bluuebunny/crossref_metadata_2025 huggingface dataset:
Supramolecular gels and mesoscopic structure
Authors: Lin Nai-Bo  , Lin You-Hui  , Huang Qiao-Ling  , Liu Xiang-Yang  ,   Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Laboratory for Soft Functional Materials Research, College of Mateirals, College of Physical Science and Technology, Xiamen University, Xiamen 361005, China;,   Department of Physics, National University of Singapore, 117542 Singapore
Published: December 2020

From the perspective of mesoscale, the formation mechanism of crystal network structure of supramolecular gel, the influence of structure on macroscopic properties, and the design and control of supramolecular gels are reviewed Crystal network is a key character of the hierarchical structure of the gel, the formations of the basic and multi-level crystal networks are based on the crystal nucleation and growth. The engineering and controlling of the gel structure can be implemented by various stimuli, such as additives, sonication, seeding, and thermodynamic driving force, which leads to a controllable performance of the gel In addition, the methods of characterizing supramolecular gels are systematically summarized, such as, rheology, atomic force microscope, scanning tunnel microscope, scanning electron microscope, transmission electron microscope, polarizing optical microscope, X-ray diffraction, small-angle X-ray scattering, small-angle neutron scattering, nuclear magnetic resonance spectroscopy, dynamic light scattering etc. Supramolecular gel performance is determined by the hierarchy mesoscopic structures, which can significantly improve the properties of the material. Four factors can be correlated to the structure and performance of material: topology, correlation length, symmetry/ordering, and strength of association of crystal networks. According to the more in-depth understanding of mesoscopic supramolecular gels, the research and development of such a material will be pushed to a new stage.
Molecular dynamics simulation of effects of temperature and chirality on the mechanical properties of single-layer molybdenum disulfide
Authors: Li Ming-Lin  , Wan Ya-Ling  , Hu Jian-Yue  , Wang Wei-Dong  ,   School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou 350116, China;,   Fujian Collaborative Innovation Center of High-End Manufacturing Equipment, Fuzhou 350116, China;,   School of Mechanical-electronic Engineering, Xidian University, Xi'an 710071, China
Published: December 2020

Recently, the effect of temperature on the mechanical property (the Young's modulus) of the single-layer molybdenum disulfide (SLMoS2) is shown to be insignificant, which is obviously incompatible with the previously published result, i. e. the Young's modulus of SLMOS2 decreases monotonically as temperature increases. Aiming at clarifying the relationships between the mechanical properties of the single-layer molybdenum disulfide (SLMoS2) along the armchair (AC) and zigzag (ZZ) directions and the temperature, classical molecular dynamics (MD) simulations are performed to stretch the SLMoS2 along the AC and ZZ directions at the temperatures ranging from 1 K to 800 K by using the Stillinger-Weber (SW) interatomic potentials in this paper. The mechanical properties of SLMoS2 at the temperatures ranging from 1 K to 800 K, including ultimate strength, ultimate strain, and Young's Modulus, are calculated based on the stress-strain results obtained from the simulations. Results are obtained and given as follows. (1) The mechanical properties of the SLMoS2, including the ultimate strength and Young's modulus, are found to monotonically decrease as temperature increases. Increasing the temperature, the ultimate strength of SLMoS2 in the AC direction drops faster than in the ZZ direction, whereas the Young's modulus of SLMoS2 in the ZZ direction decreases quicker than in the AC direction, which means that the chirality effect on the ultimate strength is remarkably different from the Young's modulus of SLMoS2. However, the ultimate strain in the ZZ direction at the temperatures in a range from 1 K to 800 K is close to that in the AC direction, which means that the effect of chirality on the ultimate strain is insignificant. (2) Unlike the published results in the literature, the phase transition of SLMoS2 is found to only occur at a temperature of 1 K and at the moment of initial crack formation as tensiled along the ZZ direction, and the new phase of quadrilateral structure keeps stable after unloading. (3) The linear thermal expansion coefficients along the ZZ and AC directions are also measured, the magnitudes of which are found to be consistent with the published experimental results. Our simulation results support the viewpoint that the effect of the temperature on the mechanical property of SLMoS2 is significant, and the SLMoS2 can be regarded as an anisotropic material as the chirality effect cannot be ignored. The linear thermal expansion coefficients obtained with MD simulation are all in good agreement with the experimental data.
Multiple types of local structure in liquid water
Authors: Yang Cheng  , Zhou Xin  ,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Nowadays, although our understanding on liquid water have lots of progresses due to the development of experimental tools and computer simulation techniques, the molecular level structure of water, its heterogeneity, is still elusive. In the end of the nineteenth century, Rntgen proposed that the water is a mixture of two molecular complexes, which cannot be confirmed by experiments at that time. In the middle of the twentieth century, Bernal and his followers regarded the structure of liquid water as a random tetrahedral network, which was widely accepted by most scientists. With the development of computer science and the discovery of several amorphism, more and more attentions are paid on the mixture model of liquid water. In this paper, we firstly review some latest evidences about the multiple types of local structure in liquid water in both simulations and experiments. In all-atom simulation, the distributions of the local structure index obtained by minimizing the energy of samples are double peak at all temperatures. In experiment, the X-ray emission spectroscopy of liquid water at ambient pressure shows that there are two local structures in liquid water, one is order and ice-like, the other one is disorder and gas-like. Secondly, some results of our group on this topic are presented. We transformed the Raman spectra into the high-dimensional vectors and analyze the vectors with the principal component analysis method. The results show that all the end points of vectors are in a line in the high-dimensional space which implies that they can be obtained by linearly combining two basic points in that line. This means that the Raman spectra can be decomposed into two basic spectra. We also perform the same analysis on the distributions of tetrahedral order parameter in liquid water and obtained similar results. It is an obvious signal of the existence of multi-component in liquid water. Finally, we introduce the mixture model of liquid water which can be used to explain the thermodynamic properties of liquid water. In the mixture model, the form of the Gibbs free energy of liquid water is the same as the binary regular solution. The free energy is a function of the concentration of the disorder local structure. The anomalies of liquid water are directly caused by the change of concentration of the disorder local structure. In the low temperature and high pressure region, the mixture model has a critical point, which is consistent with the liquid-liquid phase transition theory.
First-principle studies of mechanical, electronic properties and strain engineering of metal-organic framework
Authors: Wang Xiao-Yuan  , Zhao Feng-Peng  , Wang Jie  , Yan Ya-Bin  ,   Institute of Systems Engineering, China Academy of Engineering Physics, Mianyang 621900, China;,   Department of Engineering Mechanics, School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, China
Published: December 2020

Metal-organic frameworks (MOFs) have attracted a great deal of interest from both academia and industry due to their extensive potential applications. The tunable physical properties through the manipulation of composition have led to increasing attention to the exploration of the MOF applications. However, the tunability of physical property of MOF with external mechanical load, which usually steams from actual fabrication and application processes, has been rarely investigated. Here, ab initio (first-principles) density functional theory (DFT) calculations are performed to investigate the mechanical, electrical properties and strain engineering of a typical metal-organic framework, MOF-5. Preliminary calculations by using different pseudopotentials and cut-off energies are performed to verify the adopted critical parameters in subsequent simulations. Both the structural stability of MOF-5 and the effect of applied strain are investigated from an energetic point of view. With the increase of applied strain, the cohesive energy of MOF-5 decreases, inducing the reduction of structural stability. In addition, the variation of cohesive energy of MOF-5 shows an asymmetry under expansive and compressive conditions. By applying strain along different directions, the mechanical properties of MOF-5 are systematically investigated, and mechanical constants including Young's modulus, Poisson ratio and elastic constants are obtained. In addition, by analyzing the band gap of MOF-5, the intrinsic electrical property of MOF-5 is clarified. The band gap of MOF-5 is 3.49 eV, indicating that MOF-5 is a wide bandgap semiconductor, which is represented by the combination effect of both [Zn4O]6+ metal clusters and organic linkers. Analysis on the strain engineering of electrical properties of MOF-5 reveals that the applied strain induces the decrease of band gap of MOF-5, and thus leading to the increase of conductivity. This transition is induced by the decrease of conduction energy-level. Further studies on the variations of PDOS and covalent bond show that the strain engineering of electrical property of MOF-5 intrinsically originates from the variation of covalent bond in the organic linker. The applied strain apparently weakens the covalent bond, and thus inducing the relaxation and redistribution of electrons, which increases the activities of electrons, and finally leads to the overall increase of conductivity of MOF-5. This theoretical study quantitatively clarifies the tunability of electronic band gap of MOF-5 with external strain, and provides a theoretical guidance in the design optimization and property evaluation of gas sensors based on MOF-5.
Investigation on Yb3+-doped silica glass using sol-gel method and laser melting technology
Authors: Liang Wan-Ting  , Hou Zhi-Yun  , Zhou Gui-Yao  , Xia Chang-Ming  , Zhang Wei  , Wei Le-Feng  , Liu Jian-Tao  ,   Guangzhou Key Laboratory?for?Special Fiber Photonic Devices and Applications, South China Normal University, Guangzhou 510006, China
Published: December 2020

Rare earth doped silica glass can be used as the central material of optical fiber, which can be applied to the fiber laser. It becomes a focus in the field of laser materials. Compared with different kinds of rare earth elements, ytterbium is regarded as a promising laser nuclear fusion material due to its simple level structure, strong energy conversion efficiency, long fluorescent lifetime, etc. Nowadays, the usual fabrication method of optical fiber preform is the chemical vapor deposition (CVD). However, the preform made by CVD has low doping concentration, few kinds of doping elements, low homogeneity and hard-to-make into optical fiber of large core diameter. To solve these problems, a noble method, which is called non-chemical vapor deposition (Non-CVD), is developed. Sol-Gel method is a kind of Non-CVD, which can perfectly solve the inhomogeneity in material. The glass has harmonious component since the whole process is at a liquid level.Sol-Gel method is a liquid phase synthesis method. The raw materials, including TEOS, absolute ethyl alcohol, ammonium hydroxide and deionized water, are uniformly mixed and become gel from sol through the hydrolysis and condensation. AlCl3 and YbCl36H2O are also added as the dopants. After that, heat the gel and let the hydroxyl and organic release, then we will be able to obtain the SiO2-doped powder. Combining with the laser melting technology, the ytterbium doped silica glass is made. It is known from the DSC-TG curve of xerogel that during the heating process, water and organic are expelled from the system. It needs a holding period at 500 ℃ to ensure that the water and organic are expelled adequately. Moreover, the FTIR spectrum shows that after high temperature treatment the OH- concentration in the xerogel decreases dramatically. The physical and spectrum properties of ytterbium doped silica glass are also tested. The Yb-doped silica glass which shows the amorphous state has good optical properties. The absorption spectrum and fluorescence spectrum demonstrate the typical absorption peak and emission peak of Yb3+, respectively. The density and refractive index of the glass are 2.409 g/cm3 and 1.462, respectively. The fluorescence lifetime () of the silica glass is 0.88 ms, the corresponding emission cross-section (emi) is 0.54 pm2, and the gain coefficient (emi) is 0.48 pm2m. In conclusion, the Yb-doped silica glass is successfully prepared by the Sol-Gel method combined with laser melting technology, which possesses good physical and optical properties. This work is meaningful for preparing high-performance Yb-doped fiber, and even for developing the high power laser.
The applications of the wormlike chain model on polymer physics
Authors: Jiang Ying  , Chen Jeff Z. Y.  ,   School of Chemistry and Environment, Center of Soft Matter Physics and its Applications, Beihang University, Beijing 100191, China;,   Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
Published: December 2020

The continuum version of the wormlike chain model (WLC), which was initially developed by Saito, Takahashi and Yunoki in 1967, is particularly suitable for description of polymer conformational properties affected by the chain rigidity. The WLC model is capable of covering an extensive range of chain rigidity, from the flexible chains to the rigid chains, by tuning the persistence length directly. It is widely accepted as a coarse-grained model that can be used to capture the physical properties, such as conformation and structures, of a larger class of real polymers than the Gaussian chain (GSC). Recently, the WLC model attracts increasing interests because of its advantages in studying a variety of polymeric systems, including liquid crystalline polymers and conjugated polymers. This review article focuses on applications of the WLC model, incorporated in the framework of self-consistent field theory, which is an effective method in theoretical exploration of phase separation in polymer systems. The article also pays particular attention to the developments of the numerical schemes to solve the modified diffusion equation governing the probability distribution of polymers. In addition, we summarize recent applications of the self-consistent field theories based on WLC model in the following three areas: phase transitions in liquid-crystalline polymers; the influence of surface curvature on polymeric systems involving the chain orientation effects; self-assembly of wormlike block copolymers. These studies are beyond the scope of self-consistent field theories based on a GSC model, which have been utilized in a large number of theoretical studies in recent years. Finally, we propose the perspectives of theoretical developments in field-theory simulations based on the WLC model for future work. In the polymer literature, it is generally appreciated that chain-rigidity is an important factor that influences the properties of structural stabilities on the meso-scale. The theoretical studies indentify the key physical mechanisms that play crucial roles in many experimental systems with attractively promising applications in practice, for systems such as liquid crystalline polymers and organic solar cell based on the conjugated polymers.
Protein structure prediction
Authors: Deng Hai-You  , Jia Ya  , Zhang Yang  ,   College of Science, Huazhong Agricultural University, Wuhan 430070, China;,   College of Physical Science and Technology, Central China Normal University, Wuhan 430079, China;,   Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI 45108, USA
Published: December 2020

Predicting 3D structure of proteins from the amino acid sequences is one of the most important unsolved problems in computational biology and biophysics. This review article attempts to introduce the most recent effort and progress on this problem. After a brief introduction of the background and basic concepts involved in protein structure prediction, we went through the specific steps that have been taken by most typical structural modeling approaches, including fold recognition, model initialization, conformational search, model selection, and atomic-level structure refinement. Several representative structure prediction methods were introduced in detail, including those from both template-based modeling and ab initio folding approaches. Finally, we overview the results shown in the community-wide Critical Assessment of protein Structure Prediction (CASP) experiments that have been developed for benchmarking the state of the art of the field.
Dynamical studies of cellular signaling networks in cancers
Authors: Li Xiang  , Liu Feng  , Shuai Jian-Wei  ,   Physics Department, Xiamen University, Xiamen 361005, China;,   Physics Department, Nanjing University, Nanjing 210093, China
Published: December 2020

Cancer, as a conundrum, is currently the biggest killer of human health. The major viewpoint of carcinogenesis is owing to somatic gene mutations. Based on such a viewpoint and the development of gene sequencing technology, extensive genomic alterations in cancer genomes have been identified. How to develop a better understanding of the link between gene mutations and carcinogenesis as well as efficient clinical cancer therapy is therefore a major challenge. Weinberg and Hanahan have suggested 10 hallmarks of cancer. The hallmarks are highly regulated by the corresponding signaling pathways. Thus, cancer itself is also a disease of dysfunction of signal transduction pathways related to multiple fundamental cell processes, including proliferation, differentiation, apoptosis, invasion and so on. Despite the signaling pathways are extremely complex in cancer cells, one can still focus on the signaling networks that govern the corresponding cell processes for modeling to discuss its dynamics and regulation functions quantitatively. Systems biology provides appropriate approach to integrate the experimental data (clinical data) and signaling pathway for a comprehensive analysis, resulting in a further prediction for optimal therapy and drug discovery. In this paper, we review the recent progress of dynamical modeling of signaling networks by using systems biology approaches that help to exploring the mechanisms of carcinogenesis. We first discuss the motif dynamics of the signaling networks. The presented generic circuit model can be decomposed into two loops and the circuit can achieve tristability through four kinds of bifurcation scenarios when parameter values are varied in a wide range. Then, we show the relative well-studied core signaling networks that regulate the cell survival, apoptosis, proliferation, invasion and energy metabolism processes. For each fundamental cell process, we individually review the dynamics of corresponding signaling network based on the systems biology approaches, including the NF-B signaling pathway that regulates the cell survival process, the Ras signaling pathway that governs the cell proliferation process, the EMT and mitochondrial signaling pathway that modulate the cell invasion and apoptosis processes. Furthermore, two coupled signaling networks, i.e., the p53 and TNF- signaling networks are discussed. Lastly, we review the breast cancer and gastric cancer signaling networks which contain several fundamental cell processes. The potential contribution for cancer treatment is also suggested. These dynamical modeling based on the core signaling networks can facilitate the understanding of the mechanisms of carcinogenesis and provide us the possible clues and ideas of the cancer treatment and drug design. We believe more exciting research works in this field will be stimulated in the near future.
Application of video microscopy in experimental soft matter physics
Authors: Wang Guang-Hua  , Zhang Ze-Xin  ,   Center for Soft Condensed Matter Physics and Interdisciplinary Research, Soochow University, Suzhou 215006, China
Published: December 2020

Combining precise microscopic measurement with quantitative image analysis, video microscopy has become an important, real space experiment technique to study the microscopic properties of soft matter systems. On the one hand, it provides a basic tool to observe and record the microscopic world. On the other hand, it offers a essential experiment method to study the underlying physics of the microscopic world. This paper reviews the development of the video microscopy, introduces the corresponding hardware and video processing software, and summarizes the typical applications, and recent progresses of video microscopy in colloidal suspensions. The future of the video microscopy in the soft condensed matter physics and interdisciplinary research is discussed.
Preparation and DC characteristics of MgB2/B/MgB2 Josephson junctions
Authors: Zhou Zhang-Yu  , Xiao Han  , Wang Song  , Fu Xing-Hua  , Yan Jiang  ,   College of Big Data and Information Engineering, Guizhou University, Guiyang 550025, China;,   College of Chemistry and Environmental Science, Guizhou Minzu University, Guiyang 550025, China;,   Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China
Published: December 2020

Since the discovery of its superconductivity, magnesium diboride (MgB2) has been identified as a promising superconductor to be used in Josephson junction devices due to its high transition temperature, large energy gap, long coherence length, and expected easier fabrication of Josephson junctions as compared with high temperature superconductors. The high-quality MgB2 films and excellent tunnel barrier materials are the core elements for a Josephson junction. Here in this paper, all MgB2 thin film tunnel junctions with B tunnel barriers are fabricated in situ on sapphire substrates and their tunneling characteristics re investigated. The experimental results indicate that the MgB2/B/MgB2 junctions exhibit good tunneling characteristics.
The deposition of the MgB2/B/MgB2 trilayer is carried out in a completely in situ process. The bottom and top MgB2 layers are grown to a thickness of 100 nm by hybrid physical-chemical vapor deposition (HPCVD) technique at about 973 K and in 102 Pa Ar atmosphere on a single crystal Al2O3 (0001) substrate. The 35-nm-thick amorphous B insulator layer is deposited using chemical vapor deposition method at 723 K and in 103 Pa pure Ar. In the process of the top MgB2 layer deposition, the amorphous B reacts with Mg in Mg vapor, leading to its thickness decreasing to 10 nm. Square-shaped junctions each with a size of 4 mm5 mm are determined by the metallic mask method. The resistivity temperature (R-T) curves and the DC current-voltage (I-V) curves of the MgB2/B/MgB2 junctions at different temperatures are measured by the four-point probe method in the physical property measurement system (PPMS). The experimental results show excellent superconducting properties of the top and bottom superconductor with high Tc (above 39.5 K), appreciable Jc values (107-108 A/cm2). In the I-V characteristics of junction at temperatures ranging from 4.2 K to 39.2 K, the junctions exhibit clear Josephson tunneling characteristics with jc～0.52 A/cm2 at 4.2 K, which remains nonzero up to 31.3 K. The hysteresis is pronounced at 4.2 K, becoming smaller as temperature increases, and eventually disappearing at around 19.2 K. By using the differential I-V curves, only gap is observed in differential conductance vs. voltage characteristics (dI/dV-V) curves, because MgB2 layer grown using HPCVD technique is always c-axis oriented and more than 99% contribution to the conduction is from band charge carriers.
Study on the forward of mashgas CO temperature and concentration by the remote passive measurement
Authors: Tang Yuan-He  , Wang Shu-Hua  , Cui Jin  , Xu Ying  , Mei Yi-Feng  , Li Cun-Xia  ,   School of Science, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

In order to reduce the second rescue injuries and deaths after the mashgas exploding in the mine, a portable imaging interferometer system is designed to detect CO temperature and concentration by the passive and remote measurement. The CO temperature and concentration are detected according to the rotational spectral line of CO gas molecule and the linear relationship between the radiation intensity of gas molecule and the molecule number density, respectively. The optical system is designed, and then its forward is studied in this work. The forward expression is obtained after studying the following four seed models of the optical system: the radiation model of target gas, where CO six emission spectral lines R11-16 are selected from HITRAN08 database; the mine CO gas transmission model in which the absorptions by the water vapor and CO2 molecule, and absorption and scattering by the mine aerosol are calculated by the relevant rules; the filter function model, in which the matched parameters of the band width of 0.5 nm and max transmittance of 0.23 for CO temperature are measured by the method of rotational line of R11-16, and the model of imaging detector CCD in which the infrared CCD of pixel 320320 and the max quantum efficiency of 0.75 are to be used in the optical system. According to the given parameters and MATLAB programming, the forward imaging interference results of CO differentiable six spectrum of R11-16 are obtained. The forward max noise-signal ratio is 268 when the exposure time is 300 s. The max electric count is 1.5105 that is larger than the selected CCD dark noise of 400 e but less than the CCD full charge quantity of 1106 e. The forward result clearly indicates that the optical system can meet the initial design demand. The accuracies of CO temperature and concentration measured by this optical system can reach 2 K and 0.1%, respectively. This portable system can be used to detect not only the mine CO, but also other gases like the pipe smoke, bomb exploding gas, etc. in which the filter and CCD need to be changed.
On the theoretical basis of rational continuum mechanics in softmatter
Authors: Chen En-Hui  , Yang Jin-Hong  , Li Dong  , Zhao Ya-Pu  ,   State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China;,   School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Soft matter has become one of the most active fields since the 1990 s, for it has enormous interesting behaviors and a broad range of applications. Rational continuum mechanics, as a subject mainly dealing with the kinematics and deformation of materials modeled as continuous mass, is a main source of inspiration in the development of soft matter physics. Here we review the development of rational continuum mechanics and soft matter briefly, and focus on the basic mechanical models and constitutive relations relating to soft matter: entropy elasticity, hyperelasticity, viscoelasticity, poroelasticity, non-Newtonian fluid, and the constitutive equations of these models. We simultaneously introduce the applications of these equations in hot issues in recent years, such as brain, blood vessel, cartilage, muscle, gel, cell, three dimensional printing, etc. According to applications and advances in soft matter mechanics, we then propose the key scientific problems and research fronts: mechanics of the solid-liquid interfacial interactions, introducing multiple factors into constitutive equations to describe the complex behaviors of soft matter in coupling multi-physics, and enhancing connections between soft matter mechanics and soft matter physics, chemistry, biology, etc. Finally, we conclude that the rational continuum mechanics in soft matter could be further developed in energy development, fabrication and analysis of diverse soft materials, and biomedicine development areas.
Advances in the mechanism of mechanochemical coupling of kinesin
Authors: Li Ming  , Ouyang Zhong-Can  , Shu Yao-Gen  ,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;,   Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Kinesin is one of the most important linear motors for intracellular transport. It has two main features. One is its persistence: at least one head is attached to the microtubule during stepping, so that it can move a long distance before detaching. Another feature is the tight mechanochemical coupling: it consumes one adenosine-triphosphate for each step. Therefore, there should be a mechanism responsible for the coordination of the two heads to achieve the high persistence and tight coupling. The underlying mechanism is the mechanochemical coupling, which is the basic issue for all chemical-driven molecular motors. Owing to the developments of single-molecule experiments and molecular dynamics simulations, a breakthrough in the coupling mechanism has been made in recent decades. In this article, we review the progress of the relevant researches from the perspective of kinematics, energetics, coordination of two heads and force generating mechanism. We also present a personal perspective on the future studies of kinesin.
Eigenvalue problems solved by reorthogonalization Lanczos method for the large non-orthonormal sparse matrix
Authors: Jiao Bao-Bao  ,   Department of Physics, University of Shanghai for Science and Technology, Shanghai 200093, China
Published: December 2020

Using shell model to calculate the nuclear systems in a large model space is an important method in the field of nuclear physics.On the basis of the nuclear shell model,a large symmetric non-orthonormal sparse Hamiltonian matrix is generated when adopting the generalized seniority method to truncate the many-body space.Calculating the energy eigenvalues and energy eigenvectors of the large symmetric non-orthonormal sparse Hamiltonian matrix is of indispensable steps before energies of nucleus are further calculated.In the mean time,some low-lying energy eigenvalues are always the focus of attention on the occasion of large scale shell model calculation.In this paper,by combining reorthogonalization Lanczos method with Cholesky decomposition method and Elementary transformation method,converting the generalized eigenvalue problems into the standard eigenvalue problems,and transforming the large standard eigenvalue problems into the small standard eigenvalue problems,we successfully calculate the eigenvalues and eigenvectors of large non-orthonormal sparse matrices with the help of computers with limited memory.The values obtained by using this method to calculate the small matrix agree with the exact values,which demonstrates that this method is accurate and can be used to calculate the energy eigenvalues and energy eigenvectors of large symmetric nonorthonormal sparse matrix.We take 116Sn (s=8,the number of unpaired particles,namely the generalized seniority) as an example in which there are active valence neutrons but inert protons at the magic number,and calculate ten of its lowest energy eigenvalues.Through calculation,we find that among these low-lying energy eigenvalues,the lowest energy eigenvalue converges fastest.A comparison between the calculation values and the experiment values shows that the difference between the calculated high-lying energy eigenvalue and its corresponding experimental one arrives at hundreds of keV,while for the low-lying energy eigenvalue,its calculation value can reach an accuracy of a few tens of keV.The results demonstrate that the Lanczos method is feasible in Matlab programming and shell model calculations. The significance of this research lies in the fact that this method will not only greatly help to calculate and obtain the low-lying energy eigenvalues of some medium-mass and heavy nuclei,but also possess great importance in calculating partial eigenvalues involved in large matrices in other theoretical researches and engineering designs.
342 W narrow-linewidth continuous-wave thulium-doped all-fiber laser
Authors: Liu Jiang  , Liu Chen  , Shi Hong-Xing  , Wang Pu  ,   National Center of Laser Technology, Institute of Laser Engineering, Beijing University of Technology, Beijing 100124, China
Published: December 2020

High-power narrow-linewidth rare-earth-doped fiber lasers, which are well known for their high beam quality and high efficiency properties, have rapidly developed in the last decade, due to the needs of a vast range of applications such as nonlinear frequency conversion, and incoherent spectral beam combination to further scale up the total output power of fiber lasers. At the same time, many efforts have also been made to extend the operating wavelength of narrow-linewidth fiber laser toward the longer mid-infrared wavelength region, which was motivated by a large number of promising applications such as atmosphere monitoring, and pump source for mid-infrared optical parametric oscillator. In most cases, thulium-doped fiber lasers operate efficiently in a wavelength range of 1.8-2.1 m, which could be considered as being one of the most important sources of narrow-linewidth laser radiation that has been developed and intensively investigated in the last several years. Here, we demonstrate a high-power narrow-linewidth continuous-wave thulium-doped all-fiber laser based on master-oscillator power-amplifier (MOPA) configuration. The MOPA yields 342 W of narrow-linewidth laser output at the central wavelength of 2000.3 nm with a 3-dB spectral bandwidth of 90 pm. The beam quality factor is measured to be M2 of 1.15 at an output power of 300 W. No indication of stimulated Brillouin scattering could be observed at the highest output power level, and the output power is only currently limited by 793 nm available pump power. This kind of high-power narrow-linewidth thulium-doped all-fiber MOPA represents a promising achievement in the generation of high-power laser source via incoherent spectral beam combination.
Experimental research on the dispersion property of hollow core photonic bandgap fiber
Authors: Wang Xin  , Lou Shu-Qin  , Lian Zheng-Gang  ,   School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing 100044, China;,   Yangtze Optical Electronic Company, Wuhan 430074, China;
Published: December 2020

Due to the unique optical properties of low loss, low nonlinearity, high threshold and low latency, hollow core bandgap fibers are endowed with high expectations in the field of high power delivery, optical fiber communication, nonlinear optics, fiber sensors, etc. Fiber dispersion, as one of the basic transmission characteristics of optical fiber, makes the light pulse broadened during transmission, thus has adverse effects on high power pulse transmission system and high speed optical communication system. Therefore, it is significant to study the dispersion characteristics of the hollow core bandgap fiber for its applications in the field of high power pulse transmission and high speed communications. Because of the simple structure of measurement system, low cost, high accuracy and relatively short length of fiber (just needing a few meters long), interferometric technique is suitable for dispersion measurement of hollow core photonic bandgap fiber. The key to obtaining the dispersion results with interferometric technique is the phase extractiton from the interferogram. In order to meet the requirements of hollow core bandgap fiber for wide bandwidth, high efficiency and high accuracy dispersion measurement, a novel phase extraction method based on interferometry is proposed in this paper, by which the precision of dispersion measurement is improved through using the whole data-set in the interferogram. Combining with the determinations of the peak and center of symmetry points, the extraction of phase information can be implemented directly from the interferogram. The experimental results of measuring a standard single mode fiber indicate that the difference between the experimental measurement and theoretical simulation is just 0.6 psnm-1km-1, which proves that this proposed method possesses high accuracy and is suitable for the measurement of hollow core bandgap fiber. Consequently, according to the proposed phase extraction method, the measurement system based on Mach-Zehnder interferometer is set up and the dispersion measurement of a 19 cell hollow core bandgap fiber with a core diameter of 26 m is carried out. Experimental results indicate that the fundamental mode dispersion curve of the 19 cell hollow core photonic bandgap fiber in a wavelength range from 1400 nm to 1630 nm can be obtained. Moreover, four high order mode dispersion curves are obtained for the first time. The measurement results are in accordance with the simulation results. These findings are of significant importance for exploring the dispersion characteristics of hollow core photonic bandgap fibers, and also conducible to their applications in the fields of high power laser delivery, high capacity data communications, optical fiber nonlinear, etc.
Anisotropic etching of bilayer graphene controlled by gate voltage
Authors: Wang Guo-Le  , Xie Li  , Chen Peng  , Yang Rong  , Shi Dong-Xia  , Zhang Guang-Yu  ,   Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Beijing Key Laboratory for Nanomaterials and Nanodevices, Beijing 100190, China;,   Collaborative Innovation Center of Quantum Matter, Beijing 100190, China;,   School of Physics, University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Graphene nanostructures are proposed as promising materials for nanoelectronics such as transistors, sensors, spin valves and photoelectric devices. Zigzag edge graphene nanostructures had attracted broad attention due to their unique electronic properties. Anisotropic hydrogen-plasma etching has been demonstrated as an efficient top-down fabrication technique for zigzag-edged graphene nanostructures with a sub-10 nm spacial resolution. This anisotropic etching works for monolayer, bilayer and multilayer graphene and the etching rate depends on substrate temperature with a maximum etching rate at arround 400 C. It has been also founded that the anisotropic etching is also affected by the surface roughness and charge impurities of the substrate. Atomically flat substrates with no charge impurities would be ideal for the anisotropic etching. So far the understanding of hydrogen-plasma anisotropic etching, e.g. whether hydrogen radicals or hydrogen ions dominate the etching process, remains unclear. In this work, we investigated the anisotropic etching of graphene under electrical field modulations. Bilayer graphene peeled off from grahpite on SiO2 substrate was used as the experimental object. 2 nm-Ti (adhesive layer) and 40 nm-Au electrodes was deposited by electronic beam evaporation for electrical contacts. Gate voltates were applied to the bilayer graphene samples to make them either positively or negitively charged. These charged samples were then subjected to the hydrogen anisotropic etching at 400 C under the plasma power of 60 W and gas pressure of 0.3 Torr. The etching rates were characterized by the sizes of the etched hexagonal holes. We found that the etching rate for bilayer graphene on SiO2 substrate depends strongly on the gate voltages applied. With gate voltages sweeping from the negative to the positive, etching rate shows obvious decrease. 45 times of etching rate decrease was seen when sweeping the gate voltages from -30 V (positively charged) to 30 V (negatively charged). This gate-dependent anisotropic etching suggests that hydrogen ions rather than radicals plays a key role during the anisotropic etching process since the negatively charged graphene could neutralize the hydrogen ions quickly thus make them unreactive. The present work provides a strategy for fabrication of graphene nanostructures by anisotropic etching with a controllable manner.
Influence of prestress on shock behavior of polycrystalline iron via atomistic simulations
Authors: Ren Guo-Wu  , Zhang Shi-Wen  , Fan Cheng  , Chen Yong-Tao  ,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621999, China
Published: December 2020

Plasticity behavior and phase transition of metal Fe subjected to shock loading have attracted considerable attention in shock physics community, in particular for underlying relationship between them. Experimental examinations and atomistic simulations on shocked Fe have displayed a three-wave structure: elastic wave, plastic wave and transformation wave. However, these studies are primarily limited to the one-dimensional planar case. Recently, owing to the rapid development of experimental techniques, investigating dynamic property of shocked metal has extended to the multi-dimensional loading conditions, such as cylindrical or spherical shocks. In this regard, fruitful findings are achieved, for example, twinning ratio in polycrystalline Fe under implosive compression is found to be much higher than that under planar shock, implying that the the complex stress state plays a critical role.
In this paper, we explore the effects of prestress on plasticity and phase transition of shocked polycrystalline iron. The imposed presstress normal to the impact direction in one-dimensional planar shocking represents the varying deviatoric stress, and does not nearly affect the principal stress. The utilized empirical potential for iron could describe the plasticity dislocation and phase transition very well. The simulations show that as the prestress increases, the shock speed at elastic stage and Hugoniot elastic limit increase, which is in accordance with the theoretical analyses based on shock wave theory and experimental measurement. Meanwhile the plastic wave speed increases more quickly and catches up with the transformation wave more easily, resulting in a steep shockwave front. Atomistic snapshots show that plasticity dislocation stemming from the grain boundary precedes phase transition, where most of BCC atoms are transformed into the HCP atoms and shear stress significantly decreases. Further observations from these images find that plastic zone becomes narrower with increasing prestress, representing a shorter plastic relaxation time, which accelerates the completion of phase transition. This rapid phase transition process is also indicated by quantitatively evaluating the ratio of transitioned closed packed atoms as a function of evolution time. The origin based on the atomistical prediction model of Fe phase transition is attributed to the fact that higher prestress gives rise to the larger von-Mises stress for easier dislocation emission while lower one cannot. But the final transformed atoms are independent of prestress. Additionally, the measured free surface velocity profiles from planar and cylindrical impact loading validate the simulations conducted here. These findings will help to understand experimentally the microscopically dynamic evolution of Fe, imposed by complex stress state.
A new method to estimate the p-GaN carrier concentration by analyzing the reversed current-voltage characteristic curve of p-n+ junction diode
Authors: Zhou Mei  , Li Chun-Yan  , Zhao De-Gang  ,   Department of Physics, China Agriculture University, Beijing 100083, China;,   State key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

GaN and its related nitride materials have been investigated for many years due to their extensive applications in semiconductor optoelectronics and microelectronics. The realization of p-GaN plays a key role in developing the GaN-based optoelectronic devices such as light-emittingdiodes, laser diodes and ultraviolet photodetectors. Furthermore, it is very significant to acuurately obtain the carrier concentration value of p-GaN layer for device design and fabrication. Usually the Hall measurements are employed to obtain the hole concentration of p-GaN layer. However, this method is not suitable for very thin samples, especially the p-GaN layer in the device structure, which is commonly very thin. Furthermore, the good Ohmic contact to p-GaN is not easy to realize. In consideration of the importance of p-GaN in determining the performance of GaN-based devices, it is necessary to find other new methods to measure or check the carrier concentration data of p-GaN. In this paper, a new method to estimate the carrier concentration of p-GaN by analyzing the current-voltage characteristic curve of p-GaN/n+-GaN diode is proposed. The main physical process is as follows: generally the carrrier concentration of p-GaN layer is far less than that of n+-GaN layer, and the depleted region is mainly located in the p-GaN. When the reversed bias voltage is very small, the diode shows conventional properties of p-n+ junction and the corresponding reversed current is very low since the p-GaN is not completely depleted. With the increase of reversed bias voltage, the depleted region of p-GaN also increases. Once the p-GaN is completely depleted, the case turns different. The diode will show Schottky junction properties and the corresponding reversed current increases obviously when the p-GaN is completely depleted under a certain reversed bias voltage since the ideal reversed current of Schottky junction is larger than that of p-n+ junction. The hole concentration could be derived according to the device physics if the bias voltage is discovered, which leads to the properties changing from the p-n+ junction to conventional Schottky junction. The simulation results confirm the idea, and the calculated p-GaN carrier concentration is almost equal to the originally assumed value. The proposed method is interesting and may be helpful to accelerate the research of p-GaN and related optoelectronic devices.