bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical model of phase-matching angles for KDP crystals and its verification analysis
Authors: Zhang Yang  , Li Ting  , Yuan Xiao-Dong  , Xiong Zhao  , Xu Xu  , Ye Lang  , Zhou Hai  , Zhang Bin  ,   College of Electronics and Information Engineering, Sichuan University, Chengdu 610065, China;,   Research Center of Laser Fusion, China Academy Engineering Physics, Mianyang 621900, China
Published: December 2020

In final optics assembly of high-power solid-state laser, in order to improve the third harmonic generation efficiency, the accurate assembly and calibration of ultra-thin KH2PO4 (KDP) crystal with large-aperture is one of the key technologies to realize inertial confinement fusion. In order to meet the requirements for high efficiency and precision crystal of online installation, it is necessary to measure crystalline phase matching angle for achieving the highest third harmonic conversion efficiency of high power laser. In this paper, for the third harmonic conversion by ultra-thin type Ⅰ/Ⅱ KDP crystals with large-aperture, the relationship between phase matching angles at different locations on the crystal is obtained according to the nonlinear optical properties of the crystal. Based on the analysis of the propagation path of the laser beam in the crystal, the relationship among the crystal surface shape, the phase matching angle and the best deflection angle is given. On this basis, the theoretical model for phase-matching angle of type Ⅰ/Ⅱ KDP crystal is proposed, and verified by the experimental results. The results show that the difference in phase matching angle between the prediction values and the experimental results is within 10.0 rad, showing that the theoretical model for phase-matching angles of type Ⅰ/Ⅱ KDP crystals is valid. This model provides a simple and efficient prediction method to obtain the phase matching angle distribution in full aperture of KDP crystal.
“Inverted-image” frequency chirp induced by self-phase modulation in highly noninstantaneous medium
Authors: Hong Wei-Yi  ,   School of Information and Optoelectronic Science and Engineering, Laboratory of Nanophotonic Functional Materials and Devices, South China Normal University, Guangzhou 510006, China
Published: December 2020

Nonlocal nonlinearity is one of the hottest topics in the nonlinear optics and even the nonlinear science. In this paper, the frequency chirp induced by the self-phase modulation (SPM) in a high noninstantaneous medium is investigated. It is found that the temporal distribution of the SPM-induced chirp can be approximated by the “inverted image” of the pulse intensity in the highly noninstantaneous limit. Moreover, this property does not depend on the envelope of the pulse. By using these properties, the temporal characteristics of the pulse propagation in a highly noninstantaneous medium is analyzed.
Influences of temperature, humidity and pressure on the attenuation characteristics of laser beam in water
Authors: Shi Jiu-Lin  , Guo Peng-Feng  , Huang Yu  , Qian Jia-Cheng  , Wang Hong-Peng  , Liu Juan  , He Xing-Dao  ,   Key Laboratory of Nondestructive Test (Ministry of Education), Nanchang Hangkong University, Nanchang 330063, China
Published: December 2020

In this paper, the attenuation characteristics of 532 nm laser beam in water under different atmospheric conditions (temperature, humidity, air pressure) are investigated experimentally. Experimental results show that the attenuation coefficient of laser beam in water is significantly influenced by the atmospheric environment. The attenuation coefficient decreases with the increase of air pressure, and increases with the increase of temperature. The maximum value of attenuation coefficient of light appears in the case of high temperature and low air pressure, while the minimum value appears in the high air pressure and low temperature. The maximum attenuation coefficient of laser in water is about three times the minimum value. The mechanisms of these phenomena are discussed. These results are valuable for Brillouin lidar to achieve the remote sensing of ocean.
A robust localization method for source localization based on the auto-correlation function of wide-band signal
Authors: Zhang Tong-Wei  , Yang Kun-De  , Ma Yuan-Liang  , Wang Yong  ,   National Deep Sea Center, Qingdao 266061, China;,   College of Marine, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

It is very difficult to estimate the relative arrival delay of the eigenrays for an unknown source in shallow water. The effects of a source position changing in the neighborhood and sound speed profile perturbation on arrival time of eigenvays are similar. In this paper, we present a robust localization method based on the auto-correlation function of wide-band signal of single hydrophone. By designing neighboring location constraints, a weighting function is constructed to change the peak cross-interference of the auto-correlation function to useful information that is conducible to the improving of targeting performance. In this method there is no need to estimate the relative arrival delay of the eigenray. Computer simulation shows that the robust method can achieve better localization performance, and even has tolerences of environment mismatch and searching grid mismatch. The performance of the robust method is validated through the broad-band data collected on a vertical line array during the Shallow Water 2006 experiments.
Analysis of waveguide time-frequency based on Warping transform
Authors: Lu Li-Cheng  , Ma Li  ,   Key Laboratory of Underwater Acoustic Environment, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China;,   Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Sound propagation in underwater will induce dispersion due to the natural sea waveguide, and then it will degrade the results of the signal processing. Based on the waveguide invariant, a general warping transform is presented. This warping transform could extract the waveguide mode dispersion curve and remove the effect of the waveguide dispersion. Results from the simulation and experiment show that the transform woks well.
Characteristics on drag reduction of bionic jet surface based on earthworm's back orifice jet
Authors: Gu Yun-Qing  , Mou Jie-Gang  , Dai Dong-Shun  , Zheng Shui-Hua  , Jiang Lan-Fang  , Wu Deng-Hao  , Ren Yun  , Liu Fu-Qing  ,   College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014, China;,   Zhijiang College, Zhejiang University of Technology, Hangzhou 310024, China
Published: December 2020

In order to reduce the drag reduction of the fluid on the solid wall, based on the biology characteristics of earthworm, the earthworm's back orifice jet characteristic is analyzed. The bionic jet surface is modeled by imitating the earthworm's back orifice jet, and the SST k-ω turbulent model is used for numerically simulating the drag reduction characteristics of bionic jet surface, simultaneously the result of the numerical simulation is verified experimentally. On this account, the drag reduction mechanism of bionic jet surface is studied based on the imitation of the earthworm's back orifice jet. The results show that under certain conditions, the drag reduction characteristics of bionic jet surface for imitating the earthworm's back orifice jet are very effective. At the same angle of jet direction, the drag reduction rate increases with the increase of jet velocity; at the same jet speed, the drag reduction rate presents a tendency to increase after the first decrease with increasing the angle of the jet direction. The maximum drag reduction rates obtained from numerical simulation and experimental measurement both on condition that jet velocity is 1 m·s-1 and the angle of jet direction angel is -30°, are 8.69% and 7.86%, respectively. Jet surface changes the original boundary layer structure in smooth wall, thereby effectively controlling the wall boundary layer, and reducing the wall shear stress and also the velocity of the wall boundary layer.
Mode and hysteresis of laminar methane/oxygen inverse diffusion flame
Authors: Li Xin-Yu  , Dai Zheng-Hua  , Xu Yue-Ting  , Li Chao  , Wang Fu-Chen  ,   Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, East China University of Science and Technology, Shanghai 200237, China;,   Shanghai Engineering Research Center of Coal Gasification, East China University of Science and Technology, Shanghai 200237, China
Published: December 2020

Flame modes and liftoff hysteresis of the methane/oxygen inverse diffusion flame (IDF) are experimentally studied in still air. The effects of gas velocity on flame mode and liftoff hysteresis are investigated by changing the gas flow rate, and the influences of gas velocity on OH* distribution in different modes of flame are investigated using an ultraviolet camera. The results show that methane velocity, oxygen velocity and history of the flame mode are the key factors in determining the flame mode. Flame mode regimes are identified according to the three factors. The OH* profile along the axis of the nozzle in the IDF indicates that the reaction zone is narrow in fuel rich condition and broad in fuel lean condition. The hysteresis characteristics of the IDF are significantly influenced by the coaxial methane velocity. With the increase of coaxial methane velocity, the liftoff velocity and attachment velocity of the IDF decrease linearly, while the transition velocity increases linearly from partly premixed flame to IDF.
First-principles calculations of the diffusion behaviors of C, N and O atoms in V metal
Authors: Yang Biao  , Wang Li-Ge  , Yi Yong  , Wang En-Ze  , Peng Li-Xia  ,   School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China;,   State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Mianyang 621010, China;,   Science and Technology on Surface Physics and Chemistry Laboratory, CAEP, P. O. Box 718-35, Mianyang 621907, China
Published: December 2020

Based on the density functional theory, the diffusion behaviors of C, N and O atoms in V metal are studied by using the first-principles calculation method. Firstly, the site occupations of C, N and O atoms in the interstitials of the bcc V lattice are discussed. The interactions of interstitial C, N and O atoms with V lattice are analyzed, and the influence of the electronic structure on the interaction is explored. The study results show that C, N and O atoms are more stable in octahedral interstice of V metal, and a relatively strong bonding interaction is formed between their 2p-electron and the 3d-electron of V metal. The diffusion barriers of C, N and O atoms are 0.89 eV, 1.26 eV and 0.98 eV, respectively. Thus, the expressions of their diffusion coefficients are obtained. Finally, the diffusion coefficients of C, N and O atoms are compared by the Arrhenius plot. Their diffusion coefficients are calculated at 500-1100 K, and the calculation results are consistent with experimental values.
Preparation of the high-quality highly (100) oriented diamond films with controllable growth
Authors: Liu Cong  , Wang Jian-Hua  , Weng Jun  ,   Key Laboratory of Plasma Chemical and Advanced Materials of Hubei Province, Wuhan Institute of Technology, Wuhan 430073, China;,   Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

The high-quality highly (100) oriented diamond films each with controllable surface morphology, quality, orientation, and growth rate are prepared at low pressure by microwave plasma chemical vapor deposition. The results show that there is a coupled effect between substrate temperature and methane concentration on the growth of (100) oriented diamond films. The substrate temperature should be increased with increasing the methane concentration in order to obtain similar surface morphologies. When the methane concentration is 3.0%, the results indicate that there are five states for the orientation change with the substrate temperature increasing from 740 ℃ to 1100 ℃, and the diamond films with (100) orientation can be deposited at the substrate temperatures ranging from 860 ℃ to 930 ℃. Moreover, the quality and growth rate of each of (100) oriented diamond films are proportional to the substrate temperature and methane concentration, respectively. In order to obtain the high-quality highly (100) oriented diamond films, the substrate temperature and methane concentration should be both appropriate.
Investigation of atom-attaching process of three-dimensional body-center-cubic dendritic growth by phase-field crystal model
Authors: Guo Can  , Wang Jin-Cheng  , Wang Zhi-Jun  , Li Jun-Jie  , Guo Yao-Lin  , Tang Sai  ,   State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

On the basis of the Gaussian kernel phase field crystal model (PFC), we propose a modified PFC model. The atom-attaching process of three-dimensional body-center-cubic (BCC) dendritic growth is examined by using the modified PFC model. Our simulations indicate that in the process of the morphology evolution from regular dodecahedron to dendrite shape, the nucleation position of new layer is transferred from the center of {110} planes into the region of {110} plane near the tips, and then the BCC dendritic morphology is obtained. In the process of dendritic growth, first, new solid atom absorption takes place near dendrite tips, then liquid atoms start to grow up on the existing solid phase rapidly. After the dendrite tips are completely occupied by new atoms, new nuclei begin to form again. Increasing the initial atom density n will increase the velocity coefficient C and the anisotropy of C.
Optically tuned wideband terahertz wave amplitude modulator based on gold-doped silicon
Authors: Tian Wei  , Wen Qi-Ye  , Chen Zhi  , Yang Qing-Hui  , Jing Yu-Lan  , Zhang Huai-Wu  ,   State Key Laboratory of Electronic Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China;,   National Key Laboratory of Science and Technology on Communication, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

In this paper, we present a broadband terahertz wave amplitude modulator based on optically-controlled gold-doped silicon. Gold dots with a diameter of 40 μm are used as a dopant source. Experimental results indicate that interstitial Au atoms provide effective recombination centers for photo-generated electron-hole pairs in Si body, leading to a significant decrease of the minority carrier lifetime from more than 10 μs to about 110 ns. Dynamic modulation measurement at 340 GHz carrier shows a modulation depth of 21% and a maximum modulation speed of 4.3 MHz. This modulator has advantages such as wideband operation, high modulation speed, polarization insensitivity, and easy manufacture by using the large-scale integrated technology, and thus can be widely used in terahertz technology.
A real-time axial activeanti-drift device with high-precision
Authors: Huo Ying-Dong  , Cao Bo  , Yu Bin  , Chen Dan-Ni  , Niu Han-Ben  ,   CAS Key Laboratory of Ultrafast Diagnostics, Xi'an Institute of Optics and Precision Mechanics of CAS, Xi'an 710119, China;,   Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China;,   State Key Laboratory of Precision Measurement Technology and Instruments, Tsinghua University, Beijing 100084, China
Published: December 2020

In a fluorescent nano-resolution microscope based on single molecular localization, drift of focal plane will bring an additional deviation to the accuracy of single molecular localization. Consequently, this will reduce the final resolution of the reconstructed image and cause image degradation. Therefore, it is vital to control the system drift to a minimum level as much as possible. In recent years, the anti-drift ways emerged in endlessly. In this paper we made a systematic study aiming at the method in which optical measurement and negative feedback control are used. The basic principle and its implementation of the system are analyzed, and possible error is also evaluated. Finally, the precision of the system is tested experimentally. With this device, axial drift can be detected and corrected automatically in time, and the axial anti-drift accuracy as high as 9.93 nm can be achieved, which is one order higher than that of the existing commercial microscopies.
Detection of significant external trend in long-term air temperature records
Authors: Huang Yan  , Yuan Nai-Ming  , He Wen-Ping  ,   Chinese Academy of Meteorological Sciences, Beijing 100081, China;,   National Climate Center, China Meteorological Administration, Beijing 100081, China
Published: December 2020

Long-term historical air temperature records of four stations from Global Historical Climatology Network-Daily are analyzed in this study. By applying detrended fluctuation analysis of the second order to the monthly anomalies, different long-term correlations are found in different time periods at both the maximum and minimum temperatures, which indicate the existence of internal stochastic trend. By generating surrogate data with the same long-term correlations and data length, internal stochastic trends are estimated with confidence probability intervals of 95% and 99% provided. We find the longer data length, the shorter confidence probability interval we have; the stronger long-term correlation, the wider confidence probability interval is obtained. By comparing the temperature trends observed from the historical temperature records with the corresponding confidence probability intervals of the internal stochastic trends, significant external trends can be detected. We find that except for the maximum temperature in SAGINAW MBS INTL AP, temperatures from the four stations all show significant external trends when long historical data (>100 years) are considered. However, if only the past 30 years are taken into account, the observed trends are still not strong enough to exceed the confidence probability interval. Although we cannot exclude the existence of external trends, considering the possible influence from internal stochastic trends, the external trends are not significant. From this detection method, we can judge, in the context of global warming, whether an observed trend is significantly induced by external forcing. Therefore, it is useful for our further study targeting the internal (external) climatic impact factors.
Impulsive synchronization and initial value effect for a memristor-based chaotic system
Authors: Wu Hua-Gan  , Chen Sheng-Yao  , Bao Bo-Cheng  ,   School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China;,   School of Information Science and Engineering, Changzhou University, Changzhou 213164, China
Published: December 2020

Taking Chua's circuit with a smooth cubic flux-controlled memristor as an example, the impulsive control synchronization method for two identical memristor-based chaotic systems is studied. Based on the Lyapunov stability theory, the asymptotic stability condition for the impulsive synchronization of the memristor-based chaotic systems is given. Combining with the maximum conditional Lyapunov exponent spectrum of the error system, effects of the system initial values on the performances of impulsive synchronization are discussed, and corresponding simulation experiments are performed. Results indicate that using impulsive synchronization for the two identical memristor-based chaotic systems is feasible and effective with appropriate impulsive control parameters; the initial values of the memristor-based chaotic systems have some effects on the performances of impulsive synchronization, which can be inhibited by increasing the impulsive coupling strength.
Theoretical and empirical studies on group behaviors
Authors: Feng Chen-Jie  , Wang Peng  , Wang Xu-Ming  ,   School of Physic and Electrical Information, Ningxia University, Yinchuan 750021, China;,   Department of Physics, Beifang University of Nationalities, Yinchuan 750021, China;,   Ningxia Key Laboratory of Intelligent Sensing for Desert Information, Yinchuan 750021, China
Published: December 2020

Human behaviors are usually determined by some social and/or economic trend. In the past few years, many attempts have been made, in the field of complex scientific systems, to describe the dynamics of these behaviors quantitatively and have an accurate understanding of the corresponding mechanisms. In this paper, a generalized potential, that is, a migration desire function defined by the age of the migrating people, the migrating distance, and the so-called economic-population density of the emigration area, is proposed. It can be transformed into Hamilton-Jacobi equation by using a random dynamical method, Langevin equation, so that the decision-making behavior can be investigated, based on a statistic framework during a group migration process. By taking use of the multi-dimensional steepest descent method, the Hamilton-Jacobi equation is solved; the solution shows that the information entropy of the system varies, leading by a single peak, as the age of the migrating people increases. It also demonstrates that the second derivative of the migrating distance to the information entropy has a change of zero-crossing (which actually means a phase change). The third characteristic of the solution is that the information entropy follows another single peak as the economic-population density increases. A deeper analysis reveals the significance behind these findings and the corresponding mechanisms. So some new understandings of the group human behaviors can be obtained, and some worthy references can be provided for some related administrative offices.
Molecular dynamics simulation on cavitation bubble formation in canonical ensemble
Authors: Qiu Chao  , Zhang Hui-Chen  ,   Transportation Equipments and Ocean Engineering College, Dalian Maritime University, Dalian 116026, China
Published: December 2020

Research on cavitation is very significant for preventing cavitation erosion and for making use of bubbles effectively. Characteristics of cavitation in canonical ensemble are studied by molecular dynamics simulation. Effects of temperature and numerical density on cavitation are analyzed. Comparison with lattice Boltzmann method is also conducted. Simulation results indicate that the temperature and numerical density may affect cavitation remarkably. The formation of cavitation bubbles becomes unstable as the temperature increases, and even hard to occur. A lower numerical density makes cavitation bubble form easier. Moreover, as numerical density reduces, the temperature effect on cavitation becomes less.
Performance analysis of double incidence derivative metamaterial based on double-triangular structure
Authors: Tian Zi-Jian  , Li Wei-Xiang  , Fan Jing  ,   School of Mechanical Electronic & Information Engineeriing, China University of Mining and Technology (Beijing), Beijing 100083, China;,   Department of Electronics and Electrical Engineering, Nanyang Institute of Technology, Nanyang 473004, China
Published: December 2020

A new two-dimensional left-handed material based on double-triangled sructure is proposed. The simulation software HFSS is used to analyse the structure and its derivative structure. Results show that this type of structure can present left-handed properties when electromagnetic waves are incident on either perpendicularly or parallelly the plane of the substrate. And the general rule for this type structure is that: When the incident electromagnetic wave is in the perpendicular or parallel direction, and for each additional metal strip in the middle of the metal wires, the resonant frequency of the structure moves to higher frequencies around 0.5 or 4 GHz. These can be of reference values in further development of multi-dimensional left-handed material.
Propagation of non-uniform partially coherent beams in free space
Authors: Zhang Lei  , Chen Zi-Yang  , Cui Sheng-Wei  , Liu Ji-Lin  , Pu Ji-Xiong  ,   Department of Information Science & Engineering, Huaqiao University, Xiamen 361021, China
Published: December 2020

This paper introduces the concept of non-uniform partially coherent beams and investigates the spatial coherence change during beam propagation. Results show that non-uniform spatial coherence would make significantly changes during propagation, which is completely different from the classical beams. These changes have relationships with propagation distance, spatial coherence, and intensity distribution of the source. The points adjoining self-coherence area would mutate when beams propagate from the source; the high coherence area in the source may decrease after the beams propagate a short distance. Curves of spatial coherence would not overlap after propagation, while the spatial coherence tends to be uniform with increasing propagation distance.
Propagation properties of partially coherent Hermite-cosh-Gaussian beams in non-Kolmogorov turbulence
Authors: Liu Li-Hui  , Lü Wei-Yu  , Yang Chao  , Mai Can-Ji  , Chen De-Peng  ,   Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

Based on the extended Huygens-Fresnel principle and non-Kolmogorov spectrum, the analytical expressions for beam width and M2-factor of partially coherent Hermite-cosh-Gaussian beams going through a non-Kolmogorov turbulence are derived by means of second moments for the Wigner distribution function. Results show that the relative beam width and normalized M2-factor of partially coherent Hermite-cosh-Gaussian beams going through a non-Kolmogorov turbulence will increase when propagating in the turbulent atmosphere, and will be less affected by turbulent atmosphere with a larger beam, smaller coherent length, smaller Ch-part parameter. The relative beam width has a maximum value for increasing waist width, and normalized M2-factor has a minimum value for increasing waist width in a specific extent of coherent length. The relative beam width and normalized M2-factor both have maximum values according to the generalized power law, but decrease with increasing inner scale, and have nearly no change with increasing outer scale.
Observation of two-dimensional distributions of NO2 with airborne Imaging DOAS technology
Authors: Liu Jin  , Si Fu-Qi  , Zhou Hai-Jin  , Zhao Ming-Jie  , Dou Ke  , Wang Yu  , Liu Wen-Qing  ,   Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

The airborne imaging DOAS (differential optical absorption spectroscopy) method which can obtain two-dimensional distributions of trace gas is introduced in this paper. Based on this method, pollution source in a wide range of area can be found quickly, and a map of trace gas distribution can be obtained to study the pollutant diffusion tendency. In this paper we report the flying experiment over Tianjin and Tangshan. The airborne imaging system is introduced in detail and an image of two-dimensional NO2 distributions is obtained with a resolution of about 30 m×80 m. Combined with wind field data, the emission rate of a point source on the flight path is calculated to be 1570 kg/h.
Lamb vector in isotropic turbulence
Authors: Lee Chao  , Ran Zheng  ,   Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China
Published: December 2020

The Lamb vector is known to be of profound importance for fluid dynamics generally and for the dynamics of turbulence in particular. Based on the new developments of the statistical theory of isotropic turbulence, some new analytical indications are found that the Lamb vector has a contribution in the potential and solenoidal parts, which are almost equal for some typical parameters.
Numerical simulation and experimental study on drag reduction performance of bionic jet hole shape
Authors: Li Fang  , Zhao Gang  , Liu Wei-Xin  , Zhang Shu  , Bi Hong-Shi  ,   College of Mechanical and Electrical Engineering, Harbin Engineering University, Harbin 150001, China
Published: December 2020

Since the lateral jet in a horizontal stream can reduce the friction of bionic jet surface, a bionic jet surface model is established by using the SST k- turbulence model in numerical simulation of bionic jet surface for jet hole with different shape, and experimental verification of the numerical simulation results is done. Results show that, when the flow length and span length of the jet hole are kept constant, the drag reduction of the third model with broken-line jet hole is the best; the broken-line jet hole is simplified to an arc-shaped hole, when its radius r=35mm, the drag reduction rate increases with jet velocity; furthermore, the best drag reduction can be obtained when r = 4 mm, the maximum drag reduction rate is 9.51%. Drag reduction is produced because the jet fluid injected to the lateral mainstream field through jet holes, would change the flow field structure of boundary layer near jet surface, and make the thickness of the underlying viscous sublayer in boundary layer increase. As a result, the gradient of normal velocity, perpendicular to jet surface, is decreased, and thus reduces the wall shear stress. Meanwhile, the low speed jet fluid is blocked at the boundary layer, reducing the sweep of high speed fluid on the wall, which contributes to the drag reduction.
Theoretical study on the influence of rare earth doping on the electronic structure and magnetic properties of cobalt ferrite
Authors: Hou Yu-Hua  , Huang You-Lin  , Liu Zhong-Wu  , Zeng De-Chang  ,   School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, China;,   School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, China
Published: December 2020

Spinel ferrite is one of the very important magnetic materials, having the unique physical properties, chemical properties, magnetic properties, and electronic properties. CoFe2O4 is widely used due to their good electromagnetic properties. We have studied the electronic structure and magnetic properties of CoRE0.125Fe1.875O4 (RE = Nd, Eu, Gd)by first-principles plane-wave pseudopotential method based on density functional theory (DFT), combined with the generalized gradient approximation (GGA + U) in this paper. Results show that the lattice constants of the compunds CoFe1.875RE0.125O4 (RE=Nd, Eu and Gd) will decrease due to the decreasing ionic radius of RE as the atomic number increases. Their magnetic properties depend on the unpaired 4f electrons of RE3+ ions, and the net magnetic moment of CoFe2O4 will increase with Eu and Gd doping, mainly because there are more unpaired 4f electrons in Eu3+ and Gd3+. Thus the doping of Eu3+ and Gd3+ may have a greater impact on the magnetic properties of cobalt ferrite. The contribution from the doping of Nd is not remarkable on the magnetic properties, since the Nd3 + ion, having a larger ionic radius, could distort the crystal structure of CoFe2O4.
Speed of sound measurement from spontaneous Brillouin scattering
Authors: Zhang Ying  , Wang Sheng  , Zheng Xiong  , He Mao-Gang  ,   Key Laboratory of Thermo-Fluid Science and Engineering, Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

In order to overcome the problem of poor accuracy of resonant interferometer method in the measurement of thermodynamic sound speed and hypersound speed of liquids an experimental setup for measuring the sound speed of liquids is established based on the principle of spontaneous Brillouin light scattering. A Fabry-Perot interferometer is used to filter the scattered light and a data acquisition card as well as a photon counting head is used to detect and analyze the scattered light, then a data acquisition and analysis method of scattered light is presented. This method overcomes the limitation of the signal distortion in conventional Brillouin light scattering and increases the measuring accuracy of the sound speed of liquids remarkably. The sound speed of saturated liquid CCl4 is measured in the frequency range of 308.6 to 906.2 MHz at 298.15 K. Results agree well with the data reported in the literature, and show that the experimental method is feasible. In addition, the method for measuring the ultrasonic speed is proposed by adding several free spectral ranges to the measured Brillouin frenquency-shift. The ultrasonic speed of CCl4 measured is in the frequency range of 5406.1–5521.0 MHz. It is shown that the thermodynamic sound speed does not change with the sound frequency, while the hypersound speed increases with the increase of sound frequency and it is much greater than the thermodynamic sound speed, which proves the dispersion phenomena of CCl4.
Color tuning based on micro-nano structure and metal nanolayer
Authors: Chen Li-Cheng  , Zhang Dong-Xian  , Zhang Hai-Jun  , Wang Xu-Long-Qi  ,   Department of Optical Engineering, State Key Laboratory of Modern Optical Instruments, Zhejiang University, Hangzhou 310027, China
Published: December 2020

This article reports a novel color tuning technology based on micro-nano structure and metal nanolayer. On the basis of theoretical analysis, a color tuning model is established. Aluminum(Al) metal nanolayers are magnetron-sputtered on the surfaces of porour alumina (PA) templates with the pore-depths of 250 nm and 410 nm, and their pictures and reflective interference spectra show clearly green and red colors, respectively. These results indicate that different colors can be achieved just by controlling the pore-depth in PA templates. As comparison, a nanolayer of chromium(Cr) metal is magnetron-sputtered on the surface of PA template about 410 nm in pore-depth, the reflective interference spectra show that color tuning can also be achieved in the visible spectrum by changing the material and the thickness of the metal nanolayer. Moreover, a color pattern is further prepared based on mask and local sputtering method. Theoretical and experimental results validate the feasibility of this color tuning method.
Effects of CH3NH3I on fabricating CH3NH3PbI(3-x)Clx perovskite solar cells
Authors: Xia Xiang  , Liu Xi-Zhe  ,   Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China;,   Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy, Jilin University, Changchun 130012, China
Published: December 2020

Perovskite solar cell, which is prepared by using the organic-inorganic hybrid halide CH3NH3PbX3 (X = I, Cl and Br), receives widespread attention because of its solution processability and high photon-to-electron conversion efficiency. The highest reported photon-to-electron conversion efficiency is that using CH3NH3PbI(3-x)Clx as an absorber. It is reported that the diffusion length is greater than 1 micrometer in this mixed halide perovskite. The method most commonly used in preparing CH3NH3PbI(3-x)Clx film is the one-step pyrolysis method, which has a complex reaction mechanism. In this paper, we review the work about CH3NH3PbI(3-x)Clx perovskite, in which emphasis is put on the importance of the preparation process, and analyze the role of CH3NH3I in the one-step pyrolysis method for fabricating the CH3NH3PbI(3-x)Clxperovskite layer. Scanning electron microscope images show that CH3NH3I can improve the coverage and crystallinity of the perovskite layer for precursors in low CH3NH3I concentrations (CH3NH3I/PbCl2=2.0 and 2.5). For precursors in high CH3NH3I concentrations (CH3NH3I/PbCl2=2.75 and 3), this change is not obvious. X-ray photoelectron spectroscopy confirms the change of coverage, and indicates that the content of Cl in CH3NH3PbI(3-x)Clx will be less than 5% for precursors with high CH3NH3I concentrations (CH3NH3I/PbCl2>2.5). Perovskite solar cells based on CH3NH3PbI(3-x)Clx with different Cl dopant concentrations are studied by photoelectric measurements. Photocurrent density-photovoltage curves show that the performance of the devices increases with the increase of CH3NH3I concentration in precursors. And the incident-photon-to-current conversion efficiency (IPCE) measurements indicate that the devices fabricated by using precursors with high CH3NH3I concentration have a relatively high external quantum efficiency. These results imply that only CH3NH3PbI(3-x)Clx with very low Cl dopant concentration will be effective material for photovoltaic application. To further understand the difference between these devices during working condition, transient photovoltage/photocurrent measurements are carried out to investigate the carrier dynamics in the device. Transient photovoltage decay curves indicate that high Cl dopant concentration may decrease the photoelectron lifetime in CH3NH3PbI(3-x)Clx, and results in a relative low open-circuit photovoltage in the corresponding photovoltaic devices. The charge transport time in the devices of various Cl concentrations are studied by transient photocurrent decay method. CH3NH3PbI(3-x)Clx with low Cl dopant concentration has relative short transport time, which can avoid the recombination process and increase the charge collection efficiency.
Recent advances in planar heterojunction organic-inorganic hybrid perovskite solar cells
Authors: Wang Fu-Zhi  , Tan Zhan-Ao  , Dai Song-Yuan  , Li Yong-Fang  ,   Beijing Key Laboratory of Novel Thin Film Solar Cells, School of Renewable Energy, North China Electric Power University, Beijing 102206, China;,   Beijing Key Laboratory of Energy Security and Clean Utilization, North China Electric Power University, Beijing 102206, China;,   Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

The development of highly efficient and low-cost solar cells is the key to large-scale application of solar photovoltaic technology. In recent years, the solution-processed organic-inorganic perovskite solar cells attracted considerable attention because of their advantages of high energy conversion efficiency, low cost, and ease of processing. The ambipolar semiconducting characteristic of perovskite enables the construction of planar heterojunction architecture to be possible in perovskite-based solar cells. This kind of architecture avoids the use of mesoporous metal oxide film, which simplifies the processing route and makes it easier to fabricate flexible and tandem perovskite-based solar cells. Planar heterojunction perovskite solar cells can be divided into n-i-p type and p-i-n type according to the charge flow direction. Two interfaces are formed between perovskite film and hole/electron transport layer, where efficient charge separation can be realized. Hole and electron transport layers can form separated continuous paths for the transport of holes and electrons, thus beneficial to improving exciton separation, charge transportation, and collection efficiency. In addition, this planar architecture avoids the use of high temperature sintered mesoporous metal oxide framework; this is beneficial to expanding the choice of the charge transport materials. In this paper, we review the recent progress on the planar heterojunction perovskite solar cells. First, we introduce the material properties of perovskite, the evolution of device architecture, and the working principle of p-i-n type and n-i-p type planar heterojunction perovskite solar cells. Then, we review the recent progress and optimization of planar heterojunction perovskite solar cells from every aspect of perovskite preparation and the selection of electron/hole transport materials. Finally, we would like to give a perspective view on and address the concerns about perovskite solar cells.
S-shaped current-voltage characteristics in perovskite solar cell
Authors: Shi Jiang-Jian  , Wei Hui-Yun  , Zhu Li-Feng  , Xu Xin  , Xu Yu-Zhuan  , Lü Song-Tao  , Wu Hui-Jue  , Luo Yan-Hong  , Li Dong-Mei  , Meng Qing-Bo  ,   Key Laboratory for Renewable Energy, Chinese Academy of Sciences; Beijing Key Laboratory for New Energy Materials and Devices; Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Analysis of the DC current-voltage (I-V) characteristics is an effective approach to investigate the charge transport properties in a solar cell. The perovskite solar cell attracted wide research interest in the past two years due to their outstanding photovoltaic capacity. However, the charge transport characteristics and working principles of this kind of cells have not been clearly clarified. In this work, the I-V characteristics of the perovskite solar cell have been investigated from the experimental and theoretical perspective views. Moreover, the S-shaped I-V feature coming from the limitation of interfacial charge transport was focused on. With a series connected diode model, the I-V characteristics of the solar cell are investigated and simulated. It is found that the charge accumulation appears gradually when the interfacial charge transport velocity is decreased, lowering the output of the cell. When the interfacial charge transport decreases gradually, the short-circuit current density and the fill factor of the cell also decrease obviously. In experiments, limitations of charge transport at the front and back contacts of the cell have been designed, successfully producing varied S-shaped I-V features. It is found that both in the hole transport material-free and in the p-i-n perovskite solar cells, the S-shaped I-V characteristics can appear. Moreover, the origins of these features in various experimental conditions have also been discussed, which can be the energy barriers or large charge transport resistances in the cell. These energy barriers and resistances will lower the charge transport velocity and may cause charge accumulation, thus leading to the appearence of the S-shaped features. Meanhiwle, the emerging S-shaped I-V curves all have their own features, which may be due to the specific interfacial energy band structures. Thus, to promote the cell performance, the charge transport and interface energy barrier should be attached importance to and carefully designed. This work directly shows the interface factors that can significantly affect the cell performance, and gives a theoretical guide in cell design. By considering these limiting factors, the cell fabrication has been carefully designed with the control on the thickness of the mesoporous layer and the perovskite absorber film deposition, and a forward-swept efficiency of 15.5% can be achieved without any modification of the cell.
The catalytic effect of transition matel doped Al (111) surfaces for hydrogen splitting
Authors: Fan Li-Hua  , Cao Jue-Xian  ,   Department of Physics, Xiangtan University, Xiangtan 411105, China
Published: December 2020

To investigate the catalytic activity of transition metals in hydrogenation process, the density-functional method has been performed to study the hydrogen interaction with metal-doped Al (111) surfaces. Results indicate that Al (111) surfaces doped with Sc, V, Fe, or Ti atom can effectively enhance hydrogenation reaction. H2 dissociation barriers on Sc, V, Fe and Ti doped surfaces are 0.54 eV, 0.29 eV, 0.12 eV, and 0.51 eV respectively, while diffusion barrier for H atom away from the Sc, V, and Ti doped surfaces are 0.51 eV, 0.66 eV, and 0.57 eV correspondently. Especially, V doped Al (111) surface has shown an amazing catalytic hydrogenation performance for the lower activating energy and diffusion barrier. Moreover, the metal atoms tend to be uniformly distributed on the Al (111) surface. And increasing the number of doping metal atoms, the catalytic performance are similar to that of the isolated transition metal atom doped Al (111) surface. This research may provide a reference to study the metal activity of hydrogen reuptake for NaAlH4.
History and latest development of ferroelectric-semiconductor coupled photovoltaic devices
Authors: Yang Biao  , Liu Xiang-Xin  , Li Hui  ,   Key Laboratory of Solar Thermal Energy and Photovoltaic System, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

This paper introduces the history and current research status of the novel ferroelectric-semiconductor coupled photovoltaic devices, in which a ferroelectric field of polarized dipoles from nanoparticles separates the photogenerated carriers. Fabrication of such devices by combining a CdS nanodipole and a CdTe absorber via a feasible method is described, which involves a phase segregation process of CdS from a CdS-CdTe pseudobinary system. An irregular behavior is observed on this type of devices, i.e. the hysteresis of open circuit voltage due to external bias of direct-current (DC) electric field. Other macroscopic and microscopic evidences of the dipole field photovoltaic effect are also described. Meanwhile, similar photovoltaic mechanism observed in other types of solar cells are also discussed, such as organic photovoltaic devices and quantum dot devices with photo-induced dipole polarization field, piezo-phototronic devices, ferroelectric photovoltaic devices, as well as perovskite solar cells. It is apparent that the polarization field of dipoles not only exists in the various types of photovoltaic devices, but also may dominate the behavior of devices. Therefore, we propose that a new concept of dipole field semiconductor devices could be properly used to explain the photovoltaic behavior of both junctional and un-junctional devices. The junctional devices could function with either pn junction or Schottky junction, while the un-junctional devices include all the devices mentioned above. We expect that various innovation should be inspired by this concept in photovoltaic community.
A parameter optimization nonlinear adaptive denoising algorithm for chaotic signals
Authors: Wang Meng-Jiao  , Wu Zhong-Tang  , Feng Jiu-Chao  ,   School of Electronic and Information Engineering, South China University of Technology, Guangzhou 510641, China;,   Department of Information Science and Engineering, Hunan Institute of Humanities, Science and Technology, Loudi 417000, China
Published: December 2020

In the parameter optimization issue of nonlinear adaptive denoising algorithm for chaotic signals, the window length is affected by different factors. In this paper, a criterion is proposed for selecting the optimal window length. According to the difference in autocorrelation function between chaotic signal and noise, first, the different window sizes are used for denoising noisy chaotic signals. Then, the residual autocorrelation degree (RAD) of each window length is computed. Finally, the optimal window length is obtained by shrinking the window length corresponding to the minimum RAD. Simulation results show that this criterion can automatically optimize the window length efficiently under different conditions, which improves the adaptivity of the denoising algorithm of chaotic signals.