bluuebunny/crossref_metadata_2025 huggingface dataset:
Localization of blue phase liquid crystal with ordered crystallographic direction and well-defined micro-patterning
Authors: Zhou Kang  , Yuan Cong-Long  , Li Xiao  , Wang Xiao-Qian  , Shen Dong  , Zheng Zhi-Gang  ,   Department of Physics, East China University of Science and Technology, Shanghai 200237, China;,   School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China
Published: December 2020

The construction of uniform orientation of crystallographic direction of blue phase is of great importance for its practical applications and the scientific research of multi-dimensional controllable growth of soft matter. With the consideration of the weak thermal stability of blue phase, the uniform lattice orientation of blue phase is combined with localized polymer-stabilization in this work. So the relatively stable fabrication of micro-patterns for blue phase can be realized, and it is promising for researchers to prepare brand new photonic devices. To the best of our knowledge, the relevant reports are rather rare, and the successful implementation of the above ideas is full of difficulties according to current conditions. In this paper, the uniform, patterned and stable orientation of crystallographic direction of blue phase is achieved by using the aforementioned integrated method. Here in this work, facile rubbing alignment is used as the primary way to realize the uniform lattice orientation. Meanwhile, the polymer-stabilization, as an effective technological way, is used to stabilize the frustrated topological structure of aligned blue phase for a better stability and its application perspective. Furthermore, we construct the well-defined micro-patterned blue phase array including one-dimensional and two-dimensional pattern in virtue of facile and effective localized exposure. Simultaneously, the stability of such a micro-pattern under external field is also investigated to evaluate the validity of stabilized superstructure and characteristic behavior of unstable region. As a result, the micro-patterned blue phase array keeps good state even under the adequate exposure to high voltage. Finally, the potential photonic application is explored based on the above micro-patterns which exhibit good optical diffraction effects in the experiment that follows. In conclusion, it really provides a feasible route for achieving stable control about orientation of soft matter, like liquid crystal, and fabricating field-stable and periodic superstructure. Such a research will speed up the development of blue phase liquid crystal in crystallography, electronics, and photonics.
Numerical reference plane algorithm for effectively solving tilt distortion of a phase image in digital off-axis holography
Authors: Li Fang  , Wang Ming-Qing  , Zheng Ming  , Lu Wei  , Yu Qing-Nan  , Jia Yan  , Wu Jian  ,   School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, China
Published: December 2020

It is a simple and commonly-used approach to use an inclined plane reference wave to remove zero-order diffraction and conjugated image in digital off-axis holography. However, this method is encountering a difficulty, since an additional carrier frequency is incorporated into the inclined reference wave and it is difficult to accurately obtain this additional carrier frequency via experimental measurement, a certain tilt distortion of the phase image will occur in the hologram reconstruction. In this paper, a numerical reference plane algorithm is proposed to solve this problem. This method innovatively constructs a numerical reference plane which is able to exactly characterize the tilt of the phase image by choosing three different points from a local flat of the reconstructed image, and establishes a mathematical relation between the plane parameters and the carrier frequency of the reference wave, which is used as a criterion of correcting the tilt distortion of the phase image in the subsequent iterative computation. The procedures of the algorithm are as follows. 1) Input the nominal carrier frequencies, (fx', fy') of the plane reference wave and reconstruct the hologram. 2) Unwrap the phase with PUMA algorithm and suppress the noise using bilateral filtering and short time Fourier transform with wavelet shrinkage. 3) Construct the numerical reference plane reflecting the image inclination and establish the mathematical relation between the plane parameters and the carrier frequencies of the reference wave. 4) Perform the iterative computation to correct the nominal carrier frequencies, (fx', fy') by using the differential coefficients, (a, b) of the reference plane equation as the criterion. 5) Output the computation result and the corrected phase image. The algorithm is simple and effective. It is able not only to achieve accurate correction to the tilt phase distortion, but also to exactly obtain the additional carrier frequency of the inclined plane reference wave. Since in the phase unwrapping reconstruction, the proposed approach combines with bi-lateral filtering processing, wavelet shrinking and short time Fourier transform to remove the noise influence while the image details are preserved, the method would still be valid under the influences of environmental and system noise. The experimental result supports the theoretical prediction very well.
Entanglement dynamics of three atoms in optical cavity coupled to reservior
Authors: Xing Gui-Chao  , Xia Yun-Jie  ,   Shandong Provincial Key Laboratory of Laser Polarization and Information Technology, Colleg of Physics and Engineering, Qufu Normal University, Qufu 273165, China
Published: December 2020

Quantum entanglement is one of most remarkable features of quantum mechanics,and in recent years it has played a more and more important role in quantum information.However,real quantum system inevitably interacts with the environment,resulting in the entanglement decay or even entanglement sudden death,so it is necessary to study the entanglement dynamical properties of an open system under different environments.In this paper,we investigate the entanglement dynamic behaviors of three interacting two-level atoms in an optical cavity which is coupled to a structured zero-temperature bosonic reservoir.Laplace transform,LBC and other methods are utilized,through numerical method we analyze the entanglement dynamic behavios of tripartite of three atoms and bipartite of cavity and reservoir.We also discuss how the coupling parameters affect the entanglement dynamics.Results show that in a short time,the entanglement of tripartite increases with coupling strength of three atoms increasing,and a periodic oscillation appears, but entanglement of bipartite decreases.The entanglement of tripartite decreases with the coupling strength between atoms and cavity increasing and damping oscillation appears,but the entanglement of bipartite increases.In a long-time limit,the entanglement approaches to a steady value.The non-Markovian dynamics of the qubits is determined by both the coupling strength and the spectral width.The strong system-reservoir coupling regime results in the non-Markovian dynamics of system.As the spectral width increases,the system of three atoms transforms from non-Markovian regime to Markovian regime.The increasing of spectral width results in the Markovian dynamic behavior of system,but the system of the atoms falls into the non-Markovian regime once more.When the coupling between the cavity and reservoir is weak,the entanglement of three atoms increases as the detuning of the cavity and reservoir increases,but it is not obvious.When the coupling between the cavity and reservoir is strong,the entanglement of three atoms increases and a periodic oscillation appears with increasing the detuning between the cavity and reservoir,so we can effectively restrain the effects of dissipation of reservoir on entanglement decay by adjusting the detuning between the cavity and reservoir.
Design of circular composite sputtering cathode and simulation of its discharge characteristics
Authors: Wang Tian-Long  , Qiu Qing-Quan  , Jing Li-Wei  , Zhang Xiao-Bo  ,   Applied Superconductivity Key Laboratory, Chinese Academy of Sciences, Institute of Electrical Engineering of the Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   SuPro Instruments Company Limited, Shenzhen 518035, China
Published: December 2020

Based on the two-dimensional finite element method, the magnetic field of circular composite magnetron sputtering cathode is calculated by COMSOL software. The genetic algorithm and simulated annealing algorithm combined with Matlab optimization toolbox are used to optimize the structure of circular composite magnetron sputtering cathode, and the structural parameters with the largest utilization rate of target are obtained. For the resulting optimized magnetron cathode, based on the self-consistent particle simulation method, the discharge characteristics under different working conditions are simulated by VSim software. It is found that with the increase of non-equilibrium degree of magnetic field, the cathode surface potential drops to the maximum position and the location of the plasma aggregation, moving from the outer surface of the cathode to the center, the intensity of the magnetic field on the cathode surface decreases When the two coils have no currents flowing, the density of the plasma is largest and the thickness of the sheath is smallest In the two coils there flow reverse 5 A currents, the non-equilibrium magnetic field reaches a maximum value and the thickness of sheath is largest, the corresponding electric field strength is weak, which is not conducive to the impact ionization, so the plasma density is smallest However, in the two coils there flow positive 5 A currents, and the non-equilibrium magnetic field is smallest, the plasma density and the sheath thickness are not only related to the non-equilibrium magnetic field, but also to the magnetic field strength. Finally, according to the results of particle simulation, the target erosion depth of the magnetron cathode is studied. Combined with the sputtering yield curve, the curve of etching depth of the cathode target surface is obtained. It is found that the erosion range of the target extends from 60 mm to 76.2 mm (target radius) before and after optimization. By adjusting the magnitudes and directions of currents in the two coils, all the target surfaces can be etched, which greatly improves the target utilization.
Far-field super-resolution imaging based on wideband stereo-metalens
Authors: Gao Qiang  , Wang Xiao-Hua  , Wang Bing-Zhong  ,   Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

The resolution of traditional far-field imaging system is generally restricted by half of wavelength of incident light due to the diffraction limit. The reason is that evanescent waves carrying subwavelength information cannot propagate in the far-field and make no contribution to the imaging. To realize the far-field super-resolution imaging, the imaging system should be able to collect both propagation and evanescent waves. Many ideas were presented to provide feasible alternatives but with narrow frequency band. In this paper, a wideband metalens is proposed to realize far-field super-resolution based on stereometamaterials. A typical model of stereometamaterials is studied, which consist of a stack of two identical spiral resonators in each cell, with various twist angles. For each case, there are two observable resonances (-and +), obviously. The phenomenon can be explained as the plasmon hybridization between the two resonators due to their close proximity. The case with a twist angle of 90 is chosen as the basic cell to constitute the stereo-metalens (S-ML). The last S-ML can work in a frequency range from 1.06 to 1.53 GHz, which is much wider than the planar-metalens. Simulations of near-and far-field spectra are conducted to validate the conversion between evanescent waves and propagation waves. Then with the help of antennas in the far-field to receive the information, sub-wavelength image can be reconstructed. The simulations in frequency-and time-domain are performed to verify the super-resolution characteristics of the S-ML. In frequency-domain, an imaging simulation of L-shaped extended target is combined with multiple signal classification imaging method. The resolution defined by full width at half maximum is 19 mm, corresponding to /12. For comparison, a similar simulation without the S-ML is performed, indicating a resolution of 1.5. It shows the ability of the S-ML to enhance the imaging resolution. In time-domain, by using time reversal technique, the spatial super-resolution characteristic of the S-ML is validated. Compared with the planar-metalens, the S-ML has good spatial super-resolution characteristic. All results show that the S-ML has a good potential application in imaging.
Microwave electromagnetically induced transparency and Aulter-Townes spectrum of cesium Rydberg atom
Authors: Fan Jia-Bei  , Jiao Yue-Chun  , Hao Li-Ping  , Xue Yong-Mei  , Zhao Jian-Ming  , Jia Suo-Tang  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China;,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

We present an electromagnetically induced transparency and Aulter-Townes (EIT-AT) spectrum of a Rydberg three-level atom that is dressed with a microwave field in a room-temperature cesium cell. The EIT is a quantum coherent effect produced by the interaction of atoms with electromagnetic waves, which leads to the decrease of the absorption for a weak resonant probe laser. AT splitting refers to the phenomenon, that the absorption line splits when an electromagnetic field that is in resonance or near resonance acts on the transition of atoms. Rydberg atoms are extremely sensitive to an external electric field due to their large polarizabilities and microwave transition dipole moments, which can be used to measure the external field. In this work, a Rydberg three-level EIT is used to detect Rydberg atom and AT splitting induced by the microwave field. Cesium levels 6S1/2, 6P3/2 and 50S1/2 constitute a Rydberg three-level system, in which a weak probe laser locking to the transition from 6S1/2 to 6P3/2 couples ground-state transition and the strong coupling laser resonates on the Rydberg transition from 6P2/3 to 50S1/2. The two Rydberg levels 50S1/2 and 50P1/2 are coupled with the microwave field at a frequency of 30.852 GHz, leading to the AT splitting of EIT line and forming an EIT-AT spectrum, which is used to measure the electric field amplitude of microwave. In order to further study the EIT-AT splitting characteristics of the Rydberg levels, we carry out a series of measurements by changing the microwave field. The experimental results show a broadened EIT-AT signal for the weak field range and the four-peak spectrum for the strong field, which is attributed to the inhomogeneity of the microwave field. The microwave in cesium cell, emitted by a function generator, shows inhomogeneous behavior such that the atoms interacting with the laser field experience the different fields, leading to the line broadened and multi-peak EIT-AT spectra. For the microwave transition of nS1/2-nP1/2 in this paper, a pair of EIT-AT lines should be obtained for an electric field value. The broadening of the EIT-AT spectrum and the multi-peak structure here are due to the inhomogeneity of the microwave field measurement. We propose a method to increase the spatial resolution by reducing the length of cesium cell. The result in this work provides a method of measuring the field amplitude and monitoring the distribution of microwave electric field, meanwhile the spatial resolution of the measurements can be improved by reducing the size of the cell.
Acoustic rotational relaxation of hydrogen around normal temperture
Authors: Zhang Xiang-Qun  , Wang Shu  , Zhu Ming  ,   School of Electronic Information and Communications, Huazhong University of Science and Technology, Wuhan 430074, China;,   School of Information Engineering, Xuchang University, Xuchang 461000, China
Published: December 2020

Hydrogen is an important energy carrier, and it is widely used due to its extraordinary advantages, such as high heat, clean fuel, being large-scale and renewable. The detection of hydrogen is essential in practical application. Therefore, many researches have focused on monitoring the hydrogen concentration over the past years. Acoustic relaxation theory based on molecular relaxation process is a very promising method of detecting hydrogen gas. However, the existing acoustic relaxation models for gas detection are developed from the vibrational relaxation of gas molecules, and thus they are not applicable for hydrogen and its mixture. In this paper, we present a model for the rotational relaxation process of hydrogen. Firstly, the molecular relaxation process of hydrogen is different from those of other gases due to its large spacing of rotational energy-level and special molecular physical structure. Acoustic relaxation process of hydrogen is mostly determined by the molecular rotational relaxation. Hydrogen molecule is made up of one quarter of para-hydrogen and three quarters of ortho-hydrogen at normal temperature. There is three-rotational-level model for hydrogen rotational relaxation, such as rotational level in states with J=0, 2, 4 (J is rotational quantum-number) for para-hydrogen and J=1, 3, 5 for ortho-hydrogen. Secondly, we introduce effective specific heat into one-mode rotational relaxation at constant pressure, and then extend it to multi-mode rotational relaxation. Upon periodic perturbation of acoustic waves, the temperature and the number of molecules in each rotational level change periodically in the relaxation process. On the basis, we obtain the relaxation equations in a matrix form and calculate effective specific heat at constant pressure for rotational relaxation process. With the relationship between the complex wave number and the effective thermodynamics acoustic speed, we calculate the frequency-dependent acoustic speed and relaxation absorption, and then discuss the difference between the rotational relaxation and the vibrational relaxation. Thirdly, we compare the predicted acoustic speed and absorption spectrum with their corresponding experimental data and investigate the influences of rotational characteristics on absorption spectra in hydrogen and its mixtures. The simulation results show that acoustic speed and relaxation absorption curves calculated by the proposed model are in good agreement with their corresponding experimental data. The model is not only applicable to pure hydrogen gas but also can be used to obtain the acoustic relaxation spectra of gas mixtures with multiple vibrational modes. This model provides a theoretical foundation for the acoustic detecting of hydrogen gas mixtures.
Interrogation of spin polarized clock transition in strontium optical lattice clock
Authors: Guo Yang  , Yin Mo-Juan  , Xu Qin-Fang  , Wang Ye-Bing  , Lu Ben-Quan  , Ren Jie  , Zhao Fang-Jing  , Chang Hong  ,   Key Laboratory of Time and Frequency Primary Standards of Chinese Academy of Sciences, National Time Service Center, Xi'an 710600, China;,   School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

We demonstrate a spin-polarized clock transition spectrum of the 87Sr optical lattice clock. The clock transition 5s2 1S05s5p 3P0 of isotope 87Sr has a hyperfine structure due to non-zero nuclear spin, inducing ten -polarized transitions from each individual mF state under the condition of a bias magnetic field along the probing polarization axis. In this experiment, atoms are driven to a certain mF state by a circular-polarization pump light to maximize the atomic population, which is beneficial to the stability and uncertainty evaluation of the optical lattice clock. After two stages cooling and trapping, about 3.5106 atoms are trapped in the red magneto-optical trap with a temperature of 3.9 K. A grating-feedback external cavity diode laser with a tapered amplifier is used to build the optical lattice with a magic-wavelength of 813.426 nm. Both waists of the counter-propagating lattice beam along the horizontal direction are overlapped to form a one-dimensional (1D) optical lattice. The lifetime of the atoms trapped in the 1D optical lattice is 1600 ms. The clock laser at 698 nm is a grating-feedback diode laser, which is locked to an ultra-low expansion cavity by the Pound-Drever-Hall technique to stabilize the frequency and phase. As a result, the linewidth of clock laser is narrowed to Hz level. By the normalized shelving method, we obtain a resolved sideband spectrum of 87Sr 5s2 1S05s5p 3P0 transition. According to the spectrum, the lattice temperature along the longitudinal direction is approximately 4.2 K. After that a linewidth of 6.7 Hz of the degenerate clock transition is obtained at a probing time of 150 ms by utilizing a three-dimensional (3D) bias magnetic field, which is used to eliminate the stray magnetic fields. Then a small bias magnetic field of 300 mGs is applied along the polarization axis of the lattice light to achieve the spectrum of Zeeman magnetic sublevels of the clock transition. Furthermore, the mF=+9/2 and mF=-9/2 magnetic sublevels are picked to be respectively pumped by the +-polarized and --polarized light at 689 nm, a variable liquid crystal wave plate is employed to switch on both polarizations. Finally, the spin polarized clock transition spectrum is obtained at the interrogating pulse of 150 ms, and the linewidths of the mF=+9/2, mF=-9/2 magnetic sublevel transitions are 6.8 Hz and 6.2 Hz respectively.
Improvement of current characteristic of perovskite solar cells using dodecanedioic acid modified TiO2 electron transporting layer
Authors: Du Xiang  , Chen Si  , Lin Dong-Xu  , Xie Fang-Yan  , Chen Jian  , Xie Wei-Guang  , Liu Peng-Yi  ,   Siyuan Laboratory, Guangzhou Key Laboratory of Vacuum Coating Technologies and New Energy Materials, Department of Physics, Jinan University, Guangzhou 510632, China;,   Instrumental Analysis and Research Center, Sun Yat-sen University, Guangzhou 510275, China
Published: December 2020

In the classical planar heterojunction perovskite solar cells (PSCs), the electron conducting TiO2 layer shows lower conductivity than the hole transporting materials such as spiro-OMeTAD, which becomes one of the key problems in improving the power conversion efficiency (PCE) of PSCs. In this study, the surface of compact TiO2 layer is modified by a thin self-assembled dodecanedioic acid (DDDA) molecular layer. The TiO2 substrates are immersed into the DDDA solution for 0.5, 2.5, 4.5, 22 h, respectively. It is found that the PCE of PSCs is improved when using the DDDA modified TiO2, showing optimized PCE of 15.35%0.75% under AM 1.5G illumination at 100 mWcm-2 after 4.5 h modification. The short current density (JSC) of the best device is improved from 20.34 mA cm-2 to 23.28 mA cm-2, with the PCE increasing from 14.17% to 15.92%. And it is found that the hysteresis of the PSC is also reduced remarkably with hysteresis index decreasing from 0.4288 to 0.2430. In the meantime, the device with DDDA modification shows a significant improvement in light stability, keeping 71% of its initial PCE value after 720 min exposure under AM 1.5G illumination at 100 mW cm-2 without encapsulation. As a contrast, the device without DDDA modification keeps 59% of its initial PCE value under the same condition. To reveal the mechanism, we investigate the surface energy level change using ultraviolet photoemission spectroscopy. It is found that after DDDA modification, the valence-band maximum energy (EVBM) of TiO2 decreases from -7.25 eV to -7.32 eV, and the conduction-band minimum energy (ECBM) of TiO2 from -4.05 eV to -4.12 eV. The shifting of energy level optimizes the energy level alignment at the interface between the TiO2 and perovskite. It promotes the transport of electrons from perovskite layer to compact TiO2 layer and obstructs the transport of holes from perovskite layer to compact TiO2 layer more effectively. In addition, the decrease of ECBM implies the increase of conductivity of TiO2. We further design a series of electrical experiments, and confirm that the modification improves the conductivity of TiO2 obviously with both contact resistance and thin-film resistance decreasing. In summary, our results indicate the enormous potential of the compact TiO2 layer with a thin self-assembled DDDA molecular layer modification to construct efficient and stable planar heterojunction PSCs for practical applications.
Numerical simulation of fractured-vuggy porous media based on gamblets
Authors: Zhang Qing-Fu , Huang Zhao-Qin , Yao Jun , Li Yang , Yan Xia ,   China University of Petroleum (East China), Qingdao 266580, China,   Department of Oilfield Exploration and Development, Sinopec, Beijing 100728, China
Published: December 2020

Numerical simulation of a fractured-vuggy porous medium is a challenging problem. One reason is the coexistence of matrix, fractures and vugs on multiple scales that need to be coupled, and the other reason is that the high-resolution fractured-vuggy model may contain up to several millions of gridcells in applications, which brings severe computational challenges into the numerical methods. Therefore, the requirement for accurate and efficient technique is widely increasing. Fractured-vuggy porous medium is generally represented by triple-continuum model in which the matrix system, fracture system and vug system each are treated as a parallel continuous system. Although triple-continuum model is widely used because of its easy-implementation and high efficiency, it fails to capture the detailed flow patterns of reservoir with disconnected long fractures. Discrete fracture-vug network (DFVN) model can precisely model the fluid flow in fractures and vugs. However, the simulation of this model is deemed intractable even with the advent of supercomputers because of the large amount of calculation. In view of the fact that the multigrid method is now well known as one of the fastest method of solving elliptic problems, in this paper we introduce a nearly linear complexity multiresolution decomposition method for fluid flow in a fractured-vuggy reservoir. The detailed flow patterns are described by combing the advantages of continuum model and discrete model. That is, the homogenization theory is used to construct an equivalent permeability in each coarse grid block in which the vugs and small-scale fractures are represented by discrete fracture-vug network model. We decompose the solution space into several subspaces and then we compute the corresponding solutions of heterogeneous discrete fracture network model in each subspace. Gamblets are constructed and they are elementary solutions of hierarchical information games associated with the process of computing with partial information and limited resources. These gamblets have a natural Bayesian interpretation under the mixed strategy emerging from the game theoretic formulation. This method could realize its fast simulation by decomposing the solution space into a direct sum of linear subspaces that are orthogonal to each other. Finally, the pressure difference distribution of fractured-vuggy porous medium is obtained by combing the DFVN solutions of all subspaces. Numerical results are presented to demonstrate the accuracy and efficiency of the proposed multiresolution decomposition method. The results show that this method is a promising method of numerically simulating the fractured-vuggy porous medium.
Recognition of denatured biological tissue based on variational mode decomposition and multi-scale permutation entropy
Authors: Liu Bei , Hu Wei-Peng , Zou Xiao , Ding Ya-Jun , Qian Sheng-You ,   School of Physics and Electronics, Hunan Normal University, Changsha 410081, China
Published: December 2020

It is an important practical problem to accurately recognize whether biological tissue is denatured during high intensity focused ultrasound (HIFU) treatment. Ultrasonic scattering echo signals are related to some physical properties of biological tissues. According to the characteristics of ultrasonic scattering echo signals, the recognition of denatured biological tissues is studied based on the variational mode decomposition (VMD) and multi-scale permutation entropy (MPE) in this paper. The ultrasonic echo signals are decomposed into various modal components by the VMD. The noise components and the useful components are separated according to the power spectrum information entropy of various modal components. The separated useful signals are reconstructed and the MPE are extracted. Furthermore, Gustafson-Kessel (GK) fuzzy clustering analysis is employed to obtain the standard clustering center, and the recognition of denatured biological tissues is carried out by Euclid approach degree and principle of proximity. The proposed method is applied to ultrasonic scattering echo signal during HIFU treatment. In order to determine the parameters of MPE algorithm for ultrasonic scattering echo signals, the embedding dimension of the MPE is discussed, and the scale factor of the MPE algorithm is optimized by genetic algorithm. When the delay time and the embedding dimension are 2 and 7 respectively, the MPE values decrease with scale factor increasing. Assuming that the scale factor is 12 from optimization results, the 293 ultrasonic scattering echo signals from normal tissues and denatured tissues are analyzed by the MPE. It is found that the MPE values of the denatured tissues are higher than those of the normal tissues. The MPE can be used to distinguish normal tissues and denatured tissues. Comparing with the recognition methods of the EMD-MPE-GK fuzzy clustering method and the VMD-WE-GK fuzzy clustering, the proposed method has good clustering performance and separability. Its partition coefficient (PC) is close to 1 and the Xie-Beni (XB) index is smaller. There are fewer feature points in the overlap region between MPE features of denatured tissues and normal tissues. The recognition results of denatured biological tissues in this experimental environment show that the recognition rate based on this method is higher, reaching up to 93.81%.
Analysis of propagation characteristics of Gaussian beams in turbulent plasma sheaths
Authors: Lü Chun-Jing , Han Yi-Ping ,   School of Telecommunitions Engineering, Xidian University, Xi’an 710071, China,   School of Physics and Optoelectronic, Xidian University, Xi’an 710071, China
Published: December 2020

In this paper, the characteristics of Gaussian beam propagation through turbulent plasma sheath are studied. According to the generalized Huygens-Fresnel principle, the random phase screen is generated by power spectrum inversion method based on the fast Fourier transform. The random phase screen is used to simulate turbulence effect. The thickness of the plasma sheath is of about centimeter order of magnitude. Compared with the single fast Fourier transform algorithm, the double fast Fourier transform algorithm is not prone to under-sampling and can obtain good image results, even if the diffraction distance is 1 mm. Therefore, double fast Fourier transform algorithm is used for investigating the beam propagation between two phase screens. The turbulence effect of the plasma sheath surrounding a hypersonic vehicle is simulated by the multi-random phase screens. When the flight altitude is 45 km and the flight speed is 18 Mach, the intensity of refractive index fluctuation variance ranges from \begin{document}${10}^{ - 11} $\end{document} to \begin{document}$ {10}^{ - 14} $\end{document} indicated by analyzing the plasma flow field around the hypersonic vehicle. The characteristics of the Gaussian beam propagation through the turbulent plasma are numerically simulated. The results show that the refractive index fluctuation, wavelength and transmission distance are important factors affecting the Gaussian beam quality. The larger the refractive index variance, the more severe the spot dispersion and the more obvious the light intensity fluctuation. As wavelength is longer, the ability of the Gaussian beam to resist turbulence becomes stronger and the dispersion of the light spot and the intensity fluctuation are smaller. The beam distortion and the spot dispersion become more severe as the transmission distance is longer.
Investigation of n-α scattering by combining complex momentum representation and Green’s function
Authors: Wang Xiao-Wei , Guo Jian-You ,   School of Physics and Materials Science, Anhui University, Hefei 230601, China
Published: December 2020

Nuclear scattering is a very important physical phenomenon in which the resonance state plays an important role. In order to study the two-body system n-α scattering, Green’s function is introduced under the complex momentum representation, so the complex momentum representation-Green’s function approach is established. This method is used to study the elastic scattering of n-α system. By extracting the resonances, it is found that the contributions of resonances in continuum level density, phase shift, and cross section are more important. In the case without introducing any non-physical parameters, it is very helpful to understand the resonant states and the non-resonance continuum states by analyzing the data of scattering states. In this work, we mainly study the p-wave scattering with the orbital angular momentum l = 1, where P1/2 is a wide resonance state and P3/2 is narrow resonance state. The study shows that the sharp resonance peak of p-wave scattering gives rather broad distribution to the scattering phase shift and the cross section of the n-α system. By comparison, we can see that the theoretical calculation results and experimental data are in good consistence.
Light-enhanced gating effect on the persistent photoconductivity at LaAlO3/SrTiO3 interface
Authors: Dao Liu-Yun , Zhang Zi-Tao , Xiao Yu-Tong , Zhang Ming-Hao , Wang Shuai , He Jun , Jia Jin-Shan , Yu Le-Jun , Sun Bo , Xiong Chang-Min ,   Department of Physics, Beijing Normal University, Beijing 100875, China,   College of Information Science and Technology, Beijing Normal University, Beijing 100875, China
Published: December 2020

The LaAlO3/SrTiO3 interface has been one of the topics studied most during the past few years due to its many intriguing properties such as the two-dimensional electron gas, transient photoconductivity (PC), persistent photoconductivity (PPC), and the coexistence of the PC and PPC. Of them, the PPC effect is the most interesting because of its potential application in exploring the photoelectric memory devices. Until now, tuning of the PPC of the LaAlO3/SrTiO3 interface under the external stimuli, such as electric or magnetic field is less addressed, while the relevant knowledge is of great value for exploring the memory devices with multifunctionality. In this paper, we report on an electric field control of the persistent PPC at the LaAlO3/SrTiO3 interface. Our LaAlO3/SrTiO3 heterojunction is fabricated by growing the LaAlO3 film on the SrTiO3 substrates through using pulsed laser deposition. The substrate temperature is kept at 750 ℃ and the partial pressure of oxygen is maintained at 3.3 × 10–5 Torr (1 Torr = 1.33322 × 102 Pa) during the deposition. The thickness of LaAlO3 film is controlled to be about 2 nm by setting an appropriate deposition time. The X-ray diffraction experiment confirms that the LAO film is well epitaxial and of single phase. To guarantee the good electric contacts, Al electrodes are soldered at the LaAlO3/SrTiO3 interface and the back side of the SrTiO3 respectively by ultrasonic welding. We find that the PPC at the LaAlO3/SrTiO3 interface can be significantly reinforced and modulated by the light-enhanced gating effects: that is, after a negative back gate voltage processing combined with a simultaneous light illumination, the LaAlO3/SrTiO3 interface can exhibit a notable PPC effect. And the PPC effect increases as the negative gate voltage increases, and then attains a maximum at a back gate voltage of about –70 V. Further increase of the negative gate voltage can cause the PPC to decrease. Additionally, the PPC is also found to increase monotonically with increasing the gating time. The present result can be understood in terms of the migration of the oxygen vacancies under the influence of photoelectric synergetic effect. This field enhanced PPC effects at the LaAlO3/SrTiO3 interface may find their applications in designing the photoelectric memory devices with electric tunability.
Surface-enhanced Raman scattering effect of composite structure with gold nano-cubes and gold film separated by polymethylmethacrylate film
Authors: Wang Xiang-Xian , Bai Xue-Lin , Pang Zhi-Yuan , Yang Hua , Qi Yun-Ping , Wen Xiao-Lei ,   School of Science, Lanzhou University of Technology, Lanzhou 730050, China,   College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China,   Center for Micro- and Nano-scale Research and Fabrication, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

The composite structure of metal nanoparticle and metal film can be used as a surface-enhanced Raman scattering (SERS) substrate to significantly enhance the Raman signal of adsorbed molecules due to the strong coupling between local surface plasmons and propagating surface plasmons. An SERS substrate of the composite structure with gold nano-cubes and gold film separated by polymethylmethacrylate (PMMA) film is proposed. The optimum thickness of PMMA is 15 nm obtained by numerical simulation through using finite element method. The composite structure of PMMA spacer with a thickness of 14 nm is prepared experimentally. Using R6G as the Raman probe molecules and He-Ne laser with a wavelength of 633 nm as an excitation source, the SERS effect of the composite structure and single gold nano-cubes are studied. It is found that the composite structure can make the probe molecules produce a stronger Raman signal than the single structure. Furthermore, the SERS spectra of R6G molecules on the composite structure under the condition of aqueous solution of gold nano-cubes with different concentrations are studied. The results show that when the concentration of gold nano-cubes’ aqueous solution is 5.625 \begin{document}${\text{μ}}{\rm g/mL}$\end{document}, the SERS signal of the R6G molecules on the composite structure is strongest. The lowest concentration of R6G molecules which can be detected is about 10–11 mol/L.
Tilting fan beam back-projection filtration algorithm for local reconstruction in helical cone-beam computed tomography
Authors: Xi Xiao-Qi , Han Yu , Li Lei , Yan Bin ,   National Digital Switching System Engineering and Technological Research Center, Zhengzhou 450002, China
Published: December 2020

Dose reduction becomes one of the hot research fields in the most commonly used helical computed tomography (CT) for clinical diagnostic. Local imaging using a collimator can effectively lower the CT radiation dose by reducing the direct irradiation area. Due to the limitation of the exposing area, the projection data used for local imaging reconstruction are usually truncated, resulting in local reconstruction problems. The key in local image reconstruction is how to deal with the horizontal truncation of the projection data. The helical cone beam back-projection filtration (BPF) algorithm only needs to ensure the integrity of the projections of PI line to realize the reconstruction of the entire PI line, making local reconstruction possible. Due to the complexity and irregularity of the spatial distribution of PI lines, the existing helical BPF algorithms can only realize local surface reconstruction, whereas the local volume reconstruction is difficult. For the BPF algorithm in designing the PI line and the sampling points in helical cone beam CT and the difficulty in local volume reconstruction, the tilted fan-beam back-projection filtration (TFB-BPF) reconstruction algorithm is proposed by utilizing the weighted correction and coordinate expansion, based on the circular fan beam BPF. The algorithm divides the reconstruction area into several slices, constructs the inclined fan beam geometry for each layer, and slice-by-slice reconstruction is conducted by using the weighted modified tilted fan beam BPF algorithm. The most powerful feature of the algorithm is that the filter line, equivalent to the PI line in the original helical BPF algorithm, is selected in a two-dimensional plane. Therefore, it is more concise and efficient and can be applied to the reconstruction of local volume regions. In this paper, the helical cone beam CT imaging geometry and the original helical cone beam BPF algorithm are introduced. Then, the TFB-BPF reconstruction algorithm is deduced. Experimental results show that the algorithm can effectively realize the local volume reconstruction and overall improved image quality without obvious truncation artifacts.
Graphene-based field effect transistor with ion-gel film gate
Authors: Song Hang , Liu Jie , Chen Chao , Ba Long ,   State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China
Published: December 2020

Graphene is a kind of two-dimensional material with high light transmittance, high mechanical properties and high carrier mobility. The energy band of graphene can be turned by doping and electric field. Researches on the application of graphene to electronic devices focused on field effect transistors. For improving the performance, one generally improves the fabrication process and device structure, but many researchers chose to change the material or structure of dielectric layer. Ion-gel is a kind of mixture of organic polymer mesh structure with good thermal stability and high dielectric value, prepared by macromolecule organic polymer and ionic salt electrolyte material. With the effect of electric field, cations and anions in ion-gel diffuse to form a double charge layer distribution with a charge layer on the surface of material. This capacitance characteristic is similar to that of traditional capacitor. In this paper, ion-gel (PVDF-[EMIM]TF2N) film is used as a dielectric layer material to prepare the bottom-gate graphene-based field effect transistor (GFET), which is compared with the GFET with SiO2 bottom-gate, according to electrical characteristic curves. The effect of the ion-gel film on the transconductance, switching ratio and Dirac voltage of the GFET are analyzed. The effect of the vacuum environment and temperature on the GFET performance with ion-gel film gate are also investigated. The results show that in the room-temperature environment, the switching ratio and transconductance of the ion-gel film gate GFET device increase to 6.95 and 3.68 × 10–2 mS, respectively, compared with those of the SiO2 gate GFET, while the Dirac voltage decreases to 1.3 V. The increase in transconductance and switching ratio of ion-gel film gate GFETs are mainly due to the high capacitance of ion-gel film compared with those of conventional SiO2 gate dielectrics. There will be more carriers inside the graphene while in the carrier accumulation region of GFET transfer characteristic curve, which makes graphene more conductive. The Dirac voltage of ion-gel film gate GFET can be reduced to 0.4 V in the vacuum environment; as the temperature increases, the transconductance of GFET can increase up to 6.11×10–2 mS. The results indicate that the ion-gel film-based graphene field effect transistor shows good electrical properties in serving as high dielectric constant organic dielectric materials.
Identification of spent nuclear fuel with multivariate analysis based on database
Authors: Su Jia-Hang , Wu Jun , Hu Si-De ,   Graduate School of China Academy of Engineering Physics, Beijing 100088, China,   Center for Strategic Studies, China Academy of Engineering Physics, Beijing 100088, China,   China Academy of Engineering Physics, Beijing 100088, China
Published: December 2020

In recent years, as the international situation about nuclear arms control changes, the multilateral international arms control cooperation including non-proliferation, nuclear terrorism and nuclear security has drawn more and more attention. As a key technology, nuclear forensics plays a significant role in the deterrence, prevention and response to illegitimate nuclear activities, for which it needs studying in depth. At present, there are plenty of researches into nuclear forensics, mostly focusing on the characterization of materials and the interpretation of data. As one of the most important aspects of nuclear forensics research, the interpretation is faced with a variety of different objects, including uranium ore, yellow cake, nuclear fuel, spent nuclear fuel and so on, among which spent nuclear fuel has attracted more and more attention due to its potential threats. In this paper, we primarily focus on the development of multivariate statistical analysis with an aim to interpret the comparative signatures of spent nuclear fuel. A database is established with uranium and plutonium isotopic compositions of spent nuclear fuel samples through simulation. These samples are of different reactor types, initial fuel enrichments and burn-ups. Subsequently, multivariate analysis, including factor analysis, discriminant analysis and regression analysis, are used to the database to validate the feasibility of the identification work. First of all, dimension reduction and visualization work is carried out to determine the possibility for classification by factor analysis. Afterwards, some known samples are assumed to be unknown to further study the possible capabilities of quantitative attribution by conducting factor analysis, including the determination of initial fuel enrichment and burn-up. To eliminate the errors in the identification work and to achieve better outcomes, the discriminant analysis and regression analysis are used to the database to assist with the identification of the reactor type, initial fuel enrichment and burn-up. As revealed by the study, factor analysis is more suitable for the dimension reduction and visualization work, disciminant analysis is more suitable for the identification of reactor type, and regression analysis is more suitable for the identification of initial fuel enrichment and burn-up. Upon the comparison drawn of the three different multivariate analysis methods, a framework for identification process is established to provide a theoretical basis and feasible scheme for the possible identification work of spent nuclear fuel with database, and facilitate the related nuclear forensics work.