bluuebunny/crossref_metadata_2025 huggingface dataset:
Dependence of peak width of energy distribution on profile of combined field
Authors: Lin Nan-Sheng  , Han Lu-Xue  , Jiang Miao  , Li Ying-Jun  ,   State Key Laboratory for GeoMechanics and Deep Underground Engineering, China University of Mining and Technology, Beijing 100083, China;,   Department of Physics, College of Science, China University of Mining and Technology, Beijing 100083, China
Published: December 2020

In this paper, we use the quantum field theory to solve the generation process of particle-anti-particle pairs (PAPs), and study the generation characteristics of PAPs by changing the profile of the field combining an oscillating field and a static electric field. We find a way to increase the generation of PAPs and change the energy distribution. As the field strength of the oscillating field increases, the quantity of particle pairs generated increases. Increasing the field strength of a static electric field yields higher energy pairs of particles. If the frequency of the oscillating field becomes higher, the peak of the energy distribution shifts to higher energy but the width of the peak remains unchanged. The reduction of the field width of the oscillating field increases the generated quantity of PAPs on the one hand, and reduces the peak width of the energy distribution on the other hand. Therefore, we can obtain a narrower range of the energy distribution and more PAPs at less energy cost. Meanwhile, the relationship among the generation yield, the width of energy distribution and the width of the oscillation field is obtained. The width of the oscillating field only significantly narrows the peak width of the energy distribution in a range and reaches a limit after that. This provides useful details for future experiments, and suggests an appropriate width of the oscillating field to produce enough quantity of PAPs with concentrated energy distribution. According to previous studies, varying field width will inevitably lead to the change in the intensity of the electric field. It will be shown that the concentrating of the energy distribution is induced by narrowing the oscillating field instead of increasing the electric field intensity. Therefore, more concentrated PAPs will be obtained and their mutual annihilation will lead to the generation of -ray, which can be used as a -ray in experiments that follow. We suggest reducing the width of the oscillating field to improve the energy concentration of both particles and anti-particles while their quantities are still large enough.
Polarization-controlled dual-band broadband infrared absorber
Authors: Yang Peng  , Han Tian-Cheng  ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

As an important branch of metamaterial-based devices, metamaterial absorber (MA) has aroused great interest and made great progress in the past several years. By manipulating the magnetic resonance and the electric resonance simultaneously, the effective impedance of MA will match the free space impedance, thus resulting in a perfect absorption of incident waves. Due to the advantages of thin thickness, flexible design and tunable property, MA has been extensively studied at various frequencies, e. g. microwave frequency, THz, infrared frequency, and optical frequency. Infrared MA, having important applications in infrared stealth, infrared detection, radiative cooling, and sensors, receives more and more attention, especially for those absorbers based on easy-fabricated one-dimensional grating structure. However, such a grating-based absorber is usually workable in narrow band and effective only for transverse magnetic (TM) wave.In this paper, a dual-band broadband absorber is proposed based on the easy-fabricated grating structure. The basic unit of the proposed absorber consists of eight gradient subunits, each of which is composed of vertically cascaded two pairs of metal-dielectric bilayers. The as-designed absorber has perfect absorption for both TM and transverse electric (TE) waves. More importantly, the absorption band is different for different polarized wave, which provides more choices and greater flexibility for application. Full-wave simulation shows that the absorption of TM wave is above 90% from 1.68 μm to 2 μm, while the absorption of TE wave is very small (no more than 6%). The absorption of TE wave is above 90% from 3.8 to 3.9 μm, while the absorption of TM wave is very small (no more than 5%). In order to reveal the working principle of the proposed absorber, the electric-field distributions of the whole structure are calculated at different frequency, which demonstrates that the broadband absorption is achieved by exciting multiple resonant coupling. Furthermore, we investigate the performance of the proposed absorber in oblique incidence, and find that the designed absorber can exhibit a good absorption within a broad incident angle ranging from 0 to 60 degrees. It is worth noting that there is an absorption fracture band in the absorption spectrum of TM waves, which is because no resonance occurs in all subunits, resulting in almost no absorption.In conclusion, we have proposed a dual-band broadband absorber that demonstrates independent absorption of the TM waves and the waves in different bands, which has potential applications in thermal detectors and thermal emitters. The proposed scheme can be extended to microwave, THz, and even visible light band.
Charging mechanism and application of lunar dust grains
Authors: Xue Dan  , Liu Jin-Yuan  , Li Shu-Han  ,   School of Physics, Dalian University of Technology, Dalian 116024, China
Published: December 2020

Since the moon has an extremely rarefied atmosphere, the full spectrum of the electromagnetic radiation of the sun reaches the surface, charging the surface dust and affecting its current charge state. Lunar surface dust thus remains electrostatically charged at all times. Charged lunar dust will adversely affect the operations of most mechanical systems required by manned and unmanned exploration missions. Charged dust will also stubbornly adhere to solar panels and thermal radiators, thus reducing their efficiencies. Researches on the charged lunar dust can help to investigate lunar dusty environment as well as to solve those particle-induced problems by both simulation and experiment in laboratory. In this work, two different charging processes of charged lunar dust in the environment of electron beam and the radiation of ultraviolet source are considered. The computer numerical simulation method is used to analyze these two different charging processes of lunar dust, to explore the charging mechanisms of lunar dusts, and to choose an appropriate way of charging for the lunar environment simulation device in laboratory. On the basis of the classic dust charging equation, the charging equation of a dust in pure electron environment is given for the first time in this work. Meanwhile, the charging process under ultraviolet radiation is discussed and combined with the specific application of charging dusts. A solver of fourth-order Runge-Kutta algorithm is made to solve differential equations under two different irradiation sources. The main simulation results show that:1) in electron environment, the surface dust charge number increases as the particle size and the current intensity of electron guns increase, while the charge number increases as the beam spot radius of electron guns decreases; 2) under ultraviolet radiation, the dust charge number increases with the particle size and irradiance increasing, but charging efficiency is slow. A great dust charge number needs a long time radiation from sun (equivalent to 74 deuterium lamps), which means that more ultraviolet radiation sources are essential to speeding up the experiment in laboratory. Although the calculated efficiency of ultraviolet radiation is lower than electron irradiation, the secondary-electron emission, the scattering and the transmission process of electron irradiation are ignored, which can greatly reduce the efficiency of charging by energetic electron guns in the actual experiment. Therefore, comparing these two charging mechanisms and considering the actual design requirements for the space environment simulation device, charging by lots of ultraviolet radiation is an appropriate scheme for electrification of lunar dusts.
Supperssion of higher order modes in gain-guided index-antiguided planar waveguide laser
Authors: Kang Da  , Luo Bin  , Yan Lian-Shan  , Pan Wei  , Zou Xi-Hua  ,   Center for Information Photonics and Communication, School of Information Science and Technology, Southwest Jiaotong University, Chengdu 611756, China
Published: December 2020

In order to suppress the higher order modes and improve beam quality in high power waveguide laser, based on gainguided index-antiguided theory, a new symmetric layered waveguide structure is designed, and an interval layer is proposed to be sandwiched between waveguide layer and cladding layer in traditional symmetric GG-IAG waveguide structure. As a result, while reducing the leakage loss of fundamental mode, the threshold gain coefficient differences between fundamental mode and higher order modes will be further increased. When the gain in waveguide layer is between threshold gain coefficient of fundamental mode and that of higher order mode, the fundamental mode will have a greater advantage in mode competition than others, so higher order modes can be suppressed and the laser can obtain a single mode output. In the meantime, the guided-mode principle of this waveguide structure is explained with the theory of wave optics in this paper, the eigen equation of each mode is derived from the wave equation, and the field distributions of fundamental mode and higher order mode are also given. Additionally, in this paper we give the solution process of the threshold gain coefficient of each mode in this waveguide structure. The mode leakage losses of fundamental mode and higher order mode, after adding the interval layer, are numerically calculated, and the parameter optimization process of the interval layer is also given in this paper. In addition, the field distributions of fundamental mode and higher order mode are numerically simulated. The calculation results show that comparing with the traditional symmetric GG-IAG planar waveguide, after adding the interval layer, the loss of fundamental mode can be greatly reduced, while ensuring that the leakage loss of higher order mode reaches a maximum value by reasonably controlling the parameters of interval layer. In this way, we can suppress higher order modes and improve laser efficiency. This paper provides a new idea for improving the beam quality of high power waveguide laser with a large mode area.
Analysis of orbital angular momentum spectra of Hankel-Bessel beams in channels with oceanic turbulence
Authors: Yin Xiao-Li  , Guo Yi-Lin  , Yan Hao  , Cui Xiao-Zhou  , Chang Huan  , Tian Qing-Hua  , Wu Guo-Hua  , Zhang Qi  , Liu Bo  , Xin Xiang-Jun  ,   School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China;,   Beijing Key Laboratory of Space-Ground Interconnection and Convergence, Beijing University of Posts and Telecommunications, Beijing 100876, China;,   School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China;,   School of Physics and Optoelectronic Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China
Published: December 2020

Beams with different-mode-number (l) orbital angular momenta (OAMs) are mutually orthogonal to each other, which makes it possible to enlarge the channel capacity in an OAM multiplexed underwater optical communication (UOC) system. Nevertheless, the implementation of this strategy is limited by oceanic turbulence. Hankel-Bessel (HB) vortex beams carrying OAM are relatively less affected by atmospheric turbulence due to their ability to propagate without changing the intensity profile (non-diffraction nature) and remarkable ability to be reconstructed after encountering an obstacle (self-healing mechanism). Consequently, HB vortex beams can be used as the carriers to increase the channel capacity of information transmission. In this paper, based on the Rytov approximation theory, the analytical expressions of OAM spectra for HB vortex beams under weak horizontal oceanic turbulent channels are derived. The influences of oceanic turbulence parameters on the OAM spectra of HB vortex beams are investigated via numerical calculations. The results indicate that oceanic turbulence leads to the decline of detection probability of transmitted OAM mode and the broadening of OAM spectra as well. Similarly, the spatial coherence length in oceanic turbulence decreases with increasing propagation distance and the dissipation rate of mean-squared temperature and with decreasing the dissipation rate of turbulent kinetic energy, which lead to the decline of detection probability of transmitted OAM mode for HB vortex beams. On the other hand, beams with larger OAM mode numbers each have a wider beam spreading after propagating in the turbulence, which results in the decrease of the detection probability for transmitted OAM modes of HB vortex beams. And the HB vortex beams are more affected by salinity fluctuation than by temperature fluctuations, which indicates that salinity fluctuations are much more effective than temperature fluctuations in determinating the effect of oceanic turbulence. In addition, for weak turbulence and a distance of several tens of meters, the transmission performance of HB vortex beams is worse than that of Laguerre-Gaussian vortex beams with the optimal waist setting. These results provide references for the realization of optical communication links in the marine environment.
Chip-based controllable Ioffe-typed electrostatic mirotrap for cold molecules
Authors: Xu Xue-Yan  , Hou Shun-Yong  , Yin Jian-Ping  ,   School of Mechanical and Electronic Engineering, Chaohu College, Heifei 238000, China;,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
Published: December 2020

Trapping particles (atoms or molecules) allows long interaction time and therefore potentially high resolution in precision measurements. Moreover, the particles in the trap are thermally isolated from the outside world and can be cooled to very low temperatures. As a result, the atomic (or molecular) traps have been widely used in many research areas. However, the molecules in these traps exhibiting zero field in the trap center undergo nonadiabatic transitions, which is the major loss of particles. The loss of atoms in this type of trap seriously hinders the generation of the first BEC (Bose-Einstein condensates). In this paper, we propose a chip-based controllable Ioffe-type electrostatic mirotrap, in which nonadabatic loss can be avoided due to the non-zero electric field. The mirotrap is composed of a pair of L-typed gold wires, which is 1 m in height and deposited on a glass substrate. The non-zero potential well originated in the microsize electrodes offers a steep gradient enable to trap low-field-seeking state polar molecules. The electric field strength in the trap center can be changed in a wide range by adjusting the applied voltage or/and the widths of the electrodes. For instance, under the conditions in the paper, the electric field strength in the trap center can be changed from 0.15 to 5.5 kV/cm. The height of the potential well is about 10 m above the chip and can also be tuned in a large range by adjusting the parameters of the electrodes. Under the conditions in the paper, the height of the potential well can be adjusted from 6.0 to 17.0 m. The electric fields of the microtrap near the surface of the chip are calculated by using a finite element software. Monte-Carlo simulations of the loading and the trapping processes are also carried out in order to justify the feasibility of our scheme. Taking ND3 molecules for example, the loading efficiency of molecules as a function of longitudinal velocity of molecular packet is studied. Our proposed surface microtrap can be used not only for integrating the molecular chips but also for producing the quantum degenerate gas near the chip surface. It offers a platform for many research fields such as precision measurements, quantum computing, surface cold collisions and cold chemistry.
Morphology characterization and growth mechanism of Au-catalyzed GaAs and GaAs/InGaAs nanowires
Authors: Yuan Hui-Bo  , Li Lin  , Zeng Li-Na  , Zhang Jing  , Li Zai-Jin  , Qu Yi  , Yang Xiao-Tian  , Chi Yao-Dan  , Ma Xiao-Hui  , Liu Guo-Jun  ,   State Key Laboratory of High Power Semiconductor Laser, Changchun University of Science and technology, Changchun 130022, China;,   College of Physics and Electronic Engineering, Hainan Normal University, Haikou 571158, China;,   Jilin Provincial Key Laboratory of Architectural Electricity and Comprehensive Energy Saving, Jilin Jianzhu University, Changchun 130118, China
Published: December 2020

The nanowires (NWs) of heterostructure with GaAs based materials have received great attention in the past decades, due to their potential applications in electronics and optoelectronics. Therefore it becomes more and more important to investigate the technology of fabricating NWs with GaAs based materials. In our study, Au-catalyzed GaAs nanowires and GaAs/InGaAs heterostructures are grown by metal-organic chemical vapor deposition following the vapor-liquid-solid mechanism. The growth process, which is vital for morphology research, is found to be strongly affected by growth temperature via scanning electron microscope testing. The GaAs NWs are grown at varying temperatures to investigate the influence of temperature on NW morphology. It is observed that the axial growth decreases with growth temperature increasing while radial growth exhibits the opposite trend, which causes the length of NWs to decrease with temperature increasing at the same time. As radial growth rate is inhibited and radial growth rate is enhanced at relatively high temperature, the geometry of GaAs nanowires turns from columnar to taper and eventually pyramid with temperature rising. The GaAs/InGaAs nanowire heterostructures with distinct heterostructure interfaces, which are columnar and vertical to substrates, are obtained and analyzed. Energy dispersive X-ray spectroscopy (EDX) is used for element monitoring while radial growth is hardly observed during axial heterostructure fabrication, indicating well controlled fabrication technology of NWs growth. The InGaAs segments of axial heterostructures are grown after GaAs segments and occur at the bottom of NWs instead on the top, the analysis of which shows that In atoms would take part in the growth of NWs via migrating at the surface of substrate preferentially, rather than being absorbed in Au-Ga alloy catalytic droplets. Radial heterostructures of GaAs/InGaAs nanowires are grown with GaAs as cores and InGaAs as shells, respectively. Because the axial growth rate would be restricted with temperature increasing, the growth temperature of radial heterostructures is higher than that of axial heterostructures. A small amount of axial growth occurs during the growth of radial heterostructures as indicated by the EDX monitoring result, which is analyzed to be caused by the diffusion of In atoms at radial growth temperature, resulting in a segment of InGaAs nanowire at the interface of nanowires and Au-Ga alloy catalytic droplets.
Chaotic analysis of fractional Willis delayed aneurysm system
Authors: Gao Fei  , Hu Dao-Nan  , Tong Heng-Qing  , Wang Chuan-Mei  ,   School of Science, Wuhan University of Technology, Wuhan 430070, China
Published: December 2020

The dynamic system of Willis aneurysm (WAS) has played an important role in theoretical and clinical research of cerebral aneurysms. Fractional differential is an effective mathematical tool that can describe the cerebral aneurysm system accurately and profoundly. However, the existing fractional Willis aneurysm system (FWAS) cannot describe the delayed aneurysm rupture of unknown cause in reality. Therefore, by introducing the time-delay factors into the existing fractional Willis aneurysm system as a rational extension, a new fractional Willis aneurysm system with time-delay (FWASTD) is proposed in this paper.First, FWASTD is introduced in the context, and the comparison of time sequences map between FWAS and FWASTD proves that FWASTD is feasible in the depiction of time-delay situations. The bifurcation diagram and the largest Lyapunov exponent diagram as well as the phase diagram of fractional order also confirm the chaotic characteristics of the FWASTD.Then, the classical analysis methods in chaotic dynamics, such as time series diagram, phase diagram and Poincar section are used to analyze FWASTD in detail. When studying the diagrams of time-delay factors for the important physiological parameters of the system, we find that blood flow resistance coefficient can exert a remarkable effect on the system stability under time-delay. Besides, the experimental results show that the FWASTD becomes stable with the increase of blood flow resistance under a certain condition. Usually, promoting thrombosis is a kind of adjunctive therapy in clinic for cerebral aneurysm. The results of this part can accord with the treatment in clinic and has great significance in clinical diagnosis.Finally, as the chaotic state of the time-delay system indicates that cerebral aneurysm is in a dangerous situation, the primary task of the control for this new system is to achieve stability rather than synchronization. The stability theory of fractional time-delayed system is adopted in a strict proof of the uniqueness of solution for the FWASTD. To make FWASTD stable, a corresponding linear controller is designed based on the stability theory of fractional order delay system. The numerical simulation indicates that the linear controller can control the blood flow velocity and speed up the periodic fluctuation within a small range, which illustrates that it is not easy to rupture the cerebral aneurysm. We also make self-synchronization control between FWASTD and FWAS just in case that the coefficients of the system are not clear.The research results in this paper, to some extent, can serve as theoretical guidance for the clinical diagnosis and the treatment of aneurysm.
Enhancement of quantum Fisher information of quantum teleportation by optimizing partial measurements
Authors: Wu Ying  , Li Jin-Fang  , Liu Jin-Ming  ,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
Published: December 2020

The purpose of quantum teleportation is to achieve perfect transmission of quantum information from one site to another distant site. In the teleportation process, the quantum system is inevitably affected by its surrounding environment, causing the system to lose its coherence, which will result in distortion of the transmitted information. In recent years, weak measurement and measurement reversal have been proposed to suppress the decoherence of quantum entanglement and protect some quantum states. On the other hand, quantum Fisher information (QFI) is an important physical quantity in quantum metrology, which can give the optimal value estimating the accuracy of parameters. As is well known, QFI is highly susceptible to environmental noise and can lead its measurement accuracy to decrease. Therefore, it is of great importance to examine how to protect QFI from being influenced by the external circumstance during the teleportation procedure. In this paper, we study how to improve the QFI of teleporting a single-qubit state via a Greenberger-Horne-Zeilinger state in a finite temperature environment with the technique of weak measurement and weak measurement reversal. According to different qubit transmission cases of three quantum teleportation schemes, we consider their respective QFIs in detail. After constructing the quantum logic circuit of each teleportation scheme, we first analyze the variance trend of QFI against the generalized amplitude damping noise parameters. Then by introducing weak measurement and measurement reversal on each noise particle of the three schemes, we optimize the related partial measurement parameters and explore the corresponding improved QFI, namely, the difference between the QFI with optimal partial measurements and that without partial measurements. We find that optimizing partial measurements can efficiently enhance the QFI of the teleported state for the three kinds of teleportation schemes at finite temperature. Moreover, with the value of p fixed, the lower the environment temperature, the larger the value of the improved QFI is. Our results could be useful in further understanding the applications of weak measurement and measurement reversal to the quantum communication process and may shed light on estimating some relevant quantum parameters and implementing quantum information tasks.
Network structure optimization algorithm for information propagation considering edge clustering and diffusion characteristics
Authors: Yang Li  , Song Yu-Rong  , Li Yin-Wei  ,   School of Automation, Nanjing University of Posts and Telecommunications, Nanjing 210023, China;,   Jiangsu Engineering Laboratory for IOT and Intelligent Robotics, Nanjing 210023, China;,   School of Computer, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
Published: December 2020

Optimizing network structure to promote information propagation has been a key issue in the research field of complex network, and both clustering and diffusion characteristics of edges in a network play a very important role in information propagation. K-truss decomposition is an algorithm for identifying the most influential nodes in the network. We find that K-truss decomposition only considers edge clustering characteristics, without considering the diffusion characteristics, so it is easily affected by the local clustering structure in the network, such as core-like groups. There are mutually closely connected the core-like groups in the network, but the correlation between the core-like groups and the other parts of the network is less, so the information is easy to spread in the core-like groups, but not in the other parts of the network, nor over the whole network. For the reason, we propose an index to measure the edge diffusion characteristics in a network, and it is found that the diffusion characteristics of some edges in the periphery of the network are relatively high, but the clustering characteristics of these edges are relatively low, so they are not beneficial for rapid information propagation. In this paper, by considering the relationship between the clustering characteristics and diffusion characteristics of the edges, we propose a novel network structure optimization algorithm for information propagation. By measuring the comprehensive ability strength of the clustering characteristics and the diffusion characteristics of the edges, we can filter out the edges whose comprehensive ability is poor in the network, then determine whether the edges should be optimized according to the relative relationship between the clustering characteristics and the diffusion characteristics of the edges. To prove the effectiveness of the proposed algorithm, it is carried out to optimize the structures of four real networks, and verify the effective range of information propagation before and after the optimization of network structure from the classical independent cascade model. The results show that the network topology optimized by the proposed algorithm can effectively increase the range of information propagation. Moreover, the number of leaf nodes in the optimized network is reduced, and the clustering coefficient and the average path length are also reduced.
Single molecule transverse magnetic tweezers based on light sheet illumination
Authors: Ma Jian-Bing  , Zhai Yong-Liang  , Nong Da-Guan  , Li Jing-Hua  , Fu Hang  , Zhang Xing-Hua  , Li Ming  , Lu Ying  , Xu Chun-Hua  ,   Key Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;,   Institute for Advanced Studies, College of Life Sciences, Wuhan University, Wuhan 430072, China
Published: December 2020

Magnetic tweezers are a high precision single-molecule manipulation instrument. A gradient magnetic field is used to generate a force on the order of pN, acting on biomolecule-tethered superparamagnetic beads and to manipulate them. By tracking the bead with an inverted microscope, an imaging system and an image process software, one can obtain the extension length information of the biomolecules, thus can study the mechanism and dynamics of the molecules at a single molecule level. Magnetic tweezers include transverse magnetic tweezers (TMT) which are cheap and simple, and longitudinal magnetic tweezers (LMT) which are expensive and complicated. As the traditional TMT can only track the long biomolecule-tethered beads and their spatial resolution is poorer than that of the LMT according to the error theory of magnetic tweezers and the experimental results, the TMT is not so widely used. To solve this problem, we utilize a light sheet to illuminate the beads only in TMT, and then observe the bead sticking on the lateral surface. The tracking error on the extension axis is 4 nm, which is very small. Then we track and obtain the “folding-unfolding” state transition trace of a hairpin DNA. The hairpin DNA is inserted into a 0.5 μm dsDNA. This experiment proves its ability to study short DNA, RNA or protein. Instead of the fully folded and unfolded state, we observe a semi-stable state at the 1/3 length of the hairpin. The semi-stable state is precisely at the place of the CG rich area of the hairpin, so the CG rich area should be the reason for the semi-stable state. Then we use the 16 μm λ -DNA to further test the novel TMT system. Having obtained the stretching curve of the dsDNA, we fit the length-force data with the worm-like-chain model. The fitted persistence length of the dsDNA is (47±2) nm, which is consistent with the result in the literature. Finally, we compare the noise of traditional TMT, novel TMT and LMT with that of short and long dsDNA at weak and strong force, and we find that at weak force, the novel TMT distinctly enhances the resolution to the LMT level; while at strong force, the resolution of the novel TMT is about half that of the LMT. The results above prove that (1) the short DNA, RNA or protein can be studied by the novel TMT, which extends the application scope of the instrument; (2) the resolution of TMT is enhanced distinctly under weak and strong force, making the novel TMT competent of more experiments.
Computer simulation of adsorption properties of polymer on surface under external driving force
Authors: Li Hong  , Ai Qian-Wen  , Wang Peng-Jun  , Gao He-Bei  , Cui Yi  , Luo Meng-Bo  ,   College of Mathematics, Physics and Electronic Information Engineering, Wenzhou University, Wenzhou 325035, China;,   Department of Information, Wenzhou Vocational and Technical College, Wenzhou 325035, China;,   Department of Physics, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Monte Carlo simulation is performed to study the adsorption properties of polymers on an attractive surface. Annealing method is adopted to simulate the adsorption characteristics and conformational changes of polymer chains driven by an external driving force F. In simulations using cooperative motion algorithm, the ensembles of monomers located at lattice sites are connected by non-breakable bonds. When the external force is F=0, the finite-size scale method can be used to determine the critical adsorption temperature (Tc) of the polymer chain on the attractive surface, but when the external force is F>0, the dependence of the average number of surface contacts M> on the chain length N is unrelated to temperature T. Therefore, Tc cannot be obtained by the finite-size scale method. However, the pseudo-critical adsorption temperature Tc can be estimated by a function of the average number of surface contacts M> and the temperature T for the chain length N=200. And then Tc decreases with external force F increasing. The phase diagram is obtained for the polymer chain between the desorbed state and the adsorbed state under temperature T and external driving force F. Furthermore, the influence of the external driving force on the conformation of the polymer chain is analyzed by the mean square radius of gyration of polymer chains. The critical adsorption point Tc can be checked roughly by the minimum location of the mean square radius of gyration or by the variation of its components in the Y and Z direction perpendicular to the external force. With the increase of the external force F for adsorbed polymer, the temperature T can determine whether polymer is changed from the adsorption state to the desorption state and where the force is located at the transformation. There are two different cases, that is, the polymer can be desorbed at the temperature Tc* TTc and the polymer cannot be desorbed at T Tc*. In this paper, we discuss these two cases for the adsorption of polymer on the attractive surface:weak and strong adsorption. In the first case, the adsorption is strongly influenced by the external driving force. By contrast, in the strong adsorption, the adsorption is weakly influenced by the external force. Our results unravel the dependence of adsorption of polymer on external driving force, which is also consistent with the phase diagram of adsorption and desorption of polymer chains.
Mechanisms of trapping effects in short-gate GaN-based high electron mobility transistors with pulsed I-V measurement
Authors: Zhou Xing-Ye  , Lv Yuan-Jie  , Tan Xin  , Wang Yuan-Gang  , Song Xu-Bo  , He Ze-Zhao  , Zhang Zhi-Rong  , Liu Qing-Bin  , Han Ting-Ting  , Fang Yu-Long  , Feng Zhi-Hong  ,   National Key Laboratory of ASIC, Hebei Semiconductor Research Institute, Shijiazhuang 050051, China
Published: December 2020

Deep-level trapping effect is one of the most critical issues that restrict the performance improvement of GaN-based microwave power devices. It is of very importance for material growth and device development to study the trapping behavior in the device. In the past decades, there have been made a lot of efforts to characterize and investigate the deep-level trapping phenomena. However, most of the previous researches focused on the large-scale devices. For pursuing higher frequency, the devices need to be scaled down. Consequently, it becomes more difficult to characterize the deep-level traps in small-scale GaN-based devices, since none of the traditional characterization techniques such as capacitance-voltage (C-V) measurement and capacitance deep-level transient spectroscopy (C-DLTS) are applicable to small devices. Pulsed I-V measurement and transient simulation are useful techniques for analyzing trapping effects in AlGaN/GaN high electron mobility transitors (HEMTs). In this work, AlGaN/GaN metal-oxide-semiconductor HEMTs (MOSHEMTs) with very short gate length (Lg=80 nm) are fabricated. Based on the pulsed I-V measurement and two-dimensional transient simulation, the influence of deep-level trap on the dynamic characteristic of short-gate AlGaN/GaN MOSHEMT is investigated. First, the pulsed I-V characteristics of AlGaN/GaN MOSHEMT with different quiescent bias voltages are studied. In addition, the current collapse induced by the trapping effect is extracted as a function of the quiescent bias voltage. Furthermore, the transient current of AlGaN/GaN MOSHEMT is simulated with the calibrated model, and the simulation exhibits a similar result to the measurement. Moreover, the physical mechanism of trapping effect in the device is analyzed based on the experimental data and simulation results. It is shown that the current collapse of AlGaN/GaN MOSHEMT varies non-monotonically with the increase of the gate quiescent bias voltage, which results from the combination effect of the gate leakage injection-related and hot electron injection-related mechanism. In the off state, the current collapse is mainly induced by the traps below the gate, which is dominated by the gate leakage injection mechanism, leading to the decrease of current collapse with the increase of the gate bias voltage. In the on state, the hot electron injection mechanism becomes the dominant factor for trapping effect in the drain access region, resulting in the increase of current collapse. The results in this work indicate that the trap-induced current collapse can be further suppressed by improving the quality of gate dielectric to minimize the gate reverse leakage and by reducing the trap density in the epitaxial layer.
Optimization exploration of laser ablation propulsion performance of infrared dye doped glycidyl azide polymer
Authors: Luo Le-Le  , Dou Zhi-Guo  , Ye Ji-Fei  ,   State Key Laboratory of Laser Propulsion and Application, Space Engineering University, Beijing 101416, China;,   Department of Basic Theories, Space Engineering University, Beijing 101416, China
Published: December 2020

The energetic polymer glycidyl azide polymer (GAP) is selected as the propellant of laser ablation micro thruster, and the effect of infrared dye doping on the propelling performance of laser ablative GAP is analyzed. By comparing the propulsion performance data with the plumes of infrared dyes doped GAP under different laser intensities, doping concentrations, target thickness and laser ablation modes, the optimization of the propulsion performance of infrared dye doped GAP is explored preliminarily. The experimental results show that the exponential attenuation characteristics of laser energy and the strong viscosity of GAP doped with infrared dye in the transmission mode lead to the existence of incomplete ablative GAP in the plume. The propulsion performances of GAP are influenced by the doping concentration of infrared dye and the thickness of propellant. Only when the target thickness is close to the laser absorption depth, can the mass of incomplete ablation along the direction of laser propagation be the least and can the laser energy be fully absorbed by the propellant to make the central ablation region reach the temperature threshold of the release of chemical energy. At the same time the optimum value of propulsion performance can be achieved. The GAP doped with infrared dyes in which laser ablation process follows the rule of absorbing laser energy first and spraying first is decomposed adequately under the reflection mode and the propelling performance is better than that in the transmission mode.
Self-phase modulation pre-compensation of narrowlinewidth pulsed fiber lasers
Authors: Su Rong-Tao  , Xiao Hu  , Zhou Pu  , Wang Xiao-Lin  , Ma Yan-Xing  , Duan Lei  , Lü Pin  , Xu Xiao-Jun  ,   Institute of Software, Chinese Academy of Sciences, Beijing 100190, China;,   College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China;,   Hunan Provincial Collaborative Innovation Center of High Power Fiber Laser, Changsha 410073, China
Published: December 2020

High peak power, single frequency nanosecond fiber lasers have aroused the intense interest in their applications such as nonlinear frequency generation, LIDAR, and remote sensing. However, self-phase modulation (SPM) will induce a temporally dependent phase shift φNL (L, t)=|Ap (0, t)|2γLeff, where Ap is the amplitude of pump wave, γ is the nonlinear parameter, and Leff is the effective fiber length. The nonlinear phase shift will broaden the spectral linewidth of pulsed laser, which degrades the coherence of the laser and influences the performance of the laser. In order to obtain laser pulses with narrower linewidth, we can phase-modulate the pulsed laser with a value of-φNL(L,t). Thus, the SPM induced the nonlinear phase shift can be eliminated, and the spectra of pulsed laser can remain during the amplification and transmission in the fiber. Stimulated Brillouin scattering (SBS) has very low threshold and should be taken into consideration in narrow linewidth fiber lasers. The SBS threshold, which is dependent on the linewidth of laser, will be changed at the same time when the SPM is pre-compensated for. Because the SPM pre-compensation will change the linewidth of the pulsed laser. According to three coupled amplitude equations, we numerically analyze the influence of SPM pre-compensation on SBS threshold and spectral characteristics. The stimulation results show that in a master oscillator power amplifier structured fiber laser system, when SPM is completely compensated for (φM(t)=φNL(L,t)), the spectrum of the output pulsed laser can be maintained as that of the laser seed, but the SBS threshold usually decreases. When the SPM is compensated for incompletely (φM(t) φNL(L,t)), the spectral linewidth of the output laser cannot be compressed to that of the laser seed, and the SBS threshold in this situation is lower than the SBS threshold obtained when φM(t)=φNL(L,t). When the SPM is overcompensated for (φM(t) > φNL(L, t)), the spectral linewidth of the output laser cannot be compressed to that of the laser seed either, but the the SBS threshold in this situation is higher than the SBS threshold when φM(t)=φNL(L,t). We also build an experimental setup to verify the feasibility of SPM compensation. In our experiment, the linewidth of the pulsed laser is reduced from 1.4 GHz to 120 MHz when SPM is compensated for by phase modulation. The SBS threshold of the system are measured before and after SPM pre-compensation, and correctness of theoretical simulation is experimentally verified. This analysis method can provide the design guidelines for narrow-linewidth pulsed fiber laser systems.
Theoretical calculation of Kα and Kβ X-ray satellite and hypersatellite structures for hollow argon atoms
Authors: Ma Kun  , Jiao Zheng  , Jiang Feng-Jian  , Ye Jian-Feng  , Lv Hai-Jiang  , Chen Zhan-Bin  ,   School of Information Engineering, Huangshan University, Huangshan 245041, China;,   School of Science, Hunan University of Technology, Zhuzhou 412007, China;,   College of Science, National University of Defense Technology, Changsha 410073, China
Published: December 2020

A systematical knowledge of the satellite and hypersatellite structures of X-ray transitions is of great interest for various research areas, such as the explanation of the X-ray radiation from universe, plasma diagnostics, extreme ultraviolet (EUV) and X-ray sources and so on. Among these researches, the detailed explanation of the complex structures of X-ray satellites and hypersatellites are crucial for understanding the X-ray emission mechanism and the hollow atom formation mechanism. In this paper, the Kα and Kβ X-ray satellite and hypersatellite structure are theoretically studied for hollow argon atoms with the relativistic multiconfiguration Dirac-Fock (MCDF) method, which includes the Breit and quantum electro-dynamics (QED) corrections. To check the applicability of the method, the transition energies and rates of the diagram lines for Ar are calculated,. and the results are in agreement with previously published data. Then the MCDF calculations of the transition energies and probabilities of Kα 1, 2 (K →L3, 2) and Kβ 1, 3 (K → M3, 2) X-ray satellites and hypersatellites, which originate from the argon atoms with additional vacancies in the L shell, are carried out. To obtain the overall profile of the K X-ray spectrum, the diagram lines are integrated with the satellites and hypersatellites on the assumption that the intensity is proportional to the corresponding transition probability and each discrete line has a Gaussian distribution profile with a full width at half maximum (FWHM) value of 20 eV. From the convoluted profile, we can obtain the dependence of the average transition energy and relative transition intensity of the satellites and hypersatellites on the initial hollow configuration. It is found that the transition energy shift increases linearly with the number of spectator vacancies in the L shell increasing. For instance, the energy shift of the Kα satellite caused by L-shell hole is about 20 eV, and that of the Kβ satellite is 48 eV. While for hypersatellite, the energy shift increases greatly due to the double ionization in the K shell. The energy shift increment of Kα and Kβ hypersatellites corresponding to L vacancy are 21 and 52 eV, respectively. Finally, four simple empirical formulae for estimating the energy shifts of the Kα, Kβ X-ray satellites and hypersatellite for Ar atom with any number of L-shells vacancies are deduced by using the least square method. These results are useful in explaining various K X-ray spectra and better understanding the collision process.
Mode separation for multimode Lamb waves based on dispersion compensation and fractional differential
Authors: Ni Long  , Chen Xiao  ,   Jiangsu Key Laboratory of Meteorological Exploration and Information Processing, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   School of Electronics and Information Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Nanjing University of Information Science and Technology, Nanjing 210044, China
Published: December 2020

With the rapid development of material science and industrial technology, the application of ultrasonic Lamb wave to the industrial nondestructive testing has received considerable attention due to its advantages of rapidness, high efficiency, high accuracy, and low cost. However, the multimode and dispersion problem of Lamb waves are still challenging. Multimode mixed Lamb wave signals are often present at the same excitation frequency in the actual detection. To separate dispersive multimode Lamb waves overlapped in time and frequency domains, a separation method based on dispersion compensation and fractional differential is presented. The multimode Lamb waves overlapped in time and frequency domains are first compensated by using the dispersion characteristic. Based on the dispersion compensation, the time-delay function is modeled. The function is used as a transfer function. Its inverse is considered as a dispersion compensation function. Then, the amplitude spectra of Lamb waves are divided into fractional order differentials. The parameters of each mode are extracted by using the fitting polynomial between the maximum amplitude and the differential order and that between the peak frequency and the differential order. Its amplitude spectrum is extracted based on its parameters. By combining with its phase spectrum, the individual mode is constructed after the dispersion has been recovered. Simulation and experiments are performed on a 1 mm-thick stainless steel plate. The oblique transducers with the angle of 26 and the central frequency of 3 MHz are used to excite the S1 and A1 mode overlapped Lamb wave signal in the plate. The transducers are coupled with the stainless steel plate by using the ultrasonic couplant. Simulation and experimental analysis show that the present method can not only achieve the separation of time-frequency overlapped multimode Lamb waves, but also guarantee the separation precision. The main advantage of the presented method is the combination of the dispersion compensation and the fractional differential, which solves the problem of mixing with other mode signals after the single mode dispersion has been compensated, and improves the extraction precision of each mode. Therefore, this method can be used for separating the time-frequency overlapped multimode Lamb waves. It is conducible to the signal processing of multi-mode Lamb wave dispersion.