bluuebunny/crossref_metadata_2025 huggingface dataset:
A memristor-based chaotic system and its field programmable gate array implementation
Authors: Xu Ya-Ming  , Wang Li-Dan  , Duan Shu-Kai  ,   School of Electronic and Information Engineering, Southwest University, Chongqing 400715, China
Published: December 2020

A nanoscale memristor can replace the nonlinear part of a chaotic system, which can greatly reduce the physical size of the chaotic system. More importantly, it can enhance the complexity of the chaotic system and the randomness of signals. In this paper, a new memristor-based chaotic system is designed based on a new three-dimensional autonomous chaotic system. In order to study the complex dynamic characteristics of the memristive system, the chaotic system is investigated by the theoretical derivation, numerical simulation, stabilization of equilibrium points, and Lyapunov exponent spectrum. The influences of different parameters on the phase diagram and the stability of equilibrium point of this system are also discussed in detail. It is interesting that when system parameters a and c take different values, the location and stability of the equilibrium point of the system will be changed, then two scrolls of the system will be overturned at a different angle, and it will produce a different degree of aliasing between the two scrolls. Parameter b has a large variable range, when it is changed, and the system will transform into three kinds of classical chaotic systems defined by Vaněček and Celikovsk. These indicate that the memristor-based chaotic system has a lot of valuable dynamic behaviors, so it has applications in the field of secure communication, information processing etc. Field programmable gate array (FPGA) technology has a large capacity and high reliability, which is widely used in modern digital signal processing. And with the development of FPGA technology, applying FPGA technology to realizing the chaotic systems has gradually become a hot topic. Moreover, the improved Newton iteration method is used to design a square root operator of memristor in this paper by using verilog hardware description language (verilog HDL) which only needs three times iteration to reach the required accuracy. The results of FPGA hardware are consistent with the numerical simulation results. It breaks through the previous bottleneck that the chaotic system based on titanium dioxide memristor can only be simulated in computer, which is of great significance for further studing of memristor, and provides a reference for further research on the memristor-based chaotic system and applications in secure communication and information processing.
Dynamics simulation on the segregations of Cu induced Co-based cluster structures and their properties
Authors: Sun Ling-Tao  , Guo Chao-Zhong  , Xiao Xu-Yang  ,   Research Institute for New Materials Technology, Chongqing University of Arts and Sciences, Chongqing 402160, China;,   School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, China
Published: December 2020

The structure and thermodynamic properties of Cu-Co alloy cluster with Cu atoms distributed in inner layer and outer surface of Co cluster are investigated by the molecular dynamics simulation combining with an embedded atom potential method. The results demonstrate that there are huge differences in structure, energy and melting point between the inner layer and outer surface of Co clusters due to various doping layers comprised of the same number of Cu atoms. The different doping positions of Cu atoms in Co cluster make atoms shift towards lower energy state. However, after relative movement, the supplementary deposition of subsequent atoms leads to the relatively non-diffusive phase transformation of cluster structure. The segregations of Cu atoms from inner layer to outer surface of Co cluster are the main reason for the enormous difference in melting point between the inner layer and outer surface of Co clusters with the same percentage of Cu atoms.
Optomechanical interaction with triple membranes
Authors: Xiao Jia  , Xu Da-Hai  , Yi Zhen  , Gu Wen-Ju  ,   School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou 434023, China
Published: December 2020

Cavity optomechanics becomes a promising field in quantum and nano technologies. Motivated by the optomechancial experiment with the membrane located in a high-finesse optical cavity and theoretical treatment on two membranes cavity optomechanics, we here study the optomechanical interaction of the system consisting of triple membranes within an optical cavity. The increase of membranes will increase the normal modes of the cavity and mechanical fields, and thus enrich the forms of optomechanical interaction. Firstly, we use the transfer matrix and resonance transmission methods to obtain the dispersion relation between the eigen-frequencies of the optical modes and the mechanical motions. Owing to the existence of triple mechanical membranes, the system possesses different forms of collective mechanical motion, and here we focus on the center-of-mass (COM) motion and relative motion of the equally placed membranes. The numerical solutions of the dispersion relation show that the optical eigenmodes are comprised of a group of closely spaced avoided-crossing quaternion of wave numbers, which arise from the transmission and reflection of the optical field at the membranes and the tunneling couplings between subcavity modes. Moreover, the change of each eigen wave number along each form of the mechanical motion is different, which implies the different forms of optomechanical coupling between eigenmodes and mechanical motions. Then, to achieve the explicit expressions of the optomechanical coupling, it is sufficient to use the perturbation method under the equilibrium condition of the system, where the amplitude of mechanical motion is much smaller than the optical wavelength. With using the implicit function differentiation theorem, the optomechanical coupling strengths between the four optical modes and the COM and relative mechanical motions are obtained respectively. We find that the strong quadratic optomechanical coupling between the optical modes and COM motion can be achieved, and the linear and quadratic couplings between the optical modes and relative motion can both be realized. By tuning the laser to pump different optical modes, we can choose either the linear or the quadratic coupling to the relative motion. Our method is universal to multi-membrane system, and the results may provide some references to theoretical and experimental investigations on the multi-membrane cavity optomechanics.
Experimental determination of key parameters in the spin-flip model of 1550 nm vertical-cavity surface-emitting laser
Authors: Yang Ji-Yun  , Wu Zheng-Mao  , Liang Qing  , Chen Jian-Jun  , Zhong Zhu-Qiang  , Xia Guang-Qiong  ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

Spin-flip model (SFM) is a mostly used approach to analyzing the nonlinear dynamics of vertical-cavity surface-emitting laser (VCSEL), and therefore the value selections of some key parameters in this model are crucial. In this work, based on experimentally measured dynamical characteristics of a 1550 nm vertical-cavity surface-emitting laser (1550 nm-VCSEL) under free running and parallel optical injection, some key parameters (field decay rate k, total carrier decay rate N, linewidth enhancement factor , active medium birefringence rate p, spin relaxation rate s, and active medium linear dispersion rate a) are estimated. Through experimentally measuring the noise spectrum of the laser, the relaxation oscillation frequency and the damping rate of the relaxation oscillations are calculated, and the photon lifetime can be preliminary estimated. After further amending the photon lifetime by considering the effect of the gain saturation on the damping rate of the relaxation oscillations, the value of k is determined. Based on the function relation between the laser relaxation oscillation frequency and the electrical pumping, the value of N is obtained. By experimentally acquiring the dynamical distribution mapping of the laser under parallel optical injection, the minimum Hopf bifurcation point of the Hopf bifurcation curve can be found, and then the value of is roughly estimated. According to the frequency difference between the two polarization components of the laser in the measured optical spectrum, the value of p can be calculated. The value of s is obtained by using the relationship between s and p. On the basis of the above determined parameter values, the value of a can be specified by numerically simulating the optical spectrum of the laser and comparing with experimentally obtained results. Moreover, by comparing the experimentally measured dynamical mapping of optical injection VCSEL with corresponding dynamical mapping simulated on the basis of the above mentioned parameters, the value of is rectified. Finally, further simulated results agree with relevant experimental observations.
Fabrication of self-standing binary Gabor zone plate and its single order diffraction
Authors: Li Zhao-Guo  , Meng Ling-Biao  , Zhou Min-Jie  , Diao Kai-Di  , Yi Yong  , Zhu Xiao-Li  , Wu Wei-Dong  , Zhang Ji-Cheng  ,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China;,   Key Laboratory of Microelectronic Devices and Integration Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China
Published: December 2020

The Gabor zone plate is an ideal zone plate with single focus spot, which has the potential applications in spectroscopy, X-ray imaging, etc. However, the Gabor zone plate is very difficult to prepare because of its sinusoidal transmission characteristic, thereby restricting its applications. Traditionally, the zone plate is prepared on the transparent substrate such as quartz glass, polyimide, etc. This restricts the applications of Gabor zone plates in the extreme ultraviolet and soft X-ray frequency band due to the strong absorption of quartz and polyimide in such bands.In this work, we report a method of preparing the self-standing binary Gabor zone plate by using the focused ion beam direct writing. By combining the techniques of focused ion beam and chemical wet etching, the binary Gabor zone plate with self-standing and curved structure is fabricated. The main characteristic parameters of the Gabor zone plate are as follows: the diameter of 1400 m, the radius of the first zone 90 m, the outset zone number of 60, and a gold absorber thickness of 500 nm. The focusing properties of the self-standing binary Gabor zone plate are measured at different transfer distances with a 355 nm laser. The experimental results show that the high-order focus is removed with only the first-order focus spot reserved, and the focal distance is 2.28 cm, which is in agreement with the theoretical value of 2.41 cm. The self-standing Gabor zone plate is free from the influence of the substrate. Therefore, this kind of binary Gabor zone plate has potential applications in ultraviolet and soft X-ray regions.
Extraction of density of localized states in indium zinc oxide thin film transistor
Authors: Wang Jing  , Liu Yuan  , Liu Yu-Rong  , Wu Wei-Jing  , Luo Xin-Yue  , Liu Kai  , Li Bin  , En Yun-Fei  ,   School of Electronic and Information Engineering, South China University of Technology, Guangzhou 510640, China;,   Science and Technology on Reliability Physics and Application of Electronic Component Laboratory, CEPREI, Guangzhou 510610, China;,   State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China
Published: December 2020

Density of localized states (DOS) over the band-gap determines the electrical and instability characteristics in the indium zinc oxide thin film transistor (IZO TFT). In order to propose an accurate extraction method for DOS in the bulk region, low frequency noise and multi-frequency capacitance voltage characteristics are measured and analyzed in this paper. Firstly, the relationship between surface potential and gate voltage is extracted based on subthreshold I-V characteristics. The extraction results show that the surface potential increases with the increase of gate voltage in the sub-threshold region. When the Fermi level is close to the bottom of conduction band, the increase of surface potential should be saturated. Secondly, drain current noise power spectral densities in the IZO TFTs under different operation modes are measured. Based on carrier number fluctuation mechanism, the flat-band voltage noise power spectral density is extracted and localized state near IZO/SiO2 interface is then calculated. By considering the emission and trapping processes of carriers between localized states, the distribution of bulk trap density in the band-gap is extracted based on low frequency noise measurement results. The experimental results show an exponential tail state distribution in the band-gap while NTA is about 3.421020 cm-3eV-1 and TTA is about 135 K. Subsequently, contact resistances are then extracted by combining capacitance-voltage characteristics with I-V characteristics in the linear region. The extrinsic parasitic resistances at gate, source, drain are separated. By considering charges trapped in the localized states and free carriers, the distributions of deep states and tail states in the active layer of IZO TFT are extracted through multi-frequency capacitance-voltage characteristics. The experimental results also show an exponential deep state and tail state distribution in the band-gap while NDA is about 5.41015 cm-3eV-1, TDA is about 711 K, NTA is about 1.991020 cm-3eV-1, and TTA is about 183 K. The above two proposed extraction methods are compared and analyzed. The deviation between two extraction results may relate to the existence of neutral trap in the gate dielectric which is also an important source of low frequency noise in the IZO TFT.
Dynamic structure factors and sum rules in two-component quantum gases with spin-orbit coupling
Authors: He Li  , Yu Zeng-Qiang  ,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China;,   Institute of Theoretical Physics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Sum rules for the dynamic structure factors are powerful tools to explore the collective behaviors in many-body systems at zero temperature as well as at finite temperatures. The recent remarkable realization of synthetic spin-orbit (SO) coupling in quantum gases is opening up new perspective to study the intriguing SO effects with ultracold atoms. So far, a specific type of SO coupling, which is generated by a pair of Raman laser beams, has been experimentally achieved in Bose-Einstein condensates of 87Rb and degenerate Fermi gases of 40K and 6Li. In the presence of SO coupling, the dynamic structure factors for the density fluctuation and spin fluctuation satisfy different sum rules. In particular, in the two-component quantum gases with inter-species Raman coupling, the f-sum rule for the spin fluctuation has an additional term proportional to the transverse spin polarization. Due to the coupling between the momentum and spin, the first moment of the dynamic structure factor does not necessarily possess the inversion symmetry, which is in strong contrast to the conventional system without SO coupling. Such an asymmetric behavior could be observed in both Fermi gases and Bose gases with Raman coupling. As a demonstration, we focus on the uniform case at zero temperature in this work. For the non-interacting Fermi gases, the asymmetric first moment appears only when the Raman detuning is finite. The asymmetric amplitude is quite limited, and it vanishes at both zero detuning and infinite detuning. For the weakly interacting Bose gases, the first moment is asymmetric in momentum space even at zero detuning, when the ground state spontaneously breaks the Z2 symmetry in the plane-wave condensation phase. Using the Bogoliubov method, the dynamic structure factor and its first moment are explicitly calculated for various interaction parameters. We find that the asymmetric behavior in the spin channel could be much more significant than in the density channel, and the asymmetric amplitude is enhanced as the interaction strength increases. Experimentally, the dynamic structure factors can be directly measured through the two photon Bragg scattering. Numeric simulations show that to observe the deviation of inversion symmetry in the first moment, the resolution of the Bragg spectroscopy should reach a required value. For the typical parameters of the rubidium atomic gas, the required resolution is about 10-2Er with Er being the recoil energy. Our predictions can be tested in the future experiment.
Design of a broadband and high-gain shared-aperture fabry-perot resonator magneto-electric microstrip antenna
Authors: Zhang Chen  , Cao Xiang-Yu  , Gao Jun  , Li Si-Jia  , Zheng Yue-Jun  ,   Information and Navigation College, Air Force Engineering University, Xi’an 710077, China
Published: December 2020

The demands for highly directive antennas are becoming more stringent, especially in microwave regions. Traditional ways to enhance the antenna gain such as reflectors, dielectric lenses, waveguide horns and microstrip antenna arrays suffer design complexity, high cost and power loss in the feeding network, so it is urgent to find a simple way to solve the problem. Fabry-Perot (F-P) antenna has a high directivity and low sidewall, owing to the resonance of the cavity in a cophasal and tapered field distribution along the lateral direction. However, the disadvantage of F-P antenna is obvious for the inherently narrow gain bandwidth which inhibits their many applications. In this paper, a broadband and high-gain shared-aperture F-P resonator magneto-electric (ME) microstrip antenna working at X band is designed and fabricated. In order to design a wideband metamaterial superstrate unit, the structure with two different frequency selective surface (FSS) layers is presented: the metal pattern at the top of the unit is a square patch and has a high reflection coefficient in the high frequency band, and at the bottom the metal pattern is a cross patch, it has a high reflection coefficient in the low frequency band, therefore, the whole unit should resonate in a broadband frequency range. Theoretical analysis and simulation result indicate that the unit has a linearly increasing phase response and a high reflection coefficient across a broadband range and it has the potential to construct a wideband F-P resonator antenna. In the proposed antenna, a novel wideband ME microstrip antenna is used as the feeding source. For the antenna covers the whole X band, the bandwidth of the F-P resonator superstrate should be further expanded. Simulated calculation results indicate that different sizes of two-layer FSSs have different reflection phases but the same coefficient, therefore a shared-aperture structure with three different sizes of FSSs is obtained. The arrangement utilizes the phase compensation property along different FSSs, and broadens the gain enhancement bandwidth effectively. When the superstrate is set to be approximately 15.5 mm above the ground plane of the ME antenna, the antenna possesses an impedance bandwidth of 44.7% for the reflection coefficient (S11) below -10 dB from 7.8 GHz to 12.3 GHz, covering the whole X band. From 7.9 GHz to 12.1 GHz, the antenna has an obvious gain enhancement, with a peak of 7 dB. Numerical and experimental results indicate that compared with the traditional F-P resonator structure, the shared-aperture metamaterial superstrate can effectively broaden the antenna gain enhancement bandwidth, and it has great application values for designing new broadband metamaterial superstrate high-gain antennas.
Algorithm for reconstructing vibrational relaxation times in excitable gases by two-frequency acoustic measurements
Authors: Zhang Ke-Sheng  , Zhu Ming  , Tang Wen-Yong  , Ou Wei-Hua  , Jiang Xue-Qin  ,   School of Information Engineering, Guizhou Institute of Technology, Guiyang 550003, China;,   School of Electronic Information and Communications, Huazhong University of Science and Technology, Wuhan 430074, China;,   School of Big Data and Computer Science, Guizhou Normal University, Guiyang 550001, China
Published: December 2020

Vibrational relaxation time is a parameter describing the macroscopic behavior of vibrational energy transition rate between molecular internal degrees of freedom (DOF) and external DOF in excitable gas, which determines the relaxation frequency of the maximum point in acoustic absorption spectrum. To measure the vibrational relaxation time, the traditional methods are used to obtain the acoustic absorption spectra by changing the ambient pressure at several operating frequencies. However, these traditional methods are not suitable for real-time measurement due to the complexity of equipment implementation and the non-ideality of test gas under high pressure. In order to solve those problems, we have developed an algorithm [2013 Meas. Sci. Technol. 24 055002] to capture the primary vibrational relaxation processes only based on the measurements of sound absorption and sound speed at two operating frequencies and a single pressure. But the algorithm only can reconstruct the absorption maximum and it cannot capture the relaxation time with high precision. To measure the frequency dependence of the complex effective specific heat of the relaxing gas, an algorithm synthesizing relaxation processes is given by Petculescu and Lueptow [2005 Phys. Rev. Lett. 94 238301]. In its derivation process, relaxational angular frequency was set to be the inverse ratio to relaxation time. However, the relaxational angular frequency was measured in the adiabatic process of transmission thermodynamic, while the relaxation time was obtained in the thermodynamic isothermal process, the derivation confused the two thermodynamic processes, making the algorithm unable to capture the relaxation frequency with high precision. In order to estimate the relaxation time with higher accuracy, in this paper we first obtain the theoretical relationship among the relaxation times under the three types of thermodynamics conditions, i. e., isothermal, adiabatic constant pressure and adiabatic constant volume. Then we correct the relaxation time derivation and propose our corrected algorithm to reconstruct the relaxation frequencies and relaxation times under the conditions of isothermal, adiabatic constant pressure and adiabatic constant volume. In experiments and simulations, the relaxation times and relaxation frequencies reconstructed by our corrected algorithm for various gas compositions including carbon dioxide, methane, chlorine, nitrogen, and oxygen around room temperature are consistent with the experimental data.
Effect of weak convection on the rod eutectic growth in direction solidification
Authors: Xu Xiao-Hua  , Chen Ming-Wen  , Wang Zi-Dong  ,   School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China;,   School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

Eutectic solidification is very important for exploring new materials in which the periodic multiphase structures may have a remarkable or enhanced functionality. An asymptotic solution of the solute diffusion equation with flow terms for the rod eutectic in the weak convective melt in directional solidification is obtained by using the asymptotic method, and the effect of weak convection on the rod eutectic growth is studied. The so-called weak convection is defined in this paper as the condition in which the intensity of convection flow ahead of the solid liquid interface is relatively small. The relationships between the intensity of convection flow, the growth velocity, the rod spacing and the average interface undercooling can be derived. The result shows that the weak convection has a significant effect on the rod eutectic growth in directional solidification. The average interface undercooling is related to not only the rod spacing and the growth velocity, but also the intensity of convection flow. When specifically focusing on the effect of the intensity of convection flow on the average undercooling in directional solidification, the growth velocity is kept the same. For a certain growth velocity, the average interface undercooling of the rod eutectic decreases as the intensity of convection flow increases, especially at low growth velocity. The rod spacing, which is formed by solidified melt of eutectic or near-eutectic composition, plays a very important role in determining the properties of final products. In this study, by minimizing the average interface undercooling it is found that the rod spacing is a function of growth velocity and the intensity of convection flow. It is shown that for the small growth velocity, the rod spacing increases as the intensity of convection flow increases; for the large growth velocity, the rod spacing increases very slowly as the intensity of convection flow increases. In other words, the smaller the growth velocity, the greater the effect of the weak convection flow on the rod spacing. Our analytical result is compared with the results from other models, and it is also used to calculate the practical case such as the rod spacing of the typical eutectic alloy, Al-Cu eutectic, under the condition of weak forced convection induced by the accelerated crucible rotation technique. It is shown that the rod spacing increases as the rotation rate or the radial position increases, which is consistent with the experimental results obtained by Junze et al.
Particle-in-cell simulation of a new X-band low-impedance high power microwave source
Authors: Yan Xiao-Lu  , Zhang Xiao-Ping  , Li Yang-Mei  ,   College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China;,   Institute of Tracking and Telecommunications Technology, Beijing 100094, China
Published: December 2020

High power microwave (HPM) source is attractive in generating gigawatt (GW) class microwaves based on the beam-wave interaction. Generally, HPM source with a high beam-wave conversion efficiency has a higher impedance. To improve the single-tube output power of HPM source, reducing the impedance of the device and increasing its power capacity are necessary. In this paper, a new low-impedance HPM source is proposed and proved to be capable of generating two phase-locked high power microwaves, which makes it promising to realize a higher combined power in a single HPM device.The new low-impedance HPM device consists of a two-cavity TKA (denoting the outer sub-source in the following) and a multiwave Cerenkov generator (referring to the inner sub-source below) inserted in the TKA inner conductor. These two sub-sources are connected in parallel and share a common magnetic field. A dual-concentric annular cathode is used in this microwave source, which is capable of emitting two concentric annular electron beams and driving the internal and external sub-source simultaneously. The advantages of this device are reducing the impedance and improving the injection electric power. When a voltage pulse is applied to the diode, part of microwaves generated in the inner subsource will leak into the outer sub-source (i.e., TKA) through the A-K gap. By amplifying the leakage microwaves, the TKA will be easily locked by the inner sub-source. Considering the fact that the microwave source consists of two sub-sources, the power capacity will also be greatly improved.As a result, particle-in-cell simulation indicates that when the diode voltage is 687 kV and the axial magnetic field is 0.8 T, two microwave beams that have a nearly identical frequency of 9.72 GHz and output powers of 1.20 GW and 2.58 GW respectively, are generated. The corresponding power conversion efficiencies are 28% and 30%, respectively. The frequency difference between these two microwaves fluctuates within 3 MHz and their phase difference is not in excess of 3. When the diode voltage changes from 665 kV to 709 kV, frequency difference between the two sub-sources fluctuates within 3 MHz and their phase difference fluctuation is within 5 in one voltage burst; the phase difference changes 10 in this voltage range. The impedance of this HPM source is as low as 36 .To sum up, the new HPM source proposed in this paper has a lower impedance and higher power capacity. The phase difference between the inner sub-source and the outer sub-source is very stable and favorable for the coherent power combination, which indicates that the new HPM source promises to realize a higher output power in a single-tube device.
An electromagnetic street scattering channel model for outdoor vehicular-to-vehicular communication systems
Authors: Zhou Jie  , Yao Ying-Li  , Shao Gen-Fu  , Shen Xiao-Yan  , Liu Peng  ,   Department of Communications, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Deptartment of Electronic and Electrical Engineering, Niigata University, Niigata 950-2181, Japan;,   Deptartment of Communication Engineering, Hangzhou Dianzi University, Hangzhou 310000, China
Published: December 2020

The vehicular-to-vehicular (V2V) communications have recently received great attention due to some traffic telematic applications that make transportation safer, more efficient, and more environmentally friendly. Reliable traffic telematic applications and services require V2V wireless communication systems to be able to provide robust connectivity. To develop such wireless communication systems and standards, accurate channel models for the V2V communication systems are required. In this paper, a geometric street scattering channel model for a V2V communication system is presented under line-of-sight (LOS) and non-LOS (NLOS) propagation conditions. Starting from the geometric model, a stochastic reference channel model is developed, where the scatterers are uniformly distributed in rectangles in the form of stripes parallel to both sides of the street. A typical propagation scenario for the proposed model is presented, where the buildings and the trees can be considered as scatterers. Analytical expressions for the probability density functions (PDFs) of the angle-of-departure (AOD) and the angle-of-arrival (AOA) are derived. By obtaining the PDF of the total Doppler frequency, the Doppler power spectral density (PSD) and the autocorrelation function (ACF) of the proposed model are also investigated and computed, assuming that the mobile transmitter (MT) and the mobile receiver (MR) are moving, while the surrounding scatterers are fixed. In this respect the underlying radio channel model differs from the traditional cellular channels. We can draw the conclusion that the PDFs of AOD and AOA first increase and then decrease within a certain angle range; the Doppler power spectral density of the signal in the outdoor street environment presents the peak value in fmax. In addition, while the Rice distribution factor is larger, the value of the autocorrelation function increases relatively, the stability of the fluctuation increases correspondingly as well. To validate the reference channel model, its Doppler parameters are compared with those of a real-world measured channel for urban and rural areas. The numerical results show a good fitting of the theoretical results to the computer simulations. In the proposed geometry-based channel model, we not only study the influence of the street scatterers on the performance of V2V communication system, but also broaden the research of the channel modeling of outdoor wireless communication in turn. To evaluate the propagation characteristics of the outdoor V2V communication systems and the simulation of wireless communication system, this paper provides a powerful research tool.
Effect of inelastic scattering process of gluons on dilepton productions of quark-gluon plasma
Authors: Guan Na-Na  ,   College of Physics and Electronic Engineering, Guangxi Teachers Education University, Nanning 530023, China
Published: December 2020

Dileptons have large mean free paths due to their small cross sections for electromagnetic interaction in plasma. Therefore they are considered to be an important probe for the formation and evolution of the quark matter. In this work, we calculate the dilepton production of quark-gluon plasma (QGP) produced in Au197+ Au197 central collisions at relativistic heavy ion collider (RHIC) energy based on the evolution model of a chemically equilibrating viscous QGP. The evolution of the QGP system is described by a set of coupled relaxation equations containing the master equations of partons, the equation of baryon number conservation and equation of energy-momentum conservation. Solving the set of evolution equations, one can obtain the evolution of temperature T, quark chemical potential q, fugacities q for quarks and g for gluons. To discuss the shear viscosity of QGP, the contributions of the elastic scattering of quarks qqqqand gluons gggg, as well as the inelastic scattering process of gluons ggggg are included. Based on the evolution model including the viscosity, we perform a complete calculation of the dilepton production, including the processes of quark-antiquark annihilation qqll, next-order annihilation qqgll, Compton-like scattering qg qll, qg qll, multiple scattering of quarks, as well as gluon fusion gg cc, annihilation qqcc. It is found that the spectra from the quark-antiquark annihilations qqll and qqgll are dominated. The contributions from multiple scattering cannot be neglected. We also find that the dilepton yields remarkably decrease with considering an additional gluon inelastic process in the calculation compared with the results with considering only elastic scatterings of quarks and gluons. This indicates that the evolution of QGP system is accelerated and the evolution time is shortened by the inelastic scatterings of gluons.
Numerical simulation analysis of high efficient SFG and color separation in far field in high power laser facility based on noncollinear phase matching by KDP crystal
Authors: Liu Chong  , Ji Lai-Lin  , Zhu Bao-Qiang  , Lin Zun-Qi  ,   Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China;,   Shanghai Institute of Laser and Plasma, Chinese Academy of Engineer and Physics, Shanghai 201800, China
Published: December 2020

Asymmetric property of wedge lens in 3 optical path which is used as frequency separation, and focusing element is considered to be an unfavourable factor for target alignment in inertial confinement fusion (ICF). Furthermore, the thickness of wedge lens in 3 optical path will lead to laser induced damage inevitably. For the purpose of scheme improvement of final optical assembly, types I and II noncollinear sum frequency generation in KDP crystal at room temperature are discussed based on nonlinear coupled wave theory. As illustrated by simulated result, in addition to type II collinear SFG used in ICF recently, 351 nm (3) waves can be generated by type I or II noncollinear SFG process. This method can realize color separations of , 2, 3 in far field without asymmetric element such as wedge lens and posses adequate tolerance of matching angle corresponding to the high efficiency conversion. As calculated, for type I SFG, when the noncollinear angle is in the interval from 0 to 19.99, phase matching condition can be satisfied in KDP crystal. The noncritical phase matching angle 3 is 90 and the corresponding noncollinear angle is about 19.99. The tolerance of mismatching angle is about 20 mrad. For type II SFG, the noncollinear angle interval that can satisfy phase matching process is about 0-13.55. Like type I SFG, there is also an noncritical solution in type II process whose matching angle is about (3) = 86.53. Because of the smaller effective nonlinear coefficient in this case, high efficiency conversion needs about 5 cm thick SFG crystal under 1 GW/cm2. Correspondingly, tolerance of mismatching angle is about 20 mrad. Because of the harsh tolerance of noncollinear angle between and 2 and for the purpose of compactness of final optical assembly, another method of noncollinear SFG is proposed: a piece of silica wedge with 12 wedged angle is mounted behind the SHG crystal in order to produce a 3.5 mrad intersection angle between and 2, and after type II noncollinear SFG process, , 2, 3 will be frequency separated in far field automatically by using thin lens. The tolerance of incident angle corresponding to high efficient conversion is about 1.0 mrad. This scheme can improve the the final optical assembly used recently.
Application of inductively coupled microplasma jet on rapid manufacturing
Authors: Zhang Yi-Chuan  , Yang Kuan  , Li Huan  , Zhu Xiao-Dong  ,   Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Metal rapid manufacture has received great attention in recent decades. Energy source with high power density is requisite for the metal deposition. Atmospheric pressure inductively coupled microplasma jet is commonly characterized by high temperatures, which is one of excellent candidates for metal rapid manufacture on a micro scale.In this paper, we investigate the microplasma jet driven by a 150 MHz very-high-frequency power supply at atmospheric pressure. A microplasma of 3 cm in length and about 3 mm in diameter can be produced at 90 W power applied, with gas temperatures above one thousand degree centigrade. The jet length rises first, and then decreases by increasing gas flow rate, showing a transition from laminar flow to turbulence. The jet length also increases by enhancing applied power, but then keeps a maximum value with further increasing power, which is attributed to the attainment of equilibrium between the energy absorption and losses in the transport process in plasma.Copper powders are carried by the argon flowing into plasma, and melted fast by the microjet. An alumina ceramic plate is used as a substrate, which is set on the substrate holder with a precisely controlled X-Y-Z manipulator. A copper spherical cap with 2 mm in diameter and a column with 1 cm in height are fabricated in a few seconds, respectively, on the alumina ceramic substrate. The Cu spherical cap is characterized by scanning electron microscopy. Particles obtained on the sample surface are far smaller than the source powders, indicating a melting process of copper powders in plasma, as well as high gas temperature exceeding the melting point of copper. The weak peak of Cu2+1O is present besides strong copper diffraction lines in X-ray diffraction pattern, suggesting that the weak oxidation happens during rapid fabrication.
Simulation of translocating pore of DNA in non-uniform force by coarse-grained model
Authors: Ma Shan  , Ma Jun  , Yang Guang-Can  ,   School of Physics and Electronic Information, Wenzhou University, Wenzhou 325035, China
Published: December 2020

Translocating pore of biomacromolecules is a common phenomenon in many biological processes, such as DNA transcription, cell infection of virus and transmembrane of proteins. The understanding of translocating pore of DNA is important for studying the DNA sequencing, gene therapy and virus infection. According to the coarse-grained model, we use molecular dynamics simulations to investigate the process of translocating pore of DNA under the actions of different non-uniform forces. In the present study, we consider five kinds of non-uniform forces, i.e., linearly increasing, linearly decreasing, V-type, inverted V-shaped, and periodic type. In the simulations of coarse-grained DNA, we find that the force on the pore opening palys a key role in the process of translocation of polymer. When the force is small, the probability of successful translocation of DNA is low accordingly. In the case of inverted V-shaped potential, the difference between the maximum and minimum force should be in a limited range to a probable translocation of DNA. Out of the range it might lead to clogged pores in the polymer chain. In the action of a non-uniform force, the translocating pore of DNA shows a series of complicated behaviors. For example, the end of a polymer can move faster than its head, resulting in the hole clogging and accumulation of polymers. A reversion can occasionally occur after a successful translocation of polymer. Therefore, non-uniform force leads to various scenarios of translocating pore of polymers.In summary, due to the complicated interactions between external forces and internal potential of polymer chains, particles can be clogged in the pore since the following particles overtake the leading ones in the chain. It is also found that the success of pore translation of DNA is significantly dependent on the acting force on the pore. Among all the cases of translating the pore successfully, the translation time in the case of non-uniform force is about half that in the case of uniform force. These results might provide an insight into the understanding of the complicated pore translating mechanism of DNA.
A global homogenizing coupled pattern of interdependent networks
Authors: Gao Yan-Li  , Chen Shi-Ming  ,   School of Electrical and Electronic Engineering, East China Jiaotong University, Nanchang 330013, China
Published: December 2020

Many infrastructure networks interact with and depend on each other to provide proper functionality. The interdependence between networks has catastrophic effects on their robustness. Events taking place in one system can propagate to any other coupled system. Recently, great efforts have been dedicated to the research on how the coupled pattern between two networks affects the robustness of interdependent networks. However, how to dynamically construct the links between two interdependent networks to obtain stronger robustness is rarely studied. To fill this gap, a global homogenizing coupled pattern between two scale-free networks is proposed in this paper. Making the final degrees of nodes distributed evenly is the principle for building the dependency links, which has the following two merits. First, the system robustness against random failure is enhanced by compressing the broadness of degree distribution. Second, the system invulnerability against targeted attack is improved by avoiding dependence on high-degree nodes. In order to better investigate its efficiency on improving the robustness of coupled networks against cascading failures, we adopt other four kinds of coupled patterns to make a comparative analysis, i.e., the assortative link (AL), the disassortative link (DL), the random link (RL) and global random link (GRL). We construct the BA-BA interdependent networks with the above 5 coupled patterns respectively. After applying targeted attacks and random failures to the networks, we use the ratio of giant component size after cascades to initial network size to measure the robustness of the coupled networks. It is numerically found that the interdependent network based on global homogenizing coupled pattern shows the strongest robustness under targeted attacks or random failures. The global homogenizing coupled pattern is more efficient to avoid the cascading propagation under targeted attack than random failure. Finally, the reasonable explanations for simulation results is given by a simply graph. This work is very helpful for designing the interdependent networks against cascading failures.
High-precision measurement of terahertz frequency using an unstabilized femtosecond laser
Authors: Sun Qing  , Yang Yi  , Deng Yu-Qiang  , Meng Fei  , Zhao Kun  ,   Division of Optics, National Institute of Metrology, Beijing 100029, China;,   Beijing Key Laboratory of Optical Detection Technology for Oil and Gas, China University of Petroleum, Beijing 102249, China;,   Division of Time and Frequency, National Institute of Metrology, Beijing 100029, China
Published: December 2020

Frequency is one of the most important physical quantities of electromagnetic (EM) waves. With the development of terahertz (THz) technology, high-precision measurement of THz frequency is required in THz laser development, wireless communication and ultra fine spectrum measurement. The traditional Fabry-Perot (F-P) interferometry and heterodyne detection method are both difficult to achieve high-precision measurement of THz frequency. Within the range of light wave band, the femtosecond optical frequency comb has long been applied to the light wave frequency measurement due to its extremely high accuracy and stability. By using frequency comb method, measurement with accuracy in the order of 10-11 can also be achieved in THz band. To generate THz frequency combs with stable and controllable frequency, it is required to conduct precise stabilization control on repetition frequency of the femtosecond laser. As a result, some special designs are needed for the femtosecond laser in addition to repetition frequency control devices, including the reference signal source, servo-control module, HV drive module, temperature control module, etc., resulting in a rather complicated system. In this paper, a new method for THz frequency measurement by using an unstabilized femtosecond laser is introduced. The laser is free running and the repetition frequency continuously reduces approximately 8 kHz in 6 h, which is the result of a lengthened laser cavity due to the thermal expansion caused by temperature rise after the laser has been switched on. The repetition frequency and beat signal frequency are simultaneously and continuously measured by two frequency counters. The THz frequency can be calculated from the data with accuracy in the order of 10-10. Although the measurement precision is reduced by one order compared with that obtained by using stabilized femtosecond laser, the system is greatly simplified. The femtosecond laser and complicated repetition frequency control devices no longer need to be specifically designed. This new method will greatly expand the applicable scope of the frequency comb method in measuring THz frequency.