bluuebunny/crossref_metadata_2025 huggingface dataset:
The first-principle study on the formation energies of Be, Mg and Mn doped CuInO2
Authors: Mo Man , Zeng Ji-Shu , He Hao , Zhang Liang , Du Long , Fang Zhi-Jie ,   College of Science, Guangxi University of Science and Technology, Liuzhou 545006, China,   Materials Science and Engineering Research Center, Guangxi University of Science and Technology, Liuzhou 545006, China
Published: December 2020

Exploring new type of optoelectronic materials has fundamental scientific and practical significance in the development of society and economy. Recently, intense research has focused on the use of the wide band-gap bipolarity semiconductor material CuInO2 which will allow to the fabrication of that total transparent optoelectronic materials. However, the conductivity of CuInO2 is significantly lower than other n-type conductivity of other TCOs. As a result, one of the key question is how to improve the electric properties of CuInO2 by doping method. Motivated by this observation, in this paper, using the first-principles methods, the formation energetics properties of dopant (Be, Mg, Mn) in transparent conducting oxides CuInO2 were studied within the local-density approximation. Substituting dopant (Be, Mg, Mn) for In, substituting dopant (Be, Mg, Mn) for Cu and dopant as interstitial in their relevant charge state are considered. By systematically calculating formation energies and transition energy level of defect, the calculated results show that, substituting Mg for In does not induce the large structural relaxation. in CuInO2. One can expect that substituting the Mg and Mn for In introduces acceptor because the relative lower formation energies, furthermore, Be atoms would be substitute for In atoms when the Ef move to CBM. In addition, the donor-type extrinsic defects(such as substituting dopant for Cu and dopant as interstitial) have difficulty in inducing n-conductivity in CuInO2 because of their deep transition energy level or the higher formation energies. Considering the transition energy level position, BeIn, MgIn, and MnIn have transition energy levels at 0.06, 0.05, and 0.40 eV above the VBM, respectively. Thus, for all the acceptor-type extrinsic defects, substituting Mg for In is the most prominent doping acceptor with relative shallow transition energy levels in CuInO2 under O-rich condition. Based on our calculated results and discussion mentioned above, in order to increase p-type conductivity in CuInO2, we could substitute Mg atoms for In atoms by the sit-selective doping method through atomic layer epitaxy growth or controlling the oxygen partial pressure in the molecular beam epitaxy or metal-organic chemical vapor deposition crystal growth process. The calculation results will not only provide the guide for design of new type In-based optoelectronic materials, but will also further understand the potential properties in CuInO2.
Color image encryption method based on computer generated hologram and θ modulation
Authors: Xi Si-Xing , Yu Na-Na , Wang Xiao-Lei , Zhu Qiao-Fen , Dong Zhao , Wang Wei , Liu Xiu-Hong , Wang Hua-Ying ,   School of Science, Hebei University of Engineering, Handan 056038, China,   Institute of Modern Optics, Nankai University, Tianjin 300350, China
Published: December 2020

In this paper, a new method of encrypting a color image based on θ modulation is proposed by using the tricolor principle and computer-generated hologram (CGH) technology. The encryption process includes the θ-modulated three primary color components and the coding of computer-generated hologram, which is implemented in a Fresnel diffraction and spatial filtering system. Firstly, the color image modulated by the first random phase key is divided into three encryption channels by red laser, green laser, blue laser, and tricolor filters. Each channel is introduced by a transmissive amplitude-type sinusoidal grating with different directions, which is used to separate the three primary color components in the spatial spectrum plane. Secondly, the modulation results of tricolor components are superimposed together to form a compound image, and the phase truncation of the superposition result is performed to achieve the asymmetric encryption. Finally, the amplitude of the compound image is modulated by the second random phase key and is encoded into a binary real-value gray-color CGH by Roman-type coding method. Therefore, the gray-color information of the original image is completely hidden in the encrypted CGH, which is more general and deceptive in the storage and transmission process. Decryption is an inverse process of the encryption. Firstly, the encrypted CGH is placed on the input plane of the spatial filtering and Fresnel diffraction system. Secondly, the demodulation of CGH phase key and the spatial filtering based on optical filter are performed. Finally, the color plaintext image is obtained by using the correct Fresnel diffraction. The simulation results show the validity and feasibility of the proposed method. In addition, the anti-noise attack and anti-shearing attack performance of this color image encryption method are investigated. Compared with results from the three presented methods reported in the literature, our investigated results demonstrate that this method has good robustness to noise attack and shearing attack, and has obvious advantages when the attack noise density is larger. Due to the characteristics of high security and anti-noise, we believe that this color image encryption method promises to have important applications in the information transmission and multi-user authentication.
First principle study of occupancy, bonding characteristics and alloying effect of Zr, Nb, V in bulk α-Fe(C)
Authors: Liu Fei , Wen Zhi-Peng ,   Department of Mechanical Engineering, Zhonghuan Information College, Tianjin University of Technology, Tianjin 300380, China,   Pushi Intelligent Technology Co., Ltd, Yibin 644000, China
Published: December 2020

The volume change rate, total energy, binding characteristics, state density, charge distribution number and mechanical properties of cells formed by solid solution of Zr, Nb and V in α-Fe(C) are calculated by using the first-principles method. Thus, the effect of Zr, Nb, V on α-Fe(C) are studied in this paper. The results show that V displaces Fe atoms which is at the apex angle of α-Fe (C) cells preferentially, while Zr and Nb displace Fe atoms at the body center of α-Fe(C) cells. Zr and Nb reduce the stability of ferrite, but Zr is more difficult to solidly solubilize in α-Fe(C) than Nb. Solid solution of V increases the binding energy of crystal cells, meanwhile the toughness of crystal cell is mainly improved. After solid is solubilized in ferrite, Zr and Nb atoms only form metal bonds with Fe atoms while V and Fe atoms form the metal bonds and Fe—V ionic bonds. The ionic bonds of Fe—V are stronger than metal bonds of Zr and Nb atoms with Fe atoms, which is the main factor of the cell increasing. Zr and Nb mainly improve the mechanical properties of steel material by means of dispersion strengthening. To some extent, V solid solution can improve the toughness of ferrite, which is the main reason for improving the mechanical properties.
All-optical broadcast ultra-wideband signal source based on semiconductor fiber ring laser
Authors: Zhao Zan-Shan , Li Pei-Li ,   Nanhai Research Station, Institute of Acoustics, Chinese Academy of Sciences, Haikou 570100, China,   College of Electronic and Optical Engineering and College of Microelectronics, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
Published: December 2020

A novel scheme for all-optical ultra-wideband signal source based on semiconductor fiber ring laser (SFRL) is proposed, in which three monocycle signals can be generated simultaneously. The effect of the bias current of the semiconductor optical amplifier (SOA) in the SFRL, the wavelength of the lasing light, the power and the wavelength of input signal light on the performance of the monocycle signals are analyzed through numerical simulation. The results show that the output monocycle pulses with better symmetry can be obtained when the bias current of SOA is in a range of 200−220 mA. The average power, the amplitude of the positive and negative pulses of the output monocycle pulses increase as the wavelength of the lasing light increases. A better performance of the monocycle pulses can be obtained under lower input signal optical power. The wavelength of the input signal light has a little effect on the output monocycle pulses.
Terahertz frequency coding metasurface
Authors: Li Shao-He , Li Jiu-Sheng , Sun Jian-Zhong ,   China Jiliang University, Centre for THz Research, Hangzhou 310018, China
Published: December 2020

Metasurface is an artificial structure composed of sub-wavelength units which can realize the arbitrary control of electromagnetic wave energy by coding and arranging metasurface. Unlike the previous coding metasurface with a fixed phase difference of the neighbor coding unit cells, the frequency coding metasurface possesses the main feature that it has the linear change phase difference and different phase sensitivities in the whole working frequency band of the digital unit cells. And it can flexibly control the reflected terahertz waves to the numerous directions by changing the working frequency without redesigning the coding metasurface structure. In this paper, the frequency coding metasurfaces are designed by using four herringbone unit cells with the same shape and different sizes. They have the same phase response at the initial frequency and the different phase sensitivities throughout the frequency band. To describe the frequency coding characteristics of the unit cells, the digital numbers "0" and "1" are used to represent the low phase sensitivity and high phase sensitivity, respectively. Using the frequency digital coding, it can control the electromagnetic wave energy radiations by a single digital coding metasurface without changing the spatial coding pattern. By the combination of the spatial coding and frequency coding, It can manipulate the electromagnetic wave energy radiations more flexibly. We demonstrate 1-bit, 2-bit periodic frequency coding metasurfaces and 2-bit non-periodic frequency coding metasurface. They are all designed in the pre-designed coding sequence to control the electromagnetic wave energy radiations. Numerically simulated results confirm that the frequency coding metasurface can flexibly control the reflected terahertz waves to the numerous directions by changing the working frequency without redesigning the coding metasurface structure. Additionally, the number of the backward diffusion-like scattering beam increases with the change of frequency for the 2-bit random terahertz frequency coding metasurface. It has a good dispersion effect on the main lobe energy of terahertz wave radiation. The radar cross section can be reduced effectively, and the maximum value of radar cross section reduction can reach 29 dB in the direction of θ = 0, φ = 0. It has a great application value in the terahertz wave cloaking.
Integer quantum Hall effect in a spin-orbital coupling system
Authors: Liang Tao , Li Ming ,   Key Laboratory of Quantum Engineering and Quantum Materials of Guangdong Province, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006, China
Published: December 2020

Electron transport mechanism of a two-dimensional infinite slab subjected to Rashba spin-orbital coupling is studied in this paper. We calculate the Hall conductance and the longitudinal resistance of the integer quantum Hall effect (IQHE). In a strong magnetic field, the Landau levels of electrons increase rapidly at large wave vectors due to the constraint of the two edges of the sample while they remain flat at small wave vectors. Although the Zeeman effect can split the energy levels of spin degeneracy under a strong magnetic field, the spacing between the Landau levels is exactly equal to the spin splitting, thus the spin degeneracies have not been fully resolved. The spin-orbital coupling fully resolves the spin degeneracies of the energy levels. This is the key to reproducing the IQHE. Electrons with rapid increasing energies are localized at the two edges of the sample and transport along the edges to form separated currents with opposite directions. In this case, back scattering of electrons is prohibited due to the localization of these two branches. Since the electrons on the upper and lower edges originate respectively from the left and right electrode, they also have the chemical potentials of the electrons in those electrodes, respectively. The computation result shows that the Hall conductance appears as plateaus at integer times of e2/h. Temperature influences the accuracy of the Hall plateaus. As an international resistance standard, exceeding a critical temperature can produce significant errors to the Hall plateaus. Below the critical temperature, the accuracy can reach 10–9. Finally the mechanism of the longitudinal resistance of the IQHE is discussed and computed numerically. It is shown that only the wave-functions with opposite and small wave vectors have a significant overlap in the bulk of the sample and thus contribute to the longitudinal resistance. Due to the separation of currents in different directions in space, the longitudinal resistance does vanish at the Hall plateaus but it appears when the Hall conductance jumps from one plateau to another one.
Shaping self-accelerating Bessel-like optical beams along arbitrary trajectories by magnetic fluid deformable mirror
Authors: Wei Xiang , Wu Zhi-Zheng , Cao Zhan , Wang Yuan-Yuan , Dziki Mbemba ,   Department of Precision Mechanical Engineering, Shanghai University, Shanghai 200072, China
Published: December 2020

 With the development of laser technology, the application scope of nondiffracting beams, such as Bessel beams, Mathieu beams, cosine beams, and parabolic beams, which remain invariant along their propagation, continues to expand. During its propagation, the main lobes of these beams tend to bend towards off-axis position, which is called self-accelerating (or self-bending) property. A Bessel-like beam with self-acceleration can realize the propagation of the main lobe along a curved trajectory while maintaining the non-diffraction. Because of the above property, Bessel-like beams have been utilized in various areas such as guiding particles along arbitrarily curved trajectories, self-accelerating beams in nonlinear medium, plasma guidance, and laser-assisted guiding of electric discharges around objects.

 In this paper, we propose a method of bending the trajectory of Bessel-like beams by using a magnetic fluid deformable mirror (MFDM) instead of traditional spatial light modulator (SLM) and Pancharatnam-Berry (PB) phase manipulation. The MFDM provides a method without pixelation, where all parameters can be rapidly modified for fine-tuning. Furthermore, compared with the conventional deformable mirror, the MFDM has the advantages of a continuous and smooth mirror surface, large shape deformation, low manufacture cost, easy extension, and large inter-actuator stroke. Therefore, it is easy for the MFDM to generate the ideal shape of an axicon. Firstly, according to geometric analysis, the asymmetrical mirror profile to produce a self-accelerating Bessel-like optical beam is proposed. The proposed mirror profile can be used to compensate for the difference in optical path length for each annular slice of the axicon. If a collimated Gaussian beam is incident on the mirror combining the axicon and the asymmetrical mirror profiles, which can obtain Bessel-like beams with arbitrarily curved trajectories. Secondly, the resultant of the self-accelerating Bessel-like beams along parabolic trajectories is validated by the simulation in MATLAB. Finally, a prototype of MFDM consisting of the dual-layer arrays of miniature electromagnetic coils, a Maxwell coil and the magnetic fluid filled in a circular container is fabricated for the experiment. The experimental results show that the Bessel-like beams propagate along the parabolic trajectories, with the MFDM used, and the accuracy of the curved trajectories is verified. The proposed method in this paper opens a new experimental way to the study of Bessel-like beam; the theoretical approach can also be generalized mathematically for other non-paraxial beam propagation.
Node importance based on the weighted K-order propagation number algorithm
Authors: Huang Li-Ya , Tang Ping-Chuan , Huo You-Liang , Zheng Yi , Cheng Xie-Feng ,   College of Electronic and Optical Engineering, College of Microelectronics, Nanjing University of Posts and Telecommunications, Nanjing 210023, China,   National and Local Joint Engineering Laboratory of RF Integration and Micro-Assembly Technology, Nanjing 210003, China
Published: December 2020

The measurement of node importance is significant for analyzing a network structure. To comprehensively reflect the global and local network features, in this paper we abstract the propagating process of epidemic diseases based on the network topology structure, and then respectively sets each node as an infection source. After a certain dissemination time K, the number of infected nodes in the network is defined as the K-order propagation number, and the weighted sum of K-order propagation numbers under different values of K is taken as the important index of nodes. The simulation experiments of Watts-Strogatz small-world networks and a dolphin network show that the weighted K-order propagation number algorithm is more effective than the traditional method in evaluating the importance of nodes. For the Watts-Strogatz small-world networks, it can reflect the influence of long-distance connections on information transmission in detail. For the dolphin network, the weighted K-order propagation number algorithm significantly raises the profile of those nodes which play a key role in the information communication between different dolphin communities. In addition, in this paper we use a deliberate attacking method to analyze the western power grid of the United States, the road transportation network of the Chicago region, the co-authorship network in network science and the axonal tracts’ network between neurons of mouse. According to the specific order of the node importance from high to low, network nodes are attacked in turn, that is, all edges of the attacked nodes are removed. The analysis results of network parameters such as the network efficiency and the node number of the maximum sub-graph changing with the attacking times show that comparing with other evaluation indices of node importance such as degree, Ren method, Chen method, eigenvector method, Katz index, PageRank, CI method and K-shell, the weighted K-order propagation number algorithm focuses much on destroying the major structure, and all of the above four networks will break down if only a small number of important nodes are attacked. For example, after attacking only 100 nodes, the network efficiency of the western power grid of the United States is down by 90%, and after attacking 200 nodes, the network scale of the maximum sub-graph is nearly 3% of the original network.
A method of accurately determining temperature of cold atomic cloud in atomic fountain
Authors: Shi Jun-Ru , Wang Xin-Liang , Guan Yong , Ruan Jun , Liu Dan-Dan , Bai Yang , Yang Fan , Zhang Hui , Yu Feng-Xiang , Fan Si-Chen , Zhang Shou-Gang ,   National Time Service Center, Chinese Academy of Sciences, Xi’an 710600, China,   Key Laboratory of Time and Frequency Primary Standards, Chinese Academy of Sciences, Xi’an 710600, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

 The Gaussian radius and temperature of cold atomic cloud are important parameters in describing the state of cold atoms. The precise measuring of these two parameters is of great significance for studying the cold atoms. In this paper, we propose a new method named knife-edge to measure the Gaussian radius and temperature of the cold atomic cloud.

 A near-resonant and supersaturated laser beam, whose size is controlled by a knife-edge aperture, is used to push away the cold atoms in the free falling process of cold atomic cloud. By detecting the intensity of fluorescence signal, the numbers of residual atoms under different-sized near-resonant beams can be obtained. According to the characteristic of cold atoms′ distribution, we construct a theoretical model to derive the Gaussian radius of cold atomic cloud from the recorded residual atom number and near-resonant beam size. Since the Gaussian radius and temperature of cold atomic cloud are associated with each other, we can finally obtain the temperature of cold atomic cloud through the recorded residual atom number and beam size.

 By using this method, we successfully measure the Gaussian radii of cold atomic cloud at the heights of 10 mm and 160 mm below the center of 3D-MOT (three dimensional magneto-optical trap) to be (1.54 ± 0.05) mm and (3.29 ± 0.08) mm, respectively. The corresponding temperature of cold atomic cloud is calculated to be (7.50 ± 0.49) μK, which is well consistent with the experimental result obtained by using the time-of-flight method under the same condition. This experiment is conducted on the platform of Cesium atomic fountain clock of National Time Service Center, China.
First-principles study of lattice dynamical and thermodynamic properties of Li2NH
Authors: Zhao Yu-Na , Cong Hong-Lu , Cheng Shuang , Yu Na , Gao Tao , Ma Jun-Gang ,   BeiJing JiaoTong University HaiBin College, Huanghua 061199, China,   Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China
Published: December 2020

One of the key issues for scale applications of hydrogen energy is the availability of safe, efficient and ecnomicical hydrogen storage technologies. In the past few years, light metal hydrides have attracted considerable attention due to their high hydrogen capacity. With a hydrogen capacity up to ~6.5 wt%, Li2NH is regarded as one of the most promising hydrogen storage materials. Although the hydrogen physical and thermodynamic properties of Li2NH have been studied, the electronic structure, phonon vibration mode and thermodynamic properties of Li2NH have not yet been resolved. In this paper, by using the first principles based on the density functional theory (DFT), we investigate the electronic structure, lattice dynamical and thermodynamic properties of Li2NH in detail.

Firstly, the structure of Li2NH is optimized and the lattice parameters and total energy of the crystals are calculated. As shown by the calculation results, the lattice parameters are in good agreement with previous theoretical and experimental results. Our lowest-energy structure of Li2NH has orthorhombic Pnma symmetry at T=0 K for all of the proposed structures. Secondly, the electronic band-structure studies reveal that Li2NH has a small band gap of about 2.0 eV. The analysis of total and partial density of states of Li2NH show that the bonding between the N and H has a covalent character. Thirdly, the lattice dynamical properties of Li2NH are investgated at the corresponding equilibrium states. These results show that only the phonon dispersion curves of Li2NH (Pnma) without negative frequencies are calculated along the high-symmetry points. The optical modes of phonon frequencies at Γ point are assigned as Raman and Infrared-active modes. Based on the calculated phonon density of states, the thermodynamic properties are computed, such as the Helmholtz free energy, internal energy, entropy and the constant-volume specific heat versus temperature. The calculation results may explore the applications in areas of hydrogen storage for Li-N-H, which is of great importance forusing hydrogen in the future.
One-dimensional spin-orbit coupling Bose gases with harmonic trapping
Authors: Li Zhi-Qiang , Wang Yue-Ming ,   Institute of Theoretical Physics, Shanxi University, Taiyuan 030006, China,   School of Physics and Electronic Engineer, Shanxi University, Taiyuan 030006, China,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Rabi model is a popular model in quantum optics and describes a two-level system coupling to a quantum resonator. The fruitful physics appears when the coupling strength is comparable to the frequency of the resonator. We investigate the Bose gases of Raman induced spin-orbit coupling with an external harmonic trapping. Using the displacement Fock state in quantum optics we seek for an approximate ground state. We find the superposition state of left and right displaced oscillator state with odd parity has lower energy than the displaced state itself. Besides, we study the time evolution of both the momentum and the position of the system at single particle level to demonstrate the Zitterbewegung oscillating characteristics, which present an intuitive physical picture and are in qualitative agreement with the relevant experimental results. The results are useful to study the Rabi model in deep-strong coupling regime, the model that is difficult to realize in today’s experiment based on the high controllability property of laser, and these results are also instructive for the cold atom physics field.
Quantitative analysis of Cu and Pb in Coptidis by reheated double pulse laser induced breakdown spectroscopy
Authors: Zheng Pei-Chao , Li Xiao-Juan , Wang Jin-Mei , Zheng Shuang , Zhao Huai-Dong ,   College of Optoelectronic Engineering, Chongqing University of Posts and Telecommunications, Chongqing Municipal Level Key Laboratory of Photoelectric Information Sensing and Transmission Technology, Chongqing 400065, China
Published: December 2020

Coptidis plays an important role in the field of traditional Chinese medicine. However, it is easily polluted by heavy metals in environment (water and soil), and thus can affect human health. In order to detect the heavy metal elements Cu and Pb in Coptidis, which was purchased from the Chinese herbal medicine market in Chongqing, the reheated double-pulse laser-induced breakdown spectroscopy (RDP-LIBS) is investigated. In order to reduce the experimental error caused by the irregular shape, it is necessary to pretreat the Coptidis samples prior to the determination step. The Coptidis samples are dried, milled, and sieved to form thin cylindrical tablets each with a diameter of 13 mm and thickness of 2 mm, which are formed under a mechanical press of 10 MPa for 2 min. The influences of the main experimental parameters, such as double-pulse LIBS detection delay, double-pulse LIBS laser energy, and double-pulse LIBS pulse interval are optimized. According to the LIBS signal intensity and signal-to-background ratio, the optimal laser energy set of the characteristic line Cu I (324.46 nm) covers E1 = 15 mJ and E2 = 35 mJ, and the pulse interval and detection delay time are 1.4 μs and 1.5 μs respectively; the laser energy set of Pb I (405.78 nm) also covers E1 = 15 mJ and E2 = 35 mJ, and the pulse interval and detection delay time are 1.6 μs and 1.7 μs, respectively. Comparing with the scenarios of single-pulse laser-induced breakdown spectroscopy, it can be seen that the spectral intensity of Cu I (324.46 nm) increases from 5779 counts to 12749 counts, i.e. it increases about 2.2 times; the spectral intensity of Pb I (405.78 nm) characteristic line increases from 4703 counts to 15838 counts, i.e. it increases about 3.3 times. It is shown that the second laser pulse re-excites the plasma which is generated by the first laser pulse, thus making the plasma emission spectrum stronger. The detection performances of heavy metal elements in Chinese medicinal materials are evaluated by RDP-LIBS and SP-LIBS. The results show that the detection limit of Cu decreases from 5.13 mg/kg to 1.91 mg/kg, and the detection limit of Pb decreases from 10.87 mg/kg to 3.03 mg/kg. There was observed a noticeable difference in the limit of detection between Cu and Pb, which meets the requirements of the Green Industry Standard for Import and Export of Medicinal Plants. Moreover, the linear curve fitting degree of RDP-LIBS is higher than that of SP-LIBS, which indicates that the RDP-LIBS technology has better detection performance in Chinese herbal medicine.
Dynamic reconstruction of chaotic system based on exponential weighted online sequential extreme learning machine with kernel
Authors: Li Jun , Hou Xin-Yan ,   School of Automation and Electrical Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China.
Published: December 2020

For the dynamic reconstruction of the chaotic dynamical system, a method of identifying an exponential weighted online sequential extreme learning machine with kernel(EW-KOSELM) is proposed. The kernel recursive least square (KRLS) algorithm is directly extended to an online sequential ELM framework, and weakens the effect of old data by introducing a forgetting factor. Meanwhile, the proposed algorithm can deal with the ever-increasing computational difficulties inherent in online kernel learning algorithms based on the ‘fixed-budget’ memory technique. The employed EW-KOSELM identification method is firstly applied to the numerical example of Duffing-Ueda oscillator for chaotic dynamical system based on simulated data, the qualitative and quantitative analysis for various validation tests of the dynamical properties of the original system as well as the identification model are carried out. A set of qualitative validation criteria is implemented by comparing chaotic attractors i.e. embedding trajectories, computing the corresponding Poincare mapping, plotting the bifurcation diagram, and plotting the steady-state trajectory i.e. the limit cycle between the original system and the identification model. Simultaneously, the quantitative validation criterion which includes computing the largest positive Lyapunov exponent and the correlation dimension of the chaotic attractors is also calculated to measure the closeness i.e. the approximation error between the original system and the identification model. The employed method is further applied to a practical implementation example of Chua's circuit based on the experimental data which are generated by sampling and recording the measured voltage across a capacitor, the inductor current from the double-scroll attractor, the measured voltage across a capacitor from the Chua's spiral attractor and an experimental time series from a chaotic circuit. The digital filtering technique is then used as a preprocessing approach, on the basis of wavelet denoising the measured data with lower signal-noise ratio (SNR) which can produce the double-scroll attractor or the spiral attractor, the reconstruction attractor of the identification model is compared with the reconstruction attractor from the experimental data for original system. The above experimental results confirm that the EW-FB-KOSELM identification method has a better performance of dynamic reconstruction, which can produce an accurate nonlinear model of process exhibiting chaotic dynamics. The identification model is dynamically equivalent or system approximation to the original system.
Discriminative sparsity graph embedding based on histogram of rotated princial orientation gradients
Authors: Tong Ying , Shen Yue-Hong , Wei Yi-Min ,   College of Communication Engineering, The Army Engineering University of PLA, Nanjing 210007, China,   School of Information and Communication Engineering, Nanjing Institute of Technology, Nanjing 211167, China
Published: December 2020

The unconstrained face images collected in the real environments include many complicated and changeable interference factors, and sparsity preserving projections (SPP) cannot well obtain the low-dimensional intrinsic structure embedded in the high-dimensional samples, which is important for subsequent sparse representation classifier (SRC). To deal with this problem, in this paper we propose a new method named discriminative sparsity graph embedding based on histogram of rotated principal orientation gradients (DSGE-HRPOG). Firstly, it extracts multi-scale and multi-directional gradient features of unconstrained face images by HRPOG feature descriptor and incorporates them into a discriminative feature dictionary of sparse representation classifier. Secondly, it seeks an optimal subspace of HRPOG feature dictionary in which the atoms in intra-classes are as compact as possible, while the atoms in inter-classes are as separable as possible by adopting the proposed DSGE dimensionality reduction method. Finally, an optimal algorithm is presented in which the low-dimensional projection and the sparse graph construction are iteratively updated, and the accuracy of unconstrained face recognition is further improved. Extensive experimental results on AR, Extended Yale B, LFW and PubFig databases demonstrate the effectiveness of our proposed method.
Simulations of Ti nanoparticles upon heating and cooling on an atomic scale
Authors: Wang Ya-Ming , Liu Yong-Li , Zhang Lin ,   Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110819, China,   School of Material Science and Engineering, Northeastern University, Shenyang 110819, China
Published: December 2020

Titanium (Ti) has many advantages including high specific strength, low density, and biocompatibility, and is an excellent option for biomedical implant applications. Traditionally manufacturing processes have great difficulties in processing the hexagonal α-Ti with complex geometries, which would be transformed into the BCC β-Ti at high temperatures. Additive manufacturing (AM) or metal three-dimensional(3D) printing has made it possible to accurately fabricate Ti products with complex morphology. As nanoparticles have been used in the AM processing, an interesting issue arises naturally to understand packing changes of Ti particles with nanometer size during heating and cooling. The information provides the possibility in understanding the processing-structure-property-performance relations in the AM processes with the intent of producing the desirable microstructural features, and thus achieving the mechanical properties comparable or even superior to the conventionally manufactured parts. Because of lacking appropriate experimental techniques, computational approach becomes a good option to obtain various static and dynamic properties of metals reliably, in bulk or surface configurations. On a nanoscale, as the number of atoms in one particle increases, the computational cost increases exponentially and the data complexity increases correspondingly. Molecular dynamics (MD) simulation is a well-established technique to characterize microscopic details in these systems involving combined behaviors of atom movements and locally structural rearrangements. In this paper we conduct the simulations within the framework of embedded atom method provided by Pasianot et al. to study packing transformations of Ti nanoparticles upon heating and cooling on an atomic scale. Based on the calculation of the potential energy per atom, pair distribution function, pair analysis, and the specific heat capacity, the results show that the particle size and temperature changes play key roles in the packing transformations. Small size particles preferentially form icosahedral geometries. As the particle size increases, particles can hold their HCP packing at room temperature. Upon heating, the structural transformation from HCP to BCC occurs in these large size particles, and there coexist the HCP structure and the BCC structure. At a high temperature, these particles present the melting behavior similar to that of the bulk phase. When the molten particles are cooled, the atoms in the particles undergo melting-BCC-HCP structural transition, and the freezing temperature lags behind the melting temperature. The simulations provide an estimate of the critical size, and are applicable to classical theory for melting the Ti particles.
Theoretical analysis and design of G-band extended interaction klystron amplifier
Authors: Zeng Zao-Jin , Ma Qiao-Sheng , Hu Lin-Lin , Jiang Yi , Hu Peng , Chen Hong-Bin ,   Institute of Applied Electronics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Extended interaction klystron is a very important millimeter-wave and sub-millimeter-wave vacuum electron device with many actual and potential applications, such as space-borne cloud profiling radar, communication, imaging system, precision guided missiles, etc. Kinematical theory and space charge wave theory are extensively used to analyze the bunching process of electrons. Kinematical theory is precise when electron beam is especially small because the influence of space charge effect is ignored, while space charge wave theory is accurate when the modulation of electron beam is small since it is based on the premise of small amplitude. Based on kinematical theory, law of induce current, principle of charge conservation in a one-dimensioanl mode and small signal condition, the influence of electron beam on standing wave electric field in multiple-gap cavity is analyzed, and the expression of beam-loading conductance and beam-loading susceptance in multiple-gap cavity are derived. The influence of the direct current transmit angle of single gap, the number of multiple gaps and the direct current transmit angle of between center of adjacent gaps on beam-loading conductance and beam-loading susceptance are analyzed. The results show that the beam-loading conductance and beam-loading susceptance of multiple-gap cavity can change to a bigger extent when the number of cavity gaps is bigger, which means that the maximum beam-wave conversion efficiency and the range of loaded frequency increase with the number of cavity gaps increasing. The results also show that the direct current transmit angle between centers of adjacent gaps is the most important parameter for the beam-wave interaction effect. Based on the above analysis, a G-band extended interaction klystron amplifier consisting of three five-gap cavities is designed by an three-dimensional PIC code. An output power of 225.5 W at 217.94 GHz with an efficiency of 6.26%, whose gain and 3 dB bandwidth are 30.5 dB and 470 MHz respectively, is obtained by simulation. This study is of great significance for the physical design and process in engineering the G-band extended interaction klystron amplifier.
Ultrafast multiexciton Auger recombination of CdSeS
Authors: Qin Chao-Chao , Cui Ming-Huan , Song Di-Di , He Wei ,   College of Physics and Materials Science, Henan Normal University, Xinxiang 453007, China
Published: December 2020

Multiexciton generation is a process where multiple excitons are generated by absorbing single photons. Efficient multiexciton generation in quantum dots may be a revolutionary discovery, because it provides a new method to improve the solar-to-electric power conversion efficiency in quantum dots-based solar cells and to design novel quantum dots-based multielectron or hole photocatalysts. However, the mechanism of ultrafast multiexciton generation and recombination remain unclear. In this paper, alloy-structured quantum dots, CdSeS, are prepared by the hot injection method. The generation and recombination mechanism of charge carriers in quantum dots samples are discussed in detail. The bivalent band structure of alloy-structured quantum dots is determined by ultraviolet-visible absorption spectra. It is found that the 1S3/2(h)-1S(e) (or 1S), 2S3/2(h)-1S(e) (or 2S) and 1P3/2(h)-1P(e) (or 1P) exciton absorption bands of these quantum dots are at 510 nm, 468 nm and 430 nm, respectively. Femtosecond transient absorption spectroscopy and nanosecond time-resolved photoluminescence spectroscopy are used to investigate the ultrafast exciton generation and recombination dynamics in the alloy-structured quantum dots. By fitting the transient kinetics of 1S exciton bleach, an average biexciton decay time is obtained to be about 80 ps, which is almost twice the decay time of traditional quantum dots (less than 50 ps). Combined with the recently developed ultrafast interface charge separation technology that can extract multiple excitons before their annihilation, it will have a promising application prospect. Moreover, there is a hole relaxation on a the time scale of 5-6 ps via a phonon coupling pathway to lower-energy hole states in addition to the above-described ultrafast exciton-exciton annihilation process in 2S and 1P excitons. Furthermore, by nanosecond time-resolved photoluminescence spectroscopy, it can be concluded that the charge separated state is long-lived (200 ns). Our findings provide a valuable insight into the understanding of ultrafast multiexciton generation and recombination in quantum dots. These results are helpful to understand the intrinsic photo-physics of multiexciton generation in quantum dots, to implement the photovoltaic and optoelectronic applications, and to ascertain the exciton relaxation dynamics of quantum dots.
Surface plasmon resonance “hot spots” and near-field enhanced spectroscopy at interfaces
Authors: Feng Shi-Liang , Wang Jing-Yu , Chen Shu , Meng Ling-Yan , Shen Shao-Xin , Yang Zhi-Lin ,   Department of Physics, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Xiamen University, Xiamen 361005, China
Published: December 2020

Optical excitations and mutual couplings of surface plasmons with specific modes in metal nanostructures are the physical basis for developing the high spatial resolution, high sensitivity, and high precision spectroscopy. Here, we systematically review latest advances in optical excitations, classifications and identifications of surface plasmon resonance modes and their typical applications in several typical interfaces. We discuss several aspects below. First, the intrinsic mechanism of creating " hot spots” in metal particle-film systems is elucidated by the finite-difference time-domain numerical method. Spatial transfers and influence factors of the " hot spots” under plasmon-induced electric- resonance and plasmon-induced magnetic-resonance conditions are discussed. Second, the plasmon-induced magnetic-resonance in the visible-light region is successfully realized in a gold nanoparticle-film system. Meanwhile, experimental results of surface-enhanced Raman spectroscopy show that the " hot spots” in the magnetic-resonance mode can output Raman scattering with a much higher enhancement factor than that in the conventional electric-resonance mode. Third, we design nonlinear nanorulers that can reach approximately 1-nm resolution by utilizing the mechanism of plasmon-enhanced second-harmonic generation (PESHG). Through introducing Au@SiO2 (core@shell) shell isolated nanoparticles, we strive to maneuver electric-field-related gap modes such that a reliable relationship between PESHG responses and gap sizes, represented by " PESHG nanoruler equation”, can be obtained. Fourth, a critical and general solution is proposed to quantitatively describe the spatial resolution and directional emission in tip-enhanced Raman spectroscopy and tip-enhanced fluorescence. These results may help enhance our understanding of the intrinsic physical mechanism of the surface plasmon resonance, and offer opportunities for potential applications in surface-enhanced Raman spectroscopy, tip-enhanced Raman spectroscopy, second harmonic generation, and other plasmon-enhanced spectroscopy.
Some recent advances on quantum plasmonics
Authors: Xu Fei-Xiang , Li Xiao-Guang , Zhang Zhen-Yu ,   Institute for Advanced Study, Shenzhen University, Shenzhen 518060, China,   International Centre for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at Microscale, Synergetic Innovation Centre of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Plasmonics, focusing on the fundamental researches and novel applications of plasmons, has rapidly developed as an important branch of nano-optics in recent years. Essentially, surface plasmons are highly localized collective electron excitation at a metal-dielectric interface. This elementary excitation can be strongly coupled with electromagnetic fields, which enable one to collect, manipulate, and emit micron-scale optical signals through using nano-scale structures. Recently, the quantum properties of plasmons have received tremendous attention as nanofabrication techniques approach to the quantum limit. On this scale, with the unique intrinsic properties of plasmons, i.e. the particle-like nature of photons and wave-like nature of electrons, quantum plasmonics exhibits very attractive prospects in quantum information, high-efficiency optoelectronic devices, and highly sensitive detection, etc. Here in this paper, we review the development of quantum plasmonics in recent years, by introducing the research progress of relevant theories and the experimental breakthroughes. Some perspectives of the future development of quantum plasmonics are also outlined.
Performance analysis of spinning magnet as mechanical antenna
Authors: Shi Wei , Zhou Qiang , Liu Bin ,   The Sixty-third Research Institute, National University of Defense Technology, Nanjing 210007, China
Published: December 2020

Long wavelength results in the low radiation efficiency of a portable conventional antenna operating at very low frequency (VLF) and below. This has motivated one to develop an innovative approach to design an electrically small antenna in a frequency band lower than VLF. The time-varying electromagnetic fields can be generated by spinning a permanent magnet. In this way, the mechanical energy is converted to the electromagnetic energy, and the impedance matching networks with nonnegligible insertion loss are not required. Therefore, this mechanical antenna with spinning magnet can improve radiation efficiency in a low frequency band. In this paper, we give the detailed analysis procedure for the spinning magnet, which is seldom discussed in other published reports. In order to analyze the electromagnetic characteristics of the spinning magnet, in this paper we use the ampere return circuit theorem to investigate the equivalent relation between a spinning magnet and the orthogonal magnetic dipole. We introduce an initial spinning angle of the magnet into the dyadic green’s function. With this modification, we provide the rigorous analytic formula for field computation of the orthogonal magnetic dipole. Thus the electromagnetic characteristics of the spinning magnet and spinning magnet array can also be analyzed. For a spinning NdFeB magnet with a magnetization of Br = 0.8 T and a volume of Vr = 270 cm3 as well as 9600 revolutions per minute, the simulation results reveal that the magnetic field of 15 fT at 1 km in air space can be obtained. But the magnetic field of the spinning magnet decreases quickly to 1 fT at 250 m in sea water. Considering the potential demand for increasing the field strength in the near field region, we recommend to use a magnet array with small-sized elements. The magnet array can be used to control the near field pattern. We take two magnets as an example for studying the performance. It can be found from the simulation results that the magnetic near field is increased by 3 dB with the linear magnet array consisting of two elements. With the initial spinning angle of the magnet element adjusted, the near field pattern of the magnet array can be controlled. This is analogous to beam steering of traditional phased array for high band operation. It can be concluded from our study that the spinning magnet is a possible alternative solution for low frequency small transmitter antenna.