bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical investigation of cavity formation mechanism for micron-waterdrop impact on deep pool
Authors: Pei Chuan-Kang  , Wei Bing-Qian  ,   State Key Laboratory of Eco-hydraulics in Northwest Arid Region of China, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

As one of the most fundamental and iconic fluid motion, droplet impact exists widely in scientific technologies and natural environment, and the phenomenon has been studied both for fundamental mechanism and for industrial applications in aerospace engineering, inkjet printing, agricultural irrigation and hydraulic structure erosion. Therefore, it is of great significance to study such basic movements for understanding the interfacial deformation of gas and liquid flow and improving the applications of droplet impact movement in engineering. Droplet impacting on a deep liquid pool has been extensively investigated for droplets with millimeter diameter. In this article, focusing on the cavity formation mechanism during a Micron-sized waterdrop impact on a deep pool, we perform systematic numerical simulations with adaptive mesh refinement technique and volume of fluid method to study the impact of a 290 μm water droplet on a deep water pool at velocities in a range of 2.5-6.5 m/s. The free surface motion, geometric variation of the cavity, local pressure field and vorticity field at selected times are presented to identify the pool-drop water mixing, capillary wave propagation, cavity formation, vortex ring generation and bubble entrapment phenomenon, and the dynamic mechanism of cavity motion is further explored. It is found that under the premise of neglecting the surface tension effects on the cavity whose depth is in a range of h∈(D, hmax), where D is the radius of initial droplet and hmax is the maximum depth, the cavity growth time to reach its maximum depth still scales as t∝h5/2, where t is time, but in the end, the formation of the bottom of the cavity is driven by capillary waves. There are two types of the initial cavity shapes: one is U-shape and the other is hemispherical shape, the former one generally changes into V-shape, and in the latter case, the bottom of the cavity will gradually transform into cylindrical shape, resulting in a thin jet and possible bubble entrapment. Cavity collapse is closely related to capillary wave propagation. When the impact velocity is low (Fr=567.1, Re=1595, We=121.8), the low-pressure zone is initially generated at the junction between the cavity sidewall and the bottom, a large vortex ring is then generated near the free surface and the bottom of the cavity, respectively. Under high impact velocities (Fr=792.1, Re=1885, We=170.2), the thin jet is observed, the generation of the vortex ring is suppressed. The low-pressure zone is first generated at the junction between the wave bottom and the cavity sidewall, after the cavity becomes cylindrical, the cavity collapses before the capillary wave arrives at the bottom, causing a bubble entrapment.
An interconnected state observer for lithium-ion battery based on reduced electrochemical model
Authors: Pang Hui  , Zhang Xu  ,   School of Mechanical and Precision Instrument Engineering, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

The accurate estimation of the solid concentration distribution in anode and cathode, and state-of-charge (SOC) for a Li-ion battery cell is significantly important for developing the real-time monitoring algorithm of the Li-ion cell's working operation, and further establishing an efficient and reliable advanced battery management system (BMS). Firstly, according to the porous electrode theory and concentration theory, in this article we present a systematic optimized model and a method of identifying the key internal state parameters based on a Li-ion cell's enhanced single-particle-model (ESPM), in which, an appropriate parameter vector is identified in the typical hybrid-pulse-power-characterization (HPPC) operation scenario by using the parameter sensitivity analysis method, and then this parameter optimization problem is evaluated by genetic algorithm. It is verified that the maximum relative errors of the cell's output voltage for ESPM are 1.92%, 3.18% and 2.86% under HPPC, 1C-discharge and urban dynamometer driving schedule (UDDS) current profiles, respectively. Secondly, by introducing some assumptions and reduction techniques, the battery ESPM is further reduced and then a novel interconnected state observer is proposed through the combination of the reduced ESPM and H∞ robust control theory framework, which can realize the concurrent estimation of solid concentration and SOC in anode and cathode. Finally, the comparative validation and analysis study are conducted by using the experimental data acquired in HPPC and UDDS condition to demonstrate the effectiveness and feasibility of the proposed interconnected observer. The results show that the maximum relative errors of output voltage for the ESPM, the single-electrode concentration observer (Obsv-1) and the proposed interconnected observer (Obsv-2) of Li-ion cell are 2.0%, 3.8% and 2.6%, respectively, under HPPC operation at 23 ℃; under the same input current profile and operating condition, the maximum relative errors of SOC estimation are 2.4%, 4.7% and 3.4%, respectively. Moreover, the maximum relative errors of cell's output voltage for ESPM, Obsv-1 and Obsv-2 model are 1.9%, 3.2% and 2.1%, respectively, and the maximum relative errors of SOC estimation values for these three mathematical models are 2.1%, 4.4% and 3.2%, respectively. It is concluded that the proposed robust observer for a Li-ion cell can accurately predict the output voltage and SOC, and can also improve the dynamic performance and robust stability of Li-ion cell, which provides a solid theoretical foundation for developing the BMS.
Ultrafast polarization modulation of laser pulses at terahertz frequencies via optical Kerr effect
Authors: Lin Xian  , Jin Zuan-Ming  , Li Ju-Geng  , Guo Fei-Yun  , Zhuang Nai-Feng  , Chen Jian-Zhong  , Dai Ye  , Yan Xiao-Na  , Ma Guo-Hong  ,   1. Department of Physics, Shanghai University, Shanghai 200444, China;,   2. SIOM & STU Joint Laboratory for Superintense Lasers and the Applications, Shanghai 201210, China;,   3. College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou 350002, China
Published: December 2020

Polarized light has already been widely used for photography and display technologies. Magneto-optical Faraday effect, i.e., the light polarization rotates in the magnetic field applied to the material in the direction of light propagation, plays a crucial role in the interaction between light and spin. Faraday effect allow us to understand the nature of magnetization in condensed materials. As an effect opposite to the Faraday effect, the magnetization can be induced in a transparent medium exposed to a circularly polarized electromagnetic wave, which is called inverse Faraday effect. Knowledge of the mechanism provides the opportunities of modulation devices in photonics, ultrafast opto-magnetism and magnonics. In this paper, we experimentally demonstrate a proof-of-concept ultrafast polarization modulation by employing circularly polarized light to demonstrate a strengthened terahertz (THz) frequency Kerr modulation signal, at room temperature. By using the transient pumpprobe spectroscopy with the reflected geometry, we are able to demonstrate the feasibility of such an ultrafast magneto-optical polarization modulation at 0.19 THz in a paramagnetic Li:NaTb (WO4)2 crystal with a thickness of 3 mm. The time-resolved modulation signal is explained by the interaction between two counter-propagating laser pulses (central photon energy of 1.55 eV) within the crystal via the optical Kerr effect. We find that the amplitude of the modulation increases with the pump fluence increasing, while the modulation frequency is dependent neither on the pump fluence nor on polarization of pump beam. However, it can further be found that the phase and amplitude of the transient Kerr modulation are strongly dependent on the helicity of the circularly polarized pump pulses. Indeed, these oscillating signals may be mistaken for spin excitation modes. The present findings allow us to get an insight into the transient magneto-optical dynamical process in transparent medium. In addition, the polarization modulation of ultrashort laser pulse on a picosecond time scale will facilitate all-optical data processing, as well as the polarization-dependent ultrafast dynamics in various material systems, which span from condensed matter to molecular spectroscopy. In this regard, our experimental results provide a possibility for designing novel all-optical (magneto-optical) modulators operating at THz clock frequencies. The magneto-optical polarization response modulated at THz frequencies may have new possibilities for designing all-optical devices, such as ultrafast modulators.
Preparation and performance of high-efficient hole-transport-material-free carbon based perovskite solar cells
Authors: Fan Wei-Li  , Yang Zong-Lin  , Zhang Zhen-Yun  , Qi Jun-Jie  ,   School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

Carbon based perovskite solar cells (C-PSCs) have attracted much attention because of their high stability and low-cost of production. However, due to the high interfacial resistance and the low energy level matching between perovskite and carbon electrodes, the maximum power conversion efficiency (PCE) is less than that of the metal-based perovskite solar cells. In this paper, a carbon-based perovskite solar cell is fabricated with the device structure of FTO/c-TiO2/m-TiO2/CH3NH3PbI3/Carbon. The perovskite films and carbon based perovskite solar cells are characterized by scanning electron microscope, atomic force microscope, X-ray diffraction (XRD), UV-Vis absorption spectrum, the steady-state spectrum, the time-resolved PL (TRPL) spectrum, and an electrochemical workstation. In addition, the internal mechanism of the efficiency improvement of carbon-based perovskite solar cell is discussed in depth. Then, the rotation speeds of mesoporous TiO2 layer (TiO2 paste diluted by ethanol with mass ratio of 1:4) are 1500, 1600, 1700 and 1800 r/min and the speeds of perovskite layer (CH3NH3I and PbI2 at a 1:1 molar ratio are stirred in a mixture of DMF and DMSO (9:1, v/v)) are 2000, 3000, 4000 and 5000 r/min; When the speed of m-TiO2 layer is 1700 r/min and the speed of perovskite layer is 4000 r/min, the mesoporous TiO2 layer thickness is about 500 nm, Thickness of CH3NH3PbI3 capping layer is about 400 nm. The cooperation of these two layers eventually leads to the high-quality perovskite with enlarged grain size, prolonged photoluminescence lifetime, lowered defect density, increased carrier concentration, and the finally enhanced photovoltaic performance. The device obtains the highest PCE of 11.11% with an open circuit voltage (Voc) of 0.93 V, a current density (Jsc) of 21.75 mA/cm2 and fill factor (FF) of 55%. At the same time, the stability of the carbon-based perovskite solar cell is also studied. The XRD is used for initial perovskite and the perovskite after 15 days to investigate the photo- and humidity stability of the full cells without encapsulation. The device exhibits excellent air stability with only 5% degradation when aged in ambient air at room temperature with 40%-50% humidity without any encapsulation after 15 days, which is better than the metal based perovskite solar cell. Our results open the way for making cost-efficient and stable PSCs toward market deployment.
Determination of carrier bulk lifetime and surface recombination velocity in semiconductor from double-wavelength free carrier absorption
Authors: Wang Qian  , Liu Wei-Guo  , Gong Lei  , Wang Li-Guo  , Li Ya-Qing  ,   School of Optoelectronic Engineering, Xi'an Technological University, Xi'an 710021, China
Published: December 2020

In microelectronic and photovoltaic industry, semiconductors are the basic materials in which impurities or defects have a serious influence on the properties of semiconductor-based devices. The determination of the electronic transport properties, i.e., the carrier bulk lifetime (τ) and the front surface recombination velocity (S1), is important for evaluating the semiconductor material. In this paper, a method of simultaneously measuring the bulk lifetime and the front surface recombination rate of semiconductor material by using double-wavelength free carrier absorption technique is presented. The effect of the carrier bulk lifetime and the front surface recombination rate on the modulated free carrier absorption signal (Ampratio and Phadiff) are qualitatively analyzed. The process of extracting the bulk lifetime and the front surface recombination rate by the proposed double-wavelength free carrier absorption method are also given. At the same time, the uncertainties of the parameters extracted by this method are calculated and compared with those obtained by the traditional frequency-scan free carrier absorption technique. The results show that the proposed method can significantly reduce the uncertainties of the measurement parameters, especially for the samples with higher surface recombination rate. For the sample with a lower front surface recombination rate (S1=102 m/s), the uncertainty of the carrier bulk lifetime and the front surface recombination velocity obtained by the proposed method are almost in agreement with those obtained by the conventional frequency-scan method. On the contrary, for the samples with higher front surface recombination rate (S1 ≥ 103 m/s), the uncertainties of the carrier transport parameters are much smaller than those from the conventional frequency-scan method. For example, the estimated uncertainty of the carrier bulk lifetime and the front surface recombination velocity for the sample with τ=10 μs and S1=103 m/s are approximately ±5.55% and ±2.83% by the proposed method, which are more improved than ±18.50% and ±31.46% by the conventional frequency-scan method with a wavelength of 405 nm. Finally, we explain the above phenomenon by analyzing the distribution of excess carrier concentration at different pump wavelengths. As the pump wavelength decreases, the more excess carriers are excited near the surface of the sample due to the greater absorption coefficient, and the influence of the surface recombination by the impurities and defects on the signal is more obvious. Therefore, the measurement accuracy of the front surface recombination rate can be improved effectively by using double wavelength pumping.
Antiferromagnetic order and spin dynamics in iron-based superconductors
Authors: Gong Dong-Liang  , Luo Hui-Qian  ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Like the superconductivities in other unconventional superconductors, high-temperature superconductivity in the iron pnictide often emerges after the static antiferromagnetic order has been suppressed, and is always accompanied by strong spin fluctuations. Therefore, understanding the magnetism and its origin could be an important premise for ascertaining the microscopic mechanism of iron-based superconductivity. Neutron scattering, as a powerful tool for studying magnetic ordering and spin dynamics in condensed matters, plays an essential role in understanding the relationship between magnetism and superconductivity in iron-based superconductors. In this paper, we review the neutron scattering results for iron pnictides, including static magnetic structures, magnetic phase transitions, spin excitations and electronic nematicity, and discuss their relationship with superconductivity.
Periodic orbits of diffusionless Lorenz system
Authors: Dong Cheng-Wei  ,   Department of Physics, School of Science, North University of China, Taiyuan 030051, China
Published: December 2020

The strange attractor of a chaotic system is composed of numerous periodic orbits densely covered. The periodic orbit is the simplest invariant set except for the fixed point in the nonlinear dynamic system, it not only reflects all the characteristics of the chaotic motion, but also is closely related to the amplitude generation and change of chaotic system. Therefore, it is of great significance to obtain the periodic orbits in order to analyze the dynamical behaviors of the complex system. In this paper, we study the periodic orbits of the diffusionless Lorenz equations which are derived in the limit of high Rayleigh and Prandtl numbers. A new approach to establishing one-dimensional symbolic dynamics is proposed, and the periodic orbits based on a topological structure are systematically calculated. We use the variational method to locate the cycles, which is proposed to explore the periodic orbits in high-dimensional chaotic systems. The method not only preserves the robustness characteristics of most of other methods, such as the Newton descent method and multipoint shooting method, but it also has the characteristics of fast convergence when the search process is close to the real cycle in practice. In order to apply the method, a rough loop guess must be made first based on the entire topology for the cycle to be searched, and then the variational algorithm will bring the initial loop guess to evolving toward the real periodic orbit in the system. In the calculations, the Newton descent method is used to achieve stability. Two cycles can be used as basic building blocks for initialization, searching for more complex cycles with multiple circuits around the two fixed points requires more delicate initial conditions; otherwise, it will probably lead to nonconvergence. We can initialize the loop guess for longer cycles constructed by cutting and gluing the short, known cycles. For this system, such a method yields quite a good systematic initial guess for longer cycles. Even if we deform the orbit manually into a closed loop, the variational method still shows its powerfulness for good convergence. The topological classification based on the entire orbital structure is shown to be effective. Furthermore, the deformation of periodic orbits with the change of parameters is discussed, which provides a route to the periods of cycles. The present research may provide a method of performing systematic calculation and classification of periodic orbits in other similar chaotic systems.
Characteristics and expressions of entangled microwave signals
Authors: Li Xiang  , Wu De-Wei  , Miao Qiang  , Zhu Hao-Nan  , Wei Tian-Li  ,   Information and Navigation College, Air Force Engineering University, Xi'an 710077, China
Published: December 2020

Entangled microwave signal is the reflection of the quantum characteristics of electromagnetic field in a GHz frequency range. Its generation is mainly dependent on superconducting circuits. Owing to the fact that there is no canonical expression to describe the format of entangled microwave signals, two expressional methods are presented on the basis of analyzing the characteristics of entangled microwave signals. One is in quantum frame, and the other is in classical frame. In quantum frame, we express entangled microwave signals in two-mode squeezed vacuum state. According to input-output relationship and parametric amplifier property in the generating process of entangled microwave signals, we describe the characteristics by two-mode squeezing operator and quantum Langevin equation. In the representation of photon number and Wigner function, we analyze the photon number distribution and the quadrature components' distribution of two-mode squeezed vacuum state, which shows the entangled two-photon correlation and the non-localized positive (negative) correlation of quadrature components. These are consistent with the characteristics of entangled microwave signals. Therefore, the results demonstrate that the entangled microwave signals can be expressed by two-mode squeezed vacuum state. In classical frame, we express entangled microwave signals in correlated random signals approximately. According to the relationship between quadrature components and the quantization of electromagnetic field, we construct the relation among electric-field intensity, input angular frequency, and squeezed parameter. The random number with Gaussian distribution is used as an input state to implement the simulation analysis. We illustrate the waveforms of entangled microwave signals after measurement and the extracted quadrature component waveform varying with time. The simulation results are consistent with the measurement results. These results show that the classical expression can reflect the one-path randomicity and two-path correlativity, which are the intrinsic characteristics of entangled microwave signals. Therefore, it is rational to express entangled microwave signals in correlated random signals. These two expressions properly reflect the continuous variable entanglement characteristics of entangled microwave signals. The expression of two-mode squeezed vacuum state is complete. Plenty of parameters that represent quantum information can be calculated by two-mode squeezed vacuum state, such as entanglement degree or the power of noise fluctuation. The merit of the expression of correlated random signals is intuitive, which makes it easier to understand the nonclassical characteristics of entangled microwave signals.
Molecular dynamics simulations on scattering of Ar molecules on smooth and rough surfaces
Authors: Zhang Ran  , Chang Qing  , Li Hua  ,   College of Aeronautics and Astronautics, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Molecular dynamics method is used to investigate the scattering characteristics of Ar molecule on smooth and rough Pt(100) surface. In this paper, a velocity sampling method is proposed to obtain the tangential momentum accommodation coefficients (TMACs) and the sticking probabilities of gas molecules on smooth and rough surface under different temperature conditions. The results show that the TMAC and the sticking probability decrease with increasing temperature under smooth surface condition. The results of our work are in excellent agreement with the results of the reference for a three-dimensional gas flow in a nanochannel. Unlike the scenario of smooth surfaces, the roughness of rough surfaces greatly promotes the accommodation of tangential momentum between the gas molecules and surfaces. When the roughness becoming larger, the TMAC approaches to 1.0 and the sensitivity to temperature decreases gradually. Unlike the relationship between TMAC and roughness, although the sticking probability of gas molecules increases with roughness increasing, its dependence on temperature does not change. Furthermore, the beam method where the incident velocity and angle are determined is used to quantitatively analyze the scattering characteristics of gas molecules on different surfaces. According to the number of collisions between gas molecule and the surface, we classify the scattering of gas molecules on a smooth surface into two types: single collision scattering and multiple collision scattering. For those gas molecules that experience one collision, their average tangential momentum decreases to a certain extent, however, the gas molecules scattered after multiple collisions tend to maintain the original tangential momentum. For gas molecules reflected from the smooth surface, their velocity distribution exhibits a typical bimodal distribution. The position of the first peak appears at the incident velocity value, and the position of the second peak appears at a velocity value of zero. Regarding rough surfaces, the existence of roughness changes the mode of exchange of momentum and energy between gas molecules and walls, resulting in a significant decrease in the average tangential momentum of gas molecules scattered on rough surfaces. Besides, the more the gas molecules colliding on the surface, the more severe the energy loss after scattering will be. For gas molecules reflected from the rough surfaces, their velocity distribution conforms to the characteristics of Gaussian distribution.
Interface enhanced superconductivity in monolayer FeSe film on oxide substrate
Authors: Ding Cui  , Liu Chong  , Zhang Qing-Hua  , Gong Guan-Ming  , Wang Heng  , Liu Xiao-Zhi  , Meng Fan-Qi  , Yang Hao-Hao  , Wu Rui  , Song Can-Li  , Li Wei  , He Ke  , Ma Xu-Cun  , Gu Lin  , Wang Li-Li  , Xue Qi-Kun  ,   State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China;,   Beijing National Laboratory for Condensed Matter Physics, Laboratory for Advanced Materials and Electron Microscopy, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
Published: December 2020

We report on the observation of a superconducting gap of about 14-15 meV, significantly enlarged compared with the value of 2.2 meV for bulk FeSe, in monolayer FeSe film interfaced with MgO epitaxial on SrTiO3(001) substrate by using the scanning tunneling microscopy. While the MgO exhibits the same work function as SrTiO3 substrate, the gap magnitude is in coincidence with that of surface K-doped two-unit-cell FeSe film on SrTiO3(001), suggesting that the interface enhanced superconductivity might be attributed to cooperation of interface charge transfer driven by band bending with interface electron-phonon coupling as discovered at FeSe/TiO2 interfaces. On the other hand, the observation of such an enlarged superconducting gap, complementary to our previous transport observation of an onset superconducting transition temperature of 18 K in monolayer FeSe film on a bulk MgO substrate, implies that FeSe/MgO interface is likely to be a new interface high-temperature superconducting system, providing a new platform for investigating the mechanism of interface hightemperature superconductivity.
Sound radiation from finite cylindrical shell excited by inner finite-size sources
Authors: Yang De-Sen  , Zhang Rui  , Shi Sheng-Guo  ,   1. Underwater Acoustic Science and Technology Laboratory, Harbin Engineering University, Harbin 150001, China;,   2. Key Laboratory of Marine Information Acquisition and Security(Harbin Engineering University), Ministry of Industry and Information Technology, Harbin 150001, China;,   3. College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin 150001, China
Published: December 2020

The study of the characteristics of noise sources in cylindrical shells is the foundation of sound field prediction. Although noise sources are usually regarded as point sources to simplify the calculation model in noise source localization and waveguide sound propagation, the approximation is limited to far-field problems. For the near-field acoustics problems in engine room and ship cabin, the radiated noise possesses the spatial directivity because of the complex vibration distribution of the noise source surface. Moreover, the sound scattering on the surface of finite-size sources makes the noise source itself act not only as the energy input of sound field, but also as the scatterer to change the structure of sound field in the environment. These factors lead to large errors when the finite-size source is simplified into a point source. In order to explore the influence of finite-size source on the acoustic field inside and outside the underwater vehicle structure, the shell coupled equation is constructed by combining thin shell theory, equivalent source and Green function. The effects of source surface scattering and directivity on the acoustic field inside and outside the cylindrical shell are studied. The results show that the accuracy of finite-size source construction is related to the equivalent source location. It proves that equivalent source allocation should be arranged in the middle of the geometric center of sources and its structural surface. Sound scattering from the surface of the finite-size source will change the sound field inside the shell, and then the resonant peaks of the cavity are shifted to the high frequencies as the source volume increases, which causes a strong sound transmission phenomenon in some frequency bands. In addition, the directivity of the finite-size source has little effect on the intensity of the sound field inside and outside the shell, which is evident in changing the far-field directivity of the radiated sound field. The research results are valuable for noise prediction and noise control.
Experimental investigation on ultraviolet multiphoton dissociation dynamics of methylamine
Authors: Wang Xiao-Li  , Yao Guan-Xin  , Yang Xin-Yan  , Qin Zheng-Bo  , Zheng Xian-Feng  , Cui Zhi-Feng  ,   Anhui Province Key Laboratory of Optoelectric Materials Science and Technology, Anhui Normal University, Wuhu 241000, China
Published: December 2020

Methylamine is the simplest alkylamine. It is a typical molecule in the field of surface physicochemistry. The basic properties of the structure and reaction activity of this molecule are essential to understand its role in many chemical reactions. Its energy state and ionic structure, ionization dissociation channel and competition have aroused the interest of astronomical and physicochemical researchers. In order to further understand the mechanism of multiphoton dissociation and ionization of methylamine in this energy region, the photodissociation channels of methylamine are studied based on the measured resonance enhanced multiphoton ionization-time-of-flight mass spectrum (TOFMS), mass-selected excitation spectra of the ionized fragment, and laser power index of each ion in a range of 280-287.5 nm. The multiphoton ionization TOFMS of methylamine molecule is obtained at the excited laser wavelength of 283 nm. After calibration, the weaker ion peaks correspond to the C+, CH+, CH2+, CH3+, NH2+, NH3+, CN+, CH2NH+(CHNH2+, CH3N+), CH3NH2+; the mass-to-charge ratio of stronger peaks except H+ ions are 27, 28 and 30, respectively, and the mass-to-charge ratio of 28 and 30 belong to CHNH+, CH2NH2+ after analysis and discussion. Combining with the mass separation excitation spectra of the parent ions, it is concluded that there is a repulsive electronic state in the single photon energy. The main dissociation channel is the resonant photodissociation of the parent molecule in the repulsive state produced by one photoabsorption, followed by the photoionization of the fragment through the (1+1) multiphoton process and the further photodissociation of the ionized fragment.
Two-color photoassociation spectra of ultra-cold Cs (60D5/2)2 Rydberg molecule
Authors: Bai Jing-Xu  , Han Xiao-Xuan  , Bai Su-Ying  , Jiao Yue-Chun  , Zhao Jian-Ming  , Jia Suo-Tang  ,   1. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China;,   2. Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

The long-range multipole interactions between ultra-cold Rydberg atoms form adiabatic potentials, one of which shows a binding potential that can be used to bind Rydberg-Rydberg molecules. Rydberg-atom molecule, known as macrodimer due to its larger size (~μm), has the properties of the abundant vibrational energy levels and large electric dipole moment and so on. Compared with Rydberg atom, the Rydberg molecule, including Rydberg-ground molecule and Rydberg-Rydberg molecule, is susceptible to manipulate by an external field and possesses potential applications in the weak-signal detection, the quantum gas correlation measurement and the vacuum fluctuation and so on.
In this paper, we investigate a (60D5/2)2 Rydberg macrodimer theoretically and experimentally. In the calculation, we take into account the multipole interaction of a Rydberg-atom pair, including dipole-dipole, dipole-quadrupole, dipole-octupole and quadrupole-quadrupole interaction and so on. The adiabatic potential of 60D5/2 Rydberg-atom pair is obtained by diagonalizing the interaction Hamiltonian on a grid of internuclear separations, R. The potential depth and binding length of the Rydberg molecular potential well are obtained. In experiment, we prepare the ultra-cold Cs (60D5/2)2 Rydberg molecules by a two-color photoassociation method in a cesium ultracold atom trap. The first-color (pulse-A) resonantly excites a seed Rydberg atom A, and the second color (pulse-B) is detuned and resonantly excites the second Rydberg atom B near to the atom A. Both pulse-A and pulse-B are two-photon excitations (852 nm + 510 nm), between which their 852-nm lasers have the same frequency, whereas the 510-nm laser frequency of the pulse-A is set to be resonant with the atomic transition and the frequency of the pulse-B is detuned by using a double-passed acousto-optic modulator. When the pulse-B is detuned to the molecular binding energy, atom-A and-B are bonded, forming an ultra-cold Cs (60D5/2)2 Rydberg molecule. The two-color photoassociation spectra of Rydberg-Rydberg molecules are detected by the field ionization of Rydberg atoms and molecules with a ramped electric field. Molecular spectra are compared with calculated adiabatic molecular potentials, which yields the binding energy and equilibrium internuclear distance. The two-color photoassociation method used in this work has a doubly resonant character that results in the enhanced excitation rate.
Ultrasonic sacttering unified theory for polycrystal material with grain sizes distribution
Authors: Li Shan  , Li Xiong-Bing  , Song Yong-Feng  , Chen Chao  ,   1. School of Traffic and Transportation Engineering, Central South University, Changsha 410075, China;,   2. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China
Published: December 2020

The existing unified theory of ultrasonic scattering can model the attenuation and phase velocity in the frequency domain by using the microstructure and mechanical properties of polycrystalline materials. However, this theory does not consider the influence of grain size distribution, thus degrading the calculation accuracy in the forward modeling. A new unified theory, which is mainly corrected by considering the grain size distribution, is developed. First, the second-order Keller approximation and the full-field Green's function are used to calculate the wave equation of inhomogeneous medium and derive the average wave in the medium, respectively. Second, the method of the truncated lognormal distribution is used to describe the grain size distribution and construct the weighted spatial correlation function. Finally, the new unified theory of ultrasonic scattering is established to reveal the influence of grain distribution on ultrasonic scattering.
Using the new unified model, the effects of the grain distribution widening on the ultrasonic scattering while the average grain size is unchanged, are analyzed for the longitudinal wave and the shear wave. The attenuation increases in the Rayleigh scattering region and the geometric scattering region, while there is less attenuation variation in the stochastic scattering region and two adjacent transition regions. The phase velocity varies strongly in the stochastic-geometric transition region, while the variation is relatively small in other scattering zones. Experiments are conducted by using a 304 stainless steel specimen. The results show that when the grain distribution characteristics are considered, the discrepancy between the longitudinal wave attenuation spectrum and experimental results, and that between the phase velocity spectrum and experimental results are reduced by 49% and 64%, respectively; for the shear wave, these discrepancies are reduced by 12% and 4%, respectively.
From all above aspects, the accuracy of the new model is higher than that of the traditional model. The new unified theory proposed in this paper can effectively correct the discrepancy of the attenuation spectrum and phase velocity spectrum caused by the grain size distribution and provide a theoretical basis for inverse problem of grain distribution. Also, the theory can be extended to materials containing elongated grains, macroscopic texture or multiple phases.
Bottom reverberation for large receiving depth in deep water
Authors: Wang Long-Hao , Qin Ji-Xing , Fu De-Long , Li Zheng-Lin , Liu Jian-Jun , Weng Jin-Bao ,   State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China,   91900 Unit of Chinese Navy, Xingcheng 125100, China,   College of Meteorology and Oceanology, National University of Defense Technology, Changsha 410073, China,   Ocean Laboratory of Acoustics and Remote Sensing, Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China
Published: December 2020

Ocean reverberation is an important issue in underwater acoustics, which usually influences the working performance of the active sonars significantly. The deep-water reverberation data are collected from the South China Sea experiment including the reverberation signals at large receiving depths near the bottom, showing that the wave intensity increases obviously at some moments with time increasing. To analyze in depth the data, a uniform bottom-reverberation model is proposed based on the ray theory, which can calculate monostatic and bistatic reverberation intensity and explain the generation process of deep-water reverberation. The mesh method is first used in this model by dividing bottom scatterers into a number of grids. Then reverberation is calculated based on the exact time of generating the scattering signal from each grid. Due to the exact arrival time, the presented model can provide more accurate result than classical models, in which scatterers are usually treated as circular rings or elliptical rings. Numerical results are compared with experimental reverberations at different receiving distances and depths. The simulated and experimental results agree well overall for large receiving depths, whereas agreement extent decreases for the case of receiving depth close to the sea surface. The analytical results indicate that the applied scattering coefficient is suitable for this experimental sea area, and meanwhile verify that this scattering model is more accurate for low-angle bottom backscatters corresponding to the reverberation at large receiving depths.
Development and application of MoS2 and its metal composite surface enhanced Raman scattering substrates
Authors: Li Jin-Hua , Zhang Si-Nan , Zhai Ying-Jiao , Ma Jian-Gang , Fang Wen-Hui , Zhang Yu ,   International Joint Research Center for Nanophotonics and Biophotonics, Jilin Key Laboratory of Nanophotonics and Biophotonics, Changchun University of Science and Technology, Changchun 130022, China,   Key Laboratory of Ultraviolet Emitting Materials and Technology, Minstry of Education, Northeast Normal University, Changchun  130000, China
Published: December 2020

Surface-enhanced Raman scattering is an ultra-sensitive molecular detection technology, and the exploration of its mechanism and the improvement of sensitivity, uniformity and stability have always been significant challenge to researchers. In this paper, the development of surface-enhanced Raman scattering mechanism and its research progress, and thus review the mechanism, research status and existing problems of single metal substrate, molybdenum disulfide substrate and metal/molybdenum disulfide composite substrate are summarized; The preparation method of the molybdenum disulfide substrate including hydrothermal/solvothermal method, micromechanical peeling method, chemical meteorological deposition method, and preparation method of metal/molybdenum disulfide composite substrate are briefly introduced, in which the electrochemical method, thermal reduction method, seed-mediated growth method, and electron beam lithography method are covered, and the advantages and disadvantages of the above preparation methods are evaluated; The research progress of the applications of molybdenum disulfide and its metal composite substrates in food testing, biomedicine, environmental pollution monitoring, etc. are briefly overviewed The surface-enhanced Raman scattering study is extended to other transition metal binary compounds and their metal composite structures. Therefore, the metal/molybdenum disulfide composite substrate expands the types of surface-enhanced Raman scattering substrates, thereby making up for the deficiency of low reproducibility, poor stability, and weak adsorption. Moreover, it has the advantages of fluorescence quenching effect, high sensitivity, wide detection range, and it can be combined with on-site rapid separation technology, and thus has widespread application prospects. Finally, the shortcomings of surface-enhanced Raman scattering technology and prospects for its development are also pointed out.
S-band high-efficiency relativistic backward waveoscillator with low magnetic field
Authors: Wu Yang , Zhou Zi-Gang ,   Institute of Applied Electronics, CAEP, Mianyang 621900, China,   College of Science, Southwestern University of Science and Technology, Mianyang 621010, China
Published: December 2020

New applications for high-power microwave (HPM) have aroused the intense interest in the development of HPM sources. The relativistic backward wave oscillator (RBWO), as one of the most promising HPM sources, has proved to be a competitive candidate for generating multi-gigawatt HPM at L, S, C, and X-band. But for the conventional RBWO, in order to maintain high conversion efficiency, a high enough magnetic field is required to confine the intense relativistic electron beam. Obviously, it can lead to high energy consumption and bulkiness. Therefore, to fulfill the requirements for applications, enhancing the conversion efficiency of the RBWO at low magnetic field has received much attention and has been investigated extensively.

In this paper, we present a well-designed RBWO model with a cavity-chain modulator and a TM02 mode extractor to enhance the conversion efficiency at a low guiding magnetic field. The operation characteristics of the device are investigated in detail in this paper. Moreover, the function of each part of the device for enhancing the conversion efficiency is confirmed by the particle-in-cell simulation. In the device, the cavity-chain modulator is introduced to strengthen the beam bunching process. The TM02 extractor after the modulator increases the Q-factor of the RBWO due to its partial reflection to the outgoing microwave. The increase of the Q-factor can enhance the standing electric field in the extractor. If the phase is appropriate, the extractor can convert the kinetic beam power into the RF power efficiently. The drift tubes between the reflector, the modulator and the extractor are used to adjust the bunching phase and the conversion phase of the modulated electron beam in the RF field. Moreover, an S-band high efficiency RBWO is designed and verified by the particle-in-cell simulation. An output power of 4.2 GW at a frequency of 2.38 GHz is obtained in the simulation. And the conversion efficiency reaches 50% when the guiding magnetic field is 0.7 T.
A method of designing asymmetric double-sided off-axis aspheric mirror detection compensation zoom light path
Authors: Feng Shuai , Chang Jun , Niu Ya-Jun , Mu Yu , Liu Xin ,   School of Opto-Electronics, Beijing Institute of Technology, Beijing 100081, China,   Tianjin Jinhang Institute of Technical Physics, Tianjin 300192, China
Published: December 2020

With the development of multispectral common-aperture high-precision detection technology, the asymmetric double-sided off-axis aspheric mirror is playing an increasingly important role in characterizing the correcting phase difference, increasing the relative caliber of system, expanding the view angle of field, simplifying system structure, and reducing weight and volume. But high-precision detection is a key step restricting the applications of these mirrors. At present, the compensation method of the interference test is the most effective mean of off-axis aspheric surface detection which has a simple structure, large compensation range, small number of components and is easy to control. However for the detection of asymmetric double-sided off-axis aspheric mirrors, two sets of alone compensators are still used, in which the efficiency is low and the switching compensator will reduce the accuracy of detection. Aiming at this problem, in this paper we propose a zoom null compensation method which is based on the Offner refracting compensation method. In this method, the off-axis aperture stop causes the light to be off-axis and split, the common lens group is moved to zoom, and the mirror folds the light path. There are two off-axis apertures are provided for off-axis and splitting, four lenses which form three lens groups are used to move positions for zooming, two mirrors are used to fold light. An optical design software is used to simulate the experiment, and implements the design for the high-precision detection of optical path for the asymmetric double-sided off-axis aspherical mirror by using this set of null compensation method. The simulation result shows that the theoretical residual wave aberration increases up to 0.0003λ root-mean-square (RMS) and 0.0001λ RMS with the designed system compensation, which meet the requirement for detection. At the same time, the tolerance analysis is carried out according to the design result, the actual residual wave aberrations within the existing tolerance range are 0.0326λ RMS and 0.0316λ RMS, which meet the requirements for manufacturing and assembly. The present work provides a new idea for the high-precision detection of asymmetric double-sided off-axis aspheric mirror. At the same time, the quality of the detected beam in this paper is achieved under ideal conditions, and the quality of beam will be considered in the next research work.