bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of quantum correlations in the Yang-Baxter spin-1/2 chain mode
Authors: Gou Li-Dan  , Wang Xiao-Qian  ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

Quantum correlations among different parts of a composite quantum system are the fundamental resource of several applications in quantum information. In general, quantum discord can measure quantum correlations. In that way, the quantum correlations in the Yang-Baxter spin-1/2 chain mode are investigated. In the second part of the paper, the Yang-Baxter spin-1/2 chain modes are constructed from the Yang-Baxter equation. First, we analyze the two matrix representations of Temperly-Lieb algebra. Second, the two solutions of the Yang-Baxter equation are generated using the Yang-Baxterization. Finally, we can change the usual two-particle spin-1/2 chain to the Yang-Baxter spin-1/2 chain modes by means of the unitary Yang-Baxter matrix-R. In the third part, the density matrices of the two chain modes are generated in the thermal equilibrium state in a canonical ensemble. According to the definition of the geometric measure of quantum discord, the analytical expressions of the geometric measure of quantum discord, in the temperature and the external magnetic field, are obtained for the Yang-Baxter spin-1/2 chain modes. When the temperature and the magnetic field intensity increase, the geometric measure of quantum discord decreases. Under the specific conditions, the result of the second chain mode is similar to that of the first one. Then we obtain the numerical results of quantum discord, the geometric measure of quantum discord, and concurrence. It is found that the concurrence can quickly decrease to the value of zero when the temperature is greater than the value of one. At the same time, quantum discord and the geometric measure of quantum discord are not of the value of zero. Thus the quantum discord and the geometric measure of quantum discord can go beyond the concept of entanglement and obtain the “quantumness” of the correlations between the two parts of a system for the Yang-Baxter spin-1/2 chain modes. They are very good quantum resources for quantum information and quantum computing.
Sliding mode control of fractional order chaotic system based on an online error correction adaptive SVR
Authors: Xue Kai-Jia  , Wang Cong-Qing  ,   College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Published: December 2020

In this paper, a sliding mode control based on an online error correction adaptive SVR is put forward for a class of fractional order chaotic system with nonlinear uncertainty. In order to solve the problem that the uncertainty of the fractional order chaotic system model is difficult to predict, so the nonlinear function of the system is estimated by the offline SVR and the state trace error is forecasted by using incremental learning adaptive online SVR. In addition, the adaptive parameter adjustment law is selected by using the Lyapunov stability theory. Result of simulation of the fractional order Arneodo system shows that the sliding mode control based on the online error correction adaptive SVR can stabilize the nonlinear uncertain fractional order chaotic system with external noise disturbance to an expected state within a limited time. At the same time, both the control performance and the prediction precision of the system's nonlinear function can be improved.
Adaptive fuzzy synchronization for uncertain fractional-order chaotic systems with unknown non-symmetrical control gain
Authors: Liu Heng  , Li Sheng-Gang  , Sun Ye-Guo  , Wang Hong-Xing  ,   College of Mathematics and Information Science, Shaanxi Normal Universtiy, Xi'an 710119, China;,   Department of Mathematics and Computational Science, Huainan Normal University, Huainan 232038, China
Published: December 2020

In this paper the synchronization problem for the uncertain fractional-order chaotic systems with unknown non-symmetrical control gain matrices is investigated by means of adaptive fuzzy control. Fuzzy logic systems are employed to approximate the unknown nonlinear functions. We decompose the control gain matrix into a positive definite matrix, a unity upper triangular matrix, and a diagonal matrix with diagonal entries +1 or -1. The positive matrix is used to construct the Lyapunov function; the diagonal matrix is employed to design the controller. Based on the fractional Lyapunov stability theorem, an adaptive fuzzy controller, which is accompanied by fractional adaptation laws, is established. The proposed methods can guarantee the boundedness of the involved signals as well as the asymptotical convergence of the synchronization errors. It should be pointed out that the methods for using quadratic Lyapunov function in the stability analysis of the fractional-order chaotic systems are developed in this paper. Based on the results of this paper, many control methods which are valid for integer-order nonlinear systems can be extended to control fractional-order nonlinear systems. Finally, the effectiveness of the proposed methods is shown by simulation studies.
Multivariate chaotic time series prediction using multiple kernel extreme learning machine
Authors: Wang Xin-Ying  , Han Min  ,   Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116023, China
Published: December 2020

Multivariate chaotic time series is widely present in nature, such as in economy, society, industry and other fields. Modeling and predicting multivariate time series will help human to better manage, control, and make decision. A prediction method based on multiple kernel extreme learning machine is proposed in this paper to model the complex dynamics of multivariate chaotic time series. First, the multivariate chaotic time series is reconstructed in phase space, transforming the temporal correlation into spatial correlation. Then, a prediction model-multiple kernel extreme learning machine, which combines the multiple kernel learning and extreme learning machine with kernels, is proposed to approximate the nonlinear function of the input - output data in phase space. The proposed multiple kernel extreme learning machine could effectively combine the simple training of extreme learning machine with kernels and the data fusion capabilities of multiple kernel learning. Simulation results based on Lorenz chaotic time series prediction and San Francisco monthly runoff prediction demonstrate that, compared with other state-of-art chaotic time series prediction methods, the proposed multiple kernel extreme learning machine could get a better prediction accuracy.
Outer synchronization analysis of two time-varying networks with double delays based on pinning control
Authors: Han Min  , Zhang Ya-Mei  , Zhang Meng  ,   Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116023, China
Published: December 2020

It is well known that time delay is universal in complex networks. However, in most existing researches outer synchronization is realized between two networks with time delay by adding controllers to all nodes which may bring great economic costs and increase the difficulties in control in practice. In this paper, in order to deal with the problem of outer synchronization between two time-varying coupling networks with node delay and coupling delay, an adaptive pinning control scheme is proposed. First, a more realistic drive-response complex network model is constructed by introducing double delays and asymmetric coupling configuration matrices. Then, we design an adaptive pinning controller which is easy to implement, and choose an effective pinning strategy to control a crucial part of the nodes in the response network. Based on LaSalle' invariance principle and the linear matrix inequality, we may rigorously prove that the outer synchronization between the proposed drive-response networks can be achieved, and meanwhile some sufficient conditions are derived by adopting an appropriate Lyapunov-Krasovskii energy function. Finally, numerical simulation experiments are employed to verify the correctness and the effectiveness of the proposed method. Results indicate that the drive-response networks with double delays can indeed achieve outer synchronization by pinning control. Moreover, the synchronization is independent of coupling delay. And the remarkable influences of coupling delays on the synchronization speed are also revealed.
Sub-Nyquist sampling and reconstruction of short pulses based on Gabor frames with exponential reproducing windows
Authors: Chen Peng  , Meng Chen  , Sun Lian-Feng  , Wang Cheng  , Yang Sen  ,   Department of Missile Engineering, Mechanical Engineering College, Shijiazhuang 050003, China;,   National Center for Nanoscience and Technology, Beijing 100190, China
Published: December 2020

Sampling and reconstruction of short pulses based on Gabor frames have been proved to be effective, which overcome the difficulties that finite rate of innovation (FRI) sampling is unable to reconstruct the pulse streams without the prior information of waveforms. However, the windows sequences of sampling scheme based on Gabor frames proposed at present show complicated structure and are hard to realize physically. The exponential reproducing windows are then introduced in this paper and the windows sequences can be simplified as a first-order analog Butterworth filter. At the same time, the compressed sensing (CS) measurement matrix is constructed for the recovery of Gabor coefficients. In order to satisfy the restricted isometry property (RIP) of the measurement matrices for perfect signal reconstruction, we select appropriate windows for support according to the energy accumulation property. A restricted condition is deduced for perfecting the signal reconstruction and the system robustness is analyzed. By numerical simulations the above analysis is verified. This novel scheme can be used to implement short pulses sampling and reconstruction in the field of instrumentation, condition monitoring, radar and the communication.
Numerical studies on a 0.14 THz coaxial surface wave oscillator with double-ring metamaterial slow wave structure
Authors: Guo Wei-Jie  , Chen Zai-Gao  , Cai Li-Bing  , Wang Guang-Qiang  , Cheng Guo-Xin  ,   School of Electronics and Information Engineering, Xi'an Jiao tong University, Xi'an 710049, China;,   Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

This paper presents a relativistic coaxial overmoded surface wave oscillator (SWO) working at the terahertz band in the double-ring metamaterial slow wave structure (SWS). A relativistic electron beam passes through the SWS between the inner and outer rings. A coaxial overmoded SWS made up of metal metamaterial is designed to generate the high-power terahertz wave by increasing the beam-wave interaction efficiency and enlarging the transverse size of the terahertz device. It consists of double rings periodically arrayed along the z-direction, and a coaxial conductor with a radius of 2.4 mm. By its dispersive relation the proposed device is studied, from which we choose the 0.14 THz as the operating frequency of the device. Then the parameters of the geometric structure and the electron beam are optimized; the transitional section for extracting the terahertz signal is designed of the largest propagation coefficient. Particle simulation code UNIPIC is employed to verify the initial expectation and potential advantages. When the beam voltage and current are increasing, the operating frequency of the device remains almost constant, and this is the typical characteristic of the SWO. Particle simulation results show that the coaxial inner conductor has a stable operating mode of double-ring metamaterial SWS and can increase the beam-wave interaction efficiency of the SWO at the terahertz band. For a guiding magnetic field of 2.0 T, with the electron beam of 600 kV and a current of 1.0 kA, a 0.141 THz wave output power of 316.8 MW is obtained.
Effect of Ohmic loss on coaxial surface wave oscillator in terahertz band
Authors: Chen Zai-Gao  , Wang Jian-Guo  , Wang Yue  , Zhang Dian-Hui  , Qiao Hai-Liang  ,   School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China;,   Northwest Institute of Nuclear Technology, P. O. Box 69-12, Xi'an 710024, China
Published: December 2020

When the working frequencies of vacuum electronic devices reach the terahertz frequency (0.1–10 THz), the Ohmic loss has a great impact on the vacuum electronic devices. To study the effect of the Ohmic loss on the working characteristic of the vacuum electronic devices in the terahertz band, this paper presents the boundary condition of surface impedance used in the 2.5-dimensional fully electromagnetic particle simulation code UNIPIC, which is verified by simulating the terahertz wave in the circular copper waveguide; the simulation result indicates that the code can correctly simulate the propagation of terahertz waves in the waveguide with an Ohmic loss. Then, the coaxial surface wave oscillators (SWO) with slow wave structures (SWS) made of different metals are numerically studied by using the above code, and the dependences of output power on the SWOs with different metal SWSs are analyzed. Numerical results show that the metal conductivity has a considerable effect on the output power of the device: When the conductance of the metal decreases, the quality factor of the device becomes smaller, the start-up time becomes longer, also the output power of the device decreases also. For the coaxial SWOs operating at 0.14 THz, the output powers from the copper and stainless steel SWSs are reduced by 13.4% and 63.9%, the start-up times of the devices are delayed by 0.4 ns and 15 ns, respectively. Meanwhile, the working frequencies of the devices with the SWSs made of different metals keep unchanged.
Observation of ambient CH4 variations using ground-based high resolution Fourier transform solar spectrometry
Authors: Tian Yuan  , Sun You-Wen  , Xie Pin-Hua  , Liu Cheng  , Liu Wen-Qing  , Liu Jian-Guo  , Li Ang  , Hu Ren-Zhi  , Wang Wei  , Zeng Yi  ,   Key Lab of Environmental Optics & Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China;,   College of Environmental Optics & Technology, University of Science and Technology of China, Hefei 230031, China
Published: December 2020

Concentration of CH4 in ambient atmosphere is quite low (～1.8 ppmv) and mixed well. So observation of CH4 variation with high precision has to rely on high-precision of inversion technique. This paper demonstrates the observation of CH4 variations using high resolution (0.02 cm-1) Fourier transform solar spectrometry, in which a high precision and large scale of retrieval algorithm is investigated. In the CH4VCD (vertical column density) retrieval, both a nonlinear least-square method and an iterative scheme are applied after the measured spectrum is modeled with various a-priori parameters. The XCH4 (column-averaged dry air mixing ratio) is calculated by using the O2 VCD derived from the 7885 cm-1 O2-A band. Fitting errors for both CH4 VCD and XCH4 are less than 1%, and most XCH4 retrievals are within the 4 variations are also investigated based on one typical daily observation. It shows that the daily CH4 VCD decreases with time and the variations of the XCH4 is within 0.02 ppmv.
Simulation of the experiments on thermal desorption spectroscopy of hydrogen isotope in tungsten with the framework of rate theory
Authors: Zou Da-Ren  , Jin Shuo  , Xu Ke  , Zhao Zhen-Hua  , Cheng Long  , Yuan Yue  ,   School of Physics & Nuclear Energy Engineering, Beihang University, Beijing 100191, China
Published: December 2020

Simulation of thermal desorption spectroscopy (TDS) of the hydrogen isotope-deuterium in tungsten has been investigated in this paper based on rate theory. Data are obtained using polycrystalline tungsten, which is under the irradiation of a plasma with an energy of 40 eV and a dose of 1× 1026 D/m2 at 520 K. By adjusting the trapping energy, trapping rate, and other parameters in the rate theory, we can obtain the TDS simulation spectrum, which coincides with the experimental results. It is found that there mainly exist three trapping states for deuterium in tungsten, whose trapping energies are 1.14, 1.40 and 1.70 eV, and the temperature peaks of them is 500, 600 and 730 K, respectively. These three trapping energies correspond to the energy for trapping the 3rd-5th hydrogen by vacancy (the zero point energy correction has been taken into account), the energy for trapping the 1st-2nd hydrogen by vacancy, and the energy for trapping the hydrogen by vacancy cluster, obtained from first-principle calculation, respectively. It is suggested that the vacancy and vacancy cluster are the main trapping objects for deuterium in tungsten, under the experimental condition mentioned above.
Molecular structure and spectrum of dibutyl phthalate in an external electric field
Authors: Du Jian-Bin  , Wu De-Qi  , Tang Yan-Lin  , Long Zheng-Wen  ,   College of Physics and Electrical Information, Langfang Normal University, Langfang 065000, China;,   Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China;,   Department of Physics, Guizhou University, Guiyang 550025, China
Published: December 2020

Dibutyl phthalate (DBP) is the main component of the plasticizers. In order to study the influence of an external electrical field on the molecular structure and spectra of DBP, the method B3LYP of the density functional theory (DFT) at 6-311++G(d, p) level has been used in this paper to calculate its geometrical parameters and infrared (IR) spectra, in the ground state of DBP molecule under different external electric fields (from 0 to 0.020 a.u.). On this basis, the UV-Vis absorption spectra of DBP are studied using the time-dependent density functional theory (TDDFT) in the same fundamental groups and compared with the ultraviolet(UV) absorption peak of the molecules measured by UNICO ultraviolet and visible spectrophotometer. The rule of variation of wavelength and oscillator strength of the first twenty-six excited states of a DBP molecule under the influence of the external electric fields are studied. Results show that the molecular geometric parameter is strongly dependent on the external field intensity, and the dipole moment of DBP is proved to be sharply increased, and the total energy first decreases with the increases of the external field intensity; the significant negative (“red”) and positive (“blue”) frequency shifts are observed, i.e., vibrational Stark effect (VSE) is shown obviously; the ultraviolet absorption peaks of the excited states of DBP show an observable red shift, and the oscillator strength decreases sharply with increasing field intensity.
Tunable terahertz photonic crystal structures containing graphene
Authors: Deng Xin-Hua  , Yuan Ji-Ren  , Liu Jiang-Tao  , Wang Tong-Biao  ,   School of Science, Nanchang University, Nanchang 330031, China;,   State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China
Published: December 2020

We introduce graphene into conventional photonic crystals to build new photonic crystal structures, and strictly derive the dispersion relations of the structures based on the electromagnetic boundary conditions and the Maxwell's equations required. The dispersion relations are different from that of the conventional photonic crystals, and the optical properties of the structures may also differ from that of the conventional photonic crystals because of the presence of graphene conductivity in the dispersion relations. By changing the Fermi energy of graphene, the conductivity of it can be changed, the dispersion relations adjusted, the energy band structure altered, and its light propagation manipulated as well. With increasing Fermi energy, the energy band can be transformed from the allowed bands to the prohibited bands and then transformed along the opposite direction to the allowed bands. Because the conductivity changes rapidly in low frequency range, while changes slowly in high frequency range, as the Fermi energy increases, the energy band in the low frequency region will move quickly to higher frequency region, and the energy band in the high frequency region moves slowly, leading to the band compression and mutual conversion between the allowed and the prohibited bands. The larger the Fermi energy, the more obvious the band compression, and the more easy the mutual conversion.
Qusia-random rectangular holes self-supporting transmission grating
Authors: Liu Yu-Wei  , Zhang Wen-Hai  , Zhang Ji-Cheng  , Fan Quan-Ping  , Wei Lai  , Yan Zhuo-Yang  , Zhao Yi-Dong  , Cui Ming-Qi  , Qiu Rong  , Cao Lei-Feng  ,   Joint Laboratory for Extreme Conditions Matter Properties, Southwest University of Science and Technology and Research Center of Lser Fusion, Mianyang 621900, China;,   Research Center of Laser Fusion, CAEP. P. O. Box 919-986, Mianyang 621900, China;,   Institute of High Energy Physics, the Academy of Sciences, Beijing 100049, China
Published: December 2020

Support-mesh structures of a self-supporting transmission grating may decrease the transmission area and diffraction efficiency, thus exert a ill effect on the original diffraction pattern of the grating and make it complicated to apply, especially in soft X-ray region. To solve this problem, we put forward a method to realize a kind of totally self-supporting transmission grating by arranging the rectangular transmission holes in a high Z foil quasi-randomly. Based on Fraunhofer's diffraction theory, we make a theoretical analysis on the diffraction pattern of this new kind of grating. We also calculate the diffraction pattern of this new kind of grating based on the Kirchhoff's diffraction theory. What's more, we fabricated a sample grating of 1000 lines/mm using focused ion beam (FIB) technology and then tested it on beam line 4B7B on the Beijing synchrotron radiation facility. Theatrical analysis and experimental result both proved that the diffraction of the transmission grating can get rid of the bad influence of the support-mesh structures by using this new designed method. Such a methodology can profit applications of this kind of X-ray dispersive element in a wide field.
Effect of medium on nanopowders prepared by Cu wire electrical explosion
Authors: Peng Chu-Cai  , Wang Jin-Xiang  , Liu Lin-Lin  ,   Science and Technology on Transient Physics Laboratory, Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

To analyze the influence of environmental media on nanopowders prepared by electrical explosion method, electrical explosion experiment is carried out using copper wire under water and different air pressures. Voltage and current waveforms are measured by Rogowski coil and high-voltage probe. The basic process of electrical explosion and the function of environmental media in the course of electrical explosion are analyzed by combined characters of the voltage, current, and energy deposition. The particle size of explosive products is analyzed by transmission electron microscopy. Results show that it is mainly after the vaporization stage of the copper wires that the medium may affect the formation of the products. Effects of the medium on the electric explosion of metal wires include the restriction of the medium on the expansion of the metal vapor, the influence of the medium ionization on breakdown of the copper surface as well as the cooling of the copper vapor and the plasma. For the water medium, the diameter of the products distributes in a wide range but is mainly in the range about 10 to 20 nm, while in the air medium, the average particle size is about 40 nm, basically ranging from 20 to 100 nm.
Granular structure and the nonequilibrium thermodynamics
Authors: Sun Qi-Cheng  ,   State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

Granular materials posses disorder structures which are the origin of dynamical heterogeneity. On the basis of non-equilibrium thermodynamics, the structure characteristics, complex deformations, and energy dissipations are analysed. Based on the photoelastic tests, the granular elasticity is discussed. The strain increments are classified into three categories. By means of the non-equilibrium thermodynamics, two granular temperatures, Tk, Tc, are introduced as the state variables, which denote the fluctuations of the kinetic energy and the elastic energy, respectively. Further, a two-granular-temperature thermodynamics (i.e. TGT theory) are developed for granular materials. The thermodynamic forces and fluxes are particularly analyzed. TGT theory is also compared with the previous internal variable thermodynamics for sands (IVT theory) developed a few decades ago. It is found that from TGT the Gibbs free energy in the IVT theory can be deduced, and the energy dissipation function can be apparently expressed from TGT theory.
Tuning the spin, chirality, and adsorption site of metal-phthalocyanine on Au(111) surface with hydrogen atoms
Authors: Xiao Wen-De  , Liu Li-Wei  , Yang Kai  , Zhang Li-Zhi  , Song Bo-Qun  , Du Shi-Xuan  , Gao Hong-Jun  ,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Metal-phthalocyanines (MPcs) and their derivates have attracted increasing interest in recent years, due to their potential applications in molecular electronics, spintronics, sensors, and so on. To this end, it is essential to tune the structural, electronic and spin properties of MPcs. Using the low-temperature scanning tunneling microscopy (LT-STM), we demonstrate that the spin, chirality and adsorption site of MnPc on Au(111) surface can be tuned by hydrogen atoms. STM experiments and density functional theory (DFT) calculations reveal that the preferential adsorption sites for the MnPc molecules may switch from the fcc regions to the hcp regions on the Au(111) surface after a hydrogen atom is adsorbed on top of the central Mn ion of each MnPc molecule. Moreover, the molecular spin decreases from S=3/2 to S=1 and the molecule-substrate coupling is weakened after the adsorption of a hydrogen atom on a MnPc molecule, leading to the quenching of Kondo effect at 4.2 K. However, the molecular spin and Kondo effect can be recovered by local voltage pulse or sample heating. Adsorption of three hydrogen atoms on a MnPc molecule not merely lowers the molecular symmetry from 4-to 2-fold, but also breaks down the mirror symmetry of the entire adsorbate complex (molecule and surface), thus rendering it to become chiral without any realignment at the surface. Dehydrogenation of the adsorbate by means of inelastic electron tunneling can also restore the mirror symmetry of the adsorbate complex. STM experiments as well as DFT calculations show that the chirality is actually imprinted into the molecular electronic system by the surface, i.e., the lowest unoccupied orbital is devoid of mirror symmetry. Our novel reversible spin and hand control scheme can be easily realized at single-molecule level, thus opening up a new avenue to broader applications based on the molecular electronic and spin states.
Theoretical study on the photophysical properties of the newly designed guanine analog y-guanine and its tautomers
Authors: Zhang Lai-Bin  , Ren Ting-Qi  ,   School of Physics and Engineering, Qufu Normal University, Qufu 273165, China;,   College of Electronic Communication and Physics, Shandong University of Science and Technology, Qingdao 266590, China
Published: December 2020

Recently, newly created unnatural fluorescent nucleobase analogs have gained increasing attention. In the present work, a comprehensive theoretical study on the structural, electronic, and excited-state properties of y-guanine (yG-t1) and its five possible tautomers (yG-t2, yG-t3, yG-t4, yG-t5 and yG-t6) is performed. Tautomerization analysis reveals that the canonical form of yG is not the most stable tautomer in the gas phase since it has three tautomers with the same stabilities. The spectroscopic properties are investigated: It is found that these tautomers have different absorption spectra, and so we can distinguish them by their spectroscopic signatures. In addition, effects of methanol solution and hydrogen bonding with cytosine on the absorption and emission spectra are examined. The methanol solution is found to red-shift both the absorption and emission maxima of the studied bases except for yG-t1, for which the absorption and emission maxima have blue-shifts after solvation. On the other hand, hydrogen bonding with cytosine is found to are blue-shifted both the absorption and emission maxima of yG-t1, yG-t2, yG-t5, and yG-t6. Theoretical predictions here are helpful for the investigation of the tautomerism of yG and the optical properties of yDNA.
Influences of electron-phonon interaction on the thermoelectric effect in a parallel double quantum dot system
Authors: Wu Hai-Na  , Sun Xue  , Gong Wei-Jiang  , Yi Guang-Yu  ,   College of Science, Northeastern University, Shenyang 110819, China
Published: December 2020

A quantum-dot system is a typical low-dimensional system, and previous researches showed that its thermoelectric conversion efficiency can be markedy improved due to its unique physical properties. In this poper, we choose the parallel double-quantum-dot structure and discuss the influence of the electron-phonon interaction on the thermoelectric-related parameters, i.e., the electric conductance, thermopower, the figure of merit, and thermal conductance, by using the nonequilibrium Green's function method. Our theoretical calculation results show that under the condition of low temperature, the occurrence of the Fano interference can assist to enhance the thermoelectric effect. When the electron-phonon interaction is taken into account, it can suppress the electric and thermal conductances to a certain extent because of its negative effect on the Fano interterence. However, we readily find that apparently the strengthening of the electron-phonon interaction cannot suppress the maximum of the thermopower. Instead, in some regions, the thermopower has an opportunity to enhance due to the appearance of a new channel caused by the electron-phonon interaction. Meanwhile, the figure of merit is found to cause similar effects to the thermopower. Therefore, in the case of low temperature, the electron-phonon interaction contributes little to the destruction of the thermoelectric effect, namely, it is not the necessary condition for the suppression of the thermoelectric effect. With the increase of temperature, the negative effect of the electron-phonon interaction on the Fano interference becomes relatively distinct, which inevitably weakens the thermoelectric effect. Results of this paper will help to clarify the influence of electron-phonon interaction on the thermoelectric effect.
Progress of surface plasmon research based on time-dependent density functional theory
Authors: Zhang Hong  , Yin Hai-Feng  , Zhang Kai-Biao  , Lin Jia-He  ,   College of Physical Science and Technology, Sichuan University, Chengdu 610065, China;,   Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610065, China
Published: December 2020

Localized surface plasmon (LSP) of nanoparticles has become one of the world's research hotspots due to its novel optical properties. Based on the time-dependent density functional theory (TDDFT), this paper studies the physical nature of plasmon excitation which is modulated in metal clusters and graphene nanostructures. Compared with the plasmon in the macroscopic material, the plasmon in nanostructures has some different properties due to the effects of the size and the dimensional confinement. In lower-energy resonance zone, the spectral band is greatly broadened, and the photoabsorption strength line splits. Because of the electromagnetic coupling between the nano-monomers, aggregated nanostructures exhibit different optical properties. For plasmon regulation and control, these results provide a solid theoretical guidance.
Surface morphology of F8BT films and interface structures and reactions of Al on F8BT films
Authors: Pan Xiao  , Ju Huan-Xin  , Feng Xue-Fei  , Fan Qi-Tang  , Wang Chia-Hsin  , Yang Yaw-Wen  , Zhu Jun-Fa  ,   National Synchrotron Radiation Labratory, University of Science and Technology of China, Hefei 230029, China;,   National Synchrotron Radiation Research Centre of Taiwan, Hsinchu 30076, China
Published: December 2020

The surface morphology and molecular orientation of -conjugated polymers, along with the chemical interaction and electronic structure at the interface between metals and these polymers, strongly affect the performance of the polymer-based organic electronic and optoelectronic devices. In this study, atomic force microscopy (AFM), synchrotron radiation photoemission spectroscopy (SRPES), and near edge X-ray absorption fine structure (NEXAFS) have been used to in situ investigate the morphology, structure, and molecular orientation of spin-coated poly(9,9-dioctylfluorene-co-benzothiodiazole) (F8BT) films and their interaction with the vapor-deposited Al metal. F8BT films were prepared by spin-coating the F8BT chloroform solution onto clean gold-coated silicon wafer surfaces. The room temperature spin-coated F8BT film is rather flat, while mild annealing treatments (120 ℃) below the glass transition temperature (Tg=130 ℃) lead to an apparent increase of surface roughness of F8BT film, which is helpful to effectively increase the contact areas between metals and F8BT. After 70 ℃ annealing in vacuum, the aromatic rings of F8BT preferentially stand more edge-on, making an average tilt angle of approximately 49 with the substrate, while the 9,9-dioctylfluorene unit (F8) and the benzothiodiazole unit (BT) nearly lie in the same plane. Upon vapor-depositing Al metal onto F8BT at room temperature, strong chemical interactions occur between Al and F8BT, as evidenced by the distinct changes of the S 2p, N 1s and C 1s spectra. Al reacts with S atoms more strongly than with N and C atoms in F8BT. In addition, obvious structural changes in valence band of F8BT are also observed during the Al deposition. Furthermore, Al dopes electrons into F8BT, leading to downward band bending, formation of interfacial dipole at the Al/F8BT interface, and partial occupation of lowest unoccupied molecular orbits (LUMO). However, no doping-induced gap states can be observed during the formation of Al/F8BT interface. Through the investigation of the core-level and valence band spectra evolution of F8BT together with the shifts of secondary electron cutoff during Al deposition, an energy level alignment diagram at the Al/F8BT interface is derived. The information gained through this study will help better understand the correlation between the interface structures of metal electrodes on semiconducting, -conjugated polymer materials and the performances of real polymer-based electronic and optoelectronic devices, which will in turn help develop the more efficient polymer-based organic devices.
Design and fabrication of a broadband metamaterial absorber based on a dielectric and magnetic hybrid substrate
Authors: Guo Fei  , Du Hong-Liang  , Qu Shao-Bo  , Xia Song  , Xu Zhuo  , Zhao Jian-Feng  , Zhang Hong-Mei  ,   College of Science, Air Force Engineering University, Xi'an 710051, China;,   Key Laboratory of Electronic Materials Research of Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

In this paper, a broadband metamaterial absorber is designed based on a hybrid substrate consisting of the dielectric and magnetic materials. The absorber is composed of the resistance film, dielectric layer, magnetic layer, and metal backboard. Numerical simulation of the absorbing properties is performed by means of the finite-difference time-domain method, and the bandwidth of the reflectivity below -10 dB is optimized by the genetic algorithm. Simulated results indicate that a bandwidth of reflectivity below -10 dB can be achieved over the frequency range from 7.8 to 18 GHz when the thickness of the absorber is only 2.5 mm. The proposed metamaterial absorber has many advantages, such as thin thickness, broadband, and polarization insensitivity. The operation mechanism of the absorber has also been analyzed and discussed within the model of equivalent circuit. In the end, an absorber sample is fabricated based on the design. It is found that the experimental result is well consistent with the design requirements.
Scanning tunneling microscopy study of in-plane graphene-hexagonal boron nitride heterostructures
Authors: Liu Meng-Xi  , Zhang Yan-Feng  , Liu Zhong-Fan  ,   Center for Nanochemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China;,   Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, China
Published: December 2020

In-plane heterostructure of hexagonal boron nitride and graphene (h-BN-G) has become a research focus of graphene due to its predicted fascinating properties such as bandgap opening and magnetism, which hence has ignited the attempt of experimentally growing such in-plane two-dimensional (2D) hybrid materials. Many previous researches demonstrated the synthesis of such heterostructures on Cu foils via chemical vapor deposition (CVD) process. The obtained 2D hybrid materials would offer a possibility for fabricating atomically thin electronic devices. However, many fundamental issues are still unclear, including the in-plane atomic continuity, the edge type, and the electronic properties at the boundary of hybridized h-BN and graphene domain. To clarify these issues, we report the syntheses of h-BN-G monolayer heterostructures on strongly coupled Rh(111) substrate and weakly coupled Ir(111) substrate via a two-step growth process in an ultrahigh vacuum (UHV) system, respectively. With the aid of scanning tunneling microscopy (STM), it is revealed that graphene and h-BN could be linked together seamlessly on an atomic scale at the linking boundaries. More importantly, we find that the atomically sharp zigzag-type boundaries dominate the patching interface between graphene and h-BN as demonstrated by atomic-scale STM images. To understand the physical origin of the atomic linking of the h-BN-G heterostructures, we also perform density functional theory (DFT) calculations, including geometry optimizations and binding energy calculations for different kinds of linking interfaces. The calculated results reconfirm that graphene prefers to grow on the h-BN domain edges and form zigzag linking boundaries. Besides the atomic structures on the linking interfaces, the electronic characteristics are also of particular importance. It is worth noting that the substrates coupled strongly with graphene by π-d orbital hybridization (such as Rh(111) and Ru(0001)), lead to downward shift of graphene π-bands away from the Fermi level, or decay of the intrinsic electronic structure of graphene. In this regard, the influence of h-BN on the electronic property of graphene is hard to identify on such h-BN-G heterostructures. The weakly coupled Ir(111) is chosen to be a perfect substrate to investigate the interface electronic properties of h-BN-G heterostructure due to the absence of substrate electronic doping effect. Scanning tunneling spectroscopy studies indicate that the graphene and h-BN tend to exhibit their own intrinsic electronic features near the linking boundaries on Ir(111). Therefore, the present work offers a deep insight into the h-BN-G boundary structures and the effect of adlayer-substrate coupling both geometrically and electronically.
Synthesis of SnO2 quantum dots/graphene composite and its photocatalytic performance
Authors: Ye Peng-Fei  , Chen Hai-Tao  , Bu Liang-Min  , Zhang Kun  , Han Jiu-Rong  ,   School of Physics Science and Technology, Yangzhou University, Yangzhou 225000, China
Published: December 2020

With SnCl4·5H2O and graphene oxide as raw materials and aqueous solution of ethanol as the solvent, we have prepared SnO2 quantum dots (diameter about 3-5 nm)/graphene nanocomposites using a facile hydrothermal method in one step, and solved the reunion of quantum dots successfully. The visible-light-driven photocatalytic efficiency of SnO2 quantum dots depends to a great extent on their dispersity. Because of the large-sized two-dimensional surface, the graphene sheet could behave as a solid support for quantum dots through interfacial interaction to avoid particle aggregation. Composites of SnO2 quantum dot/graphene show a great photocatalytic performance in visible light, and the morphology and structure of the product are characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared Spectrometer (FT-IR) and other techniques. The optical properties are investigated by using UV-visible (UV-vis) absorption spectrum. Additionally, the photocatalytic activity of the product is measured by the degradation of rhodamine-B dye solution in visible light. Results show that the preparation of samples with high catalytic activity in visible light, the shift in the optical response of composites may produce a positive effect on the improvement of photocatalytic efficiency in UV to visible spectral range Moreover, owing to its special π-conjugation structure, large specific surface area as well as high conductivity, graphene can enhance the photocatalytic activity. Compared with the pure SnO2, pure graphene catalytic performance is greatly improved in visible light, its excellent photocatalytic activity is due to the combination of strong absorption and effective separation of photogenerated carriers in the samples. Finally, the formation mechanism of the composite and its photocatalytic mechanism are studied.
Transmission characteristics and potential applications of plasmon-assisted parallel-plated waveguide
Authors: Sun Jie  , Yang Jian-Feng  , Yan Su  , Yang Jing-Jing  , Huang Ming  ,   Wireless Innovation Lab of Yunnan University, School of Information Science and Engineering, Kunming 650091, China;,   School of Information and Electronics, Beijing Institute of technology, Beijing 100081, China;,   Key Laboratory of Spectrum Sensing and Borderland Radio Safety of University in Yunnan Province, Kunming 650091, China
Published: December 2020

Flexible control of terahertz waves is now a research hotspot. Based on the electromagnetic theory the dispersion relation and field distributions in a plasmon-assisted parallel-plated waveguide are deduced. The transmission property of such a waveguide is obtained and confirmed by the full-wave simulation. Results show that the plasmon-assisted parallel-plated waveguide shows a band gap characteristic, and the cutoff frequency of the upper sideband is equal to the plasmon frequency; generally, the thinner the plasmon layer, the higher the cutoff frequency will be, and the narrower the bandwidth will become. Emergence of the band gap is due to the excited surface plasmon polaritons, and the coupling between surface plasmon and the medium in the waveguide. Besides, the influence of plasmon frequency and collision frequency on the transmission properties is investigated, and a method for adjusting the filter characteristic of the waveguide by tuning the plasmon frequency is proposed. Moreover, the plasmon layer is realized by a textured metallic structure, and a sensing model based on the parallel-plated waveguide is designed. Simulation results show that a 0.1 percent change in permittivity of the sample materials filling in the groove will give rise to a significant change of the cutoff frequency, which is 1.8 GHz in average; interestingly, different liquid samples such as nitrogen, gasoline, paraffin, glycerine and water can be identified through detecting the change of cutoff frequency, which further confirms the excellent terahertz sensing characteristic of the proposed sensor. This work may be helpful for the study of terahertz wave transmission, and may have potential applications in the design of terahertz devices.
Regularized seismic velocity inversion based on inverse scattering theory
Authors: Duan Xiao-Liang  , Wang Yi-Bo  , Yang Hui-Zhu  ,   School of Aerospace, Tsinghua University, Beijing 100084, China;,   Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Published: December 2020

In this paper, the regularized finite difference contrast source inversion algorithm based on inverse scattering theory is utilized to invert the seismic velocity distribution in the underground medium, and this algorithm is a waveform inversion method in frequency domain based on wave equation. Velocity distribution is updated iteratively by minimizing the cost function using the nonlinear conjugate gradient method. The geophysical inversion problem has the characters of ill-posedness and instability, we handle this problem by adding an additional regularization item based on total variation of inversion parameter, making the inversion problem become a well-posed problem, and the algorithm has the ability of anti-noise interference. In the inversion process we use the frequency-space domain 9-point difference propagation operator under PML absorption boundary condition. Compared with other inversion algorithm, the construction of forward modeling operator and other matrix factorization calculation process can be avoided in each iterative step because the background medium remains unchanged throughout the inversion process, this makes the algorithm more suitable for large-scale three-dimensional inversion. In addition, the MPI parallel computation is applied, by which the efficiency of inversion process is improved greatly. The two-dimensional CSEG model inversion results show that this algorithm can obtain high resolution seismic velocity reconstruction, and provide an accurate velocity information for seismic data processing and interpretation.
Spatiotemporal evolution model of vehicular movement Behavior under path constraints
Authors: Pan Deng  , Zheng Ying-Ping  ,   School of Electronic & Information Engineering, Tongji University, Shanghai 201804, China
Published: December 2020

The path of vehicle movement in a complex geographical environment has the 3D space feature, which is evidently the constraint for vehicular movement behaviors and cannot be described in one-dimensional or two-dimensional space. But the path of vehicle movement in a complex geographical environment can be abstracted into a space curve. By introducing theories in differential geometry, we can build a Serret-Frenet frame moving along this space curve with the geometric invariants of arc length, curvature, and torsion. And then, we can give a mathematical description to the dynamic behavior of the Serret-Frenet frame with the time-varying property at an arbitrary point of space curve. Finally, the spatiotemporal evolution model of the vehicle movement behaviors under the path constraint conditions is established and is rigidly proven in mathematics to be suitable for the longitudinal movement and uniform circular motion of a vehicle (in Serret-Frenet frame). It will lay the theoretical foundation for the future study of vehicular movement behaviors on the transport line in a complex geographical environment, including vehicular microscopic behaviors such as the vehicle following operation, lane changing, as well as the vehicular macroscopic behavior in traffic flows.