bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence on the recovered spectrum caused by thermal optics effect of the collimation lens used in static Fourier transform infrared spectrometer
Authors: Chen Cheng  , Liang Jing-Qiu  , Liang Zhong-Zhu  , Lü Jin-Guang  , Qin Yu-Xin  , Tian Chao  , Wang Wei-Biao  ,   State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Science, Changchun 130033, China;,   University of Chinese Academy of Science, Beijing 100049, China
Published: December 2020

In a stepped-mirror-based static Fourier transform infrared spectrometer, the collimation lens is located adjacent to the light source and the thermal radiation would lead to the partial temperature increase, and the refractive index of the infrared material unavoidably changes. Then the light beam passing through the collimation lens will induce a divergence angle, directly affecting the resolution of the recovered spectrum. Meanwhile, the angular divergence results in a displacement in the interference signal, making increasing difficulties in the interferogram processing and the spectrum recovery. In this paper, the distribution of temperature in different areas of the collimation lens is studied under the working condition, and the defocusing value of the collimation lens is 0.153 mm that is caused by the refractive index gradient of the infrared material along with the temperature. In addition, the divergence angle induced by defocusing is calculated, its distribution being nonuniform but symmetrical within the sample area. Moreover, the divergence angle brings about additional optical path difference, its effect on the recovered spectrum is analyzed. Compared with the ideal recovered spectrum, much noise emerges and the peak value is reduced in the real recovered spectrum. The spectrum-construction error of the real recovered spectrum is 18.72%, indicating that the recovered spectrum is seriously distorted, and the resolution at the center wavelength in the ideal recovered spectrum and the real spectrum are 4.71 cm-1 and 5.57 cm-1, respectively. This indicates that the spectrum resolving power is weakened. Furthermore, the reasonable temperature range is obtained by analyzing the curve of spectrum-construction error versus temperature of the collimation lens. When a spectrum-construction error of less than 5% is demanded, the temperature difference between the front len of collimation and the ambient must be less than 8 ℃. Finally, experiments are performed using a SiC rod as the light source, and interferograms are made by four steps including dark current electric noise elimination, spatial gain correction, image signal averaging, and spectrum recovery. Results show that the spectrum-construction errors (SCE) from the cold light source and non-cold light source are 8.48% and 21.51%, respectively. Although they are all larger than the theoretical value, the SCE of cold light source decreases by 13.03% compared to cooling-free light source. Hence, it is necessary to reduced the thermal radiation influence on collimation lens from the light source. This result is helpful in solving the analogous problems.
Theoretical calculation of the vib-rotational interaction potential and the scattering cross section for the Ar-H2 (D2, T2) collision system
Authors: Di Ma-Ke  , Shen Guang-Xian  , Zhao Yun-Qiang  , Zeng Ruo-Sheng  , Wang Rong-Kai  ,   School of Chemistry and Material Science, Guizhou Normal University, Guiyang 550001, China;,   School of Physics and Electronic Science, Guizhou Normal University, Guiyang 550001, China
Published: December 2020

Based on the ab initio coupled-cluster CCSD(T) method in quantum mechanics, the charge distribution of Ar atom and its vib-rotational interaction with H2 molecule are calculated using augmented correlation consistent basis sets aug-cc-pV5Z and 3s3p2d1f1g Gaussian bonding function, and the basis set superposition error (BSSE) is eliminated using Boy and Bernardi's full counterpoise method. Afterwards, the analytical expression of the interaction potential of the Ar-H2 system is fitted with Tang-Toennies potential function. With this interaction potential, the scattering cross section of Ar-H2(D2, T2) collision system is calculated by using close-coupling method when the incident energy of Ar atoms is 83 meV. The calculated differential cross section of Ar-D2 collision system is consistent with the experimental results. Calculated result and analysis show that the dispersion energy plays a key role in the long-range attractive potential scattering, and the exchange energy plays an important role in the short-range repulsive potential scattering. The direction of the radial dipole of the Ar-H2 (D2, T2) collision system is turned twice in the range of impact parameters from 0.27 to 0.47 nm.
Potentials of long-range cesium Rydberg molecule
Authors: Han Xiao-Xuan  , Zhao Jian-Ming  , Li Chang-Yong  , Jia Suo-Tang  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
Published: December 2020

Rydberg atom, with a large principal quantum number n, has big size, long lifetime, strong long-range interactions, and so on. These properties make Rydberg atoms potential candidate of quantum gate and single-photon source. Rydberg electron can interact with nearby ground-state atom, which is polarized by the Rydberg electron and is bound to the orbit of Rydberg electrons forming Rydberg molecule. As the kinetic energy of the Rydberg electron is very low, only the lowest partial waves will contribute to the molecular potential.#br#In this paper, the low electron-atom scattering with the semi-classical approximation is introduced, and the pseudopotential of interaction between Rydberg electron and ground-state atom is used to describe the long-range Rydberg molecular potential. Molecular potential curves for cesium (nS, n=30-60) are plotted according to the results of numerical computation, from which the outermost potential depth De and the equilibrium distance r0 of long-range cesium Rydberg molecule are deduced. Potential curves of cesium Rydberg molecules are consistent with the distribution curves in radial probability densities of cesium Rydberg electrons. Dependences of De and r0 on the principal quantum number n are investigated, this has an important role for the experimental measurements. The size of a Rydberg molecule depends on the equilibrium distance r0 and is proportional to the square of effective principal quantum number (n-δ )2. The calculated outermost potential depth De of Rydberg molecule becomes smaller with the increase of principal quantum number n. Rydberg molecule is very sensitive to the external field and can be used to measure and monitor weak signals.
Guided filter-based blind image restoration method
Authors: Li Xin-Nan  , Huang He-Yan  , Jia Xiao-Ning  , Ma Si-Liang  ,   School of Mathematics, Jilin University, Changchun 130012, China;,   School of Science, Changchun University, Changchun 130022, China;,   School of Science, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

As a major branch and research focus in the image processing field, the study on image restoration is always of practical significance and application value. Blind image restoration has always been one of the most difficult problems in image restoration. In view of the image motion blurring induced by the relative motion between the camera and the subject, we present a blind image restoration method based on guided filter. We first estimate the point spread function by using the iteration algorithm in the frequency domain. And then, because the guided filter has the edge-preserving smoothing property, we restore the target image by the non-blind image restoration algorithm based on the guided filter. By iterating the above two steps, we can obtain the original clear image. In order to verify the effectiveness of the proposed algorithm, we give several groups of experiments. Experimental results show that the proposed algorithm can not only effectively eliminate the noise and suppress the ringing, but also well preserve the edge and texture details. Therefore, the proposed algorithm can restore the image with high quality.
Energy dissipation and periodic segregation of vibrated binary granular mixtures
Authors: He Fei-Fei  , Peng Zheng  , Yan Xi-Ping  , Jiang Yi-Min  ,   School of Physics and Electronics, Central South University, Changsha 410083, China
Published: December 2020

For a vertically vibrating column filled with binary mixtures consisting of big copper beads and small glass beads, the phenomenon of periodic segregation (PS) is observed experimentally, in which distinct segregation patterns of Brazil nut effect (BNE), reversed Brazil nut (RBN) and sandwich (SW) are emerged successively under a certain vibration condition. The periodic time increases with increasing vibration frequency or decreasing acceleration, and the SW pattern holds 90% duration of a cycle. Since the three segregation patterns emerging sequentially in a cycle are all well defined, the energy dissipation power for each segregation pattern is measured under the same vibration condition. It is found that the dissipation power is the largest in RBN pattern and the smallest in BNE pattern during a cycle. Moreover, in the periodic segregation region the same patterns (BNE, RBN or SW) emerging at different vibration accelerations have almost the same dissipation power within the experimental error. Based on the viewpoint of competition between condensation and percolation from Hong, the periodic segregation phenomenon can be explained qualitatively by combining with our measurements of energy dissipation power.
Mechanical properties and phase transformation of porous unpoled Pb(Zr0.95Ti0.05)O3 ferroelectric ceramics under uniaxial compression
Authors: Jiang Zhao-Xiu  , Xin Ming-Zhi  , Shen Hai-Ting  , Wang Yong-Gang  , Nie Heng-Chang  , Liu Yu-Sheng  ,   Key Laboratory of Impact and Safety Engineering, Ministry of Education of China, Ningbo University, Ningbo 315211, China;,   Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China;,   National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Four kinds of unpoled lead zirconate titanate (PZT95/5) ferroelectric ceramics were fabricated in a range of different porosity levels by systematic additions of added pore formers. By using the non-contact digital image correlation (DIC) optical technique to measure the full-field strain, the response of unpoled PZT95/5 ferroelectric ceramics to statically applied uniaxial stresses was investigated. The influences of porosities on the mechanical behavior, domain switching, and phase transformation of the porous unpoled PZT95/5 ferroelectric ceramics were explored. All the measured stress versus strain curves for the tested porous unpoled PZT95/5 ferroelectric ceramic samples can be divided into three stages: the initial linear elastic region, the approximate plateau region, and the second linear elastic region, similar to the behavior of foam or honeycomb materials. However, the deformation mechanism of porous unpoled PZT95/5 ferroelectric ceramics should be attributed to the domain switching and phase transformation processes, but not related to the collapse of voids. With the increase of porosity, the elastic modulus, fracture strength and fracture strain of the porous unpoled PZT95/5 ferroelectric ceramics would decrease. Effect of dispersed voids does not improve plasticity of the porous unpoled PZT95/5 ferroelectric ceramics, which is mainly attributed to no effect of the pores on the obstacle and proliferation of crack propagation during the axial splitting failure processes. Critical stresses of the domain switching and phase transformation decrease linearly with increasing porosity. The macroscopic critical volumetric strain needed for phase transformation is independent of the porosity in the unpoled PZT95/5 ferroelectric ceramics.
Study of precondition for simulating low-speed turbulence
Authors: Chen Yong  , Guo Long-De  , Peng Qiang  , Chen Zhi-Qiang  , Liu Wei-Hong  ,   Facility Design and Instrumentation Institute of China Aerodynamics Research and Development Center, Mianyang 621000, China
Published: December 2020

Precondition for simulating low-speed turbulence is studied in this paper. Against the stiffness of the time-dependent scheme applied to low-speed turbulence, the precondition based on conservative variables is developed, which adopts an implicit iterative method for solving main control equations coupled with turbulence transport equations. In order to ensure the iterative solution stable, a reference Mach number, the dual-time stepping no-matrix scheme, and the method for processing implicitly the source terms of turbulence equations etc. have been developed reasonably, making the software platform unified for all-speed turbulence. Reference Mach number is defined in terms of global and local velocity by a single parameter, and the parameter can be used to control stability, numerical result accuracy, and switch of the precondition. The dual-time stepping LU-SGS method based on conservative variable precondition is developed, realizing no-matrix iterative solution for unsteady flow problems. Against the stiffness in solving the main control equations coupled with turbulence transport equations, the dissipation term of the turbulence equations is processed implicitly, which can enhance main diagonal dominance of the turbulence equations and make the iteration with greater stability. In simulating the turbulence in a nozzle and around a square cylinder or an airfoil, the precondition depicts correctly the structural character of the flowfield; and the computational results are in good agreement with those of theory and experiment etc., and its iterative convergence and numerical accuracy is excellent. It is shown that the precondition in this paper for low-speed turbulence is very effective.
Numerical simulation on oscillation of micro-drops by means of smoothed particle hydrodynamics
Authors: Ma Li-Qiang  , Su Tie-Xiong  , Liu Han-Tao  , Meng-Qing  ,   Shuozhou, North University of China, Shuozhou 036000, China
Published: December 2020

In this paper, we present a modified smoothed particle hydrodynamics (SPH) method. SPH is a Lagrangian meshfree particle method, and it is attractive in dealing with free surfaces, moving interfaces, and deformable boundaries. The improved SPH method modifies the kernel gradient in the traditional SPH method with a new kernel function and a modified SPH discrete form. Use of improved smoothed particle hydrodynamics is made to carry out numerical analysis on micro liquid drop oscillation process. The study focuses on the relation between the micro liquid drop oscillation damping and the oscillating period and amplitude in different aspect ratio and Re number. It is shown that for the micro liquid drop oscillation process with aspect ratio λ≤ 4, under the circumstance of constancy of other parameters, the larger the Re number, the more intense the change of liquid drop's shapes, the weaker the damping effect, and the longer the period of liquid drop's oscillation. Under the circumstance of constancy of Re number, as the initial aspect ratio of liquid drop increases, the amplitude of liquid drop oscillation is stronger, and the period of liquid drop's oscillation is longer.
Study on the photocatalytic mechanism of tio2 sensitized by zinc porphyrin
Authors: Li Pei-Xin  , Feng Ming-Yang  , Wu Cai-Ping  , Li Shao-Bo  , Hou Lei-Tian  , Ma Jia-Sai  , Yin Chun-Hao  ,   Surface And Magnetism Lab, School of Science, China University of Mining and Technology, Xuzhou 221116, China
Published: December 2020

We have investigated the photocatalysis efficiency and electron transfer of the znic prophyrin/TiO2 composite photocatalyst, a sensitised hybrid porphyrin material, and prepared it successfully by sol-gel method. The UV-visible spectroscopy and electron paramagnetic resonance spectra are used to analyze and characterize the znic prophyrin/TiO2 composite photocatalyst. The proportions 0%, 0.2%, 0.5% and 0.9% (mass ratio) of zinc porphyrin, and the photocatalytic mechanism of TiO2 sensitized by zinc porphyrin are reasonably explained by ultraviolet visible spectroscopy and electron paramagnetic resonance spectroscopy (EPR). Different samples' UV-visible spectra show that the degradation efficiency of methyl orange solution by TiO2 may be improved via adding appropriate amount of zinc porphyrin sensitizer. Prohibitive incorporation of the sensitizer would cause excess of particles in the mixed catalyst, leading to the TiO2 surface covered by the sensitizer, thus affecting the absorption of photons, and the light degradation rate of TiO2 may be lowered, even lower than the pure TiO2. EPR spectra show the excited state of electrons in zinc prophyrin generated by irradiation of light can promote the generation of Ti3+ with strong oxidizing and superoxide radicals when using UV-visible light to irradiate the powder samples, thus effectively enhancing the separation of photogenerated electron-hole pairs, and improving the photocatalytic performance of TiO2.
Suppression of secondary electron multipactor on dielectric surface in TM mode
Authors: Li Shuang  , Chang Chao  , Wang Jian-Guo  , Liu Yan-Sheng  , Zhu Meng  , Guo Le-Tian  , Xie Jia-Ling  ,   Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024, China;,   School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China;,   Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

To suppress the secondary electron multipactor on dielectric surfaces of a dielectric load accelerator under an electromagnetic field in TM mode, the method of adopting both groove structure and external axial magnetic field is introduced. As the electric field distribution of the TM mode is composed of both normal and tangential components, it is different from that under the condition of dielectric window in HPM. Thus, theoretical analysis and numerical simulation are employed to study the movement of electrons under different conditions: such as dielectric surface shapes, electric field strength, and magnetic field strength etc. Based on the particle-in-cell (PIC) simulation, the collision energy and transmit-duration of secondary electrons in different groove structures and axial magnetic fields are compared with one another. Results show that the magnetic field is useful for suppressing the development of secondary electron on dielectric surface, while it is not very efficient under high electric field strength. The method of introducing groove structure and certain axial magnetic field on dielectric surface at the same time is capable of affecting the movement of electrons in electric field of different strength. So it is great helpful in improving the ability of multipactor suppression, which is significant for improving the threshold of breakdown on dielectric surface and the power of cavity. However, a too high or too low magnetic field is not very useful for the suppression of multipactor. Furthermore, employing only one of the two parts of the method is also less effective in suppressing the multipactor.
Preparation and upconversion luminescence properties of Ba5SiO4Cl6: Yb3+, Er3+, Li+ phosphors
Authors: Yang Jian-Zhi  , Qiu Jian-Bei  , Yang Zheng-Wen  , Song Zhi-Guo  , Yang Yong  , Zhou Da-Cheng  ,   College of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China
Published: December 2020

The Ba5SiO4Cl6: Yb3+, Er3+, Li+ phosphor has been prepared by high temperature solid state reaction, and their upconversion (UC) luminescence properties and mechanisms are investigated. The UC emission bands located at 525 nm (2H11/24I15/2), 548 nm (4S3/24I15/2), and 662 nm (4F9/24I15/2) due to Er3+ are observed under the excitation of 980 nm. UC luminescence of Ba5SiO4Cl6: Yb3+, Er3+ phosphors is increased with increasing Er3+ and Yb3+ concentration due to the energy transfer enhancement of Er3+ and Yb3+. Based on the relations of UC luminescence intensity and excitation light power, the UC luminescence mechanisms are discussed. At a low excited power (below 0.8 W), the two-photon processes are involved in both green and red UC emission mechanisms. When the power exceeds 0.9 W, the green and red UC emission is a four-photon process. One new and interesting UC emission mechanism may occur in the Ba5SiO4Cl6: Yb3+, Er3+ phosphors. Both green and red UC emissions at a higher pumping power are generated by photon avalanche UC process. Influence of Li+ doping on the UC luminescence of Ba5SiO4Cl6: Yb3+, Er3+ phosphors is investigated. Result demonstrates that Li+ ion doping could enhance the UC luminescence of Ba5SiO4Cl6: Yb3+, Er3+, which is attributed to the distortion of the local symmetry around Er3+.
A method of chaotic secure communication based on strong tracking filter
Authors: Li Xiong-Jie  , Zhou Dong-Hua  ,   Department of Automation, Tsinghua University, Beijing 100084, China;,   Department of Electronic and Information Engineering, Zhejiang Business Technology Institute, Ningbo 315012, China
Published: December 2020

Chaotic secure communication is an active research field of chaotic application. A novel method for chaotic secure communication is proposed based on strong tracking filter (STF) in this study. STF is an extended Kalman filter with suboptimal fading factors, especially suitable for estimating the state and parameter of nonlinear time-varying stochastic systems. The main idea of the proposed method is summarized below. At the emitting end, the chaotic mapping and the information symbol are modeled as a nonlinear state space model, and the information symbol is modulated by additive chaos masking or multiplicative chaos masking and then is outputted through the channel. At the receiving end, the driving signal is received, and the message symbol is recovered dynamically by STF with Bayesian classifier. Simulation tests of the logistic chaotic mapping show that STF can restore the information symbols in chaotic signals when information symbols are binary code, with either additive or multiplicative chaos masking modulation. Compared with STF, the conventional Kalman filter has poor ability to track the discrete information symbol. It is difficult to restore the information symbols in the chaotic mapping, and the bit error rate is high. Therefore, the STF-based chaotic secure communication method is effective.
Theoretical investigation of femtosecond-resolved photoelectron spectra of three-level ladder K2 molecules
Authors: Feng Xiao-Jing  , Guo Wei  , Lu Xing-Qiang  , Yao Hong-Bin  , Li Yue-Hua  ,   School of Electric Engineering, University of South China, Hengyang 421001, China;,   School of Nuclear Science and Technology, University of South China, Hengyang 421001, China;,   State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Dalian 116023, China
Published: December 2020

We investigate the effect of delay time, pulse width and pump wavelength on photoelectron spectra and wave packet forming process of the three-level K2 molecules via time-dependent wave packet approach. There is no Autler-Townes splitting for weaker pump intensity or shorter pulse width. Delay time and pump wavelength can affect peak structure, position, and relative height. The vibration period of wave packet does not vary with pump wavelength, while the oscillating amplitude decreases with increasing pulse width. Results may provide important basis for realizing the optical control of molecules experimentally.
Influences of environmental factors on low frequency abnormal sound transmission through sea-air interface
Authors: Guo Ye-Cai  , Lian Chen-Fang  , Zhang Xiu-Zai  , Zhao Yi-Bo  ,   Jiangsu Key Laboratory of Meteorological Observation and Information Processing, Nanjing University of Information Science and Technology, Nanjing 210044, China;,   Jiangsu Collaborative Innovation Center on Atmospheric Environment and Equipment Technology (CICAEET), Nanjing 210044, China;,   College of Atmospheric Science, Nanjing University of Information Science and Technology, Nanjing 210044, China
Published: December 2020

In view of low frequency abnormal sound transmission of sound source in the sea at the sea-air interface, according to the two-layer medium sound transmission model, we analyze the relationships of the sound speed and the density of the atmosphere with the atmospheric pressure, the air temperature, the humidity; we also analyze the relationships of the sound velocity and the density of seawater with the sea surface temperature (SST) and salinity; we investigate the low-frequency abnormal sound transmissions influenced by temperature, pressure, salinity, humidity and other environmental factors; we analyze the influences of various factors on the sound transmission. The obtained results are as follows. 1) the sound power in the air, obtained by the sound transmission of sound source in the shallow sea, is negatively correlated with atmospheric temperature and humidity, and positively correlated with the SST, salinity, and atmosphere pressure. 2) The sound power that is radiated into the sea by the monopole and horizontal dipole source at the sea, is negatively correlated with SST and salinity, while the sound power that is radiated into the sea by the vertical dipole sound source, is positively related to SST and salinity. 3) The sound transmission directivity is positively related to SST and negatively correlated with atmospheric temperature. 4) The air temperature and SST have the greatest influence on low-frequency abnormal sound transmission, while the effects of air pressure and humidity on them are smaller than that of salinity. The effect of temperature on the low frequency abnormal sound transmission of vertical dipole sound is greater than those of the horizontal dipole and a monopole sound source.
Non-resonant direct laser acceleration in underdense plasma channels
Authors: Liu Ming-Wei  , Gong Shun-Feng  , Li Jin  , Jiang Chun-Lei  , Zhang Yu-Tao  , Zhou Bing-Ju  ,   School of Physics and Electric Science, Hunan University of Science and Technology, Xiangtan 411201, China
Published: December 2020

Mechanisms that electrons are directly accelerated by the laser-plasma interaction in non-resonant cases are studied. First, by use of a linearly polarized Gaussian laser beam, a three-dimensional model is presented to demonstrate that the frequency and the amplitude of electron oscillations can be significantly modulated by the transverse ponderomotive force, within the confinement of an underdense plasma channel. On the one hand, the transverse ponderomotive force can felicitously make electrons to experience the large amplitude oscillations and push them to the regions at a low dephasing rate. On the other hand, when the electrons oscillate across the channel with small amplitudes, the dephasing rate also can be effectively reduced by the nonlinear modulation arising from the transverse ponderomotive force. These kinds of modulations can lead electrons to stay in phase with the laser field for a longer time and thus enhance their energy gain, which also enables the mechanism of transverse ponderomotive modulation being in direct laser acceleration. This mechanism is determined by the plasma density and the laser intensity and radius. Detailed numerical results are also given which show that the electron acceleration induced by this ponderomotive modulation quite distinguishes from the parametric instability and the resonance from a driving force. Moreover, a theoretical model for the parametric amplification, which makes up the restriction of the quasi-two-dimensional model, is provided to verify that non-resonant direct laser acceleration can come from the parametric instability in the three-dimensional case.
Investigation on the energy loss in low energy protons interacting with hydrogen plasma
Authors: Deng Jia-Chuan  , Zhao Yong-Tao  , Cheng Rui  , Zhou Xian-Ming  , Peng Hai-Bo  , Wang Yu-Yu  , Lei Yu  , Liu Shi-Dong  , Sun Yuan-Bo  , Ren Jie-Ru  , Xiao Jia-Hao  , Ma Li-Dong  , Xiao Guo-Qing  , R. Gavrilin  , S. Savin  , A. Golubev  , D. H. H. Hoffmann  ,   Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya 25, 117259 Moscow, Russia;,   Institut für Kernphysik, Technische Universität Darmstad, Darmstadt 64289, Germany
Published: December 2020

Energy loss of protons with energy 100 keV penetrating the partially ionized hydrogen plasma target was measured. The plasma target was created by electric discharge in the hydrogen gas, the state of the plasma target was diagnosed by using the laser interferometry method: the free electron density is up to 1016 cm-3, temperature is about 1-2 eV, and the plasma target may exist at the microsecond level. It is found that the energy loss of protons is closely related to the free electron density, and the energy loss data enable us to infer the value of the Coulomb logarithm (10.8) for the stopping power of the free electrons. This agrees well with the theoretical prediction which is 4.3 times higher than that given by the Bethe formula for neutral hydrogen, which is a little bigger than Hoffmann's result but much smaller than Jacoby's result. Comparing our result with Hoffmann's, the energy we used is only 100 keV, much lower than 1.4 MeV/u, and the low-energy regime we applied could be the cause of the increase in the enhancement factor. However, in the comparison between our result and the Jacoby's, the effective charge for protons is almost constant, unlike the Kr+ impact in wihch the enhanced ion charge state induces the giant enhancement factor. Compared to the gas target, the energy loss enhancement factor in plasma target is 2.9.
Low energy phonon instabilities and magnetic abnormalities in ordered crystalline state alloys of Fe3Pt at high pressure
Authors: Cheng Tai-Min  , Zhang Long-Yan  , Sun Teng  , Zhang Xin-Xin  , Zhu Lin  , Li Lin  ,   Department of Mathematics and Physics, Shenyang University of Chemical Technology, Shenyang 110142, China;,   College of Sciences, Northeastern University, Shenyang 110004, China
Published: December 2020

The ordered crystalline Fe3Pt invar alloy is in a special magnetic critical state under which the lattice dynamic stability of the system is extremely sensitive to the external pressure. Using projection augmented plane wave method based on the density functional theory, we calculate the dependences of enthalpy and magnetism of different crystalline alloys of Fe3Pt on external pressure. The results reveal that the P4/mbm structure is thermodynamically stable under pressures below 18.54 GPa. The total magnetic moments of Pm3m, I4/mmm and DO22 structures decrease rapidly and oscillate near the ferromagnetic collapse critical pressure. Furthermore in I4/mmm and DO22 structures the atomic magnetic moment of Fe1 reverses near the critical pressure. At a pressure of 43 GPa, the micro-ferrimagnetic property in DO22 structure becomes apparently strengthened while its volume increases rapidly. The lattice dynamic calculation shows that the spontaneous magnetization of the system in ferromagnetic states induces the softening of the transverse acoustic phonon TA1(M) in the Fe3Pt of Pm3m structure, and there exists a strong spontaneous volume magnetostriction at pressures below 26.95 GPa. Especially, in the pressure range between the ferromagnetic collapse critical pressure 41.9 GPa and the magnetism completely disappearing pressure 57.25 GPa, the lattice dynamic stability is more sensitive to the pressure. The pressure induces the stability of the phonon spectrum of the system at pressures above 57.25 GPa.
Application and foundation on inversion lattice potential of gold and silver
Authors: Ren Xian-Li  , Chen Song  , Xie Ming  , Li Mu-Yang  , Hu Jie-Qiong  , Yang Yun-Feng  , Yang Wei-Yi  ,   Sate Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metal, Kunming Institute of Precious Metals, Kunming 650106, China
Published: December 2020

How to construct an accurate interatomic potential function is an important and basic problem in the simulation procedure. Using first-principles method, the single atom energies in different lattice constants are calculated to achieve the ground state curves of Au and Ag. These energies are calculated in the Perdew and Zunger form of the local-density approximation ultra-soft pseudo potentials. The cut-off energies of the plane wave bases of Au and Ag are set to be 320 eV and 300 eV respectively, which are sufficient for their full converge. The Brillouin zone is all sampled with a 12×12×12 Monkhorst-Pack mesh of k points for Au and Ag. Allowable error in total energy is smaller than 1×10-6 eV per atom. The lattice cohesive energies in different lattice constants are calculated to achieve the lattice energy and atom distance curves after subtracting the value of ground state energy from each of these energy. Then the accurate inversion potential curves are obtained according to the Chen-Möbius inversion theory and self-compiled program. Based on the fitting consequences of inversion potential curves, using different potential function formulas, a double exponential potential function to fit the inversion potential is presented. This function provides the accurate formulas and parameters for the following research. Moreover, the phonon spectra and the densities of states of Au and Ag are calculated respectively by using the inversion potential data, the embedded atom method (EAM) potential theory and first principles method to verify the reliability of the inversion potential. The comparison of the results among the three methods shows that the tendencies of these curves are similar. But they still have some deviations especially in the range of high frequency. However these curves indicate that the inversion potential can reasonably reflect the interaction between atoms. Meanwhile, the inversion potential method has great advantage in calculation quantity compared with the EAM potential method. The inversion method needs less time in calculation. In addition, the thermal expansion coefficients, the elastic moduli and the Grüneisen constants of Au and Ag are also calculated based on the fitting formulas and parameters. The results agree well with the experimental data, which implies that these inversion potentials are effective and accurate.
Effect of bipolarons on spin polarized transport in magnetic permeated sublayer of organic spin device
Authors: Jiang Li-Na  , Zhang Yu-Bin  , Dong Shun-Le  ,   College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China
Published: December 2020

According to the permeation phenomenon of magnetic atoms in organic device, such as Co/organic semiconductor (OSC)/La0.7Sr0.3MnO3, the evolution of spin polarons and spinless bipolarons are calculated with the drift-diffusion equations to investigate the effect of polaron-bipolaron interaction on spin polarized transport in a magnetic permeated sublayer (MPS). It is found that the MPS has different spin-flip time and mobility from those in pure organic semiconductor. The splitting of spin-flip time will be adjusted by the effect of the magnetization of the impurity atoms. Mobilities of spin carriers in the MPS will be reduced due to the scattering of the Co atoms. Both the spin-flip time and the mobility will affect the polaron-bipolaron interaction and further influence the spin polarized transport. It is found that the splitting of spin-flip time is the main factor responsible for the spin relaxation, while the polaron-bipolaron interaction is the secondary factor.
First-principles study of the electronic structure, magnetism, and spin-polarization in Heusler alloy Co2MnAl(100) surface
Authors: Jiang En-Hai  , Zhu Xing-Feng  , Chen Ling-Fu  ,   Department of Physics, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

Using the first-principles calculations within the generalized gradient approximation frame work, we systematically investigate the atomic relaxation, electronic structure, magnetism, and spin-polarization in L21 and B2 structure of Heusler alloy Co2MnAl (100) surface. Due to the difference of Co–Mn and Co–Al bonding, surface atoms in the L21 and B2 structure prefer to move toward and away from the vacuum. By comparison with the bulk, the spin magnetic moments of surface Co and Mn atoms are obviously enhanced due to the surface effects. Our electronic structure calculations show that the gap in L21 structure of bulk Co2MnAl has been destroyed by the surface states and the spin-polarization of CoCo atomic terminated surface in both structures decreases. However, the spin-polarization of MnAl atomic terminated surface is not significantly affected by the surface effects and has a large value in both structures, and this may be the potential in application to magnetic tunneling junctions.
Theoretical study of photoinduced charge transfer in molecule and multi-metalnanoparticles system
Authors: Gao Jing  , Chang Kai-Nan  , Wang Lu-Xia  ,   Department of physics, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

Photoinduced enhancement effect of the metal nanoparticle is one of the hot topics in the field of nanomaterial. Interaction between one molecule and a number of metal nanoparticles in different configurations in an applied external field is theoretically investigated in the scheme of density matrix theory, where the molecule and metal nanoparticles are excited simultaneously, and the subsequent charge transfer dynamics is simulated. Besides, the Coulomb interactions between the molecule and metal nanoparticles are calculated in the framework of dipole-dipole approximation. Parameters for metal nanoparticles with a 10 nm radius are used in the text and the polarization of the molecule has the same direction as that of external laser field. It is found that plasmon enhancement is closely related to the relative positions between the molecule and metal nanoparticles. Effects of enhancement due to the surface plasmon is discussed in detail for different configurations of the molecule and metal nanoparticles, and the surface plasmon hybridization, as well as the molecular excitation energy and the frequency of external field applied. Plasmon hybridization levels are formed when metal nanoparticles have strong enough interactions between themselves. The blue shift of the resonant frequency can be found for shorter distance of different metal nanoparticles. In the case that the centers of mass of metal nanoparticles and the molecule are on the same plane, it is found that the population in excited state of the molecule at a resonance frequency increases for a shorter distance between metal nanoparticles and the molecule. On the contrary, in the case that the centers of mass of four metal nanoparticles are located in a plane which is parallel to the x-y plane and above it by 10 nm, the population in the excited state of the molecule on resonant frequency will decrease at a shorter distance between the four metal nanoparticles.
Photoluminescence properties of Eu doped Si nanowires
Authors: Fan Zhi-Dong  , Zhou Zi-Chun  , Liu Chuo  , Ma Lei  , Peng Ying-Cai  ,   College of Physics Science and Technology, Hebei University, Baoding 071002, China;,   College of Electronic and Informationl Engineering, Hebei University, Baoding 071002, China;,   State Key Laboratory of Mesophysics, Beijing University, Beijing 100871, China
Published: December 2020

High-density (～1010 cm-2) silicon nanowires are grown directly from n-(111) single crystal silicon based on solid-liquid-solid mechanism by using Au-Al films as metallic catalyst. The results indicate that the optimal parameters to realize Si nanowires with high density and uniform distribution are as follows. The thickness of Au-Al film is between 5 and 15 nm, the temperature is 1100℃, and the flow of N2 is 1.5 L/min. The diameters and lengths of the formed Si nanowires are 100 nm and from several micrometers to sereral tens of micrometerss, respectively. Then Eu-doped Si nanowires are studied. The influences of the different lengths of Si nanowires, doping temperature (900-1100℃), and doping time (15-60 min) on the luminescence of Eu3 + are experimentally investigated. The morphologies and microstructures of the SiNWs, the photoluminescence properties and growth crystall orientations are characterized and analyzed by the scanning electron microscopy, the Hitachi F-4600 fluorescence spectrophotometer and X-ray powder diffraction. The results show that the Eu-doped Si nanowires have a stronly red luminescencent with an emission peak position at 619 nm (5D0→7F2) when the doping temperature is 1000℃, the grow time of SiNWs is 30 min, and the optimal excitation wavelength is 395 nm. At the same time, there are four emission bands of 576 nm (5D0→7F0), 596 nm (5D0→7F1), 658 nm (5D0→7F3), and 708 nm (5D0→7F4) that are observed. Compared with the scenario of the silicon substrate, the Eu-doped Si nanowires present strong red light emission. The photoluminescence properties of Eu-doped Si nanowires have potential applications in the lighting and the silicon optoelectronic integration. However, the parameters of Si nanowires such as diameter, density, surface morphology have great influences on the photoluminescence properties of Eu-doped Si nanowires, which are necessary to be further studied.
Investigation of photo-induced phenomenon in the silicon nanowires made by chemical etching in HF/Fe(NO3)3 solution
Authors: Liu Lin  , Wang Yong-Tian  ,   School of Energy Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China;,   Beijing Key Laboratory of Energy Conversion and Storage Materials, Beijing Normal University, Beijing 100875, China
Published: December 2020

The photo-induced phenomenon in the silicon nanowires made by chemical etching in HF/Fe(NO3)3 solution is investigated systematically by using monocrystal n-type silicons with different doping concentrations as substrates, silver as catalyst, and iron nitrates with different concentrations as oxidants. It is found that the length of silicon nanowires is determined not only by the doping concentration of substrate and the mass of oxidant, but also by the photo-induced effect. The prepared silicon nanowires may have potential applications in green energy storage device and the substrate material for sensor. In this paper, we discuss the formation mechanism from the band structure, electrochemical characterization and photoluminescence in depth. The results in this paper provide physical theoretical evidence for the development of the method, and have important guiding significance to promote the technology.
Raman spectra based pressure calibration of the non-gauge sapphire anvil cell at high temperature and high pressure
Authors: Jiang Jian-Jun  , Li He-Ping  , Dai Li-Dong  , Hu Hai-Ying  , Zhao Chao-Shuai  ,   Key laboratory for High Temperature and High Pressure Study of the Earth's Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;,   Graduate school of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Gem anvil cell is on important tool in high pressure experimental research, and the key of its application is the accurate calibration of the pressure in sample chamber. To date, the pressure has been routinely calibrated by the extra gauge such as ruby. This may increase the difficulty in building a setup and changing the chemical environment, even chemical reaction happens with the sample, thereby degrading the experimental results. In this study, using the synthesized pale sapphire and the heatable Zha-Bassett type cell, the relationships between Raman shift of sapphire-anvil interface and the pressure, and also temperature in chamber are investigated by the confocal Raman microscope at 0-6.3 GPa and 300-573 K, which is used to establish a non-gauge sapphire anvil cell system. The result shows that the pressure induced Raman shift of sapphire anvil at room temperature is 1.6443 cm-1/GPa and the temperature induced shift at room pressure is -0.0198 cm-1/K. We fit the experimental data at simultaneous high temperature and high pressure (HTHP) and find that: ∂ν12/∂T=-0.01913-0.00105×P, ∂ν12/∂P=1.9158-0.00105×T. The effect between the pressure and temperature can be described by ∂ν12/∂P∂T=-0.00105. After this calibration: P=(Δλ-0.01913×ΔT)/(1.9158-0.00105×ΔT), the pressure in the sample chamber can be calculated by the Raman shift of the interface of anvil cell in the HTHP experiment, which can be directly used in hydro-thermal reaction system and has great importance in physics, material science and geoscience.
Simulation study on the correlation between the ground cosmic rays and the near earth thunderstorms electric field at Yangbajing (Tibet China)
Authors: Zhou Xun-Xiu  , Wang Xin-Jian  , Huang Dai-Hui  , Jia Huan-Yu  , Wu Chao-Yong  ,   School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, China;,   Institute of High Energy Physics, CAS, Beijing 100049, China
Published: December 2020

Coincident study on the intensity change of the ground cosmic rays during thunderstorms is very important for understanding the acceleration mechanism of secondary charged particles caused by atmospheric electric field. It is found that the strength of the near earth thunderstorm electric field can be up to 1000 V/cm or even higher from ARGO-YBJ (where YBJ stands for Yangbajing, 4300 m a.s.l., Tibet, China) data in 2012. In this paper, Monte Carlo simulations are performed by using CORSIKA program to study the correlations between the intensity of the ground cosmic rays and the near earth thunderstorm electric field at YBJ. When the atmospheric electric field strength is higher than the threshold field strength (ERB) for the development of a runaway breakdown process, the total number of electrons and positrons is exponentially increases. At an electric field strength of 1500 V/cm, the number increases exponentially and reaches a maximum value at an atmospheric depth of ～520 g/cm2, where the electric field is slightly stronger than the threshold field strength. These results are consistent with the theoretical results of relativistic runaway electron avalanche (RREA) which was proposed by Gurevich et al. (Gurevich A V, Milikh G M, Roussel-Dupre R 1992 Phys. Lett. A 165 463) and also supports Dwyer's theory. The total number of electrons and positrons increases with the strength of the field in the negative field or in the positive field greater than 600 V/cm, while a certain degree of decline occurs in the positive field less than 400 V/cm. In the range 400-600 V/cm, the energy of the primary proton should be taken into account. For the primary energy that is lower than 80 GeV, the total number of electrons and positrons increases. And it does not change obviously when the energy is between 80 GeV and 120 GeV. For the primary energy exceeds 120 GeV, the number drops off, and the decrease is of ～4%. During thunderstorms, a short duration occurs in which the single particle counting rate increases as energy lowers, while a decrease happens with energy becoming higher than that from ARGO-YBJ data. Our preliminary results can give reasonable explanations to the experimental observations of ARGO-YBJ.