bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of salt concentrations and pore surface structure on the water flow through rock nanopores
Authors: Yin Yu-Ming , Zhao Ling-Ling ,   Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy & Environment, Southeast University, Nanjing 210096, China
Published: December 2020

The surface dissolution of rock nanopores, caused by the acidic environment, increases the salt concentration of water solution flowing in the nanopores, thereby destroying the surface structure of the rock, which can be found in CO2 geological sequestration and crude oil and shale gas exploration. In this paper, the molecular dynamics method is adopted to study the flow characteristics of water solution in the forsterite (Mg2SiO4) slit nanopores, by which the effects of salt concentration and structure destruction of pore surface on the velocity profiles of water solution confined in nanopores are systematically analyzed. The hydrogen bond density, radial distribution function (RDF) and water density distribution are calculated to explain the changes in viscosity, velocity profiles and interaction between water and nanopore surface. The results show that as the salt concentration increases, the water solution flow in the rock nanopore obeys the Hagen-Poiseuille equation, and the velocity profiles of water solution remain parabolic shape. However, the hydrogen bond network among water molecules becomes denser with salt concentration increasing, which can account for the linear increase in the viscosity of water solution. Besides, the higher salt concentration gives rise to the larger water flow resistance from the pore surface. As a result, with the salt concentration increasing, the maximum of water velocity decreases and the curvature radius of the parabolic velocity profile curve becomes bigger. Moreover, the surface structure destruction in rock nanopores changes the roughness of surface in the flow channel, which enhances the attraction of nanopore surface to H2O. As the structure destruction of nanopore surface deteriorates, the water density near the rough surface moves upward, whereas the velocity of water near the rough surface declines obviously. Interestingly, when the degree of surface structure destruction reaches 50%, a significant negative boundary slipping near the rough surface appears.
Live streaming: Data mining and behavior analysis
Authors: Guo Shu-Hui , Lu Xin ,   College of Systems Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

With the rapid development of mobile communication and Internet technologies, online live streaming has gradually become popular for information communication and entertainment in the new media environment. Live streaming has been widely used in teaching, reality show, E-sports games and events, brand marketing and other aspects. With the active participation of millions of streamers and hundreds of millions of viewers, massive online crowd behavior activity data are generated, which offers rich experimental scenarios for large-scale crowd behavior dynamics research, live streaming channel recommendation and online community evolution. In this paper, we summarize the relevant research literature of live streaming, and review current studies from a comprehensive list of aspects: workload pattern, viewers and streamers behavior, community network discovery and analysis, etc. We summarize the temporal and spatial patterns of live streaming platform workload, heavy tailed effect of large-scale crowd behavior in live streaming platform, etc. We believe that the future work on live streaming can be directed in the examination of formation and evolution mechanism of various community networks formed by large-scale users, as well as the recommendation and detection of live streaming content.
Design of gain region of high-power vertical external cavity surface emitting semiconductor laser and its fabrication
Authors: Zhang Ji-Ye , Zhang Jian-Wei , Zeng Yu-Gang , Zhang Jun , Ning Yong-Qiang , Zhang Xing , Qin Li , Liu Yun , Wang Li-Jun ,   State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China,   Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

 The vertical external cavity surface emitting laser (VECSEL) is one of the hottest research fields of semiconductor lasers, due to its high power and good beam quality. However, there are few reports about how to systematically design the active region of VECSEL. In this paper, the gain design of quantum wells, which are the most important region within the VECSEL, is carried out.

 To achieve low power consumption under high temperature condition, epitaxial structure of the VECSEL is optimized by using the commercial software PICS3D. Firstly, the relationship between the structure of quantum well and the gain is simulated by the k·p method. Then, the gain spectra of quantum wells at different carrier densities and temperatures are compared with each other, and the optimal composition and thickness of quantum well are thus determined. The temperature drift coefficient is 0.36 nm/K, obtained by simulating the drift of the gain peak wavelength at the working temperature. Finally, the gain spectra of quantum wells with five different barriers are compared with each other. The slight blue shift of the gain peak in the quantum well with five different barriers accommodates the different emission thermal drifts of the quantum well at high temperature operation. With the GaAsP barriers on both sides of quantum well the gain characteristics of quantum wells can be improved efficiently.

 The designed structure is deposited by the MOCVD system. According to the reflection spectrum of the gain chip, measured by ellipsometer, the stop-band over 100 nm is centered at the about 970 nm wavelength, confirming accurate growth of the VECSEL. The 808 nm pump laser is focused on the surface of VECSEL chip at an incident angle from 30° to 50°. The VECSEL light-light characteristics are tested under the output coupling mirror with different reflectivity. The output power of VECSEL with a 97.7% reflectance output coupling mirror reaches 9.82 W at the pumping power of 35 W, without saturating the power curve. By using the external mirrors with different reflectivity, there appears the wavelength shift with the pumping power changing from 0.216 nm/W to 0.16 nm/W. Thus, the internal heating effects are different for VECSEL with different mirrors. The divergence angles at two orthogonal directions are 9.2° and 9.0°, respectively. And the circle profile of optical field shows good symmetry.
Sound focusing in inhomogeneous waveguides
Authors: Guo Wei , Yang De-Sen ,   Acoustic Science and Technology Laboratory, Harbin Engineering University, Harbin 150001, China,   Key Laboratory of Marine Information Acquisition and Security (Harbin Enhineering University), Ministry of Industry and Information, Harbin 150001, China,   College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin 150001, China
Published: December 2020

A method for analytically studying sound focusing in inhomogeneous waveguides is presented. From the viewpoint of acquiring the maximum acoustic pressure at an arbitrary position with normalized energy flux injection, optimal incident waves can be derived based on the multimodal admittance method. The method involves two steps. The first step is to expand the wave solution onto a complete orthogonal basis set so that the Helmholtz equation can be transformed into two sets of first-order coupled differential equations in the modal domain. The second step is to solve the coupled equations numerically by introducing admittance matrices and propagators, which can be used to derive reflection matrices and transmission matrices. Using the multimodal admittance method, one can circumvent the contamination caused by exponentially diverging evanescent modes and acquire stable wave solutions. Then the mapping between the acoustic pressure at an arbitrary position and that of the incident wave can be constructed, and this mapping changes the problem of wave focusing into solving the extrema of inner products in Hilbert space. The optimal incident waves that generate wave focusing at an arbitrary position can be readily computed together with the corresponding wave solutions. In this paper, we study the sound focusing in waveguides with varying cross-sections, scatterers and sound-speed profiles. The results show that the optimal incident waves will take full advantage of wave scattering caused by the boundaries and inhomogeneities during propagation to achieve the maximum pressure at foci, leading to good single-point and multi-point sound focusing performance. In addition, we find when injecting the spatially sampled optimal incident waves or the optimal incident waves with random perturbations, the resultant wave focusing phenomena will be still apparent. The focusing behaviors are highly robust to the perturbations of the moduli of the incident waves and slightly less robust to that of the arguments of the incident waves. Our method is also available for analyzing wave focusing in other kinds of inhomogeneous waveguides. We believe that our research can provide guidance on designing acoustic lenses or metamaterials to focus sound waves in complex media, and can offer inspiration in wave communications, imagings and non-destructive testing.
Diagnosis of capacitively coupled plasma driven by pulse-modulated 27.12 MHz by using an emissive probe
Authors: Zhou Yu , Cao Li-Yang , Ma Xiao-Ping , Deng Li-Li , Xin Yu ,   Department of Physical Science and Technology, Soochow University, Suzhou 215006, China
Published: December 2020

There are several methods of diagnosing the capacitively coupled plasma, such as microwave resonance probe, Langmuir probe, etc, but methods like microwave resonance probe are mainly used for determining the electron density. Moreover, in the diagnosing of plasma potential, the emissive probe has a higher accuracy than the traditional electrostatic probes, and it can directly monitor the potential in real time. However, in the existing work, emissive probe is mostly applied to the diagnosis of plasmas with high density or plasmas modulated by pulsed dual frequency (one of the radio frequency sources is modulated), the experiments on the emissive probe diagonising plasma excited by a pulsed single frequency are quite rare. In this paper, the temporal evolution of the plasma potential and electron temperature with input power and pressure in a pulsed 27.12 MHz capacitively coupled argon plasma are investigated by using an emissive probe operated in floating point mode. The plasma potential is obtained by measuring emissive probe potential under a strongly heated condition, while the electron temperature is estimated from the potential difference between the emissive probe under strongly heating and cold conditions. The measurements show that as the pulse is on, the plasma potential will rise rapidly and become saturated within 300 μs due to the requirement for neutrality condition; while the pulse is off, the plasma potential undergoes a rapid decline and then stabilizes. An overshoot for the electron temperature occurs as the onset of the pulse, because of the influence of radio frequency electric field and residual electrons from the last pulse; during the pulse-off time, rapid loss of high-energy electrons causes the electron temperature to rapidly drops to 0.45 eV within 300 μs, then it rises slightly, which is related to the electrons emitted by the probe. The plasma potential basically has a linear dependence on the change of input power and pressure for the pulse-on and pulse-off time; and the input power has a greater influence on the difference between the overshoot electron temperature and the steady state electron temperature during the pulse-on time. Corresponding explanations are given for the temporal evolution of plasma potential and electron temperature in different pulse stages and under different discharge conditions.
Avalanche photodiode single-photon detector with high time stability
Authors: Zhang Hai-Yan , Wang Lin-Li , Wu Chen-Yi , Wang Yu-Rong , Yang Lei , Pan Hai-Feng , Liu Qiao-Li , Guo Xia , Tang Kai , Zhang Zhong-Ping , Wu Guang ,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China,   School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China,   Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
Published: December 2020

Avalanche photodiode single-photon detector is one of the ultra-sensitivity photoelectric detector, which has important applications in the fields of long-distance laser ranging, laser imaging, and quantum communication. However, due to the high temperature sensitivity of the avalanche voltage, the avalanche photodiode single-photon detector is prone to fluctuation of the avalanche gain when it works in the field environment, which leads to the delay drift and seriously reduces the time stability. In this paper, we proposed a method of stabilizing the delay of the single-photon detector. An embedded system was used to control avalanche photodiode at constant low temperature and compensate the delay drift of the detection circuit caused by the change of environment temperature in real time. A high time stability avalanche photodiode single-photon detector was realized by this method. In the experiment, the environment temperature changed from 16 ℃ to 36 ℃, and the avalanche photodiode was controlled at 15 ℃. After compensation, the delay drift of the avalanche photodiode single-photon detector was within ±1 ps, and the time deviation was 0.15 ps@100 s. This work is expected to provide an effective solution for the application of high-stability single-photon detector in the field and space environment.
Pseudospin states and topological phase transitions in two-dimensional photonic crystals made of dielectric materials
Authors: Wang Yan-Lan , Li Yan ,   School of Physics and Physical Engineering, Qufu Normal University, Qufu 273165, China
Published: December 2020

Based on the transmission properties of against backscattering and robustness against defects, photonic topological insulators have opened up a novel way to steer the propagation of electromagnetic wave. In order to construct the photonic analogs of the quantum spin Hall effect in an electronic system, we propose a simple two-dimensional photonic crystal made of dielectric materials to realize topologically protected edge states associated with the photonic pseudospin. The photonic crystal comprises a honeycomb array of equilateral-triangle-ring-shaped silicon rods embedded in an air host. By simply rotating the silicon rods around their respective centers by 60°, the band inversion between a twofold degenerated dipolar mode and a twofold degenerated quadrupolar mode is clearly observed in the Brillouin zone center. For the double twofold degenerated states, the chirality of the time-averaged Poynting vector surrounding the unit cell center (i.e., right-hand or left-hand circular polarizations) plays the role of the pseudospin degree of freedom in the present photonic system, and their point group symmetry can be utilized to construct a pseudo-time-reversal symmetry. By utilizing \begin{document}${{k}} \cdot {{p}}$\end{document} perturbation theory, we develop an effective Hamiltonian for the associated dispersion relation around the Brillouin zone center and calculate the spin Chen number, which indicates that the band inversion leads to a topological phase transition from a trivial to a nontrivial state. With numerical simulations, we unambiguously demonstrate that the unidirectional propagation of pseudospin-dependent edge state along the interface between a topologically nontrivial photonic crystal and a trivial one, and robustness of the edge states against different defects including sharp bend and cavity, regardless of the type of interface. The photonic system proposed by us consists of dielectric materials and the corresponding lattice structure is simple. And without changing the fill ratio or changing the positions of the silicon rods, a simple rotation of the silicon rods can generate the topological phase transition. So the potential applications of the pseudospin-dependent edge states based on our design are expected in more efficient way.
New method of determining height of atmospheric boundary layer and numerical experiment
Authors: Zhou Jian-Yin , Xiang Jie , Huang Si-Xun ,   College of Meteorology and Oceanography, National University of Defense Technology, Nanjing 211101, China,   State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China
Published: December 2020

In this paper, we propose a new method of numerical differentiation to determine the height of the top layer of the atmospheric boundary layer. In this method, a regularization technique is used to convert the problem of calculating the differential of the curve of the corners into the problem of finding the minimum value of the objective function. The two-parameter model function method is used to select the regularization parameters. Finally, the maximum gradient method is used to determine the top height of the boundary layer. Firstly, the effectiveness of the new method is validated through two numerical experiments. The experimental results show that as the noise of the occultation data increases, the fluctuation of the height of the boundary layer top obtained by the difference method and the numerical differentiation method combined with the L curve scheme increases. And the height obtained by the two-parameter model function method is very stable, which shows that the new method can filter the noise well, thereby retaining the main information about the profile. Then, based on the COSMIC angle data in January, April, July and October 2007－2011, the new method is used to analyze the seasonal characteristics of the height of the global oceanic and atmospheric boundary layer, compared with the seasonal distribution obtained by “zbalmax” with the occultation data. The results show that the seasonal distribution characteristics of the two data are very consistent: the height of the boundary layer is higher in the area where the sea surface temperature is higher than that in the surrounding sea area; on the contrary, the height of the boundary layer top is lower. In the sea area where the warm current passes, the height of the boundary layer is higher; in the sea area where the cold current passes, the height of the boundary layer is lower.
Experimental research on Rayleigh-Taylor instability of oxygen-free high conductivity copper under explosive loading
Authors: Li Bi-Yong , Peng Jian-Xiang , Gu Yan , He Hong-Liang ,   School of Science, Nanjing University of Science and Technology, Nanjing 210094, China,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621999, China
Published: December 2020

The instability of metal interface is an important problem in the process of implosion physical compression, which is significantly different from the traditional fluid interface instability. Due to the limitation of related theory and experimental diagnosis technology, this problem is studied still insufficiently. In order to understand in depth the perturbation growth behavior of metal interface instability, the technique for high explosive driven Rayleigh-Taylor instability experiment on the oxygen-free high conductivity (OFHC) copper is developed. The perturbation growth on OFHC copper interface with varying initial perturbation amplitude at a specific time is recorded by radiography. According to the data processing on the X-ray images, the perturbation growth behaviors of the interface at different times are obtained. The experimental results show that the larger the initial perturbation amplitude, the faster the perturbation grows, but the perturbation wavelength of the interface remains almost unchanged at the explosive loading. The perturbation on the front interface will have an effect on the back free interface, and cause some corresponding disturbance to occur on the surface, namely, on the back free interface, the position corresponding to the perturbation trough of the front interface first moves and gradually evolves into a spike, while the position corresponding to perturbation crest evolves into a bubble. The strain rate of instability perturbation growth reaches ～105/s, and the perturbation amplitude of the interface increases to about 700% of the initial value at 5.26 μs. The corresponding numerical simulation results show that the normal SCG model underestimates the strength of copper and cannot well describe the stabilizing effect of material strength at this high strain rate, thereby leading to the fact that the simulation results are higher than the experimental results.
Anisotropic dissipation in a dipolar Bose-Einstein condensate
Authors: Zhao Shan-Shan , He Li , Yu Zeng-Qiang ,   Institute of Theoretical Physics, Shanxi University, Taiyuan 030006, China,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China
Published: December 2020

The ability to support frictionless motion is one of the manifestations of superfluidity. An impurity immersed in a superfluid can move without dissipation below the critical velocity, which, according to the Landau criterion, is determined by the elementary excitation spectrum of the system. In a quantum gas of the ultracold atoms, the critical velocity can be measured by stirring a laser beam through the atomic cloud, and the emergence of dissipation can be observed via the heating effect above the threshold stirring speed. Recently, such a technique is exploited to study the superfluidity of the Bose-Einstein condensate (BEC) of 162Dy atoms with dipole-dipole interactions. It is shown that both the critical velocity and the heating rate reflect the anisotropy of the underlying dipolar excitation spectrum.

In this work, we theoretically investigate the anisotropic dissipation of a point-like impurity moving through a dipolar BEC. For the motion along the principal axis, the dissipation rate above the critical velocity is analytically derived according to the linear response theory. At a given reduced velocity, we find the dissipation rate being of a higher value in the direction parallel to the dipole moment, which qualitatively explains the recent experimental observation in dysprosium atoms. Moreover, in the moving direction away from the principal axis, the asymptotic expressions for the dissipation rate are obtained in the high-speed limit, as well as in the regime close to the dissipation threshold. By combining these analytical results with the numerical calculations, we conclude that, in a dipolar BEC, the angular dependence of the dissipation rate always shows the same anisotropy as the critical velocity. Our predictions can be examined in the current experiments with cold atoms, and the results presented here may be also helpful in understanding the anisotropic superfluidity in other systems.
Generation of quadripartite entanglement based on four-wave mixing process and linear beam splitter
Authors: Yu Sheng , Liu Huan-Zhang , Liu Sheng-Shuai , Jing Jie-Tai ,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

As a crucial quantum resource in quantum information processing, multipartite entanglement plays an important role not only in the field of testing basic quantum effects, but also in the applications of quantum network, quantum communication and quantum computing. The generation of multipartite entanglement usually involves many complex linear processes and nonlinear processes. In this paper, we theoretically propose a scheme for generating genuine quadripartite entanglement by linking two independent four-wave mixing (FWM) processes with one linear beam splitter (BS). Here, we use one linear BS to mix the probe beams amplified by two independent FWM processes. We first set the transmissivity of the linear BS to be 0.5 and study the effect of the intensity gain of the system on quadripartite entanglement by applying the positivity under partial transposition (PPT) criterion. The results show that there exists genuine quadripartite entanglement in all gain regions, and the degree of entanglement increases with intensity gain increasing. And then, the dependence of quadripartite entanglement on the transmissivity of the linear BS is studied when the intensity gains of two independent FWM processes are both set to be 3. We find that the transmissivity of the linear BS can affect the entanglement properties of the system. At the same time, we also find that the system can generate genuine quadripartite entanglement when the transmissivity of the linear BS is not equal to 0 or 1. Finally, in order to reveal the entanglement structure of the system, we further investigate the dependence of the possible tripartite entanglement and bipartite entanglement on the intensity gain of the system by using the PPT criterion. The results show that there exists the genuine tripartite entanglement in this system, and the degree of entanglement increases as the intensity gain increases. However, there exists no genuine bipartite entanglement in this system, some of bipartite states are always separable, and the entanglement of the other bipartite states gradually become weak and eventually disappear with the increase of the intensity gain. Our theoretical result provides a simple and reliable scheme for generating genuine quadripartite entanglement by using FWM process in atomic ensemble and linear BS.
Epidemiological parameters and models of coronavirus disease 2019
Authors: Li Ying-Ke , Zhao Shi , Lou Yi-Jun , Gao Dao-Zhou , Yang Lin , He Dai-Hai ,   College of Mathematics and Physics, Xinjiang Agriculture University, Urumqi 830052, China,   JC School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong 999077, China,   Department of Applied Mathematics, Hong Kong Polytechnic University, Hong Kong 999077, China,   Department of Mathematics, Shanghai Normal University, Shanghai 200234, China,   School of Nursing, Hong Kong Polytechnic University, Hong Kong 999077, China
Published: December 2020

The coronavirus disease 2019 (COVID-19) has become a major public health concern internationally. To capture the epidemic growing patterns and quantify the transmissibility, some key epidemiological parameters and dynamic models are of significance for helping us to understand the features of COVID-19 and thus informing the strategic decision-making in combating the outbreak. In this study, we review and summarize the recently released research results about the reproduction numbers, incubation period and serial interval of COVID-19. We summarize the estimates as well as estimation approaches adopted to calculate these epidemiological parameters in the existing literature. These studies found that the basic reproduction number is estimated at 2.6, the mean incubation period at about 5.0 days, and the mean serial interval at about 5.5 days. The COVID-19 infections can increase rapidly if it is not controlled. The control measures including the isolation, quarantine, contact tracing, improvement of public awareness, and adoption of self-protection measures can effectively mitigate the COVID-19 outbreak.
Statistical analysis and autoregressive modeling of confirmed coronavirus disease 2019 epidemic cases
Authors: Cao Wen-Jing , Liu Xiao-Fei , Han Zhuo , Feng Xin , Zhang Lin , Liu Xiao-Fan , Xu Xiao-Ke , Wu Ye ,   School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China,   School of Management Science and Engineering, Hebei GEO University, Shijiazhuang 050031, China,   School of Media and Communication, City University of Hong Kong, Hongkong 999077, China,   School of Information and Telecommunication Engineering, Dalian Minzu University, Dalian 116600, China,   Computational Communication Research Center, Beijing Normal University, Beijing 100875, China
Published: December 2020

Based on the information about more than 800 cases reported by Anhui provincial health commission on February 19 2020, the directional transmission relationship between the confirmed patients is constructed according to the contact history published in the cases, and it is found that the majority of the patients who can infect others are male and most of the patients who are infected are female. According to the analysis of case information, the early confirmed coronavirus disease 2019 (COVID-19) cases in Anhui province had the history of residence or exposure in Wuhan. In the later stage, the cases spread in small communities mainly by local transmission, and the strict prevention and control measures can effectively cut off further transmission in the communities. The time interval between diagnosing the source-infected patients and infected patients is fitted by Γ distribution, with a median of 2 days and an average of 2.67 days. Based on the statistical characteristics of directional transmission relationship, an autoregressive transmission model is constructed in the late stage of epidemic development in Anhui province, and the simulation results are consistent with the epidemic development data. Autoregressive model and simulation are also used for predicting the data of confirmed cases in the whole country except for Hubei province. This discovery can be referenced by regional epidemic prevention and control except for where it originated. Through strict protection measures and isolation measures, the spread of the epidemic outside the original place is highly viscous. It usually spreads by close contact between family members, and the local spread of COVID-19 can be effectively controlled.
Influence of electro-optic modulator on Er-doped fiber femtosecond laser
Authors: Cao Shi-Ying , Lin Bai-Ke , Yuan Xiao-Di , Ding Yong-Jin , Meng Fei , Fang Zhan-Jun ,   Division of Time and Frequency Metrology, National Institute of Metrology, China, Beijing 100029, China
Published: December 2020

Narrow-linewidth femtosecond optical frequency comb plays an important role in the fields, such as optical clock comparison, time frequency transfer, ultrastable microwave generation, absolute distance measurement, high precision spectroscopy, etc. Due to the influence of the lifetime of the upper energy level in the gain medium, the linewidth of Er-fiber combs is generally on the order of several hundred kilohertz. In order to narrow the linewidth of comb teeth, an effective method is to insert a fast response electro-optic modulator (EOM) into the laser cavity, so that the servo bandwidth of fiber comb is extended to several hundred kilohertz, which provides a feedback mechanism for fast servo locking. Among them, a high quality femtosecond laser is the core. Based on this, the influence of the EOM on the parameters of Er-fiber femtosecond laser is studied in this paper. By calculating the refractive index, group velocity dispersion, and phase delay of the electro-optic crystal, the influence of the introduction of the EOM on the laser performance is analyzed. A LiNbO3 (LN) crystal with a length of 3 mm and x-cut is selected as the EOM and inserted into the laser cavity. The influence of the applied voltage of the EOM on the repetition rate and carrier envelope offset frequency of the laser are obtained experimentally. When the voltage on the LN crystal changes from -200 to 200 V, the adjustment of repetition rate is 60 Hz and the carrier envelope offset frequency is 25 MHz. Then the two parameters are phase locked through the EOM. Furthermore, by phase locking the beat note between the fiber comb and a narrow-linewidth continue wavelength laser at 1542 nm, it is verified that the introduction of the EOM can expand the servo bandwidth of the laser to more than 236 kHz, which provides a technical basis for establishing narrow linewidth femtosecond optical frequency combs. The following work will verify the performance of comb line, that is, when the comb is locked to a narrow-linewidth laser (such as 1542 nm), the performance of comb line at wavelength (such as 698, 729 nm, and so on) of distant place will be analyzed in detail.
Propagation characteristics of focused astigmatic Gaussian beams in Kerr nonlinear media
Authors: Hu Jing , Wang Huan , Ji Xiao-Ling ,   Department of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610068, China
Published: December 2020

When a powerful laser beam propagates in a Kerr nonlinear medium, the Kerr effect on the beam propagation characteristics is very significant. The astigmatic laser beams are often encountered in practice. Until now, much work has been carried out on the propagation characteristics of astigmatic laser beams in linear media, but a few researches have been reported about the propagation of astigmatic laser beams through nonlinear media. To the best of our knowledge, the propagation or the transformation of astigmatic laser beams through an optical system in a Kerr nonlinear medium has not been investigated. In this paper, the propagation characteristics of focused astigmatic Gaussian beams in a nonlinear Kerr medium are studied. The Kerr effect on the beam astigmatism and the focal shift of focused astigmatic Gaussian beams are investigated in detail, and the self-focusing focal length and focus control of focused astigmatic Gaussian beams in the Kerr nonlinear medium are also studied. For the beam spreading case, the analytical formula for each of the beam width, the beam waist position, and the focal shift of focused astigmatic Gaussian beams in the Kerr nonlinear medium is derived. It is shown that in the self-focusing medium, as the beam power increases (i.e. the self-focusing effect becomes stronger), the beam astigmatism becomes stronger, but the focal shift decreases. However, in a self-defocusing medium, as the beam power increases (i.e. the self-defocusing effect becomes stronger), the beam astigmatism becomes weaker, but the focal shift increases. On the other hand, for the beam self-focusing case, the analytical formula of the self-focusing focal length of focused astigmatic Gaussian beams in the Kerr nonlinear medium is derived. It is found that the number of foci can be controlled by applying beam astigmatism. The results obtained in this paper are of theoretical and practical significance.
Electron transport through Su-Schrieffer-Heeger chain with spin-orbit coupling
Authors: Xue Hai-Bin , Duan Zhi-Lei , Chen Bin , Chen Jian-Bin , Xing Li-Li ,   Key Laboratory of Interface Science and Engineering in Advanced Materials of Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China,   College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China
Published: December 2020

In the Su-Schrieffer-Heeger (SSH) chain, the nontrivial topological edge states will have different winding numbers when the intra-cell and inter-cell hopping amplitudes are spin-dependent ones. Consequently, how to detect the edge states with different winding numbers theoretically and experimentally has become one of important topics in condensed matter physics. In this paper, in the framework of the tight-binding approximation, we study the topological properties and the electron transport properties of the edge states of the SSH chain with the spin-orbit coupling. It is demonstrated that the winding numbers of the quadruple-degenerate and twofold-degenerate edge states are two and one, respectively. Importantly, the electron transport properties in the vicinity of the zero energy can characterize the energy spectra of the edge states, when the spin-polarized electrons tunnel into the SSH chain from the source lead, namely, the source lead is a ferromagnetic one. With increasing the tunneling coupling strengths between the SSH chain and the two leads from the weak coupling regime to the strong coupling one, the number of transmission resonance peaks of the quadruple-degenerate with the winding numbers being two and twofold-degenerate edge states with the winding numbers being one will be reduced by four and two, respectively. In other words, the transmission resonance peaks related to the edge states will disappear when the SSH chain is strongly coupled to the two leads. Therefore, these results suggest an alternative way of detecting the nontrivial topological ones with different winding numbers by changing the number of transmission resonance peaks of edge states.
In-situ liquid phase transmission electron microscope and its application in nanoparticle characterization
Authors: Liu Xuan-Xuan , Guo Hong-Xuan , Xu Tao , Yin Kui-Bo , Sun Li-Tao ,   Key Lab of MEMS of Ministry of Education, School of Electronic Science and Engineering, Southeast University, Nanjing 210096, China,   FEI Nano-Pico Center, Southeast University, Nanjing 210096, China,   School of Microelectronics, Southeast University, Wuxi 214000, China
Published: December 2020

Based on the improvement of transmission electron microscope (TEM), nano fabrication, and film deposition, and with the development of the in-situ liquid TEM and nano characterization platform, various relevant nano researches have been carried in different fields. In this article, the principle, basic design requirements, development and typical preparation technologies of the liquid cell are briefly introduced. Subsequently, the state-of-the-art applications of liquid cell transmission electron microscope in the nucleation and growth of nanoparticles are reviewed. Finally, the opportunities and challenges faced by the frontier development of this technology are also discussed. This article provides constructive discussion about and support for advanced nano characterization technology and precise manipulation of atomic structures.
Mummified baboons reveal the far reach of early Egyptian mariners
Authors: Dominy Nathaniel J , Ikram Salima , Moritz Gillian L , Wheatley Patrick V , Christensen John N , Chipman Jonathan W , Koch Paul L
Published: December 2020

The Red Sea was witness to important events during human history, including the first long steps in a trade network (the spice route) that would drive maritime technology and shape geopolitical fortunes for thousands of years. Punt was a pivotal early node in the rise of this enterprise, serving as an important emporium for luxury goods, including sacred baboons (Papio hamadryas), but its location is disputed. Here, we use geospatial variation in the oxygen and strontium isotope ratios of 155 baboons from 77 locations to estimate the geoprovenance of mummified baboons recovered from ancient Egyptian temples and tombs. Five Ptolemaic specimens of P. anubis (404–40 BC) showed evidence of long-term residency in Egypt prior to mummification, consistent with a captive breeding program. Two New Kingdom specimens of P. hamadryas were sourced to a region that encompasses much of present-day Ethiopia, Eritrea, and Djibouti, and portions of Somalia and Yemen. This result is a testament to the tremendous reach of Egyptian seafaring during the 2nd millennium BC. It also corroborates the balance of scholarly conjecture on the location of Punt.
Neural mechanisms underlying expectation-dependent inhibition of distracting information
Authors: van Moorselaar Dirk , Lampers Eline , Cordesius Elisa , Slagter Heleen A
Published: December 2020

Predictions based on learned statistical regularities in the visual world have been shown to facilitate attention and goal-directed behavior by sharpening the sensory representation of goal-relevant stimuli in advance. Yet, how the brain learns to ignore predictable goal-irrelevant or distracting information is unclear. Here, we used EEG and a visual search task in which the predictability of a distractor’s location and/or spatial frequency was manipulated to determine how spatial and feature distractor expectations are neurally implemented and reduce distractor interference. We find that expected distractor features could not only be decoded pre-stimulus, but their representation differed from the representation of that same feature when part of the target. Spatial distractor expectations did not induce changes in preparatory neural activity, but a strongly reduced Pd, an ERP index of inhibition. These results demonstrate that neural effects of statistical learning critically depend on the task relevance and dimension (spatial, feature) of predictions.
Structural basis for effector transmembrane domain recognition by type VI secretion system chaperones
Authors: Ahmad Shehryar , Tsang Kara K , Sachar Kartik , Quentin Dennis , Tashin Tahmid M , Bullen Nathan P , Raunser Stefan , McArthur Andrew G , Prehna Gerd , Whitney John C
Published: December 2020

Type VI secretion systems (T6SSs) deliver antibacterial effector proteins between neighboring bacteria. Many effectors harbor N-terminal transmembrane domains (TMDs) implicated in effector translocation across target cell membranes. However, the distribution of these TMD-containing effectors remains unknown. Here, we discover prePAAR, a conserved motif found in over 6000 putative TMD-containing effectors encoded predominantly by 15 genera of Proteobacteria. Based on differing numbers of TMDs, effectors group into two distinct classes that both require a member of the Eag family of T6SS chaperones for export. Co-crystal structures of class I and class II effector TMD-chaperone complexes from Salmonella Typhimurium and Pseudomonas aeruginosa, respectively, reveals that Eag chaperones mimic transmembrane helical packing to stabilize effector TMDs. In addition to participating in the chaperone-TMD interface, we find that prePAAR residues mediate effector-VgrG spike interactions. Taken together, our findings reveal mechanisms of chaperone-mediated stabilization and secretion of two distinct families of T6SS membrane protein effectors.
Identification of histone deacetylase genes in Dendrobium officinale and their expression profiles under phytohormone and abiotic stress treatments
Authors: Zhang Mingze , Teixeira da Silva Jaime A. , Yu Zhenming , Wang Haobin , Si Can , Zhao Conghui , He Chunmei , Duan Jun
Published: December 2020

The deacetylation of core histones controlled by the action of histone deacetylases (HDACs) plays an important role in the epigenetic regulation of plant gene transcription. However, no systematic analysis of HDAC genes in Dendrobium officinale, a medicinal orchid, has been performed. In the current study, a total of 14 histone deacetylases in D. officinale were identified and characterized using bioinformatics-based methods. These genes were classified into RPD3/HDA1, SIR2, and HD2 subfamilies. Most DoHDAC genes in the same subfamily shared similar structures, and their encoded proteins contained similar motifs, suggesting that the HDAC family members are highly conserved and might have similar functions. Different cis-acting elements in promoters were related to abiotic stresses and exogenous plant hormones. A transient expression assay in onion epidermal cells by Agrobacterium-mediated transformation indicated that all of the detected histone deacetylases such as DoHDA7, DoHDA9, DoHDA10, DoHDT3, DoHDT4, DoSRT1 and DoSRT2, were localized in the nucleus. A tissue-specific analysis based on RNA-seq suggested that DoHDAC genes play a role in growth and development in D. officinale. The expression profiles of selected DoHDAC genes under abiotic stresses and plant hormone treatments were analyzed by qRT-PCR. DoHDA3, DoHDA8, DoHDA10 and DoHDT4 were modulated by multiple abiotic stresses and phytohormones, indicating that these genes were involved in abiotic stress response and phytohormone signaling pathways. These results provide valuable information for molecular studies to further elucidate the function of DoHDAC genes.
Genome-wide member identification, phylogeny and expression analysis of PEBP gene family in wheat and its progenitors
Authors: Dong Lei , Lu Yue , Liu Shubing
Published: December 2020

The phosphatidylethanolamine binding protein (PEBP) family comprises ancient proteins found throughout the biosphere that play an important role in plant growth and development, flowering, seed development and dormancy. However, not all PEBP genes have been identified or analyzed in common wheat (Triticum aestivum L.) and its progenitors. In this study, we identified the PEBP genes in common wheat, Triticum dicoccoides, Triticum urartu and Aegilops tauschii by searching whole genome sequences, and characterized these genes by phylogenetic and transcriptome analyses. A total of 76, 38, 16 and 22 PEBP genes were identified in common wheat, T. dicoccoides, T. urartu and Ae. tauschii, respectively. Phylogenetic analysis classified the PEBP genes into four subfamilies (PEBP-like, MFT-like, TFL-like and FT-like); the PEBP-like subfamily was identified as a new subfamily with genes in this subfamily were conserved in plants. Group 2, 3 and 5 chromosomes of common wheat and its progenitors contained more PEBP genes than other chromosomes. The PEBP genes were conserved in wheat during evolution, and tandem duplication played a more important role in the amplification of PEBP genes than segmental duplication. Furthermore, transcriptome analysis revealed that PEBP genes showed tissue/organ-specific expression profiles and some PEBP genes were induced to express by biotic stresses. Quantitative real-time PCR (qRT-PCR) analysis revealed that seven randomly selected PEBP genes expressed differently during seed germination under cold, drought, flood, heat and salt stress treatments, and five of these genes (TaPEBP1, TaPEBP5, TaPEBP9, TaPEBP66 and TaPEBP69) showed significantly higher expression under different stress treatments, indicating that these genes play important roles during seed germination under stress conditions.
Effect of Replacement Levels of Wheat Flour on the Physicochemical and Sensory Properties of Smoke- Dried Sausage
Authors: Iwanegbe I. , Omonigho I. G.
Published: December 2020

In the olden days, there was no refrigeration for meat preservation and sausage making was a way to solve this problem. Sausage making evolved as an effort to economize and preserve meat which could not be consumed immediately after slaughter. This study evaluated the effect of replacement levels of wheat flour on the physicochemical characteristics and sensory qualities of smoke-dried sausage. Beef, wheat flour, sodium chloride, seasonings (Table 1) were bought, pre-processing operations were carried out. Sausage was processed by adding wheat flour, seasonings, salt to minced meat at different replacement levels (5%, 10% and 15%) with 0% as control and later smoke-dried. Sensory evaluation and physicochemical properties were determined. Data generated were analyzed. The results from sensory evaluation showed that Product A had the highest response (5.00) to sausage colour. Product A (5.00), B (5.00) and C (4.90) had the highest response for product juiciness. Product A (5.00) and product B (5.00) had better response to taste. For overall acceptability, Product A (5.00) was not different from other products. The addition of wheat flour resulted in higher and greater elasticity and increased acceptability due to higher scores for texture and colour. The protein content showed that Product D (56.33%) had the lowest value, followed by Product B (58.23%), next was Product C (59.57%), and the highest was observed in Product A (60.42%). Product C had the highest value for potassium and phosphorus (122.0 mg/100g and 13.40 mg/100g). Product B and C had the same value (6.17) for pH, next was product A (6.13), the least pH was observed in Product D (6.07). Sausage manufacture is a means of adding value to off-cuts and thereby increasing the utilization of meat. The incorporation of 10% wheat flour to sausage is highly nutritive with better sensory qualities and better economic value.