bluuebunny/crossref_metadata_2025 huggingface dataset:
Transformation thermotics: thermal metamaterials and their applications
Authors: Shen Xiang-Ying  , Huang Ji-Ping  ,   Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China
Published: December 2020

Heat transportation is one of the most ubiquitous phenomenon in the mother nature. Manipulating heat flow at will is of tremendous value in industry, civil life and even military. It would be a common sense that in different materials thermal properties are different. According to this knowledge people may design thermal materials to control heat conduction. One of the most common and successful example is blanket, which has been invented for thousands of years to keep us warm in cold days and keep icecream cool in summer. However, those great inventions are not powerful enough to manipulate heat flow at will. So there are still a lot of demands for designing the so-called metamaterials which have special properties that should not exist in nature.
In 2006, Leonhardt and Pendry's research group (Pendry, Schurig and Smith) independently proposed a type of optical metamaterial which is also called invisible cloak. This device is well known for bending light around an object to make it invisible. Such a significant progress soon enlightened a lot of scientists in different aspects since it offers a powerful approach to design metamaterials. The principle of invisible cloak, which is concluded as transformation optics has been applied to light waves, acoustic, seismic, elastic waves, hydrodynamics and even matter waves as they all satisfy with wave equation.
Although the conduction equation which governs the process of heat conduction is totally different from wave equation, from 2008 to 2012, Fan's group and Guenneau's group established the theoretical system of transformation thermotics. Since then, many thermal metamaterials with novel thermal properties have been figured out. Therefore, a boom in transformation thermotics and thermal metamaterials has begun.
In this article, we will introduce some most recent achievements in this field, including novel thermal devices, simplified experimental method, macro thermal diode based on temperature dependent transformation thermotics, and the important role that soft matters play in the experimental confirmations of thermal metamaterials.
These works pave the developments in transformation mapping theory and can surely inspire more designs of thermal metamaterials. What is more, some approaches proposed in this article provide more flexibility in controlling heat flow, and it may also be useful in other fields that are sensitive to temperature gradient, such as the Seebeck effect and many other domains where transformation theory is valid.
Soft matters from nano-atoms to giant molecules
Authors: Zhang Wen-Bin  , Chen Er-Qiang  , Wang Jing  , Zhang Wei  , Wang Lin-Ge  , Cheng Stephen Z. D.  ,   Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Center for Soft Matter Science and Engineering, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China;,   South China Advanced Institute of Soft Matter Science and Technology, South China University of Science and Technology, Guangzhou 510640, China;,   College of Polymer Science and Polymer Engineering, University of Akron, Akron Ohio 44325-3909, USA
Published: December 2020

In this brief review, we look back on the conception of nano-atoms and their gradual evolutions into a new class of giant molecules in the context of soft matter science. The structural features and the characteristics about giant molecular self-assembly are summarized. It is found that these giant molecules with high conformational rigidities and precisely-defined shapes and symmetries can exhibit unusual phase structures and phase transition behaviors which are not commonly observed in conventional polymers. Their self-assembly is robust due to collective and cooperative interactions among nano-atoms, forming hierarchical structures that are sensitive to their primary structures. This modular feature is reminiscent to the domain concept in protein science. It is thus proposed that nano-atoms can serve as unique elements for macromolecular science.
Research progress of field-inducedd soft smart materials
Authors: Wu Jin-Bo  , Wen Wei-Jia  ,   Materials Genome Institute, Shanghai University, Shanghai 200444, China;,   Department of Physics, the Hong Kong University of Science and Technology, Hong Kong, China
Published: December 2020

The field-induced soft smart material is a kind of soft matter whose macroscopic properties (mechanical, or optical) can be significantly and actively controlled and manipulated by external field such as magnetic field, electric field, temperature or light. In this paper, we briefly review the research and application progress of the filed-induced soft smart materials in recent years and discuss the development problems and trend in this research area. In particular, we focus on three typical field-induced soft materials of smart materials: magnetorheological fluid, electrorheological fluid, and temperature and light sensitive polymer gel.
Recent advances of theoretical researches in morphologies of lipid vesicles
Authors: Yang Pan  , Tu Zhan-Chun  ,   Department of Physics, Beijing Normal University, Beijing 100875, China
Published: December 2020

Lipid membrane is a continuous barrier between cell and organelle, providing relatively separate room for the vital biological reaction to take place and guarantee substance, energy and information exchange between cells and organelles. Helfrich proposed a spontaneous curvature model to describe the free energy of lipid bilayer. This article reviews the equations describing the equilibrium morphologies of closed lipid membranes and lipid membranes with free edge based on the spontaneous model, and some analytic solutions are provided as well. The practicality of proving linking condition for splitting vesicle is also discussed.
Memristor-based Lorenz hyper-chaotic system and its circuit implementation
Authors: Ruan Jing-Ya  , Sun Ke-Hui  , Mou Jun  ,   School of Physics and Electronics, Central South University, Changsha 410083, China
Published: December 2020

To study the application of memristor in chaotic system, we employ the smooth continuous nonlinear flux-controlled memristor model and feedback control technique to design a hyperchaotic system based on the simplified Lorenz system. By using memristor as a positive feedback of the simplified Lorenz system, the dimensionless mathematical model is derived. The differences between the memristor-based chaotic system and ordinary chaotic system are then further studied. Firstly, the stable equilibrium and unstable equilibrium point sets of the system are analyzed theoretically, and it is found that the system has infinite equilibrium points including stable and unstable equilibrium points. The stable and unstable ranges of the system with different parameters are also determined. Theoretical analysis shows that the system has the same symmetry as the simplified Lorenz system. Thus the system has rich dynamical behaviors, such as limit cycle, chaotic attractor, and hyper-chaotic attractor. Secondly, by the methods of bifurcation diagram, Lyapunov exponent spectrum, Poincar section, and Spectral Entropy algorithm, the dynamical behaviors of the system are analyzed in detail. By calculating the Lyapunov exponent spectrum, the dynamical behaviors are studied and they change with system parameters and the initial conditions of memristor respectively. The maximum positive Lyapunov exponent of the memristor-based Lorenz hyperchaotic system is higher than that of the simplified Lorenz system, which indicates the memristor-based Lorenz hyperchaotic system is more complex. Further, we find all the complex dynamical behaviors to be coexisting with the infinite equilibrium sets, which is quite different from those of many ordinary hyper-chaotic systems. Meanwhile, we observe the attractors coexisting and state transition phenomenon in this system, caused by changing the initial conditions of the memristor. State transition phenomenon is then further studied by means of phase portraits and spectral entropy algorithm for the first time. Finally, by using operational amplifiers, diodes and other discrete components, we design an equivalent circuit of the smooth continuous nonlinear flux-controlled memristor model, and the equivalent circuit is used to design and realize the analog electronic circuit of the memristor-based Lorenz hyper-chaotic system. By using an analog oscilloscope, the phase portraits of hyper-chaotic attractor are observed clearly. The state transition phenomenon can also be seen using the oscilloscope. It is found that the circuit experimental results are in agreement with those of the theoretical analysis and numerical simulation. It verifies that the system is physically realizable, and lays a strong foundation for its applications in engineering. Next, we will try to investigate the chaotic secure communication based on this hyper-chaotic system.
Adaptive optimal measurement for the squeezed vacuum and coherent state
Authors: Chen Kun  , Chen Shu-Xin  , Wu De-Wei  , Yang Chun-Yan  , Wang Xi  , Li Xiang  , Wu Hao  , Liu Zhuo-Wei  ,   Information and Navigation College, Airforce Engineering University, Xi'an 710077, China
Published: December 2020

The output phase of the Sagnac interferometer has been measured with quantum balanced homodyne technique when coherent light and squeezed vacuum light are fed into the Sagnac interferometer simultaneously [Chen Kun et al., Acta Phys. Sin. 65 054203(2016)]. Nevertheless, there exist two deficiencies: 1) the phase sensitivity is related to the phase itself; 2) there are strict requirements for the phases of local oscillator light, coherent light and squeezed vacuum light. For overcoming these deficiencies, an adaptive optimal measurement scheme is suggested for the phase estimation. Firstly, we calculate that the quantum Fisher information (QFI) of the squeezed vacuum and coherent state is sinh2r+||2e2r by treating them as a quantum pure state, for they satisfy a condition of the quantum pure state, namely ()=()2. The QFI is related to quantum Cramer-Rao lower bound which can be used to evaluate the performance of the estimator. Secondly, we make an analysis of positive operator-valued measure (POVM) and design a set of the optimal measurement operators for reaching the quantum Cramer-Rao lower bound, whereas the optimal measurement operators depend on the true value of the phase which is what we want to estimate. In order to solve the problem and estimate the parameter effectively, an adaptive method is suggested. We set an initial value of the phase parameter to obtain a set of measurement operators which are not optimal at the first step. And then the initial measurement operators are used for POVM and to obtain a conditional probability function, from which we can obtain a new value of the phase with maximum likelihood estimator. Therefore, the measurement operators and conditional probability function will be updated with the new value. As the measurement operators and conditional probability function are updated step by step, we can estimate the value adaptively. In fact, the results of the maximum likelihood estimator will converge at the true value of the phase parameter gradually, which is then proved with the theoretical analysis. All in all, an adaptive measurement method of estimating the phase parameter of the squeezed vacuum and coherent state in Sagnac interferometer is suggested, and is proved theoretically to be that the scheme will converge at the true value of the phase with a probability of 1 and can reach the quantum Cramer-Rao lower bound.
Numerical study of leading-edge receptivity on the infinite-thin flat-plat boundary layer
Authors: Lu Chang-Gen  , Shen Lu-Yu  ,   School of marine science, Nanjing University of Information Science and Technology, Nanjing 210044, China
Published: December 2020

The laminar-turbulent transition has always been one of the most concerned and significant research topics. Receptivity is the first stage of the laminar-turbulent transition process in the boundary layer, and also plays a key role in the laminar-turbulent transition. However, previous studies for leading-edge receptivity mostly focused on the external sound disturbances, while it is seldom to see the relevant research on the leading-edge receptivity to free-stream turbulence in the boundary layer which is universal in the free stream. In view of this, direct numerical simulation is utilized in this paper to study the leading-edge receptivity to free-stream turbulence exciting the Tollmien-Schlichting (T-S) wave in the boundary layer. The high-order high-resolution compact finite difference schemes based on non-uniform meshes and fast Fourier transform are used in spatial discretization, and the fourth order modified Runge-Kutta scheme is used in temporal discretization to solve Navier-Stokes equations for direct numerical simulation. Perturbation waves with short wavelengths, whose wavelengths are approximately one-third of the disturbance wavelengths of free-stream turbulence, are excited in the boundary layer under the free-stream turbulence; and our numerical results show that the dispersion relations, growth rates and neutral stability curve of the group of the excited perturbation waves with different frequencies are in line with the solutions obtained from the linear stability theory. These obtained numerical results confirm that the group of the excited perturbation waves with different frequencies are a group of T-S waves with different frequencies and the interaction between leading-edge of flat plate and free-stream turbulence to excite unstable waves in the boundary layer is one of the receptivity mechanisms. Furthermore, it is found that the amplitudes of the excited T-S waves in the boundary layer increase linearly with increasing the amplitude of the free-stream turbulence; while the normal wave number and incident angle of free-stream turbulence are approximately 60 and 20, the leading-edge receptivity coefficient KI reaches a maximum; and the values of leading-edge receptivity coefficient KI
Wide-band composite electromagnetic scattering from the earth soil surface and multiple targets shallowly buried
Authors: Ren Xin-Cheng  , Zhu Xiao-Min  , Liu Peng  ,   School of Physics and Electronic Information, Yanan University, Yan'an 716000, China;,   Key Laboratory for Information Science of Electromagnetic Waves(MoE), Fudan University, Shanghai 200433, China
Published: December 2020

Wide-band electromagnetic scattering from multiple objects shallowly buried beneath rough earth soil surfaces has been an important research topic in recent years because of its extensive applications in detecting the buried objects such as mines, pipes, and tunnels. Due to the advantages of finite-difference time-domain (FDTD) method in simulating wide-band electromagnetic scattering from rough surface in the presence of multiple objects, the FDTD method under Gaussian differential pulse wave incidence is utilized in the present study to analyze the frequency response of rough soil surfaces with shallowly buried objects, which serves as a basis for the detection and discrimination of objects buried below rough soil surfaces. The Topp equation model that can predict the dielectric constant of soil-water mixture is adopted in the present study to properly describe the dielectric property of earth soil with water. The actual rough land surface is modeled as the realization of a Gaussian random process with exponential spectrum by using Monte Carlo method. Simulation results show that the variation of composite scattering coefficient with frequency is oscillatory. It is also shown that the composite scattering coefficient versus frequency increases with the increase of root-mean-square of soil surface, water ratio of soil, the target section height, and the separation distance of target. However, simulation results indicate that the composite scattering coefficient versus frequency decreases with the increase of target section width. In summary, the variation of wide-band scattering coefficient is very complicated and is very sensitive to the incidence angle of electromagnetic wave. However, the wide-band scattering coefficient under Gaussian differential pulse wave incidence is less sensitive to the correlation length of rough soil surface, the depth of buried objects, and the dielectric constant of target. These qualitative results relating to the frequency response of rough soil surfaces in the presence of multiple objects are potentially valuable for detecting and discriminating the objects buried below rough soil surfaces by utilizing a wide-band ground penetrating radar system, although the present study is limited to one-dimensional rough soil surface due to the severe computational burden encountered in the large-scale Monte Carlo simulations. In addition, compared with frequency-domain numerical methods, the FDTD method has significant advantages in calculating wide-band composite scattering from rough surfaces in the presence of multiple objects, and thus has extensive applications in radar imaging simulation of multiple objects below or above rough surfaces, which goes beyond the scope of this paper.
Water-entry cavity of heated spheres
Authors: Li Jia-Chuan  , Wei Ying-Jie  , Wang Cong  , Deng Huan-Yu  ,   School of Astronautics, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

The present study aims to address the effect of sphere temperature on water-entry cavity. For this purpose, an experiment on vertical water-entry cavity of a heated sphere is conducted by utilizing a high-speed video camera. The temperature of the sphere ranges from 17℃ to 800℃. The complex flow phenomena of water entry, produced by a change in temperature of a sphere, is obtained for the first time. According to the finding, cavity is not formed around the room temperature sphere under the condition of the impact velocity of 1.5 m/s. When the temperature of the sphere is 300℃, the cavity appears, while it disappears when the temperature reaches up to 400℃. Interestingly, cavity appears again as the sphere is heated to a temperature of 700℃. The degrees of drag reduction of the sphere are different in various temperature conditions. Based on the theory of heat transfer and fluid dynamics, we analyze the mechanism for the influences of temperature and velocity on the forming of cavitation. The results show that the heat-transfer efficiency and heat-transfer mode between sphere and water change with the increase of temperature. Meanwhile the turbulent characteristic around the sphere, the surface roughness and hydrophobicity of the sphere are affected by the bubbles and vapor layer. In consequence, these characteristics influence the formation of cavity. The results of the effect of impact velocity on water-entry cavity reveal that the heat transfer performance plays a significant role in the forming of cavity, while the heat transfer efficiency is improved by the increase of impact velocity. The water-entry characteristics are similar to those in flow field under high temperature at low impact velocity as well as under low temperature at high impact velocity. The flow field of water entry looks similar under 330℃ at high impact velocity as well as under 400℃ at low impact velocity. Thus, an abnormal phenomenon appears. That is to say, the cavity size first decreases, and then disappears with the increase of impact velocity for the sphere at 330℃. The heat transfer performance can determine whether a cavity forms under the conditions of the impact velocity ranging from 1.5 m/s to 3.8 m/s. Meanwhile, the impact velocity itself can merely affect the cavity shape. The pitch-off time of the 300℃ sphere is irrelevant to impact velocity, which shows a good consistency with the literature result. Also, this research will be conductive to gaining an insight into the complex flow of water-entry with a heated sphere.
-ray detector based on n-type 4H-SiC Schottky barrier diode
Authors: Du Yuan-Yuan  , Zhang Chun-Lei  , Cao Xue-Lei  ,   Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Silicon carbide (SiC) is a wide band-gap, high-temperature-resistant, and radiation-resistant semiconducting material, which can be used as a radiation detector material in harsh environments such as high radiation background and high temperatures. Schottky barrier diode radiation detectors are fabricated using 100 upm-thick n-type 4H-SiC epitaxial layers for low energy -ray detection. The spectrum responses of 4H-SiC Schottky barrier detectors are investigated by irradiation of -ray from 241Am source. Schottky diodes are prepared by magnetron-sputtering 100 nm-thick nickel on epitaxial surface (Si face) to obtain Schottky contact and Ni/Au on substrate surface (C face) to obtain Ohmic back contact, respectively. Room temperature current-voltage (I-V) and capacitance-voltage (C-V) curves are measured to study the properties of Schottky diodes. Ohmic characteristic measurement shows that the Ohmic contact is formed after annealing in a temperature range of 900-1050℃, and the lowest specific contact resistivity of 2.5510-5 cm2 is obtained after annealing at 1050℃. The forward I-V curve reveals that the Schottky barrier height and the ideality factor are 1.617 eV and 1.127, respectively, indicating that the main current transportation process is the thermal electron emission. From the C-V curve, besides the net dopant concentration being inferred to be 2.9031014 cm-3, the profile of the free carrier concentration in epitaxial layer is also studied. A comparision of the reverse I-V curves of SiC Schottky diodes with different epitaxial layer thickness shows that the diode with 100 upm-thick epitaxial layer has a constant reverse leakage current when the bias voltage is less than 400 V, showing good rectification characteristics. By applying a reverse bias of 500 V, the diode has a leakage current of 2.11 nA, exhibiting a relatively high breakdown voltage. The depletion layer width of SiC detector is calculated to be 94.4 m at 500 V, indicating that the epitaxial layer is almost fully depleted. The signal of SiC detector through preamplifier displays a relatively low amplitude pulse (15 mV). A typical -ray spectrum response from SiC detector shows 9.49% (5.65 keV) energy resolution for 59.5 keV with a reverse bias of 300 V. The potential causes of poor count rate and energy resolution of fabricated detectors are analyzed in this article. The lower count rate is mainly caused by the narrow depletion layer, resulting in fewer photons deposited in sensitive region which can generate carriers. The poor energy resolution of SiC detector can be attributed to the electronic noise of read-out circuit, the pre-match amplifier circuit for detector needs to be improved, in addition, the extra defects existing in detector caused by increasing thickness of epitaxial layer can also deteriorate the detector performance.
A three-dimensional refined modeling for the effects of SF6 release in ionosphere
Authors: Zhao Hai-Sheng  , Xu Zheng-Wen  , Wu Zhen-Sen  , Feng Jie  , Wu Jian  , Xu Bin  , Xu Tong  , Hu Yan-Li  ,   School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710071, China;,   National Key Laboratory of Electromagnetic Environment, China Research Institute of Radiowave Propagation, Qingdao 266107, China
Published: December 2020

The traditional simulation model of sulfur hexafluoride ionosphere release is a simple point-source model and the simulation precision is not high. The three-dimensional refined simulation model of rocket SF6 release is established in this paper, in which the rocket pose and velocity, gas injection velocity and flow, and wind velocity are all taken into account in the diffusion equation. Meanwhile, the influences of geomagnetic inclination and the field diffusion on artificial disturbance form are considered in the plasma diffusion equation, and the two-dimensional plasma diffusion equation is extended to three-dimensional case. The ray tracing method is used to study the influence of ionospheric artificial disturbance on the short wave propagation path. The research results of the ionosphere kinetics process, ionospheric uneven body generation mechanism and evolution are of great significance.
Polarization switching characteristics of polarization maintaining optical feedback and orthogonal optical injection of 1550 nm-VCSEL
Authors: Zhang Xiao-Xu  , Zhang Sheng-Hai  , Wu Tian-An  , Sun Wei-Yang  ,   College of Science, Information Engineering University, Zhengzhou 450001, China
Published: December 2020

Based on the spin flip model, four schemes for the polarization switching of the 1550 nm vertical cavity surface emitting laser are studied by using numerical simulation, which are free running laser orthogonal injection free running laser, free running laser orthogonal injection polarization maintaining optical feedback laser, polarization maintaining optical feedback laser orthogonal injection free running laser, and polarization maintaining optical feedback laser orthogonal injection polarization maintaining optical laser. We can draw three conclusions from the numerical results. Firstly, changing the feedback strength can make the polarization switching point of the injection intensity in the different regular movements when the normalized injection current is small. The injection intensity of the polarization switching point increases with the increase of the feedback strength for the free running laser orthogonal injection polarization maintaining optical feedback laser; the injection intensity of the polarization switching point decreases with the increase of the feedback strength for the polarization maintaining optical feedback laser orthogonal injection free running laser; the injection intensity of the polarization switching point is nonlinear and fluctuates with the increase of the feedback strength for the polarization maintaining optical feedback laser orthogonal injection polarization maintaining optical laser. The reason is that the non dominant X polarization component cannot go up when the normalized injection current is small, then, as the feedback intensity increases, the difference between the two polarization components will be increased. Secondly, when the normalized injection current is large, changing the feedback intensity can make the polarization switching point of the injection intensity in the irregular movement. The reason is that the non dominant X polarization component can go up when the normalized injection current increases up to a certain value, which can form the significant nonlinear wave together with the dominant Y polarization component. Thirdly, changing the frequency detuning can make the polarization switching point of the injection intensity in the same regular movement. The injection strength required for the occurrence of polarization switching point first decreases and then increases for the four schemes, when the frequency detuning is from approximately -60 GHz to the minimum, presenting the symmetrical distribution of V type with -60 GHz as the axis. The same regular movement of the polarization switching point of the injection intensity is not changed with the change of the normalized injection current.
Construction of Bi-Pearcey beams and their mathematical mechanism
Authors: Ren Zhi-Jun  , Li Xiao-Dong  , Jin Hong-Zhen  , Shi Yi-Le  , Yang Zhao-Qing  ,   Institute of Information Optics, Zhejiang Normal University, Jinhua 321004, China;,   Key Laboratory of Optical Information Detecting and Display Technology, Zhejiang Normal University, Jinhua 321004, China
Published: December 2020

We present a theoretical expression in the form of the Pearcey function by deducing the Fresnel diffraction distribution of an elliptic line. Then, we numerically simulate and experimentally generate this kind of new Pearcey beams by using the Fresnel diffraction of optical ellipse line. This kind of beams can be referred to as Bi-Pearcey beams because their appearance of the topological structure is very similar to the combination of two face-to-face classical Pearcey beams. It is no doubt that so-called Bi-Pearcey beams are the new member of a family of form-invariant Pearcey beams. Subsequently, we also provide the theoretical mechanism of generating Bi-Pearcey beams based on the Zeeman catastrophe machine of catastrophic theory. By solving the critical equation of potential function of Bi-Pearcey beams generated by an ellipse line, we find that the optical morphogenesis of Bi-Pearcey beams is determined by the number of roots of the critical equation. The critical equation of potential function of Bi-Pearcey beams is a classical Cartan equation, which has at most three real roots. For the Fresnel diffraction of ellipse line, three real roots of the critical equation are corresponding to three stable points and represent three diffraction lines, hence they can be used to examine the optical topological structure of Bi-Pearcey beams. By choosing the appropriate control variable of Bi-Pearcey beams, two diffraction lines of an ellipse line overlap, and the strong caustic line of Bi-Pearcey beams is correspondingly generated when the two of the three real roots of the critical equation are equal. If the three real roots of the critical equation are all equal, the strongest cusps of Bi-Pearcey beams are generated, accordingly. Moreover, the equation of the caustic line and their positions of four cusps of Bi-Pearcey beams are given by solving the control variable equation of Bi-Pearcey beams. In conclusion, we elucidate the mathematical mechanism of topical morphogenesis of Bi-Pearcey beams based on catastrophic theory.
A source range and depth estimation method based on modal dedispersion transform
Authors: Guo Xiao-Le  , Yang Kun-De  , Ma Yuan-Liang  , Yang Qiu-Long  ,   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 wideband source localization is analysed widely in shallow water. It is pointed out that its performance is poor when the number of array elements is few or the ocean environment is uncertain. A method of estimating the range and depth is studied by using a single hydrophone based on the relationship of the horizontal wavenumber difference between two modes with the waveguide invariant for low frequency underwater acoustic pulse signals in a range-independent shallow water waveguide. This localization method estimates the source range by using the rangedispersion two-dimensional（2D) plane focus phenomenon and also the source depth by matching the modal energy. So it can separately estimate the source range and source depth by single hydrophone. First, the signal received on a single hydrophone can be decomposed into a series of modes within the framework of normal mode theory. In order to obtain a better localization performance, the first few order modal dispersion parameters and waveguide invariant are regarded as the unknown parameters. And then the first few order modal dispersion parameters and waveguide invariant can be estimated by comparing the differences between the modal phase velocity calculated by Eq.(8) and that calculated by the Kraken model. Second, using the estimated dispersion parameters and waveguide invariant for dedispersion transform, the amplitudes of each normal mode can achieve maximum values but only when the range of the received signal after dedispersion transform is equal to the range of source. On range-dispersion 2D plane, there appears the sound pressure focus phenomenon, and this phenomenon can be used to estimate the source range. Simulation results from a shallow water Pekeris waveguide show that the time-frequency distribution represents well the dispersion characteristics of the underwater acoustic pulse signal and the dedisperision transform can eliminate this dispersion at the range of source, so that the source range can be estimated. Besides, the first few order modal signals received are clearly separated in time domain after dedispersion transform, and the first few order modal energy can be calculated accurately. So the source depth can be estimated by matching the modal energy. The errors in range estimation and depth estimation are little in simulation. Finally, the data collected from airgun sources during an experiment in the shallow water are used to verify the presented method, and the experimental results obtained using airgun sources on a straight line are shown. The presented method is very significant for estimating the range and depth in shallow water.
Structure of BP3S monolayer on Au(111)
Authors: Li Bai  , Wu Tai-Quan  , Wang Chen-Chao  , Jiang Ying  ,   Department of Physics, China Jiliang University, Hangzhou 310018, China
Published: December 2020

The first-principle technique is employed to determine the structure of the BP3S monomer, the structures of the molecular chains and monolayers on virtual Au（111), and the atomic structure of BP3S/Au（111) adsorption system. The results show that the BP3S monomer presents a symmetric structure, and the angle between two benzene rings is 3510. At first, many BP3S monomers are assembled into one stable molecular chain in the virtual Au（111), the distance between the neighbor monmers is 0.516 nm, and the bind energy between the monmer and the molecular chain is 0.071 eV. It is a self-assembly system. Then many molecular chains are assembled into two stable monolayers in the virtual Au（111)-(37) and Au（111)-(313), and their coverages are 0.20 ML and 0.14 ML, respectively. In the virtual Au（111)-(37) and Au（111)-(313), the angles between the molecular chains and the virtual surface are 60 and 30, respectively, and the binding energies between the monmer and two monolayers are 0.101 eV and 0.125 eV, respectively. They are both the self-assembly systems. Finally, two monolayers are adsorbed on the Au（111)-(37) and Au（111)-(313) at four adsorption sites. The S atom is easy to obtain two electrons and turn into S2- ion, and the Au atom is easy to lose one electron and become Au+ ion, so the bridge site（two Au+ ions) is more stable than the top site（one Au+ ion), while the hcp and fcc hollow sites（three Au+ ions) are both unstable. In the Au（111)-(37), the chemisorption energy of the bridge site（-1.879 eV) is lower than that of the top site（-1.511 eV). And in the Au（111)-(313), the chemisorption energy of the bridge site（-1.691 eV) is lower than that of the top site（-1.492 eV). The results are confirmed in the other S-Au adsorption systems, such as the C6H13S/Au（111). A comparison between the structures of the BP3S monolayer before and after being adsorbed on Au（111) clearly shows that the structural parameters of the adsorption system depend mainly on the interaction in the monolayer, and that the contribution of Au（111) to the structure of the monolayer is weak. These results are confirmed in the other self-assembly adsorption systems.
Plasmon induced transparency in the trimer of gold nanorods
Authors: Ma Ping-Ping  , Zhang Jie  , Liu Huan-Huan  , Zhang Jing  , Xu Yong-Gang  , Wang Jiang  , Zhang Meng-Qiao  , Li Yong-Fang  ,   School of Physics and Information Technology, Shaanxi Normal University, Xi'an 710119, China
Published: December 2020

The localized surface plasmon resonance can be generated on the surface of the nano-metamaterial by the interaction between the nano-metamaterial and the light field, and also many plasmon oscillation modes can occur in the process of the hybridization between many infinitesimal composite structures, which is widely used for adjusting the resonant frequency in the optical frequency domain. Recently, analogue of the electromagnetically induced transparency（EIT) has been realized in the low-loss nano-metamaterial, and is well known as the plasmon induced transparency（PIT). In atomic physics, EIT is an effect which originates from the destructive quantum interference of two different excitation pathways. A sharp dip of nearly ideal transmission can arise within the broad absorption profile, which indicates that the EIT can be used in the fields of slow slight, delay lines and low-loss metamaterial. In this paper, a trimer consisting of a vertical nanorod（serving as a dipole antenna) and two parallel nanorods（used as a quadrupole antenna) is employed to investigate the process mechanism of the PIT in detail. It is found that the vertical nanorod with a large broad linewidth can be strongly coupled with the light. However, the parallel nanorods are weakly coupled with the light and their narrow linewidths are almost from the intrinsic metal loss（Drude damping) that is much smaller than the radiative damping of the dipole antenna. These two antennas can be strongly coupled due to their close similarities. Moreover, the absorption spectra of the trimer obtained by using three-dimensional finite element method vary with its coupling distance and geometry size, and the dipole bright mode corresponding to the dipole antenna splits under the action of the dark mode for the quadrupole antenna. Thus, a fresh physical interpretation is given:the PIT is mainly due to the coherent superposition after the splitting of the dipole oscillation mode in the vertical nanorod, rather than the parallel nanorods. Taking into consideration the phase correlation associated with coupling process of two oscillators, we introduce a modified Lorentzian oscillator model to investigate the effects of the coupling phase factor on the modulation of the absorption spectra and the coherent superposition between the splitting bright modes on the PIT. These findings will provide theoretical references for the applications of artificial atom, optical switching and slow light devices designed in the nanosize range.
High-efficiency wavefront control with based on helical metamaterials
Authors: Wang Zhao-Kun  , Yang Zhen-Yu  , Tao Huan  , Zhao Ming  ,   School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China;,   Shenzhen Research Institute of Huazhong University of Science and Technology, Shenzhen 518057, China
Published: December 2020

Metamaterials or metasurfaces have been widely studied to manipulate the propagation of light by controlling the wavefront. In previous work, more and more structures were designed to study the reflected or the transmitted light. However, as far as we know, it is rarely reported how to efficiency tailor the wavefront, especially for transmitted light. Helical metamaterial, which has a relatively strong coupling effect among the helical nanowires, may provide an alternative to the wavefront control. In this study, a kind of complementary helical metamaterial with a left-handedness and a right-handedness helixes coupled to each other is proposed. The complementary helical metamaterial has a strong circular conversion dichroism, and it is expected to be a good candidate for generating phase shift and controlling wavefront with high efficiency. Using the finite-difference time-domain method, we find that this kind of helix has a high circular polarization conversion in a broadband, which often implies a high efficiency of the transmitted light. Moreover, it is also found that the structure will introduce a controllable phase shift（) between the incident and the transmitted light whose polarizations are orthogonal to each other. By calculating the surface current density of the helix, the performance of high circular polarization conversion is explained. Meanwhile, we also find that the phase shift has a linear relationship with the initial angle of the helix（), which is =2. This relationship can be explained exactly by Jones calculus. According to the generalized Snell's law, the refracted beam can have an arbitrary direction by designing a suitable constant gradient of phase discontinuity. And then, by arranging 12 helixes in an array with a constant phase gradient along the X-axis, the phenomenon of anomalous refraction with a high efficiency（64%) is observed in the near infrared range（1.0-1.4 m). The angle of the anomalous refraction is in good agreement with the theoretical value. Compared with the metasurface, the helical metamaterial has a relatively complex structure. But with the development of the nanotechnology, there are several methods that can complete the propagations of nano helical structures, such as the direct laser writing, the glancing angle deposition, and the molecular self-assembly techniques. And by carefully designing the structure parameters of the helix, this kind of complementary helical metamaterial is expected to be an ideal candidate not only for traditional optics but also for biological detection and medical science.
Simulation of polymer filling process by an improved smoothed particle hydrodynamics method based on higher-order Taylor expansion
Authors: Jiang Tao  , Lu Wei-Gang  , Ren Jin-Lian  , Xu Lei  , Lu Lin-Guang  ,   Department of Mathematics, School of Hydraulic, Energy and Power Engineering, Yangzhou University, Yangzhou 225002, China
Published: December 2020

In this work, an improved smoothed particle hydrodynamics (SPH) method based on higher order Taylor expansion (CSPH_HT) is proposed and tentatively applied to the filling process of the viscoelastic fluid. Owing to the disadvantages of the traditional SPH method and the presented corrected SPH methods, the CSPH_HT method based on the higher order Taylor expansion is proposed and described in detail. In order to illustrate the validity and merits of the CSPH_HT method, two benchmark problems are simulated and discussed. The numerical results show that the proposed CSPH_HT method has higher numerical accuracy and better stability. Subsequently, the proposed improved SPH method is extended to simulate the filling processes of the viscoelastic fluid in the ring-shaped mold, for the purpose of exhibiting the capacity of the proposed method. The extended pom-pom (XPP) model and finitely extensible nonlinear elastic-Peterlin (FENE-P) model fluid are all considered in this case, in which the viscoelastic fluid flow and extra stress are shown. The differences in fluid flow between the XPP model and FENE-P model are also discussed. Finally, the filling process of the viscoelastic fluid in the square mold with single inlet or two inlets are tentatively simulated. The differences between the filling process of XPP fluid and the filling process of FENE-P fluid are shown, and the influences of the parameters of the mold on the flow are analyzed. Especially, the influences of locations and sizes of two inlets on the filling process of viscoelastic fluid are illustrated. The XPP model fluid and FENE-P model fluid show different characteristics in the filling process and small change of the size of the mold can lead to obvious change of the flow.
Semiclassical methods for strong field ionization of atoms
Authors: Xiao Xiang-Ru  , Wang Mu-Xue  , Li Min  , Geng Ji-Wei  , Liu Yun-Quan  , Peng Liang-You  ,   State Key Laboratory for Mesoscopic Physics and School of Physics, Peking University, Beijing 100871, China;,   Wuhan National Laboratory for Optoelectronics and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China;,   Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
Published: December 2020

As the advances of laser technology, more and more nonlinear phenomena are observed in the atoms and molecules driven by strong laser pulses. Systematic investigations on these findings, such as above threshold ionization and high-order harmonic generation, will lead us to understanding the mechanisms in the microscopic world. The most exact way to simulate the experimental measurements is to solve the time-dependent Schrdinger equation (TDSE) numerically, in which the system is described by the wave function and thus one cannot have an intuitive insight into the underling process. Therefore, several semiclassical methods have been developed to understand the strong field ionization. In the classical point of view, the electrons tunnel out when the strong laser field suppresses the Coulomb potential. Then the electrons are driven by the laser electric field according to the Newtonian equations. Semiclassical methods take into account the tunnelling of the electron, the classical orbit of the electron, and the action as the phase of trajectory, which have successfully explained main structures in the ionization spectrum. Two of the most popular semiclassical methods are the quantum trajectory Monte Carlo method and the Coulomb-corrected strong field approximation method. In the present review, we will introduce these basic methods and show how they have been developed step by step, covering the most relevant and important works in the strong field physics. Finally we give two example of applications to show how these methods work. With the advantage of the classical picture, we can identify different kind of structures in the 2D photoelectron momentum distributions and tell how the structures are formed. Nonadiabatic effects can be studied by comparing the results of the two methods, together with accurate simulation from the numerical solution of TDSE. The current semiclassical methods can be further developed into advanced ones, which can be used in more complex molecular systems or multi-electron systems, and be widely used in the study of dynamics of molecule and atoms in strong laser fields.
Study of above-threshold ionization by Wigner-distribution-like function method
Authors: Guo Li  , Han Shen-Sheng  , Chen Jing  ,   Key Laboratory of Quantum Optics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China;,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
Published: December 2020

A Wigner-distribution-like function is proposed to obtain various distributions of photoelectron emitted from H atoms in few-cycle laser pulses with different frequencies:time-energy distribution, time ionization distribution for linearly polarized laser field and time-emission angle distribution, angular distribution, and time ionization distribution for elliptically polarized laser field. With decreasing frequency, all the distributions clearly show a transition of ionization process from the multi-photon regime to the tunneling regime. For the case of linearly polarized laser pulse, accompanying this transition, the semiclassical relationship between the ionization moment and the final drift energy is becoming more and more close to the time-energy distribution. Meanwhile, the time-energy distribution clearly shows the interference structures in the tunneling regime, which can be attributed to the interference between the electrons with the same energy ejected at different times. For the case of elliptically polarized laser pulse, both the angular offset in the angular distribution and the time offset in the time ionization distribution are obtained by comparing the quantum calculation with the semi-classical result. The results show that the time offset is much smaller than the angular offset. This indicates that the attoclock technique which is based on the correspondence between two offsets is in principle inaccurate. Furthermore, the time offset can be both positive and negative. So this time offset cannot be interpreted as the tunneling time.