bluuebunny/crossref_metadata_2025 huggingface dataset:
Weak ultrasonic signal detection in strong noise
Authors: Wang Da-Wei1\2  , Wang Zhao-Ba  ,   School of Information and Communication Engineering, North University of China, Taiyuan 030051, China;,   School of Physics and Information Engineering, Shanxi Normal University, Linfen 041000, China
Published: December 2020

In order to solve the problem of extracting ultrasonic signals from strong background noise, a novel method, which is termed APSO-SD algorithm and based on improved adaptive particle swarm optimization (APSO) and sparse decomposition (SD) theory, is proposed in this paper. This method can convert the ultrasonic signal denoising problem into optimizing the function on the infinite parameter set. First, based on the sparse decomposition theory and the structural characteristics of ultrasonic signal, the objective function of particle swarm optimization algorithm and the reconstruction algorithm of the denoised signal are constructed, so that particle swarm optimization and ultrasonic signal denoising can be combined. Second, in order to improve the robustness of the proposed approach, an APSO algorithm is proposed. What is more, because particle swarm optimization algorithm can be used to optimize in continuous parameter space, and according to the empirical characteristics of the ultrasonic signals used in practical engineering, a continuous super complete dictionary for matching ultrasonic signals is established. Since the super complete dictionary is continuous, there are an infinite number of atoms in the established dictionary. The redundancy of dictionaries is enhanced by the method in this paper. Based on the fact that the inner product of the optimal atom and the ultrasonic signal is one and the inner product of the noise and the optimal atom is zero in the established dictionary, the objective optimization function of APSO-SD algorithm is established. Finally, the optimal atom is determined based on the optimization result of the objective function. In this way, the denoising ultrasonic signal can be reconstructed by using the optimal atom according to the reconstruction algorithm. The processing results of simulated ultrasonic signals and measured ultrasonic signals show that the proposed method can effectively extract weak ultrasonic signals from strong background noise whose signal-to-noise ratio is lowest, as low as-4 dB. In addition, compared with the adaptive threshold based wavelet method, the proposed method in this paper shows the good denoising performance. In this paper, it is demonstrated that the problem of ultrasonic signal denoising can be transformed into the optimization of constraint functions. Furthermore, the ability of the proposed APSO-SD algorithm to accurately recover signals from noisy acoustic signals is better than that of the common wavelet method.
Electron correlation effects in even Rydberg series converging to 4f13(2F7/2o)6s(7/2, 1/2)4o and 4f13(2F7/2o)6s(7/2, 1/2)3o of thulium atom
Authors: Zhang Dian-Cheng  , Zhang Ying  , Li Xiao-Kang  , Jia Feng-Dong  , R. Li  , Zhong Zhi-Ping  ,   Collage of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;,   TRIUMF, University of British Columbia, Vancouver, British Columbia, Canada V6T 2A3;,   Center of Excellence in Topological Quantum Computation, Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

In the frame work of multi-channel quantum defect theory (MQDT), the energy levels of three even Rydberg series 4f13(2F7/2o)6s(7/2, 1/2)4onp3/2, 4f13(2F7/2o)6s(7/2, 1/2)3onp3/2 and 4f13(2F7/2o)6s(7/2, 1/2)3onp1/2 converging to 4f13(2F7/2o)6s(7/2, 1/2)4o or 4f13(2F7/2o)6s(7/2, 1/2)3o of thulium atom are calculated by relativistic multi-channel theory. Compared with the experimental data from National Institute of Standards and Technology (NIST), the theoretical result shows two different types of electron-correlation effects: 1)the interaction between two Rydberg series results in energy shifts for these Rydberg series; 2)an isolated perturbed state is embedded in the energy range of a Rydberg series and interacts with the whole series, and breaks the regularity of the Rydberg series, and quantum defects show a large jump around the perturbed state. More specifically, by comparing the present calculated quantum defects with the experimental data, we reassign two Rydberg series: 1)4f13(2F7/2o)6s(7/2, 1/2)4onp3/2 Rydberg series from NIST is reassigned as 4f13(2F7/2o)6s(7/2, 1/2)4onf5/2, J=(5/2)+, 4f13(2F7/2o)6s(7/2, 1/2)4onf5/2, J=(7/2)+ and/or 4f13(2F7/2o)6s(7/2, 1/2)4onp1/2, J=(9/2)+ Rydberg series, and the difference between experimental and calculated quantum defects is generally better than 0.1; 2)4f13(2F7/2o)6s(7/2, 1/2)3onp3/2 Rydberg series from NIST is reassigned as 4f13(2F7/2o)6s(7/2, 1/2)3onf7/2, J=(5/2)+, 4f13(2F7/2o)6s(7/2, 1/2)3onf7/2, J=(7/2)+ and/or 4f13(2F7/2o)6s(7/2, 1/2)3onf5/2, 7/2, J=(9/2)+ Rydberg series, and the difference between experimental and calculated quantum defects is generally better than 0.05. As for the 4f13(2F7/2o)6s(7/2, 1/2)3onp1/2 Rydberg series from NIST, we find there is a perturbed state at about 49900 cm-1, and assign the perturbed state as 4f13(3F4)6 d5/26s2, J=7/2 and the total angular momentum for the Rydberg series is J=7/2.
Magnetic property of CeFe2-xInx alloys and critical parameters of magnetic phase transition of CeFe1.95In0.05 alloy
Authors: Chen Xiang  , Zhao Ming-Hua  ,   College of Physics and Electronic Information Engineering, Neijiang Normal University, Neijiang 641100, China;,   The Ames Laboratory, U. S. Department of Energy, Iowa State University, Ames, Iowa 50011-3020, USA
Published: December 2020

Magnetic properties of CeFe2-xInx alloys and scaling critical behaviors of CeFe1.95In0.05 alloy are investigated by measuring the magnetic susceptibility and isothermal magneteization. The X-ray diffraction (XRD) patterns show that the solid solubility of the In substituted for the Fe in CeFe2-xInx alloy is limited. Because the intensity diffraction peak of impurity at 2=30.75 and 35.80 in CeFe1.95In0.05 XRD pattern are very low, the effect of impurity on magnetism is not considered in this paper. Magnetic measurements indicate that using 2.5 at.% indium to substitute for Fe in CeFe2 alloy can strengthen the orbital hybridization interaction between Ce-4f and Fe-3d, but it cannot reach the critical point to make the antiferromagnetic stable. The AFM fluctuation still keeps in a value ranging from 2 K to 80 K. The second order paramagnetic-ferromagnetic transition of CeFe1.95In0.05 at TC=230 K is confirmed by Arrott plot analysis. The effective ferromagnetic moment of Fe atoms can be increased by replacing part of the Fe atoms with In atoms in the CeFe2 alloy, which can increase the paramagnetic and effective magnetic moment and the magnetic saturation magnetic moment of the alloy. For a magnetic field change of 0-50 kOe, the maximum value of the magnetic entropy change-△ SM is 3.13 J/(kgK) at 230 K and RCP is 151.3 J/kg, which are higher than the values of Ce0.95Gd0.05Fe2, Ce0.9Gd0.1Fe2, and Ce0.9Ho0.1Fe2 alloys under the same magnetic field. The high self-consistent scaling critical exponents determined by modified Arrott plot and Kouvel-Fisher methods are[=0.3212(8) and =0.9357(9)] and[=0.3304(1) and =0.9249(1)], respectively. The parameter obtained from the critical magnetization isotherm MTC=DH1/ satisfies the Widom scaling relation =1+/. Moreover, the plot of M1/ vs. (H/M) 1/ constructed by the above critical parameters completely complies with the scaling hypothesis. At the same time, the critical parameters of n and obtained by|△ SM| Hn and RCP H(1 + 1/) fitting are 0.6191(8) and 5.0559(1), respectively. In all, non-local effect of spin interaction causes a certain difference between the critical parameters and 3D-Ising model standard values (=0.325, =1.241, n=0.569, and =4.818). But these differences are small, especially for critical parameter , which suggests that the magnetic interaction in CeFe1.95In0.05 alloy is a short-range interaction.
Super-high accurate new method of common-view time comparison based on space station
Authors: Liu Yin-Hua  , Li Xiao-Hui  ,   National Time Service Center, Chinese Academy of Science, Xi'an 710600, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

With the development of science and technology, the super high accurate time comparison techniques with several ten picoseconds or higher accuracy are required in many advanced and basic fields. The atomic clock system in the space station has better performance than that on the ground, but the traditional common-view time comparison method cannot be applied to the space station because there are some limitations. At first, the space station common-view time comparison principle aiming at several ten picoseconds accuracy is analyzed, and the sources of delay larger than 1 picosecond are considered. According to the space station common-view time comparison principle, the visibility of the space station is simulated based on several main geographical cities in China. The analysis results show that the time interval is short for ground station to observe the space station, and the common-view time interval is shorter. A more serious problem is shown that some areas cannot receive the signal send by the space station simultaneously, so the traditional common-view time comparison method is invalid when the ground stations are in these areas. Then the effect of space station orbit error is studied in theory and simulation based on the traditional method. The research result shows that the orbit error cannot be cancelled effectively by the traditional method, and the remnant orbit error is on the order of about several hundred picoseconds. These remnant orbit errors have a direct influence on the time comparison. A new asynchronous common-view time comparison method is proposed, and its principle and advantages are introduced. The geometric expression that describes the position relationship between the space station and two ground stations is proposed to find the observation time when the orbit errors can cancel completely. And the high stability of the space atomic clock and the ground atomic clock are advantaged to model and extrapolate the space-ground clock bias. The geometric position relationship and the modeling and extrapolating of the space-ground clock bias are combined together to solve the problems of time comparison accuracy and common-view blind area, because the optimized method does not require that two ground stations observe the space station simultaneously. Finally, the simulation experiments are done to validate the new method. The experimental result shows that the asynchronous common-view time comparison method is valid to realize the time comparison with the accuracy of several ten picoseconds. And it also shows that the new method is helpful in solving the problem of blind area that exists in traditional space station common-view time comparison method.
Novel superconducting qubits and quantum physics
Authors: Zhao Shi-Ping  , Liu Yu-Xi  , Zheng Dong-Ning  ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Institute of Microelectronics, Tsinghua University, Tsinghua National Laboratory for Information Science and Technology, Beijing 100084, China;,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

In the past years, superconducting quantum computation has received much attention and significant progress of the device design and fabrication has been made, which leads qubit coherence times to be improved greatly. Recently, we have successfully designed, fabricated, and tested the superconducting qubits based on the negative-inductance superconducting quantum interference devices (nSQUIDs), which are expected to have the advantages for the fast quantum information transfer and macroscopic quantum phenomenon study with a two-dimensional potential landscape. Their quantum coherence and basic physical properties have been demonstrated and systematically investigated. On the other hand, a new type of superconducting qubit, called transmon and Xmon qubit, has been developed in the meantime by the international community, whose coherence time has been gradually increased to the present scale of tens of microseconds. These devices are demonstrated to have many advantages in the sample design and fabrication, and multi-qubit coupling and manipulation. We have also studied this type of superconducting qubit. In collaboration with Zhejiang University and the University of Science and Technology of China, we have successfully fabricated various types of the coupled Xmon devices having the qubit numbers ranging from 4 to 10. Quantum entanglement, quantum algorithm of solving coupled linear equations, and quantum simulation of the many-body localization problem in solid-state physics have been demonstrated by using these devices. Also, we have made significant achievements in the studies of the macroscopic quantum phenomena, quantum dissipation, quantum microwave lasing, and some other quantum optics problems. In particular, Autler-Townes splitting under strong microwave drive, electromagnetically induced transparency, stimulated Raman adiabatic passage, microwave mixing, correlated emission lasing, and microwave frequency up-and-down conversion have been successfully studied, both experimentally and theoretically.
Recent progress of multiferroic magnetoelectric devices
Authors: Yu Bin  , Hu Zhong-Qiang  , Cheng Yu-Xin  , Peng Bin  , Zhou Zi-Yao  , Liu Ming  ,   Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Multiferroic composites possess the coupling effect among mechanical, electrical, and magnetic ordering, showing potential applications in compact, fast, and low-power magnetoelectric devices. Owing to the increasing application demand, the researches of device design, micro-/nano-fabrication, and performance test of magnetoelectric devices have made continuous progress. In this review, we briefly introduce several prototype devices based on magnetoelectric coupling, analyze the noteworthy application techniques, and summarize the working mechanisms and performances of devices including tunable inductors, RF/microwave filters, magnetoelectric memories, energy harvesters, magnetoelectric sensors, magnetoelectric antennas, etc. Besides, we discuss the issues and challenges in researches of multiferroic magnetoelectric devices, and present the perspectives for improving the device performance.
Numerical investigation on antispiral and antitarget wave in reaction diffusion system
Authors: Ni Zhi-Wei  , Li Xin-Zheng  , Bai Zhan-Guo  , Li Yan  ,   School of Sciences, Hebei University of Science and Technology, Shijiazhuang 050018, China
Published: December 2020

In this paper, the antispiral and antitarget wave patterns in two-dimensional space are investigated numerically by Brusselator model with three components. The formation mechanism and spatiotemporal characteristics of these two waves are studied by analyzing dispersion relation and spatiotemporal variation of parameters of model equation. The influences of equation parameters on antispiral and antitarget wave are also analyzed. Various kinds of multi-armed antispiral are obtained, such as the two-armed, three-armed, four-armed, five-armed, and six-armed antispirals. The results show that antispirals may exist in a reaction-diffusion system, when the system is in the Hopf instability or the vicinity of wave instability. In addition to the above two types of instabilities, there is the Turing instability when the antitarget wave emerges. They have the periodicity in space and time, and their propagation directions are from outside to inward (the phase velocity vp 0), just as the incoming waves disappear in the center. The rotation directions of the various antispiral tips are the same as those of the waves, which can be rotated clockwise or anticlockwise, and the rotation period of wave-tip increases with the number of arms. Furthermore, it is found that the collision sequence of the multi-armed antispiral tip is related to the rotation direction of the wave-tip. With the increase of the number of anti-spiral arms, not only the dynamic behavior of the wave-tip turns more complex, but also the radius of the center region increases. Due to the influence of perturbation and boundary conditions, the multi-armed antispiral pattern can lose one arm and become a new antispiral pattern in the rotating process. Under certain conditions, it can be realized that the single-armed antispiral wave transforms into an antitarget wave. It is found that the change of control parameters of a and b can induce the regular changes of the space scale of antispiral waves, and antispiral waves gradually turn sparse with the increase of a, on the contrary, they gradually become dense with the increase of b. When the parameter of D_w exceeds a critical value, the propagation direction of wave is changed, and the system can produce the transformation from antispiral wave to spiral wave and from antitarget wave to target wave.
Adiabatic conversion of ultracold atoms into molecules via square-shaped pulse field
Authors: Qin Yan  , Li Sheng-Chang  ,   School of Science, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

On the basis of the stimulated Raman adiabatic passage technology, we study the conversion of ultracold atoms into diatomic molecules by using a square-shaped pulse field. By the method of adiabatic fidelity, we analyze the dynamical evolution process of the coherent population trapping state for the atom-molecule conversion system. We introduce two adiabatic fidelities to describe the efficiency of ultracold atom-molecule conversion, i.e.:1) the final adiabatic fidelity, which gives the value of the adiabatic fidelity at the end of the evolution:the closer to 1 it is, the higher the conversion efficiency is; 2) the final maximum adiabatic fidelity, which denotes the maximum value that can be achieved at the end of evolution, indicating the highest conversion efficiency. With these two quantities, we discuss how to achieve higher adiabatic fidelity for the coherent population trapping state through optimizing the pulse-delay time and the pulse-laser intensity of the stimulated Raman adiabatic passage. In addition, we also discuss the effects of the width of pulses on the ultracold atom-molecule conversion efficiency and the feasibility of continuous light. It is shown that the final adiabatic fidelity of the coherent population trapping state demonstrates a large periodic oscillation with the pulse-laser intensity. By calculating and analyzing the final adiabatic fidelity and the final maximum adiabatic fidelity, we obtain the conditions for higher efficiency conversion, which gives the best choice of the pulse-laser intensity, the pulse-delay time, and the width of pulses. The results show that the scheme of square-shaped pulses we discussed has obvious advantages compared with that of Gaussian-shaped pulses, which can achieve high adiabatic fidelity and realize higher ultracold atom-molecule conversion efficiency via employing the pulse-laser field with low intensity. Further detailed comparison between the square-shaped pulses and the Gaussian-shaped pulses is also given. Particularly, we find that the final adiabatic fidelity shows a periodic oscillation with the pulse width, which means that the high efficiency atom-molecule conversion can be achieved by using a pulse field with small width. Moreover, we find that the high efficiency conversion can also be achieved by using special continuous light under certain conditions.
Photothermal properties of core-capped gold nanoparticles
Authors: Hong Xin  , Wang Chen-Chen  , Liu Jiang-Tao  , Wang Xiao-Qiang  , Yin Xue-Jie  ,   School of Biomedical Engineering, Faculty of Electronic Information and Electrical Engineering, Dalian University of Technology, Dalian 116024, China
Published: December 2020

Photothermal effects associated with noble metal nanostructures have shown wide potential applications in photo-thermal cancer therapy, photo-thermal imaging, nanomedicine, etc. These applications benefit from the localized surface plasmon resonance (LSPR) effect of the nanoparticles. Due to the LSPR effect, the nanoparticles exhibit unique optical properties such as strong scattering and absorption in the band ranging from visible to near-infrared region. The absorption enables the plasmonic nanoparticle to be a thermal source to increase the temperature of itself and the localized surrounding environment. Among these particels, the anisotropic core-capped nanostructures distinguish themselves by their strong polarization selectivity. The absorptions are different when the incident light is polarized in the directions vertical (90) and parallel (0) to its symmetry axis, respectively. At 90, a large red-shift can be achieved and the absorption cross section is greatly enhanced. Moreover, their absorption peaks can be flexibly manipulated by slightly adjusting one of the geometrical parameters. However, the photothermal responses to these parameters are left blank. In this paper, photothermal effects of SiO2@Au core-capped nanoparticles are studied based on the numerical finite elemental analysis method (COMSOL software). The thermal response to each of the paramenters, including shell thickness, core diameter, core-shell ratio, and metal surface coverage is achieved. The calculation shows that the temperature of these core-capped nanoparticles can be adjusted efficiently in the near infrared band by easily rotating the polarization, i.e. slightly adjusting the geometric parameters. Especially in a range between 30 and 70, the temperature varying with the polarization follows almost a linear relationship. The comparisons with other popular structures including solid sphere, core-shell and nanorod are also made. The results indicate that at a similar size, the core-capped structure can offer a higher temperature than solid spheres and core-shell structures. To obtain the same temperature variation, the core-capped one has a smaller size than a nanorod. The comparisons demonstrate that the core-capped structure can be an alternative to a high-efficient nano heat source in the photothemal applications.
Band gaps of piezoelectric/piezomagnetic phononic crystal with magneto-electro-elastic interlayer
Authors: Sun Wei-Hai  , Zhang Chao-Qun  , Ju Gui-Ling  , Pan Jing-Wen  ,   Department of Vehicle Engineering, Army Armored Forces Academy, Beijing 100072, China;,   Department of Fundamental Courses, Army Armored Forces Academy, Beijing 100072, China
Published: December 2020

Laminate piezoelectric (PE)/piezomagnetic (PM) composites consisting of alternating PE and PM layers can facilitate the conversion of energy between electric and magnetic fields, i.e., they possess the magneto-electric (ME) coupling effects, which recently has attracted much attention due to the huge potential applications in the field of high technology. The PE/PM phononic crystal is an ideal material for manufacturing high-tech precision parts such as resonator components, magnetoelectric sensors, weak magnetic field detectors, electric field tunable filters and magnetic field probes. In the practical applications, the adhesive interfaces of PE/PM phononic crystals are prone to deformation and failure during their use, because of the big difference between PE and PM material. In this paper, the magneto-electro-elastic (MEE) interlayer of magneto-electro-mechanical coupling is introduced into the PE/PM phononic crystal. The thickness of the MEE interlayer, the volume fraction of the piezoelectric material in the MEE interlayer and the type of the piezoelectric materials in the MEE interlayer are changed separately, with the thickness of the unit cell kept at a fixed value. The dispersion relation between the k and the is obtained by using the transfer matrix method and Bloch theorem. The influence of MEE interlayer on the band gap characteristics of PE/PM phononic crystal is studied by the dispersion relation diagram. The results show that as the thickness of the MEE interlayer increases, the central frequency of the band gaps shifts toward a higher frequency and the width of band gap becomes wider. As the volume fraction of the piezoelectric material increases, the center frequency and the width of the first band gap decrease. However, the width of the second band gap increases, and the width of the third band gap remains unchanged. The type of piezoelectric material in the MEE interlayer has an obvious influence on both the width and the central frequency of the band gaps. The effect of MEE interlayer on the central frequency of band gap of PE/PM phononic crystal is more significant in the high frequency region than in the low frequency region. Therefore, the width and central frequency of the band gaps can be adjusted to a certain extent by adding different MEE interlayers into the phononic crystal structure when designed.
Linear dependence of magnetocaloric effect on magnetic field in Mn0.6Fe0.4NiSi0.5Ge0.5 and Ni50Mn34Co2Sn14 with first-order magnetostructural transformation
Authors: Zhang Hu  , Xing Cheng-Fen  , Long Ke-Wen  , Xiao Ya-Ning  , Tao Kun  , Wang Li-Chen  , Long Yi  ,   School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China;,   Chengxian Technology Co. Ltd., Foshan 528513, China;,   Chuandong Magnetic Electronic Co. Ltd., Foshan 528513, China;,   Department of Physics, Capital Normal University, Beijing 100048, China
Published: December 2020

The study on the field dependence of magnetocaloric effect (MCE) is considered to be of fundamental and practical importance, since it not only guides us in understanding and optimizing the MCE, but also helps us estimate the MCE for higher magnetic field which is not available in some laboratories. The magnetic field (0H) dependence of magnetic entropy change (△SM) has been studied extensively in many materials with second-order magnetic transition. However, the field dependence of MCE for first-order magnetic transition (FOMT) materials has not been sufficiently studied due to their complexity and diversity. In the present work, polycrystalline Mn0.6Fe0.4NiSi0.5Ge0.5, Ni50Mn34Co2Sn14, and LaFe11.7Si1.3 compounds with FOMT are prepared, and the magnetic and magnetocaloric properties are investigated systematically. In order to avoid a spurious △SM, the M-0H curves are measured in a loop process. The M-0H curves are corrected by taking into account the demagnetization effect, i.e. Hint=Hext-NdM. It is found that the -△SM follows a linear relationship -△SM=-△S0 +0H with the variation of magnetic field in Mn0.6Fe0.4NiSi0.5Ge0.5 compound when 0H 1 T. In addition, it is also noted that the △SM is approximately proportional to the square of 0H at low field. The origin of this linear relationship between △SM and 0H at high field and the deviation at low field are discussed by numerically analyzing the Maxwell relation. In addition to the △SM peak value, it is found that other △SM values at different temperatures also follow the linear relation at high field by performing the same numerical analysis. Moreover, it is found that the fitted △SM curve matches the experimental data very well. This result indicates that the linear relationship between △SM and 0H could be utilized to predict the △SM for higher magnetic field change when the field is lower than the saturation field. The applicability of this linear relationship is also verified in other systems with first-order magnetostructural transformation, such as Ni50Mn34Co2Sn14. However, it fails to describe the field dependence of △SM in LaFe11.7Si1.3, which exhibits a strong field dependence of transition temperature. Consequently, our study reveals that a linear dependence of △SM on 0H could occur in magnetostructural transition materials, which show the field independence of transition temperature.
Effect of electrode position and cross section size on transport properties of molecular devices
Authors: Fan Shuai-Wei  , Wang Ri-Gao  ,   Department of Physics, College of Science, China Three Gorges University, Yichang 443002, China
Published: December 2020

Many investigations indicate that molecular electronics opens up possibilities for continually miniaturizing the electronic devices beyond the limits of the standard silicon-based technologies. There have been significant experimental and theoretical efforts to build molecular junctions and to study their transport properties. The electron transport in molecular device shows clearly quantum effect, and the transport property for molecular device would be strongly affected by chemical and structural details, including the contact position and method between molecule and electrodes, the angle between two electrodes connecting to the molecule. Till now, the micro-fabrication technology still does not guarantee metal electrodes contacting the molecules surfaces ideally. During molecular device fabrication, any tiny variations for the contact configuration usually exist in the molecular device, which would change the device transport property. Hence, it is necessary to investigate the effects of electrode position and electrode cross section size on the transport property.We take Au-benzene-1, 4-dithiol (BDT)-Au (Au-BDT-Au) molecular junctions as example, and systematically calculate its transport properties with various contact positions, and several electrode cross section sizes. The contact face for Au electrode is set to be the (001) face. In the calculations, the density functional theory combined with the Keldysh non-equilibrium Green's function formalism is utilized. The local density approximation is selected as an exchange correlation potential, and atomic core is determined by the standard norm conserving nonlocal pseudo-potential.Our investigations show that the relative position between the electrodes plays a crucial role in the transport behavior of Au-BDT-Au device. When both electrodes are set to be at the counter-position, the preferable transport behavior could be found. The counter-position indicates that the two electrodes are on the same line, which is beneficial to the fabrication. As the angle, which is defined as the angle of electrode deviating from the axis, is larger than five degrees, the transport behavior deteriorates. Hence, the angle for the electrode deviating from its axis should be less than five degrees. To study the effect of electrode cross section size, we calculate the transport properties for three electrode cross sections, i.e. 3×4, 4×4 and 5×4 supercell. Our calculations indicate that when electrode cross section is less than 4×4, the transmission, near the Fermi level, is discontinuous, which would deteriorate the transport performance. Hence, the section size of electrode should not be less than 4×4. This research will provide a scientific index for the electrode position and its cross section size during the fabrication.
Molecular dynamics study of bubble nucleation on a nanoscale
Authors: Zhang Long-Yan  , Xu Jin-Liang  , Lei Jun-Peng  ,   Beijing Key Laboratory of Multiphase Flow and Heat Transfer for Low Grade Energy, North China Electric Power University, Beijing 102206, China
Published: December 2020

With the rapid development of nanotechnology, nucleate boiling has been widely applied to the thermal management of nanoelectronics, owing to its highly-efficient heat transfer characteristics. Considering the scale effects, such as temperature jump at solid-liquid interface, a further study of nucleation boiling mechanism at a microscopic level is needed. At present, extensive studies have been carried out for providing a significant insight into the formation of nano-bubbles in a nanoscale thermal system, but the effect of heat transfer efficiency affected by the surface wettability on bubble nucleation over solid substrate is rarely available in the literature. Therefore, in this paper, the effect of surface wettability on the initial nucleation process and growth rate of bubbles are investigated and the mechanism of bubble nucleation on a nanoscale is analyzed, by the molecular dynamics simulation. The modified Lennard-Jones potential is used for investigating the solid-liquid interaction. Changing the potential parameters α and β can obtain different surface wettability. The atomic sites, liquid density profiles and bubble nucleus volumes are computed to compare the processes of bubble nucleation on different surfaces. The variation of liquid temperature, potential and absorbed heat flux with heating time are evaluated to explore the mechanism of bubble nucleation. The simulation results show that the surface wettability influences the bubble nucleation and heat transfer at liquid-solid interface significantly. On the one hand, the bubble nucleation is promoted by properly increasing the liquid-solid interaction, which is distinctly different from the existing classical theory related to nano-bubble preferably formed on a hydrophobic surface. This is because the thermal resistance of the solid-liquid interface on a nanoscale cannot be neglected. The interface thermal resistance will decrease with the increase of wettability. Therefore, the heat transfer efficiency is higher for a stronger liquid-solid interaction so that the liquid over the hot wall obtains more energy to make bubble nucleus generated earlier. On the other hand, the surface wettability also influences the bubble growth rate. The stronger the liquid-solid interaction, the faster the bubble grows. When the volume of bubble reaches a certain value, a vapor film is formed on the substrate, leading to film boiling. Furthermore, it also illustrates that initial heat flux increases with time. In this stage, the heat flux curve shows two kinds of slopes, corresponding to the occurrence of evaporation and bubble nucleation, respectively. Then, after a certain time, the heat flux profile presents a declining trend, indicating a change into film boiling.
Laser ablation mechanism of contamination on surface of single crystal iron
Authors: Bai Qing-Shun  , Zhang Kai  , Shen Rong-Qi  , Zhang Fei-Hu  , Miao Xin-Xiang  , Yuan Xiao-Dong  ,   1. School of Mechanical and Electrical Engineering, Harbin Institute of Technology, Harbin 150000, China;,   2. Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The laser induced damage in high-power laser system has received much attention in the area of laser engineering. Optical components with contaminants, which are installed in the final optical assembly (FOA), can be severely damaged under the action of extremely high laser energy. So the ultra-high cleanliness inside the high-energy laser system is required for both optical and mechanical components. Research shows that a large part of the metal particulate contaminants inside the device come from the mechanical components. The metal particulate contaminants are produced when mechanical structure surface is damaged under the irradiation of stray light. However the research about the cleanliness inside the device is mostly concentrated on the surfaces of optical components currently. The laser ablation of the mechanical components absorbing contaminants is studied little, so it is quite important to investigate the ablation mechanism of mechanical components under laser irradiation. Due to the presence of contaminants on the surfaces of mechanical components, laser ablation of monocrystalline iron absorbing contaminants is investigated by using molecular dynamics simulation. The ablation process of iron material under laser irradiation is presented. The influences of loading mode and energy density of laser as well as contamination on the surface are analyzed in the ablation process of monocrystalline iron. The results indicate that the surface atoms of monocrystalline iron show different motion states under the violent collision of contaminants atoms after laser loading. Ablated iron can be divided into ablation zone, melting zone and crystal zone according to the variation of the temperature and mass density of the atoms in each region of the ablated material. The atoms in each region show macroscopic characteristics of gaseous, liquid and solid atoms respectively. Iron is damaged more easily when laser energy is instantaneously loaded. Contaminants on the surface of iron can be removed, and iron cannot be damaged when laser energy density is below 0.0064 J/cm2. The result of the analysis shows that the presence of contaminants makes the ablation of iron easier. Different energy loading modes affect the heat transfer mode directly. Monocrystalline iron materials are more likely to be damaged in the mode of adiabatic laser ablation in the case of short laser pulse. Thermal effect can be thought as a dominant factor for the ablation in the case of long laser pulse. The research results of this paper are helpful for providing the theoretical basis for improving the cleanliness of high-power laser system.
Review of Parameter extraction methods for single-diode model of solar cell
Authors: Xiao Wen-Bo  , Liu Wei-Qing  , Wu Hua-Ming  , Zhang Hua-Ming  ,   Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang 330063, China;,   Key Laboratory of Nondestructive Testing(Ministry of Education, Nanchang Hangkong University, Nanchang 330063, China
Published: December 2020

In recent years, the parameter extraction methods of solar cell have attracted a lot of research attention. The reason is that the matching solar cell parameters can effectively reduce the influences of internal and external factors on photovoltaic efficiencies. In this paper, the five-parameter extraction methods of solar cell single-diode model are discussed in detail. The five parameters are the photocurrent, the reverse diode saturation current, the ideality factor of diode, the series resistance, and the shunt resistance. In fact, the existing research methods are classified as four categories, namely, analytically extracting parameter methods, extracting parameter methods with the help of Lambert W function, constructing or using special functions to extract parameter methods, and using intelligent algorithm to extract parameter methods. In this article, we not only elaborate their main theories and approaches, but also discuss their advantages and disadvantages. The main conclusion is that the analytical method for the extraction of solar cell model parameters requires some assumptions. Therefore, this method is fast but less accurate due to various approximations. In addition, the parameter extraction using the analytical method needs a thorough calculation, and deducing the actual values of (dI/dV)|V=Voc and (dI/dV)|I=Isc and peak power point is also challenging. When the five parameters of solar cell are calculated using the Lambert W-function method, the results show that the extraction process is easier when using the consecrated software such as MATLAB, but the larger computational time is needed. Generally, the Lambert-W function provides the exact explicit expression for parameter extraction. As a result, the accuracy of approximate solution using Lambert-W function is much higher than that of the above method. It is obvious that the accuracy of using special functions to extract cell parameters is limited by those function characteristics. Of course, those special functions, such as Green's function, seem to be complex approaches. The accuracy of the extracting cell parameters by using intelligent algorithm strongly depends on the type of fitting algorithm, the fitting criterion, objective function and the starting values of the parameters. Finally, based on the conducted review, the future research trend of parameter extraction is also predicted
Oxygen vacancies induced tuning effect on physical properties of multiferroic perovskite oxide thin films
Authors: Zhao Run  , Yang Hao  ,   College of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009, China;,   College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China
Published: December 2020

By controlling the position and concentration of oxygen vacancies, the relevant physical properties of the multiferroic ABO3 perovskite thin film can be modulated, including electric, optical and multiferroic properties. In this paper, we briefly review the various typical multiferroics. The details of oxygen vacancies are introduced, including the formation mechanism, oxygen octahedral structure, relationship between strain and oxygen vacancy, and specific tuning effect on the physical properties (multiferroic, superconductivity and electrochemical behavior). The latest research progress of the oxygen vacancies induced tuning effect, especially in the field of the multiferroic, provides valuable reference for exploring novel magnetoelectric functional materials and devices.
Density reconstruction based on energy loss in proton radiography
Authors: Chen Feng  , Zheng Na  , Xu Hai-Bo  ,   Graduate School of China Academy of Engineering Physics, Beijing 100088, China;,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

A method of using energy loss to reconstruct the density is presented with protons at intermediate and high energy for proton radiography, and the equation and condition of density reconstruction are given based on the Bethe-Bolch formula. For the intermediate and high energy proton radiography, the stopping power of material is changed slowly within a certain energy range, and the stopping power can be approximated as a constant, then the multi-material object can be reconstructed by using the energy loss information. In this work, the protons at 1.6 GeV which can be obtained by China Spallation Neutron Source are used in the radiography, and the energy loss information is used in the reconstruction, and the Geant 4 is applied to Monte Carlo simulation. From the theoretical calculation and the Geant4 simulation, it can be seen that when the protons energy ranges from 1.45 GeV to 1.6 GeV the stopping power of material can be approximately constant, and the relative change of material stopping power is less than 1%, thus the stopping power of material is only dependent on the incident proton energy, and the density of the multimaterial object can be reconstructed by the energy loss information. The proton scanning imaging system which can avoid blurring image caused by multiple coulomb scattering at the receiving plane is used in the proton radiography to obtain the energy loss information. In the imaging system, two energy detectors are employed to record the incident energy and exit energy of protons, the object is scanned by the protons with a certain step length, and the object is rotated 180 or 360. The energy loss distribution of the object can be obtained by the scanning imaging system, and the density of the object can be reconstructed by solving corresponding equations. The Geant 4 is used to simulate the proton scanning imaging system. In the simulation, the object is the scaling french test object (FTO) that the areal density is 113 g/cm2, the protons are monoenergetic at 1.6 GeV, the scanning interval is 0.5 mm, and the rotation angle is 0.9. The results of the density reconstruction of the scaling FTO are in good agreement with the true values.
Experimental and theoritical research on the dynamical transmission of 30 keV H+ ions through polycarbonate nanocapillaries
Authors: Niu Shu-Tong  , Pan Peng  , Zhu Bing-Hui  , Song Han-Yu  , Jin Yi-Lei  , Yu Lou-Fei  , Han Cheng-Zhi  , Shao Jian-Xiong  , Chen Xi-Meng  ,   School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China
Published: December 2020

The ions with different incident energies transmitting through insulating nanocapillaries are studied in various configurations. For the low energy ions transmitting through nanocapillaries, Stolterfoht et al.[2002 Phys. Rev. Lett. 88 133201] have observed the guiding effect. Subsequent studies revealed that the self-organizing charge patches on the capillary wall inhibit charge exchange and the ions are transmitted along the capillary axis direction. The high energies of ions transmitting through nanocapillaries are measured, the main transmission mechanism is multiple random inelastic collisions below the surface, and the charge patches will not affect the transmitted ions trajectories.
The transmission features of the intermediate energy ions are different from those of the low and high energy ions. The ion beams with intermediate energies have many applications, so it is necessary to understand the transmission features of the intermediate energy ions though nanocapillaries. Recent studies have focused on the transmission of the intermediate energies ions through the nanocapillaries.
In the present work, we investigate thie transmission features, such as the two-dimensional transmitted angular distributions, the charge states and position distributions, and the evolution of the relative transmission rate and the charge purity of 30 keV H+ transmitting through nanocapillaries in a polycarbonate membrane at the angles of-1 and-2. The experimental data clearly show that the transmitted H+ ions consist of the transmitted scattering H+ ions, which are located around the direction of the incident beam, and the transmitted guiding H+ ions, which are located around the direction of the capillary axis. With the charges depositing in the capillary, the proportion of the transmitted scattering H+ ions increases and the proportion of the transmitted guiding H+ ion decreases, which directly demonstrates the dynamical evolution of the scattering ions and the guiding ions.
To understand the competition between the transmitted scattering ions and the transmitted guiding ions and the physical picture of the intermediate energy ions transmitting through the insulating nanocapillaries, the trajectories of the H+ ions in the capillary and the potential distribution and electric field intensity distribution in the capillary are numerically simulated. The results show that the potential distributions and electric field intensitiesy are different for H+ ions transmitting through nanocapillaries at various tilt angles, and the simulation results are in good agreement with the experimental data. The experimental and simulation results give us a further insight into the mechanisms of guiding and scattering in intermediate energy ions transmitting through nanocapillaries.