bluuebunny/crossref_metadata_2025 huggingface dataset:
Entropy and glass formation
Authors: Li Rui-Xuan  , Zhang Yong  ,   State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

Entropy is a state function of the real physical system, which relates to the chaos of a system. During the long-term exploring glass-forming systems, many empirical rules are put forward, including “confusion principle” and three empirical rules.Over a long period of exploring, many glass-forming alloys are developed based on those principles, while some questions have been raised in recent years based on the experimental results, because some other uncertain factors also have influence on the glass-forming ability (GFA) except a number of constituents, e.g., entropy. Greer claimed that in the “confusion principle” the higher the entropy value, the better the glass-formation ability will be, which does not accord with the recent experimental results.The effects of entropy on the glass-formation ability are summarized from the viewpoints of thermodynamics, kinetics, and complexity of atomic structures. In the aspects of thermodynamics and structure, the increase of entropy has a positive effect on glass formation, while in kinetics, the influence is negative. From the viewpoint of thermodynamics, the increase of entropy leads to the decrease of the entropy difference between solid phase and liquid phase, and therefore, the difference in Gibbs free energy between these two phases decreases. At a certain time during solidification, compared with the low-entropy alloy, the high-entropy alloy in the solid phase has an atomic arrangement close to that in the liquid, and it is more likely to form the amorphous phase.In the aspect of kinetics, the increase of entropy results in the decrease of the viscosity of the system according to the Adam-Gibbs equation. As a result, atoms diffuse easily in the system and the ordered-phase is more likely to form, which means that the glass-formation ability decreases with the increase of entropy. Furthermore, in the aspect of atomic structure, the increase of mismatch entropy relates to the big misfit degree between atoms, i. e., the large atomic size difference. Atoms in the high-entropy alloy tend to distribute disorderly in the system, and therefore the stress between atoms increases. As a result, with the increase of the entropy, the ordered-phase becomes unstable and the GFA will be enhanced.Furthermore, the high-entropy-glass is briefly reviewed and analyzed, which is a new system between high-entropy alloy and amorphous alloy. There have been many high-performance high-entropy-glass systems reported up to now. Researches about this unique system will contribute to developing some new amorphous alloys with excellent performances, and more importantly, to exploring the complex relationship between GFA and multicomponent alloys.
Ion irradiation of metallic glasses
Authors: Bian Xi-Lei  , Wang Gang  ,   Labrotary for Microstructures, Institute of Materials, Shanghai University, Shanghai 200444, China
Published: December 2020

Metallic glasses (MGs), as new disordered materials prepared by rapidly quenching melted alloys, have attracted tremendous attention in the material science community. Due to their long-ranged disorderd and short-ranged ordered structures, MGs usually exhibit uniquely physical, chemical and mechanical properties, which give rise to promising applications in many fields, and especially they are expected to be potentially structural materials used in irradiation conditions, such as in nuclear reactors and aerospace.In this paper, the effects of ion irradiation on the microstructure, mechanical properties, physical, and chemical properties of MGs are reviewed. It is found that the effects of ion irradiation on the microstructures and mechanical properties depend on the ion energy as well as the composition of MG. When high energy ions interact with a solid, the collisions take place between the incident ions and atoms of the solid, which are dominated by inelastic processes (electronic stopping) and elastic processes (nuclear stopping). The inelastic processes result in the excitation and ionization of substrate atoms. In contrast, the elastic processes lead to ballistic atomic displacements. Nuclear stopping can produce structure defects and irradiation damage in glassy phase. The collisions between the incident ions and the target atoms in MGs can cause the target atoms to deviate from their original positions, and leave a large number of vacancies and interstitial atoms behind. The separations between the vacancies and the interstitial atoms form displacement cascades. The interstitial atoms with a low kinetic energy can transfer self-energies to thermal energies, resulting in a thermal spike due to the accumulation of a large quantity of the thermal energies from interstitial atoms. Such a thermal spike will cause MGs to melt and resolidify, which therefore makes the structure of glassy phase changed. Furthermore, the ion irradiation can modify the structures of MGs by introducing excessive free volumes and promoting the mobilities of atoms, which leads to the dilatation of the glassy phase and nanocrystallization. The increase of free volumes softens the MGs, and then causes the plastic deformation mechanism to transform from a heterogeneous deformation to a homogeneous deformation, which significantly enhances the plastic deformation ability.This review paper can not only improve the understanding of the relationship between microstructure evolution and macroscopic mechanical properties, and provide an experimental and fundamental basis to understand the deformation mechanism of MGs, but also summarize the performances of MGs under high dosage of ion irradiation. Moreover, it is of fundamental and practical importance for engineering applications of such advanced materials.
Quantum phase transitions of one-dimensional period-two anisotropic XY models in a transverse field
Authors: Song Jia-Li  , Zhong Ming  , Tong Pei-Qing  ,   Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, Nanjing 210023, China;,   Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex Systems, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

The quantum phase transitions of one-dimensional period-two anisotropic XY models in a transverse field with the Hamiltonian where the anisotropy parameters i take and alternately, are studied. The Hamiltonian can be reduced to the diagonal form by Jordan-Wigner and Bogoliubov transformations. The long-range correlations Cx and Cy are calculated numerically. The phase with Cx Cy0 (or Cy Cx0) is referred to as the ferromagnetic (FM) phase along the x (or y) direction, while the phase with Cx=Cy=0 is the paramagnetic (PM) phase. It is found that the phase diagrams with the ratio -1 and =-1 are different obviously. For the case with -1, the line h=hc1=1-[(1-)/2]2 separates an FM phase from a PM phase, while the line =0 is the boundary between a ferromagnetic phase along the x direction (FMx) and a ferromagnetic phase along the y direction (FMy). These are similar to those of the uniform XY chains in a transverse field (i.e., =1). When =-1, the FMx and FMy phases disappear and there appears a new FM phase. The line h=hc2=1-2 separates this new FM phase from the PM phase. The new phase is gapless with two zeros in single particle energy spectrum. This is due to the new symmetry in the system with =-1, i.e., the Hamiltonian is invariant under the transformation 2ix 2i+1y,2iy 2i+1x. The correlation function between the 2i-1 and 2i lattice points along the x (y) direction is equal to that between the 2i and 2i+1 lattice points along the y (x) direction. As a result, the long-range correlation functions along two directions are equivalent. In order to facilitate the description, we call this gapless phase the isotropic ferromagnetic (FMxx) phase. Finally, the relationship between quantum entanglement and quantum phase transitions of the system is studied. The scaling behaviour of the von Neumann entropy at each point in the FMxx phase is SL~1/3log2L+ Const, which is similar to that at the anisotropic phase transition point of the uniform XY model in a transverse field, and different from those in the FMx and FMy phases.
All-fiber radio frequency-modulated pulsed laser based on frequency-shift feedback loop
Authors: Yang Hong-Zhi  , Zhao Chang-Ming  , Zhang Hai-Yang  , Yang Su-Hui  , Li Chen  ,   School of Opto-Electronics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

Lidar-radar by using an radio frequency modulated (RF-modulated) laser transmitter is a powerful technique for applications involving remote sensing. The method is based on the use of an optically carried RF signal in order to acquire the merits of both the directivity of the optical beam (lidar) and the accuracy of RF signal processing (radar). Compared with single-frequency coherent lidars, lidar-radars are less sensitive to atmospheric turbulence and the speckle noise induced by target roughness. For long range detection, pulsed operation is usually required because of the high peak power. In order to meet the requirement for long range detection, an RF-modulated pulse train based on an all-fiber frequency shifted feedback loop is proposed in this paper. A continuous-wave single-frequency fiber laser (seed laser) is coupled into a fiber link and an acousto-optic chopper is used as a frequency shifter and beam chopper. A Yb3+-doped fiber amplifier is used to compensate for the loss of the signal in the fiber loop. The pulse duration is determined by the open time of acousto-optic chopper, which is fixed at 110 ns. A square wave generated by an arbitrary waveform generator is used as a trigger signal of the acousto-optic chopper. The RF within the pulse results from the interference of frequency shifed pulse with the seed laser. By inserting a 10 km fiber in the loop and accurately controlling the trigger cycle of the acousto-optic chopper equal to the roundtrip time of the loop, the pulse train generated by acousto-optic chopper can circulate in the loop, leading to the generation of RF-modulated pulse with about 20 kHz repetition rate and 110 ns width. The gain provided by fiber amplifier in the loop partially compensates for the loss. By adjusting the gain of fiber amplifier, the modulation depth of RF within the pulse can be continuously adjusted and the maximum modulation depth is 0.67. We also present an time-delayed scalar interference model which includes the loop length, trigger cycle, frequency-shift, and the gain. According to the theoretical model, the RF-modulated pulse affected by trigger cycle and fiber amplifier is numerically simulated. The experimental results accord well with theoritical predictions. The RF-modulated pulse has the advantage of high pulse-to-pulse coherence, which provides potential applications in lidar-radar detection. Besides, with an additional frequency doubling stage one can obtain a source for underwater detections and communications. Extension of the scheme to the 1.5 μm telecommunication window is straightforwardfor various radio-over-fiber applications.
A passive range method of underwater source based on single hydrophone
Authors: Li Xiao-Man  , Piao Sheng-Chun  , Zhang Ming-Hui  , Liu Ya-Qin  , Zhou Jian-Bo  ,   College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin 150001, China;,   Acoustic Science and Technology Laboratory, Harbin Engineering University, Harbin 150001, China
Published: December 2020

Aiming at the passive impulse wideband source range problem in shallow water waveguides, a passive source range method with single hydrophone which is applied to the shallow water waveguide with a bottom of liquid semi-infinite space is presented in this paper by combining the group delay theory and warping transformation. The receive signal is composed of several normal modes, and each mode represents many characteristics of the waveguide environment. Warping transformation is a good tool which can achieve the separation and extraction of normal modes from the received signal, and it is also an unitary and reversible transformation, so the warped signal of each normal mode can be recovered completely. The dispersion curves of normal modes can be extracted by warping transformation, and the relation between arrival time and frequency of each order normal mode can also be calculated, and then the time delay of arriving hydrophone between arbitrary two different normal modes is obtained. According to the group delay theory, different order normal mode has different arrival time at the same frequency, and the arrival time of normal mode is determined at its group speed when the distance between the source and hydrophone is certain. So the propagation range can be estimated when the time delay and the slow group speed difference between two different normal modes are known. When the waveguide environmental parameters are known, the slow group speed difference of arbitrary two normal modes can be calculated by KRAKEN. However, when the bottom parameters are unknown, the bottom reflection phase shift parameter is an important parameter describing the acoustic parameters of the bottom, and it contains nearly all the bottom information, what is more, the bottom reflection phase shift parameter is also a parameter that can be extracted by some experimental data easily. When the depth and the average sound speed of the water column are known, the slow group speed difference between two order normal modes can be represented by the seafloor phase shift parameter. Therefore, the source range can be represented by the bottom reflection phase shift parameter, the sea depth and the mean sound speed in the waveguide, and under this condition, the source location can be estimated by one single hydrophone. The effectiveness and accuracy of the method are proved by the numerical simulation results and sea experimental data processing, in which the signals are both received by a single hydrophone. The sea experimental data contain linear frequency modulation impulse source signal and explosion sound source signal, and the mean relative error of range estimation is less than 10%.
Transient structure of thin films based on one-dimensional chain model
Authors: Guo Xin  , Li Ming-Hua  , Li Yi-Fei  , Tao Meng-Ze  , Wang Jin-Guang  , Li Da-Zhang  , Xin Jian-Guo  , Chen Li-Ming  ,   School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China;,   Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China;,   IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240, China;,   Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Functional materials have received much attention in the development of scientific technology. Macroscopic function of material is usually linked to the microscopic properties. In order to understand the relationship between structure and function, it is necessary to observe transient structural change of material in real time. In the earlier experimental work femtosecond optical probes were used to measure associated modulation in optical properties like transmissivity or reflectivity and extract the information about structural dynamics through sophisticated theoretical modeling. Since the development of laser-based ultrafast X-ray sources, there has been extensive work on femtosecond X-ray diffraction measurements. The coupling of sensitive X-ray with time-resolved pump-probe technique provides a way to directly monitor the time-dependent lattice structural changes in condensed matter. Recent researches are devoted to the study of non-thermal melting and coherent acoustic photons. The classical continuous elastic equation can only provide a limited view of structural dynamics. So, simulation of structural dynamics at an atomic level and comparison of such simulation with time-resolved X-ray diffraction data are necessary.#br#In this paper, we use the one-dimensional chain model to study the effect of thermal stress on the lattice due to the inhomogeneity of temperature distribution after ultrafast laser heating. It is developed from the classic continuous elastic equation by considering a nanometer film as a chain of point mass connected by springs. The simulation can directly reveal the positon of each point mass (atom) as a function of time for a given temperature (stress) profile. The simulation results accord very well with experimental data obtained with femtosecond X-ray diffraction. Compared with simulation results, the ultrafast X-ray diffraction experimental results are not enough to distinguish the compression near the zero time, but the characteristic time (~123 ps) and broadening of the diffraction peak are clearly observed. The simulation and experimental study of the lattice structural response are of great help for understanding the direct relationship between the lattice responses caused by ultrafast laser excitation, the generation and propagation of strain, one-dimensional chain model has important applications in studying the recoverable ultrafast lattice dynamics of metals, semiconductors and other materials.
Contributions to Verdet constant of magneto-optical materials
Authors: Cai Wei  , Xing Jun-Hui  , Yang Zhi-Yong  ,   Armament Launch Theory and Technology Key Discipline Laboratory of China, Rocket Force University of Engineering, Xi'an 710025, China;,   Science and Technology on Electro-optic Control Laboratory, Luoyang 471000, China
Published: December 2020

Verdet constant is one of the key parameters to characterize the material magneto-optical properties, and dependent on wavelength and temperature. In order to thoroughly analyze the influence mechanisms of the incident wavelength and temperature on the Verdet constant and then uncover its essence, both the advantages and disadvantages of the classical electronic dynamics theory and quantum theory are discussed on account of basic theories and test data. However, neither of the two theories can be separately used to fully explain the Verdet constant and the correlative test data. Therefore, based on the essential property of the magneto-optical effect, the interactions between the incident light and magnetic matter in a magnetic field are studied, and then a hypothesis which suggests that the Faraday effect result from the combination of various factors is proposed. Furthermore, a theory of wave-transition contribution to the Verdet constant is deduced by adopting the theory of wave-particle duality. That is, the Faraday effect is caused by two different contributions simultaneously. One is the wave contribution, which is the interaction between the wave aspect of light and the magneto-optical medium, and the other refers to the transition contribution, which comes from the electronic transition. When the light enters into a deflection angle, the wave contribution is positive while the transition contribution is negative. In a diamagnetic material, since the wave contribution is greater than the transition contribution, the diamagnetic Verdet constant is positive while in a paramagnetic material, on the contrary, the transition contribution is much larger than the wave contribution, so the paramagnetic Verdet constant is negative. According to the above-mentioned theory, the diamagnetic Verdet constant model and the paramagnetic Verdet constant model are proposed by combining the two parts together. Taking the typical diamagnetic material ZF1 and the typical paramagnetic terbium gallium garnet for example, the influences of the incident wavelength and the temperature on the Verdet constant are analyzed, and the deduced theory together with the corresponding models is tested and verified by analyzing the relevant parameters and the test data. Accordingly, the research turns out that the theoretical results correspond to the real values, which proves the rationality of the hypothesis and the authenticity of the deduced theory. Compared with the traditional theories, the wave-transition contribution theory and its model are superior in the sense of precisely describing the material Verdet constant.
Confocal-cavity-enhanced Raman scattering of ambient air
Authors: Li Bin  , Luo Shi-Wen  , Yu An-Lan  , Xiong Dong-Sheng  , Wang Xin-Bing  , Zuo Du-Luo  ,   Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China;,   School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China}
Published: December 2020

Raman spectroscopy is a powerful diagnostic method for gas analysis due to its advantages like non-invasiveness and fast speed. However, its applications are greatly restricted because of the weak signal level caused by small scattering cross section. In order to enhance the Raman signal level and improve the detection sensitivity, a sample cell of confocal cavity is designed and the enhanced Raman signal of ambient air based on this cavity is demonstrated experimentally. The confocal cavity is constructed with a pair of plano-concave reflectors with a curvature radius of 150 mm and reflectivity of 92%. This low reflectivity design not only allows for bandwidth matching with the line-width of excitation laser but also makes the resonant condition satisfied easily. The measured output power of the confocal cavity is over 42 mW in resonant condition, which gives a coupling efficiency of 87.5% when divided with the input power 48 mW. The high coupling efficiency enables the output power efficiently to reach 11 times that for the intra-cavity laser power in one direction. Raman scattering of ambient air is tested to verify the performance of the confocal cavity. In our experiments, the Raman signals are collected in a forward scattering configuration by an imaging Raman spectrometer which is connected to a CCD camera. Strong Raman signals of O2 and N2, even H2O are observed with 1 s exposure time in resonant condition, and rotational lines (O-branch and S-branch) of O2 and N2 are also clearly detected when exposure time is set to be 10 s. Compared with the results obtained without confocal cavity, the Raman signal level is enhanced 17 times and the signal-to-noise ratio is improved twice. In addition, a limit of detection (3) at a magnitude of 200 ppm for CO2 in ambient air is achieved for the resonant confocal cavity. These results indicate that the system can significantly enhance the spontaneous Raman scattering signal level and improve the detection sensitivity. Furthermore, the confocal cavity is applicable to the Raman analyses of other gas samples.
Electronic structure and mechanical properties of Nb-doped -TiAl intermetallic compound
Authors: Chen Zhi-Peng  , Ma Ya-Nan  , Lin Xue-Ling  , Pan Feng-Chun  , Xi Li-Ying  , Ma Zhi  , Zheng Fu  , Wang Yan-Qing  , Chen Huan-Ming  ,   School of Physics and Electronic-Electrical Engineering, Ningxia University, Yinchuan 750021, China
Published: December 2020

This investigation aims at an Nb-doped -TiAl intermetallic compound system in which part of Ti or Al atoms are substituted by Nb atoms. The structural parameters, the energy band structures, the electronic densities of states and the elastic constants of Nb-doped -TiAl intermetallic compound are calculated and studied by using the first-principles method based on the density functional theory and other physical theory. The first-principle calculations presented here are based on electronic density-functional theory framework. The ultrasoft pseudopotentials and a plane-wave basis set with a cut-off energy of 320 eV are used. The generalized gradient approximation refined by Perdew and Zunger is employed for determining the exchange-correlation energy. Brillouin zone is set to be within 333 k point mesh generated by the Monkhorst-Pack scheme. The self-consistent convergence of total energy is at 1.010-6 eV/atom. In view of geometry optimization, it is shown that doping with Nb can change the structural symmetry of the -TiAl intermetallic compound. The calculated formation energies indicate that the formation energy of the system in which Ti atom is replaced by Nb atom is smaller than that of Al atom replaced by Nb atom. Accordingly, they tend to substitute Ti atom when Nb atoms are introduced into the -TiAl system. The calculated band structures of Nb-doped -TiAl system show that they all have metallic conductivities, which implies that the brittleness of -TiAl intermetallic compound could be tailored by Nb-doping. The partial densities of states of the Nb-doped and pure -TiAl systems indicate that the intensity of covalent bond between Ti atom and Nb atom is weaker than covalent bond between Ti atom and Al atom while the Ti atoms are replaced by Nb atoms in the -TiAl system. What is more, the density of states near Fermi energy increases after Al atoms has been replaced by Nb atoms in the -TiAl system. This is an important factor for improving the ductility of -TiAl intermetallic compound. The calculated elastic constants, bulk modulus and shear modulus of Nb-doped -TiAl systems indicate that the ductility and the fracture strength of Nb-doped -TiAl system are both better than those of pure -TiAl system, especially in the system where part of Al atoms are replaced by Nb atoms. The plastic deformation capacity of Nb-doped -TiAl system is thus improved comparatively.
Four-partite Bell inequalities based on quantum coherence
Authors: Ye Shi-Qiang  , Chen Xiao-Yu  ,   College of Information and Electronic Engineering, Zhejiang Gongshang University, Hangzhou 310018, China
Published: December 2020

It is well known that Bell inequalities are derived under the assumptions of locality and realism. Bell inequalities impose strict constraints on the statistical correlations of measurements of multipartite systems. Violating each of them guarantees the existence of quantum correlations in a quantum state. A quantum state with non-vanishing entanglement may violate some Bell inequalities. Recent progress of the fields like quantum biology and quantum thermodynamics reveals a particular role of quantum coherence in quantum information processing. Quantum coherence is identified by the presence of off-diagonal terms in the density matrix. To quantify quantum coherence of a given state, Baumgratz et al. (Baumgratz T, Cramer M, Plenio M B 2014 Phys. Rev. Lett. 113 140401) provided several kinds of coherence measures such as l1-norm of coherence and relative entropy of coherence. In this paper, we propose to use quantum coherence to derive Bell inequalities. We construct the Bell inequalities of four-partite product states with l1-norm of coherence, relative entropy of coherence. In the Bell inequalities of four-partite correlations, measurement operators are products of local measurement operators. Each local operator is one of the two arbitrary observables. We consider the violations of the four-partite Bell inequalities by the four-partite general pure Greenberger-Horne-Zeilinger (GHZ) state, cluster states, W states with real coefficients. We also investigate the violations of the four-partite Bell inequalities by the four-partite GHZ class mixed states, cluster class mixed states, W class mixed states and Dicke class mixed states. It is shown that the four-partite Bell inequalities in terms of relative entropy of coherence are always violated by the four-partite general pure GHZ states, cluster states with the real coefficients. Hence there is non-vanishing entanglement for these states.
Receptivity mechanism of cross-flow instablity modes induced in three-dimensional boundary layer
Authors: Lu Chang-Gen  , Zhu Xiao-Qing  , Shen Lu-Yu  ,   School of Marine Science, Nanjing University of Information Science and Technology, Nanjing 210044, China
Published: December 2020

Boundary-layer receptivity is the initial stage of the laminar-turbulent transition process, which plays a key role in the transition, especially for the case of three-dimensional boundary-layer flow. The research of the three-dimensional boundary-layer receptivity is theoretically significant for further understanding of the mechanisms of laminar-turbulent transition and turbulence formation. A numerical method is used to study the three-dimensional boundary-layer receptivity under the interaction of the free-stream turbulence and the three-dimensional localized wall roughness. Then whether a new cross-flow instability mode can be found in the three-dimensional boundary layer is studied. Subsequently, investigated are the conditions under which the steady or unsteady cross-flow instability mode can be induced in the three-dimensional boundary layer, the influences of the intensity, spanwise wave number and normal wave number of the free-stream turbulence, and the size and structure of the three-dimensional roughness on the three-dimensional boundary-layer receptivity under the free-stream turbulence interacting with the three-dimensional localized wall roughness, and the instability mode that can be induced and its role in the three-dimensional boundary-layer receptivity. The numerical results show that when the turbulence intensity is low, the steady cross-flow vortex excited by the three-dimensional localized wall roughness dominates the three-dimensional boundary-layer receptivity; on the contrary, when the turbulence intensity is high, the unsteady cross-flow vortex excited by the free-stream turbulence dominates the receptivity; additionally, when the interaction between the three-dimensional localized wall roughness and the free-stream turbulence is existent, three kinds of instability modes are all produced at the same time, namely, the steady cross-flow vortex, the unsteady cross-flow vortex and the new unsteady cross-flow vortex whose dispersion relation is equal to the linear combination of the positive and negative spanwise wave numbers of the first steady cross-flow vortex and the second unsteady cross-flow vortex. The in-depth research on the three-dimensional boundary-layer receptivity under the interaction of the free-stream turbulence and the three-dimensional localized wall roughness is of benefit to accomplishing the hydrodynamic instability theory and the turbulence theory, and providing the theoretical foundation for the prediction and control of the laminar-turbulent transition.
Lorentz force particle analyzer with an array probe based on speckle pattern interferometry
Authors: Dai Shang-Jun  , Wu Si-Jin  , Wang Xiao-Dong  , Shi Yi-Shi  ,   School of Material Science and Opto-electronics Technology, University of Chinese Academy of Sciences, Beijing 100049, China;,   School of Instrumentation Science and Opto-electronics Engineering, Beijing Information Science and Technology University, Beijing 100192, China;,   Academy of Opto-electronics, Chinese Academy of Sciences, Beijing 100094, China
Published: December 2020

A new contactless technique called Lorentz force particle analyzer (LFPA) with an array probe for detecting the flaws in metallic material is presented in this paper. Based on the principle of LFPA, the shape and size of the flaw or the direction of the crack can be obtained by analyzing the pulses of the force acting on the permanent magnet. In the LFPA system, the small Lorentz force on the magnet is measured by a laser-cantilever system with high sensitivity, which operates in a similar principle to that of an atomic force microscope. The traditional displacement detecting method in the LFPA is not suitable for the array probe presented in this paper due to its complex structure. Therefore, speckle pattern interferometry is introduced into the LPFA. The speckle pattern interferometry can measure not only the out-of-plane displacement of the multiple cantilever in the array probe, or of slopes of deformation, but also the in-plane displacement. Those advantages make the speckle pattern interferometry a useful tool in the LFPA for analysing the shapes of the flaws and the directions of the cracks. In this paper, a Michelson-type shear of graphic setup with enlarged angle of view is built to measure the displacement of the cantilever which is deformed by the flaws in the sample. Four frames of shear under several grams before and after the deformation are captured and recorded by a digital camera. The phase difference is processed for calculating the displacement with the software which is designed for the LFPA. A full-field measurement of the cantilever displacement is achieved and the relationship between the phase difference and the volume of the flaws is also obtained successfully. The utilization of the speckle pattern interferometry technique in the LFPA leads to the invention of a new real-time, online, in-situ contactless technique of detecting the shapes of the internal flaws and the directions of the cracks.
An improved evaluating method of node spreading influence in complex network based on information spreading probability
Authors: Ruan Yi-Run  , Lao Song-Yang  , Wang Jun-De  , Bai Liang  , Hou Lü-Lin  ,   Science and Technology on Information Systems Engineering Laboratory, National University of Defense Technology, Changsha 410073, China;,   Joint Service College, National Defense University, Beijing 100858, China
Published: December 2020

How to evaluate the node spreading ability and how to find influential nodes in complex networks are crucial to controlling diseases and rumors, accelerating or hindering information from diffusing, and designing effective advertising strategies for viral marketing, etc. At present, many indicators based on the shortest path, such as closeness centrality, betweenness centrality and the (SP) index have been proposed to evaluate node spreading influence. The shortest path indicates that the information transmission path between nodes always selects the optimal mode. However, information does not know the ideal route from one place to another. The message does not flow only along geodesic paths in most networks, and information transmission path may be any reachable path between nodes. In the network with high clustering coefficient, the local high clustering of the nodes is beneficial to the large-scale dissemination of information. If only the information is transmitted according to the optimal propagation mode, which is the shortest path propagation, the ability to disseminate the node information would be underestimated, and thus the sorting precision of node spreading influence is reduced. By taking into account the transmission rate and the reachable path between a node and its three-step inner neighbors, we design an improved method named ASP to generate ranking list to evaluate the node spreading ability. We make use of the susceptible-infected-recovered (SIR) spreading model with tunable transmission rate to check the effectiveness of the proposed method on six real-world networks and three artificial networks generated by the Lancichinetii-Fortunato-Radicchi (LFR) benchmark model. In the real data sets, the proposed algorithm can achieve a better result than other metrics in a wide range of transmission rate, especially in networks with high clustering coefficients. The experimental results of the three LFR benchmark datasets show that the relative accuracy of ranking result of the ASP index and the SP index changes with the sparseness of the network and the information transmission rate. When the information dissemination rate is small, SP index is slightly better than the ASP index. The reason for this result is that when the transmission rate is small, the node influence is close to the degree. However, when the transmission rate is greater, the accuracy of the ASP index is higher than those of other indicators. This work can shed light on how the local clustering exerts an influence on the node propagation.
Denoising of contaminated chaotic signals based on collaborative filtering
Authors: Chen Yue  , Liu Xiong-Ying  , Wu Zhong-Tang  , Fan Yi  , Ren Zi-Liang  , Feng Jiu-Chao  ,   School of Electronic and Information Engineering, South China University of Technology, Guangzhou 510641, China;,   School of Electronic and Information Engineering, Guangdong Polytechnic Normal University, Guangzhou 510665, China
Published: December 2020

Reconstructing chaotic signals from noised data plays a critical role in many areas of science and engineering. However, the inherent features, such as aperiodic property, wide band spectrum, and extreme sensitivity to initial values, present a big challenge of reducing the noises in the contaminated chaotic signals. To address the above issues, a novel noise reduction algorithm based on the collaborative filtering is investigated in this paper. By exploiting the fractal self-similarity nature of chaotic attractors, the contaminated chaotic signals are reconstructed subsequently in three steps, i.e., grouping, collaborative filtering, and signal reconstruction. Firstly, the fragments of the noised signal are collected and sorted into different groups by mutual similarity. Secondly, each group is tackled with a hard threshold in the two-dimensional (2D) transforming domain to attenuate the noise. Lastly, an inverse transformation is adopted to estimate the noise-free fragments. As the fragments within a group are closely correlated due to their mutual similarity, the 2D transform of the group should be sparser than the one-dimensional transform of the original signal in the first step, leading to much more effective noise attenuation. The fragments collected in the grouping step may overlap each other, meaning that a signal point could be included in more than one fragment and have different collaborative filtering results. Therefore, the noise-free signal is reconstructed by averaging these collaborative filtering results point by point. The parameters of the proposed algorithm are discussed and a set of recommended parameters is given. In the simulation, the chaotic signal is generated by the Lorenz system and contaminated by addictive white Gaussian noise. The signal-to-noise ratio and the root mean square error are introduced to measure the noise reduction performance. As shown in the simulation results, the proposed algorithm has advantages over the existing chaotic signal denoising methods, such as local curve fitting, wavelet thresholding, and empirical mode decomposition iterative interval thresholding methods, in the reconstruction accuracy, improvement of the signal-to-noise ratio, and recovering quality of the phase portraits.
Reverse time migration Lamb wave imaging based on mode separation
Authors: Zhang Hai-Yan  , Yang Jie  , Fan Guo-Peng  , Zhu Wen-Fa  , Chai Xiao-Dong  ,   School of Communication and Information Engineering, Shanghai University, Shanghai 200444, China;,   School of Urban Railway Transportation, Shanghai University of Engineering Science, Shanghai 201620, China
Published: December 2020

Frequency domain reverse time migration method is used to reconstruct damages in isotropic and anisotropic plates. Considering multimode overlapping, the Lamb wave signals scattered by the defects may result in artifacts in defect imaging. The scattering signals are thus pre-processed by using a mode separation method based on the vibration symmetry difference between the fundamental guided modes. Based on the multi-element array ultrasonic technique, a numerical study is carried out for defect imaging of aluminum and composite plates by using the frequency reverse time migration method. This paper is organized as follows. Firstly, in order to capture multi-directional information about damages, scattering Lamb wave signals caused by the defects are numerically collected by an annular array of transducers through using the finite element simulation. Secondly, after the pre-processing of mode separation, the separated scattering signals are time-reversed and used to stimulate the corresponding receivers. The Green's function is utilized to back-propagate the scattering Lamb signals in frequency domain, so that the back-propagated acoustic field information of monitored area can be obtained. Finally, the defect images are reconstructed by the cross-correlation between the incident acoustic field and the back-propagated acoustic field. To illustrate the influence of mode separation, the numerical experiments are carried out on an aluminum plate with single defect and on another composite plate with two adjacent identical defects. The reconstructed results from frequency domain reverse time migration method with and without mode separation are compared. The comparison indicates the importance of mode separation. Furthermore, the method is extended to detecting the double adjacent defects with different depths in the composite plate. The imaging result illustrates that the presupposed two adjacent defects with different depths are successfully identified. Numerical results demonstrate that the pre-processing of mode separation helps to effectively remove the artifacts resulting from the multimode interference in the imaging process. The proposed frequency reverse time migration method presents a strong potential for detecting and imaging defects in isotropic and anisotropic plates, which is capable of accurately measuring multi-site defects with information about geometry, size and depth.
Fabrication of zigzag-edged graphene antidot lattice and its transport properties
Authors: Zhang Ting-Ting  , Cheng Meng  , Yang Rong  , Zhang Guang-Yu  ,   Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Beijing Key Laboratory for Nanomaterials and Nanodevices, Beijing 100190, China;,   Collaborative Innovation Center of Quantum Matter, Beijing 100190, China;,   School of Physics, University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Graphene nanostructures with defined edges are proposed as a promising platform for the realization of nano-electronics and spin-electronics. However, patterned graphene nanostructure can lead to extra damage and drastically reduce its charge carrier mobility due to the edge disorder. The high flexibility of a top-down patterning method with edge smoothness is extremely desirable. Hydrogen plasma enhanced anisotropic etching graphene is demonstrated to be an efficient method of fabricating zigzag-edge graphene nanostructures. In addition, boron nitride is shown to be an excellent substrate for graphene due to its atomic flatness. Here in this work, we fabricate zigzag edge graphene antidot lattices on a boron nitride substrate via dry transfer method and traditional electron beam lithography, and reactive ion etching followed by hydrogen anisotropic etching approach. At low magnetic fields, weak localization is observed and its visibility is enhanced by intervalley scattering on antidot edges. We observe commensurate features in magnetotransport properties which stem from carriers around one antidot, signifying the high quality of our patterned samples. At high magnetic field, crossover from Shubnikov-de Haas oscillation to quantum Hall effect can be clearly observed due to the high mobility of our zigzag edge graphene antidot lattices. The transport properties of our patterned samples suggest that our fabrication method paves the way for achieving high quality graphene antidot lattices. High quality zigzag edge graphene antidot lattice might be a great platform to study the transport properties of lateral superlattice potential modulation graphene.
Growth of graphene on Al2O3 (0001) surface
Authors: Li Jin-Jin  , Li Duo-Sheng  , Hong Yue  , Zou Wei  , He Jun-Jie  ,   School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, China
Published: December 2020

At present, high quality graphene is synthesized mainly by chemical vapor deposition. It is crucial to decompose and adsorb methane (CH4) on the surface of substrate before CH4 grows into graphene. The graphene is grown mainly on metal substrate due to the catalytic effect of metal. It is difficult to grow graphene thin film on the surface of non-metallic substrate, especially on the surface of -Al2O3 (0001). In this paper, the density functional theory based generalized gradient approximation method is applied to simulating the nucleation of graphene on -Al2O3 (0001) surface, synthesized by chemical vapor deposition. First, we establish a scientific -Al2O3 (0001) surface model, then simulate the decomposition process of CH4 on -Al2O3 (0001) surface by calculating the adsorption sites and adsorption configurations of groups and atoms. Finally, we investigate the groups of CH4 decomposition and atom coupling process on -Al2O3 (0001) surface. The results show that the CH3 groups, C and H atoms are preferentially adsorbed at the top of the O atoms, and the adsorption energies are -2.428 eV,-4.903 eV, and -4.083 eV, respectively. The CH2 and CH groups are preferentially adsorbed on the bridge between O and Al atoms with the adsorption energies of -4.460 eV and -3.940 eV, respectively. The decomposition of CH4 on -Al2O3 (0001) surface is an endothermic process. It requires higher energy and cross reactive energy barrier for CH4 to be completely decomposed into C atom, which makes it difficult that the C atom stays on the substrate surface. The coupling process among CH groups on the surface of -Al2O3 (0001) is an exothermic process. When CH and CH groups are coupled, the energy of the system decreases by 4.283 eV. When (CH)2 and CH groups are coupled, the energy of the system decreases by 3.740 eV. The (CH)x can be obtained by continuous migration and coupling between the CH groups on the surface of the -Al2O3 (0001), and (CH)x group is a precursor of graphene growth. The energy of the system decreases in the process. The above results show that the activated atom or group of graphene nucleation is not C atom but CH group. The CH group migration and aggregation on the surface of -Al2O3 (0001) give priority to the formation of lower energy (CH)x structure. In order to better understand the microscopic growth process of graphene on sapphire, it is important to study the role of (CH)x in the surface of sapphire for revealing the nucleation mechanism of graphene.
Low voltage scanning transmission electron microscopy for two-dimensional materials
Authors: Li Dong-Dong  , Zhou Wu  ,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;,   CAS Key Laboratory of Vacuum Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Two-dimensional (2D) materials, such as graphene and transition-metal dichalcogenide monolayers, have unique properties that are distinctly different from those of their bulk counterparts, and hopefully possess a wide range of applications in 2D semiconductor device. Structural defects are known to have profound influences on the properties of crystalline materials; thus, correlating the defect structure with local properties in 2D material is of fundamental importance. However, electron microscopy studies of 2D materials on an atomic scale have become a challenge as most of these materials are susceptible to electron beam irradiation damage under high voltage and high dose experimental conditions. The development of low voltage aberration-corrected scanning transmission electron microscopy (STEM) has made it possible to study 2D materials at a single atom level without damaging their intrinsic structures. In addition, controllable structural modification by using electron beam becomes feasible by controlling the electron beam-sample interaction. New nanostructures can be created and novel 2D materials can be fabricated in-situ by using this approach. In this article, we review some of our recent studies of graphene and transition-metal dichalcogenides to showcase the applications of low voltage aberration corrected STEM in 2D material research.