bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and application of communication band narrow linewidth lasers
Authors: Jiao Dong-Dong  , Gao Jing  , Liu Jie  , Deng Xue  , Xu Guan-Jun  , Chen Jiu-Peng  , Dong Rui-Fang  , Liu Tao  , Zhang Shou-Gang  ,   National Time Service Centre, Chinese Academy of Sciences, Xi'an 710600, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Key Laboratory of Time and Frequency Standards, Chinese Academy of Sciences, Xi'an 710600, China
Published: December 2020

Ultra-stable lasers at optical communication wavelengths have important applications in developing optical frequency transfer via optical fibers. We report the recent development of a 1550 nm stable laser system built at National Time Service Center and its preliminary application in optical frequency transfer via laboratory fibers.
In the experiment, the conventional Pound-Drever-Hall(PDH) frequency stabilization technology is implemented to achieve the ultra-stable laser at the wavelength of 1550 nm. The output of a single laser source is split and locked onto the resonant frequency of two independent reference cavities, of 344000 and 296000 respectively. The frequency of the laser source is actively stabilized to the first reference cavity by piezo and external frequency shifters simultaneously and the total control bandwidth is measured to be 50 kHz. Then the laser frequency is shifted and stabilized to the second reference cavity by an acousto-optical modulator. A 5 m long single-mode fiber is used to bring the first laser beam to the second reference cavity which unfortunately induces unexpected phase noise by environmental distortions. The laser linewidth broadened is determined to be 0.27 Hz by the beat note measurement between the input and output beams of the fiber. To evaluate the frequency stability of the laser, the frequency control signal within the control bandwidth of the second stable laser system is analyzed by a spectrum analyzer and a frequency counter. The control signal shows a Lorentz linewidth of 2.7 Hz and a frequency stability of 2.510-14/s, corresponding to a single laser linewidth of 1.9 Hz with a frequency stability of 1.710-14/s if the two stable lasers have similar frequency stability.
Applying this ultra-stable laser system as the laser source for the fiber-based optical frequency transfer, a short-term frequency transfer stability of 7.510-17/s is demonstrated through a 50 km-long fiber spool, while a frequency transfer stability of 2.410-16/s is achieved by a similar setup except that the laser source is a kHz-level linewidth laser. In the experiment an Agilent 53232 A frequency counter is applied to record the beat note signal in the auto mode.
In the end, we discuss the possible improvements of the stable laser system, including the miniaturization of the optical setup, optimization of the control bandwidth and shortening of the response time of control loop.
Calculations of the binding energies of weakly bound He-He-Ba molecules
Authors: Gou Qing-Dong  , Li Yong  ,   Department of Physics, Central China Normal University, Wuhan 430079, China;,   Department of Physics, Jinggangshan University, Ji'an 343009, China
Published: December 2020

The three-body Schrdinger equation is approximately solved in the hyperspherical coordinates and the binding energies of the three-body weakly bound systems are calculated with the purpose to find if He-He-Ba trimers could exist. Using the special feature of the B-spline function like the flexible and highly localized properties, hypersphercial potentials are obtained by modifying the knots distribution of the B-spline basis of different weakly bound three-atom systems. Employing the best empirical interaction potentials between each pair of particles, we obtain that in the ground state binding energies of the weakly bound typical three-atom systems, the bindings of the molecules, 4He-4He-138Ba, 4He-3He-138Ba and 3He-3He-138Ba are possible. The binding energies of these systems are shown in the order of 1 Kelvin, each system could support only one bound state. These weakly bound molecules can exist only in a very cold environment. To get insight into the geometry of the molecules, the features of the channel functions associated with the hyperspherical potential curves of each system are investigated.
Focusing surface plasmon polaritons in archimedes' spiral nanostructure
Authors: Li Jia-Ming  , Tang Peng  , Wang Jia-Jian  , Huang Tao  , Lin Feng  , Fang Zhe-Yu  , Zhu Xing  ,   State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China;,   Center for Nanoscale Science and Technology, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China;,   National Center for Nanoscience and Nanotechnology, Beijing 100190, China
Published: December 2020

Surface plasmon polaritons (SPPs) are a hybrid mode of a light field and metallic collective electrons oscillated resonantly and excited at the metal/dielectric interface. Recently extensive research has been carried out due to its technological potential in nano-optics. The SPPs coupling, focusing, waveguiding and resonance enhancement are hot spots in this field. In particular, to find a simple method that can focus SPPs into a highly confined spot with the size beyond the diffraction limit is still a big challenge.
In this work, we have fabricated the Archimedes' spiral structures with different structural parameters on an Au film by using focused ion beam etching technique. Through changing the chiralities of the incident circularly polarized light and the spiral structure, we have studied theoretically and experimentally the focusing properties of the Archimedes spiral structures with different parameters. We find that besides the chiralities of the incident light and the spiral structure, the pitch of screw of the spiral structure and the wavelength of the excited light also affect the surface plasmon field. The resulting surface plasmon fields inside the structure are the zero-order, first-order, and high-order evanescent Bessel beams. By using a phase analysis and a finite-difference time-domain simulation method, we calculate the electric field and phase distribution in different spiral structures. A near-field vortex mode with different spin-dependent topological charges can be obtained in the structures. Furthermore, the results of the scanning near-field optical microscopy measurements verify the theory and simulation results.
The method of using an Archimedes' spiral structure to focus SPPs provides a new route to manipulate the SPPs optical field in nanoscale. Based on theoretical calculation and FDTD simulation in this work, we have studied the physical process of the optical field manipulation in spiral structures. The significant and innovated points of this work are: a) We have developed the phase theory, and analyzed the field manipulation process of spiral structures with different parameters and chiralities at different circular polarization and wavelengths. b) A more effective and convenient way is used for SPPs focusing in linearly polarized light and circularly polarized light. c) A near-field vortex surface mode with different spin-dependent topological charges is obtained for the structure. This work can be considered to have applications in SPPs tweezers, highly integrated photonic devices.
Study of anisotropic diffusion model based on pulse coupled neural network and image entropy
Authors: Guo Ye-Cai  , Zhou Lin-Feng  ,   Jiangsu Key Laboratory of Meteorological Observation and Information Processing, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   College of Electronic and Information Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China
Published: December 2020

In image processing, most of the anisotropic diffusion models based on partial differential equation use gradient information to detect image edge. If the image edge is seriously polluted by noise, these methods would not be able to detect image edge, so the edge features cannot be retained. Pulse coupled neural network (PCNN) has the property that similar input neurons can generate pulse at the same time; this property is used to process the noisy image, and we can get an image entropy sequence. The image entropy sequence which will be used as an edge detecting operator is introduced into the diffusion equation, and this will not only reduce the defects produced when the gradient is used as an edge detecting operator so it is easily affected by the noise, but the area image information can also retain more completely. Then, we will use the rule of minimum cross entropy to search for a minimum threshold, which would satisfy the condition that the information difference between noisy image and denoised image is the minimum. The optimal threshold designed will control diffusion intensity reasonably, and the anisotropic diffusion model based on pulse coupled neural network and image entropy (PCNN-IEAD) can be established. Analysis and simulation results show that the proposed model preserves more image information than the classical ones. It removes the image noise and at the same time protects the edge texture details of the image; the proposed model retains the area image information more completely, the performance indexes can also confirm the superiority of the new model. In addition, the operating time of the proposed model is shorter than that of the classical models, therefore, the proposed model may be the ideal one.
Dark pulses and harmonic mode locking in graphene-based passively mode-locked Yb3+-doped fiber laser with all-normal dispersion cavity
Authors: Fu Kuan  , Xu Zhong-Wei  , Li Hai-Qing  , Peng Jing-Gang  , Dai Neng-Li  , Li Jin-Yan  ,   Wuhan National Laboratory for Optoelectronics, Wuhan 430074, China;,   School of Optical and Electronic Informtion, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

Graphene has recently been proposed as an attractive material in saturable absorption (SA) applications due to its broad operation range, low saturation power, easy fabrication, high reliability, and quick recovery time. In this paper, we use laser-induced deposition to prepare graphene saturable absorber, and apply it in a mode-locked all-normal-dispersion (ANDi) Yb-doped fiber laser to experimentally investigate different operational states. By adjusting a polarization controller (PC) and the pump power, bright pulses, dark-bright pulse pairs and their second-harmonic pulses, as well as dark pulses and their second, third-harmonic pulses can all be obeserved. In particular, it is the first time to our knowledge to report on the formation of dark-bright pulse pairs, dark pulses and their harmonic mode locking (HML) counterparts in graphene-based passively mode-locked Yb-doped fiber laser with ANDi cavity. Accoding to simulation, the main causes of these pulses are different cavity nonlinear effects which result from the fiber mode-lock members including graphene. Bright pulses, dark pulses and dark-bright pulse pairs are determined both by the laser structure and their own initial signals. Bright pulse harmonic generation is ascribed to the noise gains which form new components. However, it is found that the multiple-time repetition rate of dark pulses is a result of square pulse splitting of each component. This consequence may be of potential application in new type mode-locked fiber lasers.
Semi-Dirac points in two-dimensional phononic crystals
Authors: Cao Hui-Xian  , Mei Jun  ,   School of Physics, South China University of Technology, Guangzhou 510641, China
Published: December 2020

A two-dimensional phononic crystal (PC) composed of a triangular array of square iron cylinders embedded in water is designed, in which the accidental degeneracy of the Bloch eigenstates is utilized to realize a semi-Dirac point at the Brillouin zone center. In the vicinity of the semi-Dirac point, the dispersion relation is linear along the Y direction but quadratic along the X direction. Rotating the iron cylinders around their axis by 45 and slightly tuning the side length of the cylinders, a new semi-Dirac point can be realized at the Brillouin zone center, where the dispersion relation is quadratic along the Y direction but linear along the X direction. To gain a deeper understanding of the semi-Dirac point, a k p perturbation method is used to investigate this peculiar dispersion relation and study how the semi-Dirac point is formed. The linear slopes of dispersion relations along any direction around the semi-Dirac point can be accurately predicted by the perturbation method, and the results agree very well with the rigorous band structure calculations. Furthermore, the mode-coupling integration between the degenerate Bloch eigenstates is zero in one direction but non-zero in the perpendicular direction, and this is the ultimate reason for the forming of a semi-Dirac point. With the help of the perturbation method, an effective Hamiltonian can be constructed around the semi-Dirac point, so that the Berry phase can be calculated, which is found to be zero. Actually, the different values of Berry phase indicate an important distinction between the semi-Dirac points and Dirac points. In addition, the acoustic wave transmission through the corresponding PC structure has been studied, and a switch-like behavior of the transmittance is observed along different directions. Along some particular direction, there exist deaf bands around the semi-Dirac point, and these bands cannot be excited by the externally incident plane waves due to the mismatch in mode symmetry. But the situation is different along the other direction, where the bands are active ones and therefore can be excited by the incident plane waves. Actually, such properties of the bands can be easily changed as long as the iron cylinders are rotated around their axis. The work described in this paper is helpful to the understanding of semi-Dirac point in phononic crystals and suggests possible applications in diverse fields.
Conservative sliding algorithms for hydrodynamics
Authors: Liu Quan  , Yu Ming  , Lin Zhong  , Wang Rui-Li  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

The Lagrangian hydrodynamics algorithm using staggered mesh is one of the most important algorithms for engineering design and science computing. Some questions need to use the conservative scheme. Shashkov gave the idea how to get conservation with a material. He defined the conservative scheme to be a compatible algorithm. When we perform a numerical simulation with two or more materials, we should use sliding line or contact-impact algorithm. In this case, the Wilkins algorithm is used mostly. But this algorithm is not conservative. This paper presents a conservative method for sliding line based on the compatible Lagrangian hydrodynamics algorithm and Wilkins sliding algorithm. The conservation of total energy can be got by the local modification through the idea of contact force and contact work. This method can ensure the symmetric property and conservative property, and improve the numerical accuracy. In this paper, we give the detail in how to design the conservative sliding algorithm and how to impose the slave's edge artificial viscosity. We also gave some numerical simulations to prove that our scheme is right and useful.
Semi-analytical solution of the dry baroclinic Lagrange primitive equation and numerical experiment of a non-linear density current
Authors: Hao Shi-Feng  , Lou Mao-Yuan  , Yang Shi-Fang  , Li Chao  , Kong Zhao-Lin  , Qiu Wei  ,   Zhejiang Meteorology Observatory, Hangzhou 310017, China
Published: December 2020

To solve atmospheric primitive equations, the finite difference approach would result in numerous problems, compared to the differential equations. Taking the semi-Lagrange model as an example, there exist two difficult problemsthe particle trajectory computation and the solutions of the Helmholtz equations. In this study, based on the substitution of atmosphere pressure, the atmospheric primitive equations are linearized within an integral time step, which are broadly seen as ordinary differential equations and can be derived as semi-analytical solutions (SASs). The variables of SASs are continuous functions of time and discretized in a special direction, so the gradient and divergence terms are solved by the difference method. Since the numerical solution of the SASs can be calculated via a highly precise numerical computational method of exponential matrixthe precise integration method, the numerical solution of SASs at any time in the future can be obtained via step-by-step integration procedure. For the SAS methodology, the pressure, as well as the wind vector and displacement, can be obtained without solving the Helmholtz formulations. Compared to the extrapolated method, the SAS is more reasonable as the displacements of the particle are solved via time integration. In order to test the validity of the algorithms, the SAS model is constructed and the same experiment of a non-linear density current as reported by Straka in 1993 is implemented, which contains non-linear dynamics, transient features and fine-scale structures of the fluid flow. The results of the experiment with 50 m spatial resolution show that the SAS model can capture the characters of generation and development process of the Kelvin-Helmholtz shear instability vortex; the structures of the perturbation potential temperature field are very close to the benchmark solutions given by Straka, as well as the structures of the simulated atmosphere pressure and wind field. To further test the convergence of the numerical solution of the SAS model, the 100 m spatial resolution experiment of the non-linear density current is also implemented for comparison. Although the results from both experiments are similar, the former one is better and the property of mass-energy conservation is comparatively reasonable, and furthermore, the SAS model has a convergent property in the numerical solutions. Therefore, the SAS method is a new tool with efficiency for solving the atmospheric primitive equations.
A Model of channel current for uniaxially strained Si NMOSFET
Authors: Lü Yi  , Zhang He-Ming  , Hu Hui-Yong  , Yang Jin-Yong  , Yin Shu-Juan  , Zhou Chun-Yu  ,   Key Laboratory for Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, China;,   Beijing Research Institute of Precise Mechatronic Controls, Beijing 100076, China;,   College of Science, Beijing Information Science and Technology University, Beijing 100192, China
Published: December 2020

The channel current model is used to analyse the behavior of uniaxially strained Si NMOSFET device and circuit. With the development of mobility and threshold voltage model, starting from the basic drift-diffusion equation, the channel current model for an uniaxially strained Si NMOSFET device is developed under different bias conditions. Especially, the stress intensity is explicitly included in the mobility and threshold voltage model, and this makes the model convenient to directly reflect the relationship between the device channel current and the stress intensity. Moreover, in terms of the subthreshold current model, the charge of weak inversion rather than the normal effective channel thickness approximation is involved. In this way, the model accuracy can be improved. Furthermore, this model is implemented by using verilogA language and is applied to the strained Si circuit's SPICE simulation, the model parameters extraction tool ParamPlus++ is developed at the same time. As a result, the simulation of uniaxial-strained Si NMOSFET device and circuit can be achieved; the simulation data fits the experimental results or TCAD simulation results very well, and this proves the accuracy of the model. Meanwhile the simulation results of the threshold voltage and subthreshold current with respect to stress intensity are obtained and analyzed. The results show that with increasing stress intensity the subthreshold current is increased while the threshold voltage is decreased.
Effect of inserted AlN layer on the two-dimensional electron gas in AlxGa1-xN/AlN/GaN
Authors: Yang Peng  , Lü Yan-Wu  , Wang Xin-Bo  ,   School of Science, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

This paper investigates the changes of electron transport properties in AlxGa1-xN/GaN with an inserted AlN layer. The polarization charge density and two-dimensional electron gas (2DEG) sheet density in AlxGa1-xN/AlN/GaN double heterojunction high electron mobility transistors (HEMT) affected by the spontaneous polarization and piezoelectric polarization in AlxGa1-xN and AlN barrier are studied. Relations of interface roughness scattering and alloy disorder scattering with the AlN thickness are systematically analyzed. It is found that the alloy disorder scattering is the main scattering mechanism in AlxGa1-xN/GaN heterojunction high-electron-mobility transistors, while the interface roughness scattering is the main scattering mechanism in AlxGa1-xN/AlN/GaN double-heterojunction structure. It is also known that the 2DEG sheet density, interface roughness scattering and alloy disorder scattering are depended on the thickness of the inserted AlN layer. The 2DEG sheet density increases slightly and the mobility increases obviously by inserting an AlN layer about 13 nm. Taking Al mole fraction of 0.3 as an example, if without AlN layer, the 2DEG sheet density is 1.47 1013 cm-2 with the mobility limited by the interface roughness scattering of 1.15 104 cm2V-1-1, and the mobility limited by alloy disorder scattering of 6.07 102cm2V-1-1. After inserting an AlN layer of 1 nm, the 2DEG sheet density increases to 1.66 1013cm-2, and the mobility limited by the interface roughness scattering reduces to 7.88 103cm2V-1-1 while the mobility limited by alloy disorder scattering increases greatly up to 1.42 108 cm2V-1-1.
Field-emission current densities of carbon nanotube under the different electric fields
Authors: Wang Yi-Jun  , Cheng Yan  ,   School of Physics and Electronic Engineering, Xianyang Normal University, Xianyang 712000, Shaanxi, China;,   Science and Technology on Low-Light-Level Night Vsion Laboratory, Xi'an 710065, China
Published: December 2020

The field emission current variation law of carbon nanotube in a large electric field range (0-32 V m-1) is analyzed in depth by combining the density functional theory with metal electron theory. The results show that their emission current densities are determined by their densities of states, the pseudogap, the length and the local electric field, showing the different variation laws in the different electric field ranges. In the lower electric field (corresponding macroscopic field is less than 18 Vm-1), when their density of states increases, their pseudogap decreases: the two trends are opposite, the former increases the number of electrons for emission, and the latter improves the ability to transfer electrons, they all turn to the increase of the emission current, so their field-emission current density increases linearly with increasing electric field in this range. But in the higher electric field (corresponding macroscopic field is less than 32 Vm-1 and more than 18 Vm-1), their densities of states and the pseudogaps take on the same decrease and increase, so do they in the opposite change case, therefore the emission current density behaves as a non-periodic oscillation in the increasing electric field, moreover the higher electric conductivity lead to the rising of current density, the combined effect of the emitter current density exhibits an oscillatory growth in this electric field range, and the carbon nanotubes behave as ionizing radiation. So the too high electric field may cause the emission current to be instable. The electric conductivity variation law of the metallic carbon nanotube is further studied in this paper. In the lower electric field (corresponding macroscopic field is less than 5 Vm-1), the electric conductivity of CNT increases linearly with increasing electric field; when the macroscopic electric field increases up to a value in a range from 5 to 14 Vm-1, the electric conductivity only changes like a slight concussion in (6.3-9.9)1017Sm-1 range, when the macroscopic electric field increases to a value in a range from 16 to 32 Vm-1, the electric conductivity appears as a sharp oscillation growth trend. Additionally, the specific binding energy of CNT is enhanced with increasing electric field, accordingly the structural stability turns better and the cone-capped carbon nanotubes could be used for emission cathode material. The calculation results are consistent with the experimental results of the literature.
Effect of CC bond breakage on diamond tool wear in nanometric cutting of silicon
Authors: Wang Zhi-Guo  , Zhang Peng  , Chen Jia-Xuan  , Bai Qing-Shun  , Liang Ying-Chu  ,   School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

It is well known that diamond is one of the most ideal cutting tool for materials, but the rapid tool wear can make surface integrity of the machined surface decline sharply during the nanometric cutting process for a single crystal silicon. Thus, a research on the wear mechanism of the diamond tool is of tremendous importance for selecting measures to reduce tool wear so as to extend service life of the tool. In this paper, the molecular dynamics simulation is applied to investigating the wear of the diamond tool during nanometric cutting for the single crystal silicon. Tersoff potential is used to describe the CC and SiSi interactions, and also the Morse potential for the CSi interaction. The rake and flank faces are diamond (111) and (112) planes respectively. A new method, by the name of 6-ring, is proposed to describe the bond change of carbon atoms. This new method can extract, all the worn carbon atoms in diamond tool, whose accuracy is higher than the conventional coordination number method. Moreover, the graphitized carbon atoms in the diamond tool also can be extracted by the combination of these two methods. Results show that during the cutting process, the CC bond's breaking in the surface layer of the diamond tool leads to the transformation of hybrid structure of the carbon atoms at both ends of the broken bond, from sp3 to sp2. Following to the bond breaking, the bond angle between the surface carbon atoms increases to 119.3 whose hybrid structure has changed, and the length between nearest neighboring atoms quickly decreases to 0.144 nm, indicating that the space structure formed by these carbon atoms has changed from 3D net structure of diamond to plane structure of graphite. Hence, the carbon atoms in the tool surface whose space structure has changed due to bond breaking should be defined as worn carbon atoms, but not only the carbon atoms whose hybrid structure has changed. The structure defects at both edges of the diamond tool are much more serious, which make the energy of CC bonds at the edges weakened with the enhancement of defects. The bonds with lower energy are broken under the effect of high temperature and shear stress, which also produces the tool wear. The graphitization occurs at the tool of the cutting tool because the structure defects there are the most serious. The reconstruction of the carbon atoms with lower coordination number causes its neighboring region to produce serious distortion, which leads to easy breaking of CC bonds in this region.
Chaotic compressive measurement and reconstruction of binary signals
Authors: Guo Jing-Bo  , Li Jia-Wen  ,   State Key Lab, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

Compressive sensing of binary signals is corresponding to the problem of binary symbol detection in the faster-than-Nyquist signaling systems, which has significant research value. Traditional compressive measurement of a binary signal is based on Gaussian matrix, and l1 minimization is a classic algorithm for signal reconstruction. However, stochastic matrix such as the Gaussian matrix can hardly be realized by a digital circuit, and the reconstruction performance of l1 minimization is not well enough for binary signals. Thus, it is of great meaning to construct a new kind of measurement matrix as well as a better reconstruction algorithm for binary signals. This paper constructs a chaotic circulant measurement matrix based on Cat chaotic map (CCMM), and proposes a brand new algorithm for binary signal reconstructionsmooth function approximation method (SFAM). Chaotic sequence has characteristics of both internal certainty and external randomness, while a circulant matrix requires less elements and can be realized through fast Fourier transform. CCMM conbines the advantages of both chaotic sequence and circulant matrix, so that it not only satisfies the RIPless property required by the compressive measurement matrix because of external randomness, but also has the power to resist the effect of low signaling efficiency and low SNR due to the internal certainty. Moreover, the circle structure gives CCMM the potential to be digital realized in the future. In SFAM, we first use a non-convex function to approximate the original discontinuous objective function, in order to transfer the original combinatorial optimization problem into an optimization problem with equality constraints which can be solved much easier. Then we use the interior point method to solve this optimization problem. Furthermore, sparse Bayesian learning algorithm is used to correct the reconstruction error for a more accurate result. Compressive measurement and reconstruction of binary signals in additive Gaussian white noise channel are operated. Result of numerical experiments shows that CCMM is much better than the traditional Gaussian matrix for compressive measurement, especially in the condition of low signaling efficiency and low SNR, and SFAM is much better than l1 minimization for binary signal reconstruction. At the end of this paper, we explain the essential reason why CCMM performs better than the traditional Gaussian matrix, through calculating the autocorrelation function of compressive measurement vector in various conditions.
Nonlinear solitary Rossby waves with external heating source and effect topographic effect in stratified flows described by the inhomogeneous Schrdinger equation
Authors: Li Shao-Feng  , Yang Lian-Gui  , Song Jian  ,   School of Mathematical Science, Inner Mongolia University, Hohhot 010021, China;,   College of Science, Inner Mongolia University of Technology, Hohhot 010051, China
Published: December 2020

Rossby waves are intrinsic in the large-scale systems of fluids, so they are the most important waves in the atmosphere and ocean. Theory and observation show that their basic characteristic is to satisfy the quasi-geostrophic and quasi-static equilibrium approximations. In stratified fluids, we discuss the long waves in a homogenous atmosphere and obtain the KdV equation, but the analysis is limited to the case that the velocity shear is small compared with a basic uniform zonal motion, and it gives no insight pertaining to the kinds of stream-line-flow patterns accompanying these waves. Here, the -plane approximation f= f0+ 0 y (0 is a constant) is extended into f= f0+ (y) y, which includes a nonlinear function (y) taking the place of in the -plane approximation. Such an approximation can depict more precisely the motion of the atmosphere and ocean, especially in the middle and high latitude regions. It generalizes the theory developed by Helfrich and Pedlosky for time-dependent coherent structures in a marginally stable zonal flow by including forcing. Such forcing could be due to topography or external source. We take the basic flow to be a shear and the Visl-Brunt frequency N a function of variable z. For the stratified fluids, based on the lower boundary with external heating source and topography, as well as the quasi-geostrophic potential vorticity equation with external heating source, an inhomogeneous nonlinear Schrdinger equation (including topographic forcing and an external heating source) is derived by using the perturbation method and stretching transforms of time and space. It is found that the external heating source, effect and topography effect are the important factors that could induce the nonlinear solitary Rossby by inspection of the evolution of the amplitude of Rossby waves. On the assumption that nonlinear topographic effects and the dissipation of external heating source are balanced, an inhomogenous equation in which the coefficients depend on (y), u(y,z) and N(z) is derived. Results show that the topography, external heating source and Rossby waves will interact with a basic stream function that has a shear. In stratified fluids, the inhomogeneous nonlinear Schrdinger equation is obtained for describing the evolution of the amplitude of solitary Rossby envelop solitary waves as the change of Rossby parameter (y) with latitude y, topographic forcing and the external heating source.
Hermite orthogonal basis neural network based on improved teaching-learning-based optimization algorithm for chaotic time series prediction
Authors: Li Rui-Guo  , Zhang Hong-Li  , Fan Wen-Hui  , Wang Ya  ,   School of Electrical Engineering, Xinjiang University, Urumqi 830047, China;,   Department of Automation, Tsinghua University, Beijing 100084, China;,   School of Mechanical Engineering, Xinjiang University, Urumqi 830047, China
Published: December 2020

Chaos phenomenon which exists widely in nature and society affects people's production and life. It has great important significance to find out the regularity of chaotic time series from a chaotic system. Since chaotic system has extremely complex dynamic characteristics and unpredictability, and chaotic time series prediction through traditional methods has low prediction precision, slow convergence speed and complex model structure, a prediction model about Hermite orthogonal basis neural network based on improved teaching-learning-based optimization algorithm is proposed. Firstly, according to the chaotic time series, autocorrelation method and Cao method are used to determine the best delay time and the minimum embedding dimension respectively, then a phase space is reconstructed to obtain the refactoring delay time vector. Secondly, on the basis of phase space reconstruction and best square approximation theory, combined with the neural network topology, a prediction model about Hermite orthogonal basis neural network with excitation functions based on the Hermite orthogonal basis functions is put forward. Thirdly, in order to optimize the parameters of the prediction model, an improved teaching-learning-based optimization algorithm is proposed, where a feedback stage is introduced at the end of the learning stage based on the teaching-learning-based optimization algorithm. Finally, the parameter optimization problem is transformed into a function optimization problem in the multidimensional space, then the improved teaching-learning-based optimization algorithm is used for parameter optimization of the prediction model so as to establish it and analyze it. Lorenz and Liu chaotic systems are taken as models respectively, then the chaotic time series which will be used as simulation object is produced by the fourth order Runge-Kutta method. The comparison experiments with other prediction models are conducted on single-step and multi-step prediction for the chaotic time series. The simulation results and numerical analysis show that compared with radial basis function neural network, echo state network, least square support vector machine prediction model and Hermite orthogonal basis neural network based on teaching-learning-based optimization algorithm, the proposed prediction model has the mean absolute error and root mean square error reduced significantly, has a decision coefficient close to 1, meanwhile, has a mean modeling time shortened greatly. So the proposed prediction model can improve the prediction precision, accelerate the convergence speed and simplify the model structure, thus the prediction model is effective and feasible, which makes it promoted and applied easily.
Approximations of chaotic attractors and its circuit design based on the parameter switching algorithm
Authors: Luo Shao-Xuan  , He Bo-Xia  , Qiao Ai-Min  , Wang Yan-Chun  ,   Mechanical and Electronic Engineering Department, Bengbu College, Bengbu 233030, China;,   Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

Based on the parameter switching algorithm and the discrete chaotic system, a new chaotic system based parameter switching algorithm is proposed. The principles of parameter switching algorithm and chaotic system based parameter switching algorithm are presented in detail by means of flow chart and step description. By applying phase diagram observation method, chaotic attractor approximation of the unified chaotic system is investigated based on parameter switching algorithm and chaotic system based parameter switching algorithm. It shows that chaos can be obtained by switching two periodic parameters and periodic state can be observed by switching two chaotic parameters. Thus the formulas chaos+ chaos = periodic and period+ period = chaos are proved to be workable in this paper. Chaotic attractor approximation of Rössler chaotic system is also studied by employing the two switching methods. Two cases are investigated. Firstly, a chaotic switching system is obtained by switching a chaotic parameter and a periodic parameter. Then a more complex switching scheme is carried out. Periodic system is switched by two periodic parameters and a chaotic parameter. So, the formulas chaos+ periodic = chaos and periodic+ period+ chaos = periodic are proved to be workable. It shows that the switching system is the approximation of the original system under specified parameter, and the attractor is in accordance with the attractor of the targeting system. The outputs of the Logistic map based parameter switching algorithm are more complex than those of existing parameter switching algorithm. As the distribution of logistic map is not uniform, the approximate attractor does not consist of the targeting system and shows more complicated structure. But approximate attractors can be obtained when the distribution of discrete sequence is uniform. In addition, the chaotic map based parameter switching algorithm has larger secret key space since it has the initial values and parameter of the chaotic map. Finally, the parameter switching circuit of Rössler system is designed by introducing a square wave generator. Compared with the traditional switching chaotic circuit (switching between different systems), the design of parameter switch circuit is simpler as it does not need to change the original structure of the system. The output is affected by the frequency of the square wave. By adding an appropriate frequency square wave generator, the circuit simulation agrees with the numerical simulation. It presents a theoretical and experimental base for the practical application of the parameter switching chaotic systems.
Off axial radially polarized beam and its propagation characteristics
Authors: Chen Shun-Yi  , Ding Pan-Feng  , Pu Ji-Xiong  ,   Fujian Provincial Key Laboratory of Light Propagation and Transformation, College of Information Science and Engineering, Huaqiao University, Xiamen 361021, China
Published: December 2020

Based on the theory of paraxial approximation of beam propagation, the analytical expression of the intensity of the off axial radially polarized beam (OARPB) is derived and the effect of the off axial magnitude on the distribution of intensity of the OARPB is studied. Meanwhile, according to the definition of the first-order moment of centroid, the coordinate of centroid of the OARPB is derived and the variation of cenreoid of the OARPB is studied. Simulation result shows that the intensity distribution of the OARPB is different from that of the radially polarized beam. The intensity distribution of the OARPB is not uniform in the near-field. With increasing propagation distance, the beam spreads and the uniformity of intensity of the OARPB is improved gradually. However, the intensity distribution of the radially polarized beam keeps the form of symmetric doughnut spot during propagation all the time. When the off axial magnitude is small, the intensity distribution of the OARBP is obviously asymmetric in the near-field, and it becomes nearly symmetric while the beam propagates a certain distance. The smaller the off axial magnitude, the shorter the required propagation distance to become symmetric for the OARPB. When the off axial magnitude is larger, the hollow part of intensity distribution disappears, and the doughnut beam of the OARPB changes into a Gaussian beam spot gradually during propagation. On the other hand, the centroid of the OARPB does not change with increasing propagation distance. The value of the ordinate of centroid is equal to zero all the time. And the value of the abscissa of centroid is related to the beam size and the off axial magnitude. While the beam size increases, the abscissa of centroid increases linearly at the same time. When the off axial magnitude is small, the abscissa of the centroid of the OARPB increases with the increase of the off axial magnitude, nonlinearly and slightly; however, when the off axial magnitude is larger, the abscissa of centroid of the OARPB increases with the increase of the off axial magnitude, linearly and significantly.
Physical total energy based objective function model for sparse reconstruction
Authors: Ma Ge  , Hu Yue-Ming  , Gao Hong-Xia  , Li Zhi-Fu  , Guo Qi-Wei  ,   School of Automation Science and Engineering, South China University of Technology, Guangzhou 510640, China;,   Engineering Research Center for Precision Electronic Manufacturing Equipments of Ministry of Education, South China University of Technology, Guangzhou 510640, China
Published: December 2020

Image reconstruction from sparse data is one of the key technologies in physical imaging, and it can often be mathematically described as an underdetermined linear inverse problem. Mathematical models for sparse reconstruction often choose the sparseness constraints or data fidelity term directly as objective functions. However, physics concepts and laws for these modeling or solving processes have never been explored. In this paper, sparse reconstruction is investigated for the first time from the perspective of physical motion. Firstly, a physical model is created to describe a particle motion in viscous medium, in which the particle gravity potential energy function is the norm of l2-l1 after the relaxation transformation. In discrete calculations, the particle displacement is determined by the corresponding iterative result, and its velocity can be described as the change between two adjacent iterations. Then, a new mathematical model based on the physical motion model is studied for sparse reconstruction, in which the total energy of particle is chosen as a new objective function and nonnegative displacements as constraints. This new model preserves sparse constrains and fidelity term of original l2-l1 model, and adds the constrains of deviations between two adjacent iterations so as to avoid oscillations caused by large deviations. Furthermore, a targeted gradient projection technique is adopted to solve such a reconstruction model, and its convergence is discussed as well. Especially in this algorithm, the gradient of this new objective function contains the iterative step of previous iteration, and such iterative steps play the role of physical inertia property in iterative process, which can effectively enlarge the iterative steps to accelerate the convergence and avoid local optima. Finally, two sets of experimental results are presented, including natural grayscale image reconstruction and micro focus X-ray defect detection in precision electronic package. The results demonstrate that the proposed method outperforms its competitors distinctly in time efficiency on the basis of guaranteeing the reconstruction quality. Additionally, on detecting internal defects in solder joint of integrated circuit, the proposed method is well performed in retaining edge details of the reconstructed micro focus X-ray images. Therefore, the proposed method can identify the solder joint internal defects more accurately and is more suitable to rapid and precise micro focus X-ray defect detection in industry.
Two channel photonic microwave generation based on period-one oscillations of two orthogonally polarized modes in a vertical-cavity surface-emitting laser subjected to an elliptically polarized optical injection
Authors: Zhou Ya  , Wu Zheng-Mao  , Fan Li  , Sun Bo  , He Yang  , Xia Guang-Qiong  ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China;,   State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China
Published: December 2020

Previous investigations demonstrated that a semiconductor laser subjected to optical injection can realize period-one (P1) oscillation output under suitable operational parameters, which can be used to obtain high quality photonic microwave. In this paper, we propose a scheme for simultaneously generating two channel photonic microwave based on the P1 oscillations of two orthogonally polarization modes in a vertical-cavity surface-emitting laser (VCSEL) subjected to an elliptical polarization optical injection, and the relevant characteristics of obtained photonic microwave are numerically simulated and analyzed. The results show that under suitable operational parameters, a free-running VCSEL (named master VCSEL, M-VCSEL) can output an elliptical polarization light in which both X and Y polarization components of the elliptical polarization light oscillate at the same frequency. By using the elliptical polarization light from the M-VCSEL as an injection light into another VCSEL (named slave VCSEL, S-VCSEL), both two polarization components of the S-VCSEL can be driven into P1 oscillation through selecting suitable injection strength under a fixed frequency detuning between the M-VCSEL and the S-VCSEL. Based on the P1 oscillation, two orthogonally photonic microwave signals can be obtained. With the increase of the injection strength from the M-VCSEL, the frequency of photonic microwave shows a gradually increasing trend while the power of photonic microwave displays an increasing process accompanied by slight ripples. Combining the distribution mappings of the frequency, the power, and the amplitude difference between the first sideband and the second sideband of the photonic microwave in the parameter space of the injection strength and the frequency detuning, certain regions with optimally operational parameters can be determined for acquiring high quality photonic microwave.