bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface roughness modeling based on laser speckle imaging
Authors: Chen Su-Ting  , Hu Hai-Feng  , Zhang Chuang  ,   Jiangsu Key Laboratory of Meteorological Observation and Information Processing, Nanjing University of Information Science & Technology, Nanjing 210044, China;,   Unit 94654, PLA, Nanjing 210046, China
Published: December 2020

Surface roughness is an important parameter in measuring the roughness of surface formed by laser irradiation on the workpiece. Speckle images of rough surfaces in different classes and different surface roughness values are obtained by constructing a set of laser speckle image acquisition systems. First, the texture features of speckle images including coarseness, contrast and direction are extracted using Tamura texture theory. Then, the interactions these three features with the surface roughness are analyzed. Based on the analyses of their monotonic relations, the surface roughness functions, including flat grinding, external grinding and mill grinding craftworks, are established respectively between the texture coarseness feature of the speckle image Fcrs and surface roughness Ra. Through the establishment of surface roughness function for the above three classes of workpieces, the value of surface roughness can be computed directly. However, before obtaining the value of surface roughness, the classes of processing technic should be determined because of the inconsistency of function expressions for different classes. And based on the specific connection and related dependencies between Tamura texture features and workpiece class, Bayes network is proposed to describe this uncertainty relation among different classes. Through network structure learning and parameter learning, a model for reasoning is found which can be used to determine the class of workpiece after obtaining texture coarseness feature Fcrs. Thus, not only can the value of surface roughness be measured, also the class of work-piece can be recognized. Experiments are conducted to confirm the feasibility of the proposed model for measurement. The detection results indicate that high precision and accuracy are achieved for both workpiece class recognition and roughness measurement.
Dynamic evolution of an excited atom near the left-handed slab acted by the Casimir-Polder force
Authors: Xu Jing-Ping  , Chang Sheng-Long  , Qin Li  , Yang Ya-Ping  ,   MOE Key Laboratory of Advanced Micro-Structured Materials, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China;,   Bureau of education of Hongkou District, Shanghai 200092, China;,   Shaoxing NO. 1 High School, Shaoxing 312000, China
Published: December 2020

Influence of the Casimir-Polder force on a slowly moving atom near a left-handed slab is discussed. We focus on an initially excited atom and its dynamic evolution during the spontaneous decay process. The left-haned slab is adopted based on two factors: (1) It provides a relatively stronger Casimir-Polder force on the excited atom far away from the interface, and (2) it can lead to an inhibited spontaneous decay rate within such a region. Therefore, we can discuss the dynamic evolution of atoms acted only by the Casimir-Polder force. The dynamic evolution discussed here includes both the evolution of atomic population and the atomic displacement. As the Casimir-Polder force depends on the atomic population, while the decay rate is related to the atomic positions, the atomic dynamic evolution is determined by its initial conditions, i.e. its position and volecity. We choose two initial positions for discussion, i.e. (1) the position with the maximum resonant Casimir-Polder force, and (2) the edge of the resonant Casimir-Polder force of the atom with dipole parallel to the interface. Furthermore, we also consider two kinds of orientations of atomic dipole, i. e. parallel and normal to the interface. It is found that the atom can be repulsed away from a surface by the Casimir-Polder force with a proper initial velocity in certain dipole orientaion during the sponatneous decay process. As the atomic dynamics depends on the orientation of the atom dipole momentum, our result can be used as a reference to distinguish atoms with different dipole momenta. Though the force discussed here exists during the spontaneous decay process, it is much different from the recoil force of the atom when it emits a photon during the spontaneous decay. The statistical average of the recoil force is null, but that of the resonant Casimir-Polder force is not. After reasonable estimation, such a Casimir-Polder force can counteract the thermal fluctuation of temperature of 15 μupK during sponatneous decay. If combined with other constraint methods, it is helpful to control the dynamics of an atom more efficiently.
Analysis of a novel four-mode micro-structured fiber with low-level crosstalk and high mode differential group delay
Authors: Xu Min-Nan  , Zhou Gui-Yao  , Chen Cheng  , Hou Zhi-Yun  , Xia Chang-Ming  , Zhou Gai  , Liu Hong-Zhan  , Liu Jian-Tao  , Zhang Wei  ,   South China Normal University, GuangDong Laboratory of Nanophotonic Functional Materials and Devices, Specially Functional Fiber Engineering Technology Research Center of Guangdong Higher Education Institutes, Guangzhou 510006, China;,   Guangdong Provincial Engineering Technology Research Center for Microstructured Functional Fibers and Devices, South China Normal University, Guangzhou 510006, China
Published: December 2020

In this paper, a novel four-mode micro-structured fiber with low-level crosstalk and high mode differential group delay is proposed to solve the large transmission capacity and low crosstalk problems in the mode division multiplexing system. Electromagnetic field distribution, crosstalk, mode differential group delay and dispersion of the fiber are studied by using the full-vector finite element method. To determine the particular parameters of the micro-structured fiber, the performances of the inter-core crosstalk and mode differential group delay (MDGD) are considered comprehensively under different conditions. Simulation results show that this fiber can support four-mode transmission with 19 cores over the whole C+L wavelength band when the cladding diameter is 125 μm. The inter-core crosstalks of LP01 mode, LP11 mode, LP21 mode and LP02 mode are -131.01, -96.36, -63.32, -49.96 dB respectively and the mode differential group delays are high as all of them are more than 160 ps/m. Therefore, compared with the previous work, this fiber has the lower inter-core crosstalk and larger MDGD. Owing to the large index difference between core and cladding, the n_eff differences between the linearly polarized modes are all larger than 10-3across the whole operating wavelength band, which is beneficial to low inter-mode corsstalk. Furthermore, the fabrication of this fiber is simple due to its preforming only need stacking technique to adjust the hexagonal structure geometry size without complex modified chemical vapor deposition process involved. The designed fiber can be used in short-distance and large-capacity transmission system, and it has potential applications in making the corresponding high power devices.
Analysis and experimental investigation of the temperature property of sensors based on symmetrical metal-cladding optical waveguide
Authors: Luo Xue-Xue  , Chen Jia-Bi  , Hu Jin-Bing  , Liang Bin-Ming  , Jiang Qiang  ,   University of Shanghai for Science and Technology, Shanghai Key Lab of Modern Optical System, Shanghai 200093, China
Published: December 2020

Symmetrical metal-cladding waveguide (SMCW) is a kind of new waveguide construction, and it consists of a planar glass slab sandwiched in two metal films with different thicknesses. The metal in this structure is usually a noble metal, such as Au, Ag and Cu etc. One of the characteristics of the glass is the sub-millimeter thickness, which is useful for exciting the ultrahigh order mode. Since the SMCW structure was proposed, it has received much attention from the researchers for its excellent characteristics of free-space coupling technique and ultrahigh order mode excitation. This free-space coupling technology has a higher sensitivity compared with the end-face coupling, prism coupling and grating coupling techniques. The ultrahigh order mode is very sensitive to the incident light wavelength, the thickness of guiding layer and the refractive index, but not sensitive to polarization. Based on the thermal-optical effect and thermal expansion effect of metal film and guiding layer materials, we research the temperature property of the SMCW structure. Researching methods include simulation analysis and experimental demonstration. First, we calculate the relation of the thickness and dielectric property of metal films, and the thickness and refractive index of the guiding layer with the temperature. Results show that these four factors are nearly proportional to the temperature difference. Then, we simulate the relationship of the reflectivity of the SMCW structure with those four factors by means of single-factor investigation under spectral and angular interrogation mode of operation, and find that the temperature-dependence of thickness of the guiding layer makes the chief contribution to the waveguide function of SMCW. Meanwhile, we analyze the sensitivity of the sensors based on SMCW structure, and the result shows that the sensitivity of this kind of sensor can be up to 21.89 pm/K (spectral mode) and 1.449×10-3 rad/K (angular mode). Finally, we demonstrate the simulation results by experiment. In our experiment, a series of reflectivity is measured at temperatures varying from 320 to 380 K, and the value is expressed in the form of voltage output of PSD (position sensitive diode). The sensor shows a good linearity and a high average resolution of 0.517×10-3 rad/K; furthermore, we fit the experimental data and get the linear function between angle shifts and temperature difference of Δθ = 0.02965×ΔT. So, once the temperature has any minute variation, it will easily give a change in the resonance incident angle and show the effect of sensor. Owing to the advantages of high sensitivity, low cast and easy fabrication, the temperature sensor based on SMCW will be a promising sensor in many fields.
Generation of no-diffraction hollow vertex beams with adjustable angular momentum by wave plate phase plates
Authors: Shi Jian-Zhen  , Xu Tian  , Zhou Qiao-Qiao  , Ji Xian-Ming  , Yin Jian-Ping  ,   Science College, Nantong University, Nantong 226019, China;,   State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062, China
Published: December 2020

In this article, a new scheme is proposed to generate approximately no-diffraction hollow vertex beams by wave plates. By selecting the appropriate thickness values of wave plates based on the properties of the double refraction, four-step-phase plates for o-light or e-light are formed. With linearly polarized light irradiated at the phase plate, the diffractions of o-light and e-light would overlap according to their intensities. By focusing effect of quasi-Galileo telescope system, a no-diffraction hollow vertex beam can be generated. In this scheme, the optical path is simple and convenient to adjust. Under the adaxial condition, the distributions of diffraction intensity and angular momentum of two wave plates at the numbers of cycles, s=1 and s=4, are numerically simulated according to Fresnel diffraction theory and classical electromagnetic field angular momentum theory. Simulation results indicate that the approximately no-diffraction hollow vertex beams can be generated by each of two phase plates within a long distance. The distributions of intensity and the angular momentum are essentially the same as those generated by spiral phase plates at the same number of cycles. The distributions of intensity and the angular momentum are different at different numbers of cycles s. If s increases, the diffraction bright ring radius increases, the intensity decreases and the average orbital angular momentum increases. At s=4, the length of no-diffraction region is significantly greater than at s=1 and the average orbital angular momentum is four times that at s=1. Within the no-diffraction region, the distribution of orbital angular momentum intensity varies with distance but the total angular momentum is constant. A phase compensator is inserted in the diffraction path to adjust the phase difference between o-light and e-light. Whereas the spin angular momentum of the diffraction light can be adjusted by them, and thus the total angular momentum intensity and average photon angular momentum can be adjusted. This scheme can be utilized to guide the cold atoms or molecules to obtain the adjustable torque throughout the interacting process of atoms and photons.
Quantum precision measurement based on squeezed light
Authors: Sun Heng-Xin  , Liu Kui  , Zhang Jun-Xiang  , Gao Jiang-Rui  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
Published: December 2020

According to the Heisenberg uncertainty principle, the precision of any physical quantity measurement is limited by quantum fluctuation in general, which leads to the so-called standard quantum limit (SQL). The SQL can be beaten by using squeezed light, hence enhancing the measurement accuracy. Squeezed light is a typical nonclassical light, it exhibits reduced noise in one quadrature component. Since Caves proposed the scheme of phase measurement enhancement with squeezing, squeezed light has been used to enhance measurement precision in many areas. This review focuses on the following four kinds of precision measurements based on squeezed light: the measurements of relative phase, small lateral displacement and tilt, magnetic field, and clock synchronization. For all of these measurements, vacuum squeezing has been used to enhance measurement precision, while the types of squeezing (squeezing angle, transverse mode, polarization etc.) are different. For phase measurement, quadrature squeezing is injected into the conventionally unused input port of Mach-Zehnder interferometer (MZI) or Michelson interferometer (MI). For displacement or tilt measurement, a vacuum squeezing beam of a special transverse mode is coupled into an intense coherent beam, yielding a spatial-squeezed light whose transverse position or tilt angle noise is lower than that of a classical light beam. Based on the Faraday effect of polarization rotation, the magnetic field can be detected precisely. The precision can be increased further by using the polarization squeezing. The polarization squeezing can be generated by coupling two orthogonal polarized beams together, a coherent beam and a vacuum squeezed beam. Various polarization squeezing can be illustrated on the Poincaré sphere. Finally, in the clock synchronization based on the optical frequency comb, squeezed light can be used to enhance the time measurement precision. A theoretical scheme with multimode squeezing of supermode (a kind of mode describing the frequency mode of a pulse laser beam) is introduced. The squeezing has extensively been applied into the quantum precision measurements such as gravitational wave detection as well as biological measurement and will play a more important role in the near future.
Granular axial flow characteristics in a grinding area studied by discrete element method
Authors: Han Yan-Long  , Jia Fu-Guo  , Zeng Yong  , Wang Ai-Fang  ,   Department of Engineering Northeast Agricultural University, Harbin 150030, China
Published: December 2020

Granular grinding is one of the most important unit operations used in a wide variety of industries. Examples can be found in the food industry, for instance, rice processing, etc.. The performance of grinding can be characterized by the particle flow process. Thus in order to study the stable flow process of particles during grinding, we must establish a discrete element model (DEM) of granular axial flow in the grinding area between the grinding roller and the screen drum. DEM is a numerical method used for modelling the mechanical behaviour of granular materials. When DEM is used in grinding, the particle motion is controlled by contact models that are governed by physical laws. Using EDEM software, the process of grinding can be simulated and analyzed. The simulation system chooses continuous feeding; after a period of time, it reaches a steady flow. Research results show that the uneven distribution of particle flow density (PFD) is caused by the axial movement difference of particles in the grinding area. The form, flow rate and distribution of granular axial flow are influenced by static friction coefficient difference between particles and screen drum. Axial mean square deviation of single particles in the grinding area is positively correlated with the square of time, which follows a “super” diffusive behavior defined by some studies. By an overall consideration of the grinding area, we find that the axial average velocities increase, however, the average velocities that are synthesized by three-axis velocities gradually decrease along the axial direction. This is because in a different axial position with different PFI, the PFI plays the key role in energy transfer. More energy will be transferred between high PFI particles that may cause high particle velocity. We also find that the fluctuation velocity square of particles presents the trend of first increasing then decreasing and finally increasing along the axial direction. The difference between PFIs is also elucidated by the total energy dissipation in each collisional energy level for a single particle. Results show that the single particle can endure intenser collision, more energy loss in anterior half segment than those in the second half of the grinding area. As mentioned above, the particle flow was analyzed in terms of particle flow intensity, particle velocity, collision energy, collision number, and so on. Some experimental results confirm the validity of the simulation. The simulation reflects the stable flow characteristics of particles in the grinding area and provides bases and references for further studying the product quality control and grinding equipment parameters optimization.
Propagation properties of the graphene surface plasmon in comb-like waveguide
Authors: Qiao Wen-Tao  , Gong Jian  , Zhang Li-Wei  , Wang Qin  , Wang Guo-Dong  , Lian Shu-Peng  , Chen Peng-Hui  , Meng Wei-Wei  ,   School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000, China;,   School of Electrical Engineering and Automation, Henan Polytechnic University, Jiaozuo 454000, China;,   School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454000, China
Published: December 2020

We investigate theoretically the electromagnetic propagation properties of graphene plasmons in a comb-like dielectric-graphene-dielectric (DGD) waveguide. The effective index of surface plasmon mode supported by the waveguide is analysed numerically, and it is found that the effective refractive index increases with the refractive index of the dielectric and decreases with Fermi energy of the graphene sheet. For a comb-like DGD waveguide with a finite branch length, a subwavelength plasmon filter can be formed by Fabry-Perot resonance caused by the reflection of the guided mode at the branch. The central frequencies of the gaps can be changed by varying the length of the branch, Fermi energy, the refractive index of the dielectric and the layer number of graphene sheets. The analytic and simulated result reveals that a novel nanometric plasmonic filter in such a comb-shaped waveguide can be realized with ultracompact size in a length of a few hundred nanometers in the mid-infrared range. We find that the frequencies of the stopband increase with Fermi energy and the layer number of graphene sheets, while will they decrease nonlinearly with the length of the branch and the refractive index of the dielectric. In addition, the width of the gap can be increased with the number of comb branches. Such electromagnetic properties could be utilized to develop ultracompact photonic filters for high integration.
Quantitative research into the influence of slider-disk contact force on the information intensity of the magnetic recording layer
Authors: Liu Yu-Liang  , Chen Zhi-Gang  , Sun Da-Xing  , Zhang Guang-Yu  ,   School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

In order to achieve the requirement of rapid growth of the magnetic storage density, the slider-disk spacing needs to be reduced to less than 2 nm. However, the slider-disk contact can easily occur within such a narrow spacing, and eventually result in the loss of the stored data in the magnetic recording film, i.e., demagnetization of the magnetic disk. Therefore, research into the magnetomechanical relationship related to the slider-disk contact demagnetization is significantly important to identify the demagnetization mechanism and further improve the anti-demagnetization performance of the magnetic disk. In this study, the nanoscratch experiment and the magnetic force microscope technology are used to investigate the magnetomechanical behavior induced by the slider-disk contact. And according to the phase imaging principle of the magnetic force microscope, the relationship between the information intensity of the magnetic recording layer and the magnetic contrast measured by the magnetic force microscope is found. Thus, a quantitative analysis method is proposed, which is different from the previous qualitative observation of the magnetic domain change. Experimental results show that the critical demagnetization load during the slider-disk contact is 120 up N. When the slider-disk contact force exceeds the critical demagnetization load, the increase of slider-disk contact force can lead to the decrease of the information intensity of the magnetic recording layer. And the decay rate of the information intensity will be rapidly enhanced after the slider-disk contact force reaches 380 up N. Moreover, the variation trend of the information intensity with the depth of the residual scratch is the same as that of the information intensity with the slider-disk contact force. Specially, before the slider penetrates the hard carbon layer of the magnetic disk, the slider-disk contact demagnetization still may occur, corresponding to the load cases from 120 up N to 200 up N. In addition, for any slider-disk contact force, the area of the surface damage of the hard carbon layer is always greater than that of the demagnetization of the magnetic recording layer. This phenomenon is related to the elasto-plastic force fields in the hard carbon layer and the magnetic recording layer. Moreover, when the slider repeatedly scratches the same location on the surface of the magnetic disk, the information intensity of the magnetic recording layer will decrease with the increase of scratching number. After the scratching number is beyond 20, the elastic shakedown status may occur in the magnetic recording layer, and correspondingly, the information intensity of the magnetic recording layer can be close to a constant value. This result is derived from the work hardening process during the slider-disk repeatedly scratching.
Ultrafast dynamic optical properties of graphene
Authors: Jin Qin  , Dong Hai-Ming  , Han Kui  , Wang Xue-Feng  ,   Department of Physics, China University of Mining and Technology, Xuzhou 221116, China;,   College of Physics, Optoelectronics and Energy, Soochow University, Suzhou 215006, China
Published: December 2020

Graphene exhibits excellent ultrafast optical properties due to its unique electronic structure. In this paper we investigate theoretically the ultrafast dynamic optical properties of graphene based on the Bloch-equations, and introduce the theoretical model of graphene. First, we give the energy which has a linear relationship with the wave vector k. The behavior of electrons in the vicinity of the two Dirac points can be described by the massless Dirac-equation, thus we have the Dirac equation of graphene. Second, we discuss the interaction between graphene and light field. The Bloch-equations of graphene are obtained through the Heisenberg equation and then we discuss the photon carriers,electric polarization and optical current change over time by analyzing the Bloch-equations. It is found that the nonequilibrium carriers in graphene induced by a terahertz field can be built in 20-200 fs due to the Pauli blocking and the conservation of energy principle. The photon carrier density will increase with the frequency of enhanced light field. Thus an optical current can be created rapidly within 1 ps. A graphene system responds linearly to the external optical field for 2evFE0tħ, while the graphene systems respond nonlinearly to the external optical field, where E0 and are respectively the intensity and the frequency of the light, t is the time and vF the Dirac velocity in graphene. The electric polarization and optical current increase with increasing photon energies. These theoretical results are in agreement with recent experimental findings and indicate that graphene exhibits important features and has practical applications in the ultrafast optic filed, especially in terahertz field.
Effect of synthesis temperature and N2/O2 flow on morphology and field emission property of SnO2 nanowires
Authors: Ma Li-An  , Zheng Yong-An  , Wei Zhao-Hui  , Hu Li-Qin  , Guo Tai-Liang  ,   School of materials science and Engineering, Fujian University of Technology, Fuzhou 350108, China;,   Institute of Optoelectronics and Displays Technology, Fuzhou University, Fuzhou 350108, China
Published: December 2020

A large amount of tin oxide (SnO2) nanowire arrays were synthesized on the flexible conductive carbon fiber substrate by thermal evaporation of tin powders in a tube furnace. The temperature, as well as the flow rate of the carrier N2 gas and the reaction O2 gas, plays an important role in defining the morphology of the SnO2 nanowires. Morphology and structure of the as-grown SnO2 samples are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Results show that all the samples possess a typical rutile structure, and no other impurity phases are observed. The morphology changes from rod to wire with the increase of reaction temperature. Ratio of length to diameter of the nanowires increases first and then decreases with the flow ratio of N2/O2 gas. The optimum synthesis conditions of SnO2 nanowire are: reaction temperature 780 ℃, N2 and O2 flow rates being 300 sccm and 3 sccm respectively. In our growth process, the nanowire grows mainly due to the vapor-liquid-solid (VLS) growth process, but both the VLS process and surface diffusion combined with a preferential growth mechanism play the important role in morphology evolution of the SnO2.Field emission measurements for Samples 1-6 are carried out in a vacuum chamber and a diode plate configuration is used. Relationship between the growth orientation, aspect ratio, density and uniformity of the arrays and field emission performances will be investigated first. Results reveal that the field emission performance of SnO2 nanostructures depends on their morphologies and array density. The turn-on electric field (at the current density of 10 upA/cm2) decreases and the emission site density increases with tin oxide array density, and the turn-on electric field of Sample 5 (synthesized at 780 ℃, nitrogen and oxygen flow rates being 300 sccm and 3 sccm respectively) is about 1.03 V/m at a working distance of 500 m. By comparison, for the turn-on electric fields of the not well-aligned SnO2 nanowire arrays we have 1.58, 2.13, 2.42, 1.82, and 1.97 V/m at 500 m. These behaviors indicate that such an ultralow turn-on field emission and marked enhancement in (～ 4670) can be attributed to the better orientation, the good electric contact with the conducting fiber substrate where they grow, and the weaker field-screening effect. Our results demonstrate that well-aligned nanowire arrays, with excellent field-emission performance, grown on fiber substrate can provide the possibility of application in flexible vacuum electron sources.
Theoretical investigation of the effects of impurity on the properties of Nb2GeC
Authors: Chen Jun-Jun  , Duan Ji-Zheng  , Zhang Xue-Zhi  , Jiang Xin  , Duan Wen-Shan  ,   College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China;,   Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China;,   Ningbo Institute of Industrial Technology, Chinese Academy of Sciences, Ningbo 315201, China
Published: December 2020

MAX phases are potential future materials used in the nuclear industry. Recently, a new MAX phase Nb2GeC is predicted as the most stable compound, and confirmed by thin film synthesis.In the operation of fusion reactor, the accumulation and aggregation of helium and hydrogen produced from transmutation reactions would induce bubble formation and void swelling and further result in embrittlement and irradiation-induced hardening of the materials. High solubility and permeability of tritium and solubility of interstitial impurities like O, C, and N can also lead to embrittlement. In order to further investigate the characters of Nb2Ge in irradiation environment, ab initio calculations are performed on the energetics of O, H and He impurities in Nb2Ge. The study of all the impurities is carried out in two ways, substitutionally and interstitially. Formation energies due to substitution and interstitial are calculated, lattice parameters and unit cell volume of Nb2GeC with substitutional or interstitial impurities are obtained, and its electronic property is analysed by Mulliken population and electron charge density.The formation energies of H substitution are lower than those of O substitution and He substitution, hence H atoms are trapped more easily by some irradiation-induced vacancies. The formation energies of O subtitution indicate the sequence Ef(Osub-Nb)>Ef(Osub-Ge) ≈ Ef(Osub-C), which is related to the strength of bonds. Analysis on electron charge density and Mulliken population shows that C-O bond is stronger than Nb-O and Ge-O bond, and the bond lengths of C-O, Nb-O and Ge-O are 3.256, 2.118 and 1.985 Å respectively. Due to the interaction of O atom with Nb, Ge and C atoms in Nb2Ge, the O atom would deviate from the vacancy, and goes to the deformed sites in the crystal structure. As for H substitution, the formation energies of substitution show the sequence Ef(Hsub-Nb)>Ef(Hsub-Ge) > Ef(Hsub-C). C-H and Nb-H are ionic bond and covalent bond respectively, and their bond lengths are 3.131 and 2.706 Å respectively. The formation energies of He substitution present the sequence: Ef(Hesub-C) > Ef(Hesub-Nb) > Ef(Hesub-Ge), and suggest that the He atom is the easiest to be trapped by C vacancy. All O, H and He interstitials make lattice parameter a increase, c decrease and unit cell V shrink. Besides, the results of substitution and interstitial formation energies show that O, H and He impurities prefer to stay on octahedral sites. These results could provide initial physical picture for further understanding the accumulation and bubble formation of impurities in Nb2GeC.
Hydrogen storage properties of Li-decorated C24 clusters
Authors: Qi Peng-Tang  , Chen Hong-Shan  ,   College of Physics and Electronic Engineering, Northwest Normal University, Key Laboratory of Atomic and Molecular Physics & Functional Materials of Gansu Province, Lanzhou 730070, China
Published: December 2020

Hydrogen is considered as a potentially ideal substitution for fossil fuels in the future sustainable energy system because it is an abundant, clean and renewable energy carrier. A safe, efficient and economic storage method is the crucial prerequistite and the biggest challenge for the wide scale use of hydrogen. The nanomaterial is one of the most promising hydrogen storage materials because of its high surface to volume ratio, unique electronic structure and novel chemical and physical properties. It has been demonstrated that pristine nanostructures are not suitable for hydrogen storage, since they interact weakly with hydrogen molecule and their hydrogen storage density is very low. However, the hydrogen storage capacity of the nanostructures can be significantly enhanced through substitutional doping or decoration by metal atoms. Using density functional theory, we investigate the properties of hydrogen adsorption on Li-decorated C24clusters. Results show that the preferred binding site for Li atom is the pentagonal rings. The interaction of Li atoms with the clusters is stronger than that among Li atoms, thus hindering effectively aggregation of Li atoms on the surface of the cluster. The decorated Li atoms are positively charged due to electron transfer from Li to C atoms. When H2 molecules approach Li atoms, they are moderately polarized under the electric field, and adsorbed around the Li atoms in molecular form. Each Li atom in the Li-decorated C24 complexes can adsorb two to three H2 molecules. The H-H bond lengths of the adsorbed H2 molecules are slightly stretched. The average adsorption energies are in the range of 0.08 to 0.13 eV/H2, which are intermediate between physisorption and chemisorption. C24Li6 can hold up to 12 H2 molecules, corresponding to a hydrogen uptake density of 6.8 wt%. This value exceeds the 2020 hydrogen storage target of 5.5 wt% proposed by the U. S. Department of Energy.
A fractional-order memristor model and the fingerprint of the simple series circuits including a fractional-order memristor
Authors: Yu Ya-Juan  , Wang Zai-Hua  ,   State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China;,   School of Mathematics and Physics，Changzhou University, Changzhou 213164, China;,   Institute of Science，PLA University of Science and Technology, Nanjing 211101, China
Published: December 2020

A memristor is a nonlinear resistor with time memory. The resistance of a classical memristor at a given time is represented by the integration of all the full states before the time instant, a case of ideal memory without any loss. Recent studies show that there is a memory loss of the HP TiO2 linear model, in which the width of the doped layer of HP TiO2 model cannot be equal to zero or the whole width of the model. Based on this observation, a fractional-order HP TiO2 memristor model with the order between 0 and 1 is proposed, and the fingerprint analysis of the new fractional-order model under periodic external excitation is made, thus the formula for calculating the area of hysteresis loop is obtained. It is found that the shape and the area enclosed by the hysteresis loop depend on the order of the fractional-order derivative. Especially, for exciting frequency being bigger than 1, the memory strength of the memristor takes its maximal value when the order is a fractional number, not an integer. Then, the current-voltage characteristics of the simple series one-port circuit composed of the fractional-order memristor and the capacitor, or composed of the fractional-order memristor and the inductor are studied separately. Results demonstrate that at the periodic excitation, the memristor in the series circuits will have capacitive properties or inductive properties as the fractional order changes.
The novel feed forward and decision feedback equalizer structures and improved variable step algorithm
Authors: Hao Xue-Yuan  , Yan Xiao-Hong  , Qian Li-Xia  ,   College of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210003, China
Published: December 2020

Skin effect and dielectric loss in super-long cable will cause nonlinear attenuation at different signal frequency, and in addition, coupling noise and thermal noise also cause signal distortion at the receiver end. These factors seriously affect the signal transmission speed in the super-long cable. Especially, in the field of exploration of shale gas and bed methane, the transmission cable is also used to transport high-precision synchronization pulse signal, and the synchronization pulse must reach the microsecond accuracy, which is used for data phase calibration. A synchronization signal is a high frequency signal, which suffers more severe attenuation and noise interference. At the receiving end, the sync pulse signal will be drowned in the noise environment, and so it is difficult to restore the original signal.#br#Although fiber can achieve a high transfer rate, but the fiber cable cannot transmit power energy; in addition, the tensile strength and heat resistance of the fiber are much worse than copper cable, these weaknesses limit its application in such industry. Therefore, an effective balancing algorithm is necessary to overcome the propagation effects and interference in a super-long copper cable. However, conventional equalization techniques have well-balanced effect for the short-range communications, but for the long-distance communication, they often have poorly balanced results. In order to solve the above problem and improve the long cable signal transmission speed, this paper presents a new balanced portfolio structure; the new structure uses feed-forward equalizer (FFE) as the pre-stage, and decision-feedback equalizer (DFE) as the post stage to form a new structure. The combination structures can effectively utilize the flexibility of FFE and overcome the problem of error diffusion in DFE. By mathematical modeling and simulation, this paper gives the best combination factors. Furthermore, based on the improved structure, a new convergence algorithm is proposed, which uses the arc tangent function combined with three error converge factors to form a converging function, and it has the advantages of fast convergence and steady-state error. Simulation results show that the FFE-DFE combination equalizer has low computational complexity, fast convergence, and strong channel tracking capability; in addition, it can speed up the data processing speed, and better respond to the real variation of the channel. Simulation results show also that the performance is improved by 50% by eliminating inter-symbol interference and noise.#br#The real circuit board based on the new algorithm have been tested in the East China Petroleum Bureau, the test results show that the algorithm can rectify 160 dB signal distortion, and the transmission speed can reach 5 Mbps in 6 dB signal to noise ratio.
One-dimension nonlinear and dispersive seismic wave modeling in solid media
Authors: Zhou Cong  , Wang Qing-Liang  ,   Institute of Geology, China Earquake Administration, Beijing 100029, China;,   The Second Monitoring and Application Center, China Earquake Administration, Xi'an 710054, China
Published: December 2020

The nonlinear theory in Earth Science is very important for solving the problems of the earth. When considering some of the nonlinear properties of the medium, solitary wave (a special wave with a finite amplitude and a single peak or trough) may appear. Previous studies showed that it may be related to the rupture in the earthquake process. Therefore, it would be very helpful to explain some special phenomena in actual observation data if we fully understand the characteristics of nonlinear waves.#br#In this paper, based on the nonlinear acoustic wave equation, we first perform 1-D nonlinear acoustic wave modeling in solid media using a staggered grid finite difference method. To get the stable and accurate results, a flux-corrected transport method is used. Then we analyze several different types of nonlinear acoustic waves by setting different parameters to investigate their nonlinear characteristics in the solid media. Compared with the linear wave propagation, our results show that the nonlinear coefficients have important influences on the propagation of the acoustic waves. When the equations contain only a third-order nonlinear term (consider the case β 1 ≠ 0, β 2=0, α =0), the main lobe of the wave is tilted backward and its amplitude gradually attenuates with the wave spreading, and the amplitude of its front side-lobe attenuates slowly while the back side-lobe attenuates quickly. The whole shape and amplitude of the wave remain unchanged after propagating a certain distance. When the equations contain only a fourth-order nonlinear term (consider the case β 2 ≠ 0, β 1=0, α =0), the main lobe and the two side-lobes of the wave are all slowly damped, but the shape of the whole wave is unchanged with the wave spreading.#br#In addition, for some combinations of nonlinear and dispersive parameters (consider the case β 1 ≠ 0, α ≠ 0, β 2=0), the wave acts like the linear wave, and the nonlinear acoustic wave is equal to solitary wave which is usually obtained by Kortewegde de Vries (KdV) equation. We validate our modeling method by comparing our results with the analytic solitary solutions. Solitary wave propagates with a fixed velocity slightly less than that of the linear compressional wave, which is probably due to the balance between nonlinear and dispersion effects, making the stress-strain constitutive relations show the nature of linear wave.
Quantum walk search algorithm based on phase matching and circuit cmplementation
Authors: Chen Han-Wu  , Li Ke  , Zhao Sheng-Mei  ,   School of Computer Science and Engineering, Southeast University, Nanjing 210096, China;,   School of Telecommunication and Information Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210003, China
Published: December 2020

As a new quantum computing model, quantum walk has been widely studied in recent years. It consists of discrete time quantum walk and continuous time quantum walk. Discrete time quantum walk includes coin quantum walk and scattering quantum walk. Meanwhile as a quantum search algorithm, Grover algorithm can search an unsorted database in time complexity of O(√N) . Recent years quantum walk has been used to solve search problems and some of them have been proved to be as efficient as Grover algorithm. Making full use of the novel properties of quantum walk, the quantum walk search algorithms on the 2D grid and hypercube have been proposed. Inspired by phase matching condition of Grover algorithm, we propose a new quantum walk search algorithm which is based on coin quantum walk. Firstly we give the graph to the quantum walk, and then describe the algorithm in detail. Algorithm uses different coin operators and shift operators for two different cases and draws the corresponding iteration operators. Then we prove that iteration operators used in the algorithm are unitary operators. Then we analyze the time complexity and probability of success of the algorithm. Analysis indicates that the time complexity of the algorithm is the same as that of Grover algorithm, however when the targets to be searched are more than 1/3 of the total targets, the algorithm probability of success is greater than that of Grover algorithm. Finally we give the circuit implementation of the algorithm.
Characteristics of multi-hop noisy quantum entanglement channel and optimal relay protocol
Authors: Yang Guang  , Lian Bao-Wang  , Nie Min  ,   School of Electronics and Information, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

The optimal relay path calculation and selection are important factors to affect the performance of quantum communication network. Current researches seldom consider the quantum path selection in real noisy environments. One of the difficult problems is how to analyze the influence of the noise on the quantum communication in multi-hop channels. This paper aims to solve the path selection problem of the quantum teleportation network in noisy environments. The process of entanglement swapping in the phase damping channel is first studied with an example of two-hop quantum channel, whose damping factors are p1 and p2. The entanglement states |φ> 12+ and |φ> 34+ are distributed separately in each hop. After the entanglement swapping, the density matrix of the entanglement state of photon 1 and photon 4 is obtained by performing a partial trace over the environment. Then, the Bures fidelity of this entanglement is calculated. After that, we define the path equivalent damping factor to describe the characteristic of the two-hop noisy quantum relay path. With an equivalent calculation method, the results above can be generalized to multi-hop channel. The path equivalent damping factor of the multi-hop amplitude damping channel is also obtained. According to these results, we propose an optimal relay protocol for the quantum teleportation network with the criterion of path equivalent damping factor, which means that a relay path with the minimum path equivalent damping factor can obtain the highest teleportation fidelity. The types and parameters of the messages used in the protocol are given. The processes of the relay protocol are described specifically, including neighbor finding, quantum link noise measurement, and quantum link status transmission. An improved Dijkstra algorithm is used in the optimal path calculation. Furthermore, because the entanglement resources maintained in the quantum nodes are limited and may be exhausted in superior quantum links, we propose a resource reservation method to avoid the failure of the relay path setup. Theoretical analysis and simulation show that our method can obtain a lower average equivalent damping factor and higher teleportation fidelity. It can also be seen that increasing the number of the entanglement resources will raise the performance of the quantum network, however, it brings higher cost and complexity. Therefore, the entanglement resources maintained in the quantum nodes must be configured reasonably according to the network scale, the cost, the time delay and the need of the users.