bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulence-free intensity fluctuation self-correlation imaging with sunlight
Authors: Li Ming-Fei , Yan Lu , Yang Ran , Kou Jun , Liu Yuan-Xing ,   Beijing Institute of Aerospace Control Devices, Beijing 100039, China,   Quantum Engineering Research Center, China Aerospace Science and Corporation, Beijing 100094, China
Published: December 2020

Since its first experimental demonstration in 1995, ghost imaging has attracted a great deal of attention due to its potential applications. In Yanhua Shih’s paper (Meyers R E, Deacon K S, Shih Y H 2011 Appl. Phys. Lett. 98 111115; Meyers R E, Deacon K S, Shih Y H 2012 Appl. Phys. Lett. 100 131114), he pointed out that " one of the useful features is the turbulence insensitivity of thermal light ghost imaging, i.e., atmospheric turbulence would not have any influence on the ghost images of sunlight”. However, in Jeffrey H. Shapiro’s view (Shapiro J H 2012 arXiv:1201.4513 [quant-ph]), lens-less pseudo-thermal ghost imaging is not immune to spatial resolution loss from the presence of atmospheric turbulence along the propagation paths, unless the source diameter is less than the source-plane turbulence coherence length. In the present paper, we find that the second order self-correlation of sunlight intensity is the case that can be satisfied with both theories of Shih and Shapiro. In this paper, the second order self-correlation of sunlight intensity (the intensity variance of the images acquired by the CCD camera), rather than the total intensity correlation between images and bucket detector signals (the traditional ghost imaging method), is calculated to recover the high-quality images in turbulent atmosphere under a few hundred measurements. Inspired by Boyd’s paper, titled " thermal ghost imaging with averaged speckle patterns” (Zerom P, Shi Z, O’Sullivan M N, Chan K W C, Krogstad M, Shapiro J H, Boyd R W 2012 Phys. Rev. A 86 063817), turbulence insensitivity of sunlight ghost imaging is demonstrated both theoretically and experimentally in this article. It is found that thermal ghost imaging system whose coherence time need not to be controlled to match the speed of the detectors, ghost imaging with sunlight, which has always been considered intriguing and highly desirable, now is realizable. We present theoretical and experimental results showing that a sunlight self-correlation ghost imaging system can produce high-quality images even when it uses an slow detector and passes through the turbulence near ground, as long as the signal variation is predominantly caused by the fluctuation of the sunlight intensity rather than other noise sources. Our scheme can also be used to improve the image quality in other wave bands such as infrared and ultraviolet, in the case where an poor image quality results from the turbulence or other random disturbances on the wavefront.
Design and experimental analysis of W-band extended interaction klystron amplifier
Authors: Zeng Zao-Jin , Hu Lin-Lin , Ma Qiao-Sheng , Jiang Yi , Chen Hong-Bin ,   Institute of Applied Electronics, Chinese Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Beam loading is an important parameter in extended interaction klystron, which can be used to analyze the influence of beam on resonant frequency and ohm loss Q, and study the match condition between input cavity and external power source, etc. Based on the kinematical theory, law of induce current, principle of charge conservation under the small signal condition, and one-dimensional (1D) mode, the transit time effect of electron in \begin{document}${\text{π}}$\end{document} mode standing wave electric treld in a multiple-gap resonator is analyzed, and the expressions of electron load conductance and electron load susceptance in the multiple-gap resonator are presented. The results show that the electron load conductance of extended interaction cavity can change in a bigger extension than that of traditional single gap cavity, which means that the loaded Q of extended interaction cavity can be adjusted in a bigger extension to realize a desired Q. And the results also show that the electron load susceptance of extended interaction cavity can change in a bigger extension than that of traditional single gap cavity, which means that the loaded frequency of extended interaction cavity can also be easily adjusted to a desired value. The influence of gap number on the power exchange between beam and microwave is also investigated, which shows that the maximum power exchange between beam and microwave electric field increases with the number of resonator gaps increasing, and so does the efficiency of klystron. A W band extended interaction klystron amplifoer is designed by the above theory analysis and three-dimensional (3D) PIC code. The simulation results show that when beam voltage is 20.8 kV, current is 0.28 A, input power is 30 mW at a frequency of 94.77 GHz, the extended interaction klystron can produce 443 W output power. The responding electron efficiency is 7.6%, the gain is 41.7 dB, and the 3 dB bandwidth exceeds 150 MHz. The extended interaction klystron is machined and tested, and the experimental results show that the maximum output power of 175 W is obtained with a beam of 300 mA, a voltage of 20.8 kV, and an input microwave power of 30 mW at a frequency of 95.37 GHz in a magnetic field of 0.62 T. The responding electron efficiency is 2.8%, the gain is 34.6 dB, the 3-dB bandwidth exceeds 90 MHz. This study is meaningful for designing and developing greater power extended interaction klystrons.
Multimode solid-state quantum memory
Authors: Yang Tian-Shu , Zhou Zong-Quan , Li Chuan-Feng , Guo Guang-Can ,   CAS Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China,   Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

The faithful storage and coherent manipulation of single photon state in a matter-system are crucial for linear-optical quantum computation, long-distance quantum communication, and quantum networking.To reach useful data rate in a large-scale quantum network, highly multimode quantum memories are required to build a multiplexed quantum repeater.Rare-earth-ion doped crystal (REIC) is very promising material as a candidate for multimode quantum storage due to the wide inhomogeneous broadening and long optical coherence time.In this article, we review the recent advances in multimode quantum memories based on REICs.First, we briefly introduce the properties of REIC and the atomic frequency comb protocol based on REIC.Next, we review the achievements of multimode quantum memories based on REIC in recent years, including frequency, temporal and spatial multimode storage.Afterwards, we review our experimental work on multiplexed storage based on a multiple degree-of-freedom quantum memory.Finally, we introduce the quantum mode converter and real-time arbitrary manipulations based on the multiple degree-of-freedom quantum memory. The combination of storage and real-time manipulation in a device should enable the construction of a versatility quantum repeater.This review highlights that multimode quantum memories based on REIC can be found to possess some practical applications in developing the optical quantum information processing in the near future.
Raman protocol-based quantum memories
Authors: Shi Bao-Sen , Ding Dong-Sheng , Zhang Wei , Li En-Ze ,   Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China,   Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Quantum memories are indispensable for quantum communication and quantum computation, which are able to realize the storage and retrieval of a quantum state such as a single photon, entanglement, or a squeezed state on demand. Among those memories realized by different protocols, the Raman quantum memory has advantages in its broadband and high-speed properties, resulting in huge potential applications in quantum network and quantum computation. However, the realization of Raman quantum memory for a true single photon and photonic entanglement is a challenging job. In this review, after briefly introducing the main benchmarks for quantum memories, showing the state of the art, we focus on the review of the experimental progress recently achieved in storing the quantum state by Raman scheme in our group. We believe that all achievements reviewed are very hopeful in building up a high-speed quantum network.
Design of monocentric wide field-of-view and high-resolution computational imaging system
Authors: Liu Fei , Wei Ya-Zhe , Han Ping-Li , Liu Jia-Wei , Shao Xiao-Peng ,   School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710071, China,   State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
Published: December 2020

Imaging systems with a wide field-of-view (FOV) and high-resolution, which can provide abundant target information, are always desired in various applications including target detection, environment monitoring, marine rescue, etc. Various approaches to realizing the wide FOV and high-resolution imaging have been developed, for example, fisheye lens imaging system, and panoramic optical annular staring imaging technology. In these single aperture imaging systems, the maximum resolution and FOV are determined by either the geometric aberration or the diffraction limit of the optics. Multi-scale monocentric ball-lens imaging system is of particular importance due to its high real-time ability, small image distortion, and wide FOV. The complete geometrical symmetry of multilayer monocentric ball-lens makes it possible to compensate for the geometric aberration with no need of additional assistance. However, the major problem in designing imaging system based on multi-scale monocentric ball-lens is that there are too many variables needed to be set for a ball-lens imaging structure and the problems of high time cost and computation complexity.For simplifying the design process, in this manuscript, we apply the computational imaging theory to optical system design, thereby developing a geometric aberration optimization function to determine the initial values of the desired system by the sound computation rather than repetitive iterations by using the optical system design software. Function development starts from the aberration theory. Since the monocentric ball lens does not bring in the aberrations relating to FOV, only spherical aberration and chromatic aberration are needed to be considered. The optimization function is then founded according to the principle of minimizing the spherical aberration and chromatic aberration. And then with the determined initial parameters, ZEMAX is employed to globally optimize the residual geometric aberrations, which is time-efficient. After required parameters are finally determined, the system performance is evaluated via the modulation transmission function, the spot diagram distribution, the field-curve and distortion value and the ray fan curve. Favorable results are obtained, which demonstrates the feasibility of the developed system designing approach. Imaging results from the finished prototype system are pretty satisfactory with wide FOV and high resolution which is captured through only one frame. The multi-scale wide FOV and high-resolution computation imaging system not only solves the conflict between the wide FOV and high resolution, but also provides the research foundation for computational imaging.
Measurement of quantum defect of cesium nP3/2 (n = 70—94) Rydberg states by using ultraviolet single-photon Rydberg excitation
Authors: Liu Shuo , Bai Jian-Dong , Wang Jie-Ying , He Jun , Wang Jun-Min ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, and Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China,   Collaborative Innovation Center of Extreme Optics, the Ministry of Education and Shanxi Province, Shanxi University, Taiyuan 030006, China
Published: December 2020

A narrow-linewidth continuous-wave single-frequency tunable 318.6-nm ultraviolet laser system with watt-level output power is developed in our experiment based on well-developed fiber lasers, fiber amplifiers, and efficient laser frequency conversion technique. Cesium 6S1/2—nP3/2 (n = 70—94) single-photon Rydberg excitation in a room-temperature cesium atomic vapor cell is realized by using our ultraviolet laser system. The single-photon Rydberg excitation signal is obtained via the V-type three-level atomic system which contains 6S1/2 (F = 4) ground state, 6P3/2 (F = 5) excited state and one of nP3/2 (n = 70—94) Rydberg states. When cesium atoms populated on the ground state are partially excited to Rydberg state by the ultraviolet laser, absorption of 852.3-nm probe beam which is locked to 6S1/2 (F = 4)—6P3/2 (F ′ = 5) hyperfine transition will decrease. In this way, the cesium Rydberg states are detected. The quantum defects for cesium nP3/2 (n = 70—94) Rydberg states are experimentally measured with a high-precision wavemeter. The variation trend of experimentally measured data deviates from that of calculated values. Due to the fact that the cesium vapor cell is positioned in a magnetic shielding tank, the Zeeman effect can be ignored. Considering that the polarizability of Rydberg atoms is proportional to (n*)7, in which n* is the effective principal quantum number, the Rydberg screen effect of cesium atomic vapor cell cannot completely protect cesium atoms from being perturbed by an external DC electric field. Therefore the residual DC electric field existing inside the cesium vapor cell will have a significant influence on quantum defect measurement of Rydberg atoms. Using the theoretical model of Stark effect and the relationship between polarizability of Rydberg atoms and the effective principal quantum number n*, the corrected experimental value of quantum defect for cesium nP3/2 (n = 70—94) Rydberg states is found to be ~(3.5591 ± 0.0007). The corrected experimental value of quantum defect is consistent with the calculation.
Enhancement of high-energy electron yield by interaction of ultra-intense laser pulses with micro-structured foam target
Authors: Wei Liu-Lei , Cai Hong-Bo , Zhang Wen-Shuai , Tian Jian-Min , Zhang En-Hao , Xiong Jun , Zhu Shao-Ping ,   Graduate School, China Academy of Engineering Physics, Beijing 100088, China,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China,   Center for Applied Physics and Technology, Peking University, Beijing 100871, China,   IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240, China,   Shanghai Institute of Laser Plasma Research, Shanghai 201800, China
Published: December 2020

Micro-structured targets have been widely used in the interaction between ultra-intense laser and target, aiming at improving the electron accelerating efficiency. In this paper, we perform two-dimensional particle-in-cell (PIC) simulations to study the interaction of the ultra-intense laser pulse with the micro-structured foam-attached target (the foam is composed of low density bubbles and high density interfaces between the bubbles). It is found that at the beginning of the laser-plasma interaction, the fast electrons accelerated at the front surface of the foam freely propagate into the target and drive a return current of cold background electrons. These cold background electrons are restricted to propagate along the interfaces between the bubbles in the foam due to the self-generated large sheath field. As a result, small current filaments are generated in the foam, which then leads to the generation of randomly distributed megagauss magnetic field in the foam layer. This quasistatic magnetic field then acts as an energy-selective " magnetic barrier”: the low-energy electrons are reflected back into the laser acceleration region while the high-energy electrons can penetrate through it. If the reflected electrons enter into the laser field with proper phases, they can be further accelerated to higher energy through cooperative actions of the ultra-intense laser pulse and the sheath field generated due to plasma expansion at the target surface. Our simulation results show that many of the laser accelerated low-energy electrons can be reflected back and accelerated several times until they gain enough energy to penetrate through the magnetic barrier. This is termed the " multiple acceleration mechanism”. Due to this mechanism, the electron acceleration efficiency in the foam-coated target with a thickness of several microns is significantly enhanced in comparison with that in the plane target. This enhancement in the electron acceleration efficiency will be beneficial to many important applications such as the fast ignition. Additionally, foam-coated targets with different bubble radii and layer thickness are also studied, and it is found that the yield of the high energy electrons increases with the radius of bubble size more efficiently than with the bubble thickness. In order to understand the physics more clearly, a single particle model is developed to analyze the simulation results.
Influences of nanoscale particles and interparticle compression in electrodes on voltage hysteresis of lithium ion batteries
Authors: Peng Jie-Yang , Wang Jia-Hai , Shen Bin , Li Hao-Liang , Sun Hao-Ming ,   School of Mechanical and Power Engineering, Tongji University, Shanghai 200433, China,   Shanghai Institute of Applied Mathematics and Mechanics, Shanghai 200444, China,   Air Conditioning Electronics Department, Pan Asia Technical Automotive Center Co., Ltd., Shanghai 201201, China
Published: December 2020

As one of high capacity electrode materials of lithium ion battery, silicon suffers significant stress effects, which further affects the voltage performance of battery. In this paper, a reaction-diffusion-stress coupled model is established, and the stress induced voltage hysteresis with consideration of diffusion induced stress, surface effects and interparticle compression under potentiostatic operation are investigated. It is found that stress and stress induced voltage hysteresis are dependent on particle size. For big particles, the diffusion induced stress is dominant and further aggravates the hysteresis of both stress and the overpotential consumed by it, indicating that more energy dissipates due to the stress effects. For small particles, especially ones with radius of a few nanometers, surface effects play a more prominent role than diffusion induced stress and the stress evolves into the state of compressive stress on the whole, leading the hysteresis of overpotential to be consumed by stress shrink and making the hysteresis plot of overpotential used to drive electrochemical reaction move downward. The electrode potential first reaches a cutoff voltage and finally the capacity of lithium ion battery decays. Therefore, too large or too small particle size in the electrode can both have a negative effect on the performance of lithium ion batteries, which indicates that an optimal size of the electrode particles must be designed in terms of electrode structure. Based on the calculation, particles with around 9 nm in radius are an appropriate option for electrode design in consideration of both diffusion induced stress and surface effect. In addition, for silicon electrodes, the silicon particles inevitably squeeze each other in a charge and discharge cycle. Therefore, interparticle compression is considered in this case. In detail, interparticle compression pushes the plot of stress hysteresis to the compressive state and leads to lower lithiation capacity, which makes the overpotential plot consumed by stress move downward and accordingly the overpotential plot used to drive the electrochemical reaction move upward. Denser electrode would strengthen this effect due to higher particle compression. It is indicated that for electrode design, the minimum of porosity ratio of electrodes should be adopted because higher interparticle compressive stress would reduce the battery capacity. Our results reveal that the voltage hysteresis of lithium ion batteries is related to the active particle size and the porosity ratio of the electrode, which is of great significance for guiding one in designing the lithium ion batteries.
Fabrication of synaptic memristor based on two-dimensional material MXene and realization of both long-term and short-term plasticity
Authors: Chen Yi-Hao , Xu Wei , Wang Yu-Qi , Wan Xiang , Li Yue-Feng , Liang Ding-Kang , Lu Li-Qun , Liu Xin-Wei , Lian Xiao-Juan , Hu Er-Tao , Guo Yu-Feng , Xu Jian-Guang , Tong Yi , Xiao Jian ,   College of Electronic and Optical Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023, China,   School of Materials Science and Engineering, Yancheng Institute of Technology, Yancheng 224051, China
Published: December 2020

Compared with conventional computation relying on the von Neumann architecture, brain-inspired computing has shown superior strength in various cognitive tasks. It has been generally accepted that information in the brain is represented and formed by vastly interconnected synapses. So the physical implementation of electronic synaptic devices is crucial to the development of brain-based computing systems. Among a large number of electronic synaptic devices, the memristors have attracted significant attention due to its simple structure and similarities to biological synapses. In this work, we first use two-dimensional material MXene as a resistive material and fabricate an electronic synapse based on a Cu/MXene/SiO2/W memristor. By using the unique properties of MXene, the conductance of the memristor can be modulated by the accumulation or reflux of Cu2+ at the physical switching layer, which can vividly simulate the mechanism of bio-synapses. Experimental results show that the Cu/MXene/SiO2/W memristor not only achieves stable bipolar analog resistance switching but also shows excellent long-term and short-term synaptic behaviors, including paired-pulse facilitation (PPF) and long-term potential/depression. By adjusting the pulse interval, the PPF index will change accordingly. In a biological system, the short-term plasticity is considered to be the key point for performing computational functions while the long-term plasticity is believed to underpin learning and memory functions. This work indicates that Cu/MXene/SiO2/W memristor with both long-term and short-term plasticity will have great application prospects for brain-inspired intelligence in the future.
Research progress of quantum memory
Authors: Dou Jian-Peng , Li Hang , Pang Xiao-Ling , Zhang Chao-Ni , Yang Tian-Huai , Jin Xian-Min ,   State Key Laboratory of Advanced Optical Communication Systems and Networks, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China,   Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Quantum technologies, for example, quantum communication and quantum computation, promise spectacular quantum enhanced advantages beyond what can be done classically. However, quantum states, as the element of quantum technologies, are very fragile and easily get lost to the environment, and meanwhile, their generation and quantum operations are mostly probabilistic. These problems make it exponentially hard to build long-distance quantum channels for quantum communication and large quantum systems for quantum computing. Quantum memory allows quantum states to be stored and retrieved in a programmable fashion, therefore providing an elegant solution to the probabilistic nature and associated limitation by coordinating asynchronous events. In the past decades, enormous advances in quantum memory have been made by developing various storage protocols and their physical implementations, and the quantum memory has gradually evolved from the initial conceptual demonstration to a nearly practical one. Aiming at being practicable for efficient synchronisation and physical scalability, an ideal quantum memory should meet several key features known as high efficiency, low noise level, large time bandwidth product (lifetime divided by pulse duration) and operating at room temperature. Here, we present the research status and development trends of this field by introducing some typical storage protocols. Among these protocols, a room-temperature broadband quantum memory is the most attractive due to its simplicity and practicability. However, at room temperature, noise becomes dominant and is a bottleneck problem that has impeded the realization of a real room-temperature broadband quantum memory in the last decades. Recently, the noise problem has been solved in two memory protocols, i.e. FORD (far off-resonance Duan-Lukin-Cirac-Zoller) protocol and ORCA (off-resonant cascaded absorption) protocol. In this paper, the working principles, the merits and demerits of various quantum memory protocols are illustrated. Furthermore, the approaches to eliminating noise and the applications of quantum memory are summarized.
First-principles calculations of solute-segreagtion of W-In alloys at grain boundaries
Authors: Wang Qi , Tang Fa-Wei , Hou Chao , Lü Hao , Song Xiao-Yan ,   Key Laboratory of Advanced Functional Materials, Education Ministry of China, College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China
Published: December 2020

In a tungsten-based alloy system, the appropriate solute elements are selected to produce strong segregation effect to reduce the interfacial formation energy, which can effectively improve the mechanical property and thermal stability of the system. Based on the first principles calculation, the solute segregation model of tungsten-based alloys is constructed. The W-In alloy is taken for example to study the grain boundary segregation behavior and bonding characteristics of solute at different concentrations. The bonding of the W-In system is revealed from the electronic structure, and the variation of the interface stability of the W-In system with the solute concentration is predicted. Based on the electronic structure analysis of bond population, differential charge density and density of states, the bond transition characteristics of solute atoms in the W-In system in the segregation process are found, and the microscopic mechanism of the W-In bond transitioning from the ionic bond inside the grain to the strong covalent bond in the grain boundary region is elucidated: the difference between the grain boundary and the intragranular structure leads to a decrease in the valence state of the W atom in the grain boundary and the oxidizability is weakened, eventually leading to the W-In bond transition. The non-monotonic variation of the intrinsic segregation energy of the solute with the concentration of In in the W-In system is obtained. The mechanism of the influence of solute concentration on the intrinsic segregation energy is revealed by analyzing the bond interaction and energy: the solute concentration remarkably affects the bond strength before and after the W-In bond segregation, resulting in a significant decrease in the segregation ability when the solute concentration is close to 0.0976, and finally the variation of the segregation energy with solute concentration is obtained. Based on the analysis of the phase mechanical stability and the solute segregation in the grain boundary, without considering the vacancy concentration, the optimal solute concentration range and the range that needs to be circumvented in the W-In alloy system with high thermal stability are predicted by the calculations of the model, which are 0.106−0.125 and 0.0632−0.106, respectively. This study provides theoretical basis and quantitative guidance for designing and preparing the tungsten-based alloy materials with high thermal stability.
Non-Gaussian entangled states and quantum metrology with ultracold atomic ensemble
Authors: Lu Bo , Han Cheng-Yin , Zhuang Min , Ke Yong-Guan , Huang Jia-Hao , Lee Chao-Hong ,   Laboratory of Quantum Engineering and Quantum Metrology, School of Physics and Astronomy, Sun Yat-Sen University (Zhuhai Campus), Zhuhai 519082, China,   State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-Sen University (Guangzhou Campus), Guangzhou 510275, China
Published: December 2020

Quantum metrology is the interdisciplinary of investigating how to utilize the principles of quantum mechanics to perform parameter estimation and improve the measurement precision by quantum effects. With the experimental developments of ultracold atoms, ultracold atomic ensemble provides an excellent platform for implementing quantum metrology. Attributed to well-developed techniques of quantum control, one can prepare several exotic non-Gaussian multi-particle entangled states in the ensembles of ultracold atoms. Based on many-body quanum interferometry, and using these non-Gaussian entangled states as probe, the high-precision measurement beyond the standard quantum limit can be realized. This article introduces the background and advancement of this field.
Heat transport behavior of bicrystal ZnO containing tilt grain boundary
Authors: Liu Ying-Guang , Bian Yong-Qing , Han Zhong-He ,   School of Energy, Power and Mechanical Engineering, North China Electric Power University, Baoding 071003, China
Published: December 2020

Zinc oxide (ZnO), as a conventional semiconductor material, has excellent characteristics, such as piezoelectricity, photoelectricity, gas sensitivity, etc. With the improvement of nanopreparation technology, different types of nanostructrued ZnO compounds have appeared and their heat conductions have become a main research topic in nanodevices. In order to study the effects of grain boundary on the thermal properties of materials of this kind, bicrystal ZnO containing small-angle and high-angle grain boundaries are constructed by the embedded dislocation line and coincidence site lattice method. The variation of grain boundary energy with tilt angle is studied by the non-equilibrium molecular dynamics simulation. In addition, the dislocation density is calculated by using the Frank-Bilby formula. Our results show that the grain boundary energy and dislocation density increase with the increase of tilt angle in a small-angle region, and they tend to be stable in a high-angle region. The tilt angle of 36.86° is defined as the transition angle. The trend of the Kapitza resistance is the same as that of the grain boundary energy and satisfies the theoretical value from the extended Read-Shockley model. Furthermore, it is found that both the Kapitza resistance and thermal conductivity have a significant size effect. When the sample length is between 23.2 nm and 92.6 nm, the Kapitza resistance decreases sharply with the increase of the length and then tends to be stable. The thermal conductivity of the sample increases with length increasing, but is always less than that of the single crystal. At the same time, temperature is an important factor affecting the heat transport properties. The Kapitza resistance and thermal conductivity decrease with temperature increasing. At different temperatures, the Kapitza resistance of 38.94° grain boundary sample is greater than that of 5.45° grain boundary sample. In order to further explore the influence mechanism of grain boundary angle on heat conduction, the phonon state density of 5.45° and 38.94° grain boundary sample are calculated. The results indicate that the high-angle grain boundary has stronger scattering for acoustic branch phonons and the peak frequency becomes lower, whereas the optical branch ones have almost no effect on the heat conduction.
Node influence of the dynamic networks
Authors: Ren Zhuo-Ming ,   Research Center for Complexity Sciences, Alibaba Business School, Hangzhou Normal University, Hangzhou 311121, China
Published: December 2020

Crucial to the physicists’ strong interest in the field is the fact that such macroscopic properties typically arise as the result of a myriad of interactions between the system constituents. Network science aims at simplifying the study of a given complex system by representing it as a network, a collection of nodes and edges interconnecting them. Nowadays, it is widely recognized that some of the structural traits of networks are in fact ubiquitous properties in real systems. The identification and prediction of node influence are of great theoretical and practical significance to be known as a hot research field of complex networks. Most of current research advance is focused on static network or a snapshot of dynamic networks at a certain moment. However, in practical application scenarios, mostly complex networks extracted from society, biology, information, technology are evolving dynamically. Therefore, it is more meaningful to evaluate the node's influence in the dynamic network and predict the future influence of the node, especially before the change of the network structure. In this summary, we contribute on reviewing the improvement of node influence in dynamical networks, which involves three tasks: algorithmic complexity and time bias in growing networks; algorithmic applicability in time varying networks; algorithmic robustness in a dynamical network with small or sharp perturbation. Furthermore, we overview the framework of economic complexity based on dynamical network structure. Lastly, we point out the forefront as well as critical challenges of the field.
Prediction of proton single event upset sensitivity based on heavy ion test data in nanometer hardened static random access memory
Authors: Luo Yin-Hong , Zhang Feng-Qi , Guo Hong-Xia , Wojtek Hajdas ,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi’an 710024, China,   Paul Scherrer Institute, Villigen PSI 5232, Switzerland
Published: December 2020

In order to evaluate the radiation tolerance to proton single event effect(SEE) in nanometer dual interlocked cell (DICE) hardening device accurately, single event upset (SEU) linear energy transfer (LET) threshold at heavy ion normal and tilt incidence, and the worst case SEU orientational angle are acquired based on the analysis of heavy ion SEU testing data in 65 nm dual DICE static random access memory (SRAM). It is proved that dual DICE design is effective for improving the LET threshold against SEU. Howerer, heavy ion tilt incidence at the worst orientational angle will significantly reduce the SEU threshold and increase the SEU cross section. The worst orientational angle for SEU in DICE SRAM is the large tilting angle along the well. The maximum LET value and the emission angle distribution of secondary particle induced by the nuclear reaction between protons with different energy and layers with different multiple metallization are obtained by using Monte-Carlo simulation. The maximum LET value of secondary particle from proton-copper spallation reaction is higher than 15 MeV·cm2/mg for 100 MeV and 200 MeV protons. Secondary particles with the maximum energy and longest range are emitted preferentially in the forward direction. Proton SEU sensitivity is further predicted through combining heavy ion test data with Monte-Carlo simulation. Proton SEU test data verify the effectiveness of the prediction method and the accuracy of the prediction results. The research results indicate that the tolerance of nanometer DICE hardening technique against proton SEU will be overestimated if SEE evaluation test is carried out with only 100 MeV proton accelerator or normal incidence. Proton single event upset in nanometer dual DICE SRAM has an evident dependence on tilt angle and orientational angle. By adopting the above prediction method, whether proton SEE test needs performing or not in nanometer radiation-hardening device can be judged and screened. The requirements for the maximum energy of proton accelerator can be ascertained. In order to ensure that the devices are applied to space with high reliability, SEE test should be carried out including tilt incidence at the worst orientational angle in nanometer DICE hardening device in the process of heavy ion and proton SEE test evaluation.
Application of compressive sensing based on multimode fiber specklegram in optical image encryption
Authors: Hu Yao-Hua , Liu Yan , Mu Ge , Qin Qi , Tan Zhong-Wei , Wang Mu-Guang , Yan Feng-Ping ,   Key Laboratory of All Optical Network and Advanced Telecommunication Network of Ministry of Education, Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

In order to ensure the secure and effective transmission of image information, a new method of optical image encryption using the multimode fiber (MMF) specklegram based compressive sensing combined with the double random phase encoding (DRPE) is proposed in this paper. The specklegrams obtained from the facet of the multimode fiber are used as the measurement matrix of compressive sensing (CS), and the compression and the first-stage encryption of the image are completed by compressive sensing, in which the specklegram also functions as the first secret key. Then, the second-stage encryption is implemented by using the double random phase encoding technology, in which the random phase mask acts as the second secret key. All of the specklegrams used in this paper are obtained from the facet of a 5 m-long and 105-μm-diameter-MMF and offset launching technique. Then the fiber specklegrams are proposed in several steps to provide the measurement matrix in CS. By performing an encryption and decryption test on a standard Lena image of 256 × 256 size, it is found that the decrypted image and the original image are visually consistent, and the encryption is also realized in the process of compression, which indicates the method proposed in this paper is feasible. Furthermore, the comparison studies of the performances of specklegram based measurement matrix and some classic measurement matrices show that the decrypted image quality using the specklegram matrix is better. And at the same time, comparing with the high hardware implementation complexity and high cost of other measurement matrices, specklegram based matrix can be easily realized by simple optical device, and the corresponding secret key can be easily changed by the working wavelength, which is helpful for enlarging the secret key space. It is further proved that the encryption method be able to effectively resist the statistical analysis attacks, cropping attacks and noise interference, and also have high sensitivity to the secret key, which shows good robustness and high security. Therefore, the image encryption method combined with the specklegram matrix based compression sensing with the optical DRPE can obtain good encryption effect and has a great secret key space, which may provide a good candidate scheme for the pure optical realization of image encryption.
Effects of wind-generated bubbles layer on sound propagation underneath rough sea surface in shallow water
Authors: Yao Mei-Juan , Lu Li-Cheng , Sun Bing-Wen , Guo Sheng-Ming , Ma Li ,   Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China,   Key laboratory of Underwater Acoustics Environment, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

The reflection coefficient of the flat sea surface in the ideal condition to the incident sound wave is –1. The perfect reflection effect does not introduce reflection loss. However, the sea surface is usually rough due to the wind. The wind-generated rough sea surface has not only reflection effect, but also scattering effect on the sound wave. At the same time, the wind-generated bubbles layer also has significant effect on the sound propagation. On the one hand, the bubbles layer can change the sound speed profile and result in the refraction of the incident sound wave. On the other hand, the bubbles layer has scattering effect and absorption effect on the incident sound wave and leads to the sound wave to attenuate. In fact, the rough sea surface and the bubbles layer are two main factors affecting the sound propagation in the windy weather at sea. Many researchers have paid much attention to the effect of the wind-generated rough sea surface on the sound propagation, but few of them have considered the effect of the wind-generated bubbles layer on the sound propagation. Based on the Ramsurf sound propagation model under the rough sea surface, the effects of wind-generated bubbles layer underneath rough sea surface on reflection loss and sound propagation with different wind speeds are analyzed. Based on the Hall-Novarini bubbles population model, the sound speed profile in the bubbles layer is modified and the attenuation coefficient due to scattering and absorption of the bubbles layer is calculated. The simulation results shows that when the wind speed is 10 m/s, the effect of the bubbles layer is significant on reflection loss with the frequencies higher than 2 kHz. In the given underwater acoustic environment, for a frequency of 3 kHz, when the source depth and the receiver depth are both 7 m, the enhancement of the transmission loss due to the bubbles layer is 2.6 dB for a wind speed of 13 m/s, and the enhancement is 8.1 dB for a wind speed of 16 m/s. And when the source depth and the receiver depth are both 18 m, the enhancement of the transmission loss due to the bubbles layer is 2.5 dB for a wind speed of 13 m/s and the enhancement is 4 dB for a wind speed of 16 m/s.
Experimental technique for dynamic fragmentation of materials via indirect drive by high-intensity laser
Authors: Chu Gen-Bai , Yu Ming-Hai , Shui Min , Fan Wei , Xi Tao , Jing Long-Fei , Zhao Yong-Qiang , Wu Yu-Chi , Xin Jian-Ting , Zhou Wei-Min ,   Science and Technology on Plasma Physics Laboratory, Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang 621900, China,   Departments of Experiments, Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

High intensity laser is an efficient method for shock generator to study the dynamic fragmentation of materials, in which the direct drive is widely utilized. The continuum phase plate is used for smoothing the focal spot of the laser, but the loading region is usually smaller than the designed value. In this work, we study an experimental technique for investigating the dynamic fragmentation of metal via indirectly driving a high-intensity laser. Firstly, the radiation distributions on the sample for four different hohlraums each with a diameter of 2 mm but different length are simulated via the IRAD software, in which the proper hohlraum with a diameter of 2 mm and a height of 2 mm is selected for the experiments. Secondly, the peak temperatures and radiation waves under different laser energy and pulse durations are measured. The peak temperature decreases simultaneously as the laser energy decreases. In addition, the loading shock waves under a peak temperature of 140 eV and different radiation waves are estimated via the hydrodynamic simulation. It is revealed that a peak pressure of several tens of gigapascals is acquired and the peak pressure is greatly increased when the 10 μm CH layer is placed on the sample. In the end, the dynamic fragmentation process via indirect drive is investigated by using the high energy X-ray radiography and photonic Doppler velocimetry. The radiograph is a snapshot at 600 ns and shows a typical result of the spall process. The first layer is measured to be 0.06 mm thick and 0.3 mm away from the unperturbed free surface. It is also exhibited that the hohlraum is expanded to a large extent but is not broken up. The jump-up velocity and time of spall are measured to be 0.65 km/s and 131 ns, respectively. The average velocity of the first layer is estimated to be (0.63 ± 0.1) km/s, obtained via the distance of 0.3 mm divided by the time difference of 469 ns (600 ns minus 131 ns). The one-dimensional loading region is 2 mm, and the flatness is better than 5 %. This work provides a reference for designing new hohlraum, shock wave loading technique and dynamic fragmentation process.
Dynamic model of high speed following traffic flow
Authors: Chen Yong , Zhang Wei ,   School of Electronic and Information Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China,   School of Traffic and Transportation, Lanzhou Jiaotong University, Lanzhou 730070, China
Published: December 2020

For the physical phenomenon of high-speed car following in the road traffic flow, all the vehicles with small spacing do not run at low speed. The speeds of the vehicles are significantly higher than those they normally should be when they are in this vehicles’s density. There are more than 7% of high-speed following vehicles in the measured data. At present, the traditional traffic flow model cannot simulate the phenomenon of high-speed car following, so a new nonlinear dynamic mathematical model is needed to describe and analyze the physical phenomenon. In order to study the physical phenomenon of high-speed car following in road traffic, a traffic flow dynamics model for simulating the phenomena is proposed, which combines with the prospect theory and takes into account some factors such as driver’s decision-making behavior and randomization. It is called HCCA (high-speed car following celluar automat) model. In the model, the prospect theory is used to analyze the driver’s lane changing behavior under the uncertain conditions. Combined with the characteristics of the radical driver, the dynamic prediction speed is considered for the front car followed by the radical driver, and the HCCA dynamics rules of high-speed following traffic flow mechanics are defined. By the computer numerical simulation, the evolution mechanism and the characteristics of high-speed car-following flow are studied. The results show that compared with the symmetric two-lane cellular automata (STCA) dynamic model, the HCCA dynamic model established in this paper can simulate abundant traffic physical phenomena, and reproduce complex traffic phenomena such as free flow, synchronous flow and wide-range motion congestion. Finally, the phenomenon of high-speed car following is simulated and the results of high-speed car following rate over 7% with small spacing are in good agreement with the measured results. It overcomes the shortage that traditional STCA model cannot simulate the synchronous flow. It is found that the larger the proportion of radical drivers, the larger the high-speed car following rate and traffic flow with small spacing are under the same road density. The high-speed car following traffic flow mechanics model proposed in this paper has a certain reference significance and practical value for analyzing the physical phenomenon of high-speed car following and enriching the traffic flow theory.