bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploration of the deep-ultraviolet nonlinear optical materials in the derivatives of KBe2BO3F2
Authors: Gai Min-Qiang , Wang Ying , Pan Shi-Lie ,   CAS Key Laboratory of Functional Materials and Devices for Special Environments, Xinjiang Key Laboratory of Electronic Information Materials and Devices, the Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, China,   Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The use of nonlinear optical crystal materials to extend the limited range of laser sources to the deep-ultraviolet (deep-UV, λ < 200 nm) regions by various frequency conversion techniques, has become an attractive field for generating deep-UV light. However, the lack of nonlinear optics (NLO) crystal materials capable of frequency conversion in the deep-UV light range, limits the development and application of deep-UV all-solid-state lasers. Therefore, scientists all over the world are actively exploring the new generation of deep-UV NLO crystal materials. At present, only the KBe2BO3F2 (KBBF) crystal is capable of generating deep-UV light through the direct sixth harmonic generation of the Nd:YAG laser. The infinite ∞[Be2BO3F2]− single layers, as the brilliant building blocks in the crystal structures of KBBF family, provide a relatively large second harmonic generation coefficient (d11 = 0.47 pm/V) and a sufficient birefringence (Δn = 0.07@1064 nm). However, the KBBF crystals have insurmountable intrinsic defects, such as the usage of high toxic beryllium oxide, and the serious layer growth habit, which greatly restrict its commercialization process. Since the layered structure of the KBBF crystal is still one of the most brilliant structures for generating deep-UV laser, an effective strategy is to change the interlayer connection mode and develop new NLO materials based on KBBF with less layering growth habit. In this paper, by reviewing the development history of borate deep-UV NLO crystals and the derivatives of KBBF, the relationship between layered structure and optical properties of different interlaminar connections of crystal materials is systematically analyzed. We discuss the main contradictions and solutions of the development of deep-UV NLO crystal materials which are similar to the KBBF structure. In order to provide a reference for the innovative exploration of new materials in the future, several design strategies are also proposed.
Interfacial water and catalysis
Authors: Hu Jun  , Gao Yi  ,   1. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China;,   2. Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China
Published: December 2020

Catalysis of water, normally occurring at the interface, is crucial for the development of renewable energy and the environmental protection. Understanding the structures and chemical/physical properties of interfacial water during catalysis is of paramount importance for the sustainable development of human society, such as clean energy, wastewater treatment, and etc. However, owing to its complexity structure and mysterious property, the effect of water during catalysis is still an open question. The role of water during reactions, as reactant, catalyst, solvent, or both, has not been resolved. Recently, with the fast-development of in-situ experimental techniques and the computational capacity, the scientists started to investigate the behaviors of interfacial water using the real-time characterization and theoretical modeling at the atomic level, which provides the evidences and pictures to understand the effects of interfacial water. This paper will briefly introduce the current opportunities and challenges in studying the interfacial water, and the latest development and facing difficulty in experiment and theory, which will be beneficial for the future design of efficient catalysts for their applications in water.
Ultrathin flexible transmission metamaterial absorber
Authors: Yang Peng , Qin Jin , Xu Jin , Han Tian-Cheng ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

As an important branch of metamaterial-based devices, metamaterial absorber (MA) has aroused great interest and made great progress in the past several years. By manipulating the magnetic resonance and the electric resonance simultaneously, the effective impedance of MA will match the free space impedance, thus resulting in a perfect absorption of incident waves. Due to the advantages of thin thickness, high efficiency and tunable property, MA has been widely concerned in energy-harvesting and electromagnetic stealth. Since the first demonstration of MA in 2008, many MAs have been extensively studied in different regions, such as microwave frequency, THz, infrared frequency and optical frequency. At the same time, the absorber has been extended from the single-band to the dual-band, triple-band, multiple-band and broadband. In recent years, the dual-band absorber has received significant attention and has been widely studied. So far, however, most of MAs are composed of a bottom continuous metallic layer, which prevents electromagnetic waves from penetrating and makes electromagnetic waves absorbed or reflected. In this paper, an ultrathin flexible transmission absorber with a total thickness of 0.288 mm is designed and fabricated, which can be conformally integrated on an object with a curved surface. The absorber consists of three layers of structure: the bottom is a one-dimensional grating type metal line, the middle is the medium layer, and the surface metal layer is composed of two different sizes metal lines in parallel. Simulation and experimental results show that the absorptions of TE wave are 97.5% and 96.0% respectively at the two frequency points of 5 GHz and 7 GHz. The transmission of the TM wave above 90% is maintained from 3 GHz to 6.5 GHz. We also simulate the spatial electric field distribution and magnetic field distribution at two resonant frequencies, and explain the electromagnetic absorption mechanism of the proposed structure for TE wave. Secondly, when the incident angle increases to 60 degrees, the performance of the absorber is substantially unaffected, exhibiting good wide-angle characteristics. In addition, through the analysis of structural parameters, two absorption peaks of the proposed absorber can be independently adjusted, resulting in a flexible design. In conclusion, we propose both theoretically and experimentally a polarization-controlled transmission-type dual-band metamaterial absorber that can absorb the TE waves and transmit the TM wave efficiently, which has important applications in the case requiring bidirectional communication.
Neural firing rate homeostasis via inhibitory synaptic plasticity
Authors: Xue Xiao-Dan , Wang Mei-Li , Shao Yu-Zhu , Wang Jun-Song ,   School of Biomedical Engineering and Technology, Tianjin Medical University, Tianjin 300070, China,   Cangzhou People's Hospital, Cangzhou 061000, China
Published: December 2020

Neural firing rate homeostasis, as an important feature of neural electrical activity, means that the firing rate in brain is maintained in a relatively stable state, and fluctuates around a constant value. Extensive experimental studies have revealed that the firing rate homeostasis is ubiquitous in brain, and provides a base for neural information processing and maintaining normal neurological functions, so that the research on neural firing rate homeostasis is a central problem in the field of neuroscience. Cortical neural network is a highly complex dynamic system with a large number of input disturbance signals and parameter perturbations due to dynamic connection. However, it remains to be further investigated how firing rate homeostasis is established in cortical neural network, furthermore, maintains robustness to these disturbances and perturbations. The feedback neural circuit with recurrent excitatory and inhibitory connection is a typical connective pattern in cortical cortex, and inhibitory synaptic plasticity plays a crucial role in achieving neural firing rate homeostasis. Here, by constructing a feedback neural network with inhibitory spike timing-dependent plasticity (STDP), we conduct a computational research to elucidate the mechanism of neural firing rate homeostasis. The results indicate that the neuronal firing rate can track the target firing rate accurately under the regulation of inhibitory synaptic plasticity, thus achieve firing rate homeostasis. In the face of external disturbances and parameter perturbations, the neuron firing rate deviates transiently from the target firing rate value, and converges to the target firing rate value at a steady state, which demonstrates that the firing rate homeostasis established by the inhibitory synaptic plasticity can maintain strong robustness. Furthermore, the analytical research qualitatively explains the firing rate homeostasis mechanism underlined by inhibitory synaptic plasticity. Finally, the simulations further demonstrate that the learning rate value and the firing rate set point value also exert a quantitative influence on the firing rate homeostasis. Overall, these findings not only gain an insight into the firing rate homeostasis mechanism underlined by inhibitory synaptic plasticity, but also inspire testable hypotheses for future experimental studies.
Recent progress of expansion dynamics in strongly-interacting ultracold Fermi gases
Authors: Diao Peng-Peng , Deng Shu-Jin , Li Fang , Wu Hai-Bin ,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
Published: December 2020

The evolution of non-equilibrium dynamic for many-body systems is one of the most challenging problems in physics. Ultra-cold quantum atomic Fermi gas provide an test-bed for studying many-body non-equilibrium dynamics due to its high freedom of controllability, which can be used to simulate and understand the dynamics of the early universe after the Big Bang, quark-gluon produced in heavy ion collisions and nuclear physics. Generally, the evolution of many-body systems is very complex, and usually needs to be studied by symmetry. Feshbach resonance can be used to prepare scale invariant atomic Fermi gases: non-interacting and unitary Fermi gases. When far away from equilibrium state, universal exponents and functions can be used to characterize the dynamics of the system, which can be identified by scaling the temporal and spatial evolution of the system. In this review, the recent developments in the expansion dynamics of strongly interacting ultracold Fermi gases are introduced, including the anisotropic expansion of atomic gases, scaling dynamics and Efimovian expansion dynamics.
Restraining effect of resonant propagation of acousticwaves in liquids with mixed bubbles
Authors: Chen Shi , Zhang Di , Wang Cheng-Hui , Zhang Yin-Hong ,   School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, China
Published: December 2020

There is the resonant propagation phenomenon of acoustic wave in bubbly liquid, i.e., the attenuation coefficient and the velocity of acoustic wave in range of resonant frequencies of bubbles can become very large. In previous papers, generally adopted was a simplified assumption that there is a single type of bubble in a liquid. It restricts our understanding of the resonant propagation phenomenon. In this paper the resonant propagation of acoustic wave in a liquid with mixed bubbles is studied. Here, static radii of bubbles are different from each other. Research results show that there is a restraining effect of the resonant propagation of acoustic wave in liquid with mixed bubbles. The attenuation coefficient and the velocity of acoustic wave in the liquid with mixed bubbles are obviously less than those in the liquid containing bubbles with the same static radius. The nature of the restraining effect is that the resonant vibration of bubbles is weakened due to the interaction between bubbles with different static radii. Some important properties of the restraining effect are investigated for all kinds of liquid systems with mixed bubbles. Moreover, the effect of the viscosity and the rate of cavitation on the restraining effect are also studied. Research results are shown as follows. 1) Comparing with bigger bubbles, resonant characteristic quantities (such as the attenuation coefficient and the velocity of acoustic wave) caused by smaller bubbles can be reduced more obviously; 2) the efficiency of the restraining effect increases with the number of types of bubbles increasing, however, it will gradually reach to a stable value when the number of types of bubbles is large; 3) the bandwidth of the resonant absorption of acoustic wave is dramatically affected by the distribution function of the percentage of the number of bubbles. The bandwidth of the resonant absorption will become large as the percentage of the number of smaller bubbles increases.
Thermoelectric properties of Ag2S superionic conductor with intrinsically low lattice thermal conductivity
Authors: Wang Tuo , Chen Hong-Yi , Qiu Peng-Fei , Shi Xun , Chen Li-Dong ,   State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China,   Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China,   School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

Recently, Ag2S superionic conductor has attracted great attention due to its metal-like ductility and deformability. In this work, the single phase Ag2S compound is fabricated by the melting-annealing method. The crystal structure, ionic conduction, and electrical and thermal transports in a temperature range of 300－600 K are systematically investigated. The monoclinic-cubic crystal structure transition occurs around 455 K for Ag2S. Significant reduction in the specific heat at constant volume below the Dulong-Petit limit is observed for Ag2S after the monoclinic-cubic phase transition, which is attributed to the liquid-like Ag ions existing inside the sulfur framework. Ag2S shows typical semiconducting-like electrical transport behavior in the whole measured temperature range. Around 455 K, the ionic conductivity, carrier concentration, carrier mobility, electrical conductivity, and Seebeck coefficient each show an abrupt change. The calculated ionic activation based on the ionic conductivity is 0.076 eV for the body centered cubic Ag2S. The calculated band gap based on the electrical conductivity decreases from 1.1 eV for the monoclinic Ag2S to 0.42 eV for the body centered cubic Ag2S. The abrupt increase of electrical conductivity after the monoclinic-cubic phase transition leads to a maximum power factor around 5 μW·cm–1·K–2 at 550 K. In the whole measured temperature range, Ag2S demonstrates an intrinsically low lattice thermal conductivity (below 0.6 W·m–1·K–1). The calculated phonon dispersion indicates that the weak chemical bonding between Ag and S is responsible for the low lattice thermal conductivity observed in the monoclinic Ag2S. Likewise, the presence of liquid-like Ag ions with low ionic activation energy is responsible for the low lattice thermal conductivity for the cubic Ag2S. Finally, the Ag2S shows the maximum thermoelectric figure of merit of 0.55 at 580 K, which is comparable to the thermoelectric figure of merit reported before in most of Ag-based thermoelectric superionic conductors.
Magnetic excitation of ultra-cold atoms trapped in optical lattice
Authors: Zhao Xing-Dong , Zhang Ying-Ying , Liu Wu-Ming ,   College of Physics and Materials Science, Henan Normal University, Xinxiang 453007, China,   Laboratory of Condensed Matter Theory and Materials Computation, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Spinor condensates trapped in optical lattices have become potential candidates for multi-bit quantum computation due to their long coherence and controllability. But first, we need to understand the generation and regulation of spin and magnetism in the system. This paper reviews the origin and manipulation of the magnetism of atomic spin chains in optical lattices. The theoretical study of the whole process is described in this paper, including laser cooling, the spinor Bose-Einstein condensate preparations, the optical lattice, and the atomic spin chain. Then, the generation and manipulation of magnetic excitations are discussed, including the preparation of magnetic solitons. Finally, we discuss how to apply atomic spin chains to quantum simulation. The theoretical study of magnetic excitations in optical lattices will play a guiding role when the optical lattice is used in cold atomic physics, condensed matter physics and quantum information.
Geoacoustic inversion for acoustic parameters of sediment layer with low sound speed
Authors: Li Meng-Zhu , Li Zheng-Lin , Zhou Ji-Xun , Zhang Ren-He ,   State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China,   School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, China,   School of Mechanical Engineering, Georgia Institute of Technology, Atlanta 30332-0405, USA
Published: December 2020

Acoustic inversion of sediment parameters in muddy bottom environment has received much attention in the field of underwater acoustics. In shallow water, when there is a low-speed layer of unconsolidated sediment, such as mud in which the sound speed is lower than that of the sea water, on the top of a high-speed bottom, the transmission losses at different frequencies will increase periodically under the condition of small grazing angles. Based on this phenomenon, an acoustic inversion method of seabed parameters for low speed sediments is proposed. Firstly, the analytical expressions between the frequency interval of the transmission loss (TL) periodical increasing and geoacoustic parameters, including the sound speed and the thickness of sediment layer and the sound speed of seawater near the bottom, are derived under the condition of small grazing angles. Secondly, using the broadband sound propagation signals received under the thermocline in the 2002 summer acoustic experiment conducted in the Yellow Sea, the TL at small grazing angles increases periodically with the frequency, and it is determined that the sediment of this sea area is a low-speed sediment. Then, taking the analytical expression as the constraint condition and combining with Hamilton's empirical formula, the sound speed, density, thickness of sediment layer and the sound speed and density of the seabed are inverted by matched field processing. Finally, the bottom attenuation coefficients at different frequencies are inverted by using the long-range TL, and the linear relationship between the attenuation coefficients and the frequencies is obtained. The equivalence between the two different bottom models is discussed in the end. The inversion results can provide seabed parameters for the study and application of the sound propagation law in shallow water with a low-speed sediment.
Characteristics of AlGaN/GaN high electron mobility transistor temperature sensor
Authors: Liu Xu-Yang , Zhang He-Qiu , Li Bing-Bing , Liu Jun , Xue Dong-Yang , Wang Heng-Shan , Liang Hong-Wei , Xia Xiao-Chuan ,   School of Microelectronics, Dalian University of Technology, DaLian 116024, China
Published: December 2020

Semiconductor temperature sensors have been widely used in medical, industrial, aviation and civil fields due to their advantages such as high sensitivity, small size, low power consumption and strong anti-interference ability. However, most Si-based temperature sensors are not suitable for the application in high-temperature environments. The new AlGaN/GaN heterojunction material not only has a wide band gap, but also has a high two-dimensional electron gas concentration and carrier mobility. Therefore, the device made with it not only has good electrical properties, but also can be applied in ultra-high environments. In this paper, a temperature sensor based on gateless AlGaN/GaN high electron mobility transistor structure was fabricated and its temperature-dependent electrical properties were characterized. The temperature dependence of current-voltage characteristics of the device were tested from 50 to 400 °C. The sensitivity of the device was studied as a function of the channel aspect ratio of the device. The stability of electrical properties was characterized after heating in air and nitrogen at 300—500 °C for 1 hour. The theoretical and experimental results show that as the aspect ratio of the device increases, the sensitivity of the device increases. At a fixed current of 0.01 A, the average sensitivity of the device voltage with temperature changes is 44.5 mV/°C. Meanwhile, the good high temperature retention stability is shown during stability experiments.
Numerical method of electron-positron pairs generation in photon-photon collider
Authors: Li Ang , Yu Jin-Qing , Chen Yu-Qing , Yan Xue-Qing ,   College of Nuclear Science and Technology, Naval University of Engineering, Wuhan 430033, China,   State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, China
Published: December 2020

The creation of positron and electron pairs through photon-photon collision, named Breit-Wheeler process, has been well understood in the theories of quantum electrodynamics for nearly 100 years. The photon-photon collision, which is one of the most basic processes of matter generation in the universe, has not been observed yet. The study on photon-photon collision can promote the development of two-photon physics, quantum electrodynamics theories and high energy physics. To observe photon-photon collision in the laboratory, one needs to collimate a huge number of energetic γ-ray photons into a very small spot. Recently, the development of highly collomated source generated by 10 PW laser makes photon-photon collider much more possible than before. In photon-photon collider, the study of numerical simulation plays a critical role since no experiment has achieved such a process. In this paper, a new numerical method is developed to handle the two-photon Breit-Wheeler process. This method is based on the exact two-photon collision dynamic principle, including energy threshold condition, cross-section condition, Lorentz transformation, etc. In the method, the photons are divided into quantitative photon blocks based on the spatial coordinates. Firstly, one needs to find the collision blocks according to the spatial motion law. Secondly, the ergodic method is used to look up the photons that satisfy the energy threshold condition and the cross-section condition from the blocks. Then, one can calculate the electron yield of the photon collision, and the kinetic parameters of the positrons and electrons. This method rigorously follows the physical principle so it has high precision. On the other hand, this method determines the collision of the block in advance, which can reduce the computational requirement a lot. A series of tests is carried out to confirm the accuracy and feasibility of this numerical method by calculating the collision between mono-energetic photon beams. In the tests, the collision angle is assumed to 180° and 60° separately, the results of pair momentum distribution are discussed. We also simulate the collision of the γ-ray beams generated through the interaction between ultra-intense laser and narrow tube targets. In the simulations, the collision angle is changed from 170° to 30° to see its effect on pair production. It is found that the yield of electron-positron pairs decreases with collision angle increasing, which has also been reported in previous work. Therefore, this numerical method can be efficiently used for modeling photon-photon collider, and provide theoretical reference and suggestion to the future experimental design of γ-ray collision.
Near infrared characteristics of air plasma induced by nanosecond laser
Authors: Wang Xing-Sheng , Ma Yan-Ming , Gao Xun , Lin Jing-Quan ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

The near infrared emission from laser induced air plasma has been investigated in a range of 1100–2400 nm. The infrared spectra of air plasma consist of linear spectral and continuum radiation. Most of the spectral features observed are identified, including atomic lines of O I and N I and molecular bands of N2. The spectra show trace of blackbody background emission and the plasma temperature is estimated from Planck law. We find that the continuum radiation is mainly origins mainly from the blackbody emission of plasma. There is a limitation of plasma temperature estimation by using Boltzmann method. For example, the local thermodynamic equilibrium must be satisfied, and the trend of change in plasma temperature can be estimated within a few microseconds after the laser shot. In this paper, the plasma temperature in 15 μs after laser irradiation is estimated from the Planck law, and the temperature of air plasma is estimated to be about 3900 K, which can compensate for the shortcomings of Boltzmann method. It is found that the neutral atomic spectra of N and O both may contribute to the radiation of the air plasma at 1128 nm. Then we keep the air pressure in the vacuum chamber at 80 kPa, and change the nitrogen and oxygen content in the chamber. The infrared spectrum data show that the oxygen content in the mixed gas only affect the radiation of 1128 nm wavelength. The binary linear regression analysis shows that oxygen contributes much to the radiation of 1128 nm wavelength. This can be explained by the difference in ionization potential between molecule O2 and N2. The infrared radiation intensities of the air plasma at 1128 nm under 20−80 kPa are obtained, and they are compared with the calculated results obtained with the fitting formula. The predicted value is very close to the experimental value and the relative error is negligibly at the pressure of 30−80 kPa. The study of the characteristics of infrared emission from laser induced plasma is of great significance for understanding and using the physical mechanisms of laser-matter interaction.
Raman thermometry based thermal resistance analysis of GaN high electron mobility transistors with copper-based composite flanges
Authors: Liu Kang , Sun Hua-Rui ,   School of Science, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China,   Key Laboratory of Micro-Nano Optoelectronic Information System of Ministry of Industry and Information Technology, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China
Published: December 2020

The electrical performance and the long-term reliability of GaN-based high electron mobility transistors (HEMTs) are greatly affected by the Joule self-heating effect under high power density operation condition. Measurement of the junction temperature and analysis of the thermal resistance of the constituent layers including the packaging material are critically important for thermal design and reliability assessment of GaN-based HEMTs. In this paper, Raman thermometry combined with the finite element thermal simulation is used to compare the junction temperature and the thermal resistance of a GaN HEMT mounted on a novel Cu/graphite composite flange with those of a conventional CuMo flanged device. The results show that the junction temperature of the Cu/graphite flanged device is 15% lower than that of the CuMo flanged device at a power dissipation of 1.43 W/mm, while the overall device thermal resistance is 18.7% lower in the Cu/graphite flanged device. In addition, the temperature distributions of each layer along the cross-plane direction are analyzed for the two devices; the thermal resistance ratio of the Cu/graphite flange is 40% of the overall device thermal resistance, while the CuMo flange account for 53% of the overall thermal resistance of the device. This proves the effectiveness and benefit of using the Cu/graphite composite material package of high thermal conductivity to improve the heat dissipation of GaN HEMTs. By tuning the mass fraction of the graphite, it is possible to further increase the thermal conductivity of the Cu/graphite composite flange and to further reduce the device thermal resistance. It is observed in the Raman thermal measurement that the highest thermal resistance after flanging is the interfacial thermal resistance between the GaN epitaxial layer and the SiC substrate (~50 m2·K/GW). For obtaining the better thermal characteristics of the GaN HEMT, it is crucial to reduce the GaN/SiC interfacial thermal resistance through interface engineering during the epitaxial growth. In the meantime, Raman thermometry combined with the finite element thermal simulation is demonstrated to be an effective method for implementing the thermal characterization of the GaN-based devices and the constituent material layers, and the principle and procedure of the method are described in detail in the paper.
Evolution characteristics and hereditary mechanisms of clusters in rapidly solidified Pd82Si18 alloy
Authors: Gao Ming , Deng Yong-He , Wen Da-Dong , Tian Ze-An , Zhao He-Ping , Peng Ping ,   College of Physics, Mechanical and Electrical Engineering, Jishou University, Jishou 416000, China,   College of Science, Hunan Institute of Engineering, Xiangtan 411104, China,   School of Materials Science and Engineering, Hunan University, Changsha 410083, China
Published: December 2020

Molecular dynamics (MD) simulation and first-principles calculation were used to study the heredity characteristics, evolution trend and structural stability of basic clusters during the rapid solidification of Pd82Si18 alloy. The local atomic structures were characterized by the pair distribution function g(r) and the extended cluster-type index method (CTIM). The MD simulations reveal that the number of bi-cap Archimedes anti-prism (BSAP) clusters with CTIM index (10 2/1441 8/1551) is dominant in the amorphous solids rather than three-cap triangular prism(TTP) with CTIM index (9 3/1441 6/1551), which is identified be the most popular basic units in Pd82Si18 alloys analyzed by Voronoi index Relative to other basic clusters, the Si-centered BSAP possesses much larger fraction in the glassy state of Pd82Si18 alloys. Different from the findings in Cu-Zr alloys, the Si-centered BSAP instead of icosahedra has a larger hereditary fraction than any other Kasper clusters. During the solidification, it was found that most of the other Si-centered basic clusters are transferred into BSAP. Via the DFT calculations, it is observed that the Si-centered basic clusters with higher fraction of heredity and possesses lower binding energy. Among of them, BSAP always keeps lower binding energy than any other Si-centered Kasper clusters during the rapid solidification, resulting in its highest structural stability and the largest heredity fraction.
Optimization of thermal performance of cladding power stripper in fiber laser
Authors: Xia Qing-Gan , Xiao Wen-Bo , Li Jun-Hua , Jin Xin , Ye Guo-Ming , Wu Hua-Ming , Ma Guo-Hong ,   Key Laboratory of Image Processing  &  Pattern Recognition in Jiangxi Province, Nanchang Hangkong University,  Nanchang  330063,  China,   Key Laboratory of Nondestructive Testing(Ministry of Education), Nanchang Hangkong University, Nanchang  330063,  China,   Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang  330063,  China,   College of Mechanical and Electrical Engineering, Nanchang University, Nanchang  330031,  China
Published: December 2020

In the process of eliminating the residual pump light and high-order laser light, the cladding power stripper (CPS) generates abundant heat, which can affect the performance of the fiber laser system due to the photothermal conversion. Hence the efficient dissipation of thermal energy becomes a current research focus. In this paper, the five kinds of existing CPSs are simulated and compared with the results in the literature. It is found that the surface-volume ratio between the heat source and the heat transfer medium can be effectively increased by changing the shape of the polymer filling hole when the CPS is made by the high refractive index polymer method, thus reducing the temperature peak and valley value of the CPS. Besides, the heat distribution uniformity of CPS can be improved by combining the high refractive index polymer method with the acid corrosion method to prepare the two-section fiber cladding structure with uneven thickness. According to the above results, a novel CPS structure is proposed and its thermal effect is studied. The results show that when the cladding light power is 150 W, the temperature peak value of the CPS is 298 K, the temperature valley value is 293 K, and the temperature difference is 5 K. Comparing with the above five CPSs, the peak temperature is reduced by up to 11.3%, and the valley temperature is reduced by up to 8.4%, the temperature difference is reduced by up to 87.5%, which proves that the novel CPS structure can effectively suppress the temperature rising and have excellent heat distribution uniformity.
Full reversal symmetric multiple soliton solutions for integrable systems
Authors: Lou Sen-Yue ,   School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
Published: December 2020

Multiple soliton solutions are fundamental excitations. There are many kinds of equivalent representations for multiple soliton solutions such as the Hirota forms, Wronskian and/or double Wronskian expressions and Phaffian representations. Recently, in the studies of multi-place nonlocal systems, we find that there are a type of novel but equivalent simple and elegant forms to describe multiple soliton solutions for various integrable systems. In this paper, we mainly review novel types of expressions of multiple soliton solutions for some kinds of nonlinear integrable systems. Meanwhile, some completely new expressions for the Sawada-Kortera equations, the asymmetric Nizhnik-Novikov-Veselov system, the modified KdV equation, the sine-Gordon equation, the Ablowitz-Kaup-Newell-Segue system and the completely discrete H1 equation are firstly given in this paper. New expressions usually possess explicit full reversal symmetries including parity, time reversal, soliton initial position reversal and charge conjugate reversal. These kinds of explicitly symmetric forms are very useful and convenient in the studies on the nonlinear physical problems such as the multi-place nonlocal systems and the resonant structures.
Discontinuous finite element solutions for coupled radiation-conduction heat transfer in irregular media
Authors: Wang Cun-Hai , Zheng Shu , Zhang Xin-Xin ,   School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China,   Beijing Key Laboratory of Energy Conservation and Emission Reduction for Metallurgical Industry, Beijing 100083, China,   School of Energy, Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China
Published: December 2020

The discontinuous finite element method (DFEM) is used to investigate the coupled radiation-conduction heat transfer in an irregular medium, and the highly accurate solutions for several typical media are numerically obtained. Comparing with the traditional continuous finite element method, the computational domain in the DFEM application is discretized into unstructured meshes that are assumed to be separated from each other. The shape function construction, field variable approximation, and numerical solutions are obtained for every single element. The continuity of the computational domain is maintained by modeling a numerical flux with the up-winding scheme. Thus the DFEM has the salient feature of geometry flexibility and simultaneously supports locally conservative solutions. The DFEM discretization for the radiative transfer equation and the energy diffusion equation are first presented, and the accuracies of the DFEM for coupled radiation-conduction heat transfer problems are verified. Combined radiation-conduction heat transfer problems in several irregular media are afterward solved, and the highly accurate DFEM solutions are presented.
Characteristics of heat flow as well as process of heat conduction and transport in partitioned thermal convection
Authors: Lin Ze-Peng , XU Sheng-Zhuo , Bao Yun ,   School of Aeronautics and Astronautics, Sun Yat-Sen University, Guangzhou 510275, China
Published: December 2020

How to improve the heat transfer efficiency of the system is always a hot issue in thermal convection research field. It is found that when the partitions are added at equal distances to the classical physical model -- Rayleigh-Bénard convection system and gaps are left between the horizontal plates and partitions, the heat transfer efficiency of the system increases significantly with the number of partitions increasing. The heat transfer efficiency can reach up to 3.1 times that of the non-partition device with the specific geometric parameters. In this paper, the Direct Numerical Simulation (DNS) method is used to simulate the partitioned convection system. The mechanism of the heat transfer enhancement of the system is analyzed by studying the characteristics of the heat flow as well as the heat conduction and transport in the system. After the flow in partitioned convection system is fully developed, the fluid in each channel moves vertically in alternating direction and the upward(downward) channel has a higher(lower) temperature than the average temperature of the cell. Due to the symmetry of the system, only the bottom region of the low temperature channel, the bottom region of the high temperature channel and the gap region connecting these two channels are selected for research. By discussing the lateral and longitudinal transport processes of heat flow in the above three regions, the heat flux in the channels and gap areas of the system are studied by quantitative analysis. The results show that the low-temperature fluid in the channel impacts on the bottom plate and then moves into the gap area; the fluid is continuously heated by the bottom plate and flows out of gap area with high temperature. Finally, the fluid converges in the heat transfer channel and forms a longitudinal jet. The external input heat flux of the area that has only horizontal heat transport is large, accounting for 92% of the total heat flux which is obtained from the bottom plate. The heat flux of gap area accounts for 64% of the total heat flux, but the external input heat flux of the area that has only longitudinal heat transport is smaller. The convection system with different geometric parameters has the effect of enhancing heat transfer efficiency, and enhancement capability of the system is stronger when the height of gaps is smaller. When the number of partitions n = 11 and the height of gap d = 0.01, the value of the global Nu number is largest, Nu = 82, which is more than three times that of the system without partitions.
Interaction between spatiotemporal collinear self-decelerating Airy elegant-Laguerre-Gaussian wave packets in free space
Authors: Zhang Xia-Ping ,   Department of Physics, Nanjing Xiaozhuang University, Nanjing 210017, China
Published: December 2020

Based on the (3+1)-dimensional free-space Schrödinger equation, the analytical solutions to the equation for the propagating properties of two three-dimensional collinear self-decelerating Airy-elegant-Laguerre-Gaussian(AELG) light beams in free space are investigated. The different mode numbers, the mode index for each of the collinear beams, weight factor of combined beam, and initial phase difference will affect the profiles of the wave packets, and thus giving the method to control the spatiotemporal profiles during propagation. The spatiotemporal profiles will rotate if none of the mode parameters are equal to zero, and there are vortices in the center of the phase distribution curve. If the mode parameters are positive numbers, the profiles of the beams will rotate in a helical clockwise direction. Otherwise, if the mode parameters are negative numbers,they will rotate in a helical anticlockwise direction during propagation. The wave packets will also rotate when the relative phase is varied. However, the rotation principles of these two rotation characteristics are completely different. The spatiotemporal hollow self-decelerating AELG wave packets can be attained if the mode numbers of the collinear AiELG wave packets are the same. Multi-ring structure evolves into single-ring structure along radial direction with their propagation distance increasing during propagation, which makes the hollow part expand continuously.
Realizing Talbot effect of circular grating with conformal transformation
Authors: Yang Zhe-Ning , Yue Yang-Yang , Hong Xu-Hao , Zhao Rui-Zhi , Lu Rong-Er , Feng Xia , Xu Ya-Guang , Yuan Xu-Dong , Zhang Chao , Qin Yi-Qiang , Zhu Yong-Yuan ,   College of Engineering and Applied Sciences, Nanjing University, Nanjing 210023, China,   School of Physics, Nanjing University, Nanjing 210023, China
Published: December 2020

The Talbot effect is a near-field diffraction effect that occurs in periodic structures. In a circular periodic structure with a point source as incident light, it has been found that there is no self-imaging effect of the grating at a certain propagation distance. In this paper, we combine the conformal transformation with the Talbot effect and work out a special medium in the physical space, which allows the circular grating to have a Talbot effect within it. The refractive index distribution generated by conformal transformation is calculated and the corresponding self-imaging radius expression is obtained. Lumerical product is used for simulation verification, and the applicable condition of the method is summarized. We separately carry out the simulations of a circular grating with and without the designed medium. Light field distributions in the two simulations differ from each other. The light field in the second situation shares more similarities with the light field of a plane grating than the first simulation. What is more, in the second situation, we can work out a certain Talbot radius, and the light field distribution at the calculated Talbot radius is quite similar to that at the circular grating. But for the first situation, we cannot calculate a certain Talbot radius and can obtain only the radius of the ring with highest self-imaging accuracy by comparing light field at each distance with the grating structure. We find that the small period of the circular grating we used in the second situation makes the light field at Talbot radius furcate. So we carry out a third simulation of a circular grating with a large period compared with the incident wavelength. The self-imaging result matches the grating structure quite well. However, there are some limits in this method. According to the conformal transformation, the refractive index near the center tends to be infinite, so we have to remove the medium near the center. Also, when the radius is big enough, refractive index there can be smaller than 1, so the Talbot effect should happen within this radius. In conclusion, we show that the transformation optics can be introduced into the self-imaging of circular gratings, and thus greatly expanding the range of applications for the Talbot effect.
Dark soliton molecules in nonlinear optics
Authors: Xu Dan-Hong , Lou Sen-Yue ,   School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
Published: December 2020

The study on soliton molecules is one of the important topics in nonlinear science especially in nonlinear optics. The bright soliton molecules have been experimentally observed in optics, however, the dark soliton molecules have not yet been experimentally observed. Theoretically, the soliton molecules have been found for some coupled nonlinear systems. Nevertheless, the soliton molecules have not been obtained for non-coupled single component nonlinear models. In this paper, we first study the exact periodic waves (soliton lattices) and solitary waves for a nonlinear nonintegrable optical model with second and third order dispersions and high order nonlinear effects including self-steeping, Raman scattering and nonlinear dispersion. Two types of dark soliton lattice and three types of soliton lattice are explicitly exhibited for general nonintegrable system. Five types of bright (with and without gray background), dark and gray solitons can be obtained from the limit cases of the modules of the soliton lattices. For an integrable case, using a novel generalized bilinear form of a single component nonlinear system, the multi-soliton solutions are obtained and expressed by a completely new form which are invariant under the full reversal transformations such as the parity, the time reversal, the charge conjugate and the field reversal. To find soliton molecules, a novel mechanism, the velocity resonant, is proposed. Starting from the multi-soliton solutions and using the velocity resonance mechanism, the analytical expression of the dark soliton molecules can be readily obtained. For the model given in this paper, the integrable higher order nonlinear Schrodinger equation, one can proved that the interactions among the dark soliton molecules and the usually solitons are elastic. It is worth pointing out that soliton molecules can also exist in the case of nonintegrable systems.
Corrosion mechanism of T1 phase in Al-Cu-Li alloy: First-principles calculations
Authors: Kong Min , Wu Jing-Jing , Han Tian-Ru , Tang Xin ,   Key Lab of New Processing Technology for Nonferrous Metal & Materials, Ministry of Education, Guilin University of Technology, Guilin 541004, China,   College of Material Science and Engineering, Guilin University of Technology, Guilin 541004, China
Published: December 2020

First principle calculations in the framework of density functional theory are performed to calculate the T1 phase (Al6Cu4Li3), which is the main precipitation in Al-Cu-Li alloy. In this paper, the surface energy values and surface electron work functions of different termination surfaces in T1 phase are calculated. Meanwhile, the effects of stress and common alloying elements on the T1 phase are also discussed. There are 10 different termination surfaces for T1 phase. The surface energy varies between 0.59 and 1.28 J·m–2. It is found that the surface energy is dependent on the atomic configuration of the surface. The relaxation of the surficial atoms leads to low surface energy. For work function, it is controlled by the surficial atomic species. When a surface contains Li atoms, low work function is expected, which can be attributed to the low electronegativity of Li atom. The (010) T1 surface with Li termination has a minimum work function, 3.40 eV. In addition, as is different from pure metal, work function of some T1 surfaces shows unique behavior under stress state. The (010) T1 surface with Al and Cu termination has an increasing work function under the action of tensile strain. In fact, tensile strain induces the first and second surface layer to merge, which can improve the surface electronic density and raise work function. As a result, the corrosion resistance can be enhanced. Finally, the effect of alloying elements on the precipitation of T1 phase is studied. Al(111)/T1(010) interface is built and the substitution energy of Mg, Zn and Ag are calculated. Comparing with Mg and Zn atom, the energy of Ag atom to substitute the interfacial one is low, meaning that Ag can relax the strain in the interface. Ag atom has the closest atomic radius to Al atom, and the same chemical valence as Li atom. Therefore, Ag atom is more likely to promote the precipitation of T1 phase, which is also in agreement with the experimental result.