bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrafast azimuthal beam smoothing scheme based on vortex beam
Authors: Tian Bo-Yu , Zhong Zhe-Qiang , Sui Zhan , Zhang Bin , Yuan Xiao ,   School of Electronics and Information Engineering, Sichuan University, Chengdu 610064, China,   Shanghai Institute of Laser Plasma, China Academy of Engineering Physics, Shanghai 201800, China,   College of Physics, Optoelectronics and Energy, Soochow University, Suzhou 215006, China
Published: December 2020

The illumination uniformity of laser beams in inertial confinement fusion (ICF) facility is a key factor, which plays a crucial role in suppressing the laser plasma instabilities. However, the prevailing beam smoothing techniques cannot meet all the requirements for improving the irradiance uniformity of laser beams and mitigating the laser plasma instabilities, which are determined by the high-frequency spatial modulations and the fine-scale speckles of the focal spots. An ultrafast azimuthal beam smoothing scheme based on vortex beams is proposed in this paper. In this scheme, two of the four beams in a laser quad are transformed from super-Gaussian (SG) beams into vortex beams by inserting two spiral phase plates with opposite topological charges into the beam path, whereas the other two SG beams remain unchanged. By controlling the polarization and the center wavelength of each beam, the SG beam and the transformed vortex beam in the quad are coherently superposed on the target plane, so are the remaining two beams. Owing to the difference in central wavelength and the existence of the topological charges, two focal spots rotating in a period of a few picoseconds are generated in the target plane, which can redistribute the speckles quickly in temporal domain and thus improve the irradiance uniformity of the laser quad. By establishing the physical model of the azimuthal smoothing scheme, the smoothing characteristics including the rotation period, the illumination uniformity and the fractional-power-above-intensity of the focal spots are analyzed in detail. In order to improve the smoothing characteristics significantly, the novel smoothing scheme is further combined with another ultrafast smoothing scheme, i.e. radial smoothing scheme. The influence of the key parameters of the combined smoothing scheme on the illumination uniformity and on the smoothing velocity are discussed. Results indicate that the azimuthal smoothing scheme can achieve the ultrafast smooth of the laser quad in the azimuthal direction and the best illumination uniformity within a few picoseconds as well. Though the degree of improvement in the irradiance uniformity of the azimuthal smoothing scheme is lower than that of the radial smoothing, the combination of these two schemes can improve the uniformity effectively and rapidly. The novel smoothing scheme provides a potential smoothing approach for the high-power laser facilities.
Simplification of roughness bottom backscattering model at small grazing angle in shallow-water
Authors: Hou Qian-Nan , Wu Jin-Rong ,   Key Laboratory of Underwater Acoustic Environment, IACAS, Beijing 100190, China
Published: December 2020

Bottom backscattering due to roughness seafloor is the main source of shallow water reverberation, especially in the waveguide with downward reflection profile or a calm sea-surface. Empirical backscattering models with a simple form has an important limitation to analyzing other characteristics of reverberation except for the intensity characteristics, which originates from optics and describes the relationship between the bottom backscattering strength and scattering grazing angle of plane-wave in half-infinite space. In the shallow water, such a plane-wave backscattering model cannot be used due to frequency dispersion. The model of bottom backscattering based on physical scattering principle is made to relieve such a limitation, but thereby bringing about another restraint by a geoacoustics model. The bottom backscattering model, which is formulated during modeling the full-wave reverberation theory at small grazing angle in range-independent shallow water waveguide, is simplified by combining with bottom reflection coefficient model which is independent of the geoacoustics model. The bottom reflection coefficient model as referred to the proposed phase parameter P in this paper is equivalent to velocity and density of sediment to describe sound field interacted with sea-bottom. Therefore simplification of bottom backscattering model can be handled by the phase parameter without any knowledge of bottom geoacoustic parameters. The angular dependency and intensity dependency of bottom backscattering due to roughness seafloor at small grazing angle are studied more in depth through such a simplified model. Marking 2/P as the cut-off point, the grazing angle is divided into two stages. Near the critical angle, as grazing angle is greater than 2/P and less than critical grazing angle, the angular dependency of bottom backscattering due to roughness seafloor is weighted by phase parameter of bottom reflection coefficient, while the intensity dependency is independent of phase parameter. At each small grazing angle, as grazing angle is less than 2/P, the angular dependency of bottom backscattering due to roughness seafloor is proportional to incident and scattering grazing angle squared and irrespective of phase parameter of bottom reflection coefficient which is like the empirical bottom backscattering model, while the intensity dependency is proportional to the fourth power of phase parameter. So the bottom has different influences on the angular dependency and intensity dependency of bottom backscattering in different stages of grazing angle.
Compound denoising method of laser speckle noise in laser inherent field imaging
Authors: Cheng Zhi-Yuan , Li Zhi-Guo , She Wen-Ji , Xia Ai-Li ,   Xi’an Institute of Optics and Precision Mechnics, Chinese Acdemy of Sciences, Xi’an 710119, China
Published: December 2020

Noise is an important factor affecting the image quality of laser coherent field high resolution imaging system. And there exists not only background light additive noise but also laser multiplicative speckle noise in a laser coherent field imaging system. Both of the above noise affect the imaging quality of laser coherent field system. In order to improve the imaging quality from the perspective of noise suppression and settle the imaging quality degradation problem of laser multiplicative speckle noise and background additive noise in the laser coherent field imaging system, the model for the influence of multiplicative speckle noise and background additive noise on laser echo field demodulated signal is established in atmospheric downlink. Then, based on the model, a novel homomorphic filter and sparse matrix trace cascade compound de-noising algorithm is put forward. Firstly, based on the homomorphic filtering theory, the laser multiplicative speckle noise in the laser echo demodulated signal is converted into the additive noise by logarithmic transformation. Then the low-frequency laser multiplicative speckle noise is filtered by the high-pass filter, and the high-frequency demodulated signal is retained. The logarithmic inverse transform is used to obtain the laser echo demodulation signal after the multiplicative speckle noise has been filtered out. Next, the phase random disturbance of atmosphere in laser echo demodulated signal is suppressed by phase closure technology and the imaging spectrum component is reconstructed by the spectrum iterative reconstruction method. Then the high resolution image is obtained by spectrum component inverse Fourier transform. Finally, the effect of background additive noise on the image quality is suppressed by the sparse base tracking theory. The simulated and outdoor experiment result are used to verify the denoising effect and image quality enhancement effect of the composite de-noising method. Compared with the existing single denoising method, the composite denoising method is shown to be able to effectively eliminate laser multiplicative speckle noise and background additive noise at one time. The proposed method can improve image contrast and promote the Strehl ratio of imaging quality in a coherent imaging system. It provides a theoretical basis for improving imaging quality and denosing laser multiplicative speckle noise and background additive noise in coherent field imaging system.
Stability and electronic structure of hydrogenated two-dimensional transition metal dichalcogenides: First-principles study
Authors: Wang Dan , Zou Juan , Tang Li-Ming ,   College of Science, Central South University of Forestry and Technology, Changsha 410004, China,   School of Physics and Electronics, Hunan University, Changsha 410082, China
Published: December 2020

Chemical functionalization of two-dimensional transition metal dichalcogenides (TMDs) with hydrogen is an effective and economical method to synthesize monolayer TMDs and tune their electronic properties. We theoretically study the stabilities and electronic properties of chemisorbed H atoms on monolayer TMDs by using density-functional theory calculations. The result shows that there exists a more stable adsorption site in the layers of the monolayer MX2 (M = Mo, W; X = S, Se, Te) than its surface for hydrogen. In the case of the same cation, with the increase of the anion (X2−) atomic number, the stronger the bonding between the H atom and the MX2 layer, the more stable the structure of the hydrogenated monolayer MX2 is. However, in the case of the same anion, the binding between the H atom and the MX2 layer becomes weaker as the atomic number of the cations increases. H atoms passes through one surface of the MS2 to the other surface with a relatively small diffusion barrier of about 0.9 eV. So the H atoms can more easily go through the barrier. And for the H atom to go through the other monolayer MX2 (M = Mo, W; X = Se, Te), the diffusion barrier is about 1.2 eV. H atoms are difficult to pass through the barrier at this time. The singular diffusion behavior of H atoms in monolayer MX2 is conducible to understanding the stability of hydrogenated two-dimensional transition metal sulfide system. In addition, the surface hydrogenation and interlaminar hydrogenation have different effects on the electronic properties of monolayer MX2, and mainly manifest themselves in the fact that the surface hydrogenation induces spontaneous magnetism and sharply reduces the band gap, but still retains the semiconductor properties of the original monolayer MX2. However, interlaminar hydrogenation enables monolayer MX2 to directly realize the transition from semiconductor to metal. Interlaminar hydrogenation monolayer MX2 (M = Mo, W; X = S, Se) make the system generating magnetism, while when the anion is Te2−, the magnetism almost disappears. These results can provide theoretical guidance in understanding hydrogen functionalization of MX2 layer, and also present a certain theoretical basis for realizing the application of MX2 in nano-electronic devices.
Coherent state phase estimation based on digital nonlinear phase-locked loop
Authors: Xu Han , Chen Shu-Xin , Wu Hao , Chen Kun , Hong Lei ,   Information and Navigation College, Air Force Engineering University, Xi'an 710077, China
Published: December 2020

The navigation mechanism of obtaining phase parameters based on quantum theory can break through the limitation of classical physical limit to navigation accuracy. In order to achieve the accurate estimation of the coherent state phase, it is usually assumed that the local oscillator phase must be orthogonal to the coherent state phase in the method of quantum homodyne detection. However, the coherent state phase is unknown and the hypothesis cannot be guaranteed to be correct in practice. In this paper we design a nonlinear phase-locked loop to solve the problem. Firstly, in order to obtain the Wigner distribution for a coherent state, we start with the Wigner distribution for the vacuum state and analyze the noise characteristics according to Wigner distribution of coherent state, then the output of homodyne detection is derived. Secondly, in order to avoid introducing errors in theory, caused by linearization and cope with the limiting requirement between local oscillator phase and coherent state phase in the phase tracking of coherent state, we design an orthogonal simplex cubature Kalman filter (OSCKF) algorithm to achieve the function of the nonlinear phase-locked loop. The algorithm converges by updating the state of the local oscillator phase multiple times, and then, the accurate coherent phase is obtained. Finally, according to the design of the phase-locked loop, we observe the data of homodyne detection and then verify the correctness of the OSCKF algorithm. The simulation results show that the OSCKF can converge to the real phase after observing 200 sampled data and the accuracy is higher than extended Kalmn filter (EKF) and cubature Kalman filter (CKF), and the real phase can be obtained under different local oscillator phase. In conclusion, the nonlinear phase-locked loop based on OSCKF algorithm breaks the limitation of traditional way in which the initial local oscillator phase is required to be orthogonal to the coherent state phase, and effectively avoid the linearization error and improve the anti-nonlinear ability. It is very significant in theory and application .
Deterministic quantum entanglement among multiple quantum nodes
Authors: Liu Yan-Hong , Wu Liang , Yan Zhi-Hui , Jia Xiao-Jun , Peng Kun-Chi ,   Institute of Opto-Electronics, State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Quantum entanglement is a significant quantum resource, which plays a central role in quantum communication. For realizing quantum information network, it is important to establish deterministic quantum entanglement among multiple spatial-separated quantum memories, and then the stored entanglement is transferred into the quantum channels for distributing and transmitting the quantum information at the user-control time. Firstly, we introduce the scheme of deterministic generation polarization squeezed state at 795 nm. A pair of quadrature amplitude squeezed optical fields are prepared by two degenerate optical parameter amplifiers pumped by a laser at 398 nm, and then the polarization squeezed state of light appears by combining the generated two quadrature amplitude squeezed optical beams on a polarizing beam splitter. Secondly, we present the experimental demonstration of tripartite polarization entanglement described by Stokes operators of optical field. The quadrature tripartite entangled states of light corresponding to the resonance with D1 line of rubidium atoms are transformed into the continuous-variable polarization entanglement via polarization beam splitter with three bright local optical beams. Finally, we propose the generation, storage and transfer of deterministic quantum entanglement among three spatially separated atomic ensembles. By the method of electromagnetically induced transparency light-matter interaction, the optical multiple entangled state is mapped into three distant atomic ensembles to build the entanglement among three atomic spin waves. Then, the quantum noise of entanglement stored in the atomic ensembles is transferred to the three space-seperated quadrature entangled light fields through three quantum channels. The existence of entanglement among the three released beams verifies that the system has the ability to maintain the multipartite entanglement. This protocol realizes the entanglement among three distant quantum nodes, and it can be extended to quantum network with more quantum nodes. All of these lay the foundation for realizing the large-scale quantum network communication in the future.
An ultrawideband linear-to-circular polarization converter based on multiphysics regulation
Authors: Zeng Li , Liu Guo-Biao , Zhang Hai-Feng , Huang Tong ,   College of Electronic and Optical Engineering and College of Microelectronics, Nanjing University of Posts and Telecommunications, Nanjing 210023, China,   National Electronic Science and Technology Experimental Teaching Demonstrating Center, Nanjing University of Posts and Telecommunications, Nanjing 210023, China,   National Information and Electronic Technology Virtual Simulation Experiment Teaching Center, Nanjing University of Posts and Telecommunications, Nanjing 210023, China,   State Key Laboratory of Millimeter Waves of Southeast University, Nanjing 210096, China
Published: December 2020

In order to design a tunable linear-to-circular polarization converter in microwave band, an ultra-broadband linear-to-circular polarization converter (LCPC) based on multiphysics regulation is proposed and studied by combining solid state plasma and vanadium dioxide (VO2) in this article. By using the electric control way to control the states of the solid plasma resonator, the solid state plasma can generate excitation and non-excitation state. By using the temperature (T) control way to regulate the phase transition state of the VO2 resonator, the VO2 can generate insulating and metallic state. The purpose of dynamic shift of the proposed LCPC′s operating band can be realized. The polarization conversion rate curve, reflection phase curve, the axial ratio curve and the surface current diagram of the proposed LCPC are analyzed and simulated by the full-wave simulation software HFSS and the effects of parameters r1 and r3 on the axial ratio are also discussed. When none of all the solid plasma regions are excited and T < 68 ℃ , the presented LCPC is in No. 1 state. On the basis of No. 1 state, if all the solid state plasma are excited, the presented LCPC is in No. 2 state. Similarly, on the basis of No. 1 state, the presented LCPC will be transformed to No. 3 state when T ≥ 68 ℃. The axial ratio band which is less than 3 dB (3 dB AR band) is 14.3−29.7 GHz (the relative bandwidth is 70%) in No. 2 state. The 3 dB AR bands which are 14.4−23.4 GHz and 28.6−35.9 GHz (the relative bandwidths are 47.61% and 22.64%) show that the proposed LCPC has the ability to shift the working band to high frequency range. When switching the LCPC to No. 3 state, the 3 dB AR bands which are 8.4−11.2 GHz and 18.7−29.5 GHz (the relative bandwidths are 28.57% and 44.81%) are shifted to low frequency region. Compared with traditional LCPC, our design has the advantages of diverse control means, wide bandwidth, flexible design and strong functionality. At the same time, this LCPC presents a new design method and idea for multiphysical field regulated devices.
Geometric momentum distribution for three-dimensional isotropic hormonic oscillator
Authors: Liu Quan-Hui  , Zhang Meng-Nan  , Xiao Shi-Fa  , Xun Da-Mao  ,   1. School for Theoretical Physics, Physics and Electronics, Hunan University, Changsha 410082, China;,   2. Department of Physics, Lingnan Normal University, Zhanjiang 524048, China;,   3. Faculty of Communication and Electronics, Jiangxi Science and Technology Normal University, Nanchang 330013, China
Published: December 2020

The geometric momentum was originally introduced for defining the momentum of particle constrained on a hypersurface, but it is in fact not necessarily defined on a curved surface only. If a coordinate system contains a family of hypersurfaces and a normal vector on hypersurface used as a unit vector, the geometric momentum can be defined on the family of hypersurfaces and can be used to determine a complete set of commuting observables. For instance, the spherical polar coordinate system is such a kind of coordinate, in which for a given value of radial position, the spherical surface is a hypersurface. It is well-known that any vector in the space can be decomposed into components along each axis of the spherical polar coordinates, but the geometric momentum has a different decomposition, for it requires a projection of the momentum on the hypersurface, and then needs to decompose the projection into the Cartesian coordinates of the original space where the whole spherical coordinates are defined. Explicitly, with a relation-iħ▽= p Σ + p n where-iħ▽ can be usual momentum operator in Cartesian coordinates, and p Σ is the momentum component on the hypersurface which turns out to be the geometric momentum, and p n is the momentum component along the radial direction, we have a nontrivial definition of radial momentum as p n ≡-iħ▽- p Σ. Once-iħ▽ and p Σ are measurable, p n is then indirectly measurable. The three-dimensional isotropic harmonic oscillator can be described in both the Cartesian and the spherical polar coordinates, whose quantum states thus can be examined in terms of both momentum and geometric momentum distributions. The distributions of the radial momentum are explicitly given for some states. The radial momentum operator that was introduced by Dirac has clear physical significance, in contrast to widely spreading belief that it is not measurable due to its non-self-adjoint.
Density functional study of metal lithium atom adsorption on antimonene
Authors: Luan Xiao-Wei , Sun Jian-Ping , Wang Fan-Song , Wei Hui-Lan , Hu Yi-Fan ,   School of Electrical and Electronic Engineering, North China Electric Power University, Beijing 102206, China
Published: December 2020

 Since the discovery of graphene, researchers have been being increasingly attracted by the emerging of a bunch of two-dimensional (2D) materials, such as BN, MoS2 and black phosphorene. These materials possess outstanding physical and chemical properties, which could find great potential applications in nanoelectronics, energy conversion or storage, photocatalysts, etc. Recently, a theoretically predicted pucker layered material consisting of Sb atoms, antimonene, has been prepared, and is attracting the attention in the field of lithium ion batteries.

In this paper, based on first-principle density functional theory, the adsorption characteristics of Li atoms on antimony are studied, including the most stable adsorption configuration, the adsorption density and the diffusion path of Li atom on antimonene. The results show that the most stable adsorption configuration of Li atom is in the valley site, i.e. the center of the three Sb atoms in the top layer and one Sb in the bottom layer. The adsorption energy is 1.69 eV and the adsorption distance is 2.81 Å. The band structure shows that antimony is an indirect band gap semiconductor with a band gap of 1.08 eV. After the absorption of Li atom, the Fermi level enters into the conduction band, which shows an electronic property similar to metal. The analysis of density of states shows that the p-electronic state of Sb atom and the p and s electronic state of Li atom possess distinct resonance peaks, showing hybrid bonding characteristics. With the increase of the number of Li atoms adsorbed, the lattice structure and electronic structure of antimonene change greatly. The nudged elastic band calculation shows that the diffusion barrier of Li atom on antimony surface is 0.07 eV, and a smaller barrier height is beneficial to the rapid charge-discharge process. To sum up, antimony has a good potential as an anode material for lithium ion batteries.
Surface plasmon polaritons’ propagation controlled by metal-photorefractive material composite holographical structure
Authors: Chen Lu , Chen Yue-Gang ,   School of Physics, Guizhou University, Guiyang 550025, China
Published: December 2020

Control of surface plasmon polaritons’ (SPPs’) propagation is of great importance. The groove structure in metal surface, designed by the surface electromagnetic wave holography (SWH) method, can control the SPPs’ propagation effectively. In the SWH method, all designed groove structures are etched in metal surface. The fabrication method is confined to the etching method, such as the focused ion beam lithography and electron beam lithography. And the designed structures cannot implement the real-time control of SPP propagation. We propose a new method to control SPPs’ propagation through metal-photorefractive material composite holographical (MPRCH) structures. A photorefractive material film is coated on the metal surface, and the reference SPP wave interferes with the object SPP wave in the photorefractive material film. The interference intensity is recorded by the photorefractive material film, forming the MPRCH structure. The MPRCH structure is used to control the propagation of relatively weak SPP waves. The finite difference time domain method is used to verify the method. We simulate that a reconstructed SPP wave is incident into the structure region and interacts with the structure. The incident wave is reflected and scattered by the designed MPRCH structure. These reflected and scattered wave are propagated and superposed, forming the desired SPP wave on the metal surface. Simulation results show that the MPRCH structure can control SPPs’ propagation effectively and realize the functions such as SPP wave aside single-point focusing, two-point focusing, generating zero-order and first-order Gaussian SPP beams. It is found that the optimal thickness of the MPRCH film is \begin{document}$3.3\;{\text{μ}}{\rm{m}}$\end{document} and modulation amplitude of refractive index is 0.06. This method extends the SPP device fabrication methods, and gets rid of the etching method. Based on the investigation, the real-time controlling of SPP wave may be realized through the MPRCH structure. The study provides a new idea for realizing the all-optical control of SPP propagation, thus making it possible to implement the all-optical control of SPP and further switch.
Optofluidic fluorescence resonance energy transfer lasing in a polydimethylsiloxane microfluidic channel
Authors: Li Dong-Yang , Zhang Yuan-Xian , Ou Yong-Xiong , Pu Xiao-Yun ,   Depatment of Physics, Yunnan University, Kunming 650091, China
Published: December 2020

A bare quartz fiber with single refractive index is implanted into a polydimethylsiloxane (PDMS) microfluidic channel. The lasing gain medium consists of fluorescence resonance energy transfer (FRET) donor-acceptor dye pair Rhodamine B (RhB)-LDS821 mixture solution, which has a lower refractive index than that of the optical fiber and flows in the PDMS microfluidic channel. The circular cross section of the optical fiber forms a ring resonator and hosts high-quality (Q) whispering gallery modes (WGMs). Pumping along the optical fiber axis, the FRET characteristic parameters, i.e., the FRET efficiency \begin{document}$\eta $\end{document} and the Förster distance R0 of donor-acceptor dye pair, are firstly studied by using a continuous wave laser as a pump light source with a wavelength of 532 nm. The excited states are thencreated in the donor (RhB) by using a pulse laser with a wavelength of 532 nm and whose energy is transferred into the adjacent acceptor (LDS821) through the non-radiative FRET mechanism. Finaly, the emission of LDS821 iscoupled into the WGM of the ring resonator to lase. Due to the high energy transfer efficiency and high Q-factor, the acceptor shows a lasing threshold as low as 1.26 \begin{document}${\text{μ}}{\rm J}$\end{document}/mm2.
Chaotic motion of piezoelectric material hyperbolic shell under thermoelastic coupling
Authors: Li Lin-Li  , Xue Chun-Xia  ,   College of Science, North University of China, Taiyuan 030051, China
Published: December 2020

Piezoelectric material, which exhibits excellent electro-mechanical conversion properties, is widely used in smart sensors and structures for sonar systems, weather detection and remote sensing. Hyperbolic shell structure made of piezoelectric material is liable to break down when it is used in high temperature environment, which is caused by the unexpected chaotic dynamic motion under the coupling effect of thermal filed and force field. Therefore, the chaotic nonlinear dynamic vibration of simply-supported piezoelectric material hyperbolic shell is studied under the combined action of temperature field and simple harmonic excitation. Based on the theory of finite deformation, the non-linear vibration equation and coordination equation of the hyperbolic shell are established. The non-linear dynamic equation of the structure is obtained by the Bubnov-Galerkin principle. The corresponding undisturbed Hamilton system has a homoclinic orbit. Using Melnikov function, the chaotic motion condition of the dynamic system under the criterion of Smale-horseshoe transformation is obtained. Furthermore, the mathematical model is established by Simulink software and the numerical simulations are performed by the fourth-order Runge-Kutta method. The simulation results accord well with those from the Melnikov method. The bifurcation diagram, the Lyapunov exponent diagram, the phase diagram and Poincaré section diagram are acquired to analyze the influence of temperature field on the non-linear characteristic of piezoelectric material hyperbolic shell system. When the temperature is close to 32℃ and 41℃, the Lyapunov index is less than 0 and the corresponding movement of the system is in the periodic zone, which is the same as that for a temperature range from 36℃ to 37℃. When the Lyapunov index is greater than 0, the corresponding movement of the system is in chaos zone. Therefore, the change of temperature has an additional effect on the stiffness of the system which affects the vibration of the system. The chaos and periodic zones of the system alternate with the increase of temperature and the vibration characteristics of the system can be controlled by changing the temperature field. Therefore, adjusting the temperature field can control the motion state of the system, which helps to improve reliability of the structure.
Effect of surface topography on emission properties of hot-cathode
Authors: Hao Guang-Hui , Li Ze-Peng , Gao Yu-Juan , Zhou Ya-Kun ,   Beijing Vacuum Electronics Research Institute, Beijing 100015, China
Published: December 2020

As a kind of influence factor, the surface topography determines the uniformity and current of peritoneal impregnated diffusion cathode (M-type dispenser cathode) emitted electrons. It can be seen from the emission characteristics of the cathode in the micro-range that the lathe tool grains at the cathode surface can affect the current uniformity, and the electron emission will be enhanced. But the distribution of the lathe tool grains is uncontrollable. Therefore to fully utilize the promoting effect of surface stripes on electron emission, the effect of surface topography onthe emission property of M-type dispenser cathode is investigated. And the simplest way to change the surface morphology of cathode surface is to fabricate a periodic stripe structure which can be divided into unidirectional stripe structure and orthogonal bidirectional stripe structure. And the orthogonal bidirectional stripe structure at the cathode surface can form micro-tip structure like the spindle cathode. To research the effect of surface topography on the emission properties of M-type dispenser cathode, the periodic stripe structures on the cathode surface with different sizes and shapes are processed by the femtosecond leaser in the fabrication of micro/nano-size microstructure. The cathodes are prepared with the same degassing and activated method. The test results of the cathodes show the periodic stripe structure on the cathode surface can effectively enhance the cathode electron emission capability. The emission current density of cathode with orthogonal bidirectional stripe is higher than that of cathode with unidirectional stripe. And with the stripe size declining, the emission capability is gradually enhanced. Also, this phenomenon occurs in the scandium-impregnated diffusion cathode. With the help of simulation of cathode surface topography, it is shown that the top of tip has a great electron emission capability for its strong electric field. When the ratio of bottom radius to height of the tip (r/h) is small, the side area is the main region of cathode electron emission. But as the r/h keeps decreasing, the main electron emission region is transferred from the side of tip to the top of tip, and the field assisted effect is the major component of the cathode electron emission.
Effect of aggregation morphology of nanoparticles on thermal conductivity of nanofluid
Authors: Zhang Zhi-Qi , Qian Sheng , Wang Rui-Jin , Zhu Ze-Fei ,   School of Mechanical Engineering, Hangzhou Dianzi Unversity, Hangzhou 310018, China
Published: December 2020

The great interest of many researchers has been aroused in recent two decades due to the great heat transfer enhancement of nanofluid as a heat transfer medium. The reason why the nanofluid can enhance heat transfer is that a number of nanoparticles are suspended in the carry fluid. Most of researchers believe that the microconvection induced by Brownian motion of nanoparticle, the nanolayer around the nanoparticle, the aggregation of nanoparticles and near-field radiation are the underlying mechanisms for heat transfer enhancement by nanofluid. However, contradictories and inconsistencies among experimental results, theoretical results and numerical results are existent commonly because the mechanism of heat transportation by nanoparticles remains unclear so far. Quite a few researches have proven that the aggregation of nanoparticles is one of the important mechanisms for elevating the effective thermal conductivity (ETC) of nanofluid. However, the aggregation morphology (AM) of nanoparticles evaluated by fractal dimension (FD) will greatly influence the thermal conductivity of nanofluid. Unfortunately, all of the existing ETC models are based on the effective medium theory under the assumption of " static state” and " homo-dispersion”. In the present work, equilibrium molecular dynamics (EMD) simulations are carried out to calculate the thermal conductivity of Cu-Ar nanofluid via Green-Kubo formula. In existing researches, fractal dimensions of the aggregations with various morphologies are obtained by Schmidt-Ott equation. Comparisons between the ETC and FD of the nanofluid with same volume fraction show that lower FD can possess greater ETC. It is the first time that the quantitative relationship between ETC and FD has been analyzed. In addition, the difference between loose and compact aggregation can be read out of the pair correlation function near nanoparticles. And the solvent atoms in nanolayer are mobilized and dynamically balanced. The results obtained in the present research are conducible to understanding the influence of AM of nanoparticles on the ETC of nanofluid.
Non-collinear magnetism and electronic transport of boron or nitrogen doped zigzag graphene nanoribbon
Authors: Liang Jin-Tao , Yan Xiao-Hong , Zhang Ying , Xiao Yang ,   Department of Applied Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Published: December 2020

Zigzag graphene nanoribbon (ZGNR) is important for novel carbon-based spintronic applications. Currently, most of ZGNR spintronic studies focus on the collinear magnetism where the up-spin and down-spin are separated clearly. But in some cases, e.g. doping and adsorption, the magnetization profile can be modulated and thus noncollinear magnetism can occur. In order to shed light on possible noncollinear magnetism in ZGNR, we study non-collinear magnetism and electronic transport of boron or nitrogen-doped zigzag graphene nanoribbon based on noncollinear density functional theory and non-equilibrium Green's function method. For pristine ZGNR, our results show that the ZGNR presents helical magnetization distribution due to noncollinear magnetization in left and right lead. As the ZGNR is doped with boron and nitrogen atoms, the ZGNR shows a characteristic two-zone feature in the magnetization distribution. Near the dopant site, the magnetic moment of carbon atom is small. However, the magnetic moments of carbon atoms in the left (right) region of dopant are close to those of the left (right) lead. Such a feature provides the possibility of constructing domain walls with various widths on the edge of ZGNR. Moreover, the transmission at the Fermi level (E = 0 eV) decreases with the increase of relative angle between magnetizations of left and right lead, indicating that the spin-flip scattering dominates the electronic transport. However, at E = ±0.65 eV, there is a transmission dip with low transmission, which implies that the dopant induces the strong backscattering. To understand the origin of this dip, we calculate the density of states (DOS) and project the DOS onto each atom of doped ZGNR. The projected DOS shows a large and broad peak at E = −0.65 eV for N-doped ZGNR but at E = +0.65 eV for B-doped ZGNR. The consistency between the position of dip in transmission and the position of peak in DOS indicates that the transmission dip mentioned above is attributed to strong backscattering from the dopant-induced bound state. Our theoretical results are expected to be useful for understanding the noncollinear magnetism and spin scattering in the doped ZGNR-based devices. Also, our work provides a considerable insight into the design of ZGNR-based nanoelectronic devices, such as the transistor based on spin transfer torque effect.
Characteristics of convergence zone formed by bottom reflection in deep water
Authors: Zhang Peng  , Li Zheng-Lin  , Wu Li-Xin  , Zhang Ren-He  , Qin Ji-Xing  ,   1. State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China;,   2. School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

There appears a convergence effect on the sound filed under the condition of sound channel in the deep sea due to the refraction effect of the sea water. For the deep water environment with an incomplete channel, sea bottom has an important influence on sound propagation. A long-range sound propagation experiment was conducted in the South China Sea in April 2018. Hyperbolic frequency modulated (HFM) signals with a frequency band of 250-350 Hz are transmitted by an acoustic source which is towed at a speed of 4 knots away from a vertical line array (VLA). The VLA consists of 20 hydrophones which are arranged from 85 m to 3400 m with an unequal depth space. Using the data collected in the experiment, the effects of bathymetry variation on sound propagation are studied. The physical causes of the seafloor reflection convergence phenomenon are explained by using the parabolic equation combined with ray theory. The observed phenomenon is different from the convergence phenomenon in the typical deep water environment, the spatial variation of bathymetry contributes to the formation of the seafloor reflection convergence zone in advance, and the sound intensity in part of shadow zone is significantly increased. Due to the reflection from the seabed, two obvious seafloor reflection convergence zones are observed near the range of 20 km and 40 km respectively, in which both gains increase up to 10 dB, and a high sound intensity area is formed in the shadow zone near the range of 11 km, where the gain is less than the gains in the two convergence zones. In addition, the grazing angle of the sound ray reaching the second convergence zone is smaller than that reaching the first convergence zone when the receiving depth is the same as the source depth, and the rays with smaller glancing angle have less reflection loss, which leads to a higher gain in the second convergence zone. As the water depth becomes gradually shallower with range increasing, the convergence zone near the range of 51 km under the SOFAR channel is destroyed, and the sound field energy in the corresponding range is much smaller since the number of arriving refracted sound rays is reduced. In the first convergence zone, the path of arriving rays is gradually increased as the receiver becomes deeper. Therefore, the arrival structure tends to be complicated, and the multi-path effect is more obvious. The study result is meaningful for the performance analysis of sonar in complex deep water environment.
Coherence and information conservation and their applications in Mach-Zehnder interferometer
Authors: Fu Shuang-Shuang , Luo Shun-Long , Sun Yuan ,   School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China,   Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, China,   School of Mathematical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Coherence and complementarity are two important themes in quantum mechanics, which have been widely and thoroughly investigated. Recently, with the rapid development of quantum information theory, various measures have been introduced for quantitatively studying the coherence and complementarity. However, most of these studies are independent of each other in that they focus on only one theme, for example, the wave-particle duality and Heisenberg uncertainty principle are usually regarded as manifestation of Bohr’s complementary principle, while coherence is a quantum feature closely related to quantum superposition. During the past few years, there has been a flurry of research interest in the study of quantum coherence from the quantum resource-theoretic point of view. In this paper, we establish two information conservation relations and employ them to characterize complementarity and quantum coherence. As an illustration of the main results, we discuss these two themes in the Mach-Zehnder interferometer. Our study reveals that these two quantum themes are closely related to each other. Our main results are listed as follows. Firstly, we establish two information conservation relations, one is based on " Bures distance versus fidelity” and the other based on " symmetry versus asymmetry”. Then we employ these information conservation relations to investigate coherence and complementarity. Specifically, we provide an explanation of the " Bures distance versus fidelity” trade-off relation from the information conservation perspective, establish the link between the information conservation relation and wave-particle duality, and derive the famous Englert inequality concerning " fringe visibility versus path distinguishability” from the information conservation relation. Furthermore, in the general framework of state-channel interaction, we derive " symmetry versus asymmetry” trade-off relation and explain it as an information conservation relation, reveal its intrinsic relations with coherence and complementarity. Lastly, we demonstrate that the two information conservation relations are closely interrelated, and we also discuss the coherence, decoherence and complementarity in the Mach-Zehnder interferometer, explicitly, we reveal that the Bures distance can be regarded as a lower bound of the asymmetry of state-channel interaction while fidelity is an upper bound of the symmetry of state-channel interaction. We expect that our information conservation relation can provide a unified framework for the study of coherence and complementarity.
Quantum coherence
Authors: Li Bao-Min , Hu Ming-Liang , Fan Heng ,   Solid State Quantum Information and Computation Laboratory, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   University of Chinese Academy of Sciences, Beijing 100049, China,   School of Science, Xi'an University of Posts and Telecommunications, Xi'an 710121, China,   Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Quantum coherence is not only a fundamental concept of quantum mechanics, but also an important physical resource for quantum information processing. Along with the formulation of the resource theoretic framework of quantum coherence, the quantification of coherence is still one of the recent research focuses. Quantum coherence is also very fragile, and the environmental noise usually induces a system to decohere. Hence it is also an important subject to make clear the dynamical behavior and to seek a flexible way of preserving quantum coherence of an open quantum system. Besides, there are many potential applications of quantum coherence in quantum many-body system, quantum thermodynamics, quantum biology and other related fields. We review in this paper the resource theoretic framework for quantifying coherence and the relevant quantum coherence measures defined within this framework which includes the relative entropy of coherence, the l1 norm of coherence, the entanglement-based measure of coherence, the convex roof measure of coherence, and the robustness of coherence. We also review the dynamical behaviors of quantum coherence for certain open quantum systems, the coherence generating and breaking power of typical quantum channels, and the freezing phenomenon of quantum coherence. Moreover, we exemplify applications of quantum coherence in Deutsch-Jozsa algorithm, Grover search algorithms, and the study of quantum phase transitions in multipartite systems. We hope that these results may provide not only an overview of the relevant field, but also an outlook of the future research direction of this exciting field.
Photon spectrum and angle distribution for photon scattering with relativistic Maxwellian electrons
Authors: Li Shu  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
Published: December 2020

Description of photon scattering with relativistic Maxwellian electrons is numerically complex, and computationally time consuming for the final photon energy and angle distribution. A Monte Carlo method is used to simulate photon scattering with relativistic Maxwellian electrons. The main idea of this method is to transform the interaction of photonmoving electrons in the laboratory coordinate system into that in a new coordinate system in which the electrons are at rest, then to use the exact Klein-Nishina formula to describe this interaction and obtain the outgoing photon energy and angle, finally, to transform it into the primary laboratory coordinate system. In sum, there are eight steps, i.e.two two-dimensional (2D) transforms and two three-dimensional (3D) transforms and two Lorentz transforms, and two sampling. Repeating this process, summarizing and averaging all computed energy values and angles, the distribution of scattered energy and angle can be obtained.
A Monte Carlo processor is developed to simulate a photon of any energy interacting with electrons at any temperature. Some typical cases are simulated. The computed results indicate that the photon spectrum is different from that of the photon scattering with rest electrons remarkably, especially for a low energy photon scattering with the high temperature electrons. The main phenomena are Doppler broading and blue shifting. The moving electron can extend the distribution of the outgoing photon energy, and for a low energy photon scattering with the high temperature electrons, the photon maybe obtains the energy from electrons with significant probability. The angle distribution is very complicated, and it is determined by the incident photon energy, the outgoing photon energy, and the electron temperature. This processor can calculate the energy scattering differential cross-sections or energy-angle scattering double differential cross-sections, and provide the data in a tabulated form for other transport methods.