bluuebunny/crossref_metadata_2025 huggingface dataset:
Cascading failure analysis in hyper-network based on the hypergraph
Authors: Ma Xiu-Juan  , Zhao Hai-Xing  , Hu Feng  ,   School of Computer Science, Shaanxi Normal University, Xi'an 710062, China;,   School of Computer Science, Qinghai Normal University, Xining 810008, China
Published: December 2020

In this paper, we analyze the diffusion patterns of cascading failure, which happen in the express hypernetwork and electronic hypernetwork respectively. The cascading failure of the express hypernetwork is diffused by the node, and the cascading failure of the electronic hypernetwork is diffused by the hyper-edge. According to hyper-graph theory, we propose two methods to characterize these cascading failures, which are 2-section graph analytical method and line-graph analytical method. We analyze the characteristics of the cascading failures based on node by using the 2-section graph analytical method and based on hyper-edge by using line-graph analytical method, respectively. We construct a k uniform scale-free hypernetwork and analyze the cascading failure process of this hypernetwork based on the couple map lattice according to our methods. The simulation results show that the scale-free hypernetworks are both robust and vulnerable for attack. It is found that the cascading failure based on the node of k uniform scale-free hypernetwork is associated with the hyper-degree distribution of nodes, and the scale-free hypernetwork is robust for random attack and vulnerable for deliberate attack. The more nodes a hyper-edge has, the better robustness the hypernetwork has.The cascading failure based on the hyper-edge is different from the cascading failure based on the node. The cascading failure based on the hyper-edge is associated with the hyper-edge degree distribution. The hyper-edge degree distribution of the scale-free hypernetwork is not entirely the power-low distribution. When the cascading failure is diffused by the hyper-edge, the hypernetwork is vulnerable for random attack and robustness for deliberate attack if there are 3 or 5 nodes in a hyper-edge. Moreover, the hypernetwork becomes robust for the random attack if there are 7 nodes in a hyper-edge. Furthermore, the k uniform scale-free hypernetwork is more robust than the same size Barabasi-Albert scale-free network for the same attack. The cascading failure process based on the hyper-edge is slower than based on the node. We find that the edge number is another influential factor of robustness. The network is more robust if it has more edges for fixed node number. The line-graph has more edges than the 2-section graph in the same size scale-free hypernetwork, so the cascading failure of node is slower than that of hyper-edge.
Intensity distribution of 69.8 nm laser pumped by capillary discharge
Authors: Zhao Yong-Peng  , Li Lian-Bo  , Cui Huai-Yu  , Jiang Shan  , Liu Tao  , Zhang Wen-Hong  , Li Wei  ,   National Key Laboratory of Science and Technology on Tunable Laser, Harbin Institute of Technology, Harbin 150080, China
Published: December 2020

In this paper, intensity distribution of 69.8 nm soft X-ray laser pumped by capillary discharge is studied theoretically and experimentally. In experiment, a main current of 11.5 kA is chosen to generate the plasma in a 35 cm long capillary filling with Ar at pressures in a range of 14-16 Pa. The intensity distribution is characterized by two different components. There is a big peak in the center of the intensity distribution profile, and its full width at half maximum divergence is about 0.4 mrad. There are also two small off-axis peaks on the either side of the center peak, and the peak-to-peak divergence is about 1.5 mrad. In theory, three different distributions of electron density are used to study the propagation of Ne-like Ar 69.8 nm laser in a cylindrical plasma column. The spatial intensity distribution for the 69.8 nm laser beam is calculated with the geometrical optics approximation. The results show that the center peak, which has such a small divergence, could be attributed to the slight depression of electron density on the axis.
Substantial undercooling and rapid dendrite growth of liquid Ti-Al alloy
Authors: Wei Shao-Lou  , Huang Lu-Jun  , Chang Jian  , Yang Shang-Jing  , Geng Lin  ,   School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China;,   Department of Applied Physics, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

It is highly desirable to undercool titanium based alloy melts and modulate their dendritic solidification process due to the relevant applications in aerospace engineering. But the serious chemical reactivities of this category of alloys result in potent heterogeneous nucleation and suppress remarkable undercoolings in the course of normal material processing. This paper shows that such a challenge can be solved by containerless processing approach. Liquid Ti-25 wt.%Al alloy is highly undercooled and rapidly solidified under containerless state by both electromagnetic levitation and drop tube techniques. Its metastable undecoolability, crystal nucleation mechanism and dendrite growth process are examined experimentally and analyzed theoretically. Those heterogeneous nuclei with wetting angles above 60 are found to be quite difficult to eliminate even during levitation processing, thus reducing the undercoolability of this alloy. The maximum undercooling of bulk alloy melt reaches 210 K (0.11 TL). The thermodynamic driving force to initiate the nucleation of -Ti phase increases almost linearly with the enhancement of undercooling. The phase dendrite displays a growth velocity up to 11.2 m/s, indicating that the rapid solidification is realized at the relatively slow cooling rate of levitated alloy melt. With the increase of undercooling, phase dendrite experiences a kinetic transition from solute diffusion controlled to thermal diffusion controlled growth. Once undercooling exceeds 100 K, the nonequilibrium solute trapping effect brings about the practically desirable segregationless solidification. Nevertheless, the single condition of substantial undercooling is insufficient to suppress the solid state transformation of phase. It is decomposed into 2-Ti3Al phase plus a small amount of -TiAl compound after containerless solidification at levitated state. A more efficient approach to controlling and modulating the solidification microstructures is to utilize the coupled effects of high undercooling and rapid quenching, which proves to be feasible through the rapid solidification of alloy droplets inside drop tube. For those alloy droplets with diameters ranging from 77 to 1048 m, their cooling rates attain a maximum of 1.05105 K/s, and the predicted maximum undercooling is 227-778 K. In this case, phase dendrites are well refined and kept in a metastable state until ambient temperature. The heat transfer calculations indicate that the thermal radiation is the dominant cooling mechanism for the large alloy droplets above 690 m, whereas thermal convection becomes the major cooling mechanism for the small alloy droplets below 690 m. The microgravity condition during free falling does not show apparent effect on the microstructural formation of these alloy droplets.
Enhanced superconducting properties in MOD-YBCO thick films with CeO2 interlayer
Authors: Ding Fa-Zhu  , Gu Hong-Wei  , Wang Hong-Yan  , Qu Fei  , Shang Hong-Jing  , Zhang Hui-Liang  , Dong Ze-Bin  , Zhang He  , Zhou Wei-Wei  ,   Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China;,   Key Laboratory of Applied Superconductivity, Chinese Academy of Sciences, Beijing 100190, China;,   College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
Published: December 2020

In YBa2Cu3O7-x (YBCO) film there exists thickness effect: the critical current density of YBCO film drops precipitously as the coating thickness increases, especially in the case that the thickness of YBCO film exceeds 1 m. In this paper, we introduce very thin layers of CeO2 into YBCO layers and successfully fabricate the structure of YBCO/YBCO/CeO2/YBCO superconducting thick film. Firstly, YBCO films with two layers are fabricated on a LaAlO3 substrate by a multiple coatings process using a trifluoroacetate metal organic deposition method. Secondly, CeO2 thin films are deposited on YBCO films by RF-sputtering. Finally, we prepare the third YBCO film on CeO2interlayer. No cracks are observed in scanning electron microscopy images of these films; further, the majority of the grains in the films are well-textured and c-axis oriented. The full-width-half-maximum of the out-of-plane texture is measured to be 1.395 for the multilayer YBCO film at a thickness of 2 m Using this multilayer technology, we achieve Jc values of up to 1.36 MA/cm2 (77 K, self-field) in films as thick as 2 m, for an extrapolated critical current of 272 A/cm. We attribute the enhanced performance of the thick YBCO film to the CeO2 interlayer which playsan important role in transmission texture and stress relaxation.
Angle measurement uncertainty statistical distribution of pulsed laser quadrant photodetector
Authors: Zhang Wei  , Zhang He  , Chen Yong  , Zhang Xiang-Jin  , Xu Xiao-Bin  ,   ZNDY of Ministerial Key Laboratory, Nanjing University of Science and Technology, Nanjing 210094, China;,   Industrial Center, Nanjing Institute of Technology, Nanjing 211167, China
Published: December 2020

As a positionsensitive detector, laser quadrant photodetector(QPD) is widely used in the areas such as laser guidance, laser radar and space optical communication. In the echoed laser pulse detection mode, the laser pulse signal arrived at the QPD photosensitive surface is changed in pulse amplitude, pulse width and pulse waveform due to the influences of target characteristic, atmospheric transmission and other complex factors. In addition, there are random noises in QPD itself and the signal processing circuit. These factors will have an uncertainty effect on the angle measurement accuracy of the QPD. However, the study on the statistical distribution of digital angle measurement of pulsed laser QPD has not been carried out so far. To investigate this angle measurement statistical distribution, the channel of laser angle measurement circuit and the echoed laser spot on QPD photosensitive surface should be modeled first. A measurable signal model in one quadrant of QPD processing circuit channel is established based on the type of random noise and the type of desired ideal signal. The random noise model is considered to be a Gaussian distribution, and the ideal laser pulse signal is considered to have the Gaussian or inverted parabolic distribution in the time domain. Taking into account the QPD symmetry, the statistical distributions of angle measurement value αy for five different spot centers are calculated by the Monte Carlo simulation method within the range θ0∈[0,π/4], under the conditions of different signal distribution types in the time domain, different total peak powers of the spots, different ideal signal widths at half maximum, and different standard deviations of equivalent noise voltage probability density. Simulation results show that the statistical distribution of the measured angle αy value is a normal distribution, and is influenced by the above-mentioned conditions, especially by the signaltonoise ratio in one quadrant. QPD possesses higher angular accuracy as the spot center is closer to the axis center. While the spot center is not closer to the axis center, the mean of statistical distribution of the QPD measurement angle αy is always less than the ideal angle measurement value. Therefore, in order to improve the angle measurement accuracy of the pulsed laser QPD for digital purpose, laser pulse transmit power should be increased, or the noise of each circuit channel of QPD should be reduced, or the laser pulse width should be increased by modulating appropriately.
Cyclical pulsation properties of particles in cone silo
Authors: Wang Hui  , Jia Fu-Guo  , Han Yan-Long  , Zhang Ya-Xiong  , Cao Bin  ,   Department of Engineering Northeast Agricultural University, Harbin 150030, China
Published: December 2020

Intense particle pulsation during discharging may lead to the vibration of silo, even the failure of silo structure. To date, the studies related to particle pulsation have mainly concentrated in the following aspects: the noise caused by vibration of silo, the minimum decisive height to produce silo music and the factors affecting particle pulsation. However, the above studies cannot in depth analyze the motion state nor the flow law of all particles in silo. To explore the pulsation characteristics of particles, in this paper we simulate the discharging tests of ellipsoidal particles in deep silo with different half-cone angles based on the discrete element method, in order to reveal the mechanisms of particle pulsation and variation of contact force among the particles in the silo. In each simulation discharging test, the cylinder section of silo is divided into 4 fixed areas where flow behavior and the motion characteristics of particles are analyzed. The simulation results show that the velocity fluctuation of particles exists in the whole discharging process. At the early stage of discharging, the cyclical pulsation with large amplitude appears while irregular fluctuation with small amplitude occurs in the later stages. The study also finds that the dynamic characteristics of the axial force among particles are the same as those of velocity pulsation in the corresponding areas. Besides, the amplitude of particle pulsation shows an increase trend and the contact force of particles presents more periodic pulsation along the negative direction of outlet. The pulsation characteristics(velocity pulsation and force pulsation) of adjacent particle layers are similar, including similar waveform and identical cycle. During the intense pulsation stage, each minimum of the axial force of particles in the top layer is close to the gravity, indicating that the contact force among these particles disappears. Furthermore, the periodic pulsation of particles causes the contact force among particles to periodically disappear. It is noted that the stability of discharging, frequency, amplitude and duration of the intense pulsation increase with the decrease of the half-cone angle. In order to evaluate the fluctuation degree of the velocity pulsation, the standard deviation of particle velocities is used. Note that the particle velocities are no longer subjected to the influence of rising trend, which result is obtained by the finite difference method. The results show that the standard deviation gradually increases with the decrease of half-cone angle. This is because the increase of half-cone angle causes the time and amplitude of stable fluctuation to decrease. This numerical study of particle pulsation will provide the reference for safety design of discharging devices.
Structural model of InSb IRFPAs including underfill curing process
Authors: Zhang Xiao-Ling  , Si Le-Fei  , Meng Qing-Duan  , Lü Yan-Qiu  , Si Jun-Jie  ,   School of Information Engineering, Henan University of Science and Technology, Luoyang 471023, China;,   Henan Quality Polytechnic, Pingdingshan 467000, China;,   Academy Key Laboratory of Science and Technology on Infrared Detector, China Airborne Missile Academy, Luoyang 471009, China
Published: December 2020

InSb infrared focal plane array(IRFPA) detector, active in 3-5 m range, has been widely used in military fields. Higher fracture probability appearing in InSb infrared focal plane arrays(IRFPAs) subjected to thermal shock test, restricts its final yield. In order to analyze and optimize the structure of InSb IRFPAs, it is necessary to create the three-dimensional structural model of InSb IRFPAs, which is employed to estimate its strain distribution appearing in the different fabricating processes. In this paper, the curing model of underfill is described by its volume contraction percentage combined with the elastic modulus of the completely cured underfill. Thus, both the von Mises stress and the Z-components of strain accumulated in the curing process of underfill are calculated. When InSb IRFPAs is naturally cooled to room temperature from the curing temperature of underfill, the Z-component of strain distribution appearing on the top surface of InSb IRFPAs is obtained with our structural model, which is identical to the deformation distribution on the top surface of InSb IRFPAs measured at room temperature. In the following thermal shock simulation, we find that the maximal von Mises stress appears at 100 K and the maximal Z-component of strain appears at 150 K, these two temperature points are located in the second half of the thermal shock process, these results indicate that the fracture of InSb chip happens more easily in liquid nitrogen shock test. This inference is consistent with the fact appearing in liquid nitrogen shock test. All these findings suggest that the proposed model is suitable to estimate the deformation distribution of InSb IRFPAs and its changing rule in its different fabricating stages.
Spectroscopic properties of low-lying excited electronic states for CF- anion based on ab initio calculation
Authors: Zhou Rui  , Li Chuan-Liang  , He Xiao-Hu  , Qiu Xuan-Bing  , Meng Hui-Yan  , Li Ya-Chao  , Lai Yun-Zhong  , Wei Ji-Lin  , Deng Lun-Hua  ,   School of Applied Science, Taiyuan University of Science and Technology, Taiyuan 030024, China;,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
Published: December 2020

CF- anion is very important for collisional ionization reactions, electron transfer from Rydberg atoms and electron attachment. Potential energy curves (PECs) of five low-lying excited electronic states, X3Σ-, a1Δ, b1Σ+, A3Π and c31Π of CF-, are calculated by using the internally contracted multireference configuration interaction (icMRCI) approach. Ro-vibrational levels of these electronic states are derived through solving the radial Schrödinger ro-vibrational equation, and then the molecular parameters are obtained by fitting. Our results for X3Σ- agree well with those in the references. We compute the electronic dipole moments (EDMs) of these states with different bound lengths, and analyze the relationship between the electronic configurations and EDMs. The electronic transition dipole moment matrix elements, Franck-Condon factors and oscillator strengths f00 of A3Π-X3Σ- are evaluated, and radiative lifetimes of five lowest vibrational levels of A3Π state are derived. Finally the predissociation mechanism of A3Π state is discussed in detail, and the dissociation lifetimes of high vibrational levels are obtained.
Effect of grating groove density error on the output pulses of the tiled grating compressor and corresponding compensation scheme
Authors: Zhao Dan  , Wang Xiao  , Mu Jie  , Zuo Yan-Lei  , Zhou Song  , Zhou Kai-Nan  , Zeng Xiao-Ming  , Li Zhi-Lin  , Su Jing-Qin  , Zhu Qi-Hua  ,   Science and Technology on Plasma Physics Laboratory, Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   Graduate School of China Academy of Engineering Physics, Beijing 100088, China;,   Collaborative Innovation Center of IFSA, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

The grating groove density error (GGDE) will degrade the performance of the tiled-grating compressor, and the compensation for GGDE is of significance for improving the characteristics of the output pulses. With the ray-tracing method, analytical expressions considering GGDE are derived to predict the output beam drift and the output pulse broadening. According to the numerical results, we propose a compensation method to reduce the degradation of the tiled-grating compressor by applying angular tilt error and longitudinal piston error simultaneously. The tilt angle and the translation distance of the grating, as well as the allowable tolerance range of GGDE are obtained with this compensation method. By using the equiphase lines in the spatial-spectral interference patterns, the experimental results demonstrate that this compensation method can correct the angular drift of the output beams effectively, and compensate for the second-order and the third-order dispersion error well. Our investigation provides an efficient way to guide the adjustment of the tiled grating with GGDE.
First-principles study on the electronic structures and the absorption spectra of In: Mn: LiNbO3 crystals
Authors: Zhang Yun  , Wang Xue-Wei  , Bai Hong-Mei  ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

The electronic structures and the absorption spectra of the indium and manganese codoped LiNbO3 crystals and their comparative groups are investigated by first-principles based on the density functional theory. The supercell crystal structures are established with 60 atoms, including four models:the near-stoichiometric pure LiNbO3 crystal (LN), the manganese doped LiNbO3 crystal (Mn:LN, charge compensation model as MnLi+-VLi+), the indium and manganese codoped LiNbO3 crystal (In:Mn:LN, charge compensation model as InLi2+-MnLi+-3VLi+), and the other indium and manganese codoped LiNbO3 crystal (In(E):Mn:LN, charge compensation model as InLi2+-InNb2--MnLi+-VLi+). The results show that the extrinsic defect levels within the forbidden band of Mn:LN crystal are mainly contributed by Mn 3d orbital electrons, which also affect the top of the valence band. The band gap of Mn:LN about 3.18 eV is narrower than that of LN; the band gaps of In:Mn:LN and In(E):Mn:LN sample are 2.82 and 2.93 eV respectively. The electron density of state (DOS) of manganese codoped LiNbO3 crystal shows that the orbits of Mn 3d, Nb 4d and O 2p superpose each other, i.e., forming covalent bonds, which result in conduction and valence bands shifting toward low energy. The indium ion does not contribute the extrinsic energy level within forbidden band, it affects the band gap through changing O2- electron cloud shape. The band gap narrows down if the indium ions occupy lithium ion positions, and becomes broad if the indium ions occupy niobium ion positions. It is found that the Mn:LN, In:Mn:LN and In(E):Mn:LN samples display the absorption peaks at 3.25, 3.11, 2.97, 2.85, 2.13 and 1.66 eV. The last absorption peak is contributed by the electron transferring from the Mn2+ energy level to conduction band, and the doping of indium ions leads to attenuation of this peak. The peak at 2.13 eV relates to the Mn3+, it is enhanced by the doped indium ions. The indium ions in crystal would influence the absorption, which relates to manganese ions, by transforming manganese ion valence via the formula as m Mn2++In3+→Mn3++In2+, that is, with the doping of the indium ions, the photorefractive center Mn2+ concentration decreases, which is responsible for the absorption peak at 1.66 eV. It must be mentioned that the Mn2+ possesses not only the shallow levels as mentioned previously, but also the deep ones which are responsible for the absorptions at 2.85 eV and other high energies. For the indium and manganese codoped LiNbO3 crystals, if the recording light is chosen at near 1.66 eV (748 nm), the relatively low concentration of indium ions is proposed to be chosen to achieve the high recording sensitivity.
A memristor-based time-delay chaotic systems and pseudo-random sequence generator
Authors: Wu Jie-Ning  , Wang Li-Dan  , Duan Shu-Kai  ,   School of Electronic and Information Engineering, Southweat University, Chongqing 400715, China;,   Chongqing Key Laboratory of Nonlinear Circuits and Intelligent Information Processing, Chongqing 400715, China
Published: December 2020

Memristor, a controllable nonlinear element, is easy to generate a chaotic signal. More significantly, it can improve the complexity of the chaotic system and the randomness of signals. Although the memristor chaotic system is a hot spot of research currently, little attention has been paid to the memristive time-delayed chaotic system. Therefore, a new memristor-based time-delayed chaotic system is proposed in this paper. We construct the time-delayed chaotic system with single delay time by using the nonlinear relationship between the memristance and charge of memristor. The existence of time delay enhances the complexity of chaotic system, which makes the system produce richer and more complex dynamics. In order to study the complex dynamic characteristics of this memristive time-delayed system, we investigate the proposed system by theoretical derivation, numerical simulation, stabilization of equilibrium points, and power spectrum. In addition, the corresponding parameter region of the stable equilibrium point of the system is discussed in detail. Then, we discuss the effect of parameter variation on the dynamic behavior of the system, and a series of phase diagrams with different time-delayed parameters and system parameters is described by numerical simulation. We find that different combinations of parameters and slight changes of parameters can make the system a completely different phase diagram, which indicates that the proposed system has rich nonlinear characteristic. Moreover, the proposed time-delayed system is used to generate pseudo random sequences, and the experimental results show that the proposed system has good self-correlation, cross-correlation, and the significant approximate entropy. According to the theoretical analyses and experimental results, we conclude that the proposed new time-delayed chaotic system has complex dynamic behavior and good randomness, which can meet the needs of the applications in spread spectrum communication, image encryption and many other fields. This research provides a significant reference for further studying the usage of memristor.
Trade-off optimization for low-dissipation heat engine with generic heat transfer process
Authors: Lu Can-Can  , Bai Long  ,   School of Physics, China University of Mining and Technology, Xuzhou 221116, China
Published: December 2020

The heat transfer process inevitably occurs in the operation of real heat engine. In this article, a low-dissipation heat engine with generic heat transfer process is proposed based on the low-dissipation Carnot model. The formulas for the power and the efficiency of heat engine with generic heat transfer law are derived, and the low-dissipation heat engine performance is also optimized by the trade-off optimization method, which offers a unified scheme to understand the behaviors of heat engines with generic heat transfer processes. Furthermore, the characteristics of the power as well as the efficiencies for thermal engines with the different heat transfer processes are discussed in detail, and it is found that the power and the efficiency without heat transfer process are independent of heat leak, but are related to contact time, heat dissipation and Carnot efficiency. The power output of heat engine monotonically increases as Carnot efficiency increases, but the large contact time ratio and the large dissipation ratio make it difficult to provide the big power output. When the heat leak is absent and () is fixed, the efficiency of heat engine decreases (increases) with the increase of (). It is noted that the heat transfer process greatly influences the performance of heat engine, and /C versus displays the similar properties under three heat transfer laws. It is clearly shown that /C versus shows the transition from the monotonic decrease to monotonic increase with increasing, but /C versus is opposite to the former, and the maximum value of /C also shifts rightwards with the increase of . Additionally, the corresponding efficiency of heat engine diminishes significantly as m decreases and n increases. When heat engines are dominated by different heat transfer laws, the curves of versus C are consistent as C is relatively large or small, but it is observed that there exist the evident differences among three characteristic curves in the middle regime. The relatively large or small will also lead to the reduction of the working regime where heat engine can function normally. Our results are very helpful in understanding the design principle and the optimization mechanism for actual thermal engines and refrigerators.
Theoretical analysis of spectrum reconstruction imaging using single-pixel detection
Authors: Yao Wei-Qiang  , Huang Wen-Hao  , Yang Chu-Ping  ,   Department of Physics, South China Agricultural University, Guangzhou 510642, China
Published: December 2020

As a novel imaging method, single-pixel imaging based on spectrum reconstruction is interesting. To date, however, there has not yet been a theory that can analyze the method in detail. In order to obtain a comprehensive understanding of the single-pixel imaging technique, a detailed theoretical analysis is proposed. Firstly, in the presented imaging theory, we analyze the effects of several factors involved in the imaging process on imaging reconstruction, including the direct detection, namely, the back scattering light from the imaged object is received by a detector; indirect detection, namely, the back scattering light is received after undergoing the diffuse reflections by multiple diffusing surfaces in proper sequence; multi-channel detection, namely, the scattering light is together detected after experiencing multiple diffuse reflections in proper sequence along multiple different paths; the size and location of the single-pixel detector. The theoretical results show that whether it is direct detection or indirect detection and whether it is single-channel detection or multi-channel detection, the above imaging method is valid as long as the scattering light can be received by the detector, and the obtained results are also in accord with the existing experimental results. Since the single-pixel detector is treated as a component of many point detectors due to its practical size, the effect of the single-pixel detector size on image reconstruction is equivalent to the integration of reconstructed images from multiple point detectors at different locations. Secondly, the spectrum reconstruction based on a three-step phase shift technique is also derived to increase the image reconstruction speed. Finally, the experimental results of the imaging reconstruction of an object, whose surface reflectivity is uniform, are demonstrated.
High pressure single-crystal synchrotron X-ray diffraction technique
Authors: Li Xiao-Dong  , Li Hui  , Li Peng-Shan  ,   Center for Multi-disciplinary Research, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China;,   Institute of Microstructure and Properties of Advanced Materials, Beijing University of Technology, Beijing 100124, China
Published: December 2020

A lot of great work has been done since the high pressure research carried out on synchrotron radiation facility almost 40 years ago. The history of high pressure single-crystal diffraction research on synchrotron radiation facility has also been more than 20 years. Recently, with the development of synchrotron X-ray optical techniques and high pressure technology, especially the invention and improvement of large opening diamond anvil cell (DAC), high pressure single-crystal X-ray diffraction (HPSXRD) method has become more and more popular in high pressure studies. The HPSXRD can be used to perform structure determination and refinement to obtain the information about lattice parameter, space group, atomic coordinate and site occupation. Compared with powder X-ray diffraction, the HPSXRD can not only obtain the three-dimensional diffraction information of samples, but also have much better signal-to-noise ratio. Furthermore, the HPSXRD data can be used to study the electron density distribution to obtain more information about chemical bonds and electron distribution. In this work, we introduce the HPSXRD method in synchrotron radiation facilities, including the knowledge of single-crystal X-ray diffraction experimental system, DAC for HPSXRD, sample loading, and HPSXRD data processing.
Pressure-tuned magnetic quantum critical point and unconventional superconductivity
Authors: Cheng Jin-Guang  ,   Key Laboratory of Extreme Conditions Physcis, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Magnetic quantum critical point (QCP) arises when a long-range magnetic order occurring at finite temperature can be suppressed to absolute zero temperature by using chemical substitutions or exerting high pressure. Exotic phenomena such as the non-Fermi-liquid behaviors or the unconventional superconductivity are frequently observed near the magnetic QCP. In comparison with chemical substitutions, the application of high pressure has some advantages in the sense that it introduces no chemical disorder and can approach the QCP in a very precise manner. In this article, our recent progress in exploring the unconventional superconductors in the vicinity of pressure-induced magnetic QCP is reviewed. By utilizing the piston-cylinder and cubic-anvil-cell apparatus that can maintain a relatively good hydrostatic pressure condition, we first investigated systematically the effect of pressure on the electrical transport properties of the helimagnetic CrAs and MnP. We discovered for the first time the emergence of superconductivity below Tc=2 K and 1 K near their pressure-induced magnetic QCPs at Pc0.8 GPa and 8 GPa for CrAs and MnP, respectively. They represent the first superconductor among the Cr- and Mn-based compounds, and thus open a new avenue to searching novel superconductors in the Cr- and Mn-based systems. Then, we constructed the most comprehensive temperature-pressure phase diagram of FeSe single crystal based on detailed measurements of high-pressure resistivity and alternating current magnetic susceptibility. We uncovered a dome-shaped magnetic phase superseding the nematic order, and observed the sudden enhancement of superconductivity with Tcmax=38.5 K accompanied with the suppression of magnetic order. Our results revealed explicitly the competing nature of nematic order, antiferromagnetic order, and superconductivity, and how the high-Tc superconductivity is achieved by suppressing the long-range antiferromagnetic order, suggesting the important role of antiferromagnetic spin fluctuations for the Cooper paring. These aforementioned results demonstrated that high pressure is an effective approach to exploring or investigating the anomalous phenomena of strongly correlated electronic systems by finely tuning the competing electronic orders.
Experimental and theoretical study on terahertz spectra of all-trans -carotene
Authors: Yan Wei  , Ma Miao  , Dai Ze-Lin  , Gu Yu  , Zhu Hong-Zhao  , Liu Yu-Tong  , Xu Xiang-Dong  , Han Shou-Sheng  , Peng Yong  ,   School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

The -carotene is a short chain polyene molecule containing nine -electron conjugated double-bonds. Because of its special molecular structure, -carotene has been used widely in many fields, including functional materials, optoelectronic devices and biological applications of light collection, light protection, anti-cancer, etc. Recently, new applications of -carotene in generation and detection of terahertz (THz) wave have also attracted great attention. In this work, all-trans -carotene films are prepared by spray coating, and the THz spectra in a wavenumber range of 30-400 cm-1 (a frequency range of 0.9-12 THz) of the as-prepared products are experimentally measured at room temperature by Fourier transform infrared spectroscopy. For comparison, the THz spectra in 0.5-3.0 THz are also characterized at the same temperature by THz time-domain spectroscopy. Based on these measurements, the fingerprint peaks of all-trans -carotene in the THz region are experimentally identified to be located at 54 cm-1 (1.62 THz), 57 cm-1 (1.71 THz), 64 cm-1 (1.91 THz), 77 cm-1 (2.32 THz), 90 cm-1 (2.69 THz), 98 cm-1 (2.95 THz), 115 cm-1 (3.45 THz), 124 cm-1 (3.72 THz), 134 cm-1 (4.02 THz), 170 cm-1 (5.11 THz), 247 cm-1 (7.42 THz), and 279 cm-1 (8.38 THz), respectively. It is worth noting that the recent results about the THz spectra of palm leaves are thus verified. Particularly, the B3 LYP method of density functional theory is further utilized in this work to theoretically simulate the THz spectra of all-trans -carotene molecule. It is revealed that the theoretical simulation results accord well with those experimentally measured data. In addition, we also find that the absorption peaks are caused by the torsion, deformation and rocking vibration of the molecules. Accordingly, the vibrational modes of the measured THz characteristic peaks at 148 cm-1 (4.44 THz), 132 cm-1 (3.96 THz), 115 cm-1 (3.45 THz), 76 cm-1 (2.28 THz) and 52 cm-1 (1.56 THz) are theoretically assigned, which provides a reference to explain the formation mechanism of the THz spectra. The valuable results presented in this work will be helpful for promoting the studies of the THz spectral features and response mechanisms of the organics.
Non-dipole effects in the angular distributions of photoelectrons on sodium-like ions
Authors: Ma Kun  , Xie Lu-You  , Zhang Deng-Hong  , Jiang Jun  , Dong Chen-Zhong  ,   School of Information Engineering, Huangshan University, Huangshan 245041, China;,   Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China
Published: December 2020

Photoionization processes widely exist in the astrophysical plasma and the high temperature laboratory plasma. Compared with the traditional photoelectron energy spectrum, the photoelectron angular distribution is not only related to the amplitude of the photoionization channels, but also sensitive to the phases of these channels. So the photoelectron angular distribution contains much more quantum information about the photoionization processes and is used to provide stringent tests of our understanding of basic physical processes underlying gas- and condensed-phase interaction with radiation, as well as a tool to probe physical and chemical structure in solids and surfaces. For a long time, the dipole approximation has been the basis in the study of the photoelectron angular distribution, but with the progress of light source, such as the fourth generation synchrotron facilities, more and more attention is paid to the non-dipole effect of the photoelectron angular distribution. In thispresent work, the photoionization processes of sodium-like ions (20Z92) are studied for the different incident photon energies based on the multiconfiguration Dirac-Fock method and the density matrix theory. The influences of the non-dipole terms on the photoelectron angular distributions, which arise from the multipole expansion of the electron-photon interaction, are discussed in detail. The relationship between the dipole and non-dipole parameters of the photoelectron angular distribution along with the atomic number is given. It is found that the influence of non-dipole terms on the photoelectron angular distribution is related to the incident photon energy and the atomic number of the target ion and the subshell of the ionized electron. In general, the influences of the non-dipole terms on the photoelectron angular distribution of p subshell are larger than those of the s subshell. In the electric dipole approximation, the s subshell photoelectron angular distribution is nearly independent of the photon energy and nuclear charge number, but this situation is not for the p subshell. With the increase of photon energy, an abnormal angular distribution is found for the p subshell photoelectron. However, if the non-dipole effects are included, the abnormal photoelectron angular distribution of p subshell disappears and the photoelectron distribution has maximum values respectively near 45o and 135o with respect to the polarization vector of incident light, that is, the photoelectron distribution has an obvious forward scattering characteristic.
Far-field time reversal subwavelength imaging of sources based on grating structure
Authors: Gong Zhi-Shuang  , Wang Bing-Zhong  , Wang Ren  , Zang Rui  , Wang Xiao-Hua  ,   Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

For far-field imaging applications, the imaging resolution of conventional lenses is limited by the diffraction limit because of the exponential decay of high spatial frequency waves. The key to realizing the subwavelength imaging lies in the collection of evanescent informations in far-field region. However, the collection of evanescent waves is not the only thing we need to do. The relation between target position and far-field information is also very important.
In this paper, a far-field time reversal subwavelength imaging system is constructed with the help of an evanescent-to-propagating conversion plate, i. e., a grating plate. The designed grating plate is able to convert evanescent waves into propagating waves through the modulation in space-spectrum domain. In order to clearly understand the conversion, a focusing experiment is conducted with two sources and five time reversal mirror antennas. By recording the amplitudes of the time reversal signals in the two source positions, we can see that the amplitude of the refocusing signal at the original source position is much larger than that of the other signal. Through numerical simulation and experiment, the conversion of evanescent wave into propagative wave is proved finally.
Then, according to the self-conjugation property of time reversal, the result of self-conjugation for channel response in complex environment is nearly the same as an impulse function. The image of source target can be reconstructed without exact prior knowledge of the expression of the spatial channel response. In order to exemplify the super resolution property of our designed system, experiments with simulation data and experimental data are executed with and without our designed grating plate, respectively. For imaging applications, we first record the forward signals received by the time reversal mirror antennas, and then record the refocusing field distribution on the imaging plane to obtain the image of the target. In the reconstruction process, another thing we need to notice is that the original sources should be removed. This is because in a real imaging application, we cannot know the exact position of target inadvance. The imaging results show that the resolution of our imaging system has overcome the diffraction limit.
Compared with the imaging resolution of the imaging system without the grating plate, the imaging resolution of the system with our designed grating plate is improved obviously. Since this kind of method overcomes the intrinsical diffraction limit by transmitting evanescent information to far-field region in a way of converting them into propagative waves. This kind of method offers us a promising alternative to microwave far-field subwavelength imaging applications.
Dynamic resistivity of Pb(Zr0.95Ti0.05)O3 depolarized ferroelectric under shock wave compression
Authors: Wu You-Cheng  , Liu Gao-Min  , Dai Wen-Feng  , Gao Zhi-Peng  , He Hong-Liang  , Hao Shi-Rong  , Deng Jian-Jun  ,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Explosive-driven ferroelectric generator (EDFEG) has important applications due to its excellent properties of high energy density and small volume. The output of EDFEG is based on the depolarization of ferroelectric during shock wave compression. In a normal mode configuration, a planar shock wave propagates in a direction perpendicular to the polarization axis. If the resulting depolarizing current passes through a large resistive load or a small capacitive load, high electric fields can be produced within the ferroelectric sample. In this case, a portion of the depolarizing charges are lost in the sample due to finite resistivity of shocked ferroelectrics during shock wave transit. But it is very difficult to accurately measure the resistivity of shocked ferroelectric during shock wave compression, due to high pressure and short duration time. In previous studies, the value of the resistivity of shocked Pb(Zr0.95Ti0.05)O3 (PZT95/5) ferroelectric was obtained from the experimental output charge difference for different large resistive loads or by fitting the experimental current histories. However, the current leakage was not observed directly in experiment in the past. Furthermore, the value of the resistivity obtained in each of all these studies was a time-averaged value. In the present work, a new experiment method is developed to investigate dynamic resistivity of PZT95/5 under shock wave compression, in which a pulse capacitor is used as an output load. The current leakage in shocked PZT95/5 is observed in the experiment at a shock stress of 3.5 GPa after the depolarization of all ferroelectrics. This current leakage is just related to the resistance of shocked PZT95/5 and the voltage applied. The experimental results show that the resistivity of shocked PZT95/5 continuously changes in a range of 2.2104 cm-3.5104 cm for time more than the shock transit time of the sample. Based on the experimental results, a dynamic resistance model is established to analyze the resistivity of depolarized PZT95/5 ferroelectric ceramic during shock wave transit in ferroelectric. The simulation results reveal dynamic characteristic of the resistivity of depolarized PZT95/5 ferroelectric ceramic under shock wave compression. The further analysis of experimental results shows that the resistivity continuously changes between 2.0104 cm and 8.0104 cm during shock transit in ferroelectrics. It is believed that dynamic characteristic of the resistivity of shocked PZT95/5 ferroelectric ceramic is related to pressure, electrical field applied and the defects in the material. The dynamic resistivity of shocked PZT95/5 obtained in this paper and its dynamic resistance model will be helpful for designing EDFEGs and their applications in the future.