bluuebunny/crossref_metadata_2025 huggingface dataset:
Guided circumferential wave propagation characteristics for porous cylinder immersed in infinite fluid
Authors: Su Na-Na , Han Qing-Bang , Jiang Jian ,   College of Internet of Things Engineering, Hohai University, Changzhou 213022, China
Published: December 2020

Underground water, gas and oil all exist in the fractured or porous strata. Waves that propagate through porous cylinder immersed in infinite fluid are of considerable interest in the estimation of porous parameter, such as an underwater concrete column may present pore characteristics after a long time water immersion. Compared with longitudinal guided wave, circumferential guided wave has its advantages in the ultrasonic nondestructive inspection of porous cylinder. In order to investigate the propagation characteristics of guided waves in a porous cylinder immersed in infinite fluid and analyze the effects of the porous medium parameters on the dispersion characteristic, a model of porous cylinder surrounded by fluid is built. Based on the elastic-dynamic theory and modified liquid-saturated porous theory, the characteristic equation of guided wave is established, and the dispersion curves are obtained numerically. The effects of cylindrical radius and pore parameters on the propagation characteristics of guided waves are discussed; the attenuation characteristics of guided waves are also analyzed; the time domain waveforms of the guided circumferential waves are obtained by numerical inversion, and the influence of porous parameters on waveforms is simulated. It is found that the dispersion curves are similar to that of elastic cylinder in the fluid, there exist multiple mode guided waves and approximate shear velocity of medium for higher modes, and higher order modes are more affected by the radius, but it does not change the tendency of curve. The phase velocity decreases with porosity increasing at the same frequency and the effect of porosity on higher order modes is greater than that on mode 1; due to the dissipation in the medium, the attenuation increases porosity increasing. It can be seen from the transient responses that the wave packets move backward and the displacement amplitude decreases with the porosity increasing. The characteristics of the inversed transient response are in good agreement with theoretical dispersion and attenuation. The results show that the propagation of guided circumferential wave is affected by the pore parameters, especially for porosity, which can provide a theoretical reference for the non-destructive evaluation of the porous cylinder surrounded by infinite fluid.
Control on interaction of Airy-Gaussian beams in competing nonlinear medium
Authors: Chen Wei-Jun , Song De , Li Ye , Wang Xin , Qin Xu-Lei , Liu Chun-Yang ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

An investigation of control on the interaction of Airy-Gaussian beams (AiGBs) in cubic focusing and quintic defocusing competing nonlinear medium is performed by the split-step Fourier transform method. When the initial launch angle v is zero, two in-phase AiGBs attract each other and the breathing soliton with decaying period or soliton with invariant intensity can form in the case of weaker quintic defocusing nonlinearity. However, the interaction between two in-phase AiGBs under stronger quintic defocusing causes the average width of the breathing soliton to increase and even the beam bifurcation to occur, leading to the generation of soliton pairs. For the out-of-phase case, they repel each other, and the repulsive force increases monotonically with the increase of the quintic defocusing nonlinearity. When the initial launch angle for each of AiGBs is not zero, mutual attraction and repulsion can be exhibited during their interactions by adjusting the sign of v  and the interval d. For the in-phase case, if v < 0 and d < 0 or v > 0 and d > 0, there are strong repulsive force and weak attraction between the two AiGBs, resulting in the formation of soliton pairs, and with the decrease of the interval, the attraction becomes greater. When the interval is small enough, the overlapping of the light field can make the nonlinear effect identical to the diffraction effect, the attraction between the two AiGBs increases, while the repulsion force is almost zero, and then a single breathing soliton can be generated in the center of the two AiGBs. If v < 0 and d > 0 (big enough) or v > 0 and d < 0, the constructive interference between two AiGBs causes the autofocusing beams first to be generated, then to repel each other, and the soliton pairs can form. For the out-of-phase case, if v < 0 and d < 0 or v > 0 and d > 0, the repulsion between the two AiGBs becomes bigger, and the repulsion increases with |v| monotonically. If v < 0 and d > 0 or v > 0 and d < 0, the elastic collision between the two AiGBs shows the phenomenon: first attracting and then repelling mutually. When both v and d are small enough, soliton pairs cannot form due to the unbalance between the strong diffraction effect and weaker nonlinear effect induced by the destructive interference.
Influence of photoionization rates on positive streamer branching in atmospheric air
Authors: Tu Jing-Yi , Chen She , Wang Feng ,   College of Electrical and Information Engineering, Hunan University, Changsha 410082, China
Published: December 2020

Streamer is a strong ionizing region which advances very quickly in gases, liquids and solids. Streamer is a low-temperature plasma, which produces a variety of chemically reactive substances efficiently. So, streamer discharge has been widely adopted in industry. Furthermore, streamer is the initial stage of electric breakdown in long air gap. Studying the streamer discharge characteristics and its mechanism is the basis of external insulation in power transmission systems.Streamer branching is a significant characteristic during its development. Lichtenberg figure is the first clear recording of the filamentary structure of streamers. One of acceptable explanations is that the random fluctuations of the electron density ahead of streamer trigger branching. Furthermore, photoionization provides the necessary free electrons for the development of positive streamers. The experimental results show that the branching characteristics are closely related to the photoionization rate in streamer head. The streamer shows higher possibility of branching if the photoionization rate decreases. Since previous experiment is indirect evidence of this deduction, we turn to numerical models to study the influence of photoionization rates on positive streamer branching in atmospheric air. A three-dimensional particle-in-cell model with Monte Carlo collision (PIC-MCC) scheme called Pamdi3D (Teunissen J, Ebert U 2016 Plasma Sources Sci. Technol. 25 044005) is employed in this paper. The development and branching of positive streamersin a millimeter-scale needle-plane gap are simulated at atmospheric pressure. Different streamer branching behaviors are investigated by artificially changing the nitrogen-oxygen ratio, the absorption cross section of oxygen, and the photoionization efficiency coefficient.The effects of different photoionization parameters are systematically studied. When the nitrogen-oxygen ratio, photon absorption cross section or photoionization efficiency coefficient are reduced, the streamer branching occurs earlier in three cases after reducing the photoionization rate. These results imply that the streamer shows higher possibility of branching if the photoionization rate decreases. When the streamer propagates in a non-uniform electric field region and the photoionization rate decreases to a certain value, it is believed that the seed electron distribution is more susceptible to random fluctuations. It will lead to instability in the space charge layer of streamer, thus causing the streamer to branch. Hence it is proposed that streamer branch will be triggered more easily if the photoionization rate in the streamer head decreases, in the case without considering other seed electron sources.
Quantum transport relating to impurity quantum dots in silicon nanostructure transistor
Authors: Wu Xin-Yu , Han Wei-Hua , Yang Fu-Hua ,   Engineering Research Center of Semiconductor Integrated Technology, Beijing Engineering Research Center of Semiconductor Micro-Nano Integrated Technology, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China,   Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

As the characteristic size of the transistor approaches to its physical limit, the effect of impurities on device performance becomes more and more significant. The number of impurities and the range of impurity fluctuation become very limited in channel space less than 10 nm, and ionized impurities in local nano-space can even exhibit quantum dot characteristics, providing two discrete levels for charge transport. The behaviour of carrier tunnelling through quantum dots induced by ionized impurities can reveal the abundant quantum information, such as impurity ionization energy, coulomb interaction energy, electron activation energy, orbital level filling, and spin of local electrons. Quantum transport properties are also different in different doping concentrations because whether the quantum states overlap depends on the impurity atom spacing. The silicon nanostructure transistors using impurity atoms as building blocks of quantum transport are also called dopant atom transistors, which are not only compatible with complementary metal oxide semiconductor (CMOS) technology, but also expected to be the basic components of quantum computing circuits in the future. So far, their operating temperature is relatively low due to the shallow ground state energy level of impurity atoms. It is of great significance to study the quantum transport properties in dopant atom transistors and to observe quantum effects among them at room temperature. In this article, the quantum transport properties in single, discrete and coupled impurity atomic systems are described in detail by combining Anderson localization theory and Hubbard band model. Quantum transport in a discrete impurity atomic system is not only controlled by gate voltage, but also dependent on temperature. The current transport spectrum in the coupled impurity atomic system reveals more complex quantum dot characteristics. Single atom transistor can regulate quantum transport only by one impurity atom, which represents the ultimate scale limit of solid state devices. In addition, the methods of improving the operating temperature of dopant atom transistors are also systematically introduced, thereby laying a foundation for their practical applications.
Shot noise measurement for tunnel junctions using a homemade cryogenic amplifier at dilution refrigerator temperatures
Authors: Song Zhi-Jun , Lü Zhao-Zheng , Dong Quan , Feng Jun-Ya , Ji Zhong-Qing , Jin Yong , Lü Li ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China,   Centre de Nanosciences et de Nanotechnologies (C2N), CNRS, University Paris-Sud, University Paris-Saclay, Palaiseau 91120, France
Published: December 2020

Traditionally, electrical noise is considered as an interference source for low level measurements. Shot noise is the current fluctuation caused by the discreteness of electrons. In a mesoscopic system, shot noise is sensitive to the interaction of charge carriers. Since the 20th century, it has been found that the shot noise measurement can provide the information about quantum fluctuations, which cannot be measured with traditional transport measurement method. It is usually difficult to measure weak noise signal at ultra- low temperature due to technical difficulties. It is necessary to mount a cryogenic preamplifier close to the sample to improve signal-to-noise ratio and to increase the bandwidth. Therefore, the ultra-low background noise and the power consumption of the amplifier should be used. In this report we present a shot noise measurement system at dilution refrigerator temperatures. We also introduce and analyze the noise model of our shot noise measurement system. With customized high electron mobility transistors, we make a series of ultra-low noise cryogenic preamplifiers. All the electronic components of the amplifier are packed into a shielding box, which makes the installation of the cryogenic amplifier more convenient. The amplifier is mounted on the 4 K stage of a dry dilution refrigerator and the total power consumption is less than 0.754 mW. The gains and the background noises of the amplifiers are calibrated with the Johnson-Nyquist noise of the combination of a superconducting resistor and a normal resistor at various temperatures. The measured input referred noise voltage can be as low as 0.25 nV/√Hz. In this report, the performance of the system is demonstrated by the shot noise measurement of an Al/AlOx/Al tunnel junction at various temperatures. Above the superconducting transition temperature of aluminum, the measured Fano factor of the system is very close to 1, which is in a good agreement with the theory prediction.
Synthesis of diamond co-doped with B and S under high pressure and high temperature and electrical properties of the synthesized diamond
Authors: Li Yong , Wang Ying , Li Shang-Sheng , Li Zong-Bao , Luo Kai-Wu , Ran Mao-Wu , Song Mou-Sheng ,   Department of Physics and Electrical Engineering, Tongren University, Tongren 554300, China,   School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China
Published: December 2020

As is well known, diamond is extensively used in many fields, because of its excellent properties, such as its hardness, high thermal conductivity, high electron and hole mobility, high breakdown field strength and large band gap (5.4 eV). However, its application in semiconductor area needs to be further understood, because it is irreplaceable by conventional semiconductor materials, especially in the extreme working conditions. Furthermore, the preparation of n-type diamond semiconductors is still an unsolved problem. The reason is that an effective donor element has not yet been found. Recently, both the theoretical and experimental studies show that it is difficult to obtain n-type diamond semiconductor with excellent properties by doping single element in the synthetic system. In this paper, diamond single crystals co-doped with B and S are successfully synthesized in FeNiMnCo-C system at a pressure of 6.5 GPa and temperature ranging from 1280 ℃ to 1300 ℃, by using temperature gradient method. The impurity defects in the synthesized diamond single crystals are characterized by Fourier infrared absorption spectra and the results indicate that the corresponding characteristic absorption peaks of B and S are located at 1298 cm–1 and 847 cm–1, respectively. Furthermore, the absorption attributed to B-S group is not detected. The N concentration of the synthesized diamond crystals decreases to 195 ppm, resulting from the incorporation of B and S impurities into the diamond lattices. Additionally, the electrical properties of the typical diamond single crystals are measured in virtue of Hall effects at room temperature. The measurement results display that the electrical conductivity of the diamond doped with B is obviously enhanced, resulting from the involvement of the S when B addition amount is fixed in the synthesis system. Hall mobility of the corresponding diamond crystals increases from 12.5 cm–2·V–1·s–1 to 760.87 cm–2·V–1·s–1. And then, the relative proportion of S and B will determine the p/n properties of the obtained diamond. In order to further study the electrical properties of diamond, first-principles calculations are adopted and the theoretical calculation results show that the impurity elements involved in the obtained diamond can affect the band structures of the synthetic diamond crystals, which is consistent with the experimental result.
Electrochemical model of lithium ion battery with simplified liquid phase diffusion equation
Authors: Liu Zheng-Yu , Yang Kun , Wei Zi-Hong , Yao Li-Yang ,   School of Mechanical Engineering, Hefei University of Technology, Hefei 230009, China,   Key Laboratory of Industrial Safety and Emergency Technology of Anhui Province, Hefei 230009 China
Published: December 2020

The pseudo-two-dimensional (P2D) model is the most widely used electrochemical model for lithium-ion batteries. Because of the complexity and the difficulty in using the complete P2D model, many simplified P2D models, such as the single particle model (SP model) and the parabolic profile approximation model (PP model), have been proposed. However, the using of the SP model can cause a large amount of precision to lose in its simplified process, while the PP model has a high complexity. In this paper, we propose a liquid phase simplification P2D (LSP2D) model. The using of the LSP2D model has a small precision loss and a relatively low complexity. The LSP2D model is based on the electrochemical average kinetics of the lithium ion battery. We first simplify the terminal voltage into an equation containing only the solid phase concentration cs and the liquid phase concentration ce. Then we use the partial differential equation to represent the solid phase concentration cs and the liquid phase concentration ce, and then obtain a final model. The simulation environment is based on COMSOL, and the simulation results show that when the discharge rate is 1C, the estimation accuracy and speed from the LSP2D model are similar to those from the SP model. But when the discharge rate is 3C, the estimation time from the LSP2D model is reduced by 99.73% compared with that from the P2D model, and the estimation accuracy is greatly improved compared with the estimation accuracy from the SP model.
Measurement of femtosecond pulses based on transient grating frequency-resolved optical gating
Authors: Huang Hang-Dong , Teng Hao , Zhan Min-Jie , Xu Si-Yuan , Huang Pei , Zhu Jiang-Feng , Wei Zhi-Yi ,   School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710126, China,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Femtosecond pulse measurement of ultrafast spectrum is one of the important research directions in the ultrafast laser field. The conventional femtosecond pulse autocorrelation method is implemented by measuring the autocorrelated frequency-doubling signal, and the frequency-doubling signal has wavelength selectivity, so the femtosecond pulse measurement for the case of different central wavelengths needs to replace different frequency-doubling crystals, which is very inconvenient. This paper reports a kind of modified transient grating frequency resolution optical gating for measuring the femtosecond pulses. The method combines frequency-resolved optical gating (FROG) method with four-wave mixing. Its basic process is to divide the pulse to be measured into three beams. Two of the pulses can reach spatiotemporal coincidence on optical medium through precise delay control and focus. The other pulse interacts with the transient grating, and serves as the detection light to produce signal light. The spectrum and delay time of the signal light are measured by a spectrometer, and the spectrum and electric field information of the femtosecond pulse to be measured are obtained through the inversion iterative algorithm. Because this method only needs the power density of the measured light to reach the third-order nonlinear effect, it can be applied to the femtosecond pulse measurement of any central wavelength. We use this method to measure the femtosecond pulses with the central wavelengths of 800 nm and 400 nm respectively, and the ultra-wide spectrum femtosecond pulses with the period magnitude of sub-10 fs, and compare the measurement results with the results obtained with the conventional interferometric autocorrelation instrument. They are basically consistent. The experimental results show that our frequency-resolved optical switching method based on transient grating is very effective for measuring the femtosecond pulses with different central wavelengths and pulse widths.
Numerical study of nonlinear Schrödinger equation with high-order split-step corrected smoothed particle hydrodynamics method
Authors: Jiang Tao , Huang Jin-Jing , Lu Lin-Guang , Ren Jin-Lian ,   School of Mathematical Sciences, School of Hydraulic, Energy and Power Engineering, Yangzhou University, Yangzhou 225002, China
Published: December 2020

To improve the numerical accuracy and computational efficiency of solving high-dimensional nonlinear Schrödinger/Gross-Pitaevskii (NLS/GP) equation by using traditional SPH method, a high-order split-step coupled with a corrected parallel SPH (HSS-CPSPH) method is developed by applying virtual particles to the boundary. The improvements are described as follows. Firstly, the nonlinear Schrödinger equation is divided into linear derivative term and nonlinear term based on the high-order split-step method. Then, the linear derivative term is solved by extending the first-order symmetric SPH method in explicit time integration. Meanwhile, the MPI parallel technique is introduced to enhance the computational efficiency. In this work, the accuracy, convergence and the computational efficiency of the proposed method are tested by solving the NLS equations with the periodic and Dirichlet boundary conditions, and compared with the analytical solutions. Also, the singularity of solitary waves under the periodic boundary condition is accurately obtained using the proposed particle method. Subsequently, the proposed HSS-CPSPH method is used to predict the results of complex two-dimensional and three-dimensioanl GP problems which are compared with other numerical results. The phenomenon of singular sharp angle in the propagation of nonlinear solitary wave and the process of quantum vortex under Bose-Einstein condensates with external rotation are presented accurately.
Clean transfer of chemical vapor deposition graphene film
Authors: Zhang Xiao-Bo , Qing Fang-Zhu , Li Xue-Song ,   School of Electronic Science and Engineering, State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

Graphene is believed to have promising applications in many fields because of its unique properties. At present, graphene films are mainly prepared on Cu substrates by chemical vapor deposition. The graphene films prepared in this way need to be transferred to the target substrates for further applications, while the transfer process inevitably induces contamination on graphene, which affects the properties of graphene and the performance of devices. Therefore, how to reduce or avoid contamination and realize the clean transfer of graphene is an important topic for the development of graphene transfer technology, which is the major topic of this review. Here, firstly, the transfer techniques of graphene are briefly reviewed, which can be classified according to different rules. For example, it can be classified as direct transfer, with which graphene is directly stuck to the target substrate, and indirect transfer, with which graphene is indirectly transferred to the target substrate with a carrier film. According to the way of separating graphene and the growth substrate, it can also be classified as dissolving transfer, with which the substrate is dissolved by chemical etchant, and delaminating transfer, with which graphene is delaminated from the substrate. Then the origins of contamination are discussed followed with how contamination affects graphene properties. The main contaminations induced by transfer are ions from the etchant and electrolyte, undissolved metal or metal oxide particles, and organic residues from carrier films. Contaminations have a great influence on the electrical, thermal and optical properties of graphene. Then the up-to-date progress of techniques for clean transfer is reviewed, including modifying the cleaning process or using alternative etchant/electrolyte to remove or suppress metal contamination and annealing graphene or using alternative carrier films (e.g., more dissoluble materials) to remove or suppress organic residues. Finally, the challenges of clean transfer of graphene are summarized, and future research directions and opportunities are prospected. This review not only contributes to the research of graphene film transfer technology, but also has great reference value for the clean fabrication of the whole two-dimensional materials and devices.
Temperature dependence of single-event transient response in devices with selective-buried-oxide structure
Authors: Gao Zhan-Zhan , Hou Peng-Fei , Guo Hong-Xia , Li Bo , Song Hong-Jia , Wang Jin-Bin , Zhong Xiang-Li ,   Department of Material Science and Engineer, Xiangtan University, Xiangtan 411105, China,   Northwest Institute of Nuclear Technology, Xi’an 710024, China
Published: December 2020

The silicon-on-insulator (SOI) device has been found to possess low leakage current and high operation speed due to reduced internal capacitances. The sensitive volume for charge collection in SOI device is smaller than that in bulk-silicon device, which improves the ability of SOI devices to resist single-event effect (SEE). In spite of these benefits, the SOI device has certain undesirable effects such as the kink effect. To mitigate the kink effect, selective-buried-oxide (SELBOX) SOI structure has been introduced. Space-borne electronic circuits based on SOI technology recently have been used in high radiation and extreme temperature environments. However, temperature affects internal carrier transport process and impact ionization process, which makes single-event transient (SET) pulse widths increased. Most of previous researches regarding temperature dependence of SEE were for SOI floating-body devices. But the influence of operating temperature on SEE of SELBOX SOI devices are yet unclear. In this paper, an SOI floating-body device and a SELBOX SOI device under 90 nm process are established by three-dimensional device simulation, and then temperature dependence of SET response in partially depleted SOI inverter chains is studied by a mixed-mode approach over a temperature range from 200 K to 450 K. Simulation results show that the N-type SELBOX SOI device has a better ability to resist SEE than the floating-body device, while the P-type SELBOX SOI device has the same ability to resist SEE at high linear energy transfer value as the floating-body device. And temperature dependence analysis of charge collection indicates that there is only drift-diffusion process in the N-type SELBOX SOI device. The amount of charge collection in the N-type SELBOX SOI device almost does not change with the increase of temperature. In addition, both the P-type SELBOX SOI device and the P-type floating-body device have a bipolar amplification process. With the increase of temperature, the bipolar amplification process in the substrate turns more serious. However, it suppresses the bipolar amplification process of the source because of SELBOX structure, so that the amount of charge collection is reduced in the drain significantly. According to our simulation results, compared with the floating-body device, the SELBOX SOI device can very well suppress the influence of temperature on SET pulse.
Inspiration of wrinkles in layered material for the mechanism study of several geological activities
Authors: Xu Hong , Yuan Zheng-Yi , Huang Tong-Fei , Wang Xiao , Chen Zheng-Xian , Wei Jin , Zhang Xiang , Huang Yuan ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   School of Science, China University of Geosciences, Beijing 100083, China,   China Earthquake Network Center, Beijing 100045, China,   College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China,   School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China,   Key Laboratory of Earthquake Geodesy, Institute of Seismology, China Earthquake Administration, Wuhan 430071, China
Published: December 2020

In this work, we propose a universal method of preparing wrinkle structures in layered crystals, which provides a good model for studying the physical properties of layered materials under strain. More importantly, there are some similarities between wrinkle engineering and geological activities, which inspires us to give some possible explanations to the mechanism for geological activities like earthquake and volcanic. The wrinkle structures of layered crystals can be achieved by exerting uniaxial or biaxial stress on the flexible substrate, which is very similar to the layered structure of the Earth and the formation of mountain folds on the Earth's surface. Since the Earth has an uneven mass distribution and self-rotation as well, the moments of inertia for plates are different from each other. Here in this work, we point out that there is a difference in angular velocity between the north hemisphere and south hemisphere, which may strongly influence the topography and geology activities near the equator. This work provides a possible mechanism explanation for several geological phenomena such as earthquakes, volcanoes, and continental drift. Based on China's special topography, we propose a matter flow hypothesis and discuss the orientation of matter flow in detail. We point out that the geological activity mechanism in China and the regions around plate boundaries is quite different. The matter flow hypothesis can be well applied to explain the causes of earthquake disasters in China, the distribution of mineral resources, and the possible causes of oil in the Middle East countries. Besides, it also provides a new theoretical guidance for predicting the earthquake disasters and prospecting the mineral resources in China. This work provides a new idea for humans to avoid natural disasters, to understand the natural phenomena on the Earth, and to make rational use of natural resources.
First-principles on the energy band mechanism for modifying conduction property of graphene nanomeshes
Authors: Xu Xian-Da , Zhao Lei , Sun Wei-Feng ,   Key Laboratory of Engineering Dielectrics and Its Application, Ministry of Education, Heilongjiang Provincial Key Laboratory of Dielectric Engineering, School of Electrical and Electronic Engineering, Harbin University of Science and Technology, Harbin 150080, China
Published: December 2020

By means of first-principles electronic structure calculations, the ordered graphene nanomeshes with patterned hexagonal vacancy holes are theoretically studied to explore the modification mechanism of electrical conduction on graphene atomic monolayers. According to pseudopotential plane wave first-principles scheme based on density functional theory, the band structures of graphene nanomeshes are calculated to analyze the electrical conductance in correlation with the superlattice symmetry and vacancy hole magnetism. Based on the structural features and topological magnetism of Y-shaped nodes between the nanopores on the atomic monolayer of graphene, the graphene nanomeshes are classified into three types. The quadruplet degeneracy and splitting of electronic states at Brillouin zone center are investigated by comparing the band structures of graphene nanomeshes and analogical superlattices. The effects of inversion symmetry and supercell size on the opening band-gap at Dirac cone are elaborately analyzed with the consideration of antiferromagnetic coupling and hydrogen passivation at the magnetic edge of nanopores on graphene nanomeshes. The band-structure calculation results indicate that the (3m, 3n) (m and n are integers) superlattices have fourfold degenerate electronic states at center point of Brillouin zone, which can be effectively splitted by regularly arranging porous atomic vacancy to make the (3m, 3n) nanomesh, resulting in adjustable band-gap no matter whether or not the sublattices keeping in equivalence. In the nanomeshes formed by patterned holes with magnetic edge, the antiferromagnetic coupling adds a quantum parameter to the inversion symmetry so as to break the sublattice equivalence, opening band-gap at the twofold degenerate K point. Nevertheless, the hydrogen passivation at the edge of magnetic nanopores will convert the magnetic graphene nanomeshes into non-magnetic and eliminate the band-gap at K point. The band-gap of graphene nanomeshes could also be controlled by changing the density of nanopores, suggesting a graphene nanomaterial with adjustable band-gap that can be designed by controlling the mesh pore spacing. The graphene nanomeshes represent a new mechanism of forming band-gap and thus promise a strategy for achieving special electrical properties of graphene nanostructures. These results also theoretically demonstrate that the nano-graphene is a prospective candidate with flexibly adjustable electrical properties for realizing multivariate applications in new-generation nano-electronics.
Response characteristics of inflow-stimulated Kelvin-Helmholtz vortex in compressible shear layer
Authors: Zhang Dong-Dong , Tan Jian-Guo , Yao Xiao ,   Science and Technology on Scramjet Laboratory, National University of Defense Technology, Changsha 410073, China
Published: December 2020

By numerically solving the Navier-Stokes equations, the response characteristics of inflow-stimulated Kelvin-Helmholtz vortex in compressible shear layer arestudied. The mixing characteristics and the unique growth mechanism of the vortex structure are clearly revealed. By employing the index of vorticity thickness, the mixing properties are quantitatively analyzed. Based on the flow visualization results, the spatial size and the structure angle of the flow coherent structure are investigated by utilizing spatial correlation analysis. The evolution mechanism of the vortex structure in supersonic mixing layer induced by inlet forcing is revealed by analyzing the dynamical performances of the flow structure under different frequency disturbances. The numerical results show that with low forcing frequency at f = 5 kHz, the mixing efficiency is remarkably increased in the near-field of the flow. Whereas, in the far-field downstream the flow, the size of the structure reaches saturation state and the vortex passage frequency is locked, which causes the vorticity thickness to stabilize from 12mm to 14mm. Meanwhile, in a free mixing layer, the pairing and merging process occur in the flow field to promote the growth of the vortex structure, while in mixing layer with inlet forcing, the growth mechanism is that the vortex core engulfs a string of vortices induced by Kelvin-Helmholtz instability. The process of engulfment contributes much to the growth of the vortex structure. The analysis of spatial correlation distribution shows that in the area where engulfment occurs, the contour line shows the property of long and narrow ellipse instead of full ellipse and the structure in the area possesses the characteristics of intense rotation and inclination. Besides, with high inlet forcing frequency at f = 20 kHz, the size of the vortices becomes full in the near-field, and the vorticity thickness stabilizes between 3mm and 4 mm downstream the flow field. Meanwhile, the size of the vortex in controlled supersonic mixing layer is dominated by the imposed high-frequency forcing. An equation describing the quantitative relationship between the vortex characteristics and the imposed forcing frequency is derived, that is, the size of the uniform distribution vortex is approximately equal to the ratio of the value of convective velocity to inlet forcing frequency.
Effect of surfactants on adsorption behavior of nanoparicles at gas-liquid surface
Authors: Zhang Xuan , Zhang Tian-Ci , Ge Ji-Jiang , Jiang Ping , Zhang Gui-Cai ,   College of Petroleum Engineering, China University of Petroleum, Qingdao 266580, China
Published: December 2020

Silica nanoparticles (NPs) are more and more useful in many engineering areas, but the dynamic behaviors of adsorption of NPs at surface are not clear, especially when there exist surfactants on the surface. The modified NPs with the nonionic dimethyl silane are partially hydrophobic, and in this paper, the surface behavior is investigated which is determined by interfacial tension and surface compression modulus. It is concluded that the dimethyl silane coverage, the brine salinity and the surfactant would affect the NPs’ adsorption. Higher salinity in brine or higher dimethyl silane coverage causes lower steady state surface tension, which is related to the hydrophobicity and adsorption amount of NPs at the surface. When the cationic surfactant concentration is lower than critical micelle concentration (CMC), the surface tension of mixture system is a little bit higher than cationic surfactant’s. Cationic surfactant can be adsorbed at NPs’ surface to change the hydrophobicity based on the electrostatic attraction, and then some surfactants are dissolved in liquid phase together with NPs, while the anionic surfactant will not do so. In the shrinking droplet process, the surface tension of the NPs with 1.5 μmol/m2 dimethyl silane decreases from ~59 mN/m at the steady state to ~50 mN/m, which proves that the NPs’ adsorption density can be higher even after infinite long time equilibrium due to the repulsive force between the NPs. Besides, the curve of interfacial tension (IFT) versus surface area shows three parts with different declining slopes. In the first part, the relatively low adsorption of NPs at the surface means weak interaction between NPs. Then in the second part, due to the irreversible adsorption, the spacing between NPs decreases with adsorption amount increasing and surface area lowering, so the increasing of NPs’ interaction leads to high surface compression modulus. After that, the IFT curve keeps flat since the NPs assembly reaches to the closest peck. With the increase of NPs’ hydrophobicity, the compression modulus increases up to ~70 mN/m, which satisfies the Gibbs criterion to resist coarsening of the foam or emulsion. However, for the mixing system, increasing surfactant concentration leads to a lower surface tension at steady state, then the surface tension difference or compression modulus decreases too. Finally, we find that the compression modulus order from high to low is as follows: NPs, cationic surfactant-NPs, anionic surfactant-NPs, surfactants. This investigation is meaningful for accounting for the enhancement of foam or emulsion stability with NPs affected by salinity and surfactant.
Untrafast smoothing scheme based on dynamic interference structure between beamlets of laser quad
Authors: Xiong Hao , Zhong Zhe-Qiang , Zhang Bin , Sui Zhan , Zhang Xiao-Min ,   College of Electronics and Information Engineering, Sichuan University, Chengdu 610065, China,   China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Aiming at the high requirements for illumination uniformity on the target in laser-driven inertial confinement fusion (ICF) facilities, an ultrafast smoothing method based on dynamic interference structure between beamlets of a laser quad is proposed. The basic principle of this scheme is to use a conjugate phase plate array to add the conjugate phase modulation to the multiple beamlets of a laser quad with a certain wavelength difference. Consequently, every two beamlets are coherently superposed in the far field to generate a dynamic interference pattern, resulting in the fast redistribution of the speckles introduced by continuous phase plate inside the focal spot and further improving the illumination uniformity on the target on a picosecond timescale. The coherent beamlets with a certain wavelength difference can be generated by using a broadband seed laser. Taking the laser quad of the typical ICF facilities for example, the physical model of the ultrafast smoothing method based on dynamic interference structure of beamlets is built up. The influences of the phase-plate type, the peak-to-valley value of the phase modulation and the wavelength difference between the beamlets are analyzed quantitatively, and the smoothing characteristics of the focal spot are discussed in detail and compared with those from the traditional temporal smoothing scheme such as smoothing by spectral dispersion. The results indicate that the directions of the moving speckles in the focal spot are determined by the phase-plate type. However, the required time to achieve stable illumination uniformity, i.e, the decay time, is determined by the wavelength difference between the beamlets. Moreover, the illumination uniformity on the target becomes better with the increase of peak-to-valley value of the phase modulation at first and then remains almost the same. Thus, the ultrafast smoothing method based on dynamic interference structures with well-designed phase arrays and wavelength combinations of the beamlets can realize the multi-directional and multi-dimensional speckle sweeping inside the focal spot, and further improving the irradiation uniformity on the target within several picoseconds or sub-picoseconds. Combining with the traditional beam smoothing scheme, better illumination uniformity can be achieved on an ultrashort timescale. This novel scheme can be used as an effective supplement to the existing temporal beam smoothing techniques.
Analytical solution of three-dimensional Fourier transform frequency spectrum for three-level potassium atomic gas
Authors: Zhao Chao-Ying , Tan Wei-Han ,   School of Sciences, Hangzhou Dianzi University, Hangzhou 310018, China,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China,   Department of Physics, Shanghai University, Shanghai 200444, China
Published: December 2020

With the development of laser technology in the field of optics, ultra-fast optics has become an important research field. Compared with the traditional technology, ultrafast optics can be realized not only under shorter pulse function, but also on a smaller scale, which can more quickly reflect the dynamic process. We present an analytical calculation of the full three-dimensional (3D) coherent spectrum with a finite duration two-dimensional (2D) Gaussian pulse envelope. Our starting point is the solution of the optical Bloch equations for three-level potassium atomic gas in the 3D time domain by using the projection-slice theorem, error function and Fourier-shift theorem of 3D Fourier transform. These principles are used to calculate and simplify the third-order polarization equation generated by the device, and the analytical calculation of three-dimensional Fourier transform frequency spectrum at T = 0 is obtained. We simulate the analytic solution by using mathematics software. By comparing the simulations with the experimental results, with the homogeneous line-width fixed, we can obtain the relationship among the in-homogeneous broadening, the correlation diagonal coefficients and the three-dimensional spectrum characteristics, which can be identified quantitatively by fitting the slices of three-dimensional Fourier transform spectrum peaks in an appropriate direction. The results show that the three-dimensional Fourier transform spectrum will extend along the diagonal direction with the increasing of the in-homogeneous broadening, and the spectrogram progressively becomes a circle with the increasing of the diagonal correlation coefficient, and the amplitude also gradually turns smaller. According to the analytical solution, we give a complete two-dimensional spectrum of the T = 0 interface. The results can be fit to the experimental 3D coherent spectrum for arbitrary inhomogeneity.
Generation of high-quality circular Airy beams in laser resonator
Authors: Zhu Yi-Fan , Geng Tao ,   Engineering Research Center of Optical Instruments and Systems, Ministry of Education, Shanghai Key Laboratory of Modern Optics and Systems, School of Optical-Electrical and ComputerEngineering, University of Shanghai for Science and Technology, Shanghai 200093, China
Published: December 2020

A scheme for forming high-quality circular Airy beams inside the laser resonator is presented theoretically. The desired circular Airy beam can be generated when the common reflective mirror is replaced by a designed diffractive optical element. The mode generated in the proposed cavity can be stimulated by using the so-called eigenvector method. The calculated results show that the parameters of the beams can be controlled by changing the phase distribution of the diffractive optical element. The loss of the generated mode is very low, which is close to that of the fundamental Gaussian mode. The purity of the generated mode is very high, which is much better than that from the phase-only encoding method in Fourier space. The phase distribution of the diffractive optical element needs designing for a fixed resonator length. In practice, the real resonator length may not be equal to the designed resonator length. Thus, the influence of the alignment error of the resonator length is discussed in detail. The results show that the diffraction loss of the proposed system is still very small even when the error reaches up to 2 mm. Meanwhile, the purity of the generated mode decreases little. Then, the influence of etching depth errors and the decenter of the reflective mirrors are discussed in detail. Here we assume that the fluctuations are randomly distributed. The value of the maximum fluctuation is used to represent the etching depth error degree. The results show that the diffraction loss of the proposed system is more sensitive to production error, and the purity of the generated mode is more sensitive to alignment error. Thus, we estimate that the maximum etching depth error should be less than six percent of the wavelength, and the vertical distance between the centers of the two reflective mirrors should be less than 7 μm if one wants to obtain high-quality CAB with high efficiency. The requirements for precision are acceptable for existing microfabrication and operation technologies.