bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of donor position and number on two-photon absorption properties of tetraphenylethylene derivatives
Authors: Zhao Ke , Song Jun , Zhang Han ,   School of Physics and Electronics, Shandong Normal University, Jinan 250358, China
Published: December 2020

Organic materials with strong two-photon absorption response and aggregation induced emission have aroused a great deal of interest in recent years, for their many potential applications such as two-photon fluorescence microscopy, up-conversion laser, photodynamic therapy, etc. The tetraphenylethylene units are usually employed in two-photon absorption and aggregation induced emission materials because of their good electron-donating capability and special propeller starburst structures. Theoretical study on the relationship between molecular structure and two-photon absorption property is of great importance for guiding the experimental design and synthesis of functional materials. In this paper, the two-photon absorption properties of a series of organic molecules containing tetraphenylethylene and cyano groups are studied by employing the density functional response theory in combination with the polarizable continuum model. The molecular geometries are optimized at a hybrid B3LYP level with 6-31g(d, p) basis set in the Gaussian 16 program. The two-photon absorption cross sections are calculated by response theory through using the CAM-B3LYP functional with 6-31g(d) basis set in the Dalton program. The effect of donor position and number on two-photon absorption properties are investigated. In addition, by increasing the planarity and conjugated length of the molecule, as well as by enhancing the strength of the electron donor, we design three molecular structures and calculate their two-photon absorption properties. The results show that the donor position and number have important effects on two-photon absorption properties. The methoxy donor at the end of the molecule can increase the two-photon absorption intensity effectively. As the number of substituents increases, the position of the two-photon absorption peak is red-shifted. The effects of adding electron donor groups on different side positions have a significant difference in the two-photon absorption property. Comparing with the experimental molecules, the two-photon absorption cross sections of the designed molecules are greatly enhanced. When the tetraphenylethylene group is replaced by the triphenylamine group, the two-photon absorption peak is greatly red-shifted, and the two-photon absorption intensity is significantly increased. Since all of these molecules contain tetraphenylethylene or triphenylamine group with propeller structure, they can have both two-photon absorption and aggregation induced emission properties. This study provides theoretical guidelines for synthesizing a new type of active two-photon absorption and aggregation induced emission material.
A new type of micro-X-ray diffractometer focused by polycapillary optics
Authors: Jiang Qi-Li , Duan Ze-Ming , Shuai Qi-Lin , Li Rong-Wu , Pan Qiu-Li , Cheng Lin ,   Key Laboratory of Beam Technology Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, China,   Department of Physics, Beijing Normal University, Beijing 100875, China
Published: December 2020

Micro-X-ray diffraction (μ-XRD) plays a significant role in measuring the phase structures of small samples or micro areas of larger samples. In this article, we propose a new type of desktop micro-X-ray diffractometer named μ-Hawk focused by polycapillary optics. It consists mainly of a microfocus X-ray tube, polycapillary optics, receiving slits, a silicon drift diode (SDD) X-ray detector integrated with single/multi-channel pulse analyzer, independently rotating θ-θ goniometer, high precision XYZ sample stage, computer programs developed by LabVIEW codes, etc. The main interface of the program has micro-X-ray diffraction analysis mode and micro energy dispersive X-ray fluorescence analysis mode. In addition, the monochromatization of X-ray, the angular resolution and the accuracy of the results of μ-Hawk are discussed. In order to demonstrate the feasibility of the instrument, the phase of micro area in the middle of the first stroke on the Chinese character “Jiao” from a 5-Jiao coin (Chinese currency) is measured by the μ-Hawk, and the phase of a copper wire 140 μm in diameter is also detected by it. After that, the phase of 1.0 mm × 0.6 mm area on the welding joint of the motherboard from an iPhone is two-dimensionally scanned by μ-Hawk. The θ-θ scanning is performed at each detected point inside the two-dimensional area. Four motors drive the X and Y axis of the sample stage as well as the θ1 and θ2 axis of the goniometer to accomplish the above functions. The results show that the micro energy dispersive X-ray fluorescence analysis mode of μ-Hawk can provide elementary reference information for the analysis of phase structure. Compared with conventional X-ray diffractometer, the μ-Hawk can detect the same diffraction peaks on the coin with lower background. Furthermore, the accurate diffraction peaks can be measured with a lower power and shorter time. The measured results can better reflect the true phase structure of the micro area. Six diffraction peaks and their phases can be clearly identified from the diffraction pattern of the copper wire. For the welding joint, the phase mapping of SnO2 (3 1 2) is acquired through data processing. Therefore, the μ-Hawk can adapt to the micro-X-ray diffraction analysis of small samples or micro areas of samples as well as the two-dimensional scanning analysis of phase mapping. The μ-Hawk exhibits the unique advantages of accomplishing accurate micro-X-ray diffraction analysis, convenient software, low working power, time saving, and small in size. It indicates a wide application prospect in the fields of materials, geosciences and heritage protection.
First-principles study of effects of Ga, Ge and As doping on electrochemical properties and electronic structure of Li2CoSiO4 serving as cathode material for Li-ion batteries
Authors: Yan Xiao-Tong , Hou Yu-Hua , Zheng Shou-Hong , Huang You-Lin , Tao Xiao-Ma ,   School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, China,   School of Physical Science and Technology, Guangxi University, Nanning 530004, China
Published: December 2020

Silicate cathode material Li2CoSiO4 has received wide attention due to high theoretical capacity. However, the high discharge makes the existing electrolyte unable to satisfy the requirements of its use, and the poor cyclic stability limits its further application and development. The high discharge and cycle stability of Li2CoSiO4 cathode material can be improved by doping corresponding elements. The effects of non-transition high-valent elements of Ga, Ge and As doping on structural, electrochemical and electronic properties of Li-ion battery cathode material Li2CoSiO4 are systematically studied by the first-principles calculations based on density functional theory within the generalized gradient approximation with Hubbard corrections (GGA + U). The calculation results show that the maximum expansion range of the unit cell volume of Li2CoSiO4 cathode material during lithium ion removal is 3.5%. However, the Ga, Ge and As doping reduce the variation range of unit cell volume during the delithiation of the system, which is beneficial to the improvement of the cycle stability of Li2CoSiO4 material. Furthermore, the Ga, Ge and As doping can reduce the theoretical average deintercalation voltages of extraction for the first Li+ in per formula unit; the theoretical average deintercalation voltages of the doping systems decrease by 1.65 V, 1.64 V and 1.64 V, respectively, compared with the deintercalation voltage of the undoped Li2CoSiO4 system. Meanwhile, except for the Ga doping, the Ge and As doping can also effectively reduce their theoretical average deintercalation voltagesin the secondary delithiation process. The density of states and magnetic moment show that Co2+ has a strong binding effect on the 3d orbital electrons, which makes it difficult for Co2+ in Li2CoSiO4 material to lose electrons for participating in the charge compensation in the process of Li+ removal. However, the Ga, Ge and As doping can effectively participate in the charge compensation of the system in the process of Li+ removal, which is the main reason for the decrease of the theoretical average deintercalation voltage of the system. In addition, the Ge doping reduces the band gap value of the Li2CoSiO4 from 3.7 eV to 2.49 eV, while the Ga doping and the As doping introduce the donor defects, and thus making the doping system exhibit metallic properties, which can improve the conductivity of the system to some extent.
Alternating magnetic force microscopy: simultaneous observation of static and dynamic magnetic field in three-dimensional space
Authors: Cao Yong-Ze , Zhao Yue ,   Department of Physics, Dalian Maritime University, Dalian 116026, China,   Regional Innovation Center, Akita University, Tegata Gakuen-machi 1-1, Akita  010-8502, Japan
Published: December 2020

In the scanning magnetic domain by using the conventional magnetic force microscopy (MFM), a laser beam reflection is used to detect the static magnetic force between probe and sample. Therefore, for the MFM, it is a challenge to directly detect the dynamic magnetic force between probe and sample under an external alternating-current (AC) magnetic field. In this study, it is proved that in an alternating magnetic force microscopy (A-MFM) a sensitive Co-GdOx superparamagnetic probe can be usedto detect the dynamic magnetic force under an external AC magnetic field (frequency ωm). In the present method, the magnetization of Co-GdOx probe is modulated by an external AC magnetic field. Collecting ωm and 2ωm signals by using the combination of phase-locked loop (PLL) and lock in amplifiers can accurately represent the static (DC, which stands for direct current) magnetic field areas (the external AC magnetic field has no effect on the magnetized status of the sample) and dynamic (AC) magnetic field areas (the external AC magnetic field changes the magnetized status of the sample) of an anisotropic Sr ferrite sintered magnet at the same time, respectively. The Sr ferrite sample is a single-domain-type magnet where magnetization mainly changes via magnetic rotation. The A-MFM method can measure the strength and identify the polarities of the static magnetic field of sample with a DC demagnetized state. By modifying the traditional tapping-lift mode into a tapping-multiply lift mode, the A-MFM by using superparamagnetic tips can measure the static and dynamic magnetic field distribution in three-dimensional (3D) space. It is proved that the static and dynamic magnetic field as a function of the distance z between probe and sample are both expressed as Hz(z) = Hz(0)·exp(–kz). The experimental data are consistent with the previous theoretical calculations. The A-MFM can be used to study the dynamic magnetization process and to evaluate the magnetic homogeneity (microstructural homogeneity) of magnetic materials.
Effects of multisite interaction on nonequilibrium thermodynamics of XY spin chain in a transverse filed
Authors: He Zhi , Yu Min , Wang Qiong ,   Hunan Province Cooperative Innovation Center for the Construction and Development of Dongting Lake Ecological Economic Zone, Changde 415000, China,   College of Mathematics and Physics Science, Hunan University of Arts and Science, Changde 415000, China
Published: December 2020

In recent years, the property of nonequilibrium thermodynamics in closed system, especially in spin chain system undergoing a quenching process, has become one of the hot topics in the quantum thermodynamics. The nonequilibrium thermodynamic properties of XY spin chain with XZX + YZY type of three-site interaction under a transverse field are studied by considering an exactly solvable model. First we review some basic concepts, i.e., the work distribution, the averaged work, the fluctuation of work, and the irreversible entropy in the nonequilibrium thermodynamics, and give the theoretical model and its solutions. Then, we concretely discuss the effects of the three-site interaction of XZX + YZY type on the average work, the fluctuation of work and the irreversible entropy in the extended XY chain undergoing a quench process. The theoretical calculation and numerical simulation show that the three-site interaction of XZX + YZY type may play a positive and negative role in the increase of the averaged work, which depends on the strength of initial external magnetic field. Moreover, we also find that work fluctuation can be effectively suppressed by adjusting the intensity of XZX + YZY three-site interaction. Finally, it is found that the irreversible entropy production presents a sharp peak characteristic near the critical magnetic field, and the value of the peak sharp decreases with the increase of XZX + YZY three-site interaction. Simultaneously, the corresponding physical explanations are also given. In a word, the results given in present paper may increasingly arouse one’s interest in the nonequilibrium quantum thermodynamics.
Design and simulation of integration of vertical cavity surface emitting lasers and heterojunction bipolar transistor
Authors: Zhou Guang-Zheng , Li Ying , Lan Tian , Dai Jing-Jing , Wang Cong-Cong , Wang Zhi-Yong ,   Institute of Laser Engineering, Beijing University of Technology, Beijing 100124, China
Published: December 2020

Vertical cavity surface emitting lasers (VCSELs) are widely used in the field of short-range optical communication and optical interconnection because of their advantages such as low threshold current, large modulation bandwidth, easy two-dimensional integration, easy coupling with optical fibers and low cost. The VCSELs and heterojunction bipolar transistor (HBT) are longitudinal current devices, so they can be well integrated on the same wafer, and the output light power can be modulated by the HBT base current. Integration of VCSELs and HBT are designed in this paper. The VCSELs and PNP InGaP/GaAs HBT form a direct series structure. The reflectivity of DBR is 99.72% at a resonant wavelength of 850 nm and 99.57% after adding HBT separately. Therefore, the addition of HBT has little influence on the reflectivity of DBR at the resonant wavelength. The electro-optical characteristics of the integrated structure are simulated by using PICS3D software. An interim collector is added into the model in order to ensure that the simulation can be carried out smoothly. Firstly, HBT is conducted and the current flows from the emitter to the interim collector. Then, the voltage across the interim collector and the N-type electrode is increased to make VCSELs conducted and the current of the transition collector drop to zero. The interim collector can be removed from the actual structure because the current is zero. The simulation results show that the current gain coefficient is 400, and the maximum modulation rate of the base current to the output light power rises up to 280 mW/mA. The maximum temperature in the active region increases with the base current increasing, and the output light power first increases and then tends to be saturated. The ac optical gain characteristics of the integrated structure is simulated by PICS3D, and the simulation result shows that cutoff frequency exceeds 1 GHz. The addition of HBT limits the modulation rate of the integrated structure, and further optimization of HBT structure parameters and geometric dimension are needed to improve the modulation rate. The integrated structure and simulation method established in this paper can also be used to integrate LED, LD, DFB or other luminescent devices with HBT.
Pressure-driven fluid flow characteristics in black phosphorus nanochannels
Authors: Zhang Zhong-Qiang , Liu Han-Lun , Fan Jin-Wei , Ding Jian-Ning , Cheng Guang-Gui ,   Institute of Intelligent Flexible Mechanoelectronic, Jiangsu University, Zhenjiang 212013, China,   Jiangsu Collaboratory Innovation Center of Photovoltaic Science and Engineering, Changzhou University, Changzhou 213164, China,   State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China
Published: December 2020

With the rapid development of low-dimensional materials, the opportunity that promotes the development of micro/nano fluid devices, a new low-dimensional material black phosphorus (BP) has attracted wide attention due to its excellent properties, and has been applied to many areas. In this paper, the influences of driving force, water-BP anisotropy, channels’ width and the number of black phosphorus layers on the flow characteristics of water molecules in the nanochannels are studied by molecular dynamics based on the Poiseuille flow model. The results show that the boundary slip velocity increases with the driving force increasing. The anisotropy will also affect the flow characteristics of water molecules in the nanochannel under the pressure driving the Poiseuille flow. Specifically, the boundary slip velocity decreases with the chirality angle increasing, and the viscosity coefficient of water molecules is still not affected by the anisotropy. The natural rippled structure of the BP surface leads to the coarse potential surface, and further results in the anisotropic boundary slip and interfacial friction between water and BP sheets. With the driving acceleration kept constant, the influences of the width of nanochannels and the number of black phosphorus layers on the boundary slip velocity and viscosity coefficient of water molecules are investigated. The results indicate that the slip velocity of water molecules in the nanochannels decreases with the width of the nanochannels increasing. The velocity profile of water molecules in the bilayer model is slightly different from that in the monolayer model. With the number of BP layers increasing, the energy of BP-water solid-liquid interface increases while the anisotropic interfacial property remains unchanged. The results will provide a theoretical basis for the study of the characteristics of the fluid flowing in the black phosphorus nanochannels and the design of micro/nano fluid devices based on black phosphorus materials.
New dissipative particle dynamics boundary condition for complex geometry
Authors: Lin Chen-Sen , Chen Shuo , Xiao Lan-Lan ,   School of Aerospace Engineering and Applied Mechanics, Tongji Univesity, Shanghai 200092, China,   School of Mechanical and Automotive Engineering, Shanghai University of Engineering Science, Shanghai 201620, China
Published: December 2020

Dissipative particle dynamics (DPD) is a thriving particle-based simulation method of modeling mesoscale fluids. After two decades of evolution, DPD has shown unique advantages in researches about polymer, red blood cell, droplets wetting, etc. However, DPD is limited to relatively simple geometries due to the lack of a satisfactory boundary method. In this paper, we propose an adaptive boundary method for complex geometry, which fulfills the three basic requirements of boundary method: no penetration into the solid, no-slip near boundary, negligible fluctuation of density or temperature near boundary. Specifically, first, a new vector attribution is added to each solid particle, the attribution is named local wall normal (LWN) attribution and it is a function of its neighbor solid particle’s position, the LWN attribution is used to correct the penetrating fluid particles’ velocity and position and is computed only once if the wall is stationary. Second the surface wall particles are identified by neighbor solid fraction (φ), which indicates the percentage of surrounding space occupied by solid particles, then the wall is reconstructed by only the surface particles instead of all solid particles. By doing so, the redundant bulk particles are removed from the simulation. Third, it is detected on-the-fly whether the moving fluid particle penetrates the wall by computing its φ, the fluid particles with φ greater than 0.5 are considered to enter into the solid wall, their position and velocity will be corrected based on the local wall normal attribution. We verify that the method causes negligible density and temperature fluctuation in Poiseuille flow. Then, we illustrate the implementation of LWNM in the cases of complex blood vessel network and micro-structured surface. With this method, the obstacles in flow are no longer restricted to shapes described by functions but can be generated by CAD software, and blood vessels can also be generated by CT scan images or other experimental data. Moreover, we show a case with a bent tube and droplets inside, demonstrating the practicability of constructing complex geometry and the effectiveness of LWNM. This new boundary approach empowered DPD to simulate more realistic problems.
Particle-in-cell simulation on effect of collector outgassing on relativistic backward oscillator
Authors: Wang Hong-Guang , Liu Peng-Fei , Zhang Jian-Wei , Li Yong-Dong , Cao Yi-Bing , Sun Jun ,   Key Laboratory for Physical Electronics and Devices of Ministry of Education, Xi’an Jiaotong University, Xi’an 710049, China,   School of Electronic Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China,   Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

The relativistic backward-wave oscillator has been considered to be one of the most promising high-power microwave devices. As the output microwave power is further increased, the breakdown phenomenon inside the relativistic backward-wave oscillator, including the collector pole, becomes more and more serious, which eventually leads to the pulse shortening, becoming a biggest obstacle to the development of the device with high power and high energy. Such a problem has also been one of the important issues which constrain its development. Based on the 2.5D particle-in-cell simulation software, i.e. UNIPIC-2D developed by our research group, in this paper the dynamic gassing model is used to study the effects of the relativistic backward-wave oscillator collector breakdown process and the guiding magnetic field under different outgassing coefficients. The result of particle simulation demonstrates that as the electrons continue to bombard the collector, the surface pressure of the collector is increased, and gas ionization occurs. The generated plasma enters into the slow-wave structure along the guiding magnetic field, thus affecting the beam-wave interaction process and causing the output power to drop. With the increase of the gas release coefficient, the pulse shortening phenomenon becomes more and more obvious. In the case of low guiding magnetic field, the breakdown and pulse shortening are alleviated.
New reduced matrix construction accelerated iterative solution of characteristic basis function method
Authors: Wang Zhong-Gen , Mu Jun-Wen , Lin Han , Nie Wen-Yan ,   College of Electrical and Information Engineering, Anhui University of Science and Technology, Huainan 232001, China,   College of Mechanical and Electrical Engineering, Huainan Normal University, Huainan 232001, China
Published: December 2020

The characteristic basis function method is known as an effective method to solve the electromagnetic scattering problems, but the convergence of the iterative solution of the reduced matrix equation is slow when the characteristic basis function method is used to analyze the electromagnetic scattering characteristics of the electrically large target. In order to mitigate this problem, a new reduced matrix construction method is proposed to improve the iterative solution efficiency of characteristic basis function method in this paper. Firstly, the singular value decomposition technique is used to compress the incident excitations, and the characteristic basis functions of each sub-domain under the new excitations are solved. Then, the new excitations and the characteristic basis functions are defied as the testing and basis functions to construct the reduced matrix. The diagonal sub-matrices of the reduced matrix constructed by the new testing and basis functions are all identity matrices, thereby improving the condition of reduced matrix. Thus, the total number of iterations to achieve reasonable results is significantly reduced. Numerical simulations are conducted to validate the performance of the proposed method. The results demonstrate that the efficiency of the iterative solution of the reduced matrix equation constructed by the new method is significantly improved. Furthermore, the characteristic basis functions’ generation time required by the proposed method is noticeably less than that by the traditional characteristic basis function method due to the reduced number of matrix equation solutions.
A new method of multi- atlas segmentation of right ventricle based on cardiac film magnetic resonance images
Authors: Su Xin-Yu , Wang Li-Jia , Zhu Yan-Chun ,   School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China,   Tencent Healthcare (Shenzhen) Co., Ltd., Shenzhen 518057, China
Published: December 2020

Segmentation of right ventricle (RV) in a cine cardiac magnetic resonance (CMR) image is essential for the diagnosis and therapy of cardiac diseases. Traditional image segmentation methods fail to achieve high accuracy due to the complex structure of RV. Multi-atlas frame, which transforms the segmentation into registration and fusion, has become one of the main segmentation methods of RV in recent years. In this paper, we suggest a new multi-atlas frame for the automatical and accurate segmentation of RV. Firstly, an adaptive affinity propagation algorithm is used to obtain a series of atlases, in which the atlas set most similar to the target image based on hausdorff distance and normalized mutual information is selected. Then, the target image is registered onto the selected atlas by using multi-resolution strategy-based affine transform and Diffeomorphic demons algorithm to generate a deformation field, which is applied to the label image to obtain coarse segmentation results of RV. Finally, the Consensus Level, Labeler Accuracy and Truth Estimation (COLLATE) algorithm is used to fuse the coarse segmentation result to obtain the RV. The 30 cine CMR datasets are applied to the retrospective analysis. The comparison between RV value from the present algorithm and that from the manual segmentation shows that the average dice index and hausdorff distance are 0.84 and 11.46 mm, respectively, the correlation coefficients and deviation means of endo-diastolic volume, endo-systolic volume and ejection fraction are 0.94, 0.90, 0.86, and 2.5113, –3.4783, 0.0341, respectively. Compared with convolutional neural networks, the new multi-atlas frame has an endo-systolic volume close to the manual result. The results show that the suggested method improves the accuracy and robustness of segmentation of RV from the effective atlas selection and multi-resolution Diffeomorphic demons algorithm-based registration, and it promises to be applied to clinical diagnosis.
Three-point and four-point mechanical bending test modeling and application in solar cells
Authors: He Ren , Li Ying-Ye , Chen Jing-Xin , Zhao Xue-Ling , Tang Huan , Zhang Li-Na , Shen Yan-Jiao , Li Feng , Yang Lin , Wei De-Yuan ,   Key Laboratory of Optic-electronic Informationand Materials, Institute of Physical Science and Technology, Hebei University, Baoding 071002, China,   Yingli Green Energy Holding Co., Ltd., Baoding 071051, China
Published: December 2020

Silicon (Si)-wafer-based solar cells have dominated the global market with a share exceeding 90% due to their abundant source material and well-known physical and chemical properties. The brittleness of silicon material limits its further applications. It is necessary to investigate the material strength properties of Si wafer and/or Si solar cells, which can guide the fabrication process of Si solar cells to avoid breaking the Si wafers. The Si material strength properties have been extensively investigated by the methods of three-point bending test and four-point bending test. However, the difference between these two methods has not been studied so far.

In this work, the mechanical strength properties of monocrystalline silicon (c-Si) wafer and bifacial c-Si solar cells are measured by three-point bending test and four-point bending test respectively. The average value of the maximum bending displacements has a little discrepancy between the results of the three-point bending test and four-point bending test methods. It is worth noting that the degree of dispersion of the Si wafer test results of the three-point bending test is larger than those of the four-point bending test. And the results of the dispersion of the Si bifacial solar cells, obtained from the two bending test methods, show no difference between them due to the existence of metalized electrodes. Whether the measured sample is Si wafer or Si solar cell, the average value of the maximum load, obtained from the four-point bending test, is higher than that from the three point-bending test method, and the average value of the fracture strength, obtained from the four-point bending test, is lower than that from the three-point bending test method. By establishing the models of different beams, the applied load gets dispersed through two bars of the four-point bending test method, whereas the applied load is directly applied to the sample through one bar of the three-point bending test method, which can explain the relatively large difference between these two test methods.
Kinematics and passing modes of a droplet impacting on a soap film
Authors: Yang Ya-Jing , Mei Chen-Xi , Zhang Xu-Dong , Wei Yan-Ju , Liu Sheng-Hua ,   State Key Laboratory for Strength and Vibration of Machanical Structures, School of Aerospace Engineering, Xi’an Jiaotong University, Xi’an 710049, China,   School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

 Droplet passing through a film is a ubiquitous phenomenon in nature, such as a rain drop impacting on a rain bubble in paddle and pouring beer onto the beer foam, etc. This phenomenon has not been sufficiently investigated and many interfacial interaction mechanisms are still unknown. In this paper, the passing modes and the kinematics of a droplet impacting on a soap film are studied with the help of a high-speed cameral. The impacting Weber number of the droplet varies from 10 to more than 350. The droplet position and velocity are extracted from the video by a self-designed Matlab codes.

 Experimental results show that the droplet may pass through the soap film in five modes, i.e., bouncing, bagless packaging, package peeling, bag packaging, and instaneous coalescence. A " drop-cushion-shell”-type compound droplet can be formatted in bag-[We ∈ (10.8, 60)] and bagless [We ∈ (120, 240)] packaging mode, while in the package peeling [We ∈ (60, 120)] and coalescence [We ∈ (240, 350)] mode it will form single phase droplets, however, with the surface coated with a soap solution layer (original soap film). Although compound droplets have three surfaces, i.e., the droplet’s original surface and the inner and outer surface of the soap film, the apparent surface tension for the bagless-packed droplet is just that of the soap solution, while for the bag-packed droplet it is the sum of the three surface tensions. The outer shell of the compound droplet may peel off and eject a bubble when the Weber number is in the certain range (We ∈ (60, 120) for droplet with D0 = 3.0 mm), the lower limit decreases and the upper limit increases with the increase of the initial diameter of the droplets and thus expands the bubble-shooting range. The droplet performs a free fall motion, however, it is interfered by the soap film. The droplet can be stopped and rebounded when We < 10.8, and penetrate the film and start another free fall when We > 10.8. The velocity loss before and after the penetration decrease with impact velocity increasing, hence the motion of the higher We droplet is less retarded by the soap film, the motion curve approaches to the free fall curve. The approaching is not a linear but an accelerating behavior.
Method of designing magnetic resonance active shimming coil based on target field point method and flow function
Authors: Huang Qing-Ming , Chen Shan-Shan , Zhang Jian-Qing , Yang Yang , Zheng Gang ,   School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China,   School of Medical Imaging, Shanghai University of Medicine and Health Sciences, Shanghai 201318, China,   Shanghai Key Laboratory of Molecular Imaging, Shanghai University of Medicine and Health Sciences, Shanghai 201318, China,   Laboratory of Medical Imaging Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
Published: December 2020

Uniformity of magnetic field is an important parameter of magnetic resonance system. Improving the uniformity of magnetic field is helpful for detecting the magnetic resonance time domain signal and improving the resolution of magnetic resonance frequency domain signal. Based on the idea of continuous current density distribution in an active shimming field, the shimming coil is designed by combining the target field point method with the current function method. That is to say, the relationship between magnetic field distribution and current density is determined by Biot-Savart law. After confining the coil radius and setting the constraint point, the current density distribution on the coil plane is inversely solved according to the target field distribution. Then the current density distribution is discretized by the current function, and the winding position distribution of the uniform field coil is obtained. According to the results of electromagnetic simulation, the first-order and second-order shimming coils are fabricated and applied to the magnetic resonance analyzer. The experimental results show that the shimming coils can effectively improve the magnetic field uniformity of the permanent magnet in nuclear magnetic resonance (NMR) system.
Effect of Ga droplet deposition rate on morphology of concentric quantum double rings
Authors: Li Zhi-Hong , Ding Zhao , Tang Jia-Wei , Wang Yi , Luo Zi-Jiang , Ma Ming-Ming , Huang Yan-Bin , Zhang Zhen-Dong , Guo Xiang ,   College of Big Data and Information Engineering, Guizhou University, Guiyang 550025, China,   School of Education Administrations, Guizhou University of Finance and Economics, Guiyang 550025, China,   Power Semiconductor Device Reliability Center of the Ministry of Education, Guiyang 550025, China,   Key Laboratory of Micro-Nano-Electronics and Software Technology of Guizhou Province, Guiyang 550025, China
Published: December 2020

For the fabrication of particular nanostructures, Stranski-Krastanov (SK) growth mode driven by strain is most widely used. Meanwhile, another technique that is used to form the complex nanostructures is the droplet epitaxy technique, which is based on the deposition of group III element nanoscale droplets onto substrate and followed by the reaction with group V element for crystallization into III-V compound nanostructures. Droplet epitaxy technique is simple and flexible, and it does not require additional complicated processing and has potential to develop various quantum nanostructures. It, unlike standard MBE growth, exploits the sequential supply of group-III and group-V elements to form quantum nanostructures. Quantum rings are a special class of quantum-confinement structure that can be fabricated by the droplet epitaxy technique and have attracted wide attention due to the Aharonov-Bohm effect, which is specific to the topology of a ring. In this paper, GaAs/GaAs (001) concentric quantum double rings (CQDRs) are prepared by droplet epitaxy technique at different Ga droplet deposition rates in monolayer per second (ML/S). The 2 μm × 2 μm atomic force microscope images are obtained to show the morphologies of CQDRs. We study the effects of Ga droplet deposition rates (0.09 ML/s, 0.154 ML/s, 0.25 ML/s, 0.43 ML/s) on CQDRs. The results show that with the increase of Ga droplet deposition rate, the density of CQDRs increases and the radius of inner ring and the radius of outer ring decrease. According to the nucleation theory, through the relationship between the maximum cluster density and the Ga droplet deposition rate, the critical number of atom nucleations is found to be 5, which suggests that the stable Ga atom crystal nucleus should contain at least 5 Ga atoms in the process of forming Ga droplet, and a nucleation state transformation diagram is drawn in order to obtain an insight into the process of forming Ga droplet according to the nucleation theory and fitting results. The research results could be instructive for preparing the GaAs concentric quantum double rings that the density can be controlled by droplet epitaxy.
Sensing performance of two-dimensional WTe2-based gas sensors
Authors: Ai Wen , Hu Xiao-Hui , Pan Lin , Chen Chang-Chun , Wang Yi-Feng , Shen Xiao-Dong ,   College of Materials Science and Engineering, Nanjing Tech University, Nanjing 211816, China,   Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing Tech University, Nanjing 211816, China
Published: December 2020

Since the discovery of graphene, graphene-based gas sensors have been widely studied, but the inherent zero band gap of graphene limits the response sensitivity of gas sensors. Transition metal dichalcogenides (TMDs) are ideal materials for designing nanoscaled highly-sensitive gas sensors due to their moderate band gaps, large surface-to-volume ratios and high carrier mobilities. Tungsten ditelluride (WTe2), as an important member of TMDs family, has outstanding advantages such as high specific surface area, excellent selectivity, and fast response. The WTe2 has quite a high carrier mobility and thus can provide a great response speed for gas sensor compared with graphene, which motivates us to further explore WTe2 as a promising sensing material. Recent studies have reported that monolayered and multilayered WTe2 films have been successfully synthesized, and the precise control of the number of atomic layers of monolayered WTe2 has been achieved. In this work, by density functional theory calculation, we examine the most stable adsorption configuration, adsorption energy, charge transfer, electrical and magnetic properties for each of the gas molecules (CO, CO2, NH3, NO and NO2) adsorbed on WTe2 monolayer. The results show that all the adsorptions of these gas molecules are physical adsorptions, and the adsorption energy of nitrogen-based gas is smaller than that of carbon-based gas, indicating that WTe2 is more sensitive to the adsorption of N-based gas molecules. The adsorption of NH3 behaves as a charge donor with electron obtained from WTe2 monolayer. The adsorption of CO, CO2, NO, and NO2 are charge acceptors, which accept charges from the WTe2 monolayer. Moreover, compared with the adsorption of CO, CO2 and NH3 gas molecules, the adsorption of NO and NO2 gas molecules introduce impurity states near the Fermi level, which are mainly contributed by the N p orbital and O p orbital. In addition, the adsorption of NO and NO2 induce magnetic moments of 0.99 μB and 0.80 μB, respectively. The results obtained in this work not only conduce to further understanding the charge transfer mechanism of gas molecules adsorbed on WTe2 monolayer, but also indicate the promising prospects of developing WTe2-based ultra-sensitivity gas sensing nanodevices.
Effect of anode magnetic shield on inner magnetic pole etched in anode layer Hall thruster
Authors: Zhao Jie , Tang De-Li , Xu Li , Li Ping-Chuan , Zhang Fan , Li Jian , Gui Bing-Yi ,   Southwestern Institute of Physics, Chengdu 610041, China,   Engineering and Technical College, Chengdu University of Technology, Leshan 614007, China
Published: December 2020

For anode layer Hall plasma thruster, the etching of inner magnetic pole is one of the key factors affecting its service life. In order to solve the problem of inner magnetic pole etching in anode layer Hall plasma thruster, the effect of anode magnetic shield on inner magnetic pole etched in anode layer Hall thruster is studied by combining particle simulation PIC with sputtering simulation. The magnetic shielding of anode changes the distribution of magnetic field configuration on the surface of the anode, and improves the magnetic mirror ratio of the magnetic mirror field of the thruster to the magnetic field width of the positive gradient on the central axis. The ratio of the magnetic mirror is 1.4 times that of the original one, and two additional saddle magnetic fields are added on both sides of the original saddle magnetic field region. It not only is conducive to confining electrons and improving the ionization rate of working gas, but also keeps a certain distance between the anode and the high temperature electron region, which provides the reliable reference data for the design of high power Hall plasma thruster. When the discharge voltage is 900 V and the working pressure is 2 × 10–2 Pa, the simulation results show that after the anode is shielded by the magnetic shield, the energy range of most of the incident ions on the inner magnetic pole is 40–260 eV, which is 100 eV lower than the energy range 40–360 eV in the case without shielding the anode. The probability distribution of particle energy without magnetically shielding the anode between 260 eV and 600 eV is obviously higher than that of ion energy with magnetically shielding the anode. The maximum probability distribution of cosine value of incident angle is extended from a small range near 0.1 (incident angle 84°) to a large range of 0.1–0.45 (incident angle 84°–63°). The magnetic shielding makes the incident ions disperse on the surface of the inner magnetic pole, which is helpful in reducing the etching of inner magnetic pole. The maximum etching rate of inner magnetic pole after the anode has been magnetically shielded is reduced from 16 × 10–10 m/s to 6.1 × 10–10 m/s, which is 2.62 times lower. The comparison of simulation results with experimental results in the case without magnetically shielding the anode shows that they are in good agreement.
First-principles investigation on elastic, electronic, and optical properties of Ti3O5
Authors: Fu Xian-Kai , Chen Wan-Qi , Jiang Zhong-Sheng , Yang Bo , Zhao Xiang , Zuo Liang ,   Key Laboratory for Anisotropy and Texture of Materials, Northeastern University, Shenyang 110819, China
Published: December 2020

Ti3O5 is a highly anticipated functional material due to its intriguing physical properties and multi-incentive phase transition process. This material undergoes a reversible first-order phase transition between λ phase and β phase, accompanied by drastic changes in the electronic and atomic structure. The amazing way of changing phase such as light, heat, pressure and electric current makes this material promise to be used in future optical information storage and heat storage. In this work, structural, elastic, electronic and optical properties of λ-Ti3O5 and β-Ti3O5 are calculated by using a first-principles approach, according to density functional theory (DFT). The LSDA, GGA-PBE, GGA-91, GGA-PS and GGA-RP are compared among them to obtain a suitable method of characterizing the crystal structure and electronic structure of λ-Ti3O5 and β-Ti3O5. The energy gap at the Fermi level of β-Ti3O5 can be obtained only when the extra Coulomb correlation U effect of Ti 3d electrons is considered. A complete set of elastic parameters for both phases are first reported. The calculated elastic constant satisfies the Born stability criterion, indicating that λ phase and β phase have good mechanical structural stability. The two phases are more resistant to volume changes than to shape changes and both behave as ductile materials. On the (010) plane, the elastic anisotropy of λ phase is weaker than that of β phase. Studies on the electronic structure show that the local charge of Ti3 is transferred to Ti2, resulting in the transformation of the semiconductor β phase to the metal λ phase. There are large differences in optical property such as absorption and reflectivity between these two structures, indicating that they can be applied to the field of optical storage materials. In this paper we also present a new insight into the photoinduced phase transition process of this material. The mechanism of photoinduced phase transition from λ-Ti3O5 to β-Ti3O5 is considered as stimulated emission effect. The results are of significance particularly for practically applying Ti3O5 and understanding its phase change mechanism.
Temperature-dependent properties of metastable graphene oxide
Authors: Mo Jia-Wei , Qiu Yin-Wei , Yi Ruo-Bing , Wu Jun , Wang Zhi-Kun , Zhao Li-Hua ,   School of Science, Zhejiang A&F University, Hangzhou 311300, China,   Shanghai Applied Radiation Institute, Shanghai University, Shanghai 200444, China
Published: December 2020

Monolayer of graphene oxide has great potential applications in ion and molecular screening, desalination and purification of water, gas separation, biosensing, proton conductors, lithium batteries, super capacitors and other fields, due to its excellent physical and chemical properties. However, the graphene oxide prepared by chemical and physical methods, such as the commonly used Hummers method is a metastable material. The transformation and regulation of the physical and chemical properties of the final morphology are essential, and systematic research is urgently needed. In this paper, the thermostat treatment method is used to control the metastable transformation of graphene oxide. The relationship of content, type, and morphology with temperature of oxygen-containing graphene oxide are detected by X-ray photoelectron absorption spectroscopy, Fourier infrared absorption spectroscopy, scanning electron microscope, etc.; and the effects of temperature on the stability of solution suspension stability, photon energy band and tensile strength of graphene oxide in the transformation process are analyzed by using Zeta potential, ultraviolet absorption spectrum, tensile force. The quantitative test results show that there exists a phenomenon in which the epoxy phase decreases, the hydroxyl group increases and the overall oxygen content decreases in the metastable transition process of graphene oxide, and the monolayer morphology of graphene oxide does not change significantly in this process. This structural transformation, however, greatly enhances the viscosity and hydrophilicity of the suspension, and remarkably reduces the energy band and considerably raises the tensile strength enhancement effect. When the transformation process is long enough, the hydrophilicity of the graphene oxide will decrease and precipitate. It is indicated that a further dehydration transition occurs between the hydroxyl groups. In addition, in the paper we also analyze the effect of constant temperature treatment time and concentration of suspension on this transformation process. The relevant research results are helpful in understanding the performance change of metastable graphene oxide suspension with temperature, and have certain reference value for the specific application of graphene oxide.