bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical investigation of large bubble entrapment mechanism for micron droplet impact on deep pool
Authors: Pei Chuan-Kang , Wei Bing-Qian , Zuo Juan-Li , Yang Hong ,   State Key Laboratory of Eco-hydraulics in Northwest Arid Region of China, Xi’an University of Technology, Xi’an 710048, China
Published: December 2020

Water droplet impacting into a deep liquid pool is one of the most well-known flow phenomena in fluid mechanics. As a ubiquitous natural aeration process, the coalescence of water droplets in lakes and ponds and the subsequent bubble entrapment are one of the most notable ways of gas-liquid exchange in nature, and it is of great significance for underwater sound transmission, aquatic ecosystems and chemical process. The shape of an oscillating droplet in impact under different surrounding medium and initial condition is a key factor for the subsequent cavity formation and bubble entrapment. In this study, the adaptive mesh refinement technique and volume of fluid (VOF) method are applied to the study of the water droplet impact phenomena. Five kinds of deformed micron water droplets with different aspect ratios and impact velocities of 4 m/s and 6 m/s are selected to investigate the influences of drop deformation and impact velocity on the bubble entrapment, capillary wave propagation, and vortex ring evolution. The results show that at low impact velocities (Fr = 75, We = 64.4, Re = 1160, Vi = 4 m/s), the shape of water droplet does not cause the cavity formation and bubble entrapment to change significantly. However, under higher impact velocity (Fr = 112.5, We = 145, Re = 1740, Vi = 6 m/s), deformed droplet with an aspect ratio of 1.33 coalesces with the pool, and large bubble entrainment occurs. The large bubble entrapment is affected mainly by the vortex ring generated under the free surface at the neck between the droplet and the pool. The vortex ring penetrates more deeply before it pulls the free surface to generate a rolling jet at the upper interface of the cavity. The rolling jets then contact the center of the cavity and collapse to entrain a large bubble. At the end of the bubble entrapment phenomenon, the cyclone inside the cavity pushes the sidewall of the cavity continuously, and effectively increases the lateral volume of the bubble, which plays a vital role in the bubble entrainment process. In the initial stage of the impact, the flatter the shape of the droplet, the greater the curvature of the jet generated on the neck between the droplet and the pool, the greater the strength of the vortex ring generated under the free surface. However, the vortex ring formed by the oblate-shaped water droplet is generated too close to the free surface, and the early free surface pulling reduces the strength of the vortex ring, thus the vorticity maximum value decays relatively fast.
Progress of radiation effects of silicon photonics devices
Authors: Zhou Yue , Hu Zhi-Yuan , Bi Da-Wei , Wu Ai-Min ,   State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China,   Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Silicon photonics is a fundamental technology, which has great potential applications in optical interconnection for telecom, datacom, and high performance computers, as well as in bio-photonics. Currently considered are the photonics integrated circuits that are able to work in harsh environments such as high energy equipment and future space systems including satellites, space stations and spacecraft. The understanding of the radiation effects of the photonics devices is critical for fabricating radiation hardened photonic integrate chips and maintaining the performance of the devices and the systems. In this paper, the recent progress of the radiation effects of silicon photonic components is summarized. The effects of the high energy particles that possibly degrade the performance of the device are explained, and the response of the passive and active device under radiation are reviewed comprehensively, including waveguides, ring resonators, modulators, detectors, lasers and optical fibers and so on. For passive devices, radiation-induced effects include accelerated-oxidation of the structures, radiation-generated lattice defects, and amorphous densification or compaction in the optical materials. The effective refractive index of the passive device may change consequently, leading the working frequency to shift, the optical confinement to decrease, and the optical power to leak, which accounts for the extra loss or other performance degradation behaviors. For photodetectors and lasers, radiation-induced displacement damage will be dominant. The induced point defects localized in the silicon layer bring about deep level in the forbidden band, acting as generation-recombination centers or trap centers of tunneling effect, which will compensate for either donor or acceptor levels, degrading the response of these optoelectronic device significantly. The plasma dispersion effect is the mainstream approach to building the silicon electro-optic modulators, which will suffer ionization damage in the high energy particle environment, because the interface-trapped hole caused by ionizing radiation reduces the carrier concentration in the depletion region and even induces the pinch-off of the p-doped side of the modulator, which may result in device failure. To improve the radiation hardness of the silicon photonic device, the passivation of the surface, optimization of the waveguide shape, and the choice of appropriate thickness of the buried oxide layer are possible solutions, and more effective approaches are still to be developed.
Recent advances in perovskite solar cells: Space potential and optoelectronic conversion mechanism
Authors: Wang Yan-Bo , Cui Dan-Yu , Zhang Cai-Yi , Han Li-Yuan , Yang Xu-Dong ,   State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

Perovskite solar cells, as a promising next-generation photovoltaic technology for large-scale application, have demonstrated the advantages of high absorption coefficient, tunable bandgap, considerable photoelectric conversion efficiency and low-cost fabrication. However, the photoelectric conversion process within the device is still not understood clearly. One of the major reasons is that it is difficult to directly observe the space potential inside the device and its effect on the photogenerated charge carriers. The direct measurement and analysis of the space potential inside the device and the clarification of the intrinsic relationship between the space potential and the charge carrier micro-process under illumination and different electric field conditions can reveal the photoelectric conversion mechanism in depth, and thus providing the scientific research basis for the further development. Kelvin probe force microscopy (KPFM), a testing technology that is non-contact, can detect the space potential distribution without any damage to the device, demonstrating the great potential to unveil the working mechanism of perovskite solar cells accurately. Such a characterization method can work under vacuum condition. The KPFM combines Kelvin method of measuring contact potential difference with the scan probe microscopy to characterize internal carrier dynamic behavior with high resolution on a nanometer scale. The study of the spatial potential distribution of semiconductor device plays an important role in understanding the working mechanism of new perovskite solar cells. For example, under an open-circuit condition, the intensity and width of the electric field and space charge region can be obtained from the spatial potential distribution, and the bending direction of the energy band can be judged according to the increase or decrease of the potential. While in a short-circuit case, the generation and transport of charge carriers can be obtained. In this review, we mainly introduce the research progress of the space potential distribution and optoelectronic conversion mechanism in perovskite solar cells. The key mechanism of charge carrier generation, separation, transport and recombination are revealed by using KPFM to directly observe the space potential variations caused by light or electric field. We also prospect the issues and challenges in the future research.
Mixing enhancement for supersonic mixing layer by using plasma synthetic jet
Authors: Wang Peng , Shen Chi-Bing ,   Science and Technology on Scramjet Laboratory, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Mixing enhancement for supersonic mixing layer is of great importance for developing scramjet engine. The growth rate of supersonic mixing layer is smaller than that of subsonic mixing layer. As the compressibility increases, the mixing enhancement becomes more difficult. Plasma synthetic jet is regarded as a promising flow control technology. The plasma synthetic jet generator can produce high energy jet. This generator has no moving parts and does not need additional gas source. It is the first time that plasma synthetic jet has been used to enhance the mixing in supersonic mixing layers. The influence of plasma synthetic jet on the supersonic mixing layer is investigated experimentally and numerically. The experiments are conducted in the low noise supersonic mixing layer wind tunnel. The Mach number of upper stream and lower stream are 1.37 and 2.39 respectively. The convective Mach number of this wind tunnel is 0.32. The plasma synthetic jet actuators are installed in the splitter plate. The distance between the jet hole and the splitter plate end is 15 mm. The nanoparticle-based planar laser scattering (NPLS), particle image velocimetry (PIV) and schlieren are used to obtain the response of the supersonic mixing layer to single pulse plasma synthetic jet perturbation. The NPLS successfully captures the large-scaled vortex structures induced by the plasma synthetic jet in the supersonic mixing layers. The effect of plasma synthetic jet is remarkable. The schlieren images show the process of the perturbation. An oblique shock wave is generated when the jet is ejected. The PIV is employed to obtain the influence of plasma synthetic jet on the velocity field. The y-velocity standard deviation increases due to the perturbation. The actuators’ mixing enhancement effects and actuators’ performances at three locations are investigated by two-dimensional numerical simulation. The three actuators are located on the upper, bottom and end surface of splitter plate respectively. The numerical simulation results show that the mixing layer thickness is increased by the plasma synthetic jet perturbation. There are two mechanisms of perturbations while actuators are located at different positions. The actuators installed on the upper and bottom surface of splitter plate influence the mixing layer through perturbing the upper and lower stream respectively. The actuator installed at the end of splitter plate affects the mixing layer directly. The response time of supersonic mixing layers to the perturbation of the actuator installed at the end of splitter plate is shorter than those of the others. The performance of each actuator is sensitive to the location.
First principle study on stretching and breaking process of single-molecule junction: Terminal group effect
Authors: Sun Feng , Liu Ran , Suo Yu-Qing , Niu Le-Le , Fu Huan-Yan , Ji Wen-Fang , Li Zong-Liang ,   Shandong Key Laboratory of Medical Physics and Image Processing, School of Physics and Electronics, Shandong Normal University, Jinan 250358, China
Published: December 2020

The stretching and breaking processes of stilbene-based molecular junctions, which contain S or N atoms in the terminal groups, are studied by using density functional theory. The numerical results show that for pyramid-shaped gold electrodes, a stretching force of about 0.59 nN is needed to break the molecular junction with —S terminals, which is larger than the force of 0.25 nN that is required by the molecule to stretch —SH terminals away from pyramid-shaped gold electrode. However, it is obviously smaller than the force of about 1.5 nN that is needed by the molecule to break —S terminals from planar-shaped gold electrode. If the terminal group is —NH2 or —NO2, the force for breaking the molecular junction is about 0.45 nN or 0.33 nN, respectively. More delocalized molecular orbitals formed by the coupling between the frontier occupied orbitals of molecule and electrodes, higher stretching force for breaking molecular junction is required. The natural bond orbital (NBO) analysis shows that more NBO net charges that the terminal atom possesses can enhance the stability of the molecule-electrode contact if there is no bonding orbital formed between end group of molecule and electrode. Based on the numerical results and the combination with previous studies, it can be found that —S terminal and —NH2 terminal show evident properties in distinguishing tip structures of gold electrodes, which provides useful information for precisely controlling the interactions and interface structures between molecule and electrodes.
Dimension-reduced generalized likelihood ratio detection based on sampling of normal modes in deep ocean
Authors: Kong De-Zhi , Sun Chao , Li Ming-Yang , Zhuo Jie , Liu Xiong-Hou ,   School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China,   Key Laboratory of Ocean Acoustics and Sensing Ministry of Industry and Information Technology, Xi’an 710072, China,   State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

In this paper, two generalized likelihood ratio (GLR) detectors are presented for the case of multiple snapshots of test data to detect the presence of an underwater acoustic source in the deep ocean. The two GLR detectors are termed the eigenvalue detector (EVD) and the constant false alarm rate eigenvalue detector (CFAR EVD), respectively. Theoretical analysis and numerical results show that for a given input signal-to-noise ratio (SNR) of the array, the GLR detectors achieve higher output SNRs when the spatial dimension of test data decreases. To further enhance the detection performances of the GLR detectors, we propose a dimension-reduced (DR-GLR) method based on array sampling of modal information. This DR-GLR method combines the characteristics of sound propagation and array receiving. According to normal mode theory, acoustic signals emitted from the acoustic source lie in the modal space spanned by the sampled modal information of the array. Resulting from the restriction of the array size, it often occurs in deep ocean when the dimension of " effective modal subspace” is less than that of the test data which is equivalent to the number of hydrophones. Based on this phenomenon, we reconstruct the modal information by merely retaining the " effective modal subspace” to formulate the dimension reduction matrix. The DR-GLR test statistics is deduced by employing the dimension reduction matrix when using the vertical linear array (VLA) and the horizontal linear array (HLA), respectively. The DR-GLR detectors when using an HLA require more computational amount than when using a VLA. Simulation experiments are conducted to analyze the detection performances of the two GLR detectors, and verify the performance improvement effects of DR-GLR detectors. The numerical results show that the CFAR EVD presents good robustness to the uncertainty of the noise power and the DR-GLR detectors outperform the GLR detectors in detection performance. It also turns out the acoustic signals received by the HLA lie in a lower-dimensional " effective modal subspace” than by the VLA, and thus when using an HLA the DR-GLR detectors present higher detection probabilities than using a VLA. Moreover, the smaller the dimension of the " effective modal subspace”, the better the performance improvement of the DR-GLR detectors will be. The dimension of the " effective modal subspace” increases with hydrophone spacing and/or the source frequency increasing.
Effect of alkane chain length on tribological properties of straight chain alkane liquid film
Authors: Zhang Zhao-Hui , Yu Xiao-Dong , Li Hai-Peng , Han Kui ,   School of Information Engineering, Suqian College, Suqian 223800, China,   School of Physical Science and Technology, China University of Mining and Technology, Xuzhou 221116, China
Published: December 2020

How to overcome the friction between the micro components has become a key point of the successful operation of the micro/nano-electric mechanical systems. The understanding of the friction mechanism of the alkane liquid film confined between two substrates is important when the friction law on a macro/nano scale is not applicable. In this work, the molecular dynamics simulations are used to study the effect of the chain length on the friction properties of the liquid films that are confined between two golden substrates. There are seven pure alkane liquid films that are composed of one molecule CnH2n + 2(n = 6, 8, 10, 12, 14, 16, 18), and six mixed alkane liquid films that are composed of two molecules C6H14/CnH2n + 2(n = 8, 10, 12, 14, 16, 18) with a ratio of 1∶1. The results show that the friction force and the coefficient of friction of pure alkane liquid films both increase as the chain length increases when the carbon atom number is less than 12, whereas the friction property keeps stable when the carbon atom number of the alkane molecule is greater than 10 and the pure hexadecane liquid film has the largest friction force. In the mixed films, the addition of short chain alkane molecules can strengthen the friction, and the hexane/dodecane mixed film has the maximum friction force. The short chain molecule dilutes the C8H18 film and C10H22 film which cause the friction force to decrease. During the sliding progress, the formation of solid-like high density-packet layers is the main reason for the friction reduction. When no solid-like layer or just one solid-like layer is formed at the interface of golden base, the liquid alkane film is liquid-like and its viscosity becomes much larger than that in the normal state, which leads to high friction force. The short chain molecules reduce the density of the solid-like layers, which causes the film to transform from solid-like state to liquid state, thus resulting in the increase of friction. The friction property mainly depends on the layered structure, and the interaction between the golden surface and liquid film contributes to the friction. This study helps to understand the friction mechanism of ultra-thin liquid films.
Ultrafast pulse lasers based on two-dimensinal nanomaterials
Authors: Wang Cong , Liu Jie , Zhang Han ,   School of Physics and Electronics, Shandong Normal University, Jinan 250014, china,   College of Optoelectronics Engineering, Shenzhen University, Shenzhen 518060, China
Published: December 2020

Ultrafast pulse laser has been widely used in many fields, such as optical communications, military and materials processing. Semiconductor saturable absorber mirror (SESAM) serving as a saturable absorber is an effective way to obtain ultrafast pulse laser with ps-level pulse width. The SESAM needs specially designing to meet different wavelength operations. And the low damage threshold and high fabrication cost of SESAM hinder its development. Exploring novel materials is becoming a hot topic to overcome these drawbacks and obtain ultrafast laser with excellent performance. The discovery of graphene opens the door for two-dimensional nanomaterials due to the unique photoelectric properties of layered materials. Subsequently, two-dimensional (2D) materials such as topological insulators, transition metal sulfides, and black phosphorus are reported. These materials are used as saturable absorber to obtain a pulsed laser. In this paper, we summarize the research status of fiber lasers and solid-state lasers based on 2D materials in recent years. The development status of the lasers in terms of central wavelength, pulse width, repetition frequency, pulse energy and output power are discussed. Finally, the summary and outlook are given. We believe that nonlinear optical devices based on 2D materials will be rapidly developed in the future several decades
Review on surface plasmonic coupling systems and their applications in spectra enhancement
Authors: Zhu Xu-Peng , Shi Hui-Min , Zhang Shi , Chen Zhi-Quan , Zheng Meng-Jie , Wang Ya-Si , Xue Shu-Wen , Zhang Jun , Duan Hui-Gao ,   School of Physics Science and Technology, Lingnan Normal University, Zhanjiang 524048, China,   Center for Research on Leading Technology of Special Equipment, School of Mechanical and Electric Engineering, Guangzhou University, Guangzhou 510006, China,   College of Mechanical and Vehicle Engineering, State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha 410082, China
Published: December 2020

Surface plasmon polariton is a surface oscillation wave that is bound at the interface between metal and dielectric material. Its oscillating electric field is strongly bound below the subwavelength scale near the interface, generating a huge enhancement of localized electromagnetic field, which can be used to greatly enhance the interaction between light and matter, particularly in metal surface plasmon coupling system. In this paper, we review the coupling effects, coupling theory, and typical coupling structures of the surface plasmon coupling systems. We also introduce a typical surface plasmon coupling system and its corresponding crucial applications in surface enhanced refractive index sensor, Raman scattering, near-infrared absorption, and nonlinear effect generation.
Phase structure and surface tension in quark meson model
Authors: Shen Wan-Ping , You Shi-Jia , Mao Hong ,   Department of Physics, Hangzhou Normal University, Hangzhou 311121, China
Published: December 2020

In a mean-field approximation, we study the in-medium effective potential of the two-flavor quark meson model in the presence of a fermionic vacuum term at a finite temperature and density. There exists a crossover phase transition in the low-density region, and also there is a first-order phase transition in the high-density region accompanied by a critical end point. For the first-order phase transition, when the temperature is close to the critical temperature, the values of surface tension are calculated at various chemical potentials and we find that our results are very close to the results recently found in other chiral models with two flavors. Some consequences and possible applications of our results are also pointed out for the experiments on heavy ion collisions and the evolutions of the compact stars in their early stages.
Heavy fermion materials and physics
Authors: Xie Wu , Shen Bin , Zhang Yong-Jun , Guo Chun-Yu , Xu Jia-Cheng , Lu Xin , Yuan Hui-Qiu ,   Center for Correlated Matter, Zhejiang University, Hangzhou 310058, China,   Department of Physics, Zhejiang University, Hangzhou 310027, China
Published: December 2020

As typical examples of strongly correlated electron systems, heavy fermion materials exhibit diverse quantum ground states such as antiferromagnetic order, ferromagnetic order, non-Fermi-liquid phases, unconventional superconductivity, quantum spin liquids, orbital order and topological order. In contrast to other strongly correlated electron systems, heavy fermion systems have relatively small characteristic energy scales, which allows different quantum states to be tuned continuously by using external parameters such as pressure, magnetic field and chemical doping. Heavy fermion materials thus serve as ideal systems for studying quantum phase transitions, superconductivity and their interplay. In this review, we briefly introduce the history of the field of heavy fermions and the current status both in China and in other countries. The properties of several representative heavy fermion systems are summarized, and some frontier scientific issues in this field are discussed, in particular, concerning heavy fermion superconductors, quantum phase transitions and exotic topological states in strongly correlated electron systems.
Spin filter effect of germanene nanoribbon controlled by local exchange field and electric field
Authors: Xiang Yang , Zheng Jun , Li Chun-Lei , Guo Yong ,   College of  Mathematics and Physics, Bohai University, Jinzhou 121013, China,   College of Elementary Education, Capital Normal University, Beijing 100048, China,   Department of Physics, Tsinghua University, Beijing 100084, China,   Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
Published: December 2020

Germanene, which has been synthesized recently, is a single-layered material composed of germanium atoms. Almost all the striking properties of graphene can be transferred to germanene, because both of them have the same honeycomb lattice structure. In contrast with graphene, germanene has a sizable band gap and spin dependent helical edge states, which make it attractive candidate for spintronic applications. By using the nonequilibrium Green’s function method, the effects of Z-axis local exchange field and electric field on spin-polarized transport properties in germanene nanoribbon are studied theoretically. The results reveal that by exerting an exchange field with a strength greater than twice the effective spin-orbit coupling to the edge region of germanene, the spin resolved band gaps can be generated in different energy ranges, and thus 100% filtering of spin-up or spin-down electrons can be achieved. We theoretically propose a method to reduce the threshold exchange field strength for the spin filter effect by using the electric field. The results show that the spin-filter effect can be achieved in a larger energy range under a weaker exchange field when the electric field are applied to the entire central device region. With the increase of the local exchange field intensity, the energy range corresponding to the spin filter effect will increase significantly.
Imaging performance of fractal structuresparse aperture arrays
Authors: Hao Wei-Qian , Liang Zhong-Cheng , Liu Xiao-Yao , Zhao Rui , Kong Mei-Mei , Guan Jian-Fei , Zhang Yue ,   College of Electronic and Optical Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023, China,   Beijing Institute of Space Mechanics and Electricity, China Academy of Space Technology, Beijing 100094, China
Published: December 2020

The angular resolution of optical system is limited by the ratio of the wavelength to the aperture of the entrance pupil, indicating that the optical system with large aperture has a high spatial resolution. Sparse aperture imaging is one of the effective solutions to the problem that the telescope is bulky, heavy and difficult to manufacture. According to the self-similarity and multi-scale characteristics of fractal configuration, we propose a sparse aperture array and analyze its performance for synthetic aperture imaging system. In the array Golay-3 is used as a structural unit to expand a multi-layered fractal configuration in a self-similar manner. Given the analytical expression of the pupil function which is reduced by dimensionless parameters, we calculate the modulation transfer functions (MTFs), the practical cut-off frequencies and the middle spatial frequency characteristics of the fractal configuration under different fill factors and different outer layer rotational angles. We analyze both the MTF values and the performance parameters of the fractal structure for the cases of N = 3, 9, and 18, respectively. The results show that the decrease of fill factor does not significantly change the MTF curve nor the practical cutoff frequency in a range of fill factor between 0.0952 and 0.2246. The outer layer rotational angle has a periodicity, and the change in the angle has no large influence on the practical cutoff frequency. When the reduced aperture parameter is \begin{document}$ {d_0} = 1$\end{document} and the fill factor is 22.46%, the middle spatial frequency of N = 18 array is more stable and the practical cut-off frequency is higher. Using the fractal self-similarity, the aperture of the system can be expanded effectively while maintaining the middle spatial frequency characteristics. The computing results are of scale invariance due to the adoption of the reduced aperture parameter.
Propagation matrix for lossy stratified medium containing graphene sheet
Authors: Wang Fei , Wei Bing ,   School of Physics and Optoelectronic Engineering, Xidian University, Xi’an 710071, China,   Collaborative Innovation Center of Information Sensing and Understanding at Xidian University, Xi’an 710071, China
Published: December 2020

In this paper, a propagation matrix method for lossy layered medium with conductive interfaces is presented. Firstly, on the basis of phase matching principle, an approach to calculating the real and imaginary part of wave vector in a lossy layered medium is given for the case of oblique incident plane electromagnetic wave. Since the direction of real and imaginary part of wave vector are different, the plane wave propagating in lossy dielectric layers is inhomogeneous, which extends the traditional propagation matrix method and makes it suitable for the complex lossy medium. Then, the propagation matrix across graphene interface is deduced by using the electromagnetic field boundary conditions, and the analytical expression of the reflection and transmission coefficient for “infinite thin” graphene layer are given. Finally, the propagation matrix of lossy layered medium with conductive interface is obtained by embedding graphene interface into the layered medium, which can be used for fast analyzing the reflection, transmission and propagation of plane wave in composite structure of layered medium and conductive interface. The validity of the proposed method is demonstrated by calculating the single-layered shielding effectiveness of grapheme. The effects of graphene coating on the reflection, transmission and absorption of plane wave in half-space medium and one-dimensional photonic crystal are also investigated. The results show that the graphene layer can enhance surface reflection and optical absorption.
Discussion on Verdet constant solution model of paramagnetic magneto-optical materials
Authors: Cai Wei , Xu You-An , Yang Zhi-Yong , Miao Li-Yao , Zhao Zhong-Hao ,   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

 The Verdet constant is one of the key parameters to characterize the material magneto-optical properties. The quantum theory is usually used to study magneto-optical properties and calculate the Verdet constant of paramagnetic material. However, the traditional quantum theory only takes into account the influence of the electron transition dipole moments caused by the particle property of light, which therefore cannot formulate the Verdet constant of magneto-optical material accurately.

 In view of the shortcomings of the existing theory, in this paper we propose is a wave-transition model of the Verdet constant. Due to the special wave-particle duality of light, the contribution of the non-transition dipole moment to the Verdet constant, caused by the electric field of light wave, should not be ignored.

 According to the basic theory of magneto-optical effect, in this paper we first explore the intrinsic mechanism of the paramagnetic material’s Verdet constant at a microscopic level and analyze the deficiency of traditional quantum theory. Furthermore, the classical electronic dynamic theory and quantum theory are used to reveal the contribution of volatility and transition of the light to the electric dipole moment. The density operator and statistical algorithm are introduced to derive the polarizability tensor of the paramagnetic magneto-optical material, thus obtaining the Verdet constant expression of the paramagnetic magneto-optical material, from which the Verdet constant is formulated. Taking the paramagnetic magneto-optical material TGG for example, the splitting energy levels and wave function of Tb3+ ions in the spin-orbit coupling, crystal field and effective field are calculated by the quantum method, and finally the Verdet constants under the traditional quantum theory and the volatility transition contribution model are obtained quantitatively. The comparative analysis shows that the results calculated by the wave-transition contribution model are more consistent with the experimental data and more accurate than the results calculated through the traditional quantum theory. The idea and method put forward in this paper will provide reference for further exploring the magneto-optical effect mechanism of paramagnetic magneto-optical materials.
Memcapacitor-based multivibrator and its experiments
Authors: Gu Mei-Yuan , Liu Jing-Biao , Wang Guang-Yi , Liang Yan , Li Fu-Peng ,   School of Electronics and Information, Hangzhou Dianzi University, Hangzhou 310018, China,   School of Mechanical Engineering, Hangzhou Dianzi University, Hangzhou 310018, China
Published: December 2020

Memcapacitor is a kind of non-linear capacitor with memory capability. In order to study the electrical characteristics of memcapacitor and its application circuit, a quadratic model of voltage-controlled memcapacitor is proposed, and an emulator which can dynamically simulate the q–v characteristics of the memcapacitor is designed by using a current feedback operational amplifier, multiplier and other devices. The emulator does not need to be converted by any memristor or meminductor. It can work in floating or grounding state. The constitutive relation of the memcapacitor emulator is deduced, and the circuit parameters of the emulator are designed. Based on the simulations and experimental results, the pinched hysteresis loop and its dependence on frequency are verified. In addition, the range of the memcapacitance under periodic signal excitation is discussed and the influence of periodic excitation signal on the range of memcapacitance is analyzed. Through observing the dynamic route map (DRM) of the memcapacitor, its nonvolatility and the stability of the equilibrium point are also studied. The simulation results show that the memcapacitor can exhibit infinite stable equilibrium points and can be stabilized at any equilibrium state. With respect to pulse excitation signal, the effects of pulse width and amplitude on the switching on or off of the state for the memcapacitor is analyzed, and the corresponding switching method and rule are proposed. This characteristic of memcapacitor makes it have potential applications in non-volatile memory, neural network and other fields. Based on the proposed memcapacitor model, a multivibrator circuit is designed. Then, the working principle of the oscillator is analyzed, and the equation of oscillator is derived. The output voltage of the oscillator, the terminal voltage of the memcapacitor, the flux and the charge of the memcapacitor, and the pinched hysteretic curve of the memcapacitor during oscillation are tested experimentally. Besides, various oscillation waveforms whose frequency and duty cycle are different are observed and further analyzed. The circuit structure of the memcapacitor multivibrator designed in this paper is very simple. It can generate stable rectangular wave signals with controllable frequency and duty cycle, and it can be used in testing signal or driving the device.
A quadratic polynomial receiving scheme for sine signals enhanced by stochastic resonance
Authors: Liu Guang-Kai , Quan Hou-De , Kang Yan-Mei , Sun Hui-Xian , Cui Pei-Zhang , Han Yue-Ming ,   Department of Electronics and Optical Engineering, Army Engineering University, Shijiazhuang 050003, China,   School of Mathematics and Statistics, Xi’an Jiaotong University, Xi’an 710049, China,   The Troop of 66389, Shijiazhang 050000, China
Published: December 2020

Aiming at the reception of the intermediate frequency signal of sine wave of radio and communication system at extremely low signal-to-noise ratio (SNR), a quadratic polynomial receiving scheme for sine signals enhanced by stochastic resonance (SR) is proposed. Through analyzing the mechanism of sine signals enhanced by SR and introducing the decision time, the analytic periodic stable solution with time parameters of the Fokker-Planck Equation (FPE) is obtained through converting the non-autonomous FPE into an autonomous equation. Based on the probability density function of the particle of SR output, a quadratic polynomial receiving scheme is proposed by analyzing the feature of energy detector and matching filter receiver. By maximizng the deflection coefficient, the binomial coefficients and the test statistic are obtained. For further reducing the bit error, by combining the thought of " the average of N samples”, a quadratic polynomial receiving scheme for sine signals enhanced by SR is proposed through the hypothesis under Gaussian distribution approximation of the law of large N. And the conclusion is obtained as follows. When N is 500 and the SNR is greater than –17 dB, the bit error rate is less than 2.2 × 10–2, under the constraint of the parameters of the optimally matched SR.
Structured illumination for two-dimensional laser induced fluorescence imaging to eliminate stray light interference
Authors: Yan Bo , Chen Li , Chen Shuang , Li Meng , Yin Yi-Min , Zhou Jiang-Ning ,   China Aerodynamics Research and Development Center, Mianyang 621000, China
Published: December 2020

Laser sheet imaging, also called planar laser imaging, is one of the most versatile optical imaging techniques and has been frequently used in several different areas. However, when applied to the limited operating space and strong light scattering media, the light originating from indirect reflections, multiple scattering and surrounding backgrounds can produce error especially in intensity-ratio based measurements.

This work is motivated by these challenges, with the overall aim of making laser sheet imaging technique applicable for the study of eliminating the stray light interference. Therefore a novel two-dimensional imaging technique named structured laser illumination planar imaging (SLIPI) is developed based on planar laser imaging but uses a sophisticated illumination scheme i.e. spatial intensity modulation, to differentiate between the intensity contribution arising from useful signals and that from stray light. By recording and dealing with images, the SLIPI method can suppress the diffuse light and retain the useful signals.

In this paper, we first use the MATLAB software to simulate the phase-shift SLIPI method, and the results show that the stray light interference can be eliminated completely. Furthermore, the phase-shift SLIPI is combined with the liquid solution (Rhodamine B solution) laser induced fluorescence (LIF) approach to imagine the concentration distribution. By recording three images, between which this encoding is changed noticeably only for the useful LIF signals, the phase-shift SLIPI method is evidenced to be able to remove the diffuse light contribution, thus improving and enhancing the visualization quality. The instantaneous SLIPI images of rapidly moving samples, a key feature to study dynamic liquid solution diffusion behavior, are also acquired. The lock-in amplifier SLIPI technique is then experimentally studied under Rhodamine B diffused solution, and the phase-shift SLIPI method can remove the unwanted background interferences and achieve the significant improvements in terms of pronounced concentration distribution within the Rhodamine B solution.

The SLIPI technique is relatively inexpensive: the cost does not exceed the cost of an ordinary laser sheet arrangement noticeably, and it can combine with several other linear imaging techniques, such as Rayleigh scattering, particle image velocimetry and laser-induced phosphorescence.
Synthesis and characterization of graphene nanoribbons on hexagonal boron nitride
Authors: Chen Ling-Xiu , Wang Hui-Shan , Jiang Cheng-Xin , Chen Chen , Wang Hao-Min ,   State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China,   College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China,   School of Physical Science and Technology, ShanghaiTech University, Shanghai 200031, China
Published: December 2020

Graphene, as a typical representative of the two-dimensional material family, has received a wide attention due to its excellent physical and chemical properties. Graphene nanoribbon (GNR) is graphene in a width of several to a few tens of nanometers. GNRs not only inherit most of the excellent properties of graphene, but also have their own specific properties such as band gap opening and spin-polarized edge states, which make it the potential candidate in graphene based electronics in the future. Hexagonal boron nitride (h-BN), which has similar lattice constant with graphene, normally serves as an ideal substrate for graphene and GNRs. It can not only effectively preserve their intrinsic properties, but also benefit for the fabrication of electrical devices via popular semiconductor processes. In this paper, we reviewed the development history of research of graphene and GNRs on h-BN in recent years. The recent progress of physical properties is also discussed. In order to realize the large scale production of graphene and GNRs on h-BN, high quality h-BN multilayer is necessary. In addition, recent progresses about h-BN preparation methods are presented, and the progresses could pave the way for the further application of GNRs in the electronics. Finally, the research direction of graphene and GNRs on h-BN in the future is discussed.
Effects of p-layer hole concentration and thickness on performance of p-i-n InGaN homojunction solar cells
Authors: Pan Hong-Ying , Quan Zhi-Jue ,   National Institute of LED on Si Substrate, Nanchang University, Nanchang 330047, China
Published: December 2020

In this paper, the effects of p-layer hole concentration and p-layer thickness on the performances of InGaN p-i-n homojunction solar cells with different indium components and their intrinsic mechanisms are investigated by numerical simulations. it is found that the conversion efficiency of solar cells first increases and then decreases slightly with the increase of p-layer hole concentration and p-layer thickness. Moreover, the change of p-layer hole concentration and p-layer thickness will cause great changes of the conversion efficiency of the solar cells, especially as the indium composition increases. In order to better clarify and understand the physical mechanism of this phenomenon, the collection efficiency, I-V characteristic, built-in electric field and carrier transport of solar cells are analyzed in this paper. When the hole concentration is insufficient, the build-in electric filed is not strong enough to separate the most of the electric-hole pairs. This will reduce the collection efficiency. In addition, the lower the hole concentration, the higher the series resistance of solar cells will be and the more the power loss. So a conclusion can be drawn that the lower hole concentration of p-layer would be accompanied by the reduction of collection efficiency and the increase of series resistance, thus resulting in a lower conversion efficiency. With the increase of the hole concentration which is below an optimal value, the built-in electric field reaches the threshold, which can improve the collection efficiency. At the same time, although the series resistance is reduced to a certain extent, it still reduces the effective output power and limits the conversion efficiency. When the hole concentration is higher than the optimal value, the carrier mobility becomes the main factor limiting the conversion efficiency. As for the p-layer thickness, the simulation results indicate that the lateral transport of carriers from the p-layer to the anode electrodes becomes more obstructive with the thinning of p-layer thickness. This is because when the p-layer thickness decreases, thus causing the p-layer sectional area to decrease, the lateral series resistance becomes higher. It is clear that when the p-layer is too thin, the lateral series resistance is one of the main limiting factors affecting the conversion efficiency of solar cells.
Interpolating element-free Galerkin method for viscoelasticity problems
Authors: Zhang Peng-Xuan , Peng Miao-Juan ,   Department of Civil Engineering, Shanghai University, Shanghai 200444, China
Published: December 2020

In this paper, based on the improved interpolating moving least-square (IMLS) approximation, the interpolating element-free Galerkin (IEFG) method for two-dimensional viscoelasticity problems is presented. The shape function constructed by the IMLS approximation can overcome the shortcomings that the shape function of the moving least-squares (MLS) can-not satisfy the property of Kronecker function, so the essential boundary conditions can be directly applied to the IEFG method. Under a similar computational precision, compared with the meshless method based on the MLS approximation, the meshless method using the IMLS approximation has a high computational efficiency. Using the IMLS approximation to form the shape function and adopting the Galerkin weak form of the two-dimensional viscoelasticity problem to obtain the final discretized equation, the formulae for two-dimensional viscoelasticity problem are derived by the IEFG method. The IEFG method has some advantages over the conventional element-free Galerkin (EFG) method, such as the concise formulae and direct application of the essential boundary conditions, For the IEFG method of two-dimensional viscoelasticity problems proposed in this paper, three numerical examples and one engineering example are given. The convergence of the method is analyzed by considering the effects of the scale parameters of influence domains and the node distribution on the computational precision of the solutions. It is shown that when dmax = 1.01−2.00, the method in this paper has a good convergence. The numerical results from the IEFG method are compared with those from the EFG method and from the finite element method or analytical solution. We can see that the IEFG method in this paper is effective. The results of the examples show that the IEFG method has the advantage in improving the computational efficiency of the EFG method under a similar computational accuracy. And the engineering example shows that the IEFG method can not only has higher computational precision, but also improve the computational efficiency.