bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on the electronic structures and the optical absorption mechanism of In2O3 crystals
Authors: Liu Jian  , Liu Ting-Yu  , Li Hai-Xin  , Liu Feng-Ming  ,   College of Science, University of Shanghai for Science and Technology, Shanghai 200093, China
Published: December 2020

Indium oxide with its wide gap is a multifunctional semiconductor material, which has gained application in many areas. Indium oxide films show high electrical property and high transparency, which have been applied in OLED display, flat-panel display, thin film solar cells, etc. However, the mechanisms of both high electrical and high transparent properties are still not clear up to now. So in this paper, the electronic structures of the In2O3 crystals are studied by GGA, GGA+U, HSE06 and G0W0 corrections. The mechanisms of optical transition and formation of transparent electrode in In2O3 crystals are studied using Hedin's G0W0 approximation and the Bethe-Salpeter equation. The complex refractive index, complex dielectric function and optical absorption spectrum of the In2O3 crystal have been obtained, which are in good agreement with experimental results. By analyzing the quasi-particle band structures, optical transition matrix and optical absorption spectrum, the mechanisms of optical transition and formation of transparent electrode in In2O3 can be interpreted. BSE (Bethe-Salpeter equation) calculation results show that the transition from 8 to 1 is permitted, however, the transition probability is far less than that from 10 to 1. This is because, for 8 to 1 transition, there are three even symmetry bands and two odd symmetry bands, in which only the transition from two odd symmetry bands to the conduction band is permitted. Other causes for this phenomenon are that in the In2O3 primitive cell there exist some overlapping bands, which result in the false transition. Therefore, this work argues that in the In2O3 crystals optical band gap is 4.167 eV, which corresponds to the direct transition from 10 to 1. This result will help understand the mechanisms of optical transition and the transparent electrode in In2O3.
High-order harmonics and attosecond pulse generation of a He+ ion by a chirped two-color inhomogeneous laser field
Authors: Luo Xiang-Yi  , Ben Shuai  , Ge Xin-Lei  , Wang Qun  , Guo Jing  , Liu Xue-Shen  ,   Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China;,   College of Physics, Baicheng Normal University, Baicheng 137000, China
Published: December 2020

We theoretically study high-order harmonics generation (HHG) and isolated attosecond pulse (IAP) generation in a spatially inhomogeneous chirped two-color (5 fs/800 nm and 12 fs/1600 nm) laser field by solving numerically the time-dependent Schrdinger equation(TDSE) for a one-dimensional (1D) model of He+ ion by the splitting-operator fast-Fourier transform technique. Results show that the inhomogeneity of the laser field plays an important role in the HHG process. The harmonic spectra exhibit a two-plateau structure, and the cutoff of high-order harmonics is extremely extended to 851th order and the smooth supercontinuum harmonic spectrum is obtained in a chirped two-color inhomogeneous laser field. To further understand the physical mechanism of HHG, we give a reasonable explanation for the extension of harmonic plateau by using the semi-classical three-step model, the time-frequency profile of the time-dependent dipole, and the classical electron trajectories. Explicitly, the harmonic order as a function of the ionization time and emission time can be given by the semi-classical three-step model. If we define the path with earlier ionization time and later emission time as a ongelectronic trajectory, and the path with later ionization time and earlier emission time as a short electronic trajectory, then, there exist a few electronic trajectories that contribute to the harmonics in cutoff region. Numerical results show that the short quantum path is enhanced, and the long quantum path is suppressed in spatially inhomogeneous fields, and this is advantageous to generate an IAP. We find that the quantum path can be controlled by increasing inhomogeneity parameter of the laser field. Effects of the time delay on HHG is also discussed. We find that the smooth supercontinuum harmonic spectrum is obtained by adjusting the time delay. When the time delay is t0=1.6up/1, the cutoff of the harmonics can be extended remarkably. By synthesizing the 600th to 680th (80th) order harmonics in the continuum region, an isolated 32 attosecond pulse can be generated by a spatially inhomogeneous chirped two-color laser field with parameters =0.25, =0.00105, t0=1.6/1.
The electric field effect on the hydrogen storage of (MgO)12 by ab intio calculations
Authors: Yin Yue-Hong  , Chen Hong-Shan  , Song Yan  ,   College of Physics and Electronic Engineering, Northwest Normal University; Key Laboratory of Atomic & Molecular Physics and Functional Materials of Gansu Province, Lanzhou 730070, China
Published: December 2020

(MgO)12 in a tube structure is one of the magic number clusters of (MgO)n and exhibits particular stability. To study the electric field effect on the hydrogen storage properties of (MgO)12, the H2 adsorption behavior on the surface of the tube (MgO)12 in an external electric field is explored at the level of B3LY/6-31G**. In the external electric field, the (MgO)12 keeps the frame of tube structure but with little distortion, implying that the (MgO)12 cluster can sustain the strong electric field for hydrogen storage. The NBO analysis also indicates that (MgO)12 is polarized by the external electric field; and its dipole momenta increase to 9.21 and 19.39 Debye at the field intensities of 0.01 and 0.02 a.u., respectively. Without the external electric field, H2 can be adsorbed on Mg atoms in the end on modes, while on O atoms in the top on modes. When the external electric field is applied, whether H2 is adsorbed on Mg or O atoms, the stable adsorption structures are all top on modes and the molecular orientation of H2 is turned to the direction of the external electric field. Because (MgO)12 and H2 are effectively polarized by the external electric field, the adsorption strength of H2 on some adsorption sites are enhanced remarkably. The adsorption energies of H2 on the three-coordinated Mg/O are promoted from 0.08/0.06 eV in free field to 0.12/0.11 eV and 0.20/0.26 eV at field intensities of 0.01 a.u. and 0.02 a.u., respectively. Electronic structure analysis reveals that when H2 is adsorbed on Mg atoms, this process denotes charges moving to the cluster, and the improvement of adsorption interaction of H2 on Mg atoms is mainly due to the polarization effect. While the adsorption on O atoms, on the one hand implies the polarization effect of O anion is stronger than that of Mg cation, on the other hand, H2 receives charges from (MgO)12 and its valence orbitals also take part in the bonding with the valence orbitals of the cluster. Thus the structures of H2 adsorbed on O atoms are more stable. In an external electric field, (MgO)12 can adsorb sixteen H2 molecules at most, and the corresponding mass density of hydrogen storage reaches 6.25wt%.
Propagation characteristics of power line harmonic radiation into the stratified anisotropic ionosphere
Authors: Wu Jing  , Zhou Zhi-Wei  , Yan Xu  ,   School of Automation Science and Electrical Engineering, Beihang University, Beijing 100191, China
Published: December 2020

Power line harmonic radiation (PLHR), which specifically refers to the electromagnetic wave radiation observed in ionosphere or magnetosphere, is radiated by the transmission lines of power systems on the ground. PLHR is shown as a parallel spectrogram between 400 Hz and 5 kHz in frequency-time power spectrogram of electromagnetic field. And the frequency spacing of the parallel spectrogram is 50/100 Hz or 60/120 Hz. As an artificial pollution source in the near earth space, PLHR has attracted more and more attention. However, so far, there have been little proposed quantitative researches on the formation mechanism. This paper studies the propagation model for the electromagnetic waves generated by the electric dipole source above the non-ideal conductive ground in the stratified anisotropic ionosphere. Based on the method by Lehtinen(2008), a new full-wave finite element method is give to solve the problem. By recursively calculating reflection coefficients and mode amplitudes, the method contains no index increasing items. So it can effectively overcome the numerical overflow in programming calculations. In order to verify the correctness of the method, comparison are made between the existing analytical solutions and the solutions obtained from the proposed method, and they are in excellent agreement. Further more, using the present model, the new method and the associated parameters about practical power lines, ground and ionosphere, we have studied the effects of the frequency of dipole source, the bottom boundary height of ionosphere, the earth conductivity, and the geomagnetic field direction on PLHR propagation in the ionosphere. Results show that when the frequency of radiation source equals the cut off frequency of earth-ionosphere waveguide-guided wave modes, the strength of PLHR for penetrating into the ionosphere becomes larger. Keeping the harmonic current constant, a smaller ground conductivity would be accompanied by a larger power of PLHR. PLHR propagates along the direction of the geomagnetic field in the ionosphere. Therefore, it is much easier for a high-order harmonic radiation of transmission lines to penetrate into the ionosphere along the direction of the geomagnetic field in the areas with low ground conductivity under a certain condition. Results obtained in this paper may have important implications to explain the formation mechanism of PLHR.
Influence of weak anchoring on the microwave phase modulation of liquid crystals
Authors: Ye Wen-Jiang  , Wang Meng-Ying  , Xing Hong-Yu  , An Ya-Shuai  , Qin Xiang-Lei  ,   School of Sciences, Hebei University of Technology, Tianjin 300401, China
Published: December 2020

The microwave modulation induced by liquid crystals is determined by the orientation of liquid crystal molecules under an external applied voltage. The anchoring of substrate has an important effect on the liquid crystal orientation, which results in the change of microwave modulation. In this paper, the microwave modulation property of 90 twisted nematic liquid crystals with weak anchoring without chiral dopant is studied. Based on the elastic theory of liquid crystals and the variational theory, the equations of equilibrium state and the boundary condition are given, and the variations of phase-shift per unit-length with voltage for different anchoring energy coefficients and pre-tilt angles are also simulated using the finite-difference iterative method. Results are as follows: (1) The influence of pre-tilt angle on microwave phase-shift is related to the applied voltage. When the voltage applied to the liquid crystal cell is from 0.5 to 1.6 V, with increasing pre-tilt angle, the microwave phase-shift per unit-length and the phase-shift difference relative to the strong anchoring 90 twisted nematic liquid crystal with pre-tilt angle 0 will all increase, and the applied voltage for the maximum phase-shift difference decreases. When the applied voltages are from 1.6 to 3.0 V, the microwave phase-shift per unit-length and the phase-shift difference all decrease with increasing pre-tilt angle. When the applied voltages are near 1.6 V or larger than 3.0 V, the phase-shift per unit-length has little change. (2) The anchoring energy strength has a great influence on microwave phase-shift. As the anchoring strength decreases, the microwave phase shift per unit-length and the phase-shift difference will increase, also the tunable range of microwave phase-shift increases more and more obviously. This research provides a theoretical foundation for the design of the liquid crystal modulator.
Full-vectorial analysis of a polarization demultiplexer using a microring resonator with silicon-based slot waveguides
Authors: Xiao Jin-Biao  , Luo Hui  , Xu Yin  , Sun Xiao-Han  ,   School of Electronic Science and Engineering, Southeast University, Nanjing 210096, China
Published: December 2020

Photonic integrated circuits (PICs) based on silicon-on-insulator (SOI) platform with the advantages of high-index-contrast and CMOS-compatible process can efficiently reduce the component sizes and densely integrate them at a chip scale. To meet the ever-increasing demand for the optical interconnect capacity, various multiplexing techniques have been used. However, it should still be proposed to effectively reduce the component size accompanied with the reasonable performance and wavelength division multiplexing (WDM) compatibility. To the best of our knowledge, there has no attempt so far to design a polarization demultiplexer based on a microring resonator in slot waveguide structures. In this paper, a compact silicon-based polarization demultiplexer is proposed, where two regular silicon-based waveguides are used as the input/output channels and a microring in slot waveguide structures is used as the polarization/wavelength-selective component. A full-vectorial finite-difference frequency-domain method is utilized to study the modal characteristics of the regular and slot silicon-based waveguides, where the effective indices and coupling for transverse magnetic (TM) and transverse electric (TE) modes are presented. With the unique modal characteristics of slot waveguides and the strong polarization-dependent features of microring resonator, we can show that the field distributions and the effective indices of the TM mode between the regular and slot waveguides are similar, while those of the TE mode show clearly different. As a result, the input TM mode outputs from the drop port at the resonant wavelength, while the input TE mode outputs from the through port directly with nearly neglected coupling, thus the two polarizations are separated efficiently. A three-dimensional finite-difference time-domain method is utilized to study the spectrum and transmission characteristics of the proposed device. From the results, a polarization demultiplexer with a radius of 3.489 m is achieved with the extinction ratio and insertion loss of ～ 26.12(36.67) dB and ～ 0.49(0.09) dB respectively for the TM(TE) mode at the wavelength of 1.55 m by carefully optimizing the key structural parameters. In addition, taking the fabrication errors into account during the practical process, the fabrication tolerances to the proposed device are analyzed in detail and the performance is assessed by the extinction ratio and insertion loss. For demonstrating the transmission characteristics of the designed polarization (de) multipexing (P-DEMUX) device, the evolution along the propagation distance of the input mode through the designed P-DEMUX is also presented. The present polarization demultiplexer is compatible with the WDM systems on-chip based on microring resonators and can be easily introduced into the WDM system to further increase the optical interconnect capacity.
Effects of proton and neutron irradiation on dark signal of CCD
Authors: Zeng Jun-Zhe  , Li Yu-Dong  , Wen Lin  , He Cheng-Fa  , Guo Qi  , Wang Bo  , Maria  , Wei Yin  , Wang Hai-Jiao  , Wu Da-You  , Wang Fan  , Zhou Hang  ,   Key Laboratory of Functional Materials and Devices for Special Environments of CAS; Xinjiang Key Laboratory of Electronic Information Materials and Devices; Xinjiang Technical Institute of Physics & Chemistry of CAS, Urumqi 830011, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The proton and neutron irradiation and annealing experiments are carried out on a domestic buried channel CCD (charge-coupled devices), Monte Carlo method being applied to calculate the energy deposition of scientific CCD irradiated by proton and neutron, and the radiation damage mechanism of the device is analyzed. The displacement damage dose in N+ buried channel is simulated. During irradiation and annealing experiments, the main parameter (dark signal) is investigated. Results show that the dark signal of the buried channel CCD irradiated by 10 MeV proton and 1 MeV neutron rises obviously. With the same fluence, the increase of dark signal and the displacement damage dose in N+ buried channel caused by 10 MeV proton is larger than that by 1 MeV neutron. Dark signal caused by proton irradiation is divided into surface dark signal and bulk dark signal. Oxide-trapped-charges and interface states may be caused by ionization-generated surface dark signal, and the bulk defects may be caused by displacement-generated bulk dark signal. Neutron irradiation only affects the bulk dark signal. Defects and their annealing temperature are studied. The dark signal of CCD irradiated by proton is greatly reduced after annealing, this phenomenon means that the dark signal is mainly affected by ionization. The proportion of bulk dark signals in total dark signals can be calculated by the remainder of dark signal after annealing, and it is at most about 20% or less. From the formula, the position of energy level of bulk defects has an obvious influence on the bulk dark signal. The energy level in the middle of the forbidden band can provide effective hot carriers. Combining the results of experiment and simulation, when the displacement damage doses in N+ buried channel are the same, the bulk dark signal produced by proton is nearly the same as that produced by neutron. This phenomenon means that the defect levels in the forbidden band gap caused by proton and neutron irradiation have the same contributions to dark signal generation. Effect of proton and neutron irradiation on the bulk dark signal is homogeneous. The displacement damage dose can be used to characterize the degradation degree of the bulk dark signal in CCD after irradiation.
Complex motions of grains in dusty plasma with nonuniform magnetic field
Authors: Gong Wei-Hua  , Zhang Yong-Liang  , Feng Fan  , Liu Fu-Cheng  , He Ya-Feng  ,   Key Laboratory of Photo-Electronics Information Materials of Hebei Province, College of Physics Science and Technology, Heibei University, Baoding 071002, China
Published: December 2020

We have studied various complex motions of the irregular dust grains immersed in non-uniformly magnetized plasma. The cylindrical magnet that we used for experiments significantly alters the radial distribution of the sheath potential which confines the negatively charged grains. Grains are horizontally illuminated by a 50 mW, 532 nm laser sheet and imaged by a CCD camera from the upper transparent electrode. Hypocycloid and epicycloid motions of grains are observed for the first time as far as we know. Cuspate cycloid motions, circle motion, wave motion, and stationary grains are also observed. Their trajectories can be obtained by using long-time exposure, and the characteristic parameters of the grain movement are measured by using the image processing with MATLAB. Though the dust grains can move around the magnet steadily in various trajectories, the induced magnetic field is too weak to give rise to cycloid motions of grains. Then we propose a new mechanism that an inverse Magnus force induced by the spin of the irregular grains plays an important role in their cycloid motions. The pollen pini we used for experiment is not a regular microsphere, there is a symmetry in the shape. On the basis of Bernoulli principle, the pressure difference between the left and right side of the forward moving grains produces the inverse Magnus effect. Additional comparison experiments with regular microspheres are also performed to confirm that the cycloid motions are distinctive features of an irregular dust grain immersed in the plasma. The periodical change of the cyclotron radius as the grain travels would result in the (cuspate) cycloid motions, and the maximal value of angular velocity of spin is about 105 rad/s. Our experimental observations can be well explained based on the force analysis in 2D horizontal plane.
Rectifying behaviors induced by B/N-doping in similar right triangle graphene devices
Authors: Chen Ying  , Hu Hui-Fang  , Wang Xiao-Wei  , Zhang Zhao-Jin  , Cheng Cai-Ping  ,   College of Physics and Microelectronics Science, Hunan University, Changsha 410082, China; Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Changsha 410082, China
Published: December 2020

By using nonequilibrium Green's functions in combination with the first principles density functional theory, for the similar right triangle graphene devices as the research object, we take the zigzag graphene as electrodes, to investigate the B(N) doping and B-N co-doping effect, i.e. mainly the influence of doping on the transport properties of similar right triangle graphene devices, as well as the asymmetric doping effect on the rectifying behaviors in similar right triangle graphene devices. Calculated results show that the system conductivity is increased when the vertex carbon atom of a similar right triangle graphene is substituted by a boron or nitrogen atom, and a novel rectifying effect appears. The rectification behavior can be observed because of an asymmetric movement on the molecular-level in B(N) doping in the similar right triangle graphene devices under positive and negative biases and the asymmetry in the spatial distribution of the frontier orbitals. Most importantly, when the vertex carbon atoms of the right and left similar right triangle graphenes are simultaneously doped with boron and nitrogen atoms, the rectifying effect of the system is significantly enhanced and appears also a negative differential resistance effect.
Simulation studies on the transport properties of Cu-H2O nanofluids based on water continuum assumption
Authors: He Yu-Chen  , Liu Xiang-Jun  ,   School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

Nanofluid is a kind of new engineering medium which is created by dispersing small quantity of nano-sized particles in the base fluid. The dispersion of solid nanoparticles in conventional fluids changes their transport properties remarkably. Molecular dynamics simulation (MDS) is an important approach to study the transport properties of nanofluids. However, the computation amount is huge, and it is very difficult to use the normal MDS to capture the transient flow and heat processes in Cu-H2O nanofluids if the regions in the simulation reach 149.6443 nm3 or 299.2883 nm3, and the number of Cu nano-particles reaches 6-64. Further study by means of simulation on the effects on effective transport properties of nanofluids is also difficult. In this paper, the water-based fluid region of 149.6443 nm3 or 299.2883 nm3 is assumed as continuum phase because of the very low Knudsen number of fluid, and the effects of water on nano-particles are fitted into the Cu-Cu potential parameters. Using the proposed method, the computation amount is significantly reduced. The effective thermal conductivity and dynamic viscosity coefficient of Cu-H2O nanofluids under the stationary condition are simulated and the results are verified with existing experimental data. The motion and aggregation processes of nano-particles in the water-based fluids at different velocity shear rate are simulated. Effects of velocity shear rate, fluid velocity, temperature gradient, and average temperature on the effective thermal conductivity and the dynamic viscosity of Cu-H2O nanofluids in the processes of flow and heat transfer are studied. Three conclusions can be drawn from the obtained results. Firstly, the proposed method is feasible to capture the transient flow and heat processes in Cu-H2O nanofluids, and is also capable to further study the transport properties of Cu-H2O nanofluids. Secondly, the velocity shear rate acting on a nanofluid can effectively prevent the aggregating process of nano-particles, and therefore reduce the diameter of particle-aggregations. Finally, the velocity shear rate and the average temperature of Cu-H2O nanofluids have much more effects on the transport properties, while the fluid velocity and temperature gradient have less effects; the velocity shear rate increases the effective thermal conductivity of a nanofluid but decreases its dynamic viscosity. A rise of average temperature increases the effective thermal conductivity but decreases the dynamic viscosity.
Self-excited oscillation of droplets on confined substrate with instantaneous weightlessness
Authors: Shi Feng  , Li Wei-Bin  , Li Jing-Qing  , Lan Ding  , Wang Yu-Ren  ,   School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China;,   Key Laboratory of Microgravity Science, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

In order to further explore the oscillation mechanism of constrained droplets in microgravity and extend the application and management of space fluid, the small-amplitude self-excited oscillation processes of droplets that are pinned on a confined substrate are investigated. The substrate has a 5 mm diameter contact circle, which is implemented through the use of a drop tower and high-speed photography technology. Oscillation is a recovery procedure for droplet configuration in microgravity with the confined effect at the boundary, making the contact line and diameter unchanged throughout the entire process. A self-excited oscillation could be divided into two stages: a morphological change process and a small-amplitude damping attenuation oscillation. The first stage is a morphological change process, where the heights of high and low oscillations rise gradually, which in turn correspond to the variation of gravity. And the deformation rate is inversely proportional to the droplet size. The second stage is the small-amplitude damping attenuation oscillation around the equilibrium position until it reaches the final steady state in microgravity. At this stage, the frequency is nearly constant and the attenuation of amplitude represents an exponential damping, like the free oscillation of isolated viscous droplets. The pinning contact line makes the oscillation waveform deviate from sine curve and in the process there exists a period when the heights keep constant at some positions, such as the highest, lowest and others. Studies confirm the hypothesis that the oscillation occurs with the similar second-order mode of free drop when the height fluctuates, and the third-order mode when the height is immobile. This is in agreement with the spectral analysis. Furthermore, when the liquid volume varies within this experimental system, the pinning constraint with fixed contact area on the confined substrate can generate droplets with various static contact angles and undisturbed radii. The deformation stage and oscillation mode of the droplets remains stable, although the concrete courses differ in some ways. In the case of bigger drops, the phenomenon of height unchanging should be in the middle position and vanishes with time. However, the smaller one shows no signs for this condition, and the waveform remains consistent all around. In the second stage, the amplitude decay damping rate and non-dimensional frequency of small droplet are higher.
Acoustic charge transport behaviors of sulfur-doped wide gap Ga2Te3-based semiconductors
Authors: Liu Hai-Yun  , Liu Xiang-Lian  , Tian Ding-Qi  , Du Zheng-Liang  , Cui Jiao-Lin  ,   Materials Science and Engineering College, Taiyuan University of Technology, Taiyuan 030024, China;,   School of Materials, Ningbo University of Technology, Ningbo 315010, China
Published: December 2020

Wide gap semiconductors as the thermoelectric (TE) candidates have been increasingly interested because of their inherent high Seebeck coefficients and low thermal conductivities. Ga2Te3 is one of the typical defect compounds (Eg=1.65 eV) among the A2IIIB3VI type semiconductors, in which there are periodically self-assembled 2D vacancy planes that wrap the nanostructured domains. The vacancy planes scatter phonons highly effectively and are responsible for reducing the lattice thermal conductivity. Hence Ga2Te3 might be a good TE candidate. In the phase diagram of Ga-Te, Ga2Te3 is involved in the eutectoid and peritectic reactions at the critical temperatures (CTs) of 680 10 K and 757 10 K respectively. These reactions would lead to the generation of enthalpies of reactions, and induce the alteration of some thermo-physical properties.
In the present work, we have not observed the phase transformations at CTs in the Ga2Te3-based materials with sulfur isoelectronic substitution for Te, which are prepared by powder metallurgy with the spark plasma sintering (SPS) technique, but can observe the generation of assumed enthalpies of reactions near CTs, which directly gives rise to the critical acoustic charge transport behaviors. The critical behaviors involve the remarkable increase of heat capacities and Seebeck coefficients and, at the same time, reductions of thermal diffusivities (thermal conductivities) and electrical conductivities. For example, the Seebeck coefficient () at x=0.05 increases rapidly from 376.3(VK-1) to 608.2(VK-1) when the temperature rises from 596 to 695 K, and then decreases to 213.8(VK-1) at 764 K. Similarly, all the S-doped samples, which have lowest electrical conductivities ( ) of 2.12102 (x=0.05), 0.25102 (x=0.1), 0.12102 -1m-1 (x=0.2) and 0.14102 -1m-1 (x=0.3) at 696725 K, undergo dramatic changes when the temperature rises to about 750 K, and then the electrical conductivities begin to decrease, and the changes tend to slow down. It is notable that both the Seebeck coefficients and electrical conductivities exhibit a typical zigzag temperature dependence in the temperature range from 596 to 812 K. These behaviors reveal the remarkable alterations in scattering mechanism of both phonons and carriers at temperatures near the CTs.
Although the materials with these critical behaviors near CTs do not have satisfactory thermoelectric performance (ZTmax=0.17 at 793 K for x=0.3) as compared with the known binary Cu2Se, Ag2Se(S) or ternary based AgCrSe2 alloys, however, the findings of such critical transport behaviors have a great significance for future researches.
Electrical transport properties of polycrystalline TaN1- films
Authors: Zhou Ding-Bang  , Liu Xin-Dian  , Li Zhi-Qing  ,   Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Faculty of Science, Tianjin University, Tianjin 300072, China
Published: December 2020

Tantalum nitride with a face-centered cubic structure (TaN1-) has received much attention due to its high hardness, good wear resistance, chemical inertness, thermodynamic stability, and low temperature coefficients of resistivity. First-principles calculations have indicated that cubic-TaN possesses metallic energy band structure, and the experimental results show that the carrier concentration in TaN1- films are comparable to that of normal metals. However, semiconductor-like temperature behavior of resistivity is often observed in polycrystalline TaN1- film. In the present paper, we systematically study the crystal structures and electrical transport properties of a series of TaN1- thin films, deposited on quartz glass substrates at different temperatures by the rf sputtering method. Both X-ray diffraction patterns and scanning electron microscope images indicate that the films are polycrystalline and have face-centered cubic structure. It is also found that the mean grain sizes of the films gradually increase with increasing depositing temperature. The temperature dependence of resistivity is measured from 350 K down to 2 K. The films with large grain sizes have a superconductor-insulator transition below ～ 5 K, while the films with small grain sizes retain the semiconductor characteristics down to the minimum measuring temperature, 2 K. These phenomena are similar to that observed in superconductor-insulator granular composites. Above 5 K, the temperature coefficients of the resistivities of the films are all negative. In the temperature range between 10 and 30 K, the films show hopping transport properties which are often seen in metal-insulator granular systems, i. e. the logarithm of the resistivity (log ) varies linearly with T-1/2, where T represents the measured temperature. The thermal fluctuation-induced tunneling conductive mechanism dominates the temperature behaviors of resistivities from 70 K up to 350 K. It can be seen that the thermal fluctuation induced tunneling conductive mechanism is also the main conductive mechanism in metal-insulator granular systems in the higher temperature regions. Our results indicate that the electrical transport properties of the polycrystalline TaN1- films are similar to that of metal-insulator granular films with different volume fractions of metal, where the metal possesses superconductivity at low temperatures. Hence the high resistivity and negative temperature coefficient of resistivity of TaN1- polycrystalline film can be reasonably ascribed to the similarity in microstructures between TaN1- polycrystalline film and metal-insulator granular film.
STXM observation and quantitative study of magnetic vortex structure
Authors: Sun Lu  , Huo Yan  , Zhou Chao  , Liang Jian-Hui  , Zhang Xiang-Zhi  , Xu Zi-Jian  , Wang Yong  , Wu Yi-Zheng  ,   Department of Physics, Fudan University, Shanghai 200433, China;,   Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
Published: December 2020

Magnetic recording has now played an important role in the development of non-volatile information storage technologies, so it becomes essential to quantitatively understand the magnetization distribution in magnetic microstructures. In ferromagnetic disks, squares and triangles with submicron sizes, it is energetically favorable for the magnetization to form a closed in-plane vortex and a perpendicular vortex core at the center. This vortex magnetic structure is a new candidate for future magnetic memory device because both the vortex chirality and the core polarity can be manipulated by applying an external magnetic field or a spin-polarized current. Further development of vortex-based memory devices requires quantitative measurement of vortex domain structures, which is still lacking.In this paper, magnetization configuration in a vortex structure has been quantitatively studied by scanning transmission X-ray microscope (STXM) utilizing X-ray magnetic circular dichroism (XMCD) effect in Shanghai Synchrotron Radiation Facility. Samples have been fabricated on the 100 nm silicon-nitride membranes. The patterns are first transferred to PMMA photoresist using e-beam lithography, then a 50 nm thick Ni80Fe20 film is deposited by e-beam evaporation. Magnetic vortex configurations are characterized with the X-ray energy at Fe L3 absorption edge and Ni L3 absorption edge, respectively. The image taken at Fe edge shows greater contrast than that at Ni edge. Experimental results indicate that the magnetic vortex state remains stable in permalloy circle, square and triangle structures with diameters from 2 to 5 m. The STXM images indicate that the magnetization in circular geometry changes continuously along the concentric circles without clear domain boundaries. In contrast, magnetization in square geometry consists of four distinct domains with clear diagonal domain boundaries. Similarly, three domains can be observed in triangle geometry. In order to quantify the in-plane magnetization configuration in magnetic vortices, we also use micromagnetic simulation to calculate the magnetization distributions of these three geometries. By extracting Mx along the circular profiles in both experimental and simulated vortex images, we find that the experimental magnetic profiles in the STXM images are consistent with the simulation data quantitatively. These magnetic structures are also studied by magnetic force microscopy (MFM). Since MFM is only sensitive to the dipolar magnetic field around the domain boundary, the MFM images show different configurations from the STXM images.
Raman spectroscopic study on the micro-structure of NH4H2PO4 and ND4D2PO4 crystals
Authors: Zhou Hai-Liang  , Gu Qing-Tian  , Zhang Qing-Hua  , Liu Bao-An  , Zhu Li-Li  , Zhang Li-Song  , Zhang Fang  , Xu Xin-Guang  , Wang Zheng-Ping  , Sun Xun  , Zhao Xian  ,   State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China;,   Key Laboratory of Functional Crystal Materials and Device (Shandong Universiy), Ministry of Education, Jinan 250100, China;,   Shandong Agricultural University, Taian 271018, China;,   Chengdu Fine Optical Engineering Research Centre, Chengdu 610041, China
Published: December 2020

In this paper, the lattice vibration modes of ammonium dihydrogen phosphate NH4H2PO4 (ADP) and its deuterated analog DADP are studied by using polarized Raman spectra and the first-principles calculation in the framework of the density functional theory. The vibration modes of ADP crystal, in which the basic structural units are the NH4+ and H2 PO4-groups, have been simulated by using a plane-wave pseudo potential method. Result shows that the peaks of 921 and near 3400 cm-1 are assigned as the vibrational H2 PO4-and NH4+ groups, respectively. In order to investigate the deuteration process, the polarized Raman spectra are obtained in different polarization configurations and recorded in the range of 200-4000 cm-1, so that we can study the variation of Raman peaks at 921 and 26003400 cm-1. For example, in the scattering geometryX(YY)X , with increasing degree of deuterated, the peak of 921 cm-1 red shifts and decreases in intensity, while the peaks ranging from 2600 to 3000 cm-1 decrease in intensity. Moreover, a new broadened line appears in the range of 20002600 cm-1, and the intensity of the new line increases with the degree of deuterated, but no change occurs in the peak position. With Lorentz analysis, it can be inferred that the deuterated of NH4+ group is prior to that of H2 PO4-group. We also study the spectra for other Raman scattering geometry of these crystals, and the result shows that the site symmetries of NH4+ (ND4+) and H2 PO4-(D2 PO4-) groups are determined to be C2, which means that the site symmetry of the two groups in crystals have no change during the deuteration process. These results will be a foundaton for optimizing the growth and property of this kind of material.
Dynamics of spiral waves in an asymmetrically coupled two-layer excitable medium
Authors: Li Wei-Heng  , Pan Fei  , Li Wei-Xin  , Tang Guo-Ning  ,   College of Physical Sicence and Technology, Guangxi Normal University, Guilin 541004, China
Published: December 2020

The dynamics of spiral waves in the two-layer excitable media is studied by using the Br-Eiswirth model. The two media adopts the inhibitory and excitatory asymmetric couplings. Numerical results show that the excitatory asymmetric coupling can promote the frequency-locking of two spiral waves with different frequencies. The two spiral waves can achieve frequency-locking even if the frequency difference between them is large. The coupling causes the two spiral waves to have the strongest ability of frequency-locking; when the coupling between the two media is the inhibitory asymmetric coupling, the two spiral waves can achieve frequency-locking only when the frequency difference of the initial spiral waves is small. Furthermore, the range of frequency-locking is smaller than that of the general feedback coupling, and the frequency-locking ability of spiral waves reaches the minimum level. When the coupling strength and control parameters are chosen appropriately, the inhibitory and excitatory asymmetric coupling can keep the spiral wave unchanged in one medium and result in the transition from spiral wave to the resting state or target wave with low-frequency in the other. The coupling also induces the meandering of spiral waves or leads to the transition from two spiral waves to two target waves in the two-layer media. Finally the generated target waves either disappear or develop into the plane-wave-like oscillation patterns. Furthermore, the oscillation of the patterns is in antiphase. In addition, the locally intermittent frequency-locking of the two spiral waves is observed. These results can help understand the complicated phenomena occurring in the cardiac system.
A method of wall clutter removal for through-wall radar based on entropy of expanded antenna source
Authors: Li Jia-Qiang  , Cai Hong-Yuan  , Chen Jin-Li  , Li Peng  , Ge Jun-Xiang  ,   Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing 210044, China;,   School of Electronic & Information Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China;,   Jiangsu Key Laboratory of Meteorological Observation and Information Processing, Nanjing 210044, China
Published: December 2020

Strong front wall clutter has serious impacts on the target detection and imaging in the through-wall radar (TWR) system. A method of robust wall clutter suppression based on the entropy of an expanded antenna source for ultra-wide-band through-wall radar is presented in this paper. The model of TWR scenario consists of four layers. Assume that the first and the third layers are air space, while the second and the fourth layers are composed of uniform flat concrete wall. The circular target, assumed to be a perfect electric conductor, is located in the third layer. Along the measurement line which is parallel to the front wall, the transceiver antenna scans uniformly. The echo signals that come from the target and walls are processed into discrete data at first, so that the calculation of probability space is subsequently implemented and the discrete data are expanded as well. And then the entropy of the expanded data that contain robust wall clutter and echo of target is calculated. Taking into consideration the amplitude of target signal varying in each scan, while that of clutter signal is not, it is evident that the entropy can be utilized to discriminate the signals between the target and wall. According to the difference between the entropy of the wall clutter and that of the target, a certain threshold can be set and the optimum tolerance threshold is adaptively selected on the basis of target-to-clutter ratio. With the optimum tolerance threshold, process of clutter suppression is conducted. Finally, back projection is employed for imaging of target. In this paper, data of through-wall radar for simulation are provided by GprMax2D/3D, based on the finite difference-time domain methsd. The clutter suppression and imaging are separately conducted by the method based on data entropy and the method proposed in this paper. Comparing the results of simulations, it is shown that the gain of target-to-clutter ratio for the former is 15.51 dB, and that for the latter is 19.74 dB. It is obvious that the proposed method can provide imaging with higher quality for the same measurement, and it requires fewer scans with the same quality of imaging as well. Computational complexity of the proposed method and the method based on entropy can be expressed as O(M NL) and O(M N) , respectively
Simulation analysis and experimental verification of fast neutron radiography
Authors: Lu Chang-Bing  , Xu Peng  , Bao Jie  , Wang Zhao-Hui  , Zhang Kai  , Ren Jie  , Liu Yan-Feng  ,   Xi'an Institute of High Technology, Xi'an 710025, China;,   China Institute of Atomic Energy, Beijing 102413, China;,   Dongguan Campus, Institute of High Energy Physics, Chinese Academy of Sciences, Dongguan 523803, China
Published: December 2020

Expression for the formation of the pixel value of fast neutron radiography has been derived. The contrast inequality for the photograph has been established using the derived expression; then the relationships of the image contrast with the source intensity, the exposure time, and the scattering have therefore been obtained through the acquired inequality. A simulation on the process of fast neutron radiography is carried out based on the pixel value analysis, and the spatial resolution and image contrast have also been considered. Simulation results show that the spatial resolution is better than that from experiments and the effect of image contrast is equivalent to that of the experiments. Finally, various samples, such as Pb samples, with slits, Fe samples with square holes and multiple materials-combined samples, are used to test the performance of the simulation. Results demonstrate that the simulations are in agreement with the experiments, thus providing a reference to the future experimental design and engineering application.
Review of recent experimental studies of the shock train flow field in the isolator
Authors: Yi Shi-He  , Chen Zhi  ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China;,   High Speed Aerodynamics Research Institute, China Aerodynam Research and Development Center, Mianyang 621000, China
Published: December 2020

Since the concept of hypersonic flight was proposed, progress of the related theory, experiments and simulations has been gained. As an important component of the scramjet engine, the isolator plays a key role in the engine performance and flight success. The flow mechanism it involves is very complicated. In the view point of experimental research, this paper reviews the recent progress of scramjet isolator studies, analyzes the features of the isolator flow based on fine flow diagnosis technique (nano-tracer planar laser scattering, NPLS), including the three-dimensional structures of the shock train flow field, turbulent characteristics, hysteresis motions, unstart flow and shock train leading edge detection. Studies of the isolator flow can be classified and discussed according to the wind tunnel facility, isolator design and measurement techniques. Based on this, suggestions for further research can be proposed.