bluuebunny/crossref_metadata_2025 huggingface dataset:
Maintaining large-scale gas layer by creating wettability difference on surfaces under water
Authors: Hu Hai-Bao  , Wang De-Zheng  , Bao Lu-Yao  , Wen Jun  , Zhang Zhao-Zhu  ,   College of Marine, Northwestern Polytechnical University, Xi’an 710072, China;,   State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
Published: December 2020

Superhydrophobic surfaces with micro- and nano-scale structures are conducible to maintaining a gas layer where prominent slippage effect exists. It has been demonstrated that the drag reduction of superhydrophobic surface increases with growing the fraction of the gas-water interface and the rising of the thickness of gas layer. Whereas a large thick gas layer on the superhydrophobic surface collapses easily under tangential water flow. Here, we present a new method to maintain large-scale gas layer by creating hydrophilic patterns at the superhydrophobic surface, on which the binding force of air on the solid surface can be caused by wettability difference. Through testing the states of gas layer trapped on surfaces with wettability differences equal to 54.8, 84.7, 103.6 and 144.0 in apparent contact angle, respectively, the conditions of maintaining gas layer are mainly considered. We demonstrate that the critical velocity, over which the gas layer begins to collapse under the tangential water flow, is positively correlated with the thickness of the gas layer and the wettability difference between the superhydrophobic area and hydrophilic area, however, this is negatively correlated with the width of the gas layer in the crosswise direction. It is noteworthy that even a centimeter-scale gas layer can be kept steady in ～0.9 m/s through this method. Furthermore, an obvious slip velocity up to ～25% of bulk velocity is observed at the gas-water interface, through measuring the velocity profile above the 0.6 cm-long, 0.5 cm-wide and 0.15 cm-thick gas layer by using the PIV technology. We anticipate that this novel method of gas entrapment under water will effectively widen the applications of superhydrophobic surfaces for drag reduction.
Interfacial water at microscopic level: from quasi-one-dimensional, two-dimensional confined space, to biomolecules surfaces and material surfaces
Authors: Fang Hai-Ping  ,   Division of Interfacial Water, Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
Published: December 2020

A majority of the physical, biological, chemical and environmental processes relate to the interfacial water. However, for the interfacial water itself, there are still many puzzles unsolved, which have made the interfacial water an important scientific research object for quite a long time. In this paper, we review some recent progress on the dynamics of interfacial water confined in one-dimensional and two- dimensional spaces, and on the surfaces on biomolecules and materials as well.
A summary of soft matter theories
Authors: Wu Chen-Xu  , Yan Da-Dong  , Xing Xiang-Jun  , Hou Mei-Ying  ,   Research Institute for Biomimetics and Soft Matter, College of Physics and Technology, Xiamen University, Xiamen 361005, China;,   Department of Physics, Beijing Normal University, Beijing 100875, China;,   Department of Physics and Astrophysics, Shanghai Jiaotong University, Shanghai 200240, China;,   Key Laboratory of Soft Matter Physics, Beijing National Laboratory for Condense Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

This paper summarizes some theories widely used in soft matter systems, such as elastic theory, phase transition theory, scaling law, theory of granular particles, self-consistent field theory, etc. The role entropy plays in softmatter systems is also discussed. Other dynamic theories like adhesion, diffusion, wave motion, etc. are not included here.
Hydrodynamic theory of dry active matter
Authors: Chen Lei-Ming  ,   College of Sciences, China University of Mining and Technology, Xuzhou 221116, China
Published: December 2020

In this paper we shortly review theoretical progress in the field of active matter, focusing on the continuum theory of dry systems, in which momentum of active particles is not conserved due to the interaction between the particles and a substrate or medium. In particular, we review the phenomenological way of deriving hydrodynamic equations for both polar and apolar systems, and the predictions of these theories such as long-ranged orientational order in two-dimensional polar systems and giant number fluctuations. The comparisons among theoretical predictions, numerical results, and experimental evidence are also summarized.
Bioinspired multiscale interfacial materials with superwettability
Authors: Wang Peng-Wei  , Liu Ming-Jie  , Jiang Lei  ,   Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University, Beijing 100191, China;,   Laboratory of Bioinspired Smart Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Nature always supplies inspirations to scientists and engineers. Many newfangled materials have been fabricated by learning from and mimicking nature. In daily life and industrial processes these bioinspired novel materials have been widely used. The special wettability of natural organisms is significant to their life and attractive to researchers, which inspires us to fabricate the functional interfacial materials with high performances. In the last decade, the bioinspired multiscale interfacial materials exhibiting superwettability have emerged as a new type of functional material. Superwettable materials offer great chances to solve numerous issues ranging from fundamental research to practical exploration, and from bionic philosophy to fabricating technology. Inspired by nature's example, researchers developed a series of scientific strategies of new materials and fabricating methods, technologies, and applications. Based on the requirement of developing advanced materials in the fields of energy, environment, healthcare and resource, superwettable materials possessing binary cooperative nanostructure have been widely investigated to solve scientific and technical problems. In this review, we firstly present the development history of bioinspired multiscale interfacial materials with superwettability and the theoretical basis of the wettability of solid surfaces. Secondly, the principles of superwettable functional surfaces in nature is revealed and the bionic designs of bioinspired materials are discussed in detail. Meanwhile the typical applications of superwettable materials such as self-cleaning, oil-water separation and green printing are introduced. Finally, the perspectives of the future development of bioinspired superwettable materials are proposed for further studying the superwettable materials.
Simulation of liquid channel of Fe-C alloy directional solidification by phase-field method
Authors: Kang Yong-Sheng  , Zhao Yu-Hong  , Hou Hua  , Jin Yu-Chun  , Chen Li-Wen  ,   Material Science and Engineering institute, North University in China, Taiyuan 030051, China
Published: December 2020

In directional solidification, two characteristic parameters determine the dendritic growth: the thermal gradient and the pulling velocity. To achieve the suitable microstructure and improve the performance of casting, they are usually used to resize the pulling velocity or temperature gradient in directional solidification process. The structures obtained under different directional solidification conditions, and their associated properties both have been hot research points. It is difficult to observe the microstructure, which is usually on a micrometer scale, directly in experiment, and the phase-field method becomes a strong tool to understand the dendrite growth pattern. We mainly study the liquid channel formed after Fe-C alloy dendrite tip splitting under the specific condition of directional solidification and analyze the influence on liquid channel of pulling velocity in this paper. We choose the fixed thermal gradient G =20 K/mm which is on the order of the experimental value, and pulling velocity VP no more than 10 mm/s to keep the cooling rate in the range of low speed in dendrite growth, so that the interface kinetic effect can be neglected. Recent experimental results show the different interfacial energies in various compositions of Al-Zn alloy and Fe-C alloy, then we can investigate a series of directional solidification microstructures with fixed alloy Fe-0.5 wt.%C composition at different interfacial energies in our simulations. We find that the liquid channel is formed as a result of anisotropy competition between system and materials, the length and C concentration of liquid channel increase with the pulling velocity increasing, while the diameter of liquid channel is constant. It is interesting to find that there is a minimum of pulling velocity almost equal to 1 mm/s, the tip will not split and no liquid channel forms in the following steps either when the velocity is smaller than the minimum. We also compare the segregation caused by solute enrichment in liquid channel and solute segregation between dendrite arms in a series of simulations: the former is more serious than the latter. Then we point out the way to reduce the segregation caused by liquid phase channel by reducing the pulling velocity properly. It will be more practical to couple the flow field with other external field, such as magnetic field, in the simulation.
Frontier of soft matter experimental technique: single molecular manipulation
Authors: Qian Hui  , Chen Hu  , Yan Jie  ,   Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Lab for Soft Functional Materials Research, Department of Physics, Xiamen University, Xiamen 361005, China;,   Mechanobiology Institute, National University of Singapore, Singapore 117411, Singapore;,   Department of Physics, National University of Singapore, Singapore 117542, Singapore;,   Centre for Bioimaging Sciences, National University of Singapore, Singapore 117546, Singapore
Published: December 2020

Biomolecules such as proteins and nucleic acids play critical roles in biological processes. Traditional molecular biological experimental techniques usually measure the properties of an ensemble of molecules. The detected signal originates from the average response of large number of molecules, which often conceals the detailed dynamic information about conformational transitions. In addition, many biomolecules, such as cytoskeleton proteins and molecular motors, are subjected to stretching forces or are able to generate force while playing their biological roles in vivo. It is difficult for traditional experimental methods to be used to study the mechanical response of biomolecules. Single molecule manipulation techniques developed in recent twenty years are capable of manipulating and measuring the property of single molecule. Especially, the force response of single molecule can be measured in high precision. The most popular single molecular manipulation techniques are atomic force microscope, optical tweezers, and magnetic tweezers. Here we introduce the principle, capability of force and extension measurement, spatial and temporal resolutions of these three techniques. Applications of single molecular manipulation techniques in the conformation transitions of DNA, protein, and their interactions, and mechanism of molecular motors will be briefly reviewed. This review will provide a useful reference to biologists to learn and use single molecular manipulation techniques to solve biological problems.
Influences of nonspherical aerosol particles and relative humidity of atmosphere on the performance of free space quantum communication
Authors: Nie Min  , Ren Jia-Ming  , Yang Guang  , Zhang Mei-Ling  , Pei Chang-Xing  ,   School of Communication and Information Engineering, Xi'an University of Posts and Telecommunication, Xi'an 710121, China;,   School of Electronics and Information, Northwestern Polytechnical University, Xi'an 710072, China;,   State Key Laboratory of Integrated Service Networks, Xi'an University of Electronic Science and Technology, Xi'an 710071, China
Published: December 2020

When the optical signal is transmitted in the free space, it inevitably passes through the atmosphere. The atmospheric aerosol is one of the most important components of the atmosphere, which not only affects the regional climate, but also influences the transmission of the free space optical signal. However, the study on the relationship between the non-spherical aerosols and the parameters of the free space quantum communication channel has not been carried out so far. To investigate this relationship, the spectral distribution function of the aerosol and its extinction factor should be analyzed first. According to three nonspherical aerosol particles: cylindrical particles, ellipsoidal particles and Chebyshev particles, the equation between channel attenuation of the free space quantum communication and the degree of quantum entanglement can then be established. After that, the effects of the relative humidity of the atmosphere on the degree of quantum entanglement and the fidelity of quantum communication can be analyzed and simulated finally. The simulation results show that the channel attenuations of the free space quantum communication are sequenced in ascending order as cylindrical particles, ellipsoidal particles, and Chebyshev particles, and their influences on the degree of quantum entanglement have different changing trends. When the transmission time is fixed, with the increase of aspect ratio of ellipsoidal particles, the degree of quantum entanglement shows a growing trend, with the increase of aspect ratio of cylindrical particles, the degree of quantum entanglement shows descending trend. With the increase of Chebyshev particle equivalent radius, the degree of quantum entanglement also shows the descending trend. When the relative humidity of the atmosphere is 0.2(0.9), the degree of quantum entanglement and the fidelity of quantum communication will be 0.72(0.75) and 0.32(0.22), respectively. It can be seen that the nonspherical aerosol particles and the relative humidity of the atmosphere each have a significant effect on the function of the free space quantum communication system. Therefore, in a practical free space quantum communication system, the shape factor of nonspherical aerosol particle, orientating factor, equivalent radius and the relative humidity of the atmosphere cannot be ignored, in order to improve the effectiveness and reliability of the free space quantum communication, the different parameters of the communication system should be adjusted adaptively.
Event-triggered heterogeneous master-slave synchronization with sampled-data control
Authors: Ma Da-Zhong  , Li Xiao-Yu  , Sun Qiu-Ye  , Zhang Hua-Guang  ,   College of Information Science and Engineering, Northeastern University, Shenyang 110004, China
Published: December 2020

As is well known, chaos synchronization has a good performance in secret communication. However, in most existing researches, chaos synchronization is realized between master chaotic system and slave chaotic system with real-time communication. A lot of network bandwidths are wasted in useless communication which may bring great economic costs and increase the likelihood of network congestion. In this paper, the synchronization for the heterogeneous master-slave system is studied. Compared with the homogeneous synchronization, the heterogeneous synchronization has a broad application prospect. Then the sampling controller based on event trigger is designed to achieve the heterogeneous master-slave synchronization which can save network bandwidth, with the control performance maintained. Because transmission time delay is universal in communication system, the delay model of the system is constructed and utilized firstly. Based on the proposed system model, the master-slave heterogeneous synchronization problem is equivalently converted into the asymptotical stability problem of a time-delay system by using the input delayed approach. Then, according to the Lyapunov stability theory and linear matrix inequality, we may rigouously prove that the synchronization of heteogeneous master-slave chaotic system can be achieved. Meanwhile, the heterogeneous master-slave system synchronization conditions and sampling controller can be given based on the constructing Lyapunov-Krasovskii functional with the Wirtinger inequality and free weight matrix method. The sampling controller actually is a stateback controller. But for the purpose of reducing the network usage rate, wheter the state can be transmitted can be determined by the event-triggered rules. The event-triggered rules are designed based on the error state between master chaotic system and slave chaotic system, and the synchronization performance index can be determined by choosing the system parameter. The designed sampling controller updates the control parameters when the event-triggered rules are satisfied. Finally, numerical simulation experiments are employed to verify the correctness and effectiveness of the proposed method. Results indicate that the hetergeneous master-slave chaotic system with transimission time delay can indeed achieve synchronization by event-triggerd sample control. Moreover, the number of communications between master chaotic system and slave chaotic system is less than before and the synchroization performance is also at an idea level.
Energy and angular dependence of single event upsets in ESA SEU Monitor
Authors: Luo Yin-Hong  , Guo Xiao-Qiang  , Chen Wei  , Guo Gang  , Fan Hui  ,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024, China;,   China Institute of Atomic Energy, Beijing 102413, China
Published: December 2020

The new generation ESA SEU Monitor is first applied to beam verification of Beijing HI-13 Tandem accelerator according to the popularization need of Europe Space Agency and at the desire of contrast of domestic acceleraor with international accelerator. Heavy ion single event cross section of ESA SEU Monitor obtained at HI-13 is compared with those from European facilities. Beam homogeneity is also analyzed based on the SEU physical bitmap. The accuracy of heavy ion beam monitoring technique at HI-13 accelerator is verified. Through combining the heavy ion testing result with the data from the other test sites, it can be observed that the differences between SEU cross sections with different heavy ion energies of the same LET value can reach 1-3 orders of magnitude in the sub-threshold zone of single event upset cross section curve below the direct ionization LET threshold. The geometrical structure, critical charge and collection efficiency of sensitive volume are constructed on the basis of testing data and process information. The physical mechanism of energy effect on single event upsets in ESA SEU Monitor is revealed through using the Monte-Carlo calculation. Nuclear reactions between incident heavy ions and material atoms can account for single event upsets below the direct ionization LET threshold. The differences in nuclear reaction type and cross section between the diferent energy heavy ions and material atoms are the root cause of the difference among heavy ion SEU cross sections with different energies at the same LET value. On the other hand, SEU bitmap nonuniformity among different blocks in memory array and different orientation dices in ESA SEU Monitor is first reported when the heavy ion is incident at a tilting angle at the low LET value. The analysis of device layout and calculation verification can account for this phenomenon. The material of interlayer dielectric with the tilting ion passing through is different when heavy ion reaches the sensitive volume of memory blocks with different data. This leads to the difference between efficient LET values inside the sensitive volume for different data blocks. Eventually the sensitivity difference in single event upset among blocks with different data occures. The applications of ESA SEU Monitor in beam calibrating, tuning of domestic accelerator and single event effect test can be broadened further. Prediction method of space single event upset rate including heavy ion energy dependence and special angular dependence based on full-physical simulation should be developed in the future.
Period-adding bifurcation of neural firings induced by inhibitory autapses with time-delay
Authors: Ding Xue-Li  , Li Yu-Ye  ,   Department of Basic Education, Fuyang Institute of Technology, Fuyang 236031, China;,   Mathematics and Statistics Institute, Chifeng University, Chifeng 024000, China
Published: December 2020

Neural firing rhythm plays an important role in achieving the function of a nervous system. Neurons with autapse, which starts and ends in the same cell, are widespread in the nervous system. Previous results of both experimental and theoretical studies have shown that autaptic connection plays a role in influencing dynamics of neural firing patterns and has a significant physiological function. In the present study, the dynamics of a neuronal model, i.e., Rulkov model with inhibitory autapse and time delay, is investigated, and compared with the dynamics of neurons without autapse. The bifurcations with respect to time-delay and the coupling strength are extensively studied, and the time series of membrane potentials is also calculated to confirm the bifurcation analysis. It can be found that with the increase of time-delay and/or the coupling strength, the period-adding bifurcation of neural firing patterns can be induced in the Rulkov neuron model. With the increase of the period number of the firing rhythm, the average firing frequency increases. When time-delay and/or coupling strength are/is greater than their/its corresponding certain thresholds/threshold, the average firing frequency is higher than that of the neuron without autapse. Furthermore, new bursting patterns, which appear at suitable time delays and coupling strengths, can be well interpreted with the dynamic responses of an isolated single neuron to a negative square current whose action time, duration, and strength are similar to those of the inhibitory coupling current modulated by the coupling strength and time delay. The bursts of neurons with autapse show the same pattern as the square negative current-induced burst of the isolated single neuron when the time delay corresponds to the phase. The bifurcation structure of the neural firing rhythm of the neuron without autapse can be obtained with the fast-slow dissection method. The dynamic responses of the isolated bursting neuron to the negative square current are acquired by using the fast-slow variable dissection method, which can help to recognize the new rhythms induced by the external negative pulse current applied at different phases. The new rhythm patterns are consistent with those lying in the period-adding bifurcations. The results not only reveal that the inhibitory autapse can induce typical nonlinear phenomena such as the period-adding bifurcations, but also provide the new phenomenon that the inhibitory autapse can enhance the firing frequency, which is different from previous viewpoint that inhibitory effect often reduces the firing frequency. These findings further enrich the understanding of the nonlinear phenomena induced by inhibitory autapse.
Effects of impedance wedge diffraction on backscattering from breaking waves
Authors: Zhang Xiao-Xiao  , Wu Zhen-Sen  , Su Xiang  ,   School of Physics and Optoelectronic Engineering, Xidian University, Xi'an 710071, China;,   Collaborative Innovation Center of Information Sensing and Understanding, Xidian University, Xi'an 710071, China
Published: December 2020

Electromagnetic scattering characteristics change significantly from breaking waves, which is considered to be one reason for sea spike phenomenon（HH polarization scattering intensity close to or even greater than VV polarization scattering intensity). Spiky sea clutter is often treated falsely as targets, which affects radar performance in target detection in the sea surface background. Thus the investigation on the physical mechanism of the sea spike phenomenon can help mitigate false alarms. In this paper, the authors investigate the microwave backscattering from the wedge-shaped breaking waves, which is simulated with the dihedral impedance wedge of finite length. The physical optical field of the breaking waves is calculated with the Kirchhoff approximation. Based on the Maliuzhinets method with using the precise impedance boundary condition, the impedance wedge scattering solution in spectral integral representation is presented. The spectral function is derived by the perturbation method with respect to the oblique incident angle based on the incidence normal to or grazing to the edge. After obtaining the spectral function, the asymptotic theory is used to determine the diffraction field of impedance wedge at an arbitrary skew incidence. The equivalent edge currents are derived from the uniform diffraction of impedance wedge by combining the physical optical coefficients and diffracted coefficients. Backscattering radar cross-sections（RCSs) of the diffracted field from 120 impedance wedge are calculated in both HH and VV polarizations, and the effects of frequency and permittivity on the wedge diffraction are discussed as well. The physical optical field backscattering from 135 impedance wedge is compared with the total field with considering the diffraction effects. Further calculations and analyses for backscattering from the three-dimensional extension breaking waves are presented by using the contribution of edge diffraction field to correct the physical optics field. Numerical results show that the backscattering RCS of impedance diffracted field in HH polarization is greater than that in VV polarization in the Keller cone. Therefore, the diffraction effects will make the backscattering RCS of the total field in HH polarization greater than that in VV polarization when the breaking wave grows to near-collapse stage at a small grazing angle with upwind observation. This indicates that the wedge diffraction is one of the causes of sea spike phenomenon.
Energy efficiency analysis of ArF excimer laser system
Authors: Wang Qian  , Zhao Jiang-Shan  , Luo Shi-Wen  , Zuo Du-Luo  , Zhou Yi  ,   Academy of Opto-Electronics, Chinese Academy of Sciences, Beijing 100094, China;,   Beijing Excimer Laser Technology and Engineering Center, Beijing 100094, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

The reliable functioning and continual optimizing of ArF excimer laser system is of importance when it comes to productization into the market from a laboratory test machine. The analysis of dynamic characteristics of the system is vital to understanding its operating mechanism and optimizing the design theoretically. In this article, one-dimensional fluid model is used to analyze the excimer laser discharge mechanism, and the content ratio of fluorine gas, argon gas, and neon gas, which constitute a gas mixture, is studied in a simulated ArF excimer laser system. Particles are treated as a fluid, which significantly reduces the computing cost in fluid model, and therefore is suitable for high-pressure situation. Four equations are included in one-dimensional fluid model, i.e., Boltzmann equation that describes electron energy distribution, ion continue equation that illustrates ion number density, Poisson's equation that shows the distribution of electric field, and photon rate equation that demonstrates laser outputting process. By combining these four equations, high pressure plasma discharge process and particles stimulated radiation process are studied, and calculation continues from one time step to another until the end of discharging process. The result of the calculation presents energy transfer process from three aspects:energy deposition efficiency, ArF* formation, and laser outputting. In the energy deposition process, the energy deposition efficiency is sensitive to the change of fluorine gas ratio while the variation of the content ratio of other two gases has a less influence on this process. In addition, there exists an optimal fluorine gas ratio that causes the highest energy deposition efficiency. In the ArF* formation process, the reaction between excited argon ions and fluorine gas is the main channel that generates ArF*. The proper increasing of fluorine gas ratio helps form ArF*. In the laser outputting process, photon loss is mainly because of the reaction between fluorine negative ions and photons. Therefore superfluous fluorine gas in the mixture leads to less photons, which eventually results in low energy efficiency of laser. By summarizing the three aspects of energy transfer process, the fluorine gas ratio in the gas mixture plays a significant role in determining the energy efficiency of ArF excimer laser system. This theory is verified by experiments, showing that the deviation of the optimized fluorine gas ratio severely reduces energy efficiency. This conclusion can guide us in optimizing the design and steady reliable function of ArF excimer laser system.
Average degree under different network sizes for random birth-and-death networks
Authors: Zhang Xiao-Jun  , Zhong Shou-Ming  ,   School of Mathematical Sciences, University of Electronic Science and Technology of China, Chengdu 611731, China
Published: December 2020

In the social and biological networks,each agent experiences a birth-and-death process.These evolving networks may exhibit some unique characteristics.Recently,the birth-and-death networks have gradually caught attention,and thus far,most of these studies on birth-and-death networks have focused on the calculations of the degree distributions and their properties.In this paper,a kind of random birth-and-death network (RBDN) with reducing network size is discussed,in which at each time step,with probability p(0pq=1-p.Unlike the existing literature,this study is to calculate the average degrees of the proposed networks under different network sizes.First,for the reducing RBDN,the steady state equations for each node's degree are given by using the Markov chain method based on stochastic process rule,and then the recursive equations of average degree for different network sizes are obtained according to these steady state equations.Second,by means of the recursive equations,we explore four basic properties of average degrees as follows:1) the average degrees are limited,2) the average degrees are strictly monotonically increasing,3) the average degrees are convergent to 2mq,and 4) the sum of each difference between the average degree and 2mq is a bounded number.Theoretical proofs for these four properties are also provided in this paper.Finally,on the basis of these properties,a generation function approach is employed to obtain the exact solutions of the average degrees for various network sizes.In addition to the theoretical derivations to the average degrees,computer simulation is also used to verify the correctness of exact solutions of the average degrees and their properties.Furthermore,we use numerical simulation to study the relationship between the average degree and node increasing probability p.Our simulation results show as follows:1) with the increasing of p,the convergent speed of the average degree to 2mq is increasing;2) with the increasing of m,the convergent speed of the average degree to 2mq is decreasing.In conclusion,for the proposed RBDN model,the main contributions of this study include 1) providing the recursive equations of the average degrees under different network sizes,2) investigating the basic properties for the average degrees,and 3) obtaining the exact solutions of the average degrees.
852-nm triggered single-photon source based on trapping and manipulation of a single cesium atom confined in a microscopic optical dipole trap
Authors: Liu Bei  , Jin Gang  , He Jun  , Wang Jun-Min  ,   Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China;,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University, Taiyuan 030006, China;,   Collaborative Innovation Center of Extreme Optics, Taiyuan 030006, China
Published: December 2020

Single-atom-based single-photon source has several advantages, such as narrow bandwidth, wavelength matching with the absorption line of the same atomic ensemble, and insensitivity to the environment disturbing, and it is very important not only for basic researches in quantum optic field but also for applications in quantum information processing. In this paper, we report the generation of a 10-MHz-repetition-rate triggered single-photon source at 852 nm based on a trapped single cesium atom in a far-off-resonance microscopic optical dipole trap (FORT). To generate an optical dipole trap, a far-red-detuned 1064 nm laser beam is tightly focused by using a high numerical aperture lens, a typical trap depth is 2 mK and trap waist is 2.3 m. To obtain a maximum probability of pulsed excitation, the frequency of the pulsed laser should be resonant with the atomic energy levels and the trapped single atom must be excited with a -pulse. However, the interaction between the FORT laser and the atoms causes AC Stark shifts of the atomic energy levels. Thus, in order to demonstrate the resonant pulsed excitation, it is important to calculate and measure the shift of 6S1/2|Fg=4,mF=+4-6P3/2|Fe=5,mF=+5 cyclical transition in the FORT. For a two-level system, the probability of pulsed excitation can be described by Rabi oscillations with a characteristic Rabi frequency . With an optimized time sequence, we experimentally demonstrate the Rabi oscillation between the ground state and the excited state, and the peak power of -pulse laser is about 1.25 mW. We also measure the temporal envelope of single photons after a -pulse excitation. A gated pulsed excitation and cooling technique are used to reduce the possibility that atoms are heated by -pulse laser. The typical trapping lifetime of single cesium atom is extended from~108 ups to~2536 ms. The corresponding number of excitations is improved from 108 to 360000. The second-order intensity correlations of the emitted single-photon are characterized by implementing Hanbury Brown-Twiss setup. The statistics shows a strong anti-bunching with a value of 0.09 for the second-order correlation at zero delay. In the future, we will perform a Hong-Ou-Mandel two-photon interference experiment to analyze the indistinguishability of the single photons. We will also trap single atoms in a magic-wavelength optical dipole trap where the ground and the excited states have the same shift.
Effective mass spectrum and dissipation power of granular material under the horizontal and vertical excitation
Authors: Xu Cong-Hui  , Zhang Guo-Hua  , Qian Zhi-Heng  , Zhao Xue-Dan  ,   Department of Physics, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

In this paper, in order to explore the movement characteristics of granular system under the horizontal and vertical excitation, the effective mass spectrum and dissipation power of granular material are studied by numerical simulation. We use LIGGGHTS software to simulate a granular system consisting of 13340 dispersed particles in a cubic container. For the two different vibration directions of granular system (horizontal and vertical), we carry out a pressure unloading experiment in a pressure range from 1012.10 kPa to 8.66 kPa. It is found that under the horizontal and vertical excitation, the resonance frequency fg and volume modulus k of granular system satisfy piecewise power-law with the change of pressure P applied to the top surface. It follows the laws, that is, fg∝P1/6 and k∝P1/3 at low pressure and fg∝P1/4 and k∝P1/2 at high pressure. At the same time, according to the effective mass of the imaginary part, we can obtain the dissipative characteristics of the granular system. Under the horizontal and vertical excitation, the reciprocal of quality factor of granular matter, 1/Q, decreases exponentially with the change of pressure P. In the relaxation dynamics of the granular system, both the acceleration and the stress play a role similar to the role of temperature in the thermal system. In order to further study the influence of acceleration on solid-fluid-like transition of granular system, we measure the relationships between the dissipation power and the vibration intensity (1g-30g) under different pressures (8.66-1012.10 kPa), in the horizontal vibration (500 Hz). At the fixed frequency and pressure, there is a characteristic vibration intensity Γ* in the curve of the average power dissipation of granular system with vibration intensity Γ. When ΓΓ*, the granular system exhibits a solid-like behavior, and the variation of the average power dissipation with the change of vibration intensity Γ shows a power-law scaling, p∝Γα (2αΓ > Γ*, the granular system exhibits a liquid-like behavior, and the variation of the average power dissipation of granular system with the vibration intensity Γ changes into a linear fashion. Then, the phase diagram of transition from the solid-like phase to fluid-like phase, i.e., Γ-P phase diagram, in granular system under the horizontal excitation, is obtained in this paper.
Molecular dynamics simulation of effect of grain on mechanical properties of nano-polycrystal -Fe
Authors: Wang Peng  , Xu Jian-Gang  , Zhang Yun-Guang  , Song Hai-Yang  ,   School of Science, Xi'an University of Posts and Telecommunications, Xi'an 710121, China;,   College of Material Science and Engineering, Xi'an Shiyou University, Xi'an 710065, China
Published: December 2020

The nanocrystalline metals are widely investigated due to their unique mechanical properties. Currently, the available studies about deformation mechanisms of metals mainly focus on face-centered cubic metals such as Ni, Cu and Au. However, the body-centered cubic metals are still very limited, despite their industrial importance. Here, we investigate the effects of grain size and temperature on the mechanical behavior of nano-polycrystal -Fe under uniaxial tensile loading by using molecular dynamics (MD) simulation. The models of nanocrystalline -Fe with the grain sizes of 3.95, 6.80, 9.70, 12.50, 15.50, 17.50, 20.70 and 26.00 nm are geometrically created in three dimensions by using Voronoi construction, and these models are relaxed to reach an equilibrium state. Then, each of them has a strain of 0.001 along the Z-direction in each step, keeping zero pressure in the X- and Y-directions until the strain increases up to 0.2. A 1.0 fs time step is used in all of the MD simulations. Based on the data output, the stress-strain curves at different grain sizes are obtained. The results indicate that the peak stresses of nano-polycrystal -Fe decrease with the decrease of grain size, exhibiting a breakdown in the Hall-Petch relation when the grain size is smaller than a critical size. The major deformation mechanism is found to change from dislocation slips and twinning-mediated plasticity in a model with a larger grain size to grain boundary sliding in a model with a smaller grain size. It should be noted that twinning is formed by the emission of 1/6111 partial dislocations along the {112} slip plane. The results show that crack formation during tension is a cause of reducing the flow stress of nano-polycrystal -Fe with a large grain size and that the Young's modulus of nano-polycrystal -Fe decreases with the grain size decreasing. The main reason for the crack nucleation is here that grain boundaries perpendicular to the loading direction bear higher stress and the twin band interacts with grain boundaries at a larger grain size, causing the stress to concentrate at the intersections of grain boundaries. The results also show the detwinning behavior and migration of deformed twins in nano-polycrystal -Fe. The detwinning behavior occurs via the migration of the intersection of grain boundary and twin, and this intersection is incoherent boundary. The migration of deformed twins proceeds by repeating initiation and glide of 1/6111 partial dislocations on adjacent {112} planes. In addition, we find that the nucleation and propagation of dislocation become easier at higher temperature than at lower temperature.
Topology optimization algorithm for wireless networks based on the algebraic properties of minimum rigid graph
Authors: Luo Xiao-Yuan  , Li Hao  , Ma Ju-Hai  ,   School of Electrical Engineering, Yanshan University, Qinhuangdao 066004, China
Published: December 2020

For wireless sensor networks, with energy constrained, topology optimization can reduce energy consumption and improve the structure of communication link. Based on the minimum rigid graph, a new topology optimization algorithm is presented in this paper, by considering the weights of communication links in graph and the generated algebraic properties of rigid graph. The proposed algorithm not only ensures the communication link is shorter which can prolong the network life cycle, but also keeps the graph structure more stable, which means that the network has good robustness. It is shown that communication link obtained by the proposed algorithm is shorter than that obtained by the related existing algorithms. As a result, the proposed algorithm has good network connectivity and structure stability. At the same time the trace of the generated rigid matrix is very big so that the proposed algorithm has excellent algebraic rigidity properties of a network.
Temperature measurement accuracy enhancement in the Brillouin optical time domain reflectometry system using the sideband of Brillouin gain spectrum demodulation
Authors: Liu Rui-Xia  , Zhang Ming-Jiang  , Zhang Jian-Zhong  , Liu Yi  , Jin Bao-Quan  , Bai Qing  , Li Zhe-Zhe  ,   Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education and Shanxi Province, Taiyuan 030024, China;,   Institute of Optoelectronic Engineering, College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China;,   State Key Laboratory of Coal and CBM Co-mining, Jincheng 048000, China
Published: December 2020

A novel method by demodulating the sideband of Brillouin gain spectrum (BGS) is proposed and demonstrated in order to enhance temperature measurement accuracy in a Brillouin optical time domain reflectometry (BOTDR) sensing system in this paper.Firstly,the characteristic of frequency shift of an acoustic optical modulator (AOM) is utilized to generate the sideband of BGS,and the influence of the peak power of the probe optical pulse on the temperature measurement accuracy is also investigated.Moreover,the theoretical analysis shows that benefiting from the reference continuous light from the source laser by the coherent detection,the intensity of the sideband is higher than that of the central peak,which indicates that the higher signal-to-noise ratio (SNR) can be expected by demodulating the sideband of BGS instead of the central peak.Thus the demodulating the sideband of BGS can further improve temperature measurement accuracy in the BOTDR sensing system theoretically.Secondly,the experimental setup of the distributed temperature sensing system based on BOTDR is built.The AOM is selected as the optical pulse modulator to produce high-extinction-ratio probe pulse light,following the frequency upshift of the injection light.The beat signal generated by coherently detecting the backscattering light from the fiber under test (FUT) and the reference light from the source laser is acquired.Furthermore,the central peak and the left sideband of BGS are respectively scanned by using microwave heterodyne frequency shift technique.The time domain waveforms at each frequency point are then obtained and Lorentzian curve fitting is performed at each sampling position,thus Brillouin frequency shift (BFS) along the FUT is plotted and the temperature is demodulated along the FUT based on the linear dependence of the BFS on the temperature in the optical fiber.Finally,the experimental results show that the peak power of the left sideband of Brillouin gain spectrum is about 3.27 dB stronger than that of the central peak.Meanwhile,the linewidth of left sideband of BGS is about 14.7 MHz narrower than that of the central peak at -1 dB point in the same conditions.When the left sideband of BGS is scanned,the SNR of the BOTDR system is improved by 4.35 dB due to the contribution of the reference light by coherently detecting and eliminating the effect of the coherent Rayleigh noise,and then the temperature measurement accuracy of 0.5℃ is achieved over a 10.2 km sensing fiber.
Omnidirectional photonic bandgap of the one-dimensional plasma photonic crystal based on a novel Fibonacci quasiperiodic structure
Authors: Zhang Juan  ,   Key Laboratory of Specialty Fiber Optics and Optical Access Networks, School of Communication and Information Engineering, Shanghai University, Shanghai 200072, China
Published: December 2020

The binary one-dimensional plasma photonic crystal (1DPPC) based on Fibonacci quasiperiodic structure is studied systematically in this paper. We consider the two simplest cases. In one case, the initial sequences F0 and F1 are both of single layer structure. In another case, one initial sequence (F0 or F1) is of a single layer structure, while the other one (F1 or F0) is of a double layer structure. Thus there are ten different kinds of initial sequences in total. The photonic bandgap characteristics of the 1DPPC with these different initial sequences and numbers of period are analyzed. On these bases, a novel structure of one-dimensional plasma photonic crystal (F3)3 with initial sequence of F0=AP, F1=P and F0=PA, F1=P is proposed in this paper to enlarge the omnidirectional photonic bandgap (OPBG). Compared with previously reported structures in the literature, this structure is simple in configuration with fewer layers and materials, and its OPBG width is wide. The influences of the parameters of the plasma material, such as the thickness, plasma frequency and collision frequency, on the OPBG characteristics of this structure are also discussed. The OPBG width increases with the increase of the thickness and plasma frequency of the plasma layer. Compared with the structures in the literature, the change of OPBG width is the fastest for the proposed structure when the parameters are relatively small. And with the same parameters, the OPBG width for the proposed structure is the widest when the parameters are greater than a certain value. The plasma collision frequency has no effect on the OPBG width for all the structures. But the OPBG width for the proposed structure is the widest when this parameter has the same value. The reason why the proposed structure has an optimal OPBG width is explained by analyzing the dispersion properties of the plasma. The real and imaginary part of the dielectric constant of plasma change with frequency significantly only in the low frequency region. Since the imaginary part of dielectric constant is nearly zero when the frequency is larger than 2 GHz, only the dispersion effect of the real part of dielectric constant needs to be considered in the frequency range we investigate. And its value is much greater than that of conventional medium in the same frequency range. This makes the high-reflectance bands of the 1DPPC broader than those in the case of pure photonic interference phenomena with conventional medium. On the other hand, the corresponding highest proportion of plasma layers in the whole quasiperiodic structure can also be used to explain the broadest band gap of (F3)3. These results can provide important theoretical guidance for designing the novel omnidirectional reflectors.