bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-induced damage growth of fused silica at 351 nm on a large-aperture high-power laser facility
Authors: Han Wei  , Feng Bin  , Zheng Kui-Xing  , Zhu Qi-Hua  , Zheng Wan-Guo  , Gong Ma-Li  ,   Department of Precision Instruments and Mechanology, Tsinghua University, Beijing 100084, China;,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Laser-induced damage of fused silica optics at 351 nm is a key factor limiting the output energy of high-power laser facility, especially the damage growth process. A comprehensive understanding of its damage growth behavior is of critical importance for high-power laser facility. Thus we study the laser-induced damage growth on the exit surface of fused silica under the subsequent illumination of 5 ns square pulses at 351 nm on a large-aperture high-power laser facility. Experiment is conducted with a 36 cm thick UV grade fused silica focus lens in clean atmosphere and at room temperature. 56 laser shots of 3 fluence in a range from 0.1 J/cm2 to 8.1 J/cm2 are fired during the experiment. And the damage initiation process and growth process are monitored and recorded with an online optics damage inspection instrument which has an optical resolution of about 50 m.
Experimental results demonstrate that the sizes of exit-surface damage sites exponentially or linearly grow with laser shots and the damage growth rate increases with laser fluence. However, it is found that even under the same laser conditions the damage grow rate is not a fixed value, which means that besides the laser fluence other parameters also influence the damage grow process. In order to highlight some tendencies, we consider the single-shot damage growth rate and calculate the average of inside fluence bins. Statistical analysis shows that smaller sites tend to grow with larger growth rates than larger sites under the irradiation of the same laser fluence. This result indicates that damage growth rate is influenced by both laser fluence and damage site size. It suggests that the damage growth rule needs to be incorporated into a size-dependent growth effect.
The result that higher growth rates are obtained for small damage sites may be related to the damage growth mechanism of fused silica. Damage crater of fused silica consists of a central core and numerous surrounding cracks. The defects in the central core absorb laser energy and yield plasma, then the plasma pressure will open the cracks on the periphery of the crater and lead to lateral and axial expansion of cracks which can be identified as damage growth. The fact that smaller sites grow faster than larger sites implies that smaller sites more efficiently couple laser energy into fracture energy. Our results have important implications for both the prediction of fused silica optics lifetime and the fundamental understanding of laser damage mechanism.
Nonlinear Faraday rotation in electromagnetically induced transparency medium of semiconductor three quantum dots
Authors: Chen Qiu-Cheng  ,   Department of Physics and Electronic Information Science, Hengyang Normal University, Hengyang 421008, China
Published: December 2020

In the past few years, many interesting optical phenomena, such as electromagnetically induced transparency, coherent optical control of a biexciton, slow light and optical solitons, have been investigated in single quantum dot (QD). However, in an actual semiconductor device there exist many quantum dots (QDs). Recently, QD molecule, which is comprised of double semiconductor QDs coupled by tunneling coupling, has been proposed. In this new semiconductor structure, many complex but interesting phenomena have been discovered. In fact, three QD molecules may also be composed of three QDs, which can be coupled by interdot tunneling coupling. For the three semiconductor QDs molecules, the influence of the interdot tunneling coupling strength must be considered. So, in this paper, with considering that a weak, -linear-polarized probe field can form left- and right-polarized components under the control of the parallel magnetic field, and when they are combined with the tunneling coupling among the QDs, an electromagnetically induced transparency medium of a five-level M configuration semiconductor three QDs is proposed. Subsequently, the nonlinear Faraday rotation in the semiconductor three QDs is analytically studied.
For the linear case, the linear dispersion relation is driven by a method of multiple scales. Then, by studying the linear optical properties, it is found that the system exhibits a single tunneling induced transparency window due to the quantum destructive interference effect driven by the interdot tunneling coupling under appropriate conditions, and the width of the tunneling induced transparency window can be effectively controlled by the strength of the interdot tunneling coupling. Meanwhile, the switch regulatory effect, which changes from the anomalous dispersion regime to the normal dispersion regime, is likely to be achieved by changing the strength of the interdot tunneling coupling.
For the nonlinear case, two coupled nonlinear Schrdinger equations, which govern the evolutions of left- and right-polarized components of the weak, -linear-polarized probe field under the applied longitudinal magnetic field, are derived. By studying the nonlinear properties, it is shown that a large nonlinear Faraday rotation angle can be obtained due to the quantum interference effect which is induced by the interdot tunneling coupling with a very low absorption of the weak, -linear-polarized probe field. In addition, it is also found that the nonlinear Faraday rotation direction is opposite to line Faraday rotation for the same magnetic field. What is more, the nonlinear Faraday rotation angle grows bigger than the linear Faraday rotation. These results mean that the Faraday rotation of the three semiconductor QDs with the electromagnetically induced transparency can be more effectively controlled by the nonlinear effect.
Theoretical and numerical investigations of the novel relativistic magnetron using all-cavity output and semi-transparent cathode
Authors: Yang Wen-Yuan  , Dong Ye  , Dong Zhi-Wei  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

Relativistic magnetron is a kind of compact cross-field high power microwave source. It has the virtues of wide frequency tunability and ability to operate with relative lower external magnetic field. To improve the compactness and reduce the size and weight of the relativistic magnetron further, a novel relativistic magnetron using all-cavity output and semi-transparent cathode is investigated theoretically and numerically. By using the all-cavity output structure, the radial dimension is reduced markedly (from 10.5 cm to 6.6 cm) and the axial dimension is also shortened considerably (from larger than 40 cm to less than 30 cm). Since the radiation fields in the interaction cavity are coupled through the coupling hole to the output fan waveguide, the cutoff frequencies of the fundamental mode and three higher order modes in the fan waveguide with different outer radii are calculated. The calculation results show that the mode separation is wide enough for the single mode operation on the fundamental mode. And by using the semi-transparent cathode, the high output efficiency can be obtained and the output characteristics are insensitive to the depth and width of each cathode slot. To verify the characteristic of the proposed magnetron, numerical simulations are carried out by using the three-dimensional particle-in-cell code. After careful optimization, simulations show that with a beam voltage of 395 kV and beam current of 5.6 kA, 1.15 GW output microwave with an efficiency of about 50% can be obtained at S-band with purer mode. The corresponding applied magnetic field is 4.75 kGs (1 Gs=1-4 T). In a relatively large range, both radiation power and the optimal magnetic field increase with the beam voltage. But the output efficiency keeps almost unchanged.
The effects of the depth, width and length of the coupling hole, width of the fan waveguide and the distance from the beginning position of the fan waveguide to the coupling hole center Lsc on the output characteristics are also analyzed. Simulation results show that when the dimension of the coupling hole is small, the output power is low. But there is no mode competition and the device works on the up mode. With the increase of the coupling hole, the output power increases accordingly. When the coupling hole is large enough, the mode competition between the up mode and /3 mode becomes so serious that the mode cannot win any more. At the same time, the output power decreases markedly. There also exist optimal values of both the fan width and the beginning position of the fan waveguide (Lsc) for maximal output power.
Ground state properties and spectral properties of borospherene B40 under different external electric fields
Authors: Li Shi-Xiong  , Zhang Zheng-Ping  , Long Zheng-Wen  , Qin Shui-Jie  ,   College of Big Data and Information Engineering, Guizhou University, Guiyang 550025, China;,   School of Physics and Electronic Science, Guizhou Education University, Guiyang 550018, China;,   College of Physics, Guizhou University, Guiyang 550025, China;,   Key Laboratory of Photoelectron Technology and Application, Guizhou University, Guiyang 550025, China
Published: December 2020

The recent discovery of borospherene B40 marks the onset of a new class of all-boron fullerenes. External electric field can influence the structure and property of molecule. It is necessary to understand the electrostatic field effect in the borospherene B40. In this work, density functional theory method at the PBE0 level with the 6-31G* basis set is used to investigate the ground state structures, mulliken atomic charges, the highest occupied molecular orbital (HOMO) energy levels, the lowest unoccupied molecular orbital (LUMO) energy levels, energy gaps, electric dipole moments, infrared spectra and Raman spectra of borospherene B40 under the external electric field within the range of values F=0-0.06 a.u.. The electronic spectra (the first 18 excited states contain excited energies, excited wavelengths and oscillator strengths) of borospherene B40 are calculated by the time-dependent density functional theory method (TD-PBE0) with the 6-31G* basis set under the same external electric field. The results show that borospherene B40 can be elongated in the direction of electric field and B40 molecule is polarized under the external electric field. Meanwhile, the addition of external electric field results in lower symmetry (C2v), however, electronic state of borospherene B40 is not changed under the external electric field. Moreover, the calculated results show that the electric dipole moment is proved to be increasing with the increase of the external field intensity, but the total energy and energy gap are proved to decrease with the increase of external field intensity. The addition of external electric field can modify the infrared and Raman spectra, such as the shift of vibrational frequency and the strengthening of infrared and Raman peaks. Furthermore, the calculated results indicate that the external electric field has a significant effect on the electronic spectrum of borospherene B40. The increase of the electric field intensity can lead to the redshift of electronic spectrum. With the change of the electric field intensity, the strongest excited state (with the biggest oscillator strength) can become very weak (with the small oscillator strength) or optically inactive (with the oscillator strength of zero). Meanwhile, the weak excited state can become the strongest excited state by the external field. The ground state properties and spectral properties of borospherene B40 can be modified by the external electric field. Our findings can provide theoretical guidance for the application of borospherene B40 in the future.
Measurement of audio signal by using low-frequency squeezed light
Authors: Yan Zi-Hua  , Sun Heng-Xin  , Cai Chun-Xiao  , Ma Long  , Liu Kui  , Gao Jiang-Rui  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Collaborative Innovation Center of Extreme Optics, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Measurement of audio signal plays a significant role in many applications, such as gravitational wave detection, bio-particle imaging and magnetometer. In this paper, low-frequency squeezed light is generated by a non-degenerate optical parametric amplifier. In order to avoid the effect of injected light on low-frequency squeezing, an auxiliary laser is used to lock the length of non-degenerate optical parametric amplifier and a method of locking quantum noise is employed to lock the phase between the local light and the squeezed light. By isolating the vibration noises at low-frequency and reducing back action of parasitic interference, the squeezing of (7.1±0.1) dB takes place at 19 kHz. Then the squeezed light is injected into the Mach-Zehnder interferometer to measure an audio signal which drives a piezoelectric transducer to generate a small phase variation between two arms of Mach-Zehnder interferometer. According to the low-frequency squeezing, we realize experimentally the measurement of phase signal at audio frequency which exceeds the shot-noise limit of (3.0±0.4) dB. The experiment provides technical supports for the generation of low-frequency squeezed light and the measurement of audio signal. Furthermore it can be extended to other quantum measurements, such as high-precision magnetometer and measurement of small-displacement.
Particle simulation study on anisotropic pressure of electrons in laser-produced plasma interaction
Authors: Wang Cheng-Zhen  , Dong Quan-Li  , Liu Ping  , Wu Yi-Ying  , Sheng Zheng-Ming  , Zhang Jie  ,   School of Physics and Optoelectronic Engineerings, Ludong University, Yantai 264000, China;,   Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China;,   IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

Direct-drive inertial confinement fusion (ICF) requires a symmetric compression of the fuel target to achieve physical conditions for the ignition. The fast ignition scheme reduces the symmetry requirements for the target compression and the necessary driving energy, but symmetrically compressed target will certainly help improve the efficiency of the nuclear fuel burning. In this paper, with the particle-in-cell (PIC) simulation method, characteristics of the anisotropic pressure tensor of hot electrons are reported for the ultra intense laser pulse interaction with over dense plasmas, which mimics the scenario of the last stage when hot electrons are utilized to ignite the compressed fuel core in the ICF fast ignition scheme. A large number of hot electrons can stimulate pressure oscillations in the high density plasma. As the component parallel to the electron velocity dominates the pressure tensor, the electron density distribution perturbation propagates rapidly in this direction. In order to keep those hot electrons in the high density fuel plasma core for a period long enough for them to deposit energy and momentum, a magnetic field perpendicular to the electron velocity is used. The PIC simulation results indicate that the hot electrons can be trapped by the magnetic field, and the components of the anisotropic pressure tensor related to the parallel direction are significantly affected, thereby producing a high peak near the incidence surface. Since it is a relatively long process for the energy transfer from electrons to fuel ions and the nuclear interaction to be completed, the fluid effects take their roles in the fuel target evolution. The anisotropic electron pressure will deteriorate the fuel core symmetry, reduce the density, and achieve a lower efficiency of nuclear fuel burning and a lower gain of nuclear reaction than expected. The effects of the hot electron anisotropic pressure tensor in the fast ignition scheme should be considered as a factor in experiments where the nuclear reaction gain is measured to be much lower than the theoretical prediction.
Simulation of forming process of Z-pinch dynamic hohlraum based on the program MULTI2D-Z
Authors: Chen Zhong-Wang  , Ning Cheng  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
Published: December 2020

The radiation hydrodynamics code MULTI-2D, which was developed by Ramis et al. in 2009 (2009 Comput. Phys. Commun. 180 977) and adopted the single temperature fluid and unstructured lagrangian mesh, is modified into a radiation magnetohydrodynamics code MULTI2D-Z by adding the program module of evolution equation of magnetic field, and self-consistently considering the Lorentz force in the module of motion equation and the Ohmic heating in the module of energy equation. The newly developed module for magnetic field was validated to be reliable. The module is used to study the magnetic field diffusion process, and it is found that the diffusion is weakened due to the increasing of plasma temperature and density and the fluid convection, in which there is minus grads of velocity in radial direction. The new code MULTI2D-Z is used to simulate the formation process of dynamic hohlraum driven by tungsten wire-array Z-pinch at an 8 MA current level. The obtained results are that X-ray power and energy are, respectively, ～30 TW and ～300 kJ, radiation temperature in foam is ～120 eV, and the implosion trajectory of wire-array is also obtained. The calculated results reveal that the magnetic field is mainly distributed in the outside of tungsten plasma during the hohlraum formation. The foam expands due to the radiation heating from the shock wave created by the collision between wire-array plasma and the foam. The thermal radiation wave, which is characterized by radiation temperature, spreads towards the central axis faster than the plasma temperature. When the thermal radiation wave spreads to the central axis, the radiation temperature becomes comparatively uniform in space, and is almost equal to the plasma temperature except at the place of the shock wave. These results help the people to better understand the magnetic field diffusion and convection in Z-pinch, as well as the formation mechanism of dynamic hohlraum driven by wire-array Z-pinch. It is also indicated that the newly developed code MULTI2D-Z can be considered as a new tool for simulating Z-pinch and its applications, such as inertial confinement fusion and magnetically accelerated flyer plates.
Information leakage problem in quantum secure direct communication protocol based on the mixture of Bell state particles and single photons
Authors: Liu Zhi-Hao  , Chen Han-Wu  ,   School of Computer Science and Engineering, Southeast University, Nanjing 211189, China;,   Key Laboratory of Computer Network and Information Integration(Southeast University), Ministry of Education, Nanjing 211189, China;,   Centre for Quantum Software and Information, Faculty of Engineering and Information Technology, University of Technology Sydney, NSW 2007, Australia
Published: December 2020

Recently, a quantum secure direct communication (QSDC) protocol based on the mixture of Bell state particles and single photons[Acta Phys. Sin. 65 230301(2016)] was put forward. In this QSDC protocol, the single photons and the Bell states were both used as information carriers. To be specific, each Bell state as well as single photon was encoded by three bits of classical information. After the sender told the receiver how to measure the particles, the receiver could read out the secret message sent by the sender. Speciously, the information transmission efficiency of this protocol was high. Unfortunately, there exists the information leakage problem in this protocol. When the sender announces that the receiver uses the Z-basis to measure a single photon, everyone knows that the sent secret message is 000 or 001, that is, the first two bits are leaked out; when the sender announces that the receiver uses the X-basis to measure a single photon, everyone knows that the sent secret message is 010 or 011, that is, the first two bits are leaked out too; when the sender announces that the receiver uses the Bell-basis to measure a pair of particles from a Bell state, everyone knows that the sent secret message is 100, 101, 110 or 111, that is, the first bit is leaked out. In a word, two of the three bits of classical information encoded in a single photon, and one of the three bits of classical information encoded in a Bell state are leaked out. Therefore, this scheme is not secure. On the basis of keeping the original idea and changing the contents of the protocol as less as possible, we put forward an improved message encoding rule to solve the information leakage problem, that is, the single photon is only encoded by one bit of classical information, and the Bell state is only encoded by two bits of classical information. In fact, this makes the information capacity of the improved protocol achieves the Helovo bound. So it has high coding capacity. We hope researchers pay more attention to the information leakage problem in quantum secure communication protocols, and thus design truly secure ones.
Rapid solidification mechanism and magnetic properties of Ni-Fe-Ti alloy prepared in drop tube
Authors: Zhu Hai-Zhe  , Ruan Ying  , Gu Qian-Qian  , Yan Na  , Dai Fu-Ping  ,   Department of Applied Physics, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Ni-Fe-Ti ternary alloys, as a type of structural and magnetic material, have received more attention in the industrial fields in recent decades. For the purpose of providing necessary experimental data and theoretical basis for industrial appliance of these alloys, the researches of rapid solidification mechanism and relevant application performances of Ni45Fe40Ti15 ternary alloy are carried out in this paper. Rapid solidification of undercooled Ni45Fe40Ti15 ternary alloy is realized in a 3 m drop tube under the condition of containerless and microgravity state. In an experiment, the sample with a mass of 2 g is placed in a φ16 mm×150 mm quartz tube with a 0.3-mm-diameter nozzle at its bottom. The quartz tube is then installed in the induction coil on the top of the drop tube. The tube body is evacuated to a pressure of 2×10-5 Pa and backfilled with the mixture gas of Ar and He gases to about 1×105 Pa. After that the sample is melted by induction heating and superheated to about 200 K above its liquidus temperature. Under such a condition, the melt is ejected through the nozzle by a flow of Ar gas and dispersed into fine liquid droplets. These liquid droplets solidify rapidly during free fall, and the droplets with the diameters ranging from 160 to 1050 μm are achieved. As droplet diameter decreases, both cooling rate and undercooling of the alloy droplet increase exponentially, i.e., from 1.10×103 to 3.87×104 K·-1 and from 42 to 210 K (0.14TL) respectively. The microstructure consists of γ -(Fe, Ni) solid solution and interdendritic Fe2Ti intermetallic compound. As undercooling increases, the coarse γ -(Fe, Ni) dendrites become refined, the secondary dendrite arm spacing linearly decreases. Compared with the result in the glass fluxing experiment, the dendrites are much refined by drop tube processing due to the higher cooling rate obtained. The amounts of solute Ni and Ti content in the γ -(Fe, Ni) phase enlarge evidently with the increase of undercooling, suggesting the occurrence of solute trapping. The magnetic properties of thealloy droplets sre also analyzed. When droplet diameter decreases from 1100 to 300 μm, the saturation magnetization increases from 22.47 to 41.82 Am2·kg-1, the coercive force decreases from 3.33 to 0.80 KAm-1, and the squareness ratio decreases approximately by four times. This indicates that the soft magnetic properties of the alloy are improved remarkably by drop tube processing. Furthermore, the mechanism for substantial effect of undercooling on magnetic parameter such as coercive force needs to be further investigated.
Brief retrospect of super-resolution optical microscopy techniques
Authors: Hu Rui-Xuan  , Pan Bing-Yang  , Yang Yu-Long  , Zhang Wei-Hua  ,   Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, China
Published: December 2020

In the last few decades, nanoscience and nanotechnology have been growing with breath taking speed, and how to break through the diffraction limit and tame the light on a nanoscale have become the major challenges in optics. In this field, several super-resolution optical nanoscopy techniques have been developed, leading to a series of breakthroughs in physics, chemistry, and life sciences. In the work, we give a retrospect of the newly developed techniques in diffraction theory of linear optical systems, including the solid immersion lens, structured light illumination microscopy, scanning near-field optical microscopy, metamaterial-based wide field near-field imaging technique and super-oscillatory lens. Brief discussion on their principles, advantages and applications is also provided.
Progress of point-wise scanning superresolution methods
Authors: Zhao Guang-Yuan  , Zheng Cheng  , Fang Yue  , Kuang Cui-Fang  , Liu Xu  ,   State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Optical microscope has been giving impetus to the development of modern technology. As the advancement of these techniques, high resolution microscopy becomes crucial in biological and material researches. However, the diffraction limit restricts the resolution of conventional microscopy. In 1968, confocal microscopy, the first pointwise scanning superresolution method, appeared. It improves the imaging resolution, enhances the contrast, and thus breaks through the diffraction limit. Since then many superresolution methods have come into being, among which the pointwise scanning superresolution method earns reputation for its high imaging resolution and contrast. The stimulated emission depletion microscopy becomes the most prominent method with an achievable resolution of about 2.4 nm and then widely used. Besides, the newly developed fluorescence emission difference microscopy (FED) and the saturated absorption competition microscopy (SAC) have their advantages of non-constraint on fluorescent dyes, low saturated beam power, simplified optical setups, while they achieve a resolution of lower than /6. Further explorations of FED will be keen on vivo biological observations by using it, while that of SAC can concentrate on enhancing the resolution on a nanoscale and reducing the signal-to-noise ratio. In addition, the Airyscan technique in which a detector array is used for image acquisition, can serve as a complementary tool to further enhance the imaging quality of pointwise scanning superresolution method. The detector-array enables both the narrowed size of pinhole and the increasing of the acquired signal intensity by 1.84 folds. The other methods, e.g. superoscillation lens and high-index resolution enhancement by scattering, have the potentialities to obtain superresolved image in material science or deep tissues. After being developed in the past three decades, the superresolution methods now encounter a new bottleneck. Further improvement of the current methods is aimed at imaging depth, and being used more practically and diversely. In this review, we detailedly describe the above pointwise scanning superresolution methods, and explain their principles and techniques. In addition, the deficiencies and potentialities of these methods are presented in this review. Finally, we compare the existing methods and envision the next generation of the pointwise scanning superresolution methods.
Ultrastable glasses
Authors: Yu Hai-Bin  , Yang Qun  ,   Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

Glasses are solid materials that are far from their thermodynamic equilibrium states and their stabilities play a role in many applications as well the theoretical understanding of the natures of glass systems. Recently, ultrastable glasses (SGs) have been developed. The SGs have the stabilities that ordinary glasses can obtain only after being annealed for thousands to millions of years, thereby providing a great opportunity for studying the stabilities of glasses. In this paper we present a brief review about the properties of SGs and their formation mechanisms and novel insights into the glassy physics.
Thermoplastic forming of bulk metallic glasses
Authors: Ma Jiang  , Yang Can  , Gong Feng  , Wu Xiao-Yu  , Liang Xiong  ,   Guangdong Provincial Key Laboratory of Micro/Nano Optomechatronics Engineering, College of Mechatronics and Control Engineering, Shenzhen University, Shenzhen 518060, China
Published: December 2020

The viscosities of metallic glasses gradually drop with temperature rising in their supercooled liquid region (SLR) which enables them to be thermoplastically formed and totally overturns the processing method of traditional metallic materials: their forming can be realized under temperature and stress far below those of traditional metallic materials. Based on this property, metallic glasses are considered as the ideal miniature fabrication materials due to their unique amorphous structures and no crystalline defects such as dislocation and grain boundary.The thermoplastic micro forming of metallic glasses in their SLR is studied in the present paper. A universal equation which describes the filling kinetics of viscous metallic glasses in the non-circular channel is proposed with the help of fluidic mechanics, and the results may be theoretically useful for the micro application of metallic glasses.In addition, some applications in the micro thermoplastic forming of metallic glasses are introduced. A metallic glass mold insert for hot embossing of polymers is fabricated by the micro thermoplastic forming of metallic glass, and it is found to have many advantages in mechanical property, fabrication efficiency, surface quality, etc. compared with the traditional material and method. A similar approach is used to fabricate gratings, which may provide a new material and technology to produce gratings. The superhydrophobic metallic glass surface with excellent abrasion and corrosion resistance is also fabricated by constructing micro-nano hierarchical structures on metallic glass surface. The bulk metallic glass micro fuel cell is also finished and found to have good performance.
Influence of single axis strain on site occupation and diffusion of hydrogen atom in α-Fe
Authors: Li Shou-Ying  , Wang Yong  , Zhao Wei-Min  ,   College of Mechanical and Electrical Engineering, China University of Petroleum(East China), Qingdao 266580, China;,   Qingdao Binhai College, Qingdao 266555, China
Published: December 2020

As is well known, hydrogen plays an important role in degrading mechanical properties of steel due to hydrogen embrittlement behavior. Thus, much attention should be paid to the interaction between hydrogen atom and Fe matrix especially in theoretical calculation and mechanism study. In this paper, the site occupations of hydrogen atom under different single axis strains in interstitial of α-Fe atoms are studied by the first principles calculation based on the spin-polarized density functional theory. The Kohn-Sham equations are solved under periodic boundary conditions, by using revised Perdew-Burke-Ernzerhof version of the generalized gradient approximation to account for the electron exchange and correlation. The total energy of the steady state crystal, binding energy, solution energy, density of states, charge density difference and charge population are calculated. The analyses of solution energy and density of states indicate that the hydrogen atom preferentially occupies the tetrahedral interstitial of α-Fe atoms under different single axis strains. With increasing tensile strain or reducing compressive strain, hydrogen atom prefers to occupy the site of tetrahedral interstitial. The analyses of charge population and charge density difference reveal that the hydrogen atom collects charges from Fe atoms, leading to electron density redistribution. The tensile strain reduces the charge transfer slightly while the compressive stress promotes the transfer process. The LST/QST (linear synchronous transit/quadratic synchronous transit) transition state search method is used to investigate the diffusion of hydrogen atom between two tetrahedral interstitials along the direction perpendicular to strain. Diffusion of hydrogen atom goes through transition state where the hydrogen atom is coordinated at octahedral interstitial. The minimum energy pathway for hydrogen diffusion under strainless state indicates the diffusion activation energy with a value of 0.58 eV. It is noticeable that the diffusion activation energy and the strain conforms to linear relation and are consistent with the fitting formula, Q=0.508+2.6ε. The diffusion activation energy increases with reducing compressive strain or increasing tensile strain. According to the calculation process and analysis results, we introduce the interaction between hydrogen atom and α-Fe at a level of electronic structure systematically and figure out the diffusion of hydrogen influenced by different states of stress.
Investigation and quantitative analysis on the acoustic energy tobogganing in the upslope waveguide of continental slope area
Authors: Xie Lei  , Sun Chao  , Liu Xiong-Hou  , Jiang Guang-Yu  , Kong De-Zhi  ,   Key Laboratory of Ocean Acoustics and Sensing (Northwestern Polytechnical University, Ministry of Industry and Information Technology, Xi'an 710072, China;,   School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China}
Published: December 2020

The toboggan in acoustic energy will appear at the top of the slope when the sound wave radiated by a shallow water source propagates in an upslope waveguide of the continental slope area. The grazing angles of the sound rays reflected by the ocean bottom will increase in the upslope waveguide, which leads to the acoustic energy tobogganing in the shallow water at the top of the slope. In this paper, the range of acoustic energy tobogganing (RAET) at a specified depth is defined to study this phenomenon. The transmission loss (TL) is calculated by the parabolic-equation acoustic model that ie applied to the range-dependent waveguide. The RAET is defined by an average transmission loss in the abyssal water and in the shallow water corresponding to the depth. The acoustic energy toboggan is explained using the ray-based model, and the effects of source location change on it are demonstrated, including the source depth and the range away from the bottom of the slope. The sound rays from a shallow water source which transmit in the upslope waveguide can be divided into two types:one is incident to the interface vertically and will return to the water along the original path; the other is that the rays will transmit towards the sound source (the deep sea direction). However, all of them will no longer spread forward after they have transmitted to a certain distance, leading to the acoustic energy tobogganing in shallow water. The analysis results show that the RAET becomes larger with source depth increasing, and the energy toboggan phenomenon will disappear when the source is deep enough. However, the range of source away from the slope bottom has less effect on RAET. Numerical simulations are conducted in a continental upslope environment by the RAM program based on the split-step Pad algorithm for the parabolic equation. The simulation results show as follows. 1) The TL will increase rapidly after the waves have transmitted to a certain range away from the bottom of the slope when the source depth is 110 m, and the TLs is 140-160 dB propagating to the shallow water at the top of the slope. 2) The RAET will enlarge orderly when the source depths are 110 m, 550 m and 800 m respectively, and the energy toboggan phenomenon will disappear when the source depth is more than 800 m. 3) Fix the source depth at 110 m and move it along the deep sea, then the RAET will greatly varies when the distance between the source and the slope bottom changes ina range of 1-15 km. However, the RAET remain almost constant at 69.8 km when the distance between the source and the slope bottom changes in a range of 16-50 km.
Design and application of high polarized purity metasurface lens
Authors: Gao Xiang-Jun  , Zhu Li  , Guo Wen-Long  ,   Air and Missile Defense College, Air Force Engineering University, Xi'an 710051, China
Published: December 2020

Dealing with potential applications of metasurface in lens technologies, we propose a focusing metasurface with high polarized purity based on anisotropic elements, and then put it into application of high gain antenna with high polarized purity. Firstly, we design a metasurface cell with the polarization filtering characteristic, which is capable of transmitting the x-polarized waves efficiently while reflecting the y-polarized waves completely. By changing the metallic patch size, we can modulate the phase shift for the x-polarized transmitting waves. Then by imposing a hyperboloidal phase profile onto the surface, we design a metasurface lens with 105 mm105 mm in size, 2121 in cell number, and 30 mm in focal length. According to the principle of reversibility of light path, the spherical waves emitted from the patch antenna can be converted into plane waves by the focusing metasurface lens, which is used to improve the antenna gain. As for the experiment, we tend to obtain the metasurface lens impinged by differently polarized waves in order to study the lens response to differently polarized waves. The results show that the metasurface acts as a lens when impinged by the x-polarized waves but serves as a reflector when illuminated by the y-polarized waves. That is to say, the y-polarized waves are mostly filtered out while the x-polarized waves are efficiently transmitted and focused, which is in good accordance with the designed principle. Assuming that a patch antenna emits the x/y-polarized waves at the focal point, we obtain not only the antenna gain improved remarkably but also polarized isolation above 25 dB in the operating bandwidth of the designed metasurface. The results of the antenna application give a further proof of the designed lens which eventually contributes to the high gain and high polarized purity of the lens antenna.
Comparative studies on constructal optimizations of discrete heat generation components based on entransy dissipation minimization and maximum temperature minimization
Authors: Wang Gang  , Xie Zhi-Hui  , Fan Xu-Dong  , Chen Lin-Gen  , Sun Feng-Rui  ,   Institute of Thermal Science and Power Engineering, Naval University of Engineering, Wuhan 430033, China;,   Military Key Laboratory for Naval Ship Power Engineering, Naval University of Engineering, Wuhan 430033, China;,   College of Power Engineering, Naval University of Engineering, Wuhan 430033, China
Published: December 2020

A three-dimensional (3D) turbulent heat dissipation model of cylindrical discrete heat generation components is established on a conductive basis. The whole solid section is set in a square channel with adiabatic walls, and the components, cooled by clean air flowing through the channel, are arranged in a line with equal spacings. The influences of the heat conductivities of the components, intensities of heat sources and velocity of fluid flow on the maximum temperature (MT) of components, the equivalent thermal resistance (ETR) based on entransy dissipation of the heat dissipation system, and the averaged Nu number are investigated with the constructal theory considering variable properties, compressibility and viscous dissipation of air. The total heat generation rate and the total heat conductivity of heat sources are fixed as the constraint conditions. The circumstances in which heat generation rates and heat conductivities of heat sources are unequal are considered. The results show that for the fixed total heat generation rate of heat sources, despite MT or ETR that is taken as the performance index for thermal design, there exists an optimal intensity distribution of heat sources for the best thermal performance of the system. In fact, for different objectives, the optimal intensity distributions of heat sources are corresponding to the best match between the distributions of heat sources and the distributions of temperature gradient. There are different optimal distributions for different velocities of the fluid flow and different optimization objectives. Besides, the averaged Nu number increases with the increase of intensity difference in heat sources, which means that the convective heat transfer is enhanced, but this phenomenon is relatively weak when the velocity of fluid flow is low. For the fixed total heat generation rate of heat sources, when the intensities of heat sources are equal and the thermal conductivities of heat sources are lower than that of the conductive basis, increasing heat conductivities of the heat sources can evidently improve thermal performance of the system; the MT can be lowest when the conductivities of heat sources increase along the fluid flow; and the ETR is lowest when the conductivities of heat sources are equal. Both the MT and the ETR decrease with the increasing velocity of fluid flow. The results can provide some theoretical guidelines for the practical thermal design of the electronic components with different materials and different heat generation rates.
Lattice model for pressure problems in two-dimensional granular columns
Authors: Zhang Xing-Gang  , Dai Dan  ,   College of Physics, Guizhou University, Guiyang 550025, China;,   College of Computer Science and Technology, Guizhou University, Guiyang 550025, China
Published: December 2020

In order to make it easier to investigate some problems such as the mechanism of Janssen effect and the stress distribution in granular medium, we simplify a granular column into a lattice system, in which a lattice point represents a small lump of granular medium and only neighbor interactions are considered. To study the disordered granular columns, a force propagation lattice model determined by the absorption coefficient p and the lateral transfer coefficient q is proposed, and this model is analyzed from the theoretical view. Firstly, the equation of force propagation in the matrix form is given, and this equation is determined by a tridiagonal matrix A(p,q) that is called transfer coefficient matrix. Based on the force transfer equation, the bottom force distribution varying with the top force distribution and the layer of lattice system is deduced, and its analytical solution refers to the similarity diagonalization of matrix A(p, q). Then, a method based on the second order difference equations is proposed to obtain the eigenvalues and eigenvectors of the transfer coefficient matrix. The eigenvalues and eigenvectors of A(p, q) can be rigorously deduced for a typical case, and with these results the pressure distribution relationship between the top and the bottom of the container is given. Based on these theoretical expressions, the relationship between the effective mass and the total mass of granular medium is deduced, and it means that the force propagation model and the Janssen model can lead to similar results. Moreover, the bottom stress distribution is calculated without the top load. Calculations show that the stress distribution reaches a maximum at the center bottom and drops down to either side. Finally, numerical calculations are performed to investigate the effects of parameters p and q on the relation between bottom pressure and packing height. Numerical results show that the saturated value of pressure decreases while parameter p or q increases.
Monte Carlo simulation of time-dependent dielectric breakdown of oxide caused by migration of oxygen vacancies
Authors: Li Ping  , Xu Yu-Tang  ,   Mechanical and Electrical College, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

In this article, the Monte Carlo method is used to study the formation and migration of oxygen vacancies in metal oxide dielectric. The time-dependent breakdown of the dielectric is simulated. In the direction of the electric field across the metal oxide, the migration barrier and migration work function of oxygen vacancies are found to be reduced by the applied electric field. This finding provides a good foundation for further studying the breakdown mechanism and evaluating the reliability of high gate dielectric. The Monte Carlo process is described as follows. Firstly, a three-dimensional metal oxide dielectric layer is built with two-dimensional symmetrical grid, where the thickness of the oxide layer is set to be 9 lattice points and the oxygen vacancies can migrate to the adjacent 8 arbitrary lattice positions in this simulation. Secondly, the possibilities of formation and migration of oxygen vacancies are calculated according to the distribution of oxygen vacancies. Finally, the Monte Carlo method is used to simulate the new distribution of oxygen vacancies. Therefore, we simulate the breakdown process of the metal oxide dielectric layer with different oxygen vacancy migration functions (Ea=1.15, 1.35 eV) at the interface. And we obtain the results as follows. 1) When the migration function is small, many oxygen vacancies accumulate largely at the forming interface. And the vacancies would migrate from the interface to the dielectric, forming a conductive channel. The breakdown time is determined by the migration barrier of oxygen vacancies in the dielectric. 2) When the migration function of the oxygen vacancies at the interface becomes larger, the formed oxygen vacancies will rapidly migrate to the other interface, and the reverse propagation of the conductive channel causes the dielectric breakdown. Therefore, larger migration function of the oxygen vacancies at the interface can effectively improve its reliability. 3) The original defects within the dielectric will seriously influence the migration of oxygen vacancies, and the breakdown is easier to occur with more primary defects. 4) The simulation shows that the oxygen vacancy migration function can be improved by optimizing the interface formation process. And the breakdown time could also be prolonged. Therefore, this simulation tool can be applied to the research of metal-oxide-semiconductor transistor gate dielectric breakdown and the assessment of its reliability accurately.