bluuebunny/crossref_metadata_2025 huggingface dataset:
The preparation of high-performance FTO thin film by Sol-Gel-evaporation method
Authors: Shi Xiao-Hui  , Xu Ke-Jing  ,   School of Materials Science and Engineering, Shandong University of Technology, Zibo 255091, China
Published: December 2020

The purpose of this work is to prepare the high-performance transparent conductive thin films of fluorine-doped tin oxide (FTO) by using a simple technological process. The FTO thin films are formed in the period of calcination process combined with the advantages of sol-gel method and chemical vapor deposition method, which not only avoids the shortcomings of film cracking in sol-gel coating process, but also reduces the cumbersome traditional dip-coating method and spin-coating method on glass substrates, largely simplifying process and cutting costs. The FTO thin films are deposited onto glass substrates by the sol-gel-evaporation method with SnCl45H2O as a tin source, and SnF2 as a fluorine source. The effects of F-doping content and the structure of the film on the properties of FTO film are mainly studied. The prepared films are characterized by IR, DTA-TG, XRD, TEM, SEM, etc. The results show that the maximum performance index (TC) of the FTO film, the lowest surface resistance of 14.7 cm-1, and the average light transmittance of 74.4% when F/Sn=14 mol% are achieved under the conditions of the reaction temperature of 50 ℃, the reaction time of 5 h, sintering or evaporation temperature of 600 ℃ for 2 h. It is indicated that part of O is replaced by F, and SnO2-xFx crystal structure is formed. It reveals that the crystal structure is polycrystalline and has a preferential orientation along the (110) direction and the spacing between the lattice fringes is about 0.33 nm in the FTO film. And the particles in the FTO film present a tetragonal rutile phase with an average size of 20 nm and a film thickness of 1.22 m. Fractal dimension of image by dealing with SEM image of FTO film shows that the surface resistance decreases with the decreasing of fractal dimension, which in fact critically demonstrates the lower barrier. The lower the barrier, the smoother the surface of the thin films is. So the fluorine concentration is the main factor affecting the properties of FTO thin film. Too much or too less fluorine is not conducive to the growths of SnO2-xFx crystals. And then the three-dimensional information such as structure, particle shape and size of the FTO thin film is also the factor influencing the FTO film properties. The analysis of SEM shows that the surface morphology of the thin film is in the pyramid-shaped structure, which is beneficial to improving the utilization of photons, and well used in the optoelectronic devices.
Experimental research of alignment error correction by aspheric mirror based on the function of imaging quality
Authors: Zhou Long-Feng  , Zhang Ang  , Zhang Jun-Bo  , Fan Xin-Long  , Wei Ling  , Chen Shan-Qiu  , Xian Hao  ,   Key Laboratory on Adaptive Optics, Chinese Academy of Sciences, Chengdu 610209, China;,   The Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Image definition will be influenced by alignment errors of mirrors in an optical system consisting of hyperbolic, parabolic or ellipse mirrors. The major factors of alignment errors are gravity, wind loads and heat exchange for some optical systems like ground-based telescopes, while vibration and temperature gradient for systems like space telescopes. Larger telescopes are more sensitive to these error sources, which becomes the concerns of researchers. So the alignment errors of mirrors must be corrected in time to keep systems working in best condition. In order to solve the problem, many methods are proposed based on the detection of wave-front errors using wave-front sensors like Hartmann-Shack. However, wave-front sensors may not be used or cause optical systems to be more complicated. For example, multi-fields must be tested when telescope is working. On the one hand, if a wave-front sensor is used, it must be moved around imaging plane, on the other hand, if more wave-front sensors are used, system must be more complicated. So a new method is discussed for alignment error correction by evaluating the quality of spot diagrams based on the using of stochastic parallel gradient descent (SPGD) algorithm. The method considers the performance metric like spot diagram radius as a function of control parameters and then uses the SPGD optimization algorithm to improve the performance metric. The control parameters include positions of mirrors. The iteration process must be used in the right way to control position parameters. If it is not considered, a problem may come up that positions of spot diagrams may be influenced by the iteration. Furthermore, spot diagrams will probably disappear from detectors. Then the radii of spot diagrams are not correct. So a better way is put forward by the combination of de-center and tilt of mirrors. The way ensures that the position error produced by de-center and tilt are compensated for. A formula is provided in this paper to give the relationship between them. Based on the analysis, an optical system is designed to verify the conclusion. The SPGD algorithm is achieved by computer programming and the position of the mirror is controlled by a hexapod. Firstly, the problem is verified that the spot diagram will disappear from the detector with a normal iteration process. Then the new way is implemented. In the iteration process, the spot diagram is always in the center of the detectors. In order to prove the feasibility of the method, three different alignment errors are tested and all of them each give an Airy disk finally. The experiment can provide reference for engineering practice.
Lie symmetry analysis, optimal system, exact solutions and conservation laws of a class of high-order nonlinear wave equations
Authors: Li Kai-Hui  , Liu Han-Ze  , Xin Xiang-Peng  ,   School of Mathematical Sciences, Liaocheng University, Liaocheng 252059, China
Published: December 2020

The symmetries, conservation laws and exact solutions to the nonlinear partial differential equations play a significant role in nonlinear science and mathematical physics. Symmetry is derived from physics, and it is a mathematical description for invariance. Symmetry group theory plays an important role in constructing explicit solutions, whether the equations are integrable or not. By using the symmetry method, an original nonlinear system can be reduced to a system with fewer independent variables through any given subgroup. But, since there are almost always an infinite number of such subgroups, it is usually not feasible to list all possible group invariant solutions to the system. It is anticipated to find all those equivalent group invariant solutions, that is to say, to construct the one-dimensional optimal system for the Lie algebra. Construction of explicit forms of conservation laws is meaningful, as they are used for developing the appropriate numerical methods and for making mathematical analyses, in particular, of existence, uniqueness and stability. In addition, the existence of a large number of conservation laws of a partial differential equation (system) is a strong indication of its integrability. The similarity solutions are of importance for investigating the long-time behavior, blow-up profile and asymptotic phenomena of a non-linear system. For instance, in some circumstance, the asymptotic behaviors of finite-mass solutions of non-linear diffusion equation with non-linear source term are described by an explicit self-similar solution, etc. However, how to tackle these matters is a complicated problem that challenges researchers to be solved. In this paper, by using the symmetry method, we obtain the symmetry reduction, optimal systems, and many new exact group invariant solution of a fifth-order nonlinear wave equation. By Lie symmetry analysis method, the point symmetries and an optimal system of the equation are obtained. The exact power series solutions to the equation are provided by the power series method, such solutions can be used for numerical computations in both theory and physical applications conveniently. Finally, a lot of conservation laws of the fifth-order nonlinear wave equation are presented by using the adjoint equation and symmetries of the equation.
Single molecular study on interactions between avidin and DNA
Authors: Cao Bo-Zhi  , Lin Yu  , Wang Yan-Wei  , Yang Guang-Can  ,   School of Physics and Electronic Information, Wenzhou University, Wenzhou 325035, China
Published: December 2020

Avidin is a common basic protein, widely used for connecting DNA and modified surface in single-molecule techniques of biophysics, and it can also be used as a DNA vector in gene therapy. Avidin is highly positively charged and can condense DNA in solution. Understanding the physical mechanism of its condensing DNA is a key factor to promote avidin-DNA complex to be used for many purposes, such as a probe of biomacromlecules, signal enhancer or carrier of disease diagnosis.In the present study, we use atomic force microscope (AFM), dynamic light scattering (DLS), and single molecular magnetic tweezers (MT) to systematically investigate the interaction between DNA and avidin and the underlying mechanism of DNA condensation by avidin. The conformation of DNA-avidin complex is observed and measured by AFM and we find that the condensation includes two types: one is toroidal condensation of DNA induced by avidin, the other is the condensing structure by avidin compaction. Quantitative analysis shows that the size of avidin-DNA complex decreases monotonically with the concentration of avidin increasing. However, when the concentration of avidin reaches up to a critical value of 2 ngL-1, the size of complex begins to increase suddenly with avidin concentration increasing. The phenomenon is also confirmed by the corresponding DLS measurements. For example, when the concentration of avidin increases from 0 to 2 ngL-1, the size of condensed avidin-DNA complex reduces from 170 nm to about 125 nm. In the mean while, its electrophoretic mobility changes from -2.76 (10-4cm2V-1s-1) to -0.1 (10-4 cm2V-1s-1). The negative charge of DNA is mostly neutralized by avidin. From their force spectroscopy measured by MT, it is found that the extension of DNA varies almost linearly and a few stairlike jumps appear occasionally. For example, its characteristic trend is quite similar to the one by histones. The condensing force of DNA by avidin grows up with the concentration of avidin increasing. The statistics of force-extension curves by MT shows that the peak of unraveling steps of avidin-DNA complex is around 160 nm, which corresponds to the typical toroidal structure of DNA.In DNA condensation by avidin, electrostatic interaction plays a key role due to the neutralization of negatively charged phosphate groups of DNA by cationic avidin. From the comprehensive data by AFM, DLS and MT, we conclude that the process of DNA condensation induced by avidin consists of two mechnisms: the predominant DNA-avidin electrostatic attraction and the ancillary avidin aggregation.
Transmission-type miniature micro-beam modulated X-ray source based on space application
Authors: Mou Huan  , Li Bao-Quan  , Cao Yang  ,   National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

X-ray sources have been extensively penetrated into all aspects in daily life, such as pharmaceutical analysis, X-ray diagnostics, and radioactive static elimination. Along with the burgeoning field of deep exploration, all kinds of X-ray sources are fabricated to meet the needs of space applications. Therefore a design proposal of a transmission-type miniature micro-beam modulated X-ray source, in allusion to the space application of X-ray sources, is proposed and its theoretical model is constructed. In contrast with the traditional X-ray sources, a grid electrode is added and three focusing electrodes are chosen and used. Amplitude modulation and pulse modulation of X-rays, by controlling the voltage value of the grid electrode, are realized. Electrons are restrained to pass when the grid electrode is loaded with a negative voltage and no X-ray photons are produced. When loaded with a positive voltage, the grid electrode lets electrons get through and finally reaches up to the anode electrode. Three focusing electrodes, meanwhile, are used to make the electron beam converge and finally focus on the anode target. The thickness of the transmission-type target material is considerable, considering it to be a key parameter influencing the conversion efficiency of X-rays. If the target thickness is too thin, only a part of electrons can convert into X-ray. On the contrary, when the target thickness is too thick, the produced X-ray intensity is low too. That is because some X-ray photons are absorbed by the anode target material even though all of the electrons convert into X-ray. And the optimum target thickness, in different anode voltage values and different target materials, is simulated using charged particle optical simulation software, and the results are presented in a table. In addition, the influence of grid voltage value on electron beam trajectory is also taken into account and finally a 150-m-diameter focusing spot is obtained. The prototype model is fabricated via coating film on the anode and the single-step brazing process in a vacuum furnace. After the test platform is set up, the spectrum feature of tungsten target is attained. And it is analyzed that the X-ray intensity is related to the grid electrode voltage value. The feasibility of grid amplitude modulation and grid pulse modulation are verified in the end. As a multifunctional modulated X-ray source, it will have more important scientific significance and space application prospects, and be used in inter-satellite X-ray communication, ionization blackout area communication, planetary science, pulsar simulation and single event effect simulation of space radiation environment.
Efficient method of calculating Shannon entropy of non-static transport problem in message passing parallel programming environment
Authors: Shangguan Dan-Hua  , Deng Li  , Zhang Bao-Yin  , Ji Zhi-Cheng  , Li Gang  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

For the Monte Carlo simulation of the non-static transport problem, there must be many calculation steps. Because some particles cannot finish their transport in the last step, they are naturally used as the source particles of the present step. These particles are called undied particles. It is difficult to adjust the history number of each step to obtain higher efficiency because the adjusting rule is hard to find. The most direct method is to set a large enough history number for all steps. But evidently, it is unnecessary for some steps. Among all possible rules, one candidate of adjusting the history number is to check the convergence situation of Shannon entropy (corresponding to the distribution of some undied particle attributes) every some samples in each step to determine whether or not to simulate more particles. So, this method needs to calculate the Shannon entropy frequently. Because the classical method of calculating Shannon entropy in message passing parallel programming environment must reduce massive data, it is unpractical to be used in this situation for the great increasing of computation time with the high frequency of entropy calculation. In this paper, we propose an efficient method of calculating the entropy in the message passing parallel programming environment by letting each process calculate its entropy value based on the local data in each processer and calculating the final entropy by averaging all the entropy values gotten by all processes. The entropy value calculated by this method is not the same as that by the classical method when using finite history number, but the difference goes to zero when the history number goes to infinity. The most remarkable advantage of this method is the small increasing of computation time when calculating the entropy frequently. It is a suitable method of calculating Shannon entropy when adjusting the history number automatically based on the judgment of the convergence situation of Shannon entropy.
Theoretical study on the polarizability properties of liquid crystal in the THz range
Authors: Chen Ze-Zhang  ,   College of Physics and Electronic Engineering, Xinxiang University, Xinxiang 453003, China;,   College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China
Published: December 2020

Terahertz (THz) technology developed rapidly in recent years. Liquid crystals (LCs) are one of the most promising base materials to construct switchable devices in THz range because of their high optical anisotropies. However, the practical applications of the devices are hampered by the relationships between birefringence, thickness and LCs switching time. Due to the long wavelength, THz device requires a larger birefringence LC than the device operated at optical frequencies. Yet, in order to design an efficient switchable LC-THz device, it is crucial to find or synthetize LC material which will still display a useful birefringence at THz frequencies. The birefringence properties of LC are determined by the molecular polarizability of the relevant material. Knowledge of the LC molecular polarizability and its dependence on the molecular structure is important for designing LC molecules with desired THz properties. The prediction of the photoelectric characteristics could save a considerable quantity of the man-power and materials needed for the design or synthesis of new LC compounds. A priori screening of materials and the prediction of the optoelectronic properties would make a vast opportunity for expanding the LC material application scope. Hence, the main purpose of the present work is to provide a theoretical method of calculating and analyzing the THz polarizability properties of LC single compounds for LC-THz device applications. In this work, the frequency dependent molecule polarizability values of liquid crystal PCH5, 5CB and 5OCB in THz range are calculated by the density functional theory method. The geometries of the studied LCs are optimized at B3 LYP levels with the standard 6-311G(d) basis set. From the optimized geometries the molecule THz polarizabilities of LCs are calculated by the M06-2x functional with 6-311++G(2d, p) basis set, and they are found to be in good agreement with experimental data. By plotting the polarizability density analysis (PDA), the spatial contributions of electrons to the longitudinal polarizability are presented. The influences of alkyl chain and core structure on the microscopic polarizability of the LC molecule are investigated and explained by using the finite field approach and PDA. The results show that the unsaturated group, such as benzene ring or cyanobenzyl, makes great contribution to the polarizability of LC. In the design process, the new type of LC molecule must be extended the length of up electron conjugated system, to reduce the energy gap between HOMO and LUMO, and hence improving LC molecule polarizabilty. We hope that the present work could give a useful guide in screening or designing LC molecules for THz applications, and offer an effective way to understand fundamental optoelectronic characteristic of LC materials in the THz frequency range.
Permeability of nano SiO2 aggregates in concentrated suspension
Authors: Xia Hui  , Yang Wei-Guo  ,   School of Physics and Electronics, Central South University, Changsha 410083, China
Published: December 2020

The low coherence optical fiber dynamic light scattering method is used to measure the effective diffusion coefficients of nano SiO2 aggregates suspensions with different volume fractions. The single scattering component can be detected preferentially from the multiply scattered light which is backscattered from the dense suspensions by the low coherence optical fiber dynamic light scattering. Consequently, the measured single-scattering spectrum enables the analysis of the effective diffusion coefficient by the single scattering theory. The numerical calculation results of short-time diffusion dynamics for permeable particles in dense suspension show that the effective diffusion coefficient is a function of particle size and hydrodynamics shielding depth ratio , and the volum fraction . According to the corrected Brinkman theory, the permeability of the nano SiO2 aggregates is obtained. For the volume fraction = 0.01, 0.02, 0.03, 0.04, 0.05 nano SiO2 aggregate suspensions with the average particle diameter 500 nm, the measured effective diffusion coefficients are 4.140.10, 4.060.06, 3.970.06, 3.900.08, 3.800.10 (10-13 m2/s) respectively. While according to the hard sphere model of impermeable particles, which corresponds to = , the calculated effective diffusion coefficients are 3.70, 3.61, 3.52, 3.42, 3.36 (10-13 m2/s) respectively. It can be seen that the measured values are much bigger than the theoretical values of impermeable particles: their difference comes from the influence of permeability of porous aggregates on particle diffusion. It is found that the measured values are consistent with that of = 12, in which the corrsponding permeability of the nano SiO2 aggregates is k = 4.34 10-16 m2. The pixel statistic method by Photoshop CS6 is used to deal with the SEM images of SiO2 aggregates, the calculated permeability of the nano SiO2 aggregates is k = 4.55 10-16 m2, compared with the experimental result, the standard error is 4.87%. The results show that under the condition of constant temperature, the particles of permeable aggregates spread faster than the hard sphere particles. For constant temperature, particle size and permeability, the effective coefficient decreases with the increase of the volume fraction. The measured permeability of SiO2 aggregates in concentrated suspension is consistent with that obtained from the pixel statistics by Photoshop CS6. As a result, the low coherent optical fiber dynamic light scattering can effectively measure the permeability of porous nano particles in concentrated suspension, showing high potential application in the field of chemical engineering and nano materials preparation.
Modeling of Gaussian laser beam reflection from rough sea surface
Authors: Zhang Xiao-Hui  , Zhang Shuang  , Sun Chun-Sheng  ,   Department of Ordnance Engineering, Naval University of Engineering, Wuhan 430033, China
Published: December 2020

Studies on the direction distribution of laser beam intensity reflected from the sea surface is important for engineering practice in the area of optoelectronic confrontation on the sea surface. In the traditional theory of electromagnetic scattering from rough surfaces, the scattered field from the sea surface can be obtained by solving the Maxwell's equations. As is well known, it is difficult to solve the Maxwell's equations. Therefore, the numerical calculation method and approximate analytical method are used to obtain the scattered field from the sea surface. However, for the numerical calculation method, it is difficult to meet the computing requirements of large electrically targets such as the sea surface. Meanwhile the approximate analytical method has certain restrictions on the parameters of rough surface in physical approximation. What is more, the inherent error is also caused by the physical approximation. In this paper, we investigate the laser beam reflection from rough sea surface with Monte Carlo method and principles of geometric optics. The rough sea surface which is simulated with the fractal method is divided into a lot of small planes, and the mathematical equations to describe the geometric characteristics of the planes are established in the sea reference coordinate system. After that, based on the simulation of Gaussian beam with Monte Carlo method, the laser beam is divided into a great number of rays and the statistical properties of the rays satisfy the propagation characteristics of Gaussian beam. Then, the laser beam reflection model from the sea surface is derived in the reference coordinate system. The direction distribution of the laser beam intensity reflected from the sea surface is simulated under a certain experiment condition with this model. The results show that the simulation results of laser beam reflection from the sea surface fit the experimental results well.
Analysis on mechanism of radiating microwave from vacuum diode
Authors: Ji Zeng-Chao  , Chen Shi-Xiu  , Gao Shen  , Chen Jun  , Tian Wei  ,   School of Electrical Engineering, Wuhan University, Wuhan 430072, China;,   School of Electrical and Electronic Engineering, Hubei University of Technology, Wuhan 430068, China;,   South-Central University for Nationalities, Wuhan 430074, China
Published: December 2020

In order to study the breakdown process of vacuum switch, we use a vacuum diode, which is composed of a cathode and an anode, to replace the vacuum switch. We find that there is wide band microwave radiation in the breakdown process of the vacuum diode. Because there is no structure of metallic bellow waveguide in the vacuum diode, the radiation mechanism of the vacuum diode is different from that of the plasma filled microwave device. It is hard to completely imitate the theory of the plasma filled microwave device. In order to clarify the mechanism of the microwave radiation from the vacuum diode, we analyze the breakdown process of the vacuum diode. When the anode plasma has been generated and the plasma closure has not occurred, the electrons emitted from the initial plasma will be incident on the anode plasma, and the vacuum diode will radiate microwave in this process. The self-generating magnetic field of the electron beam is a poloidal magnetic field. When the electron beam is incident on the plasma, the plasma will be magnetized by the poloidal magnetic field. The theory of magnetic fluid is used to analyze the problem in this paper, and the mathematical model of the vacuum diode radiation is obtained by using the simultaneous equations of the motion equations and Maxwell's equations. In this model, there is an interface between the electron beam and the magnetized plasma. The model is divided into two parts by the interface, i.e., inside of the electron beam and outside of the electron beam. The dispersion relation of the radiation generated by the vacuum diode is obtained by solving the mathematical model. Based on the dispersion relation and the experimental data, the dispersion curves are plotted for the different electron beam velocities. The dispersion curves show that the undulation of the dispersion curve becomes smaller and smaller with the decrease of the electron beam velocity, and the final dispersion curve will be approximated by a straight line. When the theoretical dispersion curves are compared with the actually measured time-frequency maps of the radiation, we find that they are well consistent with each other. Theoretical deduction and experiments indicate that the radiation generated by the vacuum diode originates from the interaction between the electron beam and the magnetized plasma.
Synthesis, microstructure, and magnetic properties of -Fe2O3/NiO core/shell nanoflowers
Authors: Li Zhi-Wen  , He Xue-Min  , Yan Shi-Ming  , Song Xue-Yin  , Qiao Wen  , Zhang Xing  , Zhong Wei  , Du You-Wei  ,   National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093, China;,   School of Science, Nanjing University of Posts and Telecommunications, Nanjing 210023, China;,   College of Science, Henan University of Technology, Zhengzhou 450001, China
Published: December 2020

The main purpose of this work is to explore the influences of microstructures on the magnetic properties, as well as the formation mechanism of -Fe2O3/NiO core/shell nanoflowers. The synthesis of nanoflower-like samples includes three processes. Firstly, Fe3O4 nanospheres are synthesized by the solvothermal reaction of FeCl3 dissolved in ethylene glycol and NaAc. Secondly, Fe3O4/Ni(OH)2 core/shell precursor is fabricated by solvothermal method through using the early Fe3O4 spheres and Ni(NO3)26H2O in an ethanol solution. Finally, the precursor Fe3O4/Ni(OH)2 is calcined in air at 300 ℃ for 3-6 h, and therefore resulting in -Fe2O3/NiO core/shell nanoflowers. Their microstructures are characterized by using XRD, XPS, SEM, HRTEM and SAED techniques. The results show that the final powder samples are -Fe2O3/NiO with typical core/shell structure. In this core/shell system, the -Fe2O3 sphere acts as core and the NiO acts as shell, which are comprised of many irregular flake-like nanosheets with monocrystalline structure, and these nanosheets are packed together on the surfaces of -Fe2O3 spheres. The calcination time of Fe3O4/Ni(OH)2 precursor has significant influences on the grain growth, the NiO content and the compactness of NiO shells in the -Fe2O3/NiO core/shell system. VSM and SQUID are used to characterize the magnetic properties of -Fe2O3/NiO core/shell nanoflowers. The results indicate that the 3 h-calcined sample displays better ferromagnetic properties (such as higher ms and smaller HC) because of their high -Fe2O3 content. In addition, as the coupling interaction between the FM -Fe2O3 and AFM NiO components, we observe that the -Fe2O3/NiO samples formed in 3 h and 6 h display certain exchange bias (HE=20 and 46 Oe, respectively). Such a coupling effect allows a variety of reversal paths for the spins upon cycling the applied field, and thereby resulting in the enhancement of coercivity (HC(FC)=252 and 288 Oe, respectively). Further, the values of HE and HC for the former are smaller than those of the latter, this is because of the AFM NiO content in 6 h-calcined sample much higher than that in 3 h-calcined sample. Especially, the temperature dependences of the magnetization M of the two samples under both ZFC and FC conditions indicate that an extra anisotropy is induced. In a word, the size effect, NiO phase content, and FM-AFM (where FM denotes the ferromagnetic -Fe2O3 component, while AFM is the antiferromagnetic NiO component) interface coupling effect have significant influence on the magnetic properties of -Fe2O3/NiO core/shell nanoflowers.
Great enhancement of transversal magneto-optical Kerr effect for magnetic dielectric film embedded by one-dimensional metallic grating
Authors: Chen Yu  , Liu Long  , Huang Zhong  , Tu Lin-Lin  , Zhan Peng  ,   School of Physics, Nanjing University, National Laboratory of Solid State Microstructures, Nanjing 210093, China
Published: December 2020

Transversal magneto-optical Kerr effect (TMOKE) has potential practical applications, such as biosensors, magnetic imaging, and date storage. However, these potential applications have been restricted by its very weak response (about 0.1%) in natural ferromagnetic metal material such as Fe, Co and Ni. Fortunately, with the development of the nanofabrication techniques, surface plasmons (SPs) are one of the effective strategies to solve this problem due to their special ability to manipulate light on a nanoscale and concentrate the electromagnetic energy near the metal/dielectric interface. Herein, in order to enhance the TMOKE response, we propose that a periodic gold strips array is embedded into a magnetic dielectric film of bismuth iron garnet (BIG), which is supported by a quartz substrate. Using the finite element method, we numerically study the optical properties of our proposed microstructure and the corresponding evolution of the TMOKE responses due to the coupled optical modes dependent on the structural parameters. Particularly, by optimizing the embedded depth of metal grating, a dramatic enhancement of TMOKE response (about 3.6%) is achieved when the embedded depth reaches up to 80 nm, accompanied with a high transmissivity about 22.6%, which is actually three time larger than that in the case that the gold strips are just patterned on the surface of the BIG film. As the embedding depth increases further, the TMOKE response will be weak. The relationship between the TMOKE response and the coupling efficiency of LSP resonance of the gold stripes and the waveguide (WG) mode supported by the BIG film are also discussed systematically. As the embedding depth increases up to 80 nm gradually, the coupling of the WG mode in BIG film with the LSP mode of the individual gold stripe becomes much stronger and forms a highly efficient Fano resonance, which leads to the fact that most of the electromagnetic field is localized in the BIG film and strong interaction with the BIG magnetic dielectric film, and thus, an enhancement of TMOKE response can be observed. However, when the embedded depth increases further, the uniformity of BIG film will be broken. In this case, WG mode cannot be supported by BIG film very well any more at the wavelength corresponding to excitation of the LSP, which results in a weakly coupling efficiency between LSP and WG mode. In this case, the Fano resonance cannot be formed and rare electromagnetic field can be localized in the BIG film, leading to a very weak light-magnetic dielectric film interaction and the weak TMOKE response. Our study proposes a new method to realize the amplification of weak TMOKE response by utilizing the plasmonic microstructure, which might have a potential application to designing the high-efficiency magneto-optical devices.
Performance and optimization research of triple-junction solar cell along the optical axis direction on \text{the HCPV module}
Authors: Lian Rong-Hai  , Liang Qi-Bing  , Shu Bi-Fen  , Fan Chou  , Wu Xiao-Long  , Guo Yin  , Wang Jing  , Yang Qing-Chuan  ,   Institute for Solar Energy System, School of Engineering, Sun Yet-Sen University, Guangzhou 510006, China
Published: December 2020

High concentrating photovoltaic (HCPV) technology plays a more and more important role in solar power generation due to its extremely high efficiency. However, the efficiency of the HCPV module can be reduced by many factors. Especially, there are not enough researches and knowledge on the light intensity distribution and non-uniform illumination of different wavelengths of light concentrated by Fresnel lens. It is generally considered that the maximum power of multi-junction solar cell is achieved when the cell is placed on the focal plane of Fresnel lens. But it is proved to be incorrect by our research. When light beams of different wavelengths go through the Fresnel lens, their light spot distributions on the optical axis are not the same as those when they have different refractive indexes in Fresnel lens. At the same time, the triple-junction solar cell consists of three sub-cells which absorb light beams of different wavelengths respectively. Therefore, the performance of triple-junction cells would be influenced by the light distribution along the optical axis, this is exactly what we want to study in this work. The method of simulating the light tracing is used to calculate and analyze the light intensity distribution and non-uniform characteristics of different wavelengths of light concentrated by Fresnel lens. Combined with them from the circuit network model of a triple-junction solar cell, the electrical performances of triple-junction solar cell at different positions along the optical axis are studied. It is found from the simulation that the performance of cell does not reach the best state when cell is placed on the focal plane. The power of cell on the focal plane reaches only 0.41 W while the maximum point arrives at 0.69 W. The high non-uniformity of light on cell surface when cell is placed on the focal plane causes the decline of power. And an outdoor HCPV testing system with the ability to change the distance between Fresnel lens and the cell is conducted. The experimental results and the simulation results match well, therefore our simulation approach is verified. It shows that the module achieves the maximum power on either side of the focal plane, and the output power can increase more than 20% after optimization. It is a result after equilibrium between light intensity and uniformity on cell surface.
Day-to-Day dynamical evolution of network traffic flow under bounded rational view
Authors: Li Tao  , Guan Hong-Zhi  , Liang Ke-Ke  ,   Beijing Key Laboratory of Transportation Engineering, Beijing University of Technology, Beijing 100124, China
Published: December 2020

The formation mechanism of network traffic flow and its evolution law are closely related to daily activities of travelers. The current studies indicate that the law of network traffic flow evolution is day-to-day; therefore, using days as the scale unit is an important way to illustrate the evolution of network traffic flow. In previous studies, travelers in the network were tacitly assumed to be entirely rational. When the rationality of travelers is limited, the dynamics of the evolution law needs to be re-examined. This paper presents the utility maximization hypothesis in a logit model by using the bounded rationality hypothesis and develops a bounded rational binary logit (BRBL) model. We apply the BRBL model to a day-to-day network traffic flow distribution and discuss the evolution law of day-to-day network traffic flow under the assumption of the limited rationality of travelers. Through a numerical experiment, this paper analyzes the evolution characteristics of network traffic flow. The results are as follows. Firstly, the final state of the network traffic flow process is not only correlated to the cost-sensitivity of travelers and dependence on actual cost, but also strongly related to the degree of the nationality of travelers. Secondly, the system will be either bifurcated or chaotic when either cost-sensitivity increases or dependence on actual cost increases. Moreover, within the group of travelers whose rationality level is low, no matter what the cost-sensitivity of travelers and the dependence on actual cost are, the evolution results are asymptotically stable. Finally, in particular, in certain circumstances, it is easy to achieve stability when the rationallty degree of travelers is very high or very low, while it is not easy to achieve stability when the rationality degree of travelers is medium.
Experiment research on dynamic response of copper film at high strain rate by chirped pulse spectral interferometry
Authors: Fan Wei  , Zhu Bin  , Xi Tao  , Li Gang  , Lu Feng  , Wu Yu-Chi  , Han Dan  , Gu Yu-Qiu  ,   Science and Technology on Plasma Physics Laboratory, Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

That the femtosecond laser pulses irradiate metallic materials thereby inducing ultrahigh strain rates, is an important experimental approach to studying the material behavior under extreme conditions. Femtosecond laser-generated shock waves in metal films have rise times of several picoseconds, the corresponding diagnostic technique is required to work with a higher time resolution, which makes the experimental measurements difficult. Chirped pulse spectral interferometry (CPSI) possesses capabilities of ultrafast time resolution and continuous measurement, thus it provides a diagnostic technique for studying the ultrashort shock wave. In this article, we carry out an experiment on femtosecond laser driven shock wave in copper film and the measurement by CPSI. Laser pulse of 25 fs duration at the central wavelength 800 nm is used, the tested samples are copper films of (5025) nm in thickness fabricated by electron beam sputtering deposition onto cover slip substrate of 180 m in thickness, pump beam focuses onto front surface of the copper film through the transparent substrate and this laser intensity is 2.31013 W/cm2. Chirped pulse spectral interferometry is used to detect the movements of the free rear surfaces of the copper films with temporal and spatial resolution. In the spectral interferometry, linearly chirped pulse is required and obtained by stretching the femtosecond laser pulse with a pair of gratings. The relation between frequency and time of the chirped pulse is accurately measured using asymmetric spectral interference method, which is required for explaining the experimental data. Since CPSI is a single shot diagnostic technique, we obtain the displacement and velocity history of the free rear surface with picosecond time resolution in a single measurement. From the results, the average shock velocity is calculated to be (5.60.2) km/s and the shock wave rise time is determined to be 6.9 ps. According to the shock wave relations, impact pressure and strain rate in the copper film are (57.18.8) GPa and 8109 s-1 respectively, the strain rate is so high that it is hard to achieve by long-pulse laser driven or other loading approaches. Additionally, experimental results also show that the free rear surface alternately experiences acceleration and deceleration, which indicates the spallation in the copper target. It is obvious that chirped pulse spectral interferometry is a reliable approach to studying ultrashort shock waves in metal films.
Ionization time of He atom in the strong field tunnelling ionization mode
Authors: Wang Yan-Hai  ,   School of Science, Hebei University of Science and Technology, Shijiazhuang 050018, China
Published: December 2020

The question of how long it takes for a particle to tunnel through a barrier, which was first put forward by MacColl (Phys. Rev. 40 621 (1932)), belongs to the fundamental process of quantum physics and has been the subject of intense debate since then. Many efforts have been devoted to addressing this question about how to define, explain and measure this tunneling time, but widespread controversies still exist in theories and experiments. Attosecond physics offers insights into ultrafast electron dynamics in atoms and moleculars on the attosecond (10-18 s) timescales, and therefore, ionization of atoms or moleculars in a strong laser filed allows for tackling this question in an experimentally and conceptually well-defined manner. The tunneling ionization dynamics of electrons plays an extremely important role in the field, since tunneling is the first crucial step in strong field ionizations of atoms and molecules and underlies virtually all present experiments in attosecond science. In the present paper, the tunneling ionization time of a single-active electron tunneling through a He atom subjected to a step static electric field, defined as a nonvanishing positive time delay between the instant of switch-on of the step static electric field and the one of ionization, is obtained from the numerical solution of the time-dependent Schrdinger equation in one dimension. The results show that the time delay between the instant of maximum probability current at the potential barrier exit and the one of switch-on of the step static electric field and the time delay needed by the ground wave function evolving to the continuum, which can be expressed as the transition element of the incident and transmitted parts of the wave function, are both very close to the Keldysh time explained as the time it takes for the bound electron having velocity = iIp/2 to cross the tunneling barrier. Compared with the definition of tunneling time delay in other literature, the one of the ground wave function evolution to the continuous state is much consistent with the actual ionization process. The reason why the electron tunneling time cannot be defined as the time delay between the maximum ionization rate and the instant of the laser peak field is that the wave function could penetrate the tunneling barrier earlier if a few-cycle optical field is adopted in experiment. According to the analysis in this article, an experimental method of measuring the actual electron tunneling ionization time using the optical field synthesis technique is proposed. The results of this paper will be helpful in tackling the problem of tunneling time in strong ionization.
System of label-free three-dimensional optical coherence tomography angiography with high sensitivity and motion contrast and its applications in brain science
Authors: Zhou Li-Ping  , Li Pei  , Pan Cong  , Guo Li  , Ding Zhi-Hua  , Li Peng  ,   State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Combining three-dimensional (3D) imaging ability of optical coherence tomography (OCT) with movement recognition ability of dynamic scattering technique, label-free 3D OCT angiography can be realized, which has a wide range of applications in basic science research and clinical diagnosis. At no expense of line scanning speed, the scale of capillaries can be detected by improving the sensitivity through the interframe analysis. However, there exists a certain residual overlap between dynamic flow signals and static tissue beds due to a series of reasons, thus making it difficult to completely distinguish dynamic flow signals from static tissue beds. Thus, when it comes to threshold segmentation for the blood flow signal extraction, classification error rate is inevitable, resulting in the decrease of the motion contrast of angiogram. In order to reduce classification error rate between static tissue beds and dynamic flow signals for high motion-contrast angiography, we propose a method of component compounding in wavelet domain. Three main steps are needed for this method. Firstly, on the basis of two-dimensional (2D) discrete static wavelet transform, a frame image can be decomposed into multiple levels. Each level has four components, i.e., approximation component, horizontal detail component, vertical detail component and diagonal detail component. Different decomposition levels and types of wavelet can be selected according to the demand. Secondly, the algorithm of inverse iteration compounding is used, which contains the arithmetic mean and the geometric mean of the components of adjacent decomposition levels. The adopted order for inverse iteration compounding is from the last level to the first one. The weight of the arithmetic mean to the geometric mean is one to one. In this way, four compounding components can be obtained. Thirdly, a new frame image with higher motion contrast can be obtained by using 2D discrete static wavelet inverse transform of the four compounding components. Both flow phantom and live animal experiments are performed. The results show that classification error rate decreases by 83% and 71% respectively after component compounding in wavelet domain. Besides, the angiogram has an improved motion contrast and a better vessel connectivity, which may contribute to better and wider applications of OCT angiography. Furthermore, based on the developed system, the preliminary imaging studies on the model of local stroke are conducted. In this experiment, we record the 3D data of SD mouse brain before and after the local stroke and on the tenth day. As a consequence, a clear presentation for the whole process of stroke model formation, vessel damage and vessel recovery is achieved, which may be beneficial to studying the mechanism of local stroke model.