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Mechanical performance of rock bolts under combined load conditions

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International Journal of Mining Science and Technology 2020年第2期30卷 167-177页

作者： P.C.Pinazzi A.J.S.(Sam)Spearing K.V.Jessu P.Singh R.Hawker Department of Mining and Metallurgical Engineering Western Australian School of MinesCurtin UniversityKalgoorlieWA 6430Australia Minova Global NowraNSW 2541Australia

Rock bolts are subjected to different loading conditions along their lengths such as axial,bending,and/or shear forces,which can cause failure at lower loads than those considered for design purposes.The common existing methodologies do not consider the actual loading of the rock bolts and assume it is only pure axial or pure shear.This study was conducted to investigate the un-grouted rock bolt performance under combined load conditions.Two loading regimes were evaluated:the effect of initial shear displacement on axial load capacity and displacement,and the effect of axial displacement on the shear load capacity.The first regime was also conducted for shear with a gap,when there is a spacing between the shear interfaces.The results of this study showed that the rock bolt can resist higher axial loads than shear under pure or combined load conditions.Under combined load conditions,the rock bolt capacity decreased significantly for both regimes.However,when applying the shear load with a gap,the rock bolt load capacity was not affected significantly.Also,the total bar deformation was improved for shear and axial.The findings of this study show the need to improve the rock bolt design considering the complex loading conditions in situ with/without a gap.

关键词： Rock bolt Combined load gap test Failure mechanism Axial load Shear load

Trees as large-scale natural phononic crystals: Simulation and experimental verification

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International Soil and Water Conservation Research 2019年第2期7卷 196-202页

作者： Jiankun Huang Yifan Liu Yaguang Li Key Laboratory of State Forestry Administration on Soil and Water Conservation School of Soil and Water ConservationBeijing Forestry UniversityBeijingChina

Urban trees are usually planted on a periodic layout in the spatial configuration.We regard urban trees as large-scale natural phononic crystals.The entire forest is reduced to a reasonable 'tree-soil' unit cell based on the phononic crystal theory and finite element method by COMSOL software is used to obtain the dispersion curves.The Rayleigh wave band gaps of phononic trees are distinguished by the sound cone method.The influences of soil elastic modulus and tree height on band gaps are investigated.A three-dimensional simulation model and experiment test are applied to validate the effect of phononic trees on vibration control.The numerical frequency reduction zones coincide exactly with the theoretical band gaps.Increasing soil stiffness results in a higher-frequency and wider band gap.An increasing tree height is beneficial to obtain low-frequency band gaps.A periodically arranged plantation that Rayleigh wave band gaps at frequency ≤60 Hz could be designed.This study opens up a new theoretical basis for the quantitative analyses of urban trees to the ground vibration mitigation at a certain frequency range.

关键词： Urban trees Phononic crystal Dispersion curve Band gap Rayleigh wave

Weakened interlayer coupling in two-dimensional MoSe2 flakes with screw dislocations

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Nano Research 2019年第8期12卷 1900-1905页

作者： Xiangzhuo Wang Huixia Yang Rong Yang Qinsheng Wang Jingchuan Zheng Lu Qiao Xianglin Peng Yongkai Li Dongyun Chen Xiaolu Xiong Junxi Duan Guangyu Zhang Jie Ma Junfeng Han Wende Xiao Yugui Yao Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement (MOE) Beijing Key Lab of Nanophotonics & Ultrafine Optoelectronic Systemsand School of PhysicsBeijing Institute of TechnologyBeijing 100081China Micronano Center Beijing Institute of TechnologyBeijing 100081China Institute of Physics Chinese Academy of SciencesBeijing 100190China

The screw dislocations are intriguing defects that are often observed in natural and artificial materials. The dislocation spirals break the reflection and inversion symmetries of the lattices and modify the interlayer coupling in layer-structured materials, inducing additional complexity in layer stacking and thus novel properties in materials. Here, we report on the interlayer coupling of two-dimensional (2D) MoSe2 flakes with screw dislocations by atomic force microscopy (AFM), Raman spectra and photoluminescence (PL) spectra. By controlling the supersaturation conditions, 2D MoSe2 flakes with screw dislocations are grown on amorphous SiO2 substrates by chemical vapor deposition (CVD). AFM measurements reveal that the interlayer spacing in such 2D MoSe2 flakes with screw dislocation is slightly widened with respect to the normal AA- or AB-stacked ones due to the presence of the screw dislocations. Raman and PL spectra show that the interlayer coupling is weaker and thus the band gap is wider than that in the normal AA- or AB-stacked ones. Our work demonstrates that the interlayer coupling of 2D transition metal dichalcogenides (TMDCs) flakes can be tuned by the induction of screw dislocations, which is very helpful for developing novel catalysts and electronic devices.

关键词： transition-metal dichalcogenides molybdenum selenide screw dislocations interlayer coupling band gap

Recent progress on terahertz generation based on difference frequency generation:from power scaling to compact and portable sources

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Chinese Optics Letters 2011年第11期9卷 16-25页

作者： Yujie J.Ding Pu Zhao Srinivasa Ragam Da Li Ioulia B.Zotova Ioulia B.Zotova ArkLight P.O.Box 2Center ValleyPA 18034USA

The progress achieved on power scaling and compact and portable THz sources is reviewed.By reversely stacking the gap plates,the photon conversion efficiency is improved from 25% to 40% which corresponds to the maximum value.When the number of the plates is increased from four to five,the output power decreases because of back conversion.The THz generation is also investigated by mixing the two frequencies generated by a single Nd：YLF solid-state laser.The average output power reaches 1 μW.The introduction of two Nd：YLF crystals significantly improves the output power to 4.5 μW.This configuration facilitates the generation of different output frequencies.

关键词： THz Recent progress on terahertz generation based on difference frequency generation gap

Two-Dimensional Discrete gap Breathers in a Two-Dimensional Diatomic β

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Chinese Physics Letters 2008年第10期25卷 3586-3589页

作者：徐权田强 Department of Physics Daqing Normal University Daqing 163712 Department of Physics Beijing Normal University Beijing 100875

We study the existence of two-dimensional discrete breathers in a two-dimensional face-centred square lattice consisting of alternating light and heavy atoms, with nearest-neighbour coupling containing quartic soft or hard nonlinearity. This study is focused on two-dimensionai breathers with frequency in the gap that separates the acoustic and optical bands of the phonon spectrum. We demonstrate the possibility of existence of two- dimensional gap breathers by using the numerical method, the local anharmonicity approximation and the rotating wave approximation. We obtain six types of two-dimensional gap breathers, i.e., symmetric, mirror-symmetric and asymmetric, no matter whether the centre of the breather is on a light or a heavy atom.

关键词： nonlinearity breather gap band

Estimation of effective plant area index for South Korean forests using LiDAR system

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Science China(Life Sciences) 2010年第7期53卷 898-908页

作者： KWAK Doo-Ahn LEE Woo-Kyun KAFATOS Menas SON Yowhan CHO Hyun-Kook LEE Seung-Ho Department of Environmental Science and Ecological Engineering Korea University Center of Excellence in Earth Observing Schmid College of ScienceChapman University Division of Forest Resources Information Korea Forest Research Institute

Light Detection and Ranging(LiDAR) systems can be used to estimate both vertical and horizontal forest structure.Woody components,the leaves of trees and the understory can be described with high precision,using geo-registered 3D-points.Based on this concept,the Effective Plant Area Indices(PAIe) for areas of Korean Pine(Pinus koraiensis),Japanese Larch(Larix leptolepis) and Oak(Quercus spp.) were estimated by calculating the ratio of intercepted and incident LIDAR laser rays for the canopies of the three forest types.Initially,the canopy gap fraction(GLiDAR) was generated by extracting the LiDAR data reflected from the canopy surface,or inner canopy area,using k-means statistics.The LiDAR-derived PAIe was then estimated by using GLIDAR with the Beer-Lambert law.A comparison of the LiDAR-derived and field-derived PAIe revealed the coefficients of determination for Korean Pine,Japanese Larch and Oak to be 0.82,0.64 and 0.59,respectively.These differences between field-based and LIDAR-based PAIe for the different forest types were attributed to the amount of leaves and branches in the forest stands.The absence of leaves,in the case of both Larch and Oak,meant that the LiDAR pulses were only reflected from branches.The probability that the LiDAR pulses are reflected from bare branches is low as compared to the reflection from branches with a high leaf density.This is because the size of the branch is smaller than the resolution across and along the 1 meter LIDAR laser track.Therefore,a better predictive accuracy would be expected for the model if the study would be repeated in late spring when the shoots and leaves of the deciduous trees begin to appear.

关键词： leaf area index plant area index LiDAR k-means clustering gap fraction beer-lambert law

Investigation of the stable and the metastable liquidus miscibility gaps in Fe–Sn and Fe–Cu binary systems

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International Journal of Minerals,Metallurgy and Materials 2019年第11期26卷 1427-1435页

作者： Jiang-tao Gao Chang-rong Li Cui-ping Guo Zhen-min Du School of Materials Science and Engineering University of Science and Technology Beijing

Two kinds of experimental methods were tried in the present work:(i)the powder metallurgy method combined with differential thermal analysis(DTA)to determine the metastable liquidus miscibility gap for a Fe–Cu binary system and(ii)the high-temperature melting method combined with isothermal treatment to determine the stable liquidus miscibility gap for a Fe–Sn binary system.The experimental method was adopted according to the characteristics of the liquidus miscibility gap of the specific system.Using the powder metallurgy method,a uniform microstructure morphology and chemical composition was obtained in the DTA specimen,and the phase-separation temperature of the supercooled metastable liquid was measured.The isothermal treatment was applied for the samples inside the stable liquidus miscibility gap;here,equilibrated compositions were reached,and a layered morphology was formed after rapid cooling.The liquid miscibility gaps of the Fe–Cu and Fe–Sn binary systems were measured,and the peak temperatures of the corresponding miscibility gaps were determined to be about 1417°C at x(Cu)=0.465 at%and 1350°C at x(Sn)=0.487 at%,respectively.On the basis of the experimental results,both the Fe–Cu and the Fe–Sn binary systems were thermodynamically assessed.

关键词： binary systems miscibility gap differential thermal analysis(DTA) metastable state

A novel variable topology design for a multi-flexible ejection mechanism

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Defence Technology（防务技术） 2020年第2期16卷 432-438页

作者： Hao Liu Jun Zhou Zong-lai Mo Shi-wei Zhang School of Astronautics Northwestern Polytechnical UniversityXi'an710072China School of Mechanical Engineering Nanjing University of Science and TechnologyNanjing210094China Luoyang Opto-Electro Technology Development Center 471009China

The airborne missile launch mechanism often subjects to significant deformations induced by the large ejection force during high-speed actuations in missile ejection process,leading to a substantial deviation of separation parameters from designed values that threats safety of the carrier.This study proposes a novel variable topology design for launch mechanism,achieved via a Prsmatic-Revolute-Revolute pair(PR-R)motion formed by the structural gap with a specific direction.It enables launch mechanism variability during missile ejection process and optimizes the ejection force given by the front and back ejection arms,and greatly optimizes the separation parameters during missile ejection.The kinetics simulation analysis is conducted under working conditions of the original ejection mechanism and the novel mechanism with variable topology design,respectively.The results show that the novel variable topology design is more befitting for the launch process in terms of system safety and controllability,effectively improving the separation posture,restraining the flexible effect of the mechanism,and fulfilling the effectiveness of the design value of multi-rigid body.

关键词： Variable topology gap dynamics Multi-flexible body Flexible control Ejection mechanism

Photoemission study of iron-based superconductor

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Chinese Physics B 2013年第8期22卷 98-108页

作者：刘中灝蔡贻鹏赵彦阁贾雷雷王善才 Department of Physics Renmin University of China

The iron-based superconductivity （IBSC） is a great challenge in correlated system. Angle-resolved photoemission spectroscopy （ARPES） provides electronic structure of the IBSCs, the pairing strength, and the order parameter symmetry. Here, we briefly review the recent progress in IBSCs and focus on the results from ARPES. The ARPES study shows the electronic structure of ＂122＂, ＂111＂, ＂11＂, and ＂122＂＂ families of IBSCs. It has been agreed that the IBSCs are unconventional superconductors in strong coupling region. The order parameter symmetry basically follows s form with considerable out-of-plane contribution.

关键词： iron-based superconductor angle-resolved photoemission spectroscopy gap pairing symmetry