bluuebunny/crossref_metadata_2025 huggingface dataset:
Distinguishing node propagation influence by expected index of finite step propagation range
Authors: Li Xin , Zhao Cheng-Li , Liu Yang-Yang ,   College of Liberal Arts and Sciences, National University of Defense Technology, Changsha 410073, China
Published: December 2020

On-line social networks have gradually become an indispensable tool for people. Identifying nodes with high influence in the network as an initial source of communication is of great significance in social perception and rumor control. According to the independent cascade model, in this paper we present an index describing the finite step propagation range expectation as the degree of propagation, and design an efficient recursive algorithm. Based on the local topology information, the index combines the propagation probability to characterize the influence, which can better reflect the propagation influence of a single node. For a single propagation source influence ordering problem, the node degree of propagation and propagation capability are better consistent with each other. And the propagation degree can well describe the propagation influence of nodes under different networks and propagation probabilities. For maximizing the multi-propagation source influence, in this paper we propose a propagation-based heuristic algorithm which is called propagation discount algorithm. This algorithm makes the joint influence of multiple propagation sources maximized. Finally, in this paper we apply the above method to three real networks, showing better effects than the classic indicators and methods. The algorithm has three advantages. First, the expected value of the final propagation range of each node in the small network can be accurately calculated. Second, the degree of propagation fully considers the local topology of the node and belongs to a locality indicator. Third, the indicator combines the effect of propagation probability and yields good outcomes under different networks and propagation probabilities.
An efficient Monte Carlo simulation method for thermal radiation transport
Authors: Xu Yu-Pei , Li Shu ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China,   Graduate School of China Academy of Engineering Physics, Beijing 100088, China
Published: December 2020

Thermal radiation transfer in material and the interaction between radiative photon and material are important research projects of the inertial confinement fusion, and Monte Carlo method is one of the important researching methods. Based on the implicit integral-differential transport equation, traditional implicit Monte Carlo method can accurately simulate the thermal radiation transport in material. However, the implicit Monte Carlo method would take quite a long computational time when the opacity is increased because scattering events are dominant in particles’ histories, thus reducing the simulation efficiency. In this paper, based on discrete diffusion Monte Carlo method, i.e. a radiation transport code, the discrete diffusion Monte Carlo radiation transport simulation, is developed. The code increases the efficiency of thermal radiation simulations in a high opacity range, but it can yield insufficiently accurate results in a low opacity range. There exist low opacity material and high opacity material in the inertial confinement fusion. In this work, investigated are several numerical techniques that can improve the utility and accuracy of discrete diffusion Monte Carlo for grey thermal radiation simulation. First, the discrete diffusion Monte Carlo method and implicit Monte Carlo method are combined. Second, a new method of treating the interface between the diffusive region and the transport region is proposed. Finally, a hybrid radiative transfer program is developed. In order to verify the hybrid radiative transfer program and the new interface method, a series of numerical experiments for typical thermal radiation transport problem is conducted. In these problems, materials with different opacities are tested. Then the simulation efficiencies and curves of temperature, obtained by the two Monte Carlo methods, are analyzed. According to the simulation results, the program can not only accurately simulate the radiation transport in material with high opacity, but also remarkably increase the simulation efficiency. This is because many implicit Monte Carlo steps are substituted by one diffusive step and the details in the diffusive step are ignored. Also, the propagation of thermal radiation depicted with figures and tables are consistent with the radiation transport theory. In addition, the results from the hybrid Monte Carlo method reach the same accuracy as that from the implicit Monte Carlo method, and the simulation efficiency is remarkably increased.
Effects of slant angle of sharp plasma-vacuum boundary on electron injection in laser wakefield acceleration
Authors: Zhu Xin-Zhe , Liu Wei-Yuan , Chen Min ,   Key Laboratory for Laser Plasmas of Ministry of Education, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

Plasma wakefield acceleration driven by ultra short ultra intense laser pulse interacting with gas target has been studied for almost four decades. Monoenergetic electron beams with central energy of multi-giga electron-volt have been achieved in a centimeter-scale acceleration distance. Currently, the highest energy of electrons accelerated by laser wakefield is 8 GeV. In order to further improve the quality of such electrons, many kinds of electron injection schemes have been proposed such as density gradient injection, colliding pulse injection and ionization injection. Electrons under the suitable conditions can be trapped by the strong plasma wakefield. Those trapped electrons are then accelerated in the wakefield. In a nonlinear regime, the wakefield shows a “bubble” structure. Electrons with transverse momentum can oscillate in the wakefield and produce considerably betatron radiation in the ultraviolet and X-ray region. In this paper, we study the electron injection around the sharp plasma-vacuum boundary. The effects of the slant angle of the boundary on the final electron quality are investigated in detail. Our results show that with optimal slant density transition around the vacuum plasma boundary, both the beam quality and the injection charge in the second “bubble” can be improved. Two-dimensional particle-in-cell simulations show that the injection charge in the second wake bucket can be increased three times when an optimal slant angle is used compared with a vertical boundary. The driving pulse’s polarization also affects the injection charge. When the polarization is in the injection plane the injection charge in the first bucket can be triply increased compared with the case when the polarization is out of the plane. The reasons for the enhanced injection charge and transverse oscillation are found by tracing the initial injection positions and trajectories of the electrons. These studies would benefit the electron acceleration and its applications, such as compact betatron radiation source.
Tuning upconversion emissions of Ho3+ through changing excitation conditions
Authors: Gao Wei , Wang Bo-Yang , Sun Ze-Yu , Gao Lu , Zhang Chen-Xue , Han Qing-Yan , Dong Jun ,   School of Electronic Engineering, Xi’an University of Post and Telecommunications, Xi’an 710121, China
Published: December 2020

The upconversion (UC) emission properties of rare-earth ions are not only dependent on the host materials, but also relate to the excitation conditions. In this work, taking the Ho3+ ions for example, upconversion emission properties are studied in two NaYF4 and LiYF4 fluoride microcrystals through changing excitation conditions, namely the excitation power and the sample environment. The NaYF4:20%Yb3+/2%Ho3+ and NaYF4:20%Yb3+/2%Ho3+ microcrystal are synthesized by the hydrothermal method. The typical X-ray diffraction patterns of NaYF4:20%Yb3+/2%Ho3+ and LiYF4:20%Yb3+/2%Ho3+ microcrystal indicate that the prepared samples possess pure hexagonal phase NaYF4 structure and the pure tetragonal phase LiYF4 structure with high crystallinity, respectively. Most of NaYF4:20%Yb3+/2%Ho3+ microcrystals show uniform and regular rod shape with diameter and length of approximately 3 μm and 10 μm, respectively. Few rods with a length of approximately 5 μm are also observed. The LiYF4:20%Yb3+/2%Ho3+ microcrystals are all octahedral in shape with a smooth surface, the average size is around 10 μm. The spectral peculiarities of Ho3+ are investigated by using confocal microscopy equipment under near infrared 980 nm excitation. Beautiful patterns with different upconversion emissions of Ho3+ are discovered in single NaYF4 and LiYF4 microcrystal. As the excitation power increases, the upconversion emission of Ho3+ turns from green to pink in single NaYF4 microrods due to the cross-relaxation between Ho3+ and the energy back transfer from Ho3+ to Yb3+. However, in single LiYF4:Ho3+ microcrystal no similar phenomenon is observed. Nevertheless, when the powder of NaYF4 and LiYF4 microcrystals are excited by a 980 nm laser, increasing the power can turn the output colours of Ho3+ all green. Because particles outside the laser radiation are not directly covered by the laser, most of them are excited by the scattered light from the laser, and the actual excitation energy is low compared with at the center position. This result can be proved in the single NaYF4 and LiYF4 microcrystal under low excitation power. Thus, the results indicate that UC emission of rare-earth ions is controlled by changing the excitation condition. Using the new testing methods we can not only observe more interesting spectral phenomena, but also find a new way to further study its luminescence mechanism.
Image encryption algorithm based on new five-dimensional multi-ring multi-wing hyperchaotic system
Authors: Zhuang Zhi-Ben , Li Jun , Liu Jing-Yi , Chen Shi-Qiang ,   School of Science, Hubei Mimzu University, Enshi 445000, China,   School of Information Engineering, Hubei Minzu University, Enshi 445000, China,   School of Advanced Materials and Mechatronic Engineering, Hubei Minzu University, Enshi 445000, China
Published: December 2020

The complex structure of hyperchaos and its complex dynamic behavior have a good application prospect in the fields of image encryption, digital watermarking and information security. Therefore, it has become very important to generate chaotic attractors with multi-vortex and multi-winged multi-rings with complex topologies. In this paper, we propose a new five-dimensional hyperchaotic system capable of generating multi-ring and multi-wing, and carry out theoretical analysis and numerical simulation experiments on some basic dynamic characteristics of the chaotic system. Such as equilibrium point, dissipation, Lyapunov exponent, bifurcation diagram, phase diagram and so on. In the process of encryption, first, we decompose the plaintext image matrix and the five chaotic sequences into an orthogonal matrix and an upper triangular matrix by QR decomposition. The five chaotic sequences generated by the chaotic system are respectively decomposed into an upper triangular matrix and a lower triangular matrix by the LU decomposition method. The upper triangular matrix decomposed by the QR decomposition method and the lower triangular matrix decomposed by the LU decomposition method are respectively added to obtain five discrete chaotic sequences. At the same time, the five discrete chaotic sequences are added to the upper triangular matrix decomposed by the LU decomposition method to obtain the final five discrete chaotic sequences. Secondly, the orthogonal matrix decomposed by the plaintext image matrix is multiplied by five orthogonal matrices decomposed by five chaotic sequences. At the same time, the elements in the upper triangular matrix decomposed by the plaintext image matrix are chaotically arranged by the chaotic sequence, and then the two matrices after the operation are multiplied. Finally, the multiplied matrix is chaotically placed on the bit by a chaotic sequence. Then use the chaotic sequence to perform a bitwise XOR operation to obtain the final encrypted image. The theoretical analysis and simulation results show that the algorithm has large key space and strong key sensitivity. It can effectively resist the attacks of statistical analysis and gray value analysis, and has good encryption effect on digital image encryption. This image encryption algorithm using a combination of conventional encryption and chaotic encryption does not have a defined plaintext ciphertext mapping relationship.
Effect of He ion irradiation on microstructure and electrical properties of graphene
Authors: Zhang Na , Liu Bo , Lin Li-Wei ,   Key Laboratory of Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, China
Published: December 2020

Graphene is a planar two-dimensional material composed of sp2-bonded carbon atoms with extraordinary electrical, optical and mechanical properties, and considered as one of the revolutionary electronic component materials in the future. Some studies have shown that the inert gas ion irradiation as a defect introducing technique can change the structure and properties of graphene without introducing additional effects. In this paper, the 5.4 keV He ion irradiation at the dose ranging from 0.7 × 1013 cm–2 to 2.5 × 1013 cm–2 has a strong effect on graphene deposited by CVD technology. The X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman) and semi-conductor parameter analysis instrument are used to study the changes in the microstructure and electrical properties of graphene before and after irradiation. Detailed analysis shows that the defect density increases gradually with the irradiation dose increasing. Raman spectrum shows that when the irradiation dose increases to 1.6 × 1013 cm–2, the value of ID/IG begins to decrease, and XPS shows that the irradiation changes the structure of C chemical bond in graphene which causes the bonding state of C—C sp2 to be destroyed and partly converted into the C—C sp3 bonding state. Therefore, the structure of graphene begins to transform from nano-crystalline structure into sp3 amorphous structure. Simultaneously, increasing defects causes the graphene conductivity to continuously decrease, and also gives rise to the electrical transition from defect scattering mechanism based on Boltzmann transport to the hopping transport. The positive voltage direction offset of Vdirac increases nearly in direct proportion, which is due to the enhancement of graphene’s p-type doping effect caused by defects and adsorbed impurities. This work conduces to the understanding the mechanism of He ion interaction with graphene, and also provides an effective way of controlling the electronic properties.
Research progress of diffusion sensitive gradient field encoding schemes in magnetic resonance diffusion tensor imaging
Authors: Liu Liang-You , Gao Song , Li Sha , Li Zhao-Tong , Xia Yi-Fan ,   Institute of Medical Technology, Peking University, Beijing 100191, China,   Research and Development Center of Medical Technology, Peking University, Beijing 100191, China
Published: December 2020

Magnetic resonance imaging is a medical imaging technique in which the phenomenon of nuclear magnetic resonance is used. This technique is widely used in clinical and scientific research at present. The diffusion of water molecules is isotropic in a homogeneous medium, while it is anisotropic in the structure of human tissue. Magnetic resonance diffusion tensor imaging (DTI) is for studying the microscopic structure inside body by using the water molecules’ diffusion effect which will reduce the signal intensity of magnetic resonance. Besides, it can quantitatively study the anisotropy of water molecules in three-dimensional space, and thus acquiring important pathological and physiological information without invading in vivo. In order to obtain the accurate result of the anisotropic diffusion of water molecules, according to a certain scheme, it is necessary to sequentially use diffusion sensitive gradient (DSG) magnetic fields in different diffusion orientations to measure the diffusion coefficient of water molecules for estimating the diffusion tensor. The precision of estimating diffusion tensor is affected by the applied DSG encoding scheme, and it is usually necessary to use a large number of linearly independent and evenly spatial distributions of DSG magnetic fields in order to make the tensor measurement result more accurate. Diffusion spectroscopy imaging technique and high angular resolution diffusion imaging (HARDI) technique are proposed for more complex fiber bundles crossing in human tissue, one of which, HARDI, has higher requirement for the number and the direction distribution uniformity of DSGs. In this paper, the basic principle of DTI and the DSG encoding schemes are reviewed, which includes completely random scheme, heuristic scheme, regular polyhedral scheme, numerically optimized scheme, etc. For the above various schemes their respective advantages and limitations are analyzed. At present, the Golden Ratio method is to be used in a new spherical DSG encoding scheme which meets the requirements for HARDI and can offer more accurate tensor estimation results in face of the corruption of data sets encountered in clinical practice.
A phase locking scheme of two-mode squeezed microwave preparation
Authors: Wei Tian-Li , Wu De-Wei , Yang Chun-Yan , Luo Jun-Wen , Miao Qiang , Li Xiang ,   Information and Navigation College, Air Force Engineering University, Xi’an 710077, China
Published: December 2020

As the core of quantum entanglement, two-mode squeezing is manifested in cross-correlations of incompatible observables between two subsystems, which makes the two-mode squeezed microwave an ideal resource for applications in quantum communication, quantum illumination, and quantum microwave navigation. Currently the preparation scheme of two-mode squeezed microwave, based on the Josephson parametric amplifier (JPA) and a superconducting 180° hybrid ring coupler, proves to be the most efficient and excellent in quantum properties. Nevertheless, the difficult phase locking processing restricts the further improvement of entanglement. There is no effective solution but the dual-path receiver with phase stabilization measures, and the phase error reaches as high as 0.3°, which still does not meet the requirements for phase locking precision and entanglement stability. To overcome the academic obstacle, we propose a phase locking scheme to achieve a stable two-mode squeezed microwave. There are two JPAs used to separately generate single-mode squeezed microwaves, between which the difference lies in the fact that the input of one JPA is phase-modulated but the other is not. A superconducting 180° hybrid ring coupler is used to distribute the two single-mode squeezed microwaves into two output paths, which are two-mode squeezing if the squeezing directions of the two single-mode squeezed microwave are orthogonal. That is to say, the relative phase satisfies the condition \begin{document}$\theta = {\text{π}}/2$\end{document}. By mixing the unmodulated single-mode squeezed microwave and one output of the superconducting 180° hybrid ring coupler, a relative phase is obtained in subsequent process. Proportional integral derivative (PID) controller is used as the input of phase error, and the output is used to adjust the pump phase of JPA, which is the key to phase locking and stable two-mode squeezing. The present research not only provides an effective strategy to achieve stable two-mode squeezed microwave, but also may attract more attention to the precisive measurement of two-mode squeezed microwave.
Filamentation and supercontinuum emission generated from flattened femtosecond laser beam by use of axicon in fused silica
Authors: Fu Li-Li , Chang Jun-Wei , Chen Jia-Qi , Zhang Lan-Zhi , Hao Zuo-Qiang ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China,   Shandong Provincial Engineering and Technical Center of Light Manipulations & Shandong Provincial Key Laboratory of Optics and Photonic Device, School of Physics and Electronics, Shandong Normal University, Jinan 250358, China
Published: December 2020

It is important to control the femtosecond laser filamentation and the supercontinuum (SC) for their potential applications. The use of axicon is beneficial to the filamentation elongation and SC enhancement, because the axicon can convert the incident laser into a Bessel beam and forms a unique longer depth of focus region. On the other hand, the flattened laser beam which has a uniform distribution of the beam intensity, can propagate in condense media with a higher incident energy than that of Gaussian laser beam. It has unique advantages in forming a SC with high energy and high conversion efficiency. In this paper, we combine the use of axicon and the flattened laser beam to form filament and SC in fused silica. First, we study the filamentation generated by the Gaussian beam and the flattened beam, respectively, with the same incident pulse energy (672 μJ). The results show that the flattened beam can generate filament with relative uniform intensity distribution in the focal depth of the axicon and the intensity is relatively smaller than that of the Gaussian beam. It suggests that the flattened laser beam can propagate in fused silica with a higher energy than Gaussian beam. Second, we study the filamentation of the flattened beam of 1.319 mJ. In this case, the filament intensity is close to that of the Gaussian beam with 672 μJ. Moreover, the filamentation of the flattened beam with 1.319 mJ is longer and the intensity distribution is more uniform than that of the Gaussian beam with 672 μJ. Therefore, a flattened laser beam can generate the SC with a higher energy than that of the Gaussian beam in fused silica. The comparison of the spectra shows that the relative spectral intensity of flattened beam with 1.319 mJ in the range of 550–700 nm is much higher than that of the Gaussian beam with 672 μJ. The conversion efficiency of the Gaussian beam and the flattened beam is 32.58% and 39.59%, respectively. It can be seen that the flattened laser beam has advantages not only in generating long and uniform filament, but also in generating the intense SC. This approach is helpful to many applications, such as white light LIDAR and micro-nano processing.
Rogue wave solution in ferromagnetic nanowires
Authors: Li Zai-Dong , Guo Qi-Qi ,   Department of Applied Physics, Hebei University of Technology, Tianjin 300401, China,   School of Science, Tianjin University of Technology, Tianjin 300384, China
Published: December 2020

In this paper, we introduce some new excited states of magnetization in ferromagnetic nanowires, including Akhmediev breathers, Kuznetsov-Ma soliton and rogue wave in isotropic ferromagnetic nanowires, and rogue wave in anisotropic ferromagnetic nanowires driven by spin-polarized current. The isotropic case demonstrates a spatial periodic process of a magnetic soliton forming the petal with four pieces and a localized process of the spin-wave background. In a limit case, we get rogue waves and clarify its formation mechanism. In the case of anisotropy, it is found that the generation of rogue waves mainly comes from the accumulation of energy and rapid dispersion in the center. In addition, rogue waves are unstable, the spin-polarized current can control the exchange rate of magnons between the envelope soliton and the background. These results can be useful for the exploration of nonlinear excitation in Bosonic and fermionic ferromagnet.
Super-lattice patterns in two-layered coupled non-symmetric reaction diffusion systems
Authors: Liu Fu-Cheng , Liu Ya-Hui , Zhou Zhi-Xiang , Guo Xue , Dong Meng-Fei ,   College of Physics Science and Technology, Hebei University, Baoding 071002, China
Published: December 2020

The coupling mechanism is one of most important approaches to generating multiple-scaled spatial-temporal patterns. In this paper, the mode interaction between two different Turing modes and the pattern forming mechanisms in the non-symmetric reaction diffusion system are numerically investigated by using a two-layered coupled model. This model is comprised of two different reaction diffusion models: the Brusselator model and the Lengyel-Epstein model. It is shown that the system gives rise to superlattice patterns if these two Turing modes satisfy the spatial resonance condition, otherwise the system yields simple patterns or superposition patterns. A suitable wave number ratio and the same symmetry are two necessary conditions for the spatial resonance of Turing modes. The eigenvalues of these two Turing modes can only vary in a certain range in order to make the two sub-system patterns have the same symmetry. Only when the long wave mode becomes the unstable mode, can it modulate the other Turing mode and result in the formation of spatiotemporal patterns with multiple scale. As the wave number ratio increases, the higher-order harmonics of the unstable mode appear, and the sub-system with short wave mode undergoes a transition from the black-eye pattern to the white-eye pattern, and finally to a temporally oscillatory hexagon pattern. It is demonstrated that the resonance between the Turing mode and its higher-order harmonics located in the wave instability region is the dominant mechanism of the formation of this oscillatory hexagon pattern. Moreover, it is found that the coupling strength not only determines the amplitudes of these patterns, but also affects their spatial structures. Two different types of white-eye patterns and a new super-hexagon pattern are obtained as the coupling strength increases. These results can conduce to understanding the complex spatial-temporal behaviors in the coupled reaction diffusion systems.
One-dimensional integrated simulations of magnetized liner inertial fusion
Authors: Zhao Hai-Long , Xiao Bo , Wang Gang-Hua , Wang Qiang , Zhang Zheng-Wei , Sun Qi-Zhi , Deng Jian-Jun ,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Magnetized liner inertial fusion (MagLIF) integrates the advantages of traditional magnetic confinement fusion with those of inertial confinement fusion, and thus has promising potentials because theoretically it can dramatically lower the difficulties in realizing the controlled fusion. For the systematic simulating of MagLIF, we build up an integrated one-dimensional (1D) model to describe the complex process, which includes the terms of magnetization, laser preheating, liner implosion, fusion reaction, end loss effect, and magnetic flux compression. According to this model we develop an integrated 1D code–MIST (magnetic implosion simulation tools) , and specifically we propose a simplified model to describe the end loss effect based on the flow bursting theory, so the code is able to consider two-dimensional effects within 1D calculations. We also present a specific expression of magnetic diffusion equation where the Nernst effect term is taken into consideration, which is very important if there exists a temperature gradient perpendicular to magnetic field lines. Such conditions are fully satisfied in the MagLIF process. We use experimental data of aluminum liner implosions to verify the magneto-hydrodynamic module of our code, those shots (0607 & 0523) are performed on FP-1 facility (2 MA, 7.2 μs), and results show good agreement with the calculated velocity of inner flyer or target surface and other measurements. Comparison with code LASNEX and HYDRA (used by Sandia Laboratory) is also made to assess the fusion module, and the results show that our calculations are physically self-consistent and roughly coincide with the results from LASNEX and HYDRA, a key difference appears at fuel temperature, and the factors that might cause this difference are discussed. With this integrated model and 1D code, our work would provide a powerful tool for the future experimental research of MagLIF.
Density functional theory calculation of spectrum and excitation properties of mer-Alq3
Authors: Peng Jie , Zhang Si-Jie , Wang Ke , Dove Martin ,   Sino-British Materials Research Institute, College of Physics, Sichuan University, Chengdu 610065, China
Published: December 2020

Meridional tris(8-hydroxyquinoline)aluminum (III) (mer-Alq3) is an organometallic semiconductor material with phenomenal photo-electric properties. In order to understand the molecular luminescence properties of mer-Alq3, the density functional theoretical (B3LYP) method with 6-31G* basis set is employed to calculate its structure, infrared spectrum and Raman spectrum and the frontier molecular orbital of its ground state. The UV-vis absorption and the excited state characteristics are investigated by the time-dependent density functional theory (TD-DFT) method. The results show that the calculated spectral characteristics are in good agreement with the experimental data. The electron cloud of the highest occupied molecular orbital (HOMO) is located mostly on the phenoxide ring, whereas that of the lowest unoccupied molecular orbital (LUMO) sits on the pyridine ring. The absorption peaks of the UV-visible absorption spectrum are located in the visible and ultraviolet region. S0→S2 is attributed to the superposition of the π-π* local excitation in the direction from benzene ring to pyridine ring and the n-π* local excitation in the direction from oxygen atom to pyridine ring. The π-π* local excitation from benzene ring to pyridine ring is S0→S4. The superposition of π-n local excitation from benzene to carbon and n-n local excitation from oxygen to carbon are excited by S0→S11. S0→S14 is charge-transfer excitation and contributed by the superposition of π-π* in the direction from benzene ring to pyridine ring and n-π* in the direction from oxygen atom to pyridine ring. This work is significant for understanding the basic properties of mer-Alq3 and the mechanisms of electron excitations. It provides a deeper insight into the luminescence mechanism of mer-Alq3, thus playing a guidance role in further improving the luminescence efficiency and regulating the spectral range of the light-emitting mer-Alq3.
Lattice Boltzmann method simulations of the immiscible Rayleigh-Taylor instability with high Reynolds numbers
Authors: Hu Xiao-Liang , Liang Hong , Wang Hui-Li ,   Department of Physics, Hanzhou Dianzi University, Hangzhou 310018, China,   School of Mathematics and Computer Science, Wuhan Textile University, Wuhan 430200, China
Published: December 2020

In this paper, an advanced phase-field lattice Boltzmann method based on the multiple-relaxation-time collision model is used to simulate the immiscible single-mode Rayleigh-Taylor instability with a moderate Atwoods number in a long tube, and we systematically analyze the effect of the Reynolds number on the interfacial dynamics and the late-time development stages of interface disturbance. The highest Reynolds number in the current simulation reaches up to 10000. The numerical results show that the Reynolds number significantly affects the development of the instability. For high Reynolds numbers, the instability undergoes a sequence of different growth stages, which include the linear growth, saturated velocity growth, reacceleration, and chaotic mixing stages. In the linear growth stage, the developments of the bubble and spike conform to the classical linear growth theory, and it is shown that the growth rate increases with the Reynolds number. In the second stage, the bubble and spike evolve with the constant velocities, and the numerical prediction for spike velocity is found to be slightly larger than the solution of the potential flow theory proposed by Goncharov [Phys. Rev. Lett. 2002 88  134502], which can be attributed to the formation of vortices in the proximity of the spike tip. In addition, it is found that increasing the Reynolds number reduces the bubble saturated velocity, which then is smaller than the solution of the potential model. The nonlinear evolutions of the bubble and spike induce the Kelvin–Helmholtz instability, producing many vortex structures with different scales. Due to the interactions among the vortices, the instability eventually enters into the chaotic mixing stage, where the interfaces undergo the roll-up at multiple layers, sharp deformation, and chaotic breakup, forming a very complicated topology structure. Furthermore, we also measured the bubble and spike accelerations and find that the dimensionless values fluctuates around the constants of 0.045 and 0.233, indicating a mean quadratic growth. And for low Reynolds numbers, the heavy fluid will fall down in the form of the spike, and the interface in the whole process becomes very smooth without the appearances of the roll-up and vortices. The late-time evolutional stages such as the reacceleration and chaotic mixing cannot also be observed.
Experiments and analytical solutions of light driven flow in nanofluid droplets
Authors: Liu Zhe , Wang Lei-Lei , Shi Peng-Peng , Cui Hai-Hang ,   School of Environment and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China,   School of Building Services Science and Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China,   Institute of Mechanics and Technology, Xi’an University of Architecture and Technology, Xi’an 710055, China,   School of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China
Published: December 2020

Adding nanoparticles with high light response characteristics to a light-transmitting fluid medium can form a light-driven nanofluid and achieve efficient use of light energy. This paper conducts the experimental observation and theoretical analysis of the light driven nanofluid flow behavior, which is the theoretical basis for achieving the precise control of optical drive nanofluid. To realize the efficient conversion of light energy into kinetic energy, here, the motion of Fe3O4 particles with a diameter of 300 nm in droplets induced by the Marangoni effect is studied under different light sources by using the particle image velocimetry (PIV). The experimental results show that when the number density of particles is higher than the critical value, the vertical vortices with symmetrical structure can be induced. At the bottom of the droplet, the particles move from the periphery to the center of droplet, and at the top of the droplet, the particles move from the center to the periphery of droplet. In addition, the frequency of light source and the number density of particles are the dominant factors in this process. Subsequently, for the light driven nanofluid experiment in this paper, the analytical solution of the flow field distribution is achieved by using the Stokes equation and the surface tension gradient boundary condition. The analytical solution of the flow field distribution obtained here is consistent with the experimental results, confirming the validity of the quantitative theory. Finally, the correlation between various driving modes, including surface tension at the top surface, surface pressure at the bottom surface or concentrated light radiation force in bulk phase, is discussed. This research provides theoretical support for the precise regulation of flow behavior and efficient conversion of light energy in the optical microfluidic system.
Tunable terahertz absorber with multi-defect combination embedded VO2 thin film structure
Authors: Chen Xu-Sheng , Li Jiu-Sheng ,   Centre for THz Research, China Jiliang University, Hangzhou 310018, China
Published: December 2020

The metamaterial absorber has the advantages of thin thickness, small size, simple structure and high absorption. As is different from the traditional metamaterial absorber, the adjustable material is used for designing the structure, which can realize the dynamic modulation of the device by changing the external factors without changing the device structure. In this paper, an adjustable terahertz absorber with multi-defect combination embedded VO2 thin film is proposed. It is composed of three layers: the upper metal pattern layer, the substrate and the bottom metal plate. Vanadium dioxide medium is sandwiched between the upper surface and the substrate. The absorption performance of the absorber composed of different defect combinations is studied, and the electric field distribution of each combination is analyzed. At the same time, the influences of defects on the absorption performance of the absorber are compared with each other and analyzed. After comprehensive analysis, the defects are combined into the final proposed structure, and the electric field distribution and surface current distribution are analyzed. The relevant parameters affecting the performance of the absorber are scanned and analyzed, and the final optimized structural parameters are obtained. The results show that the absorption rate at f = 4.08 THz and f = 4.33 THz are 99.8% and 99.9%, respectively. The phase transition of vanadium dioxide can be controlled by changing ambient temperature, so that the absorption rates of two frequency points can be changed from 99.8% to 1.0%. In addition, the surface normalized impedance of the proposed absorber is analyzed, which shows that the normalized surface impedance of the designed absorber matches the impedance of the free space well. By changing the incident angle and polarization of terahertz wave, the results show that the absorption rate of the absorber under TE and TM polarization wave both can be more than 98% with the incident angle ranging from 0° to 40°. The proposed terahertz wave absorber has the characteristics of high absorption, dynamic tuning and insensitive polarization. It has good application prospects in terahertz wave related fields such as detectors and stealth technology.
A channel thermal noise model of nanoscaled metal-oxide-semiconductor field-effect transistor
Authors: Zhang Meng , Yao Ruo-He , Liu Yu-Rong ,   School of Electronic and Information Engineering, South China University of Technology, Guangzhou 510641, China
Published: December 2020

With the development of the integrated circuit manufacturing process, the device dimensions have been on a nanoscale, while the device performance, such as the mobility and thermal noise, is significantly affected by the hot-carrier effect, which further affects the channel thermal noise of the device. However, the thermal noise model based on the existing electron temperature expression does not take into account the influence of the temperature gradient on the electron temperature when it deals with the influence of the hot carrier effect. As the size of the device decreases, the thermal noise model based on the existing electron temperature expression underestimates the influence of the hot carrier effect and the channel thermal noise cannot be accurately predicted with this expression.

In this paper, the expression of the channel transverse electric field is derived based on the channel potential equation and the boundary condition of the channel electric field. By combining the distribution of the temperature gradient and the expression of the transverse electric field, the energy balance equation is solved with considering the influence of the temperature gradient, and then the electron temperature expression is obtained. The electron temperature expression shows the distribution of the electron temperature along the channel. By utilizing the derived electron temperature expression and combining with the drain current expression, a channel thermal noise model is established. The hot carrier effect is taken into account in the thermal noise model by utilizing the proposed electron temperature expression. Meanwhile in calculating the thermal noise, the influence of the electron temperature on mobility degradation and the temperature gradient on thermal noise are also involved.

The results show that the temperature gradient has a significant influence on the electron temperature with the reduction of the device size, which further increases the influence of the hot carrier effect, resulting in the increase of the thermal noise caused by the hot carrier effect exceeding the decrease of the thermal noise caused by the mobility degradation, thus leading the thermal noise to increase. The influence of the hot carrier effect on the channel thermal noise also increases significantly with the bias increasing. The channel thermal noise model proposed in this paper can be applied to analyzing the noise performance and modeling the nano-sized MOSFET devices.
Linewidth compression of tunable Tm-doped fiber laser and its hyperspectral absorption application
Authors: Tao Meng-Meng , Tao Bo , Ye Jing-Feng , Shen Yan-Long , Huang Ke , Ye Xi-Sheng , Zhao Jun ,   State Key Laboratory of Laser Interaction with Matter, Northwest Institute of Nuclear Technology, Xi’an 710024, China,   Shanghai Key Laboratory of All Solid-State Laser and Applied Techniques, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Published: December 2020

Tunable diode laser absorption spectroscopy (TDLAS) is a widely used technology for measuring absorption spectrum. However, the measurement efficiency of TDLAS is greatly limited by the narrow tuning range of conventional tunable laser diode. Exploiting a wideband, narrow linewidth tuning laser source, hyperspectral absorption spectroscopy possesses the ability to provide the overall absorption information over a continuous waveband in a single scan, which would significantly improve the data volume and diagnostic capability of TDLAS. With profound and strong absorption lines of water and carbon dioxide, the 2 μm waveband is an ideal candidate for water and carbon dioxide related absorption spectrum. An absorption line recognition threshold of 0.07 nm is derived for the absorption spectrum measurement of water around 2 μm through theoretical analysis. Utilizing the wideband emission spectrum of Tm-doped fiber, a wideband tunable, narrow linewidth fiber laser operating at 2 μm is built by combining a tunable FP filter with a fiber saturable absorber. The tunable FP filter is responsible for the wavelength control of the laser system, with which a 60 nm wideband tuning range from 1840 nm to 1900 nm is achieved. With a section of Tm-Ho codoped fiber as the fiber saturable absorber which is used for linewidth compression, a static linewidth of 0.05 nm is attained. This wideband tunable, narrow linewidth fiber laser is tested for the hyperspectral absorption spectrum measurement of water around 2 μm. Drived with a 0–10 V triangle wave at a repetition rate of 50 Hz, the output spectrum of the laser spans over a wavelength range of about 30 nm from 1856 nm to 1886 nm. The laser beam propagates about 50 cm through an open air, and then enters into the detectors for direct measurement. The 35 absorption lines of water are recognized after processing the data. Within the 1870–1880 nm range, comparisons with the theoretical absorption spectra at different laser linewidths, derived from the HITRAN2012 absorption database, show that the measured data cannot effectively distinguish two absorption lines adjacent to the strong absorption line at 1873 nm and 1877 nm. And, the measured results can be best fitted to a laser linewidth of about 0.08 nm, demonstrating that in the dynamic scanning process, the linewidth of the laser is expanded beyond the absorption line recognition threshold. Thus, when operating in a fast wideband scanning mode, the laser system should further compress its linewidth.
Theoretical studies on the drive-response relationship for opinion particles in a bistable potential field
Authors: Wang Peng , Pan Feng-Chun , Guo Jing-Jing , Li Ting-Ting , Wang Xu-Ming ,   School of Physics and Electronic-Electrical Engineering, Ningxia University, Yinchuan 750021, China,   Ningxia Key Laboratory of Intelligent Sensing for Desert Information, Yinchuan 750021, China
Published: December 2020

From the perspective of physics, evolution of group opinion can be regarded as the collective effect of the state change of opinion particles. It is similar to a material particle system that there is usually a dynamic criticality in the opinion state transition of a group, and is dominated by a scaling law. To exhibit this phenomenon, a bistable potential field is introduced to mimic the opinion transition by the jump from one stable state to the other. In this investigation, we will focus on the state change of the opinion particles induced by the noise. The time correlation function and the relaxation time describing drive-response relationship are calculated, by using of the generalized Laguerre weight complete set of orthogonal functions method, to reveal the regularity and the relative mechanism governing the state change of the opinion particle confined by the bistable potential and affected by the noise. The results indicate that there is a critical value Dc for noise intensity. When the noise intensity is greater than Dc, the time correlation function will increase exponentially with correlation time τ. There also are two points at which the dependence of the relaxation time on the noise intensity/aspect ratio of the energy barrier are divergent. The divergence implies that the state transition of opinion particles cannot be achieved. It is worth noting that there is a linear relationship between the relaxation time and the aspect ratio of energy barrier. This relation means that there is a drive-response relationship for opinion particles in the bistable potential field just like the Newton’s second law, in which the time relaxation plays the role of quasi-inertia. This result also implies another important conclusion that the energy and information may be equated due to the fact that the opinion particle transiting from one stable state to the other needs obtaining energy to climb over the barrier, and from another point of view, the transition can be regarded as the opinion particle having been obtaining information via the noise correlation. These investigations may provide us with new understandings to the evolution of group opinion.