bluuebunny/crossref_metadata_2025 huggingface dataset:
A scheme for Sagnac effect improvement with squeezed vacuum input and homodyne detection
Authors: Chen Kun  , Chen Shu-Xin  , Wu De-Wei  , Yang Chun-Yan  , Wu Hao  ,   Information and Navigation College, Airforce Engineering University, Xi'an 710077, China
Published: December 2020

There has been much interest in improving gyroscope precision with quantum technology for realizing autonomous navigation. The laser light in coherent state cannot reach higher precision under shot-noise limit (SNL) caused by vacuum zero energy fluctuation, which restricts the further improvement of optical gyroscope precision. Quantum mechanics reckons that one unused port of the beam splitter (BS) is inputted with vacuum, which results in vacuum fluctuation, while another port is inputted with the laser light in optical gyroscope. In order to compress the vacuum fluctuation, we design an experimental scheme, in which squeezed vacuum light is used as another incident light into the unused port of Sagac interferometer in optical gyroscope. We analyze the physical process of this scheme theoretically and develop the quantum balanced homodyne detection technique to retrieve the relative phase information of Sagac interferometer output. There are two most important conditions that we should pay attention to. 1) We should ensure that the phase of local oscillator light arg(α L), the phase of coherent light arg (αc) and the angle of squeezed direction arg(μν) in the squeezed vacuum light satisfy the condition, i.e., arg (α L2)-arg (μν) = πup and arg (α L)-arg (αc) = 0 when we perform quantum balanced homodyne detection technique for the best sensitivity δφ = e-GδφSNL, where G denotes the squeezed degree; 2) only by deriving the fields from one common source can we ensure coherence among the squeezed vacuum, probe and local oscillator. Although the requirements for experimental settings are strict, we can meet the requirement with careful calibration. Numerical analysis shows that this proposed scheme provides much higher precision below SNL: both sensitivity detection limit and dynamic range grow with an exponential rate as the squeezed degree grows. The current technology for squeezed vacuum generation by using two consecutive crystals with the optic axes tilted allows us to reach a value as high as G ≈ 16 of squeezed degree. Only by inputting such squeezed vacuum light into the unused port of BS in the optical gyroscope, can we attain sensitivity detection limit and dynamic range with increment by 108. Our approach is a new scheme for improving optical gyroscope with current available technology.
Analysis of characteristics of combined beam in spectral beam combining system based on multilayer dielectric grating
Authors: Wu Zhen  , Zhong Zhe-Qiang  , Yang Lei  , Zhang Bin  ,   College of Electronics and Information Engineering, Sichuan University, Chengdu 610064, China
Published: December 2020

Aiming at the application of multilayer dielectric gratings (MDGs) in spectral beam combining (SBC) systems, a theoretical model of rectangular MDGs is built up and a beam propagation model of SBC systems based on the rectangular MDGs is further developed. The phase modulation introduced by the rectangular MDG is composed of the optical path difference on the top surface of reliefs and that of the relief structure itself, and is affected by the MDG parameters such as the grating groove depth, the grating duty cycle, the incidence angle of the central beam, etc. By the diffraction integral method and the principle of incoherent superposition, the intensity distribution of the combined beam of the SBC system based on the rectangular MDGs is numerically calculated and analyzed. Additionally, the beam quality of the combined beam is also obtained by the intensity second-order moments method, and the effects of the MDG parameters such as the groove depth, the duty cycle, the incidence angle of the central beam, and the fabrication errors of the MDG on the characteristics of the combined beam of the SBC systems are simulated and discussed in detail. The simulation results show that the beam quality of the combined beam after passing through the SBC systems is significantly better than that of the laser array. Since the quality of the combined beam is almost the same as that of an individual laser beam, for a SBC system without fabrication error, changing the groove depth, the duty cycle of the rectangular MDG or the incidence angle of the central beam does not affect the beam quality while it has obvious influence on the energy of the combined beam. This is mainly because the diffraction efficiency of the rectangular MDG depends on both the parameters of the MDG and the incidence angle of the central beam. However, fabrication error of MDG is unavoidable, and the fabrication error has a significant effect on both the beam quality and the energy of the combined beam. Compared with the effect generated by the groove depth error on beam quality, the influence introduced by the duty cycle error is more obvious. It is worth mentioning that the theoretical model of the SBC system based on the rectangular MDG can be applied to some other high-power laser systems due to its advantages such as low absorption and high damage threshold.
Free sink vortex Ekman suction-extraction evolution mechanism
Authors: Tan Da-Peng  , Yang Tao  , Zhao Jun  , Ji Shi-Ming  ,   Key Laboratory of E&M, Ministry of Education & Zhejiang Province, Zhejiang University of Technology, Hangzhou 310014, China
Published: December 2020

The suction-extraction phenomenon occurs in the formation process of free sink vortex (bathtub vortex), and it is a complex gas-liquid coupling matter. The Ekman layer coupling and its evolution mechanism involved in the above matter possess important scientific value and practical engineering significance. To address the above issue, a modeling and analytical method for the Ekman suction-extraction evolution mechanism of free sink vortex is proposed.#br#Based on the multiphase volume of fluid model and turbulent kinetic energy-dissipation (k-ε) model, a gas-liquid two-phase fluid dynamic model for free sink vortex Ekman suction-extraction is set up. Considering the rotating and shearing characteristics of sink vortex, a two-phase surface is reconstructed by piecewise linear interface construction method. Based on the above models, the internal relations between initial rotation velocity component, drainage capacity and Ekman suction-extraction are investigated, and the corresponding flow field profile regularities are revealed.#br#According to the results of a series of numerical instances, some regularities are obtained as follows. 1) If the initial velocity disturbance is variable, the distances of the suction and extraction holes from the container bottom both keep constant. In the suction stage, the suction hole is located at a fixed position above the container bottom surface, and the extraction hole is in the plane of the bottom surface. 2) If the initial disturbance is enhanced, the rotation velocity of the suction stage increases, and the suction and extraction heights and Ekman layer thickness become larger, while Ekman suction-extraction intensities of suction, extraction and penetration stages turn weaker. 3) If the initial disturbance is invariable, the heights of Ekman suction and extraction remain unchanged, and are independent of drainage capacity. 4) The small-scale vortexes separated from the large-scale ones in the bottom corner of container take on a phenomenon of flow around by a right-angle, which is caused by the viscosity of Ekman boundary layer and the potential flow of the sink hole. 5) Considering the stream line profiles of suction and extraction stages, the dispersion of stream lines keeps constant with the time going by, and the stream lines near the central region of vortex tend to be converged by increasing the gas-liquid coupling.#br#In general, the results can offer useful reference to the research work of free sink vortex formation mechanism, and provide technical supports for vortex suppression control of the areas of metallurgy pouring, chemistry separation and hydraulic drainage. The subsequent researches of the fractal based sink vortex evolution mechanism and lattice Boltzmann based phase surface tracing will be carried out.
Theoretical studies of geometric and electronic structures of X@C20F20 (X=He, Ne, Ar, Kr)
Authors: Cao Qing-Song  , Deng Kai-Ming  ,   Taizhou Institute of Science and Technology, Nanjing University of Science and Technology, Taizhou 225300, China;,   Department of Applied Physics, Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

Several years ago, scientists could already introduced noble gas atoms (He, Ne, Ar, Kr, and Xe) into C60 and higher fullerenes. For the specific cases of He and Ne, the calculations suggested that both atoms are slightly bound inside C60 through simultaneous van der Waals interactions with all 60 carbons. The cavity in dodecahedrane is much smaller than that in C60, but the experimental study found that by bombarding dodecahedrane with fast, neutral helium atoms, He@C20H20 is formed. The structures of C20F20 and C20H20 are similar. Are noble gas atoms also stable in the C20F20? and, are there charges transferring between noble gas atoms and the carbon cage? In this paper, the generalized gradient approximation based on density functional theory is used to analyze the geometric and electronic structures of the endohedral fullerene X@C20F20 (X=He, Ne, Ar, Kr). The geometric optimization shows that the noble gas atoms X are all stable in the center of C20F20 cage. The C-C bond lengths of the X@C20F20 increase with the atomic number X increasing, while the C-F bond length is hardly changed. The inclusion energies of the X@C20F20 (X=He, Ne, Ar, Kr) are 1.359, 3.853, 11.276 and 15.783 eV respectively. These are all positive, which shows that the X@C20F20 have good thermodynamic stabilities, and the thermodynamic stabilities of the X@C20F20 are enhanced with the increase of X atomic number. The energy gaps of the X@C20F20 (X=He, Ne, Ar, Kr) are 5.179, 4.882, 5.874 and 6.205 eV respectively, which are greater than that of C20F20. It indicates that the X@C20F20 have better dynamic stabilities than C20F20. In addition, the vibration frequencies of the X@C20F20 (X=He, Ne, Ar, Kr) are all positive. These indicate that the stability of C20F20 is significantly improved when the X atom is introduced into the cage, and is gradually increasing with the increase of X atomic number. The electronic structures demonstrate that the X atom has no contribution to the occupied molecular orbitals near the Fermi level of X@C20F20, and the contribution of the X atom to the unoccupied molecular orbitals is relatively large. The calculation also shows that the atoms of He and Kr obtain 0.126 and 0.271 electrons from the carbons of the C20F20 cage, while Ar and Ne transfer 0.060 and 0.012 electrons to the carbons of the cage repectively. Thus there are electrons transferring between the X atoms and the carbons of the cage, indicating that the formed C-X bonds of the X@C20F20 are ionic bonds.
First principles study on the H2 diffusion and desorption at the Li-doped MgH2(001) surface
Authors: Zhu Yue  , Li Yong-Cheng  , Wang Fu-He  ,   Department of Physics, Capital Normal University, Beijing 100048, China
Published: December 2020

As one of the most practical solutions to on-board hydrogen storage, MgH2 has attracted a lot of attention, which is mainly due to its high hydrogen capacity (7.7 wt%), high volumetric storage density(55 kg/m3) and low cost. The main obstacles for its large scale applications are the relatively low rates of hydrogen absorption and desorption in the material, which can be traced back to the slow diffusion of hydrogen into the crystal MgH2. In this work, the doping effect of Li on the release of hydrogen at the MgH2(001) surface is studied by the first-principles calculations based on the density functional theory and the climbing nudged elastic band method. Two possible diffusion and desorption paths for H atoms are designed. In path one, the two hydrogen atoms, which bond with the same substituted Mg atom in the first surface layer, climb over the nearest neighbor Mg atom to form a hydrogen molecule. In path two, the two nearest hydrogen atoms, which bond with two different Mg atoms in the first surface layer, combine directly together to form a hydrogen molecule. The calculated results show that the energy barriers for the two paths at the pure MgH2(001) surface are 2.29 and 2.50 eV, respectively. When the center Mg atom is replaced by Li atom, the corresponding energy barriers decrease to 0.31 and 0.22 eV, respectively. Compared with the pure surface, the Li-doped surface has the energy barriers that reduce almost 87% and 91%. It indicates that the formation and release of H2 at MgH2 (001) surface become easier after the surface has been doped with Li atoms. Furthermore, the doping effects are analyzed with the density of states. Compared with the pure surface, the Li-doped surface has a Fermi level that lowers from the band gap to the top of the valance band and the system is changed from insulator into conductor. At the same time, the bonds between Li and hydrogen atoms in the Li-doped system are weaker than those between the substituted Mg and the corresponding hydrogen atoms in the pure system. As a result, the doping of Li atoms makes it easier to form and release H2 at MgH2(001) surface.
Effect of SiO2 on the Stark splitting enlargement of Yb3+ in phosphate glass
Authors: Wang Peng  , Wang Chao  , Hu Li-Li  , Zhang Li-Yan  ,   Research and Development Center of High Power Laser Components, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of sciences, Shanghai 201800, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Up to now, high-energy large-scale Yb3+ laser has still faced to the fact that no proper gain media are available, though researchers made a more than ten year effort for it. Yb: fluorophosphate glass is the only material used in a laser system, reaching an output of more than 10 TW. As is well known, the thermal blocking of Yb3+ laser is a bottleneck in laser operation, which is closely related to the Stark splitting of Yb3+ in a gain medium. Conventional Yb: phosphate glass has the advantages in Yb3+ concentration, lifetime and cross section over silicate glass, however, its small Stark splitting is the main drawback that induces difficulties in realizing laser output at room temperature. Yb: phosphate glass will be a good gain medium for high power Yb3+ laser if the Stark splitting is improved. This study focuses on the enlargement of the Yb3+ Stark splitting in phosphate glass by introducing SiO2, thereby achieving a large Stark splitting property compared with the phosphate glass. The glass 60P2O5-7.5Al2O3-15K2O-17.5BaO-1Yb2O3 is used as the base glass, and the modified glass denoted as PS is obtained by doping a certain amount of SiO2. Such a glass is prepared by the conventional melting-quenching method. Lorentz fitting is performed to the absorption and fluorescence spectra for determining the Stark splitting scheme. Raman spectrum is used for the auxiliary judgment of the attributions of the different spectroscopic bands. Then the results are confirmed by the barycenter law of Yb3+ ion. Investigations show that the addition of SiO2 can enlarge the Stark splitting obviously from the original 670 to 771 cm-1 in PS3. Scalar crystal field parameter N_{J} and asymmetry degree around Yb3+ are also increased due to SiO2 incorporation. Meanwhile, spectroscopic properties of PS series glasses, such as fluorescence effective line width (Δλeff) and fluorescence lifetime (τf), are moderately enhanced. The glass transition temperature is improved greatly, which is very valuable for high power Yb3+ laser. These results suggest that the introduction of a second network former is an effective way to enlarge the Stark splitting of Yb3+ in phosphate glass. Next, our investigation will focus on preparing the high-homogeneity SiO2 modified phosphate glasses and the corresponding laser experiments.
Progress of new carbon material research in perovskite solar cells
Authors: Wang Jun-Xia  , Bi Zhuo-Neng  , Liang Zhu-Rong  , Xu Xue-Qing  ,   Key Laboratory of Renewable Energy and Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China
Published: December 2020

A photoelectric conversion efficiency of 3.8% was achieved based on organic-inorganic hybrid perovskites CH3NH3PbBr3 and CH3NH3PbI3 in 2009, and their efficiencies have leaped to 20.1% in the past five years, which are comparable to Cu(In,Ga) Se2 solar cells. The researchers mainly focused on appropriate materials and device structures, high-quality film depositions, careful interface designs and controllable carrier properties. Even so, it is still a long-term work to develop the low-priced, stable, environmental-friendly and highly-efficient perovskite solar cells, for example, the hole transport material spiro-OMeTAD is complicated and expensive, the electron transport material TiO2 must be processed by high temperature annealing and the Au electrode is extensively used, all of which are not conducible to the commercialized application. On this occasion, new carbon materials, such as graphene oxide, carbon nanotubes, fullerene, graphdiyne, etc. have become another highlight of perovskite solar cells due to their excellent thermal, mechanical, electrical and optical performances. Carbon materials are low-cost and highly available industrial materials, which have been applied to highly efficient counter electrodes for dye-sensitized solar cell and quantum dot-sensitized solar cells. The approximate 5.0 eV work function makes carbon material the ideal counter electrode material for perovskite solar cell. Carbon material is endowed with remarkably high charge mobility and electronic conductivity, which has been identified as one of the strongest materials for electron transport in perovskite solar cell. Similarly, a perovskite solar cell using hole transport materials incorporating carbon material shows an improved power conversion efficiency due to enhanced electrical conductivity and carrier mobility because the low electrical conductivity of hole transport material such as spiro-OMeTAD is considered to be an impediment to further enhancement of the power conversion efficiency and a hole transport material with higher conductivity should reduce the series resistance and increase the fill factor, thereby enhancing the power conversion efficiency of perovskite solar cell. In this paper, the research progress of new carbon materials for counter electrode, electron transport materials, hole transport materials in perovskite solar cells are summarized. The power efficiency of perovskite solar cell is enhanced greatly because of the introduction of new carbon materials, which provides a new idea for the further application of new carbon materials and device design of perovskite solar cells.
Core-periphery structure in heterogeneous adaptive network and its inhibiting effect on epidemic spreading
Authors: Yang Hui  , Tang Ming  , Cai Shi-Min  , Zhou Tao  ,   Web Science Center, University of Electronic Science and Technology of China, Chengdu 611731, China;,   Big Data Research Center, University of Electronic Science and Technology of China, Chengdu 611731, China
Published: December 2020

The study of epidemic spreading in node-property heterogeneous adaptive network shows that node-property heterogeneity can greatly increase the epidemic threshold, and the initial network can adaptively self-organize into a more robust degree heterogeneous network structure. The difference in epidemic spreading between homogeneous and heterogeneous node-property adaptive networks is of great importance for understanding the threshold increasing in the heterogeneous node-property adaptive network. In this paper, we study the transient spreading process in the heterogeneous node-property adaptive network. In order to capture the core-periphery structure in the network, we define two hierarchical structure indicators. When both indicators are of large values in the network, not only is the network of strong core-periphery property, but also less susceptible nodes are more likely to be in the core area of the network. By combining them with various network structure properties, such as the average degree ratio and static threshold of transient network, we analyze the evolution of network structure and show the self-organizing formation process of robust degree heterogeneous structure by numerical simulations. We find that the threshold increase is basically due to the formation of core-periphery structure, where the less susceptible nodes are more likely to be reallocated to the core area of the network by rewiring. In view of this, we propose a new preference rewiring strategy. The results show that the new strategy can increase the epidemic threshold by faciliating the formation of core-periphery structure, which verifies the correctness of the transient network structure analysis. It not only helps to deeply understand the epidemic spreading process in the node-property heterogeneous adaptive network, but also provides new ideas for putting forward the strategy of controlling epidemics.
Parameter identification for fractional-order multi-scroll chaotic systems based on original dual-state transition algorithm
Authors: Wang Cong  , Zhang Hong-Li  ,   Xinjiang University, Department of Electrical Engineering, Urumqi, Xinjiang 830047, China
Published: December 2020

Parameter estimation for fractional-order chaotic systems is a multi-dimensional optimization problem, which is one of the important issues in fractional-order chaotic control and synchronization. With the orthogonal learning strategies and the original dual learning mechanism, the original dual-state transition algorithm is proposed for solving the problem of parameter estimation in fractional-order chaotic systems. The orthogonal learning strategy is presented which can increase the diversity of initial population and improve the convergence ability. And the original dual learning mechanism is presented which can increase the space ability of states, and also can improve the search capability of the algorithm. In the process of identification, we adopt Radau IIA method to solve the fractional-order differential equation. The simulation of the fractional-order multi-scroll chaotic systems with or without noise is conducted and the results demonstrate the e?ectiveness, robustness, and versatility of the proposed algorithm.
High efficiency all-optical diode based on hexagonal lattice photonic crystal waveguide
Authors: Liu Yun-Feng  , Liu Bin  , He Xing-Dao  , Li Shu-Jing  ,   Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Aeronautical University, Nanchang 330063, China
Published: December 2020

A high efficiency all-optical diode based on 2D hexagonal lattice photonic crystal (PC) waveguide is proposed. The structure is asymmetrically coupled by a high Q factor micro-cavity-containing nonlinear Kerr medium and a F-P cavity in PC waveguide. The transmission properties are numerically investigated by finite-difference time-domain (FDTD) method. Because of interference between the two cavities, the structure can achieve the function of forward transmission and backward cut-off under a suitable light intensity. For light incidence close to the direction of micro-cavity, nonlinear Kerr effect of micro-cavity can be excited by a certain light intensity. Then the resonant frequency of Fano cavity will change and forward incidence becomes transmission from reflective state. But for light incidence away from the direction of micro-cavity, the field distribution is asymmetric due to the asymmetric structure, so backward incidence needs stronger incidence light to excite Kerr effect and keeps reflective state. This design of all-optical diode has many advantages, including high maximum transmittance, high transmittance contrast ratio, low power threshold, and ease of integration, and so on.
Numerical simulation on weld line development of injection molding in mold cavity with inserts
Authors: Li Qiang  , Li Wu-Ming  ,   School of Mathematics and Information Science, Henan Polytechnic University, Jiaozuo 454000, China;,   Department of Applied Mathematics, Northwestern Polytechnical University, Xi'an 710129, China
Published: December 2020

A gas-liquid two-phase model for a viscoelastic fluid is proposed and used to simulate and predict the behavior of melt welding in injection molding process, in which the extended pom-pom (XPP) model and cross-WLF viscosity model combined with Tait state equation are used to describe the constitutive relationship and viscosity change of the viscoelastic melt in this paper, respectively. Meanwhile, the coupled level-set and volume-of-fluid (CLSVOF) method is employed to capture the melt front, and the immersed boundary method is applied to the simulation of the polymer melt flows with the aid of a shaped level-set function to describe and treat the irregular mold cavities. A finite volume method on non-staggered grid is used to solve the mass, momentum, and energy conservation equations. Firstly, the benchmark problem of the single shear flow is simulated to verify the validity of the CLSVOF method. Then, the non-isothermal filling process of the viscoelastic fluid based on the XPP model in a mold with square inset is simulated, and the behavior of the weld line devolopment in the filling process is shown and compared with the experimental result. Finally, it is to simulate the evolution processes of the melt front interface and weld line in a mold with the circular notched inset; and the linear stress-optical rule is adopted to calculate the flow-induced birefringence. Numerical results show that the numerical model proposed in this paper can be employed to simulate the non-isothermal filling process in complex mold cavity and to capture the weld line automatically. Because of the complexity of polymer melt flows, the flow-induced stress increases quickly near the weld line region and then decreases gradually until reaching the mold cavity wall. The maximum value of the flow-induced stress appears at some point after the insert. The distributions of physical quantities, such as pressure and temperature in the mold, are given during the mold filling process. Moreover, it is also discussed the influence of melt and mold temperatures on the solidified layer thickness. The higher the melt or mold temperature, the thinner the solidified layer is. Thus, raising the melt or the mold temperature will improve or remove the weld line in melt filling process.
Electronic structure and magnetic properties of MnTe from first-principles calculations
Authors: Wang Bu-Sheng  , Liu Yong  ,   School of Science, Yanshan University, Qinhuangdao 066004, China;,   Metastable Materials Science and Technology State Key Laboratory, Yanshan University, Qinhuangdao 066004, China
Published: December 2020

Based on density functional theory (DFT) together with the projector augmented wave (PAW) method, we systematically investigate the structural, magnetic and electronic properties of the chalcogenide MnTe in six competing structures: rocksalt (RS), cesiun-chloride (CC), zinc-blende (ZB), wurtzite (WZ), iron-silicide (IS) and nickel-arsenide (NA). The ground state of MnTe is completely determined. And the structural parameters, magnetic properties, bulk modulus, phase transition pressure, and the density of states are studied, too. The density of states shows that MnTe in RS, CC and IS structures are antiferromagnetic conductors, and MnTe in WZ, ZB and NA are antiferromagnetic semiconductors. These results provide us the possibility to apply them to the spintronics of antiferromagnetic systems.
A molecular dynamics simulation of thermodynamic properties of 1, 3, 5-triamino-2, 4, 6-trinitrobenzene under high pressure and high temperature
Authors: Fan Hang  , Nie Fu-De  , Long Yao  , Chen Jun  ,   Institute of Chemical Materials, CAEP, Mianyang 621900, China;,   Beijing Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
Published: December 2020

Equation of states and thermodynamic properties of insensitive high explosive 1, 3, 5-triamino-2, 4, 6-trinitrobenzene (TATB) are investigated by using molecular dynamics simulation, where an all-atom force field for TATB developed by Richard H. Gee and isothermal-isobaric molecular dynamics (NPT-MD) methods are used. Results obtained include thermal expansion coefficient, elastic constants, tensile modulus, and debye frequency under high temperature and high pressure. The volume coefficient of thermal expansion for crystalline TATB is calculated in a temperature range of 200 to 500 K and at atmospheric pressure. The result, 35.910-5 K-1, is in general agreements with the experimental results. Results of elastic constants show that the crystalline TATB is an orthotropic material. The calculated elastic constants decrease with increasing temperature in the range from 0 to 450 K, while increase as the pressure increases from 0 to 50 GPa. And the bulk modulus at 300 K is 11.32 GPa, which is in good agreement with the available experimental results. Results obtained above have been compared with available experimental data, and also discussed in relation to the previous calculations. The above results are better than existing ones gained by others. In addition, the elastic anisotropy becomes lower with increasing temperature or pressure. As the temperature goes up to 400 K, the lattice becomes unstable. The sound speed and Debye frequency are calculated by using the data of elastic constants at different pressures. This provides a theoretical basis to calculate the anisotropic thermal conductivity for crystalline TATB.
Exploring new opening-up membrane vesicles of two holes by using the relaxation method
Authors: Kong Xiang-Bo  , Zhang Shao-Guang  ,   College of Physics and Information Technology, Shaan'xi Normal University, Xi'an 710119, China
Published: December 2020

Due to the discovery and study of opening-up lipid vesicles, the theoretical analysis and numerical calculation have aroused increasing interests of researchers. In the previous study, Suezaki and Umeda gave the opening-up vesicles near the spherical vesicles, such as the dish and cup shapes with one hole, and the tube and funnel shapes with two holes. These shapes are found at relatively low values of reduced, relaxed area difference a0. However, what are the stable shapes for high values of a0 is not known. Kang et al. found solutions of opening up dumbbell shapes with one hole. Whether or not there exist dumbbell shapes with two holes, and the phase transformation behavior between them remains unknown. The purpose of this paper is to explore a new kind of two-hole dumbbell shaped lipid vesicles and phase transformations between this kind of vesicle and previously found vesicles. Based on the area-difference-elasticity model, this paper tries to explore new solutions of the Euler-Lagrange equations of the opening-up membrane vesicles which meet the boundary conditions by using the relaxation method. A new branch of solution of dumbbell shapes with two holes is found. The phase transformations of closed dumbbell shapes and opening-up dumbbell shapes with one hole and two holes are studied in detail. To explore whether these shapes could be found in experiments, the energy of the cup, tube, and funnel shaped vesicles are also compared with the opening-up dumbbell shapes. It is found that at high values of a0, all the cup, tube, and funnel shapes will transform into closed spherical vesicles. So the energy of new opening-up dumbbell vesicles can be compared to that of closed spherical vesicles and closed dumbbell vesicles. It is found that the dumbbell shapes with one hole and two holes all have stable regions, implying that it is possible for these open dumbbells to be observed. Since the distance in the functional space is too far between the open dumbbell shapes and spherical vesicles, experimental test is needed to verify whether the dumbbell shapes with two holes will evolve continuously to the closed dumbbell shapes or to the closed spherical vesicles. It has been noticed that for relatively small values of a0, two holes vesicles may exhibit symmetrical tube shapes and asymmetric funnel shapes between which the phase transformation is continuous, because the funnel solutions bifurcate from the tube solutions. In order to check whether there exist asymmetric opening-up dumbbell shapes with two holes and the similar bifurcation behavior, a thorough search is made in the parameter space. So far no asymmetric dumbbell shape with two holes is found.
Optical design of nanowire array on silicon thin film solar cell
Authors: Geng Chao  , Zheng Yi  , Zhang Yong-Zhe  , Yan Hui  ,   College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China;,   Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

Light trapping has been considered as an important strategy to increase the conversion efficiency of silicon thin film solar cell. It shows that photonic crystal with feature size comparable to the wavelength, for example, the silicon nanowire array has a great potential to exceed the conventional Yablonovitch 4n2 limit. Silicon nanowire array has been designed and constructed on silicon thin film solar cell due to its excellent optical properties. Generally, silicon nanowire array is used as the antireflection coating, axial or radial p-n junction of solar cell. Different applications of the silicon nanowire arrays need different optical properties. Theoretical investigations show that the optical property is strongly dependent on the structural parameters. In this work, several structural parameters including period (P), diameter (D), height (H), and filling ratio (FR) are optimized when silicon nanowire array plays different roles. Here, by using the finite difference time domain (FDTD) method, we focus on the relations between the structural parameters and the optical properties including reflection and absorption from 300 to 1100 nm. In the FDTD simulation model, the substrate material is crystal silicon film, and the silicon nanowire array is on the surface of the substrate. In this calculation, the top and the bottom of the unit cell are air with perfectly matched layers, and with periodic boundary conditions at the side walls. When the silicon nanowire array is used as the antireflection coating, the silicon nanowire array shows a lowest reflection (7.9%) with H=1.5 m, P=300 nm, and FR=0.282. When silicon nanowire array acts as axial p-n junction solar cell (the p-n junction is formed by substrate and nanowire array), the absorption efficiency reaches a maximum value of 22.3% with H=1.5 m, P=500 nm, and FR=0.55. When the silicon nanowire array acts as the radial p-n junction solar cell, the absorption efficiency could obtain a maximum value of 32.4% with H=6 m, P=300 nm, FR=0.349. In addition, the optical properties of silicon nanowire array with random diameter and position are also analyzed here. The absorption efficiency of optimized random silicon nanowire array reaches 27.8% compared with a value of 19.9% from ordered silicon nanowire array. All of these results presented here can provide a theoretical support for the silicon thin film solar cell to increase the efficiency in the future application.
Reflection phase characteristics and their applications based on one-dimensional coupled-cavity photonic crystals with gradually changed thickness ofsurface layer
Authors: Qi Zhi-Ming  , Liang Wen-Yao  ,   The Open University of Guangdong and Guangdong Polytechnic Institute, Guangzhou 510091, China;,   School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510640, China
Published: December 2020

In this paper, we first improve the traditional transfer matrix method to adapt to one-dimensional photonic crystal consisting of arbitrary materials, and then use it to study the reflection phase characteristics of two kinds of photonic crystals, i.e., a simple periodic photonic crystal structure and a coupled-cavity asymmetric photonic crystal with gradually changed thickness of surface layer. For both of the structures, the reflectivity within photonic band gap is above 98% and hardly affected by the thickness of the surface layer. However, their reflection phases exhibit distinctly different properties. For the simple photonic crystal structure, the reflection phases of both TE and TM polarizations are sensitively dependent on the thickness of surface layer, but their phase difference is almost the same as the thickness of surface layer varies, which cannot change the polarization of reflected light. While for the coupled-cavity asymmetric photonic crystal structure, studies show that the degenerate defect modes within photonic band gap will split as the thickness of the surface layer varies. Moreover, around the splitting defect modes the reflection phases of both TE and TM polarizations, as well as their phase difference, are sensitively dependent on the thickness of surface layer, resulting in sensitive polarization change of reflected light. The physical reason is attributed to the dramatic phase change caused by the splitting of degenerate defect modes. The above reflection phase characteristics of coupled-cavity asymmetric photonic crystals have potential in lowering or even eliminating the coherence of lasers in some special application cases. As an example, we design a one-dimensional photonic crystal structure with two-dimensional periodic varying thickness of surface layer. After an oblique incident narrowband laser beam is reflected from this structure and then focused by a lens, various polarized light beams (including linear polarized light beams along different directions, left-hand (or right-hand) circular (or elliptical) polarized light beams) will exist simultaneously, whose superposition will produce optical field with random phase and polarizations in the focal region. These results can effectively reduce the coherence of lasers, which holds promise in many fields such as laser nuclear fusion.
Experimental investigation of open sea atmospheric optical turbulence
Authors: Wang Qian  , Mei Hai-Ping  , Li Yu-Jian  , Shao Shi-Yong  , Li Xue-Bin  , Rao Rui-Zhong  ,   Key Laboratory of Atmospheric Composition and Optical Radiation, Center for Atmospheric Optics, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China;,   Graduate University of Chinese Academy of Sciences, Beijing 100049, China;,   China Satellite Maritime Tracking and Control Department, Jiangyin 214431, China
Published: December 2020

In this article, a high-quality fiber optical turbulence sensing array is arranged on the ocean-going instrumentation ship-Yuan Wang for 37 day continuous measurement. It is the first time that the spatial multipoint simultaneous measurement of maritime atmospheric optical turbulence has been realized. According to the measurement, the essential characteristics and quantitative data of the atmospheric optical turbulence on the open sea are obtained. Then the Greenwood spatial correlation function model is used for evaluating the outer scale of optical turbulence by a nonlinear fitting algorithm. Finally, the optical turbulence spectrum is divided into two sections, and the power spectrum scaling exponent is given by a section algorithm. Results show that the intensity of maritime atmospheric optical turbulence is a little smaller than that in the near ground layer and has no obvious diurnal variation characteristic. The value of outer scale is small and in a range of 0.2-0.3 m. It is easily found that the probability that the turbulence spectrum scaling exponent conforms to -5/3 is about 25% near the surface of open sea, which is smaller than that in the near ground layer.
Triangle wave pulsating flow effect on thrombus simulated by the lattice Boltmann method
Authors: Jiang Yan-Hua  , Chen Jia-Min  , Shi Juan  , Zhou Jin-Yang  , Li Hua-Bing  ,   School of Material Science and Engineering, Guilin University of Electronic Technology, Guilin 541004, China;,   School of Information and Communication Engineering, Guilin University of Electronic Technology, Guilin 541004, China
Published: December 2020

As one of the major causes of cardiovascular diseases, the formation mechanism and the external factors of blood embolism are always the concerned problems of medical field, biological and physical field. Owing to thrombotic formation and structure being complicated, the difficulty in curing thrombosis greatly increases. Pulsation flows have a positive effect on dredging blood embolism. Owing to the blood viscosity and the inertia of red blood cells, waveform, amplitude and frequency of pulsating flow will influence the effect of dredging blood embolism. The research in this paper is mainly based on the lattice Boltzmann method. In conical pipe with embolism, in order to explore the influences of triangle wave pulsating flow waveform, the effects of differential pressure and frequency on vascular thrombus are studied by calculating the effect of dredging blood embolism. Calculation shows that the effect of dredging blood embolism is not obvious under the condition of low frequency and low differential pressure. On the contrary, the effect is good under the condition of high frequency. Appropriately increasing the differential pressure can also improve the frequency of the triangular wave of the bolt.
Shock X-ray emission image measurement in Z-pinch dynamic hohlraum
Authors: Meng Shi-Jian  , Huang Zhan-Chang  , Ning Jia-Min  , Hu Qing-Yuan  , Ye Fan  , Qin Yi  , Xu Ze-Ping  , Xu Rong-Kun  ,   Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Owing to high efficiency for delivering thermal radiation from Z-pinch plasma to an inertial fusion capsule, Z-pinch dynamic hohlraum (ZPDH) is a promising indirect-drive inertial confinement fusion (ICF) approach. ZPDH is created by accelerating an annular tungsten Z-pinch plasma radially inward to an internal low density convertor. The collision launches a radiating shock traveling inward. Radiations emitted from the shock, after being trapped and thermalized by the optically thick tungsten plasma, drive the internal fusion capsule to implode. In our previous experiments, shock propagating process has never been imaged or even never been formed, due to low drive current (about 1.3 MA). In this paper, the ZPDH has a load of single tungsten wire array embedded in a cylindrical 16 mg/cm3 C15H20O6 foam, and the tungsten wire array is explored using JuLong-1 facility (also named PTS facility) driven by current with a peak value of 7-8 MA and rising time of 60-70 ns (from 10% to 90%). Several results are presented for improving the understanding of the physics of the shock propagating and hohlraum forming. For the high optical depth in tungsten plasmas around the foam, radially directly diagnosing hohlraum radiation distribution along axis is impossible. The most convenient way to diagnose the radiation symmetry and the shock evolution is to take the end-on X-ray images. The time-resolved X-ray images of annular radiating shock evolution, which are performed with a 10-frame time-gated X-ray pinhole camera located at 0 with respect to the Z-pinch axis, are obtained for the first time in China. By analyzing the radial X-ray emission power waveform and intensity distribution of end-on radiation image, the process of wire array plasma impacting on the foam convertor and properties of dynamic hohlraum radiation are discussed. The shock emission structures are found to be circular, similar to the results predicted theoretically. The shock velocity which seems to be constant in the whole process of inward propagating is linearly fitted to be (14.21.7) cm/s. The annular width of shock emission is 0.8-0.9 mm, which is inferred from the full width at half maximum of radial lineout of end-on X-ray image at time t=-11.9 ns and the blurring effect of shock velocity. The radiation symmetry is assessed by statistic property of mean intensity of 36 sectors of end-on X-ray image evenly divided by 10. The standard deviation of azimuthal shock emission intensity is 10% while that of hohlraum region prior to shock impact is 4.2%. The azimuthal symmetry improvement from shock emission to hohlraum radiation is a piece of exciting news for ZPDH driven ICF.
First-principles study of the electronic properties and magnetism of LaMnO3/SrTiO3 heterointerface with the different component thickness ratios
Authors: Yan Song-Ling  , Tang Li-Ming  , Zhao Yu-Qing  ,   School of Physics and Microelectronics Science, Hunan University, Changsha 410082, China
Published: December 2020

Using first-principles calculations based on density functional theory and projector augmented wave method, we investigate the thickness ratio dependences of the ionic relaxation, electronic structure, and magnetism of (LaMnO3)n/(SrTiO3)m heterostructure. Polar and nonpolar oxide interfaces have become a hot point of research in condensed matter physics; in this system, polar discontinuity at the interface may cause charge transfer to occur at interfaces between Mott and band insulating perovskites. Here, we consider two types of interfaces, namely n-type (LaO)+/(TiO2)0 and p-type (MnO2)-/(SrO)0 interfaces. The results show that the different thickness ratios and interface-types lead to different degrees of ionic relaxation, inducing charges of different concentrations to transfer. The distortions of the oxygen octahedra are found to vary distinctly with the component thickness ratio (n:m), which is consistent with recent experimental results. Furthermore, both n and m are found to strongly affect the charge transfer. When the thickness of LaMnO3 reaches a thickness of critical layers of 6 unit cells, the Mn-eg electrons are transferred to the Ti-dxy orbitals of SrTiO3, which is caused by the interface polar discontinuity. Two-dimensional electron gas with high mobility is formed in an n-type (LaMnO3)n/(SrTiO3)2 interface region. Meanwhile, spin polarization of interface-layer Ti atoms becomes more obvious, which induces Ti magnetic moment to be close to 0.05B. We find that Mn magnetic moment of 3.9B is a larger value at the n-type interface than at the p-type interface. The above studied heterostructure favours ferromagnetic spin ordering rather than the A-type antiferromagnetic spin ordering of bulk LaMnO3. Whether n-type or p-type (LaMnO3)2/(SrTiO3)8 interfaces consist of ultrathin LaMnO3 layer and thicker SrTiO3 layer, there is no structure distortion at the side of SrTiO3 basically, which is in agreement with experimental results. Stronger interface-layer polar distortions for p-type interface prevent the electron transfer from occurring, and spin polarization of Ti cannot occur either. In addition, it is found that the two types of interfaces possess 2 eV potential difference by comparing the average electrostatic potential, thus charge transfer is more difficult to occur in the p-type interface than in the n-type interface.