bluuebunny/crossref_metadata_2025 huggingface dataset:
Latest developments of dynamic holographic three-dimensional display
Authors: Zeng Chao  , Gao Hong-Yue  , Liu Ji-Cheng  , Yu Ying-Jie  , Yao Qiu-Xiang  , Liu Pan  , Zheng Hua-Dong  , Zeng Zhen-Xiang  ,   Laboratory of Applied Optics and Metrology, Department of Precision Mechanical Engineering, School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200072, China
Published: December 2020

Holographic three-dimensional (3D) display is a true 3D display technique, which can provide realistic image of a real object or a scene because holography has the ability to reconstruct both the intensity and phase information, i.e., the wave front of the object or scene. Therefore, it could allow the observers to perceive the light as it is scattered by the real object itself without any special eyewear, which is quite different from other 3D display techniques, such as stereoscopic displays and volumetric 3D displays. In this paper, the achievements and developments of the latest new holographic 3D displays are presented. Holographic 3D displays can be divided into static holographic 3D displays and dynamic holographic 3D displays. Here, we briefly introduce the principle of holographic 3D display technique and static holographic 3D displays, and focus on dynamic holographic 3D displays. Large-size, high-resolution and color static holographic 3D displays have already been successfully fabricated and applied in some areas, such as holographic 3D maps and holographic 3D images. However, dynamic holographic 3D displays based on both optical materials and spatial light modulators (SLMs) are still under research, which is a challenge to their applications. Some holographic researchers study the holographic 3D displays based on the SLMs for large-size and large view angle display, but it is difficult to realize them because of limitations of SLMs and there still needs much effort to solve these problems in SLMs. Other holographic researchers work on dynamic holographic materials, such as inorganic crystals, photorefractive polymer, photochromic material etc. The response time and diffraction efficiency are key factors to these materials. Compared with other holographic media, liquid crystals with super-fast response time (about 1 ms) have been reported, which makes it possible to realize video refresh-rate holographic displays. The achievements of dynamic holography, which are helpful for holographic 3D video applications, are presented. Recently, real-time dynamic holographic display has been obtained in super-fast response liquid crystal films, which makes it possible that large-size, high-definition, color holographic 3D video displayers are developed by using these liquid crystal films in the future.
Effects of surface groove micro-structure on ejection from shocked metal surface
Authors: Zhao Xin-Wen  , Li Xin-Zhu  , Wang Xue-Jun  , Song Ping  , Zhang Han-Zhao  , Wu Qiang  ,   Key Laboratory for Shockwave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

When a shock wave releases from a metal-vacuum interface, some high velocity metal particles will be ejected from the metal surface which generally produce some tiny grooves on the metal surface. This phenomenon is often called the “micro-ejecta”. In this paper, we numerically investigate the effect of the micro-structures of these tiny grooves on the property of the micro-ejecta. To verify the numerical simulation model, a strict Pb micro-ejecta experiment is carried out, where the breakout pressure is about 40 GPa and the Pb target surface roughness is Ra1.6. The dynamic processes of the micro-ejection caused by the real surface groove of experimental target and simplified isosceles groove (both have a depth of 5 μm and wavelength of 75 μm), are respectively simulated by a two-dimensional smooth particle hydrodynamics method, and the effects of surface groove micro-structure on the micro-ejecta properties are examined. The simulation results of the tip velocity and accumulated mass, obtained from the real surface groove model, are in good agreement with the corresponding experimental results measured via DISAR and Asay foil, implying that the numerical result is exact. The tip velocity and accumulated mass caused by the real surface groove are much larger than those caused by the simplified isosceles groove, and a second ejection phenomenon is found in the micro-ejecta process from the real surface groove model. The process can produce some faster ejecta than a single ejecta process and influence the density distribution of the micro-ejection. It indicates that the micro-ejecta process can also be affected by the micro-structure of the metal surface groove, besides perturbation wavelength and surface groove depth.
Capillary-driven flow in tubes connected to the containers under microgravity condition
Authors: Zhou Hong-Wei  , Wang Lin-Wei  , Xu Sheng-Hua  , Sun Zhi-Wei  ,   Key Laboratory of Microgravity, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China;,   School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

The capillary-driven liquid flow in tubes connected to containers under a microgravity condition is systematically studied in a drop tower experimentally. The microgravity time lasts up to 3.6 s and the working liquids are mixtures of ethanol and deionized water with different ratios. Theoretically, based on the previous theory for tubes directly immersed in fluid, a modified formula is developed to describe the change tendency of the height of meniscus with microgravity time for such a container/tube system exposed to a microgravity environment. From the theoretical formula, the numerical results of meniscus height at different microgravity time can be obtained, utilizing the geometrical parameters of container/tube systems and the relevant physical quantities of Eth/H2O mixtures with different ratios. By comparing the numerical results with experimental results for different contact angles between working liquid and container in different container/tube systems, we show that the theoretical model is able to quantitatively predict the capillary-driven flow in tubes connected to containers, and the numerical results have good consistence with the experimental results. In addition, the experimental results also show that though the ratio of ethanol to deionized water can change the contact angle remarkably, it has little influence on the capillary flow if the geometrical parameters of the container/tube systems are the same. This is because not only the contact angle, but also the surface tension and viscosity coefficient of the working liquid change with the ratio of ethanol to deionized water. It is found that when the contact angle increases from 42° to 66°, the surface tension increases from 0.0328 N/m to 0.0443 N/m correspondingly, but the viscosity coefficient decreases from 2.11 cSt to1.49 cSt. As a result, the changes of surface tension and viscosity coefficient offset the influence of the change of contact angle, which can be explained by our theoretical model. Compared with the extensively studied system in which tubes are directly immersed into liquid, the container/tube system studied in this paper is more similar to many actual systems such as fluid transfer systems in the microgravity condition and in micro-fluidic devices. Therefore, this study is useful for predicting and analyzing the capillary flows of these actual systems.
Computer simulation on temperature-dependent internal charging of complex dielectric structure
Authors: Yi Zhong  , Wang Song  , Tang Xiao-Jin  , Wu Zhan-Cheng  , Zhang Chao  ,   Beijing Institute of Spacecraft Environment Engineering, Beijing 100094, China;,   Research Institute of Electrostatic and Electromagnetic Protection, Ordnance Engineering College, Shijiazhuang 050003, China
Published: December 2020

Some dielectric structures on satellites would experience temperature variation in a relatively large range, giving rise to a considerable change in its conductivity and consequently resulting in a significant influence on the dielectric internal charging. However, due to the limitation to the model of conductivity versus temperature and the tool for three-dimensional (3D) simulation of internal charging, this temperature dependence has not attracted much attention. Therefore, the conductivity of a satellite used modified polyimide is measured in a temperature changeable vacuum environment under high electric field (in MV/m). Keithley 6517 B is used to capture the mild electrical current in a relatively long measuring time (several hundred seconds). According to the Arrhenius temperature dependence and considering the conductivity enhancement due to high electric field, good agreement is obtained between fitted data and measured results by setting the activation energy to be 0.40 eV. In addition, the radiation induced conductivity (RIC) is taken into account by using the Fowler model. The conductivity at room temperature is found to be comparable to the RIC from the condition with 2 mm aluminum shielding. Using the derived results, the internal charging simulation in three dimensions is carried out for a selected part of a structure in this material, where Geant4 is used to derive the distribution of charge deposition and radiation dose in three dimensions. The incident energetic electrons are assumed to follow the exponential distribution under geosynchronous orbit severe radiation condition where the flux of electrons with energy larger than 2 MeV is assumed to be 1.0×109 m-2·-1·sr-1. It is found that the internal charging will become more serious as the temperature decreases. The charging time is about 1 h at temperature 330 K, whereas this time is increased to 10 h for temperature below 250 K. The most serious charging domain appears around the boundary line of the grounding surface close to the radiation source, where the electric field strength exceeds 107 V/m under the condition of 2 mm aluminum board with temperature 250 K. So the dielectric breakdown discharge is most likely to occur within this domain. Above all, under the condition of the material intrinsic conductivity (mainly depending on temperature) comparable to the radiation induced conductivity, temperature will play an important role in internal charging. This model for temperature-dependent conductivity and the method of 3D simulation of internal charging have great significance in both further evaluating spacecraft internal charging and implementing well protective designs.
Translation process of field reversed configuration
Authors: Li Lu-Lu  , Zhang Hua  , Yang Xian-Jun  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

Magnetized target fusion (MTF) is an alternative approach to fusion between traditional inertial confinement fusion and magnetic confinement fusion. It involves three processes: the formation of target plasma, the translation of target plasma, and compression process of implosion. In this paper, the translation process is studied with a two-dimensional magneto-hydrodynamic code MPF-2D, and the result shows that it is necessary to add a proper magnetic field in the translation process of field reversed configuration in order to maintain its topological structure. The effects of initial magnetic pressure, translation magnetic field, and the gap between coils are studied in detail.
Temporal evolutions of the plasma density and temperature of laser-produced plasma expansion in an external transverse magnetic field
Authors: Liang Yi-Han  , Hu Guang-Yue  , Yuan Peng  , Wang Yu-Lin  , Zhao Bin  , Song Fa-Lun  , Lu Quan-Ming  , Zheng Jian  ,   Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China;,   School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;,   Institute of Applied Electronics, China Academy of Engineering Physics, Mianyang 621000, China
Published: December 2020

The nanosecond laser produced plasma expansion in an external transverse magnetic field is explored by using optical imaging of plasma self-luminescence, optical spectrum and optical interferometry techniques. The plasma displays bifurcation and focusing phenomena in a transverse magnetic field, which is different from the scenarios without external magnetic field significantly. We set up a simplified magnetohydrodynamics model according to the feature of experimental parameters. The theoretical results of the temporal evolutions of the plasma density and the temperature are in good agreement with the experimental results, which confirms the important role of the magnetic diffusion in the plasma evolution.
Transmittance and reflectance of cholesteric and blue phase liquid crystal
Authors: Dou Hu  , Ma Hong-Mei  , Sun Yu-Bao  ,   Department of Applied Physics, Hebei University of Technology, Tianjin 300401, China
Published: December 2020

Blue phase liquid crystal display (BPLCD) is emerging as next-generation display, because of its fast response speed and very wide viewing angle. However, it has some weak points to be improved. The light leakage at the dark state affects the contrast ratio, and needs to be analyzed and improved. Considering the double-twist structure of blue phase liquid crystal (BPLC) and the simple twist structure of cholesteric liquid crystal (ChLC), the two twist structures are similar. The transmittances and reflectances of planar and focal conic texture of cholesteric liquid crystal and blue phase II liquid crystal are simulated by finite-difference time domain (FDTD) method. The FDTD method is based on the Maxwell’s equation, and can calculate the optical rotatory power directly. The effective optical rotatory powers of the three liquid crystal states are proposed and compared using the light leakages at the cell with crossed and parallel polarizers. The results show that the transmittance of BPLC with crossed polarizers is lower than that of planar texture and larger than that of focal conic texture of ChLC. The optical rotation of BPLC is not the same at any point in one periodic cross section in the light path because the liquid crystal arrangement is complex, the effective optical rotatory power is defined as the average value of the optical rotatory powers at all points. Comparing with the optical rotatory powers of planar and focal conic textures of ChLC, the optical rotatory power of BPLC is less than that of planar texture and larger than that of focal conic texture. Moreover, the Bragg reflections are also simulated, the results show that blue phase liquid crystal is similar to planar state cholesteric liquid crystal, only the reflection intensity is smaller, and no obvious Bragg reflection appears in focal conic state cholesteric liquid crystal. Considering the optical rotation and Bragg reflection, the light leakage and reflective light of BPLCD cannot be ignored if the helix pitch is not less enough, however, these of focal conic texture of ChLC are very small compared with those of BPLC, as a result, the focal conic texture of ChLC can replace blue phase liquid crystal to obtain the good dark state and high contrast ratio.
Improved performance of the amorphous indium-gallium-zinc oxide thin film transistor with Cu-Mo source/drain electrode
Authors: Ning Hong-Long  , Hu Shi-Ben  , Zhu Feng  , Yao Ri-Hui  , Xu Miao  , Zou Jian-Hua  , Tao Hong  , Xu Rui-Xia  , Xu Hua  , Wang Lei  , Lan Lin-Feng  , Peng Jun-Biao  ,   Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, Department of Materials Science and Engineering School, South China University of Technology, Guangzhou 510640, China;,   New Vision Opto-Electronic Technology Co., Ltd, Guangzhou 510530, China;,   National Laboratory for Infrared Physics, Chinese Academy of Sciences, Shanghai 200083, China
Published: December 2020

Copper is an alternative material for aluminum electrode to meet the stringent requirement for high mobility and low resistance-capacitance (RC) delay of amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistor (TFT) for next generation of display technology due to its intrinsic high conductivity. However, low bonding strength between copper layer and insulator/glass and easy diffusion into active layer restrict its application in the field of TFT. In this work, a 30 nm thin film of molybdenum is introduced into copper electrode to form a copper-molybdenum source/drain electrode of a-IGZO TFT, which not only inhibits the diffusion of copper, but also enhances the interfacial adhesion between electrode and substrate. The obtained Cu-Mo TFT possesses a high mobility of ～9.26 cm2·V-1·s-1 and a low subthreshold swing of 0.11 V/Decade. Moreover, it has shorter current transfer length(～0.2 μm), lower contact resistance (～1072 Ω), and effective contact resistance (～1×10-4Ω·cm2) than the pure copper electrode. Cu-Mo electrode with low contact resistance and high adhesion to substrates paves the way to the application of copper in high conductivity interconnection of a-IGZO TFT.
Superplastic deformation mechanism of nanocrystalline copper: a molecular dynamics study
Authors: Wen Peng  , Tao Gang  , Ren Bao-Xiang  , Pei Zheng  ,   School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, China;,   Yantai Branch of No.52 Institute of China Ordnance Industry Group, Yantai 264003, China
Published: December 2020

In the process of the generation of jet formed by the shaped charge explosive compression, the grain of the metal liner is refined from 30-80 μm down to sub-micron or nanometer level. There is a strong scientific significance for studying the mechanism of grain refinement and dynamic superplastic deformation at a micro level. The main contents of this study are as follows. Firstly, the models of nanocrystalline copper with the grain sizes of 7.17, 9.11, 12.55, 14.85, 18.38 and 22.48 nm are established using the Voronoi geometrical construction method, and these models are relaxed in 100 ps to the equilibrium state at 293 K. Then, the tensile deformation processes of nanocrystalline copper at various grain sizes are simulated by using the molecular dynamics method. The strain increases to 0.2 gradually at a strain rate of 2×109/s. Based on the data output, the stress-strain curves at different grain sizes are gained and the corresponding values of the averaged flow stress are calculated. The results show that the average flow stress exhibits the maximum at a grain size of 14.85 nm. Finally, the primary deformation process of nanocrystalline copper is displayed by analyzing the atomic configuration evolvement. When the grain size is 22.48 nm, the typical dislocation motion is found and there are a huge number of dislocations in the deformation process. However, the number of dislocations decreases sharply at the grain sizes of 14.85 nm and 9.11 nm, and the grain-boundary motion is visible at these small grain sizes. The most significant work is that the deformation mechanisms of nanocrystalline copper at different grain sizes are analyzed in detail. The results indicate that the dislocation motion dominates the deformation process when the grain sizes of nanocrystalline copper are larger than 14.85 nm. As the grain sizes decrease below 14.85 nm, the grain-boundary sliding and rotation become a dominant deformation mechanism. This change of deformation mechanism is the fundamental reason for softening, which is so-called reverse Hall-Petch relationship. On the basis of previous study and this molecular dynamics simulation, combining the grain coalition and the grain-boundary rotation, an ideal deformation mechanism model is established at small grain sizes, which provides the microcosmic deformation mechanism reference for the large strain deformation of the jet.
Thermal characterization of carbon nanotube fibers based on steady-state electro-Raman-thermal technique
Authors: Li Man  , Dai Zhi-Gao  , Ying Jian-Jian  , Xiao Xiang-Heng  , Yue Ya-Nan  ,   School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, China;,   School of Physics and Technology, Wuhan University, Wuhan 430072, China
Published: December 2020

Carbon nanotube (CNT) fiber is a promising material due to its extensive potential in micro/nanoelectronics, where the thermal performance is of great importance. In this work, a well-developed steady-state electro-Raman-thermal technique is employed and extended to the ambient environment for measuring thermal conductivity of the CNTs fiber. In this technique, two ends of the CNT fiber are attached to heat sinks and a steady electrical current flows in a sample to induce Joule heating. The heat dissipates to the ambient air and goes through the sample to the heat sinks. With combined effects of natural heat convection and heat conduction, a steady temperature profile along the sample can be established. The middle point temperature of the fiber is probed by measuring the local Raman spectrum. It is because the Raman scattering (such as G peak) of CNT fiber is temperature dependent and thus it can be used as a temperature indicator for thermal property measurement. In calibration experiment, the temperature coefficient of the G peak of CNT fiber is first obtained. A modified one-dimensional heat conduction solution involving free convection effect is derived as #br#T(x) =((I2R)/(hLS))(1 -(e√(hS)/(kAc)x)+e-√(hS)/((kAc)x)/(e√(hS)/(kAc)L/2)+e-√(hS)/(kAc)L/2))+ T0. It can be found that the relationship between middle point temperature (T0) and applied Joule heating power (I2R) can be used to extract the thermal conductivity of the material (k) as long as the convection coefficient (h) is available. In this work, the convection coefficient is calculated by the model established by Peirs et al. The thermal conductivity of CNT fiber synthesized from floating catalyst method is measured to be 66.93 W/(m·K)± 11.49 W/(m·K). This value is a little bit larger than that of other CNT fibers synthesized by the acid spun method or the dry-spinning method, which can be explained by the different sample structures induced from different synthesize method. This value is two orders of magnitude smaller than that of individual carbon nanotube, and two orders of magnitude larger than that of CNTs packed bed, showing that heat conduction in CNT based bulk material is determined mainly by a large number of thermal interfaces between CNTs contacts rather than the intrinsic thermal property of CNT.
Quantum capacitance performance of different nitrogen doping configurations of graphene
Authors: Yang Guang-Min  , Xu Qiang  , Li Bing  , Zhang Han-Zhuang  , He Xiao-Guang  ,   College of Physics, Changchun Normal University, Changchun 130032, China;,   School of Prospecting and Surveying, Changchun Institute of Technology, Changchun 130021, China;,   College of Physics, Jilin University, Changchun 130012, China
Published: December 2020

Supercapacitor is an energy storage device which obtains energy from the electrochemical double layer or the redox-type reactions at or beyond the surface of the electrode, which can meet the demands for high power and long cycle life. However, the electrode still has low energy density for supercapacitor device. The design of electrode material is essential for obtaining high capacity. We employ density functional theory based on the first principle to calculate the electronic structures and derive the capacitance of N-doping graphene. We find that the quantum capacitance can be substantially improved by N doping. The physical mechanism of such phenomena is discussed in this paper.
Influence of annealing temperature on the distribution of particle sizes of quantum dots doped glass
Authors: Xu Jun  , Chen Gang  ,   Department of Applied Physics, Zhejiang University of Technology, Hangzhou 310023, China
Published: December 2020

In order to understand the influence of annealing temperature on PbSe quantum dots doped glass produced by a melt-annealing technique, experiments are carried out to compare the influences of different nucleation durations, crystallization temperatures and time on the particle size, distribution and absorption spectrum. Under the condition of the same nucleation temperatures and different crystallization temperatures, the transmission electron microscope images of all samples show that a certain quantity of PbSe crystals are crystallized in the glass. While the particle sizes and densities are slightly different. The calculated distribution of the particle sizes quantitatively indicates that the particle size will be enlarged with the increase of crystallization temperature and the crystal particle density. The measured absorption spectrum shows that the peak value of absorption spectrum increases gradually with increasing the crystallization temperature. At the same time, the peak value shows a red-shift phenomenon. While under the relatively low crystallization temperature, the infrared absorption peak cannot be obtained in spite that some crystals have grown inside the glass. The absorption spectrum is covered up by the background signals because of the relatively smaller particle size and density. This work will be benefit of producing different size quantum dots with a certain density, and realizing stronger absorption and emission in multiband.
Degradation induced by voltage and current for AlGaN/GaN high-electron mobility transistor under on-state stress
Authors: Shi Lei  , Feng Shi-Wei  , Shi Bang-Bing  , Yan Xin  , Zhang Ya-Min  ,   College of Electronic Information and Control Engineering, Beijing University of Technology, Beijing 100124, China
Published: December 2020

Voltage and current degrade the AlGaN/GaN high electron mobility transistors (HEMTs) under on-state stress. To determine which one dominates the degradation, two on-state stresses which have equal power are exerted on AlGaN/GaN HEMTs: high voltage and low current on sample A, low voltage and high current on sample B. In the former stress, drain-source voltage (VDS) is 28 V, drain-source current (IDS) is 75 mA/mm. In the latter stress, VDS is 14 V and IDS is 150 mA/mm. The package temperatures of samples A and B are kept at 150 ℃. The samples are measured every 24 hours, with an extra measurement at the 8th hour in the first 24 hours (note that the time refers to the stressing time). There is an interval of 4 hours between the stressing and the measurement. The device parameters include drain-source current-voltage (IDS-VDS) characteristics, large-signal parasitic source resistance (RS), large-signal parasitic drain resistance (RD), and transfer characteristics between IDS and gate-source voltage (VGS). The emission microscope (EMMI) is used to study the leakage current after experiment. The IDS-VDS characteristics of sample B are kept constant after being stressed, while that of device A shifts downward after being stressed. RS of sample A, RS of sample B, and RD of sample B increase slightly, RD of sample A increases more obviously with most change happening in the first 8 hours. IDS-VGS characteristics of sample B kept constant, IDS-VGS characteristics of sample A shift downward. The changes of threshold voltage (VGS(th)) is obtained from the transfer characteristics, and it is similar to the changes of transfer characteristics. The VGS(th) magnitude (absolute value) of sample A decreases obviously while that of sample B decreases slightly. The measurements show that the device under low voltage and high current stress degrades little and the device under high voltage and low current stress degrades more obviously. The EMMI images show that the leakage of sample A is greater than that of sample B. The analyses of the parameter change, experiment setting and EMMI image indicate that the voltage, rather than the current, dominates the degradation for AlGaN/GaN HEMTs. The influences of hot electron effect, gate electron injection, and self-heating are recoverable, and they vanish in the interval between the stressing and the measurements. The permanent degradation of device parameter is caused by the inverse piezoelectric effect induced by high electrical field between the gate and the drain. Besides, it is found that sudden failure without precursor is easy to happen to the device under low voltage and high current stress. The microscope image of damaged area shows that the failure is due to hot spot induced by high current density.
Fabrication and characterization of the superconducting quantum interference device amplifier with Washer type input coil
Authors: Chen Zhao  , He Gen-Fang  , Zhang Qing-Ya  , Liu Jian-She  , Li Tie-Fu  , Chen Wei  ,   Tsinghua National Laboratory for Information Science and Technology, Department of Micro and Nanoelectronics, Institute of Microelectronics, Tsinghua University, Beijing 100084, China
Published: December 2020

Superconducting quantum interference device (SQUID) amplifier is best known for its low input impedance, low noise and low power consumption. Nowadays it is widely used for detecting the weak signals. Compared with other methods, the Nb/Al-AlOx/Nb structure Josephson junction based SQUID has the advantages of high transition temperature, high voltage flux modulation index and good heat recycle ability, wide critical voltage range, so it is a very good option for making SQUID amplifier. In this work, we fabricate the overdamped Josephson junction and washer dc SQUID, and test the I-V characteristics at He3 3 K stage temperature and calculate the current resolution of SQUID. The result of SQUID modulation property is good. The magnification becomes larger after increasing the input line number of loops, and the system noise becomes smaller after the join of the LC filter. This work is very important for designing and manufacturing transition edge sensor readout circuits.
A novel method to identify the scaling region of correlation dimension
Authors: Zhou Shuang  , Feng Yong  , Wu Wen-Yuan  ,   Chongqing Key Laboratory of Automated Reasoning and Cognition, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

A random fractal exhibits self-similarity over the scaling region, this is different from the regular fractal. The scaling region obtained by the proper method for the exact fractal dimension is very important. And the correlation dimension is one of the fractal dimensions which is used widely in many fields. Therefore, it is necessary and timely to identify the scaling region that plays a critical role in calculating the correlation dimension accurately in various chaotic systems. Visual identification is widely used to determine the scaling region as a quick and simple subjective method. However, this method may lead to an inaccurate result in Grassberger Procaccia algorithm. In order to reduce the error caused by human factors from computing the correlation dimension, a novel method of identifying the scaling region based on simulated annealing genetic fuzzy C-means clustering algorithm is proposed. This new method is based on the fluctuating characteristics that the second-order derivative of the curve within the scaling region is zero or nearly zero. Firstly, the second-order differential of the double logarithm correlation integral discrete data is calculated. Secondly, the simulated annealing genetic fuzzy C-means clustering method is used for dividing the data into three groups: positive fluctuation data, zero fluctuation data, and negative fluctuation data. The zero fluctuation data are selected to retain, the rest is excluded. Thirdly, the 3 σ criteria are used for excluding gross errors to retain those valid from the zero fluctuation data. Fourthly, the data of the consecutive nature point interval are chosen from the retained data. Finally, the regression analysis and statistical test are used to identify the scaling region from the data valid. In order to verify the effectiveness of the proposed method, it is used to simulate the Lorenz and Henon systems. The calculated results are in good agreement with the theoretical values. Experimental results show that the proposed new approach is easy to operate, more efficient and more accurate than the subjective recognition, K-means method, and 2-means method in identifying the scaling region.
Constructing circulant measurement matrix through alternating optimizing amplitudes together with chaotic stochastic phases of the matrix generating elements
Authors: Guo Jing-Bo  , Wang Ren  ,   State Key Lab, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

Circulant measurement matrix has been widely used in compressive sensing because of its high-speed discrete convolution algorithm. The typical work of optimizing circulant measurement matrix was introduced by Wotao Yin in Reference [16]. Motivated by his work, the construction of circulant measurement matrix in this paper is explored from the view point of generating elements' amplitudes and phases; and the optimal construction procedures are proposed based on alternately optimizing amplitudes in conjunction with chaotic stochastic phases of the matrix generating elements. The main idea of this paper is based on two innovations: The first one is to reduce the mutual coherence between column vectors of equivalent dictionary by alternately optimizing the generating elements' amplitudes, thus improving the recovery performance of the circulant measurement matrix. From the different expressions of the circulant matrixes of one-dimensional and two-dimensional signal, by setting the Welch bound for the coefficient of mutual coherence between the column vectors of equivalent dictionary as the approximation objective, two novel unified mathematical models are derived from the optimizing function for generating elements' amplitudes of the two different matrixes. Optimal solutions for generating elements' amplitudes are gained by alternately optimizing method. The second innovation is to construct the generating elements' phases of circulant measurement matrix by utilization of a chaotic sequence with independent property. The chaotic stochastic phase of the circulant measurement matrix generating elements are generated by taking advantage of the chaotic internal certainty, which means an independent identically-distributed randomness sequence can be produced by the chaotic map with the initial value at certain sampling distance. At the same time, the external randomness of chaotic sequence can satisfy the stochastic requirement of circulant measurement matrix. This paper presents the method of constructing chaotic stochastic phase using Cat chaotic map. Experimental results of one-dimensional and two-dimensional signals in the optimized circulant measurement matrix are studied in this paper, which has a better performance as compared with the results of conventional circulant measurement matrixes, such as Gaussian circulant matrix and optimized circulant matrix proposed by Wotao Yin. The column vectors of equivalent dictionary in the optimized circulant measurement matrix have lower mutual coherence, this is the essence of the superiority of the optimized circulant matrix.
A concentration retrieval method for incoherent broadband cavity-enhanced absorption spectroscopy based on O2-O2 absorption
Authors: Ling Liu-Yi  , Xie Pin-Hua  , Lin Pan-Pan  , Huang You-Rui  , Qin Min  , Duan Jun  , Hu Ren-Zhi  , Wu Feng-Cheng  ,   Institute of Electric and Information Technology, Anhui University of Science and Technology, Huainan 232001, China;,   Anhui Institute of Optics and Fine Mechanics, Key Laboratory of Environmental Optics & Technology, Chinese Academy of Sciences, Hefei 230031, China;,   School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei 230031, China
Published: December 2020

Incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) has a very high detection sensitivity, nevertheless the quantitative results retrieved by the traditional concentration retrieval method are affected by the calibration error of mirror reflectivity. Therefore, in this paper we present another concentration retrieval method based on the measurements of atmospheric O2-O2 absorption. In this method the optical cavity of IBBCEAS is equivalent to a multi-reflection cell, in which the optical path length is independent of the wavelength, i.e. a constant. First, we get the slanting column concentrations of atmospheric O2-O2 and other trace gases measured by using the differential optical absorption spectroscopy (DOAS) to fit the corrected cross sections of the measured gases to the optical density from the IBBCEAS absorption spectra and reference spectra. Second, the optical path length of an equivalent cell is determined by the known concentrations of O2-O2 in the atmosphere. Third, the concentrations measured for trace gases are retrieved by the deduction of absorption optical path length from the obtained slanting column concentrations. The above method is demonstrated by measuring the atmospheric NO2 with an IBBCEAS instrument in the range of 454-487 nm. Atmospheric NO2 concentrations retrieved by this method are compared with those by the traditional method, and the difference between them is shown to be less than 7%. Experimental results show that the absorption of atmospheric O2-O2 can be used to quantify other trace gases when measured by IBBCEAS, and, above all, the quantitative results are almost insensitive to the calibration error from mirror reflectivity.
First-principles study on the minimization of over-erase phenomenon in Si3N4 trapping layer
Authors: Dai Yue-Hua  , Jin Bo  , Wang Jia-Yu  , Chen Zhen  , Li Ning  , Jiang Xian-Wei  , Lu Wen-Juan  , Li Xiao-Feng  ,   Institute of Electronic and Information Engineering, Anhui University, Hefei 230601, China;,   Internet Network Information Center, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

The first-principles method has been used to explore how to minimize the over-erase phenomenon in charge trapping memory. Over-erase phenomenon originates from the nitrogen vacancy due to its weak localization of charge on Si atoms. Therefore, we develop a defect model for studying Si3N4 supercells. The defect model consists of an N vacancy and a substitutional atom on the Si site. The substitutional atoms can be C, N, and O atoms, respectively. The Si site belongs to the N vacancy. Then, the Bader charge distribution after program/erase operation, the interaction energy and density of states are calculated for the model so as to analyze the effects of the substitutional atoms on the over-erase phenomenon. The obtained results of the Bader charge distribution show that the substitution of O for the 128th Si can minimize the over-erase phenomenon in Si3N4, and the replacement of the 128th Si by C can also reduce the over-erase phenomenon. However, the model represents a weak localization of charge due to the replacement by C, which is not preferable for charge storage. And the results also reveal that the substitution of N for the 128th Si completely fails to reduce the over-erase phenomenon. With regard to the 162th and 196th Si sites, the substitutions of the three atoms for the two sites cannot minimize the over-erase phenomenon. Furthermore, the analysis of the interaction energies indicates that the combination of each of the three atoms with the N vacancy can form stable clusters on the 128th site in the model. In particular, the attractive interaction between O and N vacancy is the weakest of the three so that the injected charge can temporarily break the stability of the O cluster to rearrange the charge distribution, realizing the localization of charge around the O cluster. And then, the results of the density of states designate that subtitutional O atom at the 128th Si atom site produces a deep-level trap in the band gap, which has a powerful ability to localize the charge. The above results suggest that substitution of O for Si is an excellent solution for the minimization of over-erase phenomenon in Si3N4. This work can provide a method for the minimization of over-erase phenomenon in charge trapping memory and also can be helpful to the improvement of charge retention and optimization of memory window in the charge trapping memory.
Photoexcitation and photoionization of alkali atoms
Authors: Qi Xiao-Qiu  , Wang Feng  , Dai Chang-Jian  ,   Key Laboratory of Display Materials and Photoelectric Devices, Ministry of Education, Tianjin 300384, China;,   School of Science, Tianjin University of Technology, Tianjin 300384, China
Published: December 2020

The dynamical process of photoexcitation and photoionization of alkali atoms is studied with three-step laser pulses, focusing on the similarities and differences between Li and Cs atoms on their properties by making a comparison of them. Based on several excitation schemes, the present work not only establishes the rate equations of atom population for all related transition states, but also obtains the analytical solutions of photoexcitation and photoionization process. The mathematical solutions are simplified significantly by restricting the most general case to the several special cases, either designed or selected carefully, in order to highlight the main factors and obtain the physical insight underlying the complicated mathematical expressions. With self-programming, the possible impact of time configuration of laser pulses on the three-step laser excitation process of the photoexcitation and photoionization is calculated and studied systematically. Variation of the ionization efficiency with the laser parameters is investigated and discussed. With the same time configuration of laser pulses, the dependences of atom population for all the related transition states on the two different excitation paths are compared and analyzed, reflecting the impact of changing the atomic parameters. Under the similar excitation conditions, the differences of ionization efficiency between Li and Cs atoms are explored. Finally, based on the present study, several means for optimizing ionization efficiency are proposed.
A narrow linewidth diode laser at 243 nm
Authors: Hou Lei  , Han Hai-Nian  , Zhang Long  , Zhang Jin-Wei  , Li De-Hua  , Wei Zhi-Yi  ,   Institute of Physics Chinese Academy of Sciences, Key Laboratory of Optical Physics, Beijing 100190, China
Published: December 2020

The two-photon spectroscopy of 1S-2S transition in atomic hydrogen needs a narrow linewidth laser at the wavelength of 243 nm. In order to reduce the linewidth to several tens hertz level, a free operation CW ECDL 972 nm laser has been locked to a high fineness ultralow expansion reference cavity by using the Pound-Drever-Hall technique. And the part of 972 nm laser output is set into the tapered amplifier and the two enhanced doubling frequency stages to obtain the output of purple light at 243 nm. It is estimated that such a narrow linewidth laser system at 243 nm can be used well in the detection of the 1S-2S transition of hydrogen.
Experimental research on focusing anisoplanatism of sodium guide star via synchronous pulse detection
Authors: Chen Tian-Jiang  , Zhou Wen-Chao  , Wang Feng  , Huang De-Quan  , Lu Yan-Hua  , Zhang Jian-Zhu  ,   Institute of Applied Electronics, CAEP, Mianyang 621900, China;,   The Key Laboratory of Science and Technology on High Energy Laser, CAEP, Mianyang 621900, China;,   Institute of Applied Physics and Computational Mathemstics, Beijing 100049, China
Published: December 2020

No reports of measuring the focusing anisoplanatism of laser guide star were mentioned before because the guide star instantaneous wavefront measurement technique by using sodium is not mature. As directly verifying the confidence of artificial sodium guide star which takes the place of the natural star to become the reference of atmosphere adaptive optic correction, in this paper a new method is put forward that the focusing anisoplanatic error of sodium guide star can be measured via synchronous pulse detection if the atmosphere Greenwood time is constant. Results of correlation analysis show that it is feasible to establish an experimental system for the measurement. A high-precision wavelength and linewidth sodium guide star laser and a 1.3 m caliber telescope underly the experimental system for the technology research on the focus anisoplanatism. Experiment of detecting sodium guide star has been carried out. And synchronous detection about the returning light matrix of visible light of sodium and the natural star is achieved when both are in a coincident imaging path. In the experiment, the recovered single frame wavefront of sodium guide star is acquired, and experimental data analysis is carried out in several aspects: contrasting the coherence of the two types of wavefront images, comparing the Zernike coefficients, and simulating the imaging calibration. Results show that the imaging contrast in the light matrix of the plused sodium guide star is poor because of the limited experimental condition so that the precision of the recovered wavefront is restricted, but the two groups of wavefronts the sodium guide star wavefront and the natural star wavefront always keep nice comparability, which we can see from the recoverd synchronous wavefront images. And the Zernike coefficients of both are close in the first 36 orders, which we deduce from the Zernike anisoplanatic error curves. Simulation result shows that the acquired sodium wavefront data would contribute to calibrate the far-field images of natural star in astronomical observation activities. And the measured results, below 0.1 rad2, while wiping off the wavefront recovering error are close to the theoretical result. Result shows also that the low SNR of sub aperture imaging restricts the wavefront recovery precision to some extent, but the effective atmospheric wavefront distorted information has been obtained by sodium guide star experiment and it can help to correct the natural star images.
Study of vibration propagation in periodic rib-stiffened plates using advanced statistical energy analysis
Authors: Yin Jian-Fei  , Wen Ji-Hong  , Xiao Yong  , Wen Xi-Sen  ,   Science and Technology on Integrated Logistics Support Laboratory, College of Mechatronic Engineering and Automation, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Statistical energy analysis (SEA) is widely used in predicting dynamic response of complex coupled systems. This paper studies the bending wave propagation in periodic rib-stiffened plates in the framework of SEA. Effect of frequency band gap property of the rib-stiffened plate and wave filtering characteristics of the stiffened ribs on the prediction results of SEA is analyzed by using the wave approach and Bloch theory. It is found that due to the fact that classic SEA ignores an energy “tunneling mechanism” between subsystems that are not physically connected, large error up to almost 40 dB is generated in the subsystems of the plate compared with the results calculated from the finite element method. This tunneling mechanism mainly results from the wave filtering effects caused by the periodic arrangement of the ribs and it plays a significant role on the subsystem response at high frequencies. However, this is not incorporated in the modelling of classic SEA thus large errors can occur. To solve this problem, an advanced statistical energy analysis (ASEA) is used to consider the transition, transmission and transport of energy between unconnected subsystems. ASEA divides the energy of each subsystem into two parts: available energy which is the modal energy that could transmit into connected subsystems, and unavailable energy that dissipates within the subsystem; therefore the energy cannot propagate further away. Then the ray tracing algorithm is used to track the power flow across subsystems. By using ASEA, the accuracy of the prediction results can be greatly improved so that the error is reduced to less than 5 dB in most frequency bands. An experimental set-up is also designed to support the plate by simulating the simply-supported boundary conditions along the edges. The test results agree well with the finite element method, and it is sufficient to validate the theoretical models.