bluuebunny/crossref_metadata_2025 huggingface dataset:
A single short pulse produced by the excited state of Na atom exposed to an infrared laser
Authors: Jia Yan-Wen  , Guo Qiao-Ling  , Li Peng-Cheng  , Wang Guo-Li  , Zhou Xiao-Xin  ,   College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China
Published: December 2020

The time-dependent Schrodinger equation of alkali metal Na atom in an infrared laser field is solved numerically by using the pseudo-spectral method. In the calculation, an accurate model potential of Na atom is used. The bound state energy levels, which are consistent with experimental data, are obtained with the potential, so that we can study the characteristics of high-order harmonic generation for emission of the exited stated of Na atom. Our results show that the high-order generation spectrum of emission of 4s, and 5s excited states of Na atom is super-continuum in the over-barrier ionization regime. By superposed certain orders harmonics below threshold, a single pulse can be obtained with the central frequency from high frequency of visible light to the ultraviolet band. Through the calculated ionization probability of Na atom and the time-frequency analysis by wavelet transform of the superposed harmonics, it reveals that the emission process of low-order harmonic generation in over-barrier ionization regime is different from in the tunnel ionization regime.
Photonic microwave waveform generation based on polarization delay interference
Authors: Zhang Hua-Fang  , Wang Wen-Rui  , Yu Jin-Long  , Wang Ju  , Yang En-Ze  ,   School of Electronic Information Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

Techniques for generating microwave waveform such as square or triangle waveform have been a topic of general interest recently. Because they are important for applications in radar, measurement, instrument technology, medical imaging, etc. Usually, high quality microwave waveform is preferred as it largely determines the performance of the microwave system. In recent years, photonic microwave generation has aroused the great interest of both the research community and commercial sector all over the world, as it has the advantages of high frequency and large bandwidth. A variety of techniques for generating arbitrary waveforms have been demonstrated. In this paper, a new approach to photonic microwave waveform generation based on polarization delay interference is proposed and experimentally demonstrated, in which only one laser and Mach-Zehnder modulator (MZM) are used. In our scheme, odd-order optical sidebands can be generated by setting the bias of the MZM at the quadrature point. Thus, square waveform and triangular waveform can be generated, with a sinusoidal microwave signal applied to MZM and carefully controlling the modulation depth of MZM as well as the amount of delay on the differential delay line. A theoretical analysis of the principle of the proposed approach is performed. And optimum parameters of the photonic waveform generation are derived from numerical simulation. By simulation, the fourth order of approximation of the square waveform and triangular waveform is generated. In addition, it is proved that the scheme can generate the stable square waveform and triangular waveform by analyzing the stability of the bias and the modulation depth of the MZM. Experimentally, square waveform and triangular waveform with a repetition rate of 5 GHz are generated by carefully setting the bias and the modulation depth of the MZM, which are consistent with theoretical analyses. The scheme has the advantages of the low cost, simplicity, easy-to-tune, and it adopts the innovative technology of polarization delay interference. Hence the scheme is effective and worth spreading.
Multiple cutoffs in high harmonic generation via multi-XUV-photon absorption
Authors: Yu Zu-Qing  , He Feng  ,   Key Laboratory for Laser Plasmas(Ministry of Education), Department of Physics and Astronomy, Collaborative innovation center of IFSA, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

High harmonic generation (HHG) is one of the most fundamental processes in the interaction of strong laser fields with atoms and molecules. Because of wide applications of HHG, for example, imaging atomic or molecular orbitals, visualizing chemical reactions, synthesizing a single attosecond pulse, the HHG attracts huge attentions in both theories and experiments. The HHG can be explained by the famous three-step model:first, the laser field bends the Coulomb potential and the electron tunnels out; second, the electron is accelerated in the laser field and gains kinetic energy; Third, the energetic electron recombines with the parent ion and release its energy as high energetic photons. The HHG can be tailored by controlling the each step. In this paper, we conceive a strategy to control the third step. We simulate the HHG when He+ is exposed to the combined few-cycle Ti-Sapphire (800 nm) IR femtosecond laser pulse and XUV laser pulse by numerically solving the time dependent Schrdinger equation. The simulation shows that after the electron tunnels out and gains energies from the infrared laser field, extra XUV photons may be absorbed during the electron and parent ion recombination, contributing multiple cutoffs separated by XUV photon energies in the high harmonic spectrum. This scenario is confirmed by time-delay-dependent HHG in the time-frequency representation, and by the power scaling of the cutoffs' intensities as a function of the XUV intensity.
Influences of BaO doping on the properties of singe domain GdBCO bulk superconductors
Authors: Wang Miao  , Yang Wan-Min  , Yang Peng-Tao  , Wang Xiao-Mei  , Zhang Ming  , Hu Cheng-Xi  ,   School of Science, Xi'an Aeronautical University, Xi'an 710077, China;,   School of Physics and Information Technology, Shaanxi Normal University, Xi'an 710062, China
Published: December 2020

In this work, a series of single domain GdBCO bulk superconductors with different ratios of BaO addition in the solid phase pellet, is successfully fabricated to inhibit the Gd/Ba substitution in the growth process by the modified top seeded infiltration growth (M-TSIG) technique. The reaction of the precursor powders, the growth morphology, the magnetic levitation force (F), the trapped magnetic flux (Btr) and critical temperature (Tc) of the single domain GdBCO bulk superconductors are investigated in detail. First, the differential thermal analysis is performed on the precursor powders of 10 mg solid phase pellet (containing various amounts of BaO) and 15 mg liquid phase pellet in order to investigate the melting temperature (Tm) and the peritectic temperature (Tp) of the GdBCO superconductor system. The results show that the melting point of the precursor powder decreases by nearly 8℃ as the BaO composition increases from 0 wt% to 4 wt%, which leads to Tp decreasing with BaO content increasing. Second, the top view morphologies of the GdBCO samples are also discussed. All of the samples exhibit clear, fourfold growth sector boundaries on their top surfaces, and spontaneous satellite grains are observed in none of these samples. It can be seen that the different ratio of BaO addition cannot affect the growth morphology of the single domain GdBCO bulk superconductor. And thirdly, the levitation force and trapped field of each of the samples are measured under a zero field cooling state at 77 K by the three-dimensional magnetic force and field device. The values of the levitation force for the samples are slightly different for different ratios of BaO additions. The largest levitation force is 35 N, which is obtained in the sample with 2.5 wt%, and the smallest one is 28 N in the sample with 1 wt% BaO addition. And also, the trapped field of the sample can be attributed simply to the variation in the pinning strength. It can be obviously seen that these values fluctuate between 0.28 T and 0.32 T for these samples. Finally, the critical temperatures of the samples are measured by the vibrating sample magnetometer with an external magnetic field of 0.01 T. The samples exhibit outstanding features of high Tc, which indicates that these samples are of good quality and the Gd/Ba substitution is inhibited by the BaO addition. The above results show that the values of melting temperature (Tm) and peritectic temperature (Tp) of the samples have the decrease tendencies, and the superconducting properties of the samples (such as F, Btr and Tc) can be improved to a certain extent when the amount of BaO added ranges from 2 wt% to 4 wt%, which are very helpful in inhibiting the Gd/Ba substitution and fabricating the high-quality single domain GdBCO bulk superconductors.
Thermophysical properties and liquid-solid transition mechanisms of ternary (Co0.5Cu0.5)100-xSnx alloys
Authors: Liu Jin-Ming  , Zhai Wei  , Zhou Kai  , Geng De-Lu  , Wei Bing-Bo  ,   Department of Applied Physics, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

The thermophysical properties and liquid-solid phase transition characteristics of ternary (Co0.5Cu0.5)100-xSnx(x=10, 20, 30, 40 and 50 at%) alloys are systematically investigated. The liquidus temperature and latent heat of fusion, as well as the undercooling are determined by differential scanning calorimetry (DSC) method. Based on the measured data, their relationships with Sn content are fitted by polynomial functions. The liquidus temperature shows a decreasing tendency with the increase of Sn content. The undercooling of liquid (Co0.5Cu0.5)100-xSnx alloys significantly increases with increasing Sn amount, indicating that the addition of Sn element enhances the undercoolability. By using the laser-flash and DSC methods, the thermal diffusion coefficients and specific heats of solid ternary (Co0.5Cu0.5)100-xSnx alloys are respectively measured in a temperature range from 293 to 473 K. The thermal diffusion coefficients increase linearly as temperature rises. The thermal diffusion coefficient varies from 1.0610-5 to 1.1210-5 m2s-1 for ternary Co45Cu45Sn10 alloy, which is close to that of Co element but much lower than those of Cu and Sn elements in the same temperature range. However, the thermal diffusion coefficients of other (Co0.5Cu0.5)100-xSnx alloys are far less than that of ternary Co45Cu45Sn10 alloy. The specific heat shows an increasing trend with temperature, and drops apparently with increasing Sn amount. From the measured thermal diffusion coefficients, specific heats and densities, the thermal conductivities of ternary (Co0.5Cu0.5)100-xSnx alloys at 293 K are derived. With the Sn content increasing up to 40 at%, the thermal conductivities for (Co0.5Cu0.5)100-xSnx alloys monotonically decrease from 33.83 to 7.90 Wm-1K-1, and subsequently increases slightly when the Sn content further increases up to 50 at%. In addition, on the basis of the DSC curves and solidification microstructures, the liquid-solid phase transitions are also explored. When the Sn content is less than 30 at%, the primary (Co) phase appears as coarse dendrites, whose volume fraction decreases as Sn content increases. Once Sn content exceeds 30 at%, the Co3Sn2 phase preferentially nucleates and grows during solidification, which occupies about 89% volume in the solidified Co30Cu30Sn40 alloy. The phase constitution investigation indicates that with the increase of the Sn content, the (Cu) solid solution phase disappears, whereas intermetallic compounds, including Cu41Sn11, Cu3Sn, and Cu6Sn5 phases successively precipitate from the alloy melts. The (Sn) solid solution phase even appears when Sn amount reaches 50 at%.
Fast Bayesian blind restoration for single defocus image with iterative joint bilateral filters
Authors: Yin Shi-Bai  , Wang Wei-Xing  , Wang Yi-Bin  , Li Da-Peng  , Deng Zhen  ,   Department of Economic Information Engineering, Southwestern University of Finance and Economics, Chengdu 611130, China;,   Department of Information Engineering, Chang'an University, Xi'an 710064, China;,   Department of Engineering, Sichuan Normal University, Chengdu 610101, China;,   Department of Information Engineering, Ningxia University, Yinchuan 750021, China
Published: December 2020

It is significant to realize effective defocus image restoration for acquiring clear image in military and geological examination field. Most of existing algorithms have the problems of large computational cost, ringing and noise sensitivity, hence a novel approach by iterative joint bilateral filtering under Bayesian framework is proposed. Firstly, it utilizes defocus image depth estimation to compute the point spread function in the Bayesian framework. Then a minimum optimization problem is built to represent the blind restoration problem. After inferencing the solution procedure of the minimum optimization problem, we find that the joint bilateral filters can be used to search the optimal solution, which not only simplifies the searching procedure but also reduces the computational cost. Finally, an iterative joint bilateral filtering is designed to realize the image restoration. That means that the original restored image obtained from the bilateral filtering is used to design the guide image for the joint bilateral filters, and the guide image will serve as the input of the optimization problem for acquiring the better optimal result. This procedure is repeated until convergence. The experimental results indicate that this method can yield the ringing, reduce the computational cost, and remove the noise. Generally speaking, the average pixel error of 85% images is under 0.03, which has improved 19% comparing with the same error rang of existing algorithms, and 78% shorter than those of compared algorithms. It can be used in the engineering practice of blind restoration for single defocus image.
Markov decision model based handoff selection algorithm for heterogeneous wireless networks
Authors: Liang Xiao  , Qian Zhi-Hong  , Tian Hong-Liang  , Wang Xue  ,   College of Communication Engineering, University of Jilin, Changchun 130012, China;,   College of Information Engineering, Northeast Dianli University, Jilin 132012, China
Published: December 2020

Coexistence of multiple wireless access technologies will be an indicator of next-generation wireless network, and the integration of heterogeneous wireless networks will meet the needs of high-performance services for mobile users. According to unique quality of service (QoS) requirements of different service type users in heterogeneous environment, the Markov decision model based handoff selection algorithm is proposed in this paper. A heterogeneous wireless network architecture based on the software defined network (SDN) is established to realize the transparency control of heterogeneous networks. Network state information of heterogeneous wireless networks is mastered by SDN controller. It is responsible for scheduling network resources dynamically according to the performance characteristics of each network. If the network state information in equal interval is sampled, the next moment state of network is only related to the current network state and action, but it is not related to the historical state. The problem of handoff selection for heterogeneous wireless networks is modeled as a Markov process with discrete time and continuous state. To predict the next moment state of network by Markov process to obtain a reward, when the reward is positive, it represents the income; when it is negative, it represents the cost. An immediate reward function is constructed for real-time service and non real-time service users respectively according to their different state attributes of the network. Considering five state attributes of wireless network as follows:delay, delay jitter, bandwidth, error rate and network load, the immediate reward function is constructed with weighted summation. Due to the difference in attribute weight distribution among different service type users, the attribute weights are determined by the analytic hierarchy process. In the long term, the objective function which consists of immediate reward function sequence is used to measure future long-term rewards. Then expected reward function based on the state action pair is constructed to obtain the handoff strategy of the maximum expected return by the iterative method of successive approximation. The proposed Markov decision model based handoff selection algorithm is used in simulation of the Matlab platform. The simulation results show that the proposed method can select the optimal handoff strategy for different service type users and reduce the blocking rate, thereby improving the QoS of users and resource utilization of wireless networks.
Enhancement of quantum friction via coupling of surface phonon polariton and graphene plasmons
Authors: Zhang Chao-Jie  , Zhou Ting  , Du Xin-Peng  , Wang Tong-Biao  , Liu Nian-Hua  ,   Department of Physics, Nanchang University, Nanchang 330031, China;,   Institute for Advanced Study, Nanchang University, Nanchang 330031, China
Published: December 2020

In our daily life, frictions are very common when two bodies in direct contact relatively move. However, when two bodies are separated by a finite distance, due to the quantum fluctuations inside the bodies, they may still experience a friction when they relatively move. Such a phenomenon is often called quantum friction, which has been studied for more than a decade. It has shown in previous studies that the surface modes, such as surface phonon polaritions (SPhPs) or surface plasmon polaritions (SPPs) have significant contribution to enhancing the quantum friction. However, to the best of our knowledge, the contribution of coupling from SPhPs and SPPs to quantum friction is still unknown. Here, we report a detailed study on the quantum frictions between two graphene sheets with the silicon carbide (SiC) substrates. For comparison, the quantum frictions between two other samples, i.e., SiC/SiC and graphene/graphene are also studied. As indicated in previous studies, SPhPs and SPPs, supported by SiC and graphene, respectively, can couple together in special frequency ranges. The coupling of SPhPs and SPPs can be tuned by varying the chemical potential of graphene. The coupling modes shift toward higher frequency as the chemical potential increases. Firstly, we analyze qualitatively the effects of coupled surface modes on quantum friction with the help of dispersion relation. Secondly, we calculate the quantum friction coefficients numerically for the three different samples. We find that due to the coupling of SPhPs and SPPs, the quantum friction between graphene sheets with SiC substrates is larger than that between the SiC or monolayer graphene sheets. We demonstrate that the coupling of SPhPs and SPPs can be modulated by chemical potential of graphene; therefore, the relationship between quantum friction coefficient and chemical potential is also studied. We observe that with the increase of chemical potential, quantum friction coefficient follows a non-monotonic trend, i.e., it first increases to its maximum value then decreases. We believe that our studies are not only helpful in understanding the micro mechanisms of friction, but also meaningful in the fabrications of micro- and nano-electromechanical systems.
Preparations and field emission properties of multilayer AlGaN nanofilm
Authors: Shen Zhen  , Chen Cheng-Cheng  , Wang Ru-Zhi  , Wang Bo  , Yan Hui  ,   College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China;,   Beijing Products Quality Supervision and Inspection Institute, Beijing 101300, China
Published: December 2020

We report on the electron field emission (FE) from multi-layer AlGaN nanofilm grown by pulsed laser deposition, and the investigation of the multi-layer quantum structure effect on the field emission performance. The results show that the as-grown film has a good crystallinity, and the thickness values of GaN, AlN, and GaN film are 25 nm, 50 nm, and 25 nm, respectively. The FE measurement indicates that compared with single layer, the multilayer filmhas a low turn-on field and large threshold current. The turn-on filed is found to be 0.93 V/m, and the electric current density reaches to 30 mA/cm2 at 5.5 V/m. The improvement of the FE performance is attributed to resonant tunneling in the quantum well structure, and the accumulated electrons lower the effective surface barrier. The outstanding performance of multi-layer filed emission film should provide a feasible technical solution for large current and high power density thin film field emission device.
Influences of material defects and temperature on current-driven domain wall mobility
Authors: Zhu Jin-Rong  , Fan Lü-Chao  , Chao Su  , Hu Jing-Guo  ,   College of Physics Science and Technology, Yangzhou University, Yangzhou 225002, China
Published: December 2020

Current-induced domain wall motion, which has potential application in the next-generation data storage and logic device, has attracted much interest in recent years. However, how the material defect and its joule heat influence current-driven domain wall motion in magnetic nanostripe is still unclear. This paper is to deal with these issues by using the Landau-Lifshitz-Gilbert spin dynamics. The results show that the material defect can pin domain wall motion and this pinning effect strongly depends on the defect concentration, location and shape. The pinning effect induced by the defect on domain wall motion results in the increase of threshold current, and the domain wall moves steadily and continuously. Specifically, the probability for domain wall motion induced by pinning effect is nonlinearly increasing with the increase of defect concentration. Namely, the increasing of the pinning ability with the increase of the defect concentration becomes fades away. Initially, when the defect is near to domain wall, the pinning ability is obvious. However, the pinning ability is not linearly increasing with the decrease of the initial distance between the defect and the domain wall. The results also show that the single defect is larger, the probability for domain wall motion induced by defect pining is bigger. Moreover, the material defect can suppress the domain wall trending toward breakdown and make domain wall move faster, but the suppressing ability is not obviously increasing with the increase of the defect concentration. On the other hand, the temperature field can remove the pinning phenomenon, which will result in the threshold current decrease. The decrease of the threshold current is of benefit to the working of the data storage and logic device. Also the temperature field can suppress the domain wall trending toward breakdown, but the suppressing ability is less than that of the defect. In addition, the Joule heat around defects can obviously eliminate the pinning effect of the defects, so the pinning effect for a few defects on current-induced domain wall motion can be ignored. Further analysis indicates that these effects are due to the change of the out-of-plane magnetization of the domain wall induced by the material defects and the temperature field, because the velocity of the domain wall motion induced by the applied current greatly depends on the out-of-plane magnetization of the domain wall.
Nonlocal symmetries and interaction solutions of the (2+1)-dimensional higher order Broer-Kaup system
Authors: Xin Xiang-Peng  , Liu Han-Ze  , Liu Xi-Qiang  ,   School of Mathematical Sciences, Liaocheng University, Liaocheng 252059, China
Published: December 2020

Finding explicit solutions of nonlinear partial differential equation is one of the most important problems in mathematical physics. And it is very difficult to find interaction solutions among different types of nonlinear excitations except for soliton-soliton interactions. It is known that Painlev analysis is an important method to investigate the integrable property of a given nonlinear evolution equation, and the truncated Painlev expansion method is a straight way to provide auto-Bcklund transformation and analytic solution, furthermore, it can also be used to obtain nonlocal symmetries. Symmetry group theory plays an important role in constructing explicit solutions, whether the equations are integrable or not. By applying the nolocal symmetry method, many new exact group invariant solution can be obtained. This method is greatly valid for constructing various interaction solutions between different types of excitations, for example, solitons, cnoidal waves, Painlev waves, Airy waves, Bessel waves, etc. It has been revealed that many more integrable systems are consistent tanh expansion (CTE) solvable and possess quite similar interaction solutions which can be described by the same determining equation with different constant constraints.
In this paper, the (2+1)-dimensional higher-order Broer-Kaup (HBK) system is studied by the nonlocal symmetry method and CTE method. By using the nonlocal symmetry method, the residual symmetries of (2+1)-dimensional higher order Broer-Kaup system can be localized to Lie point symmetries after introducing suitable prolonged systems, and symmetry groups can also be obtained from the Lie point symmetry approach via the localization of the residual symmetries. By developing the truncated Painlev analysis, we use the CTE method to solve the HBK system. It is found that the HBK system is not only integrable under some nonstandard meaning but also CTE solvable. Some interaction solutions among solitons and other types of nonlinear waves which may be explicitly expressed by the Jacobi elliptic functions and the corresponding elliptic integral are constructed. To leave it clear, we give out four types of soliton+cnoidal periodic wave solutions. In order to study their dynamic behaviors, corresponding images are explicitly given.
Calculation of Hamilton energy function of dynamical system by using Helmholtz theorem
Authors: Wang Chun-Ni  , Wang Ya  , Ma Jun  ,   Department of Physics, School of Science, Lanzhou University of Technology, Lanzhou 730050, China
Published: December 2020

The Helmholtz theorem confirms that any vector field can be decomposed into gradient and rotational field. The supply and transmission of energy occur during the propagation of electromagnetic wave accompanied by the variation of electromagnetic field, thus the dynamical oscillators and neurons can absorb and release energy in the presence of complex electromagnetic condition. Indeed, the energy in nonlinear circuit is often time-varying when the capacitor is charged or discharged, and the occurrence of electromagnetic induction is available. Those nonlinear oscillating circuits can be mapped into dynamical systems by using scale transformation. Based on mean field theory, the energy exchange and transmission between electronic field and magnetic field can be estimated by appropriate nonlinear dynamical equations for oscillating circuits. In this paper, we investigate the calculation of Hamilton energy for a class of dimensionless dynamical systems based on Helmholtz's theorem. Furthermore, the scale transformation can be used to develop dynamical equations for the realistic nonlinear oscillating circuit, so the Hamilton energy function could be obtained effectively. These results can be greatly useful for self-adaptively controlling dynamical systems.
Contrastive analysis of neuron model
Authors: Xu Ling-Feng  , Li Chuan-Dong  , Chen Ling  ,   College of Electronic and Information Engineering, Southwest University, Chongqing 400715, China;,   School of Information Science and Technology, University of Science and Technology of China, Hefei 230027, China
Published: December 2020

In recent years,the modeling and application of biological neurons have gained more and more attention.By now, the research on neuron models has become one of the most important branches of neuroscience.Neuron models can be used in various areas,such as biomimetic applications,memory design,logical computing,and signal processing. Furthermore,it is significant to study the dynamic characteristics of neural system by using neuron models.In this paper,the historical development of neuron models is reviewed.The neuron models have experienced three development stages.In the pioneering stage,a group of scientists laid the experimental and theoretical foundation for later research. Then,the whole study started to blossom after the publication of Hodgkin-Huxley model.In the 1970s and 1980s,various models were proposed.One of the research focuses was the simulation of neural repetitive spiking.Since the 1990s, researchers have paid more attention to setting up models that are both physiologically meaningful and computationally effective.The model put forward by Izhikevich E M has been proved to solve the problem successfully.Recently,IBM presented a versatile spiking neuron model based on 1272 ASIC gates.The model,both theoretically understandable and physically implementable,has been used as a basic building block in IBM's neuro-chip TrueNorth.In the paper, seventeen neuron models worth studying are listed.To give a more explicit explanation,these models are classified as two groups,namely conductance-dependent and conductance-independent models.The former group's goal is to model the electrophysiology of neuronal membrane,while the latter group is only to seek for capturing the input-output behavior of a neuron by using simple mathematical abstractions.The complexity and features of each model are illustrated in a chart,while the prominent repetitive spiking curves of each model are also exhibited.Five of the models are further detailed,which are the Hodgkin-Huxley model,the Integrate-and-fire model,the Fitzhugh-Nagumo model,the Izhikevich model,and the most recent model used by IBM in its neuro-chip TrueNorth.Finally,three questions are put forward at the end of the paper,which are the most important problems that today's researchers must consider when setting up new neuron models.In conclusion,the feasibility of physical implementation remains to be a challenge to all researchers. Through the aforementioned work,the authors aim to provide a reference for the study that follows,helping researchers to compare those models in order to choose the properest one.
Propagation and interactions of Airy-Gaussian beams in saturable nonliear medium
Authors: Chen Wei-Jun  , Lu Ke-Qing  , Hui Juan-Li  , Zhang Bao-Ju  ,   Tianjin Key Laboratory of Optoelectronic Detection Technology and Systems, Tianjin Polytechnic University, Tianjin 300387, China;,   Institute of Electronics and Information Engineering, Tianjin Polytechnic University, Tianjin 300387, China
Published: December 2020

The propagation and interactions of Airy-Gaussian beams in a saturable nonlinear medium are investigated numerically based on the split-step Fourier transform method. We show that the propagation of a single Airy-Gaussian beam in the saturable nonlinear medium can generate breathing solitons under steady state conditions. The generation and propagation of these breathing solitons can be affected by the initial amplitude and the field distribution factor of the single Airy-Gaussian beam. In a certain power range, these breathing solitons propagate along the acceleration direction with a controllable tilted angle. In the domain existing in these breathing solitons and for a given value of the field distribution factor of the single Airy-Gaussian beam, when the initial amplitude of the single Airy-Gaussian beam increases gradually, the periodicity of these breathing solitons becomes from small to larger and the tilted angle of these breathing solitons increases monotonically. When the value of the initial amplitude of the single Airy-Gaussian beam is given, the bigger the value of the field distribution factor of the single Airy-Gaussian beam, the smaller the tilted angle of these breathing solitons. Furthermore, the stability of these breathing solitons has been investigated by using the beam propagation method, and it has been found that they are stable. We find that the propagations of two Airy-Gaussian beams in the saturable nonlinear medium can generate not only soliton pairs but also interactions between two Airy-Gaussian beams. When the two Airy-Gaussian beams interact with each other, it is found that the in-phase Airy-Gaussian beams attract each other and exhibit a single breathing soliton with strong intensity in the beam center and some symmetric soliton pairs with weak intensity near both sides of the beam center. The smaller the interval between the two incident Airy-Gaussian optical components, the stronger the attraction between two Airy-Gaussian beams, and the less the numbers of the soliton pairs. The energies of both the main lobes of two Airy-Gaussian beams and the single breathing soliton increase with the value of the field distribution factor of two Airy-Gaussian beams. On the other hand, the out-of-phase Airy-Gaussian beams repel each other and exhibit only symmetric soliton pairs on both sides of the beam center. Our analysis indicates that the repellant of two out-of-phase Airy-Gaussian beams becomes big when the interval between two incident Airy-Gaussian optical components decreases and the number of the soliton pairs becomes less when the field distributions of two beams are close to the Gaussian distribution.
Lattice Boltzamn model of phonon heat conduction in mesoporous composite material
Authors: Feng Dai-Li  , Feng Yan-Hui  , Shi Jun  ,   School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

In this paper, lattice Boltzmann method is used to simulate the phonon heat transport in NaCl@Al2O3 mesoporous composite material. Based on the Debye model, temperature coupling method is first proposed in the thermal simulation of mesoporous composite material, to calculate the effective thermal conductivity of mesoporous composite material with pores of various interface condition coefficient value, pore size, porositiy, shape and arrangement. Studies show that for the same porosity, the estimated thermal conductivity increases with increasing the value of diameter, showing the scale effect; for the same diameter, the estimated thermal conductivity decreases with increasing the value of porosity; for the same porosity and diameter, the estimated thermal conductivity decreases with increasing the value of interface condition coefficient p; porous shape and arrangement will affect thermal conductivity value, and the influences greatly increase with increasing the value of p.
Numerical simulation of molecular conformation evolution during mold filling process in a complex cavity
Authors: Li Qiang  , Shao Shui-Jun  , Li Shi-Shun  ,   School of Mathematics and Information Science, Henan Polytechnic University, Jiaozuo 454000, China;,   School of Mechanical and Power Engineering, Henan Polytechnic University, Jiaozuo 454000, China
Published: December 2020

In the mold filling process, polymer melt will suffer the shear stress and stretch, which has important influences on the mechanical properties and surface quality of the final plastic products. In this paper a gas-liquid two-phase flow model for a viscoelastic fluid is proposed and used to simulate the mold filling process, in which the finitely extensible nonlinear elastic dumbbell with Peterlin closure (FENE-P) model and cross-WLF viscosity model combined with Tait state equation are used to describe the constitutive relationship and viscosity change of the viscoelastic melt, respectively. Meanwhile, the improved coupled level-set and volume-of-fluid method is used to trace the melt front, and the finite volume method on non-staggered grid is used to solve the mass, momentum, and energy conservation equations. Firstly, the R-function, an excellent implicit modeling tool of constructive solid geometry, is employed to establish the shape level-set function to describe the complex mold cavities based on the signed distance functions that represent basic geometries. And the immersed boundary method is applied to dealing with the complex mold cavities by using the shape level-set function. The benchmark problem of the flow past a cylinder is simulated to verify the validity of the FENE-P model, where the orientational ellipses are used to describe the molecular orientation and deformation. Moreover, the visualization of polymer molecular deformation is achieved. Then, the non-isothermal filling process of the viscoelastic fluid is simulated in an annular mold cavity with two circular insets, and the behaviors of the molecular orientation, temperature and stress in the filling process are shown and analyzed in detail. Finally, the problems are also discussed that how the injection velocity, melt and mold temperatures influences on the molecular conformation and solidified layer thickness. Numerical results show that the computational framework proposed in this paper can be successfully used to simulate the non-isothermal mold filling process in the complex mold cavity. Increasing properly the injection velocity can reduce the heat loss and improve the strength of the weld line. The higher the melt or mold temperature, the thinner the solidified layer is. Thus, increasing the injection velocity, as well as raising the melt and the mold temperatures will improve or remove the weld line in melt filling process.
Penta-decomposition of instantaneous field in spanwise-rotating turbulent plane Couette flow
Authors: Gai Jie  , Liu Ze-Yu  , Luo Jia-Qi  , Cai Qing-Dong  , Xia Zhen-Hua  ,   State Key Laboratory for Turbulent and Complex Systems, College of Engineering, Peking University, Beijing 100871, China;,   Center for Applied Physics and Technology, College of Engineering, Peking University, Beijing 100871, China;,   Department of Aeronautics and Astronautics, College of Engineering, Peking University, Beijing 100871, China;,   Department of Engineering Mechanics, School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Spanwise-rotating turbulent plane Couette flow (RPCF) is one of the fundamental prototypes for wall-bounded turbulent flows in rotating reference frames. In this turbulent problem, there are large-scale roll cells which are widely studied. In this paper, a penta-decomposition method is proposed to separate the instantaneous velocity and the total kinetic energy into five parts, i.e., a mean part, a streamwise part and a cross-flow part of the secondary flow, and a streamwise part and a cross-flow part of the residual field. The transport equations for the last four shares, which contribute the total turbulent kinetic energy, are derived. According to these transport equations, the mechanisms of energy transfer among different fractions of turbulent kinetic energy can be revealed clearly. Our objective is to explore the energy balance and transfer among different fractions of the turbulent kinetic energy in RPCF based on a series of direct numerical simulation databases at a Reynolds number Rew=Uwh/=1300 (here, Uw is half of the wall velocity difference, and h is the channel half-width) and rotation number Ro=2zh/Uw (z is the constant angular velocity in the spanwise direction) in a range of 0Ro0.9. The results show that the energy is transferred between the streamwise part/cross-flow part of secondary flows and the residual field through the correlation between the vorticity of secondary flows and the shear stress of residual field. The rotation term acts as a bridge to transfer the energy between the streamwise part and the cross-flow part of either the secondary flows or the residual field. Moreover, pressure-strain redistribution term also plays an important role in the energy transfer between streamwise part and cross-flow part in residual field. For the streamwise part of residual field, in certain rotate rates, the energy obtained from the streamwise part of secondary flows by the correlation between the vorticity of secondary flows and the shear stress of residual field is larger than that obtained from mean flow through mean shear, implying that the streamwise motions of secondary flows have a significant influence on the streamwise motions of residual field.
Total dose dependence of hot carrier injection effect in the n-channel metal oxide semiconductor devices
Authors: He Yu-Juan  , Zhang Xiao-Wen  , Liu Yuan  ,   Science and Technology on Reliability Physics and Application of Electronic Component Laboratory, the Fifth Electronics Research Institute of Ministry of Industry and Information Technology, Guangzhou 510610, China
Published: December 2020

The equipment and devices which are long-time running in space are affected by space radiation effects and hot carrier injection effects at the same time which would reduce their optional times. Normally, the single mechanism test simulation method is used on the ground simulation test but the multi-mechanism effect affects the space equipments and devices, including total irradiation dose effect, hot carrier injection effect, etc. The total dose dependence of hot carrier injection (HCI) effect in the 0.35 m n-channel metal oxide.
semiconductor (NMOS) device is studied in this paper. Three samples are tested under different conditions (sample 1# with total irradiation dose (TID) and HCI test, sample 2# with TID, annealing and HCI test, sample 3# only with HCI test). The results show that threshold voltage of NMOS device with 5000 s HCI test after 100 krad (Si) total dose radiation has been negatively shifted then positively during total dose irradiation test and HCI test, and the threshold is higher than that of the device without radiation test. But the threshold voltage shift of NMOS device with 5000 s HCI test and 200 h annealing test after TID test is higher than that of the devices without radiation test and lower than that of the devices without annealing test. That is, the parameters of NMOS device vary faster with the combined effects (including the total dose irradiation effect and HCI effect) than with single mechanism effect. It is indicated that the hot electrons are trapped by the oxide trap charges induced by irradiation effect and then become a recombination centre. And then the oxide trap charges induced by irradiation effect reduce and become negative electronic. The interface trap charges induced by irradiation effect are reduced and then increased it is because the electrons of hole-electron pairs in the Si-SiO2 interface are recombined by oxide traps in the oxide during the forepart of HCI test but then the electrons are trapped by interface traps in the Si-SiO2 interface because the electrons from source area are injected to interface during the HCI test. So the threshold voltage is positively shifted due to the negative oxide trap charges and interface trap charges. The association effect is attributed to the reduction of oxide traps induced by recombination with hot electrons and the increase of the interface traps induced by irradiation trapped hot electrons.
Optical and electronic properties of N/B doped graphene
Authors: Yu Zhong  , Dang Zhong  , Ke Xi-Zheng  , Cui Zhen  ,   School of Automation and Information Engineering, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

Since its discovery in 2004, the graphene has attracted great attention because of its unique chemical bonding structure, which has excellent chemical, thermal, mechanical, electrical and optical properties. Due to the graphene being a zero band gap material, it has a limited development in the field of nano electronics. Therefore, in order to broaden its application scope, it is very important to carry out a study on opening the band gap of graphene. In this paper, we construct three models, i.e., the intrinsic graphene model, the N-doped graphene model, and the B-doped graphene model. We study the energy band structures and the electronic densities of states for the intrinsic graphene and the N/B doped graphenes with different doping concentrations. Furthermore, we study their optical and electronic properties including the absorption spectra, the reflection spectra, the refractive indexes, the conductivities, and the dielectric functions. The results are as follows. 1) The electronic states in the vicinity of the Fermi level for the intrinsic graphene are mainly generated by the C-2p orbits, while the electronic states in the vicinity of the Fermi level for the N/B doped graphenes are mainly generated through the hybridization between C-2p and N-2p/B-2p orbits. N doped graphene is of n-type doping, while B doped graphene is of p-type doping. 2) Compared with that of the intrinsic graphene, the Fermi level of N doped graphene moves up 5 eV. In the meantime, the band gap is opened, and the Dirac cone disappears. On the contrary, the Fermi level of B doped graphene moves down 3 eV compared with that of the intrinsic graphene. However, like the N doping, the band gap is also opened, and the Dirac cone disappears. Furthermore, the N doping is more effective than the B doping in opening the energy gap of the graphene for the same N/B doping concentration. 3) The N/B doping can cause the optical and electronic properties of the graphene to change, and exert great influences on the absorption spectrum, reflection spectrum, the refractive index, and the dielectric function, however it has little influence on the conductivity. When the energy of the incident wave is larger than a certain value, the optical and electrical properties of the intrinsic graphene remain unchanged. Besides, for the above case, the corresponding energies for the N/B doped graphenes are smaller than that for the intrinsic graphene. In addition, the energy for the B doped graphene is smallest. The conclusions of this paper can provide a theoretical basis for the application of graphene in optoelectronic devices.
Cycle slip detection and repair based on Bayesian compressive sensing
Authors: Li Hui  , Zhao Lin  , Li Liang  ,   College of Automation, Harbin Engineering University, Harbin 150001, China
Published: December 2020

The presence of cycle slips corrupts the carrier phase measurement which is critical for high precision global navigation satellite system static or kinematic positioning. The process of cycle slips is comprised of detecting the slips, estimating its exact integer and making a repair. In this paper, a novel approach to cycle slip detection and repair based on Bayesian compressive sensing is proposed, in order to reduce the noise effects on the performances of cycle slip detection and repair. Unlike traditional cycle slip detection and repair methods, we exploit the sparse property of the cycle slip signal, aiming to obtain the perception matrix and establish the sparse cycle slip detection model. Then in order to estimate and repair the value of cycle slips, the residuals of carrier phase double difference and the interference noise between multiple satellites, when more than one satellite has cycle slips, are taken into consideration, which is used as prior information to obtain the likelihood expression for cycle slip signal. Finally, we use the prior information about signals based on relevance vector machine principle derived from sparse Bayesian learning to predict cycle slip distribution and then estimate the value of cycle slips. The novel approach is tested with the actual collection of satellite data in the experiment. It is shown that the novel approach proposed in this paper can effectively estimate cycle slips and achieve better performance than orthogonal matching pursuit and l1 norm based algorithm when the redundancy of carrier phase is large enough. In the case of single frequency carrier phase observation, when redundancy is not less than 7, the novel approach can completely detect and repair cycle slips; in the case of dual-frequency carrier phase observation, when cycle slips happen in four of the eight satellites, 97.6% probability of accuracy is accomplished by the new approach.