bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear excitation of localized plasmon in one-dimensional atomic chain
Authors: Yin Hai-Feng  , Mao Li  ,   College of Physics and Electronic Engineering, Kaili University, Kaili 556011, China;,   College of Physical Science and Technology, Wuhan University, Wuhan 430072, China
Published: December 2020

At different frequencies of light pulse field, the coupling between plasmon resonance and electron transport of one-dimensional sodium atomic chain is investigated by using time-dependent density functional theory. Light pulse field, whose frequency is in about 0.8 eV range around the plasmon resonance point, can stimulate plasmon resonance of the system. Plasmon resonance intensity magnitude which is stimulated by these different frequency light pulse fields are in the same order of magnitude. The more closely the external field frequency approaches to plasmon resonance frequency, the larger plasmon resonance amplitude stimulated by the external field fields will be. With regard to the nonlinear excitation phenomenon of linear atomic chain plasmon, using a classical harmonic oscillator model, we gives a qualitative explanation.
Mechanism of bursting oscillations with multiple equilibrium states and the analysis of the structures of the attractors
Authors: Xing Ya-Qing  , Chen Xiao-Ke  , Zhang Zheng-Di  , Bi Qin-Sheng  ,   School of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

The main purpose of this article is to explore the bursting behaviors as well as the mechanism when multiple equilibrium states evolve into the bursting attractors. Taking the controlled Lorenz model with periodic excitation for example, the coupling effect of different scales in frequency domain corresponding to the case that an order gap exists between the exciting frequency and the natural frequency of the system with multiple equilibrium states is investigated. Unlike the autonomous slow-fast coupling system, neither obvious slow nor fast subsystems can be observed in a periodically excited system. Since the exciting frequency is far less than the natural frequency of the system, the whole exciting term can be considered as a slow-varying parameter, leading to the generalized autonomous system. With the variation of the slowly-varying parameter, the bifurcation forms as well as the behaviors for different equilibrium states in the generalized autonomous system are explored. It is pointed out that for certain conditions, Hopf bifurcation and fold bifurcations related to different equilibrium points can be observed. According to the conditions related to different bifurcations, the bursting oscillations in two typical cases are presented. In order to explore the mechanism of bursting oscillation, transformed phase portraits are introduced in which the whole exciting term is treated as a generalized state variable so that the relationship between the original state variables and the slow-varying parameter can be clearly described. By employing the transformed phase portraits, the bifurcation mechanisms of different bursting attractors are presented. For the conditions where only fold bifurcation exists between two equilibrium states in the generalized autonomous system, two un-symmetric bursting attractors can be observed. With the variation of parameters, when the repetitive spiking oscillations pass across the attracting basin of another equilibrium states, the two bursting attractors interact with each other to form an enlarged symmetric bursting attractor. For the conditions where both the Hopf and fold bifurcations evolve into the bursting attractors, multiple quiescent states as well as repetitive spiking states exist in the bursting oscillations, which may lead to complicated behaviors. It is found that the coexistence of multiple equilibrium states as well as the related bifurcation forms not only leads to multiple forms of quiescent states and the spiking states, but also results in different switching forms between different quiescent states and the spiking states.
(1+1)-dimensional spatial optical soliton in nematic liquid crystals with negative dielectric anisotropy: perturbation method
Authors: Li Ying-Bing  , Liang Guo  , Hong Wei-Yi  , Ren Zhan-Mei  , Guo Qi  ,   Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, South China Normal University, Guangzhou 510006, China;,   School of Physics and Electrical Information, Shangqiu Normal University, Shangqiu 476000, China
Published: December 2020

In this paper, we systematically study the (1+1)-dimensional spatial optical solitons in nematic liquid crystals with negative dielectric anisotropy. Firstly, with the perturbation method, we obtain a (1+1)-dimensional soliton solution in the second approximation.Numerical simulations confirm the analytical soliton solution in the strongly nonlocal case, the critical power of a strongly nonlocal solition is directly proportional to wm2/w3, where wm is a characteristic length of the material response, and w is the soliton width. Secondly, the soliton solutions in nematic liquid crystal with negative dielectric anisotropy are obtained by numerical computation. It is found that the bright solitons exist only when the degree of nonlocality is above a critical value. The analytical solutions in the second approximation accord with the numerical ones very well even under the general degree of nonlocality. Finally, to investigate the stability, we conduct the linear stability analysis, and find that all the solitons are stable, which is also confirmed by the numerical simulations.
Effect of surface tension anisotropy on the interface morphological stability of deep cellular crystal
Authors: Jiang Han  , Chen Ming-Wen  , Shi Guo-Dong  , Wang Tao  , Wang Zi-Dong  ,   School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China;,   School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

In this paper, we study the effect of anisotropic surface tension on the interface morphological stability of deep cellular crystal during directional solidification. We assume that the process of solidification is viewed as a two-dimensional problem, the anisotropic surface tension is a four-fold symmetry function, the solute diffusion in the solid phase is negligible, the thermodynamic properties are the same for both solid and liquid phases, and there is no convection in the system. On the basis of the basic state solution for the deep cellular crystal in directional solidification, by the matched asymptotic expansion method and the multiple variable expansion method, we obtain the asymptotic solution, and then the quantization condition of interfacial morphology for deep cellular crystal is obtained.
The results show that by comparison with the directional solidification system of surface tension isotropy, the interface morphological stability of surface tension anisotropy also possesses two types of global instability mechanisms: the global oscillatory instability (GTW-mode), whose neutral modes yield strong oscillatory dendritic structures, and the low-frequency instability (IF-mode), whose neutral modes yield weakly oscillatory cellular structures. Both of the two global instability mechanisms have the symmetrical mode (S-mode) and the anti-symmetrical mode (A-mode), and the growth rate of the S-mode with the same index n is greater than that of the A-mode. In this sense we say that the S-mode is more dangerous than the A-mode. All the neutral curves of the GTW-S-modes and LF-S-modes divide the parameter plane into two subdomains: the stable domain and the unstable domain. In the paper we show the neural curves of the GTW-S-modes and LS-S-modes for various n, respectively. It is seen that among all the GTW-S-modes (n=0, 1, 2), the GTW-S-mode with n=0 is the most dangerous oscillatory mode, while among all the LF-S-modes (n=0, 1, 2), the LF-S-mode with n=0 is the most dangerous weakly oscillatory mode. We also show the neural curves of the GTW-S-mode (n=0) and LS-S-mode (n=0) for various anisotropic surface tension parameters, respectively. It is seen that as the anisotropic surface tension increases, the unstable domain of global oscillatory instability decreases, and the unstable domain of the low-frequency instability increases.
Design and control of large-detuned optical lattice based on 87Rb atoms
Authors: Wei Chun-Hua  , Yan Shu-Hua  , Yang Jun  , Wang Guo-Chao  , Jia Ai-Ai  , Luo Yu-Kun  , Hu Qing-Qing  ,   Department of Instrument Science and Technology, National University of Defense Technology, Changsha 410073, China;,   Interdisciplinary Center for Quantum Information, National University of Defense Technology, Changsha 410073, China;,   Rocket Force University of Engineering, Xi'an 710025, China
Published: December 2020

An innovative and practical scheme of building far-detuned optical lattice for 87Rb atoms is proposed.The disposals of aligning the lattice beams,tuning the lattice frequency and controlling the tapered amplifier for output are described in detail.Alignment of optical lattices is quite difficult in principle,for several beams are required to hit the same atomic cloud.For the relatively near-detuned one-and two-dimensional lattices,the coarse alignment is accomplished by tuning the lattice laser onto resonance with the magnetic-optic trap(MOT) frequency,and then blowing away the MOT in real time.A more precision alignment is implemented at the end of the MOT loading,the atoms are first pumped into the lower hyperfine level by turning off the repumping for some time;then,the pulsed lattice beams are turned on for a short time at some reasonably large detuning.Finally,a fluorescent image of the MOT is taken without repumping,in order to detect only those atoms which are repumped by the lattice laser.For the purpose of controlling the detuning of the lattice easily and accurately,a home-made grating wavemeter with a resolution better than 1 GHz is used.This way allows the laser to be locked at any frequency by using a software PID and is experimentally simple to implement.The intensity of the lattice is controlled directly by pulsing the current through the tapered amplifier using a function generator and a laser diode driver.This technique has already been demonstrated before by Prof.M.Kasevich's group at Stanford.
Our experiment starts with a MOT capturing approximately 4107 atoms in 200 ms.The lattice loading is overlap with the end of polarization gradient cooling(PGC),after that,the molasses laser beams are extinguished, and the adiabatic expansion is accomplished in the same time by a decrease in the lattice light intensity according to release function.On the basis of MOT and PGC,the dependences of atomic loading on such parameters as the intensity and frequency detuning of optical lattice are investigated experimentally.The vibration frequency is measured by intentionally modulating the trap intensity.Experimental results show that the lattice structure facilitates the cooling with the temperature of atoms cloud being reduced to 1/3 compared with free space polarization gradient cooling.The system design,experimental results and conclusions are of definite significance and can serve as a fine reference for other kinds of lattices designs or alkali atomic plans.
Spontaneous emission from a V-type three-level atom in a dynamic photonic crystal
Authors: Xing Rong  , Xie Shuang-Yuan  , Xu Jing-Ping  , Yang Ya-Ping  ,   Ministry of Education Key Laboratory of Advanced Microstructure Materials, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
Published: December 2020

The spontaneous emission from a V-type three-level atom embedded in an isotropic photonic crystal with dynamic photonic band edge is studied. We consider the situation where the atom interacts with all possible radiation modes, and calculate numerically the evolution of atomic population without using Markov approximation. The calculation method can be used in related researches. In the present paper, we mainly discuss the effects of modulation parameters and the quantum interference on spontaneous emission when the band edge is modulated with step function or triangle function. We hope that the results can contribute to the applications in the dynamic photonic crystal environment in controlling the spontaneous emission via the quantum interference. The results show that in the step-modulated situation, the number of the photon-atom bound dressed states after the modulation has happened depends on atomic transition frequencies and the band edge frequency at that time, and is identical to the one in the unmodulated situation with the same parameters. The long-time evolution of the atomic population is affected by the time when the modulation happens. Depending on the system initial state, after the modulation has happened, the quantum interference can weaken the probability amplitude components corresponding to the photon-atom bound dressed states, and cause the upper-level population to decay quickly from a great value to a value near zero; or on the contrary, it can strengthen the bound dressed states, and make the upper levels retain a high population. In the modulated situation with trigonometric functions, after long enough time, the total upper-level population presents a decaying quasi-periodic oscillation behaviour. And the evolution of the total upper-level population tends to synchronize with the modulation, so the frequency of the quasi-periodic oscillation is approximately equal to the modulation frequency. But, the quantum interference can destroy the synchronization under some conditions. The decay rate of the total upper-level population is affected by the modulation frequency, and also by the initial state of the system and the angle between two dipole moment because of the quantum interference.
Ocean ambient noise model considering depth distribution of source and geo-acoustic inversion
Authors: Jiang Peng-Fei  , Lin Jian-Heng  , Sun Jun-Ping  , Yi Xue-Juan  ,   Qingdao Branch, Institute of Acoustics, Chinese Academy of Sciences, Qingdao 266023, China;,   Key Laboratory of Underwater Acoustic Environment, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

An ocean ambient noise model is established considering source depth distribution. The model is used to analyze the effect of source depth on the vertical characteristics of ambient noise field. The analyses are explained and validated by normal mode theory. The energy of normal mode excited changes with source depth. Effects of different order normal modes are different. The high order modes raise up the equivalent seabed reflection loss, whereas the low order modes depress it. It is found that the seabed sound speed, density and source depth all have significant influences on equivalent seabed reflection loss at large grazing angles. So the source depth should be taken into account and the model is used in geo-acoustic inversion. Two sets of experimental data in a bandwidth of 200-525 Hz are used to obtain geo-acoustic parameters. The results show that the geo-acoustic parameters inverted from ocean ambient noise and from sound propagation data are similar. The mean value of inverted source depth tends to be smaller as frequency increases, which demonstrates that wind waves become dominant over ship noise. The average of inverted source depth values in the band(>400 Hz) is very small when sea state is higher than grade 3, which is consistent with the result from the Monahan's bubble theory.
Enhancement of tandem organic light-emitting diode performance by inserting an ultra-thin Ag layer in charge generation layer
Authors: Tao Hong  , Gao Dong-Yu  , Liu Bai-Quan  , Wang Lei  , Zou Jian-Hua  , Xu Miao  , Peng Jun-Biao  ,   Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China;,   New Vision Opto-Electronic Technology Co., Ltd, Guangzhou 510730, China
Published: December 2020

White organic light-emitting diodes (WOLEDs) have attracted both scientific and industrial interest in the solidstate lighting and display applications due to their exceptional merits,such as high luminances,low power consumptions, high efficiencies,fast response times,wide-viewing angles,flexibilities and simple fabrications.The power efficiency of WOLED has been step-by-step improved in the last 20 years,however,the lifetime of WOLED is still unsatisfactory, which greatly restricts the further development of WOLED.In general,the tandem structure can be used to obtain high-efficiency and long-lifetime WOLED.One of the most important features of this kind of structure is that the different-colors emitting units can be connected by the charge generation layer.Therefore,the key to achieving a highperformance tandem device is how to design the charge generation layer.In this paper,we first develop a tandem green OLED by using an effective charge generation layer with an ultra-thin Ag layer between 4,7-diphenyl-1,10-phenanthroline:CsCO3 and hexaazatriphenylenehexacabonitrile,achieving high luminance,low voltage,high efficiency and long lifetime.The green tandem device with ultra-thin Ag layer (device C) obtains a highest luminance of 290000 cd/m2,which is 1.4 and 1.9 times higher than those of the tandem devices without ultra-thin Ag (device B) and singleunit device (device A),respectively.The driving voltage of device C is 7.2 V at 1000 cd/m2,1.4 V lower than that of device B.Besides,the maximum current efficiency of device C is 60.4 cd/A,which is 2.4% and 220% higher than those of device B (59 cd/A) and device A (18.7 cd/A),respectively.The power efficiency of device C is 26 lm/W,which is 21% higher than that of device B (21.5 lm/W).Moreover,the lifetime (T80) of device C reaches 250 h at an initial luminance of 10000 cd/m2,which is nearly 100 times higher than that of device B (2.7 h).Finally,we fabricate a white tandem device with the optimized charge generation layer,achieving a current efficiency and power efficiency of 75.9 cd/A and 36.1 lm/W at 1000 cd/m2,respectively.In addition,the lifetime (T80) is 77 h at an initial luminance of 10000 cd/m2.All the excellent performances are ascribed to the introduction of the ultra-thin Ag layer into the charge generation layer, which can effectively block the charge generation layer from diffusing.This exciting discovery can provide an effective way to design efficient and stable WOLED,which is beneficial to the solid-state lighting and display markets.
Theory of very low frequency/extra low frequency radiation by dual-beam beat wave heating ionosphere
Authors: Yang Ju-Tao  , Li Qing-Liang  , Wang Jian-Guo  , Hao Shu-Ji  , Pan Wei-Yan  ,   School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China;,   China Research Institute of Radiowave Propagation National Key Laboratory of Electromagnetic Environment, Qingdao 266107, China;,   Northwest institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

At high latitudes, the proposed dual-beam beat wave method has become the focus of research because of its relative amplitude modulation method. The very low frequency/extra low frequency(VLF/ELF) radiation intensity does not depend on the background of the current, and can be used as an importantparameter of VLF/ELF radiation in poor background conditions. As for the background of weak natural current in middle and low latitude regions, the amplitude modulation method stimulates the VLF/ELF radiation effect poorly, therefore, at the low latitudes, the relative amplitude modulation method, dual-beam beat waves method may be more effective. In this paper, according to the pondermotive nonlinear heating theory in the upper ionosphere, a simulation model is presented about VLF/ELF radiation generated by dual-beam heating of the ionosphere via beating waves. This model is validated by calculations and the available experimental parameters. Based on this model, a comprehensive analysis is performed, involving the dependences of radiation intensity on various parameters such as latitude, effective radiation power(ERP), heating frequency, polarization, experimental times, and beating frequency difference. Then, we compare the dual-beam beat wave method with the amplitude modulation in stimulating VLF/ELF signals in the low and moderate latitude regions. Several conclusions are drawn as follows. First, the increases of geomagnetic declination and ERP of the heating facility may lead to a considerable improvement in radiation efficiency. Second, the X-mode polarization is more efficient for radiation than the O-mode polarization. Third, the most remarkable radiation effect may appear at winter night. The optimal heating frequency and the beating wave difference could be found under certain conditions. Stimulations of VLF/ELF radiation with the dual-beam beating wave method are more effectivethan the available amplitude modulation, the difference in VLF/ELF radiation intensity between the two methods is about 10 dB.
An improved direct position determination method based on correlation accumulation of short-time signals with variable velocity receivers
Authors: Lu Zhi-Yu  , Ren Yan-Qing  , Ba Bin  , Wang Da-Ming  , Zhang Jie  ,   PLA Information Engineering University, Zhengzhou 450000, China;,   The 66159th Unit of PLA, Wuhan 430000, China
Published: December 2020

Wireless target location technology has been widely used in civil and military fields. In the two-step localization algorithms, the signal measurements, such as thetime of arrival, theangle of arrival, the frequency difference of arrival, etc., should be extracted first from the receivedsource signal. Then the target position is identified by calculating the location equation. Compared with the two-step localization algorithms, the direct position determination (DPD) method, which need not estimate the signal parameters and calculate the position step by step, but obtainsthe source position from the received signals directly based on the maximum likelihood criterion, has been shown to have a goodestimation accuracy and robustness, especially under low signal-to-noise ratio (SNR) conditions. So it has been widely studied in recent years and has made remarkable achievements in academic research. However, the DPD algorithm of wideband signals emitters is not performing well with moving receivers in the joint positioning based on time delay and Doppler shift under the low SNRs. To obtaina better positioning performance, in this paper we present a DPD algorithm with variable velocity receivers based on coherent summation of short-time signal segments, and derive the source position Cramer-Rao lower bound (CRLB). The algorithm designs a positioning model in which the multiple variable velocity receivers are usedtoobtain the source signal, then the signal received at the same receiver is patitioned into multiple non-overlapping short-time signal segments, based on which, an approximate maximum likelihood estimator for the new DPD algorithm is developed. The algorithm makes full use of the location information contained in the coherency among the signals segments, while extra target position information is acquired through the speed variability in the positioning model, and thus the problem of location ambiguity is solved. The simulation results show thatthe algorithm proposed in this paper further improves the positioning performance, and outperforms the traditional DPD algorithms with more accurate results. Especially in the low SNR, it is closer to the CRLB.
SM4 key scheme algorithm based on chaotic system
Authors: Wang Chuan-Fu  , Ding Qun  ,   College of Electronic Engineering, Heilongjiang University, Harbin 150080, China
Published: December 2020

Block cipher is a widely used encryption method. In order to improve the security of information in the network data encryption systems, the initial key should be guaranteed to be large enough. In order to overcome the threat of quantum computer to short initial keys, a key scheme based on chaotic map is proposed. The chaotic map is introduced into the original SM4 key scheme, which effectively increases the initial key space and greatly improves the resistance to key scheme attacks.#br#Due to the limited logic resources in hardware implementation, a logistic map is chosen as a chaotic system in this paper. Although the logistic map has many excellent properties of chaotic system, such as initial value sensitivity, randomness, ergodic, etc, there are still a lot of problems that we need to pay attention to. The parameter μ is the system parameter in the logistic map. The value of μ controls chaotic characteristics in the logistic map. When μ is equal to 4, the dynamic characteristics of logistic map are best. The values of data transmitted in the network are all quantified as 0 and 1. In order to implement the logistic map in a digital circuit, the digital quantization is needed. The bit sequence design quantization is very simple and saves resource consumption. Compared with other quantization methods, bit sequence design quantization can be implemented in hardware parallelly. United States National Institute of Standards and Technology launched the test program package to test the random numbers. The test program package includes frequency detection, block frequency detection, run test, etc. Those tests are used to detect the randomness in binary sequence of arbitrary length. The test program package proves that the sequence generated by the logistic map has a great randomness characteristic. After the security analysis of logistic map, the hardware implementation of logistic map is carried out in this paper. Based on the theoretical analysis and hardware implementation in the logistic map, a new SM4 key scheme combined with the logistic map is proposed. The proposed key scheme has less hardware resource consumption, larger key space and higher security than other key schemes combined with chaotic systems. The output of key scheme in this paper is tested by the test program package. The results show that the random number produced by new key scheme is larger. In the end, a key scheme attack is introduced in this paper. It is proved that the new key scheme in this paper can effectively resist existing key scheme attacks.
Influence of gradient phased interfaces on the laws of light propagation
Authors: Xiao Xiao  , Xie Shi-Wei  , Zhang Zhi-You  , Du Jing-Lei  ,   College of Physical Science and Technology, Sichuan University, Chengdu 610064, China;,   College of Physics and Electronic Engineering, Leshan Normal University, Leshan 614000, China
Published: December 2020

The gradient phased interface is characterized by a non-zero phase variation along the interface between two optical media,which could generate a phase shit between the emitted and incident light beams.Unlike common ones,gradient phased interfaces have a great influence on the laws of light propagation,including light reflection and refraction,and some novel phenomena are observed.For a comprehensive understanding the optical characteristics of those gradient surfaces,the universal laws of light propagation at gradient phased interfaces are derived and discussed in detail in this paper.According to Fermat's principle,we use the stationary phase method to successively acquire the two-dimensional (2D) and three-dimensional (3D) generalized laws of reflection and refraction.In the 2D generalized laws,the interfacial phase gradient lies in the plane of incidence,which is coplanar with the incident,refracted and reflected light beams. But in the 3D case,the phase gradient does not lie in the plane of incidence,and the non-planar reflection and refraction phenomena are observed.These generalized reflection and refraction laws indicate that the interface between two media could be an important factor when light traverses it,and gradient phased interfaces provide new degrees of freedom for manipulating the wavefront of light beams.Based on the generalized reflection and refraction laws,we analyze the influence of phase gradient on light propagation,then obtain critical angles of incidence for reflection and refraction (i.e.the critical angles for total internal reflection and total transmission) in 2D and 3D cases,and explain the reasons for some novel phenomena,such as reflection angle unequal to incidence angle,anomalous reflection and refraction, out-of-plane reflection and refraction,etc.These analysis results show that generalized laws of reflection and refraction have important value in optical design.In addition,we propose an optical design idea based on generalized laws of reflection and refraction,in which gradient phased interfaces are used as core components of optical elements to perform optical transform.And then a flat lens and flat axicon are taken for example to illustrate this idea,the design process of the two flat optical elements are shown in detail.Moreover,we experimentally simulate the gradient surfaces of the two elements by spatial light modulator,and experimental results agree well with theoretical values.It proves that this design idea is practicable.Our research is useful to understand comprehensively the generalized reflection and refraction laws,and extend the applications of generalized laws to flat optics,freeform optics and the accurate control of complex wavefront.
Low-noise optical field phase-shifting manipulated using a coherently-prepared three-level atomic medium
Authors: Guan Jia  , Gu Yi-Sheng  , Zhu Cheng-Jie  , Yang Ya-Ping  ,   School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
Published: December 2020

We propose a multifunction phase-shifting manipulator with low noise at a single-photon level,by using a threelevel atomic scheme.This three-level system interacts with a strong pumping field and a weak probe field with a large detuning.Due to this large detuning,two lower states can be coherently prepared prior to the injection of the pump and probe fields.In our configuration,the duration of the pumping field is much longer than that of the probe field. By solving the Heisenberg-Langevin equations of our system under the steady state approximation,we calculate the linear susceptibility of the system and examine the quantum noise properties of the probe field in detail.We show that this scheme,which rests on the process of two-wave mixing with initial atomic coherence,exhibits many interesting properties that neither typical electromagnetically induced transparency (EIT) schemes nor active Raman gain (ARG) schemes possess.Although both EIT-and ARG-based schemes have been widely investigated in atomic medium,the direct generalizations of these schemes to the single/few photon limit prove to be more problematic.The low fidelity due to the significant probe-field attenuation in EIT medium and the large quantum noise due to the amplification of the probe field in an active Raman gain medium are the main obstacles that prohibit a high-fidelity,low-noise phase shifter from being realized in the single/few photon limit.Physically,this scheme can be viewed as a hybrid scheme in which two processes of different physical principles are allowed to interfere with each other to achieve many desired functionalities. For instance,it can be used as a lossless two-photon-broadband phase-shifter with suitable system parameters.It can also be used as an attenuator/amplifier and a total transparency with a zero phase shift.In particular,we show that by locking the pump field intensity and the two-photon detuning simultaneously a flat constant π-phase shift can be realized with unit probe fidelity in a broad probe field frequency range.Applying the quantum regression theorem,we calculate the noise spectrum of the outgoing probe field as a large phase shift is achieved,and show that this two-photon-insensitive π-phase shift may significantly reduce the quantum noise fluctuations associated with a Raman gain process,and have a lot of potential applications for quantum information processing and optical telecommunication.The realization of this broadband π-phase-shift with significantly reduced quantum noise fluctuations makes this scheme attractive for the realization of low-noise phase-gate/polarization-gate at single-photon level.
Dual-mode large-mode-area multi-core fiber with circularly arranged airhole cores
Authors: Jin Wen-Xing  , Ren Guo-Bin  , Pei Li  , Jiang You-Chao  , Wu Yue  , Shen Ya  , Yang Yu-Guang  , Ren Wen-Hua  , Jian Shui-Sheng  ,   Key Laboratory of All Optical Network and Advanced Telecommunication Network of the Ministry of Education, Beijing Jiaotong University, Beijing 100044, China;Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

Multi-core fiber has aroused considerable interest as one of potential candidates for space division multiplexing that provides an additional freedom degree to increase optical fiber capacity to overcome the transmission bottleneck of current single-mode fiber optical networks. Few-mode fiber is also under intense study as a means to achieve space division multiplexing. We propose a novel dual-mode large-mode-area multi-core fiber (DMLMAMCF), which uses multi-core structure to realize few-mode condition when pursuing large mode-area. The proposed fiber consists of 5 conventional silica-based cores in the center region and 14 air hole cores surrounding the center cores. The outer circle with 12 air hole cores, which function similarly to the fluorine doping region in the bend-insensitive fiber, can mitigate the bending loss when keeping large mode area. The symmetrically distributed two cores on both sides of the center core in central region can reduce the half second-order LP11 mode consisting of two degenerate HE11 modes, TE01 mode, two degenerate HE21 modes and TM01 mode, thus leading to the remaining four vector modes, i.e. two degenerate HE11 modes and two degenerate HE21 modes. That is the reason why we call it strict dual-mode. We focus on large-mode-area properties and bending characteristics of the dual-mode. The influence of structural parameters that include corepitch Λ, refractive index difference between core and cladding Δn, and fiber core radius a, on mode characteristics and mode area of HE11 mode and HE21 mode is investigated in detail. The results reveal that it is helpful to increase the effective area of fundamental mode when we increase the value of corepitch, reduce the refractive index and fiber core radius. The effective mode area of HE11 is about 285.10 μm2 under the strict dual-mode condition. In addition, the relationship between bending loss and bending radius, and the relationship between effective mode area and bending radius of two modes are both investigated. For the HE11 mode, the least bending loss is about 5×10-5 dB/m while the least effective mode area with bending radius larger than 0.6 m is about 285.10 μm2. The HE21 mode is more sensitive to bend effect. The least bending loss is about 0.028 dB/m and the effective mode area is larger than 280.00 μm2 except for resonant coupling points. Large effective areas of both modes with low bending loss can be realized. Larger effective mode area with larger corepitch, appropriate refractive index difference and fiber core radius can be achieved. This fiber may find its usage in high power fiber lasers and amplifiers.
Effects of poling state and direction on domain switching and phase transformation of Pb(Zr0.95Ti0.05)O3 ferroelectric ceramics under uniaxial compression
Authors: Jiang Zhao-Xiu  , Wang Yong-Gang  , Nie Heng-Chang  , Liu Yu-Sheng  ,   Key Laboratory of Impact and Safety Engineering, Ministry of Education of China, Ningbo University, Ningbo 315211, China;,   Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China;,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyan 621900, China
Published: December 2020

The digital image correlation technique is used for full field measurements of axial strain and transverse strain of PZT95/5 ferroelectric ceramics under uniaxial compression. Based on the variations of the axial strain and transverse strain with axial stress, the effects of poling state and poling direction of PZT95/5 ferroelectric ceramics on the domain switching and phase transformation behaviors are explored. Domain switching occurs in unpoled and Z-axis poled PZT95/5 ferroelectric ceramics separately, while domain switching in the Y-axis poled PZT95/5 ferroelectric ceramic is not observed. Domain switching strain in the Z-axis poled PZT95/5 ferroelectric ceramic has obvious influences on the developments of axial strain and transverse strain, but the influence of domain switching strain in the unpoled PZT95/5 ferroelectric ceramic is very weak, which can be attributed to the different random distribution characteristics of domain orientation. By the strain decomposition analysis, it is proved that the domain switching and the phase transition process can be decoupled, and domain switching strain and phase transformation strain can be distinguished successfully. Compared with the Z-axis poled PZT95/5 ferroelectric ceramic, the unpoled PZT95/5 ferroelectric ceramic has a small critical stress of phase transformation, while the critical stress of the Y-axis poled PZT95/5 ferroelectric ceramics is big, which may be concluded that the domain switching behavior favors the phase transformation process. The polarization released behavior of PZT95/5 ferroelectric ceramic also depends on the poling direction. The depolarization mechanism of Z-axis poled PZT95/5 ferroelectric ceramic is caused by both domain switching and phase transformation, and the Y-axis poled PZT95/5 ferroelectric ceramic is caused by only phase transformation.
Experimental study on the density characteristics of a supersonic turbulent boundary layer
Authors: He Lin  , Yi Shi-He  , Lu Xiao-Ge  ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

An experimental study on the density characteristics of a zero-pressure-gradient flat plate turbulent boundary layer at Ma=3.0 is performed by the density field measurement method based on Nano-tracer planar laser scattering (NPLS) technology. The mean and the fluctuating characteristics of the density field of the boundary layer are analyzed. And the spectrum analyses of density fluctuations are performed by utilizing Taylor's hypothesis to convert spatial measurements into pseudo-temporal measurements. The mean density profile increases away from the wall, which accords well with the density profile deduced from the mean velocity distribution by using the adiabatic Crocco-Busemann relation. The root mean square (RMS) of the density fluctuations increases in the logarithmic region with a peak value of 0.2ρ∞, and its probability density distribution follows a normal distribution. However, the RMS of density fluctuations decreases in the outer region of the boundary layer. According to the spectrum analysis, the density fluctuations are characterized in a wide range of frequencies throughout the boundary layer, with the maximum frequency on the order of 1 MHz. The low frequency fluctuations are predominant near the wall and in the outer region of the turbulent boundary layer. However, the proportion of high-frequency fluctuations is nearly equal to that of low-frequency fluctuations in the logarithmic region. The combined NPLS and PIV technique provide a simultaneous density and velocity measurements of the present turbulent boundary layer. The high frequency fluctuations in the supersonic turbulent boundary layer may be induced by the density fluctuations, which are caused by the convection of the turbulent structures with nonuniform density distributions. And the contribution of the velocity fluctuations only to the low frequency fluctuations is observed. There are good similarities between the density fluctuations and the mass flux fluctuations for both the probability density distribution and the spectrum characteristics. On the contrary, a large difference between the fluctuations of velocity and density is identified. Therefore, the strong density fluctuations inside supersonic turbulent boundary layers, as well as its difference between the velocity fluctuations, should be one of the most important differences between compressible and incompressible turbulent boundary layers.
Equations of state and thermodynamic properties of hot plasma
Authors: Tang Wen-Hui  , Xu Bin-Bin  , Ran Xian-Wen  , Xu Zhi-Hong  ,   College of Science, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The equations of state (EOS) and the thermodynamics properties of plasma under high temperature are widely applied to the fields of astrophysics, controllable fusion, weapon design and damage. In this paper we mainly review the theoretical model and computing method of the EOS of hot plasma on different density scales and temperature scales. For an ideal plasma, the interaction between ions can be ignored, the EOS is simple and the theories turn matured. Under the condition of extremely high temperature, ions are ionized completely and the EOSs of ions and electrons can be approximated by the EOS of ideal gas. When the temperature is not very high and ions are just partly ionized, the EOS can be obtained by Saha model or its modified model. When atoms are strongly compressed, the EOS can be calculated by Thomas-Fermi model or its modified model. For the non-ideal plasma, there is a strong coupling between ions. No unified theoretical model can completely describe the interaction between ions at arbitrary density and arbitrary temperature. In principle, the quantum molecular dynamics (QMD) can accurately describe the EOS of plasma in large density range and large temperature range. However, due to the enormous computation and the difficulty in converging, it is difficult to apply QMD to the plasma under high temperature. With simple computing method and small computation, classical molecular dynamics using semi-empirical potential can calculate the EOS accurately at high temperature. However, it will produce great error at lower temperature. It is a simple and effective way to obtain a global EOS by using different theoretical models in different density range and different temperature range and by interpolating in the vacant density range and vacant temperature range.
Theoretical study of the equation of state for warm dense matter
Authors: Ma Gui-Cun  , Zhang Qi-Li  , Song Hong-Zhou  , Li Qiong  , Zhu Xi-Rui  , Meng Xu-Jun  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100089, China
Published: December 2020

In this paper, we present in detail various theoretical models for studying the equation of state of warm dense matter, including the fluid variational theory, the chemical model, the ionization equilibrium model, the average atom model and INFERNO model. The method of calculating the equation of state of a mixture is also given. The results from the first principles molecular dynamics simulation and the quantum Monte Carlo simulation are also provided. Typical materials such as hydrogen, deuterium, helium, xenon, gold, tungsten, etc. are studied in warm dense region by using all the methods, showing the effects of dissociation and ionization in the equation of state.
Analytical modeling for the plate with a flat-bottom hole based on the reflection and transmission theory in pulsed eddy current testing
Authors: Zhang Qing  , Wu Xin-Jun  ,   School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

Ferromagnetic structures such as pipes or vessels are widely used in petroleum, chemical and power generation industries. Periodical nondestructive testing (NDT) is vital for continued safe operation. As a NDT technology, pulsed eddy current testing (PECT) technology which is excited by a square-wave pulse rather than a sinusoidal waveform has been widely used for its advantages of non-contact and acquisition of information at various depths in one excitation process. In PECT, the analytical modeling is important because it gives a better understanding of the signal and benefits the inverse process of PECT in extracting information of structures. The foundation of theoretical model of PECT is the Dodd-Deeds model presented by Dodd and Deeds in 1968, Theodoulidis and Kriezis represented the integral solution of Dodd-Deeds model in the form of series by using the truncated region eigenfunction expansion (TREE) method. Using the Dodd-Deeds model and the TREE method, other analytical modelings have been solved. However, most modelings assume that the wall thinning of the specimen is uniform, and the analytical solution only contains the variables in the z direction (the direction perpendicular to the surface of the specimen), such as the thickness of the specimen. With the rapid development of PECT, problems such as the footprint of the probe, the quantitative analysis of local wall thinning also need to be solved. These problems are related to the variable in the r direction (the direction parallel to the surface of the specimen), so the analytical modelings mentioned above are not available any more. To solve these problems, the analytical modeling of the plate with a flat-bottom hole is proposed. Considering the fact that the boundary condition in the analytical modeling of the plate with a flat-bottom hole is complicated, the assumption that the transverse wave number and the longitudinal wave number in the layer where the flat-bottom hole located are the same is made in this paper, and the transverse wave number is set to be only related to the structure in the r direction. Firstly, the expressions of magnetic vector potential in all the layers are obtained by using the reflection and refraction theory of electromagnetic wave. Then the analytical solution is solved based on the extended Cheng's matrix method by introducing the construction coefficient Wn. Finally, the 16MnR specimen with the flat bottom holes is conducted as an example, and experiments are carried out. The good agreement between results calculated by the analytical model and the experimental results measured verifies the developed analytical model.