bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatio-temporal characteristics of microhollow cathode sustained discharge
Authors: He Shou-Jie  , Zhang Zhao  , Zhao Xue-Na  , Li Qing  ,   Hebei Key Laboratory of Optic-Electronic Information and Materials, College of Physics Science and Technology, Hebei University, Baoding 071002, China
Published: December 2020

Micro hollow cathode sustained discharge (MCSD) is simulated by using a fluid model, and the spatiotemoral characteristics of the electric potential, electron density, ion density and electric field are investigated. Results show that the MCSD acts in different modes at different times. The first stage is the Townsend discharge mode. The second is a transition mode from Townsend discharge mode to a hollow cathode effect mode, and the electron density, ion density and electric field near the cathode rise drastically, in which the MCSD is ignited initially. The third stage is the hollow cathode effect mode, and the MCSD forms generally. The last stage is stable discharge state. At the stable discharge stage, the electron density and the ion density each achieve 1015 cm-3 with a peak density located in the center of hollow cathode chamber. The value of electron density in the MCSD region is on the order of 1013 cm -3. The results also show that the micro-hollow cathode discharge (MHCD) contributes to the formation of MCSD, and the MCSD also facilitates the development of MHCD. In addition, the voltage on the second anode has important influence on the distributions of electric potential, electron density and electric field both inside the hollow cathode and outside the hollow cathode. Moreover, the influence on the MCSD is more apparent than the influence on the MHCD. With the increase of voltage on the second anode, the cathode sheath close to the first anode becomes more and more apparent. The second anode is necessary for the formation of micro-hollow cathode sustained discharge.
A complete equation of state for polyethylene based on Helmholtz free energy
Authors: Zhang Xu-Ping  , Wang Gui-Ji  , Luo Bin-Qiang  , Tan Fu-Li  , Zhao Jian-Heng  , Sun Cheng-Wei  , Liu Cang-Li  ,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China;,   China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Polyethylene (PE) is an important kind of plastic, which plays a significant role as the shell material of the fuel capsule, light weight structural element subjected to intense mechanical impact and explosion load. And it is well accepted that semi-empirical three-term equation of state (EOS) is one of the most widely used EOSs in practical work. Therefore, studies of semi-empirical three-term EOS of PE are significant for accurately predicting and analyzing the physical processes and experimental results under high pressure compression. A semi-empirical three-term complete EOS of PE based on the model of Helmholtz free energy is established in this work. According to the EOS model, the Helmholtz free energy is composed of cold energy, thermal contribution of atoms and thermal excitation of electrons. The cold energy is calculated by using the Mie potential. The optical frequency branch of atomic vibration and the thermal contribution of electrons are neglected in the calculation at temperatures below 104 K. The parameters of Helmholtz free energy are calculated by using the shock Hugoniot data and thermal parameters at ambient state. And then, the application pressure range and reliability of the semi-empirical three-term EOS of PE are evaluated. Shock Hugoniot, shock wave temperature and Grneisen coefficient of PE are deduced from the EOS. The results show that shock Hugoniot and shock wave temperature are consistent well with the experimental data and the first-principle calculation in a pressure range of 150 GPa. Because the specific volume of PE does not change obviously in the melting and chain dissociation process, the assumption of linear Hugoniot relation of PE is valid for calculating the cold energy parameters. The calculation results deviate from the experimental results at about 150 GPa while the compression lasts up to the chemical bond dissociation pressure of PE. In addition, the value of buck modulus and its derivative with respect to pressure at zero pressure and temperature depend strongly on Hugoniot parameters. Therefore, the parameter of Helmholtz free energy in this work is only valid for compression. In conclusion, the Helmholtz free energy model and parameters can well reproduce the experimental data and reasonably describe the thermodynamic state of PE at its dissociation pressure. Moreover, it should be pointed out that a more refined model of phase transition and thermal contribution of atoms and electrons should be considered when extrapolated to higher pressure.
Anderson localization effect on Mott phase in 1T-TaS2
Authors: Zhao Yang-Yang  , Song Yun  ,   Department of Physics, Beijing Normal University, Beijing 100875, China
Published: December 2020

In the layered dichalcogenide 1T-TaS2, whether there is a disorder-driven transition from insulator to metal is still a matter in dispute. It is predicted that the commensurate charge density wave (CCDW) phase at low temperature behaves as a Mott insulator due to the strong correlation of electrons. Meanwhile, the stacking of TaS layers is found to be dislocated along the c axis, which will introduce considerable effect of disorder. Therefore, further theoretical study is needed to show the cooperative effect of correlation and disorder in 1T-TaS2.
The statistical dynamical mean-field theory, which treats interactions and disorder on an equal footing, is used to study the effect of disorder on the Mott insulating phase in 1T-TaS2. Two different kinds of disorder effects are considered in the one-dimensional extended Anderson-Hubbard model, where the stacking dislocation of TaS layers is described by the off-diagonal hopping disorder and the diagonal disorder term represents the effect of disorder introduced by impurities.
We find that the off-diagonal disorder by itself could not close the Mott gap at Fermi level, suggesting that Mott mechanism should be more dominant in the CCDW phase of 1T-TaS2 with the stacking dislocation of TaS layers. On the other hand, the diagonal disorder introduced by impurities will close the Mott gap when the strength of disorder (W) is larger than the correlation of electrons (U). Proved by the lattice-size scaling of the generalized inverse participation ratio, both the off-diagonal disorder and diagonal disorder can make all states Anderson-localized. As a result, there is no disorder-induced metal-insulator transition in a correlated system with either off-diagonal disorder or diagonal disorder.
In addition, an anomalistic state is introduced by the off-diagonal disorder at the center of the energy band of the non-interacting system, which is a special Anderson-localized state with a very larger localization length. In the correlated cases, the electron-electron interactions have strong effect on splitting the anomalistic state into two individual states, which are located symmetrically in both the upper and lower Hubbard subbands with an energy interval U.
First principles study of electronic and elastic properties of Ti3AC2 (A = Si, Sn, Al, Ge) phases
Authors: Hu Jie-Qiong  , Xie Ming  , Chen Jia-Lin  , Liu Man-Men  , Chen Yong-Tai  , Wang Song  , Wang Sai-Bei  , Li Ai-Kun  ,   State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals, Kunming Institute of Precious Metals, Kunming 650106, China
Published: December 2020

A first-principles plane-wave pseudo potential method based on the density functional theory is used to investigate the phase structures, energies, electronic structures and elastic properties of Ti3AC2 (A=Si, Sn, Al, Ge) phases. In this paper, Ti3AC2 (A=Si, Sn, Al, Ge) crystal structures are first optimized, then the band structures, total and part density of states，charge density distributions and elastic properties of these compounds are analyzed, and the cohesive energies and formation energy of these phases are also calculated. The results show that the Ti3GeC2 is more stable than other compounds, the formation energy of Ti3AlC2 is the lowest in these compounds, which indicates that Ti3AlC2 is easier to generate; Ti3AC2 (A =Si, Sn, Al, Ge) each have a higher density of states at Fermi level, which shows the strong metallicity, meanwhile, the electrical conductivity of each phase is anisotropic. The DOS at the Fermi energy is mainly from the Ti-d electrons, which should be involved in the conduction properties although d electrons are considered to be inefficient conductors. The lowest valence bands are formed by the C-s states with a small mixture of Ti-p+d, and A-s+p states. The electrical properties are mainly decided by the p-d hybridizations between 3d electrons in Ti and the p electrons in A (A =Si, Sn, Al, Ge) and 2p electrons in C, and the strong hybridization of p-d states make the materials have stable structures. It should be noted that the calculated bond length of Ti-Ge is shorter than those of Ti-A (A=Si, Sn, Al) bonds. This implies that the Ti-Ge bond is stronger than Ti-A (A=Si, Sn, Al) bonds. Furthermore, the Fermi level of Ti3GeC2 is relatively low, which also indicates the relatively high stability of Ti3GeC2. The charge density provides a measure of the strength of the ionic bond, so that Ti3GeC2 and Ti3SiC2 have stronger ionic bonds than Ti3SnC2 and Ti3AlC2. The strong M-A bonds in Ti3GeC2 lead to a decreasing and c lattice parameter value increasing. The spherical shape of X represents more like an ionic bond. The z-directional localized shapes of A each is more like a covalent bond. The covalent bonds of A elements each are localized along the z direction so that they affect mostly the c lattice parameter; the calculated elastic properties of Ti3AC2 (A = Si, Sn, Al, Ge) phases show that the atomic binding force of Ti3AlC2 is weaker than those of other three phases, while the atomic binding force of Ti3GeC2 is relatively strong, which makes the strength of Ti3GeC2 quite high.
The first-principle calculation on the Li cluster adsorbed on graphene
Authors: Yang Guang-Min  , Liang Zhi-Cong  , Huang Hai-Hua  ,   College of Physics, Changchun Normal University, Changchun 130032, China;,   College of Materials Science, Jilin University, Changchun 130012, China
Published: December 2020

As a stable single sheet of carbon atoms with a honeycomb lattice, graphene has become attractive for its potential applications in electrochemical storage devices, such as anodes for rechargeable Li batteries. Since both sides of it can hold adsorbents, a graphene sheet is expected to have extra storage sites and therefore it has a possibly higher capacity than graphite. However, certain shortcomings of Li battery, such as instability lead to battery failure under overcharging or overvoltage conditions. The limit to capacity results in a short time of discharge. Thus, more attention should be paid to the stabilities of electrode materials, such as Li cluster nucleation on graphene leading to dendrite formation and failure of the Li-ion battery. In this work, we build a supercell model of single layer graphene with hexagonal structure, and then change the size of Li cluster which is used to be adsorbed on graphene, with keeping m Li:C ratio at 1:6. Using the first principle based on density functional theory, we calculate the density of states, charge density difference and energy band structure. The interaction between Li and pristine graphene is studied in detail by analyzing the electronic properties and charge distribution of the isolated Li clusters and Li clusters adsorbed on graphene. It is found that the ionic bonding can be formed at the interface between Li clusters and graphene, and the charge transfer controls the interaction of the Li-carbon nanostructure. Combing thermodynamics method with the nucleation mechanism, the relationship between the cluster size and nucleation probability is analyzed, and the nucleation on graphene of Li with a certain concentration is also investigated. We estimate the nucleation barrier for Li on graphene and investigate the stability of Li adsorption on graphene by considering the effects of Li concentration and temperature. The Li concentration of 16.7% is considered for the formation of clusters with different sizes on graphene. With the size of Li cluster increasing, the cluster adsorbed on the graphene begins to be more stable than the single Li atom. The formation energy for the cluster is found to increase with the increase of temperature, and it is negative, meaning that Li cluster can be formed. It is expected that the corresponding calculation results from this atomistic simulation will shed some light on the in-depth understanding of Li-storage on graphene and the cycling stability and dendrite formation in Li-ion batteries with graphene-based materials serving as the anode.
Structures and properties of Np(NO3)nq (n=16, q=-2+3) coordination compound
Authors: Ma Lei  , Yin Yao-Peng  , Ding Xiao-Bin  , Dong Chen-Zhong  ,   Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China
Published: December 2020

In the process of nuclear waste disposal, the valuable uranium and plutonium are recycled and separated by dissolving the spent fuel in nitric acid. However, transuranic Np greatly influences the process of separation and recovery. Therefore, it is vital to study the structure and properties of nitrate, which is combined with neptunium ions and nitric acid. Furthermore, there are few researches about nitrate formed by tetravalent neptunium ions. So in this article, by using B3LYP hybrid method of density functional theory, the Gaussian 03 program is used to optimize the geometric construction of the coordination compounds Np(NO3)nq (n=1-6, q=-2-+3) formed by the tetravalent neptunium ions (Np4+) and nitrate ion (NO3-). Under the relativistic effective core potential model, the structure parameters and properties are reported. It is found that NO3- coordinates to Np4+ as a bidentate ligand, and the NpN and NpO bonds are the shortest in Np(NO3)22+, while the binding energy of the Np(NO3)4 is the largest. The infrared spectra of Np(NO3)4 are calculated in the gas and liquid phase. Comparing with the available experimental data, the reliability of the calculation results in this work is confirmed.
Broadband circularly polarized high-gain antenna design based on linear-to-circular polarization conversion focusing metasurface
Authors: Li Tang-Jing  , Liang Jian-Gang  , Li Hai-Peng  , Niu Xue-Bin  , Liu Ya-Qiao  ,   Air and Missile Defense College, Air Force Engineering University, Xi'an 710051, China
Published: December 2020

A single-layer reflecting element is proposed based on the principle of linear-to-circular polarization conversion focusing metasurface, which can independently control the phases of x-polarized and y-polarized reflecting waves and operate in a broadband of 10-14 GHz. Following the generalized Snell's laws of reflection, a super cell is designed with a phase-gradient of -60 for x-polarized waves and 60 for y-polarized waves, and the simulation results show the well wideband anomalous reflection as expected. In the design of the multifunctional metasurface, the 1313 unit cells are used to satisfy the parabolic profile and the focal-distance-to-diameter ratio is set to be 0.5. The phase compensation for forming a constant aperture phase is provided by the individual reflected elements with different structure parameters and x-y=90 is used to realize polarization conversion. The designed sample is simulated in CST Microwave Studio and the results show that both of the x-polarized and y-polarized plane waves are well focused through the reflection of the focusing metasurface in a broadband of 10-14 GHz. Traditionally, multi-layer element is used to broaden phase coverage and bandwidth, the single-layer design in this paper greatly reduces the cost, processing difficulty and thickness of the lens. For further application, a linearly polarized Vivaldi antenna with a highest gain of 10 dB is located at the focal point of metasurface and the angle included between its polarization direction and x-axis is 45 in order to acquire right-handed circularly polarized reflecting wave. According to the reversibility principle of electromagnetic wave propagation, the spherical wave radiated by the feed antenna is converted into plane wave by the reflection of the focusing metasurface so that the antenna gain is remarkably enhanced. Simultaneously, the linearly polarized wave can be transformed into circularly polarized wave. Finally, the feed antenna and the metasurface are fabricated, assembled and measured. Numerical and experimental results are in good agreement with each other, which shows that the -1 dB gain bandwidth of the high-gain antenna is 24% (11-14 GHz) and the 3 dB axial ratio bandwidth is 29.8% (10-13.5 GHz). In addition, the gain at 12 GHz reaches a highest value of 19.6 dBic, and the aperture efficiency is more than 54%. The good performances indicate that the proposed broadband high-gain circularly polarized antenna has a well promising application in various communication systems. It is worth noting that the horizontally polarized, vertically polarized, right-handed circularly polarized and left-handed circularly polarized high-gain antenna can be realized with the rotation of feed antenna. In this case the idea is more versatile and valuable for designing the polarization reconfigurable antenna systems.
A wideband coding reflective metasurface with multiple functionalities
Authors: Chen Wei  , Gao Jun  , Zhang Guang  , Cao Xiang-Yu  , Yang Huan-Huan  , Zheng Yue-Jun  ,   School of Information and Navigation, Air Force Engineering University, Xi'an 710077, China;,   Military Representative Office at No. 765 Factory, Baoji 721006, China
Published: December 2020

A controllable wideband multifunctional reflective metasurface is presented. First of all, a polarization-rotating unit cell is proposed by combing micro-electromechanical system (MEMS) technology with reflective metasurface design. The proposed unit cell is characterized by wideband, low loss and controllable properties. Each unit cell is integrated with two MEMS switches. When the two switches operate in different states, the unit cell shows different responses to plane wave incidence, and the corresponding working states can be denoted by 0 or 1. It is worth noting that a 180 degree reflection phase difference is generated for the two working states. Then, the proposed unit cell is periodically arranged to construct a metasurface. Based on different coding matrixes, multiple functionalities can be obtained by using the proposed metasurface. When all the unit cells are controlled to operate in on- or off-state, polarization-rotating function is obtained. Besides, the agility scattering field performance is also presented by using chessboard and random codings. A series of equations is derived to reveal the relationship between reflection coefficient of the unit cell and radar cross section (RCS) reduction of the chessboard reflective surface, which is also verified by full-wave simulations. Finally, four prototypes consisting of 576-cells, which correspond to the all 0, all 1, chessboard and random coding, are fabricated and measured. The measured results demonstrate that the proposed reflective metasurface shows polarization-rotating performance in a frequency range of 8.9-13.2 GHz when all unit cells operate in 0 or 1 state. The measured results of the chessboard and random coding metasurface manifest remarkable RCS reduction compared with the same size metal plane. Good agreement between simulations and measurements is obtained. Owing to the ability to control polarization and beam shape of the reflected wave dynamically, the proposed reflective metasurface has potential applications in the field of intelligent stealth.
Low frequency band gap characteristics of double-split Helmholtz locally resonant periodic structures
Authors: Jiang Jiu-Long  , Yao Hong  , Du Jun  , Zhao Jing-Bo  , Deng Tao  ,   Aeronautics and Astronautics Engineering College, Air Force Engineering University, Xi'an 710038, China;,   Science of College, Air Force Engineering University, Xi'an 710051, China;,   Xi'an Flight College of Air Force, Xi'an 710306, China
Published: December 2020

A double-split Helmholtz periodic structure with the characteristic of local resonance is designed and constructed in this paper. The double-split periodic structural cell which can be divided into internal and external cavities is adopted in structure. In such a kind of structure, the resonating area is remarkably expanded while the inner cavity is continuously enlarged. Thus, a satisfactory feature of low frequency resonance can be obtained. At the same time, the adjustability of band gap is achieved by the designed adjustment of the arc length of the inner cavity, therefore, the effect of sound insulation in a specific low frequency band can be achieved. In the analyses of the mechanism and factors of the generation of low frequency band gap, the mathematical model of the upper and lower limits of the band gap is established by using the electric circuit analogy. And some comparative analyses between the methods of electric circuit analogy and finite element method are carried out. The result suggests that a satisfactory feature of low frequency band gap is presented, and the first band-gap ranges from 86.9 Hz to 138.2 Hz. The low frequency band gap can be influenced by the arc length of inner cavity, the space between inner and outer cavities, and the interaction of the structural cells in the periodic arrangement. The longer the arc length of the inner cavity, the lower the low frequency band gap will be; the longer the distance between inner and outer cavities, and the higher the frequency of band gap, the worse the low frequency effect will be; the lower limit of low frequency band gap cannot be influenced by reducing the space between individual structures, on the contrary, the width of low frequency band gap can be sharply increased. Plenty of practical and theoretical support in the field of low frequency noise reduction is offered in the research.
Theoretical improvement on the determination of effective elasticity charges for charged colloidal particles
Authors: Wang Lin-Wei  , Xu Sheng-Hua  , Zhou Hong-Wei  , Sun Zhi-Wei  , Ouyang Wen-Ze  , Xu Feng  ,   School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China;,   Key Laboratory of Microgravity, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China;,   School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

According to the existing shear modulus-pair potential relationship model for colloidal crystal comprised of highly charged colloidal particles, the calculated shear moduli of colloidal crystals are much larger than the measured values by the torsional resonance spectroscopy (TRS). Moreover, by using the relationship model, the effective surface charge of colloidal particles, obtained by fitting values of shear moduli measured by TRS (effective elasticity charge), is smaller than that obtained through the experimental method of conductivity-number density relationship (effectively transported charge). So far there has been no practical explanation to this discrepancy. Our analysis shows that this discrepancy is because the existing relationship model is for the perfect crystals and does not include the defects such as voids which can result in the decrease of mechanical properties of materials. The existing shear modulus-pair potential model will be improved by introducing the effect of voids, which is inspired from the Gibson-Ashby model in the study of cellular solid. The Yukawa potential, which considers Coulomb repulsions between colloidal particles and is usually used in the model expressions, will be substituted by Sogami-Ise potential, which considers a long-range attraction in addition to that Coulomb repulsions and accepts the existence of voids inside the colloidal crystals. For five different kinds of highly charged colloidal particles, the shear moduli with different volume fractions are measured by TRS. Then the fitted effective surface charges using the original and improved model respectively are compared with each other. It can be concluded that the effective elastic charge obtained by the improved model is more suitable and much closer to the renormalized charge obtained from Alexander's method. It is also clear that neither the effectively transported charge nor the Alexander's renormalized charge can be used to evaluate the shear moduli of colloidal crystals with voids inside. These results can also let us further understand and use the effective surface charge in the colloid studies.
Comparative study of irradiation swelling in monocrystalline and polycrystalline silicon carbide
Authors: Zang Hang  , Huang Zhi-Sheng  , Li Tao  , Guo Rong-Ming  ,   School of Nuclear Science and Technology, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Silicon carbide (SiC) is considered as one of the most promising structural and coating materials for advanced nuclear applications, due to its low neutron capture cross section and excellent irradiation resistance. The difference in swelling behavior between monocrystalline and polycrystalline SiC is experimentally investigated by heavy ion irradiation at room temperature (RT). In this work, single crystal hexagonal (6H) SiC and polycrystalline chemically vapor-deposited (CVD) SiC are irradiated by 1.5 MeV Si ions with the fluences of 11014-21016 cm-2 and 11015-21016 cm-2, respectively, at RT. The step height of irradiation swelling is measured by a white light interferometer and the lattice expansion of the damage layer is characterized by using X-ray diffraction (XRD) spectrometry, in addition, the actual irradiation swelling is obtained by dividing the height of swelling step by the depth of damage layer. The XRD profiles show that the lattice expansion in the damage layer increases with the increase of irradiation fluence, and the new diffraction peak relating to the lattice structure of damage layer disappears in a fluence of 21015 cm-2, which means that the damage layer is completely amorphous at this time and the threshold dose of amorphization at RT in single crystal 6H-SiC is less than 0.8 dpa. The direct-impact model is used to fit the swelling step heights of CVD SiC and 6H-SiC irradiated by 1.5 MeV Si, and the swelling results show that the amorphization threshold dose of polycrystalline CVD SiC is larger than that of single crystal 6H-SiC. In the present work, three distinct stages are found in the heavy-ion irradiation swellings between monocrystalline and polycrystalline SiC. i.e., low-fluence region, intermediate-fluence region, and high-fluence region stage. 1) In the low-fluence region, the swellings are similar to each other, since the swelling is mainly contributed to by point defects in this region, and the micron sized grains in polycrystalline CVD SiC are of single crystal structure. 2) In the intermediate-fluence region, the irradiation swelling of the polycrystalline CVD SiC is smaller than that of the single crystal 6H-SiC, since the irradiation-induced amorphousness in polycrystalline CVD SiC is relatively hard to occur due to the existence of grain boundary in this region. 3) The irradiation swellings of 6H-SiC and CVD SiC are almost the same at the high-fluence region stage, since the irradiation swelling is caused by amorphization in this region, and the swelling depends on the difference between densities before and after irradiation. In addition, in the irradiation swelling analysis of SiC materials, XRD swelling measurement method is suitable for irradiation swelling induced by point defects, especially for neutron irradiation experiments.
Photoelectron characteristics of ZnSe quantum dots-sensitized mesoporous La-doped nano-TiO2 film
Authors: Ren Lun  , Li Kui-Ying  , Cui Jie-Yuan  , Zhao Jie  ,   State Key Laboratory of Metastable Materials Technology and Science, Yanshan University, Qinhuangdao 066004, China
Published: December 2020

In the paper, the core-shell ZnSe quantum dots (QDs)-sensitized mesoporous La-doped nano-TiO2 thin film is prepared by a direct adsorption method. Photoelectron characteristics, photogenerated carriers transport mechanism, and microstructure of the QDs-sensitized nano-TiO2 thin film are probed via the stationary surface photovoltaic (SPV) and the transient photovoltaic technologies, supplemented by the Brunauer-Emmet-Teller adsorption isotherm technique, scanning electron microscope, Fourier transform infrared (FT-IR) absorption spectrum, and ultraviolet-visible (UV-VIS) absorption spectrum. The experimental results confirm that the surface of the nano-TiO2 film is covered with the ZnSe QDs with smaller particles by a chemical absorbing way, resulting in denser composite film of the QDs and the mesoporous nano-TiO2 than the nano-TiO2 film. In our experiment, the adsorption quantity of ZnSe QDs on nano-TiO2 film can be controlled effectively. The results show that ligand L-Cys capped at the outer layer of ZnSe QDs plays an important role in the sensitization process. Specifically, the peak of SH in the ligand disappears at 2552 cm-1 in the FT-IR spectrum of the ZnSe QDs capped by the ligand as a stabilizer. This indicates that the SH bond is broken. In the meantime, the peak of the CS stretching vibration in the ligand shifts from 638 cm-1 to 663 cm-1 due to the formation of ZnS bond. These imply that the core-shell ZnSe/ZnS/L-Cys QDs are obtained. On the other hand, according to the peak of COOH stretching vibration disappearing at 1600 cm-1 in the FT-IR spectrum of the core-shell QDs-sensitized mesoporous nano-TiO2 film, the unsaturated Ti atoms on the surface of the TiO2 film are bonded to carboxy groups from the ligand capped at the QDs. That is, the ligand acts as a bridge between the QDs and the nano-TiO2 film for achieving the sensitization. Some excellent photovoltaic characteristics of the composite film are found as follows. 1) The SPV responses of the QDs-sensitized film appear in a wavelength region of 300 nm to 800 nm (UV-VIS-Near-IR), causing the region of SPV response to enlarge about 200 nm over that of the ZnSe QDs, and 400 nm over that of the nano-TiO2 thin film. 2) The QDs-sensitized film displays an n-type photovoltaic characteristic that is different from that of the QDs. This may be more favorable for transferring those carriers from the film surface to the photo-anode material. 3) Both the separation rate and the diffusion length of photogenerated electron-hole pairs are obviously increased, and the lifetime of free charge carriers in the ZnSe QDs-sensitized film prolongs about an order of magnitude over that of the nano-TiO2 film and ZnSe QDs.
Effect of Mo doping concentration on the physical properties of ZnO studied by first principles
Authors: Jia Xiao-Fang  , Huo Qing-Yu  , Zhao Chun-Wang  ,   College of Science, Inner Mongolia University of Technology, Hohhot 010051, China;,   Key Laboratory of Thin Films and Coatings of Inner Mongolia, Hohhot 010051, China;,   College of Arts and Sciences, Shanghai Maritime University, Shanghai 201306, China
Published: December 2020

The experimental results of red-shift and blue-shift in absorption spectrum of Mo-doped ZnO are in mutual contradiction, and this phenomenon has not been explained rationally so far. For explaining this phenomenon, we analyze the energy band structure, state density, and absorption-spectrum distributions for each of Zn0.9583Mo0.0417O, Zn0.9375Mo0.0625O and Zn14Mo2O by first-principles calculation. The results show that within a limited doping amount range of 2.08 at%-3.13 at%, the higher Mo doping amount results in higher doping system volume, higher formation energy, lower system stability, and more difficult to dope. Meanwhile, all doping systems are converted into n-type degenerate semiconductors. Compared with the band gap of pure ZnO, the band gap of each doping system becomes narrow and the absorption spectrum shows red-shift. The higher the Mo doping amount, the weaker the narrowing of band gap becomes and the weaker the red-shift in absorption spectrum as well as the lower the electronic effective mass and the lower the electronic concentration; the lower the electronic mobility, the lower the electronic conductivity is; the lower the electronic magnetic moment is. The Curie temperature of doping system can reach a temperature higher than room temperature.
Femtosecond laser pulse energy accumulation optimization effect on surface morphology of black silicon
Authors: Tao Hai-Yan  , Chen Rui  , Song Xiao-Wei  , Chen Ya-Nan  , Lin Jing-Quan  ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China;,   Science and Technology on Electro-Optical Information Security Control Laboratory, Tianjin 300308, China
Published: December 2020

Arrays of sharp conical spike microstructures are created by repeatedly irradiating silicon surfaces with focused femtosecond laser pulses in SF6. The absorbance of light is increased to approximately 90% in a wavelength range from the near ultraviolet (0.25 m) to the near infrared (2.5 m) by the microstructured silicon surface. The microstructured surface presents pitch-black because of enhanced absorption with a broad wavelength range, which is called black silicon. The unique microstructure morphology of black silicon surface formed by femtosecond laser can also bring a lot of other surface functions, for example, self-cleaning and field emission. These functions make black silicon highly desirable in solar energy, detectors and other fields. Therefore, the forming mechanism and conditions of fabrication optimization for black silicon microstructure have always been the focus of research. In our work, the sample is moved by motor-controlled stage while the laser beam is fixed. In the case of laser beam scanning, arrays of sharp conical spikes on the silicon are manufactured in 70 kPa SF6. The aim of the experiment is to find how to optimize the distribution of the laser energy in a number of laser accumulation pulses (the combination of single pulse energy and pulse number) to control the surface morphology of the black silicon. Experimental results show that there appears a bottleneck effect of morphology size growth with the increase of laser irradiation (improving the single pulse energy or increasing pulse accumulation number). Excessive energy accumulation brings no extra effect on optimizing and controlling of microstructure morphology on the surface. Based on theoretical results obtained from a physical model we proposed, we find that the reason for this phenomenon is that the microstructure morphology induced by former sequence pulse modulates the laser energy absorption of current laser pulse, and changes the laser ablation efficiency of the current pulse. According to this physical mechanism, we propose a new way of optimizing surface morphology, with fixing the total laser irradiation energy. And the size and distribution of surface morphology can be achieved by optimizing the distribution of the laser energy in a number of laser accumulation pulses. This approach can not only improve the efficiency of silicon surface preparation of microstructures but also reduce the surface defects and damage. Furthermore, the proposed method can reduce the energy consumption in the process of femtosecond machining. It is of great significance for the engineering application of black silicon.
Intermuscular coupling characteristics based on variational mode decomposition-coherence
Authors: Du Yi-Hao  , Qi Wen-Jing  , Zou Ce  , Zhang Jin-Ming  , Xie Bo-Duo  , Xie Ping  ,   Key Laboratory of Measurement Technology and Instrumentation of Hebei Province, Institute of Electric Engineering, Yanshan University, Qinhuangdao 066004, China;,   Department of Rehabilitation Medicine, the No. 281 Hospital of Chinese People's Liberation Army, Qinhuangdao 066100, China
Published: December 2020

Intermuscular coupling is defined as the interaction, correlation and coordination between different muscles during the body movement, which could be revealed by the synchronization analysis of surface electromyogram (sEMG). The multiscaled coherence analysis of sEMG signals could describe the multiple spatial and temporal functional connection characteristics of intermuscular coupling, which could be helpful for understanding the multiple spatial and temporal coupling mechanism of neuromuscular system. Furthermore, the coupling characteristics in frequency band of sEMG generally reflect the functional connection between muscles which relate to motion control and coordinative mechanism of the central nervous system (CNS).
In this paper, we combine variational mode decomposition (VMD) and intermuscular coherence (IMC) analysis to propose a new method named VMD-IMC to quantitatively describe the muscular coupling characteristics in the corresponding frequency bands. First, sEMG data of flexor digitorum superficialis (FDS), flexor carpi ulnaris (FCU) and extensor digitorum (ED) are recorded simultaneously from twenty healthy subjects (253 years) who perform the designed grip task at sustained 20% maximum voluntary contraction under the static load. Then, the VMD approach is employed to adaptively decompose sEMG into several intrinsic mode functions to describe the information about different time-frequency scales. Furthermore, the coherence on different time-frequency scales between different sEMG signals is analyzed, and the significant coherent area index is calculated to quantitatively describe the functional coupling characteristics of the feature bands. And combining VMD with Hilbert transform, we calculate root mean square and mean instantaneous frequency (MIF) to describe the variations of energy and frequency of each muscle. The results show that coupling strengths increase with time, respectively, in beta (15-30 Hz) and gamma (30-45 Hz) band between two muscles (FDS vs FCU, FDS vs ED) during the sustained static force with low load. In addition, compared with the coupling between FDS and ED, the couplings between FDS and FCU in beta and gamma band under the condition of fatigue present more significant changes and similar trend in MIF variation with time. The obtained results reveal that the congenerous muscle is coordinated by CNS in a more synchronous way during the sustained isometric fatiguing contraction.
Interfacial properties and morphological evolution of liquid Ag film on the modified graphene
Authors: Zhao Zhen-Yang  , Li Tao  , Li Xiao-Yin  , Li Xiong-Ying  , Li Hui  ,   Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan 250061, China
Published: December 2020

The interfacial wettability and morphological evolution of liquid on a solid substrate, as natural phenomena, have received great attention in recent years. Although much work has been done to study this process, existing studies mainly focus on the wetting properties of water. Therefore, in this paper, we use molecular dynamics simulation method to study the interfacial phenomena of the nanoscale liquid silver on graphene, whose surface has been modified. By making different comparisons, such as Lennard-Jones (LJ) potential parameters, the surface structures of substrates, the thickness values of films and the shapes of films, the influences of these variables on wetting properties of liquid silver on graphene are studied. The results show that the dewetting of liquid silver occurs on graphene, implying that the wettability of liquid silver is weak, and that the potential parameters, the surface structure of substrates, the thickness of film and the shape of film have great influences on the wettability and morphology evolution of film: the change of these factors can affect the dewetting properties of liquid silver, which is evident by the detachment time and detachment speed. With the increase of LJ potential parameters, the detachment time is larger while the contraction speed and the detachment speed are smaller. Compared with the detachment times on different carbon-based substrates, the detachment time is small on the pillared graphene, followed by the vertical carbon nanotube, and the detachment time is large on the graphene. With increasing the thickness of the film, the detachment time becomes larger. The detachment time of the circle film is smaller than those of the regular hexagon film and square film, manifesting that the films with smooth boundary are beneficial to separating from the substrate. Moreover, by setting a system of two liquid films, we study the formation of silver bridge of two films and the fracture or fusion of the bridge. When two liquid films initially contact each other, the liquid bridge forms. However, the growth behaviors of liquid bridges are different from each other, some liquid bridges become slim and finally fractures, other liquid bridges do not fracture and help two droplets form one bigger drop. These different behaviors mainly depend on the size of film. This study is very valuable for well understanding the superhydrophobic surfaces and the morphological evolutions of Ag films on the graphene. Furthermore, these findings can provide an effective method to control the dewetting behavior of liquid Ag and the fracture or fusion of the two liquid drops by tuning the size of the films.
Phase shift chirped fiber Bragg grating based distributed strain and position sensing
Authors: Pei Li  , Wu Liang-Ying  , Wang Jian-Shuai  , Li Jing  , Ning Ti-Gang  ,   Key Laboratory of All Optical Network and Advanced Telecommunication Network of EMC, Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

A corresponding peak appears on the transmission spectrum, when the micro-strain is induced in a chirped fiber Bragg grating (CFBG). The center wavelength of the peak is sensitive to the location and magnitude of the strain, thus, the CFBG can be used in distributed strain and strain-points precise position sensing. The depth and center wavelength of the peak are determined by the magnitude and location of the strain. The cascaded CFBGs under different center wavelengths can realize the distributed strain and strain-point precise positioning. Considering the fact that the depth and center wavelength of the peak are related to the magnitude and location of strain, a theoretical model is established with V-I transmission matrix formalism. Theoretically, cascaded CFGBs can realize accurately the positioning of micron-scale. Experimentally, two CFBGs are cascaded and a sensitivity of 0.19 pm/ is obtained. The proposed precise position sensing can be applied to the fields of advanced manufacturing, precision machining, aerospace, railway-system, etc.
Research on improving detection sensitivity to acoustic based on coherent-OTDR distributed fiber-sensing system
Authors: Chen Wen-Jie  , Jiang Jun-Feng  , Liu Kun  , Wang Shuang  , Ma Zhe  , Zhang Wan-Chen  , Liu Tie-Gen  ,   School of Precision Instrument and Opto-Electronics Engineering of Tianjin University, State Key Laboratory of Hydraulic Engineering Simulation and Safetyof Tianjin University, Key Laboratory of Opto-electronics Information Technology Ministry of Education, Institue of Optical Fiber Sensing of Tianjin University, Tianjin Optical Fiber Sensing Engineering Center, Tianjin 300072, China
Published: December 2020

Coherent-OTDR technology is one of acoustic distributed fiber-sensing systems. Because of the advantages of anti-electric magnetic field interference, anti-corrosion and flexibility, it has been attracting more and more interest. Because the sound pressure is weak, the strain generated on the fiber is tiny and the sensitivity of the sensing system is low. Although many research has been made on expanding measuring distance and improving response frequency, the acoustic signals in the experiments are always replaced by PZT's mechanical stretching. In this work, a device for increasing sensitivity for acoustic in the passive acoustic detection system based on coherent optical time domain reflection (C-OTDR) is promoted. A way of improving sensitivity partly based on a thin-walled corrugated tube was promoted. The thin-walled corrugated tube was used as the element to transmit the energy of acoustic into the vibration of fiber.
In section 2, a mathematical model of sensing based on corrugated tube was established. Theoretical result shows that the vibration of fiber is mainly caused by the tube movement along the axis direction. And it also shows the linear relationship between the vibration and the sound pressure. The sensitivity of the improved sensing devices is calculated and a computational formula for sensitivity calculating are also given.
In section 3, the C-OTDR acoustic distributed fiber-sensing systems are set up. Fiberring and three types of thin-walled corrugated tubes are used for acoustic sensing. The minimum detection sound pressure level reaches 60.1 dB and the phase sensitivity reaches 2.975 rad/Pa. The experimental phase sensitivity of different sensing devices with different parameters change similarly to the theory results. The experimental results show that the way of improving sensitivity and the mechanical model for calculating sensitivity are effective. This research provides theoretical and experimental basis for further development of distributed optical fiber sensing.
Readout method for two-dimensional multi-wire proportional chamber
Authors: Wen Zhi-Wen  , Qi Hui-Rong  , Wang Yan-Feng  , Sun Zhi-Jia  , Zhang Yu-Lian  , Wang Hai-Yun  , Zhang Jian  , Ouyang Qun  , Chen Yuan-Bo  , Li Yu-Hong  ,   School of Nuclear Science and Technology, University of Lanzhou, Lanzhou 730000, China;,   State Key Laboratory of Particle Detection and Electronics, Beijing 100049, China;,   Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

A two-dimensional multi-wire proportional chamber detector based on 3He gas is developed for meeting the multifunctional reflection spectrum detection requirements of China Spallation Neutron Source (CSNS). Based on the previous researches in our laboratory, three different wire structures are studied for optimizing the wire readout structure of the two-dimensional multi-wire proportional chamber detector, and the performances of the detectors are measured by two readout methods:the center of gravity readout method and the digital readout method in this paper. The selected method could satisfy the requirement of multifunctional reflection spectrum instrument. Finally, the results indicate that the position resolution and the imaging capability obtained by using the center of gravity readout method should be better than by using the digital readout method. The position resolution could reach to about 160 m by using the center of gravity readout method. While the position resolution of the detector could be obtained to be about 400 m by using the digital readout method. Re-designed and compared with each other are the three different wire structures:1.5 mm of the anode wire pitch and 4 mm of the readout strip pitch with the center of gravity readout method, 1.5 mm of the anode wire pitch and 2 mm of the readout strip pitch with the digital readout method. Both of the optimized designs of the wire structure could meet the requirement of the position resolution for the reflection spectrum device.