bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical investigation on the influence of gas-particle two-way coupling to the shock fluid in the two-dimensional Lagrangian framework
Authors: Chen Da-Wei  , Sun Hai-Quan  , Wang Pei  , Yu Xi-Jun  , Ma Dong-Jun  ,   National Key Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   Graduate School of China Academy of Engineering Physics, Beijing 100088, China
Published: December 2020

When an extreme shock wave releases from the free surface of the material, some high speed particulate matters will be ejected from the material body and enter into the background gas. This induced multiphase mixing phenomenon is known as the ejecta mixing. Ejecta mixing is one of the most important problems in the scope of inner explosive compression engineering, and it is also a frontier research subject of the impact dynamics, multiphase fluid dynamics, computational mathematics, etc. The properties of ejecta mixing have been investigated experimently and analytically for many years. However, the results of numerical simuliation are very rare. At present, the ejecta mixing study mainly focuses on the gas particle one-way coupling, that is, the interests of existing works are in the characteristics of the ejected particulate matter transport in the gas. In fact, after a large number of particles entering into the gas, the gas and the particles will interact with each other. So it is necessary to consider the feedback of particles to the gas. In this paper, the theoretical modeling of gas particle two-way coupling, the discrete algorithm of the mathematical model and the particle phase feedback effects on the gas shock wave propagation are investigated in the framework of Lagrangian coordinates. In order to obtain the details of ejecta movement, the particle trajectory model is chosen as the basic model, and then the governing equations including interactions between gas phase and particle phase are derived. For giving the specific calculation formula, the physical meanings of the coupled interaction source terms in the Lagrangian framework are analyzed and a stable numerical scheme is given based on the staggered strategy. We also devise two different computing models of ejecta mixing, the planar and the column configurations, and then the numerical simulations are carried out. The phenomenon of gas shock speed acceleration caused by particle feedback is found, and the distributions of the physical quantities, such as density, velocity, specific internal energy, pressure, in the gas area are changed. Especially for the convergent configuration, the feedback effects will be amplified further by the geometrical shrinkage, which may have a significant influence on the performance of the inner explosion compression, owing to the obvious uniformity variation of the gas flow field and the gas shock rebound in advance. The mathematical model, the numerical method and the new physical findings in this paper, will provide an important theoretical support for the in-depth understanding of the ejecta mixing and also for the solving of the corresponding engineering application problems.
Electrokinetic energy conversion efficiency in a polyelectrolyte-grafted nanotube
Authors: Liu Yong-Bo  , Jian Yong-Jun  ,   School of Mathematical Science, Inner Mongolia University, Hohhot 010021, China
Published: December 2020

Analytical investigations are performed for pressure driven flow of an electrically conducting, incompressible and viscous fluid in a polyelectrolyte-grafted nanotube by using Bessel functions. Nanofluidic tubes whose walls are covered by polyelectrolyte materials, named the fixed charge layer (FCL), are identified as soft nanotubes. The flow relies on an externally imposed pressure gradient and an induced reverse electroosmotic force produced by the streaming potential field which is spontaneously developed due to the ionic charge migration with the fluid flow. Many parametrical ranges are determined to ensure the validity of Debye-Hckel approximation. The analysis is based on the solutions of the linearized Poissson-Boltzmann equation and modified Navier-Stokes equation. To obtain the streaming potential, we use a numerical treatment to solve an integral equation governing the streaming potential. Finally, the electrokinetic energy conversion efficiency is studied. The result shows that both the streaming potential and energy conversion efficiency monotonically increase with the FCL thickness d increasing. However, they present a monotonic decrease trend with the increase of K, which is the ratio of the characteristic scale of the mobile charges to the fixed charge within the FCL. We compare the results in a soft nanotube with those in a rigid one, whose zeta potential is equal to the electrostatic potential at the solid-polyelectrolyte interface of the soft nanotube. We find that the electric potential in a soft nanotube is higher than that in the corresponding rigid nanotube, which results in a larger streaming potential in the soft nanotue. Moreover, for the parameter ranges considered in this work, our results show that the electrokinetic energy conversion efficiency in a soft nanotube is 1.5-3 times higher than that in a rigid nanotube. These findings are important for investigating the streaming potential and electrokinetic energy conversion efficiency in soft nanotubes. They can be used as a kind of new method to enhance the energy conversion efficiency of the electrokinetic transport in nanotube.
Plasma recoil induced by laser radiated solid target
Authors: Zhou Lei  , Li Xiao-Ya  , Zhu Wen-Jun  , Wang Jia-Xiang  , Tang Chang-Jian  ,   Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064, China;,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China;,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
Published: December 2020

Based on the theory of conservation of momentum, a theoretical method of calculating the shock pressure induced by laser loading via diagnosing plasma recoil momentum is presented. When a high-power laser irradiates a solid target surface, the plasma jet with high velocity induced by laser has a recoil effect on the target. Then the plasma recoil momentum induced by laser irradiating solid target can be calculated by the distribution of electron plasma. At the same time, the subcritical electron plasma density could be measured by interferometry and the supercritical plasma density could be fitted into exponential function form. So the variation of shock wave pressure could be calculated via diagnosing plasma recoil momentum. This method does not consider the relationship between D and u, nor uses the window material nor needs the steady shock propagation. It is a useful method of studying the material property under high strain rate and isentropic compression. Numerical simulation results using one-dimensional radiation hydro code called MULTI for laser intensities ranging from 51012 W/cm2 to 51013 W/cm2 are presented. The electron temperature is nearly equal to the ion temperature for the laser pulse duration 2 ns but much greater than the ion temperature for = 1 ns. This means for that ns pulse duration, the difference between electron and ion temperature could be ignored in general. And in order to fit the shock pressure value more exactly, the density of ablation surface nabl = n0exp(-1) is used in the simulations. The simulation results indicate that the value of calculating shock pressure obtained via diagnosing plasma recoil momentum is similar to the shock pressure calculated by MULTI simulation for ns pulse duration. And the value of calculating shock pressure is also similar to the experimental value for pulse duration = 5 ns. From the simulation results, it is obvious that the method of calculating the shock pressure via diagnosing plasma recoil momentum is effective and feasible.
Single spin channels in Ni-doped CoTiSb semiconductor
Authors: Chang Yue-Hua  , Pan Ru-Jing  , Si Yu-Hao  , Lin Ting-Ting  , Wu Zhi-Min  , Liu Guo-Dong  , Cui Yu-Ting  ,   School of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 400044, China;,   School of Material Sciences and Engineering, Hebei University Technology, Tianjin 300130, China
Published: December 2020

Since the spin-transfer effect was predicted in 1996, the direct-current-switched magnetic storage has received much attention. A slender nanopillar with high spin-polarized ratio of the conductive electrons is the most favorable for realizing the direct-current-switched magnetic memory. Wang et al. (Sup. Mic. 2015 86 493) showed a supercell idea used to design the nanopillar array in a semiconductor matrix. Based on this idea, in this paper, the Ni-based single atomic chains are designed in the semiconductive CoTiSb matrix by continuously substituting Ni for Ti, Sb, or Ti-Sb in the [001] crystallographic direction. These single atomic chains are uniformly distributed in the matrix. We investigate the electronic structures and magnetic properties of CoTiSb supercells with the Ni-based single atomic chains by using the first-principle calculations. The calculation results show that the single atomic chains of Ni-Sb (achieved by substituting Ni for Ti) have a high spin polarization and hole conduction properties. The single atomic chain of Ni-Ti (achieved by substituting Ni for Sb) and Ni-Ni single atomic chain (achieved by substituting Ni for Ti and Sb) both have a 100% spin polarization ration at the Fermi level. The Ni-based single atomic chain has an effect on the electronic structures of other atoms surrounding it in about a lattice length and forms a nanopillar with the center of the Ni-based single atomic chain. We predict that CoTiSb matrixes with the Ni-Ti and Ni-Ni single atomic chains will be good candidates for the direct-current-switched magnetic storage.
Study of on-the-fly Doppler broadening in JMCT program
Authors: Liu Xiong-Guo  , Deng Li  , Hu Ze-Hua  , Li Rui  , Fu Yuan-Guang  , Li Gang  , Wang Jia  ,   Graduate School of China Academy of Engineering Physics, Beijing 100088, China;,   Institute of Applied Physics and Computed Mathematics (IAPCM), Beijing 100088, China;,   CAEP Software Center for High Performance Numerical Simulation, Beijing 100088, China
Published: December 2020

In this paper, we introduce the on-the-fly (OTF) Doppler method which is used to calculate the temperature-dependent cross section. After substituting Adler-Adler multilevel representation into Doppler formulation, the theoretical formulation of temperature dependent cross section is obtained. This theoretical formulation can be approximated by a Taylor series expansion and asymptotic series expansion, which is the base of OTF method. The OTF method can be used to calculate the cross section of any nuclide at any temperature in a range of 300-3000 K based on cross section library of 300 K. For the OTF method, firstly, a series of temperature dependent cross section libraries is produced by NJOY. Secondly, a uniform energy grid is evaluated by the temperature dependent cross section libraries. Thirdly, a polynomial is used to fit the temperature dependent cross section on each energy grid. The coefficient of the polynomial is obtained by single value decomposition algorithm. Finally, the coefficients of the polynomial in all energy grids and the energy grids themselves are written in a text file. To test the cross section polynomial produced by OTF method, we compare the total and absorption cross sections of 238U and 235U calculated by the polynomial with those produced by NJOY. The errors of these cross sections obtained by these two programs are presented in the paper.
The text file produced by OTF method can be read by the Monte Carlo code JMCT, which is a coupled neutron/photon transport code developed by IAPCM. After providing the temperature and energy of the particle, the temperature dependent cross sections in two adjacent energy grids are calculated by the polynomial respectively. The cross section of target energy is obtained by linear interpolation. Two benchmarks including a pin-cell model and an assembly model are used to verify the applications of OTF method in JMCT. The results are presented in the paper.
Design and analysis of a new type of wideband low-loss and small size left-handed materials
Authors: He Zheng-Rui  , Geng You-Lin  ,   Institute of Antenna and Microwaves, Hangzhou Dianzi University, Hangzhou 310018, China
Published: December 2020

A single-side and one-dimensional left handed-material on the basis of periodic Ⅱ structure is designed in this paper. The Ⅱ structure of left-handed material is very simple and has some advantages, such as large bandwidth, small size and low loss. The results of simulation with the software HFSS show that for this structure in a frequency range from 8.79 GHz to 15.75 GHz, the real part and imaginary part of refraction index are less than 0 and approximately 0 respectively, and the real part of wave impedance is greater than 0, the largest loss per unit is 0.27 dB, and the relative bandwidth is 55.78%, showing that this Ⅱ periodic structure has the negative character. Based on the simulation results, this periodic Ⅱ structure is fabricated and measured with the vector network analyzer and wave guide method. The measurements are in agreement with the simulations. All these results prove that this left-handed material has some better characters than traditional meta-materials.
A novel radial beam smoothing scheme based on optical Kerr effect
Authors: Zhong Zhe-Qiang  , Hou Peng-Cheng  , Zhang Bin  ,   School of Electronics and Information Engineering, Sichuan University, Chengdu 610065, China
Published: December 2020

Laser-beam illumination uniformity is a key issue in inertial confinement fusion facilities. In order to fulfill the requirement of improving illumination uniformity, a radial smoothing (RS) scheme is proposed. For smoothing the focal-spot pattern on a short time scale compared with the hydrodynamic response time of the target, the optical Kerr effect with extremely response time is taken into consideration. The basic principle of RS based on optical Kerr effect is that by using the interaction between optical Kerr medium and periodic Gaussian pulses to modulate a periodic spherical phase, to modulate periodic sphericel phase added at the wavefront of laser transmission wave, change the focal-spot size of the laser beam in far field, and further induce the fast radial redistribution of the speckles inside the focal spot in far field, and further induce the fast radial redistribution of the speckles inside the focal spot in far field. This fast radial redistribution of the speckles smoothes the intensity modulation of the focal spot on the target and eventually achieves the beam smoothing in the radial direction. The application of RS in the beamline is detailed. The optical Kerr medium is inserted in the front-end of the bemline, before the laser beam is injected into the main amplifier. The periodic Gaussian pulse for pumping the optical Kerr medium is obtained by the pulse stacking system based on fibers. The pulse width of stacked Gaussian pulse and the time delay between Gaussian pulses are set to be on a picosecond time scale or subpicosecond time scale. The induced refractive index of the optical Kerr medium by the pump laser fits spherical distribution with periodic variation, and results in the radial distribution of the speckles in focal plane. By establishing the theoretical model of the radial beam smoothing scheme implemented with continuous phase plate (CPP), the focusing characteristics of laser beam with RS and CPP are discussed in detail. The influences of the selection of optical Kerr medium and the characteristics of the radial redistribution on the radial smoothing effect are simulated and analyzed. Results indicate that the RS based on optical Kerr effect could efficiently achieve the periodic radial redistribution of the speckles on focal plane, and therefore improves the illumination uniformity in the radial direction while eliminating the stripe pattern presented in far field by one-dimensional smoothing spectral dispersion (SSD). The smoothing performance of RS is different from that of the conventional SSD due to its radial smoothing direction. Moreover, the combined application of RS with continuous phase plate could achieve a better smoothing level with a shorter time. The utilization of radial smoothing scheme in high power laser system may significantly improve the laser-beam irradiation with little influence on the performance of the beamline.
Bending and splitting of self-collimated beams in high symmetry sonic crystal
Authors: Song Zong-Gen  , Deng Ke  , He Zhao-Jian  , Zhao He-Ping  ,   College of Physics and Mechanical & Electrical Engineering, Jishou University, Jishou 416000, China
Published: December 2020

Self-collimation, a peculiar effect that allows acoustic signals to propagate in sonic crystals (SCs) along a definite direction with almost no diffraction, possesses a promising prospect in integrated acoustics as it provides an effective way to transmit acoustic signals between on-chip functionalities. There exists, however, the intrinsic inability of self-collimation to efficiently bend and split acoustic signals. Most of existing schemes for bending and splitting of self-collimated acoustic beams are based on SC of square lattice, thus their bending and splitting angles are restricted to 90. In this paper, the finite element method is used to investigate self-collimation of acoustic beams in an SC of hexagonal lattice. It is shown that 60 and 120 bending of self-collimated acoustic waves can be simultaneously realized by simply truncating the two-dimensional hexagonal SC. Bended imaging for a point source with a subwavelength resolution of 0.38 0 can also be realized by truncating the SC structure. In addition, a scheme for 60 and 120 splitting of self-collimated acoustic waves is also proposed by introducing line-defects into the hexagonal SC. It is demonstrated that an incoming self-collimated beam can be split into a 60 (or 120 bended one and a transmitted one, with the power ratio adjusted by the value of defect size. We believe that this hexagonal-SC-based bending and splitting mechanism will offer more flexibilities to the beam control in the design of acoustic devices and will be useful in integrated acoustic applications.
Dynamical analysis of Duffing oscillator with fractional-order feedback with time delay
Authors: Wen Shao-Fang  , Shen Yong-Jun  , Yang Shao-Pu  ,   Transportation Institute, Shijiazhuang Tiedao University, Shijiazhuang 050043, China;,   Department of Mechanical Engineering, Shijiazhuang Tiedao University, Shijiazhuang 050043, China
Published: December 2020

With increasingly strict requirements for control speed and system performance, the unavoidable time delay becomes a serious problem. Fractional-order feedback is constantly adopted in control engineering due to its advantages, such as robustness, strong de-noising ability and better control performance. In this paper, the dynamical characteristics of an autonomous Duffing oscillator under fractional-order feedback coupling with time delay are investigated. At first, the first-order approximate analytical solution is obtained by the averaging method. The equivalent stiffness and equivalent damping coefficients are defined by the feedback coefficient, fractional order and time delay. It is found that the fractional-order feedback coupling with time delay has the functions of both delayed velocity feedback and delayed displacement feedback simultaneously. Then, the comparison between the analytical solution and the numerical one verifies the correctness and satisfactory precision of the approximately analytical solution under three parameter conditions respectively. The effects of the feedback coefficient, fractional order and nonlinear stiffness coefficient on the complex dynamical behaviors are analyzed, including the locations of bifurcation points, the stabilities of the periodic solutions, the existence ranges of the periodic solutions, the stability of zero solution and the stability switch times. It is found that the increase of fractional order could make the delay-amplitude curves of periodic solutions shift rightwards, but the stabilities of the periodic solutions and the stability switch times of zero solution cannot be changed. The decrease of the feedback coefficient makes the amplitudes and ranges of the periodic solutions become larger, and induces the stability switch times of zero solution to decrease, but the stabilities of the periodic solutions keep unchanged. The sign of the nonlinear stiffness coefficient determines the stabilities and the bending directions of delay-amplitude curves of periodic solutions, but the bifurcation points, the stability of zero solution and the stability switch times are not changed. It could be concluded that the primary system parameters have important influences on the dynamical behavior of Duffing oscillator, and the results are very helpful to design, analyze or control this kind of system. The analysis procedure and conclusions could provide a reference for the study on the similar fractional-order dynamic systems with time delays.
Unsteady oscillation distribution model of liquid jet in supersonic crossflows
Authors: Wu Li-Yin  , Wang Zhen-Guo  , Li Qing-Lian  , Li Chun  ,   Science and Technology on Scramjet Laboratory, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Unsteady distribution of spray is experimentally studied when a round liquid jet is injected into a supersonic crossflow vertically. An oscillation distribution model for the liquid column and spray is established. Tyndall scattering caused by the sol medium is put forward to eliminate the interference effect of monochromatic laser passing through the supersonic gas flow field. The scattering causes the disordering of laser propagation direction and phase, thus makes the planar light source uniform and eliminate the interference effect of laser at the same time. Then a uniform light source is formed and can be set as the uniform background with a pulse width of 7 ns. The camera, with dimension of CCD pixel space of 40002672 pixel, is located directly in front of planar light source, and the shooting area is between both. The frozen liquid jet/spray images with high spatiotemporal resolution are captured using the pulsed laser background imaging (PLBI) method in supersonic crossflows. And the drag phenomenon caused by the too-long exposure time in the ordinary and traditional high-speed imaging process is avoided. Based on the maximizing inter-class variance method (Otsu) and Canny method, the out boundary of liquid jet/spray are extracted from an instantaneous image. A dimensionless parameter named intermittency factor (the logogram is r) is defined and used to quantitatively analyze the oscillation distribution characteristics of jet/spray. The intermittency factor of the whole spray field could be calculated by sample probability statistic method. An empirical jet/spray oscillation distribution model, in supersonic crossflows, is summarized based on parameter studies. Various conditions are studied, including stagnation pressure range of gas (642 kPa to 1010 kPa), practical pressure range (0.36 MPa to 4.61 MPa), nozzle diameters (0.48 mm/1.0 mm/1.25 mm/1.52 mm), distances down from nozzle (10 mm to 125 mm), and jet-gas momentum flux ratio range (0.11 to 7.49). The empirical model is used to predict the oscillation distribution of water jet penetrated in a Ma2.1 supersonic crossflow. It is indicated that the predictive result matches well with the experimental result. It could be concluded that the PLBI method presented in this paper reasonably utilizes the high energy and short pulse characteristics of the laser to successfully complete the frozen image of liquid jet/spray under the condition of supersonic crossflow. The dimensionless parameter r defined in the study can be used to quantitatively analyze the oscillation distribution characteristics of jet/spray well. This study has important significance for understanding the diffusion characteristics of liquid jet in supersonic crossflows.
Deposition and thermal conductivity of diamond-like carbon film on a silicon substrate
Authors: Ai Li-Qiang  , Zhang Xiang-Xiong  , Chen Min  , Xiong Da-Xi  ,   Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China;,   Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Science, Jiangsu Key Laboratory of Medical Optics, Suzhou 215163, China
Published: December 2020

Diamond-Like Carbon (DLC) is thought to be a potential material in solving heat dissipation problems in light emitting diode module packages. It is of vital importance in evaluating the thermal conductivity of DLC film deposited on a silicon substrate.
In this paper, the molecular dynamics method is used to simulate the formation of a DLC film by the deposition of carbon atoms on a isilicon substrate. Tersoff potential is adopted to reproduce the structures and densities of silicon, carbon, and SiC. A silicon substrate consisting of 544 atoms is located at the bottom of the simulation domain. The substrate is kept at a temperature of 600 K through a Noose-Hover thermostat. Carbon atoms are injected into the substrate individually every 0.5 ps at an energy of 1 eV. After a 7.5 ns deposition process, a 4 nm amorphous film containing 15000 carbon atoms is formed. Injected carbon atoms and substrate silicon atoms are intermixed at the bottom layer of the deposited film while the rest of the film contains only carbon atoms. The density of the film decreases slightly with the increase of the height of the deposited film and the average density is 2.8 g/cm3. Analysis of the coordination number shows that the sp3 fraction of carbon atoms in the film also decreases with the increase of the height of the deposited film, with a maximum value of 22%. It might be caused by the continuous impacts of the subsequently injected carbon atoms on the previously formed DLC film.
The thermal conductivities of the DLC film in the planar and normal directions are calculated by the Green-Kubo method. The thermal conductivity of pure diamond film is also calculated for comparison. The results show that the planar thermal conductivity of the deposited DLC film is approximately half of that of the pure diamond film with the same size. It is higher than the normal thermal conductivity of the deposited film. The thermal conductivities of the DLC film in both planar and normal directions increase with the increase of film density and sp3 fraction in the DLC film. The results indicate that the local tetrahedral structure of sp3 carbon atoms contributes to the improvement of thermal conductivity in the DLC film.
Mechanisms on the GeH/ interactions in germanene/germanane bilayer for tuning band structures
Authors: Wu Hong  , Li Feng  ,   College of Science, Nanjing University of Posts and Telecommunications, Nanjing 210046, China;,   College of Chemistry and Materials Science, Jiangsu Key Laboratory of Biofunctional Materials, Nanjing Normal University, Nanjing 210046, China
Published: December 2020

Germanene, one of the most important two-dimensional materials after graphene and silicone have been discovered, is attracting wide attentions due to its many excellent physical properties. Since a suitable band gap is needed for the electronics and optoelectronics, the lack of a band gap has essentially restricted the practical applications of germanene in macroelectronics. In this article, density functional theory calculations with van de Waals corrections is utilized to study the geometric and electronic properties of germanene (Ge), germanane (GeH) and germanene/germanane (Ge/GeH) bilayer. The band gaps for Ge and GeH are zero and 1.16 eV, respectively. For the Ge/GeH bilayer, a considerable binding energy of 273 meV/unit cell is obtained between Ge and GeH layers. This value is smaller than that of Ge bilayer (402 meV/unit cell), but larger than that of GeH bilayer (211 meV/unit cell), indicating a considerable GeH/ bonding. This means that Ge and GeH layers could be combined steadily by the interlayer weak interactions. Meanwhile, a band gap of 85 meV is opened, which is contributed to the breaking of the equivalence of the two sublattices in the Ge sheet, yielding a nonzero band gap at the K point. Charge density difference indicates that the electrons on the s orbital of H transfer to the Ge_p orbital, enhancing the interlayer interactions. It should be noted here that the van de Waals corrections are pretty important for the geometric and electronic properties of the Ge/GeH bilayer. Without the van de Waals corrections, the binding energy of the Ge/GeH bilayer is reduced from 273 meV/unit cell to only 187 meV/unit cell, severely underestimated the strength of the weak forces between Ge and GeH layers, resulting in a much smaller band gap of 50 meV. Interestingly, no band gap is obtained for the sandwich structure GeH/Ge/GeH, in which the equivalence of two sublattices in germanene is kept. Finally, all the results are confirmed by the high accurate hybrid functional calculations. At the Heyd-Scuseria-Ernzerhof level, the band gap of Ge/GeH bilayer is 117 meV, slightly larger than 85 meV at the Perder-Burke-Ernzerhof level. Our work would promote utilizing germanene in microelectronics and call for more efforts in using weak interactions for band structure engineering.
Rashba spin splitting in the Al0.6Ga0.4N/GaN/Al0.3Ga0.7N/Al0.6Ga0.4N quantum well
Authors: Zhao Zheng-Yin  , Wang Hong-Ling  , Li Ming  ,   College of Electrical and Information Engineering, Xuchang University, Xuchang 461000, China
Published: December 2020

As is well known, the structure inversion asymmetry (SIA) and Rashba spin splitting of semiconductor heterostructure can be modulated by either electric field or engineering asymmetric heterostructure. In this paper, we calculate the Rashba coefficient and Rashba spin splitting for the first subband of Al0.6Ga0.4N/GaN/Al0.3Ga0.7N/Al0.6Ga0.4N QW each as a function of thickness (ws) of the inserted Al0.3Ga0.7N layer (right well) and external electric field. The thickness of GaN layer (left well) is 40-ws . With ws increasing, the Rashba coefficient and Rashba spin splitting for the first subband increase first, because the polarized electric field in the well region increases and the electrons shift towards the left heterointerfaces, and then decrease when ws20 since the electric field in the well region decreases, and the confined energy increases as effective well thickness decreases. But when ws30 , the Rashba spin splitting decreases more rapidly, since kF decreases rapidly. Contributions to the Rashba coefficient from the well is largest, lesser is the contribution from the interface, which varies slowly with ws, and the contribution from the barrier is relatively small. Then we assume ws=20 , and find that the external electric field can modulate the Rashba coefficient and Rashba spin splitting greatly because the contribution to the Rashba coefficient from the well changes rapidly with the external electric field, and the external electric field brings about additional potential and affects the spatial distribution of electrons, confined energy and Fermi level. When the direction of the external electric field is the same as (contrary to) the polarization electric field, the Rashba coefficient and Rashba spin splitting increase (decrease) with external electric field increasing. With the external electric field changing from -1.5108 V m-1 to 1.5108 V m-1, the Rashba coefficient approximately varies linearly, and the Rashba spin splitting first increases rapidly, then approximately increases linearly, and finally increases slowly. Because the value of kF increases rapidly first, then increases slowly. Results show that the Rashba coefficient and the Rashba spin splitting in the Al0.6Ga0.4N/GaN/Al0.3Ga0.7N/Al0.6Ga0.4N QW can be modulated by changing the relative thickness of GaN and Al0.3Ga0.7N layers and the external electric field, thereby giving guidance for designing the spintronic devices.
Room temperature gas sensing property and sensing mechanism of Sn-doped ZnO thin film
Authors: Xing Lan-Jun  , Chang Yong-Qin  , Shao Chang-Jing  , Wang Lin  , Long Yi  ,   School of Materials Science and Engineering, University of Science and Technology of Beijing, Beijing 100083, China
Published: December 2020

Sn-doped ZnO and pure ZnO thin films are deposited on glass substrates with prepared electrode by the chemical vapor deposition method. The gas sensing performances of Sn-doped ZnO and pure ZnO thin films are investigated by our home-made system at room temperature, and the gas sensing test results reveal that Sn-doped ZnO thin film exhibits high gas response to ethanol and acetone, while no response is detected for pure ZnO to ethanol or acetone at room temperature. Sn-doped ZnO thin film also has high selectivity that the response to ethanol is higher than that to acetone in the same measurement conditions, and the response of Sn-doped ZnO thin film sample to ethanol is almost the third largest when the concentration is 320 ppm. The typical scanning electron microscopy images reveal that these two samples are tetrapod-shaped ZnO whiskers with diameters in a range of about 150-400 nm. X-ray diffraction results indicate that all the samples are of wurtzite structure. Neither trace of Sn, nor that of Sn alloy nor that of Sn oxide is detected in the Sn-doped ZnO film, while its diffraction peak shifts towards the left compared with that of pure ZnO sample, which suggests that Sn atoms exist in the form of interstitial atoms in the ZnO crystal. The energy dispersive spectrum shows that the Sn-doped ZnO thin film is composed of Zn and O elements, and no Sn signal is defected. Photoluminescence spectra reveal that both Sn-doped ZnO and pure ZnO films have ultraviolet light emission peaks and green emission peaks, while the intensities of the defect emissions are significantly enhanced by doping of Sn. In addition, no gas response to ethanol is detected after Sn-doped ZnO thin film has been annealed in the air, which indicates that the room temperature gas sensitivity of the Sn-doped ZnO thin film may be related to its high defect concentration. The working mechanism of Sn-doped ZnO thin film is explained by a free electron random scattering model. As is well known, ZnO semiconductor gas-sensor is of surface-controlled type. In this work, upon exposure to ethanol vapor, the physical absorbed ethanol molecules acting as scattering centers can reduce the mean free path of the electrons in the surface of the film, changing the mean free time n, which would increase the resistance of Sn-doped ZnO thin film at room temperature. This work provides a simple method of fabricating the highly sensitive ethanol gas sensor operating at room temperature, which has great potential applications in gas sensor field.
Effect of continuously graded functional layer on curvature and residual stress of solid oxide fuel cell in initial reduction process
Authors: Lu Yong-Jun  , Yang Yi  , Wang Feng-Hui  , Lou Kang  , Zhao Xiang  ,   Department of Engineering Mechanics, Northwestern Polytechnical University, Xi'an 710129, China
Published: December 2020

Solid oxide fuel cell (SOFC) is considered to be a highly efficient device to convert chemical fuels directly into electrical power. Because of multilayer composite arrangement of cells, mismatch of the thermal expansion coefficients, chemical/thermal gradient, or phase change of the materials will result in residual stresses, which are reflected in the pronounced bending of unconstrained cells and cause a reliable problem. Considerable efforts have been devoted to the analysis of residual stresses in an elastic multilayer system, and one of the efforts that are to improve not only electrochemical performance for high energy conversion efficiency but also long term stability, is to process a continuously gradient anode functional layer (CG-AFL) between dense electrolyte and porous anode. Hence to understand the stress distribution and deformation of the multilayer with a CG-AFL is needed for the cell design. As the chemical reduction takes place at the interface between NiO-YSZ and the previously reduced porous Ni-YSZ, a reduced layer, together with the unreduced layer and the electrolyte will cause the residual stresses to be re-distributed. In this paper, taking the CG-AFL into account, the curvature and residual stresses of half-cell during reduction are analyzed. The results show that the curvature of half-cell with a CG-AFL increases as the reduction process. And the curvature would also increase as the thickness of the CG-AFL increases, and decrease with the increase of the index of power function that expresses young's modulus and thermal expansion coefficient of gradient layer. The residual stresses among the layers are correspondingly influenced by the thickness of the gradient layer, the index of power function and reduction extent. When taking power function as a linear function, the gradient layer obviously reduces the residual stress in the electrolyte. However, the increase of the index in power function will cause the increase of electrolyte residual stress. These mentioned analyses reveal that the CG-AFL cannot offer a solution that simultaneously improves the residual stress and curvature in a half-cell in terms of thickness and profile exponent of CG-AFL, i.e., the mitigation of residual stress will give rise to the increase of curvature, and vice versa. On the other hand, for part-reduced half-cell, the maximum tensile stress is found at anode/gradient layer interface in anode layer, which may facilitate structural failure since tensile residual stress is so high that it reaches the fracture strength of anode material. Consequently, it is important to ensure that the anode is fully reduced in practice. In conclusion, the existing gradient layer is helpful for enhancing the cell reliability via suitable design.
Optimization design of a Gamma-to-electron spectrometer for high energy gammas induced by fusion
Authors: Jia Qing-Gang  , Zhang Tian-Kui  , Xu Hai-Bo  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   Science and Technology on Plasma Physics Laboratory, Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Apart from neutrons, the fusion core produces gamma rays during fusion reaction. The spectrum of gamma ray can provide very important information for fusion diagnosis. However, due to the gamma energy and yield in one fusion pulse being both lower, the gamma spectrometer used should have high detection efficiency and energy resolution. The concept of a Gamma-to-electron magnetic spectrometer(GEMS) provides the idea to build up such a spectrometer to meet this requirement. Based on this concept design, four important parts of this facility are investigated. The first part is the gamma-electron converter. The main physics processes include Compton scattering of gamma ray with converter material generating electron, the electron multiple Coulomb scattering(MCS) inside the converter and the electron attenuation. Affected by the thickness of convector, these processes give a complex influence on the detection efficiency and angular-energy distribution of the electrons which are emitted from the downstream face of the convector. The Monte Carlo code Geant4 is employed to investigate theeffects of Compton scattering, MCS and converter thick on the angular-energy distribution. The second one is the collimation. The collimation is used to select the forward direction, the performances of cutoff angle of the collimator on the detection efficiency and resolutions, the correlation between electron transportation direction and energy, are also studied using Geant4 code. The third part is the dipole magnetic field. There are several geometric and magnetic parameters, therefore, a multi-thread parallelized genetic algorithm is developed to obtain the best result. Both the irregular geometric shape and dipole magnetic field strength are optimized to achieve the best energy resolution and detection efficiency. The obtained magnetic field has an intensity of less than 100 Gauss, and its performance on gathering elections is also verified by Geant4 code. The last one is the location of electron detectors. The study shows that all the electron detectors should be located not in a straight line but a quadratic curve. Then the optimized spectrometer is simulated by Geant4 to obtain the responses of gamma rays with various energies. For the gammas provided by fusion reaction, the simulation shows that when the neutron yields are about 2.5×1015 and 1.2×1016, the energy resolutions reach 0.5 MeV and 0.25 MeV, respectively, provided that different thick Be converters are employed. All in all, this optimized GEMS can be employed to measure the spectrum of gamma rays generated fom the fusion reaction.
Uncertainty quantification in the calculation of keff using sensitity and stochastic sampling method
Authors: Hu Ze-Hua  , Ye Tao  , Liu Xiong-Guo  , Wang Jia  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   Software Center for High Performance Numerical Simulation, China Academy of Engineering Physics, Beijing 100088, China
Published: December 2020

The sensitivity and uncertainty analysis(S/U) method based on the first order perturbation theory is commonly employed to calculate the uncertainties in-nuclear reactor's integral parameters, such as the neutron effective multiplication factor(keff), due to uncertainties in nuclear data. However, this method is only theoretically suitable for the linear model because of its first order approximation. Moreover, S/U method is difficult to incorporate into a neutronics code, because the adjoint angular flux is needed to obtain the sensitivity coefficient of an integral parameter to nuclear data. Meanwhile, the sampling approach based on parametric random sampling of input parameters, an easy implemented method, evaluates the uncertainties in the integral parameters by performing a set of neutronics simulations inputted with a set of stochastic nuclear data sampled from a multinomial normal distribution with nuclear cross section mean values and covariance data. The sampling approach is considered as a more exact method, as linear approximation is not needed. With the increase of computational power, the sampling methods with consuming more time are now possible. The sampling approach is incorporated into SURE, a sensitivity and uncertainty analysis code developed in IAPCM, as a functional module. A careful verification of the new function is necessary before it is used to analyze complicated problems, such as multi-physical coupling calculations of nuclear reactor. Two simple fast criticality benchmark experiments, namely Godiva(HEU-MET-FAST-001) and Jezebel(PU-MET-FAST-001), are selected to verify the sampling module of SURE. The uncertainties in nuclear data are given by multigroup covariance matrices processed from ENDF/B-VⅡ. 1 data. The uncertainties in the computed value of keff resulting from uncertainties in the nuclear data are calculated with both S/U and sampling methods. The uncertainties due to reaction cross sections for each nuclide in two benchmarks given by two methods with the multigroup covariance matrices are in good agreement. Since the S/U module of SURE code is verified extensively, the correctness of the sampling function of the code is confirmed as well. The distribution of the keff from the sampling approach obeys the normal distribution pretty well, which indicates that keff varies linearly with the nuclear data under its uncertainty range, since the nuclear data used in calculations are assumed to be normal distribution in the sampling method. The results from the sampling method also support the S/U method with linear approximation as a suitable uncertainty quantification method for keff calculation.
Moving target compressive imaging based on improved row scanning measurement matrix
Authors: Wang Pan-Pan  , Yao Xu-Ri  , Liu Xue-Feng  , Yu Wen-Kai  , Qiu Peng  , Zhai Guang-Jie  ,   Key Laboratory of Electronics and Information Technology for Space Systems, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100190, China;,   Center for Quantum Technology Research, School of Physics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

Moving target imaging(MTI) plays an important role in practical applications. How to capture dynamic images of the targets with high qualities has become a hot point of research in the field of MTI. In order to improve the reconstruction quality, a new MTI model based on compressed sensing(CS) is proposed here, by using a sampling protocol of the row-scanning together with a motion measurement matrix constructed by us. It is proved by the simulation and the experimental results that a relatively high quality can be achieved through this approach. Furthermore, an evaluation criterion of reconstructed image is introduced to analyze the relationship between the imaging quality and the moving speed of the target. By contrast, the performance of our algorithm is much better than that of traditional CS algorithm under the same moving speed condition. As a result, it is suggested that our imaging method may have a great application prospect in the earth observation of unmanned aerial vehicles, video monitoring in the product line and other fields.