, which confirmsthe validity of the QCT method. The research shows that the product rotational angular momentum vector is aligned and oriented. The alignment of the product rotational angular momentum vector j' depends very sensitively on the collision energy. With the increase of the collision energy, the alignment effect recedesin the low collision energy region (1500 meV), while it is enhanced in the high collision energy region (500-1000 meV). Moreover, the k-k'-j' distributions tend to be asymmetric with respect to the k-k' scattering plane (or about φr=180°), with two peaks appearing at φr=90° and φr=270°, respectively. This indicates that the product rotational angular momentum is not only in the Y-axis direction but also along the positive Y-axis direction. The peak intensity decreases with the collision energy increasing from 1 meV to 100 meV, while it increases with collision energy increasing from 100 meV to 1000 meV. Therefore the Y-axis orientation effect turns weak with the enhancement of the collision energy in the low energy region, while it becomes strong in the high energy region. In addition, the polarization dependent differential cross sections (PDDCSs) (2π/σ)(dσ00/dωt) and (2π/σ)(dσ20/dωt) are calculated. PDDCS (2π/σ)(dσ00/dωt) results indicate that the products have almost symmetrically scattered forward and backward, and the intensity of the scattering increases with the increase of the collision energy. The PDDCS (2π/σ)(dσ20/dωt) shows that the alignment effect of the rotational angular momentum of the products is stronger at the terminal of the scattering angle than at the other directions.
Sheared-beam imaging target reconstruction based on all-phase spectrum analysis
Authors: Chen Ming-Lai  , Luo Xiu-Juan  , Zhang Yu  , Lan Fu-Yang  , Liu Hui  , Cao Bei  , Xia Ai-Li  ,   Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710119, China
Published: December 2020

Sheared-beam imaging technique is considered to be a non-conventional speckle technique for remote imaging through turbulent medium. In this high resolution imaging technique, three beams are splitted from one laser source and illuminate a remote target simultaneously in shearing distribution. Each beam is modulated by a tiny frequency shift so that these beams can interfere and beat together. The returning speckle signals are received by an array of detectors. The primary algorithm for the signal processing and image reconstruction has been developed previously. However, the reconstructed image is deteriorated by the frequency drifting error and spectrum leakage. These frequency errors are always from the transmitter and scattered signals that are caused by spectrum-shift errors from acoustic-optic modulators, atmospheric turbulence, Doppler effects of moving targets, etc. To solve the problems mentioned above, in this paper we propose a new image reconstruction algorithm based on the all-phase spectrum analysis theory. The all-phase fast Fourier transform (FFT) spectrum analysis theory, which can effectively inhibit spectral leakage and correct speckle spectrum, is used to process the scattered signals. By searching for the accurate positions of the beat frequency components in the transformed frequency domain data, the speckle amplitude and phase difference frames can be extracted accurately. Based on the speckle phase-difference frames, the phase distribution of the wavefront is derived by least-square algorithm. The phase distribution in grid is highly coherent, in which each point is related to the phases of its four nearest neighbors. If an initial phase map is given or preset, the phase map of the wavefront can be estimated accurately by Gauss-Seidel method. Meanwhile, the amplitude of wavefront is obtained by the algebraic operation of speckle amplitude frames. The reconstructed wavefront is inverse Fourier transformed to yield a two dimensional image. A series of speckled images of the same object are averaged to reduce the speckle noise. The proposed method improves the ability of system imaging in the actual imaging environment. Simulation experiments validate the effectiveness of the proposed algorithm, and simulation results show that the proposed image reconstruction algorithm can inhibit the frequency errors from influencing imaging quality when there exist frequency errors in scattered signals. Thus, the imaging quality of the algorithm based on the all-phase FFT method is much better than that of the algorithm based on the traditional FFT method. The substantial usage of this technique is widely spread after the reconstruction algorithm has been optimized.
Experimental study on increasing signal-to-noise ratio of a beat note by cascading an Yb-doped fiber in an Er-fiber comb
Authors: Liu Huan  , Cao Shi-Ying  , Yu Yang  , Lin Bai-Ke  , Fang Zhan-Jun  ,   Center for Photonics and Electronics, Department of Precision Instrument, Tsinghua University, Beijing 100084, China;,   Division of Time and Frequency Metrology, National Institute of Metrology, Beijing 100029, China
Published: December 2020

The harmonic optical frequency chain is the only tool for measuring optical frequency till the advent of a femtosecond optical frequency comb (FOFC). However, its disadvantages are obvious, such as high cost, difficult construction, complex usage, and complicated maintenance. The emergence of femtosecond optical frequency combs (FOFCs) makes it possible to measure the absolute frequency of a laser, which greatly simplifies the quantity traceability of the absolute frequency value and comparison, and allows the length unit “m” to be directly traced back to the time unit “s”. The beat note (fb) between an FOFC and a test laser is one of the most important data in measuring absolute frequency of the test laser. In order to ensure the accuracy and reliability of the measurement, the signal-to-noise ratio (SNR) of fb should be above 30 dB at 300 kHz resolution bandwidth. Among the wavelength standards recommended to replicate “meter” (SI), iodine-stabilized 633 nm lasers and iodine-stabilized 532 nm lasers have been widely used. Compared with iodine-stabilized 633 nm lasers, iodine-stabilized 532 nm lasers have the advantages of high stability, high output power, no modulation and fiber coupled output. Therefore, it is of great importance to measure and monitor the absolute frequency of an iodine-stabilized 532 nm laser. Aiming at the specific requirements for absolute frequency measurement of an iodine-stabilized 532 nm laser, the absolute frequency measurement of its fundamental 1064 nm laser has been studied. In this paper, a high-repetition-rate Er-doped femtosecond fiber laser is adopted as an optical source in the system. The repetition rate of the fiber laser is 303 MHz, the output power in the continuous-wave state is 130 mW and the average output power in the mode-locking state is 80 mW. The highest SNR of fb between the comb light and a 1064 nm laser generated by an iodine-stabilized 532 nm laser is only 30 dB due to the low intensity at 1 μm wavelength in the supercontinuum, which just reaches the SNR threshold meeting the counter's working condition. In order to improve the accuracy and reliability of absolute frequency measurement, the technique of cascading an Yb-doped fiber amplifier after spectral broadening is adopted to enhance the spectral intensity at 1 μm wavelength. The experimental results indicate that the SNR of fb between a 1 μm laser after spectral enhancement and a 1064 nm laser is increased by 5 dB and kept at 35 dB for several days, meeting requirements for long-term continuous monitoring. This method can effectively reduce the intensity requirements at 1 μm wavelength when the spectrum is directly broadened in the Er-FOFC.
Characterization of Brillouin scattering in a few-mode fiber
Authors: Zhang Yan-Jun  , Gao Hao-Lei  , Fu Xing-Hu  , Tian Yong-Sheng  ,   Key Laboratory for Special Fiber and Fiber Sensor of Hebei Province, School of Information Science and Engineering, Yanshan University, Qinhuangdao 066004, China
Published: December 2020

The few-mode fiber can be used to transmit limited orthogonal modes, which has the advantages of small modular interference and easily controlled modes. The Brillouin scattering sensor based on the few-mode fiber can effectively reduce the cross sensitivity of multi parameter measurement, and realize the measurement of multi physical quantity. In this paper, based on the wave optics theory, the Brillouin scattering spectrum parameters of the step-index few-mode fiber are analyzed, such as frequency shift, line width and peak gain and so on. Firstly, the transmission modes of the few-mode fiber are analyzed. The finite element analysis result shows that there are 5 kinds of transmission modes:LP01, LP11, LP21, LP02 and LP31, and their effective refractive indexes are 1.4664, 1.4652, 1.4637, 1.4630 and 1.4616, respectively. Secondly, the mathematical models of the Brillouin frequency shift, line width and peak gain of different modes in the few-mode fiber are analyzed. Finally, the parameters of Brillouin scattering spectrum with different modes' superposition are also discussed. In the few-mode fiber, due to the different effective refractive index, the light of each mode is propagated along its respective path and interacts with the particles in the fiber, thus producing different Brillouin scattering spectrum. The simulation results show that the frequency shift of the Brillouin scattering spectrum of each mode is in a range of 10.19-10.23 GHz, and the frequency shift increases with the decrease of the mode order. The Brillouin line width of each mode is in a range of 32-34 MHz, and the line width also increaseswith the decrease of the mode order. Moreover, the relative amplitude of the Brillouin scattering gain spectrum increases with the decrease of the mode order. The mathematical models of this paper are used respectively to analyze the Brillouin scattering spectra of other types of step-index few-mode fibers. It is shown that the Brillouin frequency shift, Brillouin line width and peak gain of other types of step-index few-mode fibers also increase with the decrease of the mode order. In a step-index few-mode fiber, intramodal Brillouin scattering spectrum and the intermodal Brillouin scattering spectrum are both in line with the distribution of Lorenz curve. However, the intermodal Brillouin scattering spectrum of modes' superposition leads to the line width broadening of the Brillouin scattering spectrum, and the relative amplitude of the intermodal Brillouin scattering spectrum of modes' superposition being generally smaller than that of intramodal.
Equivalence of energy deposition profile in target between electron beam of multi-energy composite spectrum and X-ray
Authors: Liu Xue  , Ran Xian-Wen  , Xu Zhi-Hong  , Tang Wen-Hui  ,   College of Science, National University of Defense Technology, Changsha 410073, China;,   Monitoring and Modeling of Electromagnetic Environment in Near Space Key Laboratory of General Universities of Hunan Province, Changsha University of Science and Technology, Changsha 410015, China
Published: December 2020

It has great significance to study the thermal-mechanical effects of X-ray in assessing the viability of space-crafts, the penetration ability of missiles and testing the effectiveness of the anti-nuclear reinforcement measures. However, it is rather difficult to construct a suitable X-ray source in laboratory. During recent decades, pulsed electron beam with multi-energy composite spectrum has become a most important simulation source of X-ray to study its thermal-mechanical effects. And energy deposition profile in target material is the basis for studying the thermo-mechanical effects. However, under the same incident conditions, the energy deposition profile of pulsed electron beam with multi-energy composite spectrum in target material is extremely different from X-ray's, and the equivalence between the two beams is quite low. Thus, it is very important to adjust the energy spectrum and the incident mode of pulsed electron beam so as to improve their equivalence. In this paper, we use the energy deposition profiles of electron beam and X-ray in different kinds of material. MCNP is used to calculate their energy deposition profiles in target materials. Two kinds of blackbody X-rays with the equivalent temperatures of 3 and 5 keV and energy density of 200 J/cm2 are chosen for an optimization target. Aluminum, copper and titaniumare chosen as the target materials. Based on the change law of electron beam's energy deposition profile when the electron beam hits the target material at different incident angles, a theoretical model is established. Then, taking advantage of simulated annealing algorithm, we use the MATLAB to carry out numerical calculation and finally the numerical optimization results about the incident angle spectrum and energy density of electron beam are obtained. After optimization, the energy deposition of pulsed electron beam with multi-energy composite spectrum is well adjusted. The peak energy deposition and change of gradient of electron beam are of wonderful consistency with X-ray's. The equivalence of pulsed electron beam with multi-energy composite spectrum in simulating X-ray is also effectively improved. However, the energy density of adjusted pulsed electron beam should be much higher than 200 J/cm2. Electron beam designed by this paper can be used to better simulate the thermal-mechanical effects of X-ray in different kinds of materials.
High pressure synthesis of anhydrous magnesium carbonate (MgCO3) from magnesium oxalate dihydrate (MgC2O42H2O) and its characterization
Authors: Liang Wen  , Li Ze-Ming  , Wang Lu-Ying  , Chen Lin  , Li He-Ping  ,   Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Stimulated by the extensive application and research value, the study of anhydrous magnesium carbonate (MgCO3) has been a subject of great concern recently, so that a basic problem in designing a method of effectively synthesizing MgCO3 is very worth considering. In previous studies, different methods were reported to synthesize MgCO3 successfully but they still have some obvious deficiencies. The micro-particle sizes are too small to satisfy the basic requirements of micro-analysis. Thus, it is needed to explore the new methods of artificially synthesizing MgCO3 with the simple process and the high efficiency.
By using magnesium oxalate dihydrate (MgC2O42H2O) as starting material, MgCO3 sample is successfully synthesized by a solid reaction under high temperature and high pressure for the first time in this work. The properties of as-synthesized sample are investigated by X-ray powder diffraction and Raman spectroscopy:neither of them shows any impurities existing in the sample. Significantly, the crystallinity quality is greatly improved in the terms of the maximum grain sizes up to 200 micrometers, which could provide a base for MgCO3 single crystal growth in the future. Moreover, compared with the results of previous studies, the reaction time of high pressure synthesis is controlled within 1 h so that the efficiency of the synthesis is greatly improved.
Based on thermogravimetric analyses and the results of high pressure experiment under the various pressures and temperatures, the P-T phase diagrams of MgC2O42H2O-MgCO3-MgO at high pressures of 0.5, 1.0 and 1.5 GPa are obtained, and in this case, it is reasonable to explain the principle of MgCO3 synthesis under high pressure strictly. From the P-T diagram, high pressure can greatly improve the thermal stability of material, and the decomposition temperature of MgCO3 obviously increases with pressure increasing. However, due to decomposition temperature of MgCO3 increasing more quickly than that of MgCO42H2O, the stable phase regions of MgC2O42H2O and MgCO3 are separated from each other, and hence, the corresponding temperature and pressure can be controlled to decompose the phase of MgC2O42H2O while stabilizing the phase of MgCO3 so as to obtain MgCO3 successfully. Besides, by using polarizing microscope, the morphology of MgCO3 sample as well as its crystal cleavage plane (1011) is observed clearly, and it is noted that as-synthesized MgCO3 has good optical properties and high-quality crystallinity. The electron probing analysis for MgCO3 thin section is performed to quantify the Mg content and the calculation indicates that the sample composition is Mg0.99CO3.
Superconductivities of pressurized iron pnictide superconductors
Authors: Yi Wei  , Wu Qi  , Sun Li-Ling  ,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

As one of the independent control parameters, pressure plays an important role in finding new phenomena, testing related theories and guiding the explorations for new superconductors. In this review article, we will briefly review the progress achieved from high pressure studies on some main types of the iron pnictide superconductors, including 1111-type, 122-type, 111-type, 10-3-8 type and 112-type. A few typical results from high pressure studies are introduced in more detail, including the positive pressure effect on the superconducting transition temperature TC of 1111-type iron pnictide superconductors, which indicates a way to enhance the TC by using a smaller cation to replay La ion; the maximum TC of iron pnictide superconductors estimated by high-pressure studies on a series of 1111-type iron-based superconductors etc. More importantly, high pressure studies on the parent compounds of iron pnictide superconductors clearly demonstrate that pressure can suppress the transition temperatures of magnetic order and crystal structure, and then drive a superconducting transition. Furthermore, many examples are given in this review to reveal how the magnetic order competes with superconductivity under pressure, which provides new constrains for the establishment of the theory on superconductivity. These high pressure results are expected to be helpful for the studies of high-TC superconductors and for the exploring of new superconductors.
Numerical simulation of complex immersed boundary flow by a radial basis function ghost cell method
Authors: Xin Jian-Jian  , Shi Fu-Long  , Jin Qiu  ,   School of Transportation, Wuhan University of Technology, Wuhan 430063, China
Published: December 2020

A radial basis function ghost cell immersed boundary method of simulating flows around arbitrary complex or multiple immersed boundaries is proposed in this paper. In this method, incompressible Navier-Stokes equations are discretized on fixed Cartesian staggered gridby the finite difference method. A fractional step method is used for time integration, together with third order Runge-Kutta scheme. A high-order TVD MUSCL (total variation diminishing monotonic upstream-centered scheme for conservation law) scheme is used to discretize convective terms. Two salient features are emphasized in the present study. First, boundary conditions at the immersed interface are enforced by a continuous ghost cell method to consider the influence of immersed boundary on the flow field. The immersed bodies are treated as virtual boundaries immersed in the flow. And Navier-Stokes equations are solved in the entire computation domain, including solid domain. Therefore, programming complexity is greatly reduced and the treatment of immersed boundaries is simplified. Second, a polynomial and radial basis function is introduced to implicitly represent and reconstruct arbitrary complex immersed boundaries. Iso-surface distance functions about interface geometries are fitted with some sampling points of body surfaces. It is flexible and robust. Moreover, the information about interface positions on the background grid can be easily identified by the signed distance functions. Based on our in-house developed immersed boundary method solver, typical test cases are simulated to validate the proposed method. The flows around a cylinder at Reynolds numbers of 40, 100 and 200 are first simulated and a grid resolution study is carried out. Good agreement is achieved by comparing with previous numerical results, which shows that this method is accurate and reliable. In the second case of flow around airfoil, the good agreement with previous study shows that the present method has the ability to simulate complex immersed boundary flow. In the last case of flow around array of thirteen cylinders, the ability of present method for multiple immersed boundaries is well proved. And hydrodynamic interaction among multiple bodies is briefly analyzed.
Effect of doping symmetry on electron spin relaxation dynamics in (110) GaAs/AlGaAs quantum wells
Authors: Teng Li-Hua  , Mu Li-Jun  ,   Optoelectronic Materials and Technologies Engineering Laboratory of Shandong, Department of Physics, Qingdao University of Science and Technology, Qingdao 266061, China
Published: December 2020

Considerable interest has been aroused in the study of the spin dynamics in semiconductors due to its potential applications in spintronics and quantum computation. In this paper, time-resolved circularly polarized pump-probe spectroscopy is used to study the carrier density dependences on the electron spin relaxation in approximately symmetrical and completely asymmetrical doping (110) GaAs/AlGaAs quantum wells. With the increase of the carrier density, the spin relaxation time first increases and then decrease obviously in both of the quantum wells, and the measured spin relaxation time of the approximately symmetrical doping quantum wells is always longer than that of the asymmetrical doping one. By analysis, we find that the spin relaxation is not dominated only by the Bir-Aronov-Pikus (BAP) mechanism in (110) GaAs quantum wells, that though the Dresselhaus spin-orbit coupling does not lead to any spin relaxation, the asymmetry of the doping position contributes to the asymmetry of potential energy structure, thus the built-in electric field which can induce the Rashba spin-orbit coupling to appear, and that the effective magnetic field induced by the Rashba spin-orbit coupling normal to the growth direction can lead to spin relaxation along the growth direction. Therefore, the Dyakonov-Perel (DP) mechanism plays an important role in asymmetrical doping (110) GaAs/AlGaAs quantum wells. In the approximately symmetrical and completely asymmetrical doping (110) GaAs/AlGaAs quantum wells, the DP mechanism dominates the spin relaxation at low carrier density, thus the spin relaxation time increases with carrier density increasing due to the strengthening of the electron-electron scattering and the decreasing of the momentum relaxation time. However, at high carrier density, BAP mechanism plays an important role, thus the spin relaxation time decreases obviously with carrier density increrasing, but the decay rates in both of the quantum wells are slower than that in the casethat only BAP mechanism dominates, because both the DP and BAP mechanism play an important role. The strength of the Rashba spin-orbit coupling depends on the symmetry of the quantum well. The DP mechanism in a completely asymmetrical doping quantum well is stronger than that in an approximately symmetrical doping quantum wells, thus the decay rate in a completely asymmetrical doping quantum wells is always slower than that in an approximately symmetrical doping quantum wells, and the spin relaxation time in a completely asymmetrical doping quantum wells is shorter than that in an approximately symmetrical doping quantum wells.
Mechanism analysis of influence of surface-breaking orientation on magnetic leakage field distribution
Authors: Wu De-Hui  , Liu Zhi-Tian  , Wang Xiao-Hong  , Su Ling-Xin  ,   School of Aerospace Engineering, Xiamen University, Xiamen 361005, China
Published: December 2020

Magnetic flux leakage (MFL) has been widely applied to the nondestructive testing (NDT) of ferromagnetic materials due to its simple operation, low cost, and steady signal. Its defects are evaluated based on the relationship between MFL signal and the geometrical characteristic of defect. In this paper, a three-dimensional (3D) mathematical model is developed for the magnetic leakage field of surface-breaking defects that are arbitrarily oriented inside ferromagnetic material. Firstly, a finite-length rectangular slot is used as a simplified and convenient representation of a surface-breaking defect. Then, the magnetic charge densities of slot walls in different surface-breaking orientations are analyzed theoretically. The distribution of the magnetic leakage field can ultimately be derived by vector synthesis. Both simulations and experiments are conducted to analyze the magnetic leakage field distributions in different magnetization orientations. The results show that with increasing the angle between the defect orientation and the magnetic field, the horizontal component of the leakage magnetic field increases as demonstrated by increasing the prominence of its single peak. At the same time, however, the vertical component shows a bimodal distribution. The proposed model can effectively describe the influence of defect orientation on MFL signals, which can offer practical guidelines for optimizing MFL detectors and improving defect assessment.