本质安全便携式爆破网路检测仪设计

作者针对煤矿井下爆破工作者现场检测电雷管和电爆网路可靠性的需求,采用MSP430低功耗单片机设计的一款本安型便携式爆破网路检测仪,该仪器具有体积小、功耗低,便于携带、使用简单方便等特点。文中介绍了该仪器的硬件组成、本质安全性电路设计及整机低功耗的实现。     

Modeling tree root diameter and biomass by ground-penetrating radar

Roots play a key role in ecosystem functioning as they transfer water and nutrients from soil to plants.Traditional methods for measuring roots are labor-intensive and destructive in nature,which limits quantitative and repeatable assessments in longterm research.Ground-penetrating radar(GPR) provides a non-destructive method to measure plant roots.Based on the superiority of GPR with 2 GHz frequency,we developed a new,practical method to estimate root biomass.First,average root matter density was measured ...     

Mantle dynamics of the reactivating North China Craton:Constraints from the topographies of the 410-km and 660-km discontinuities

The topographies of the 410-km and 660-km discontinuities have important implications for mantle dynamics.Here we present high-resolution seismic imaging of the 410-km and 660-km discontinuities beneath the North China Craton (NCC) employing the receiver function method.Depth anomalies (deeper or shallower than the global average depths) at both discontinuities were detected by introducing a three-dimensional regional velocity model.The depressions of the 410-km discontinuity are mostly located in the easte...     

Effect of Cooling Rate on Microstructure and Mechanical Properties of 20CrNi2MoV Steel

Thermo-mechanical process and continuous cooling process were carried out on 20 CrNi2MoV steel. Three cooling rates were implemented to optimize the mechanical properties. The microstructure evolution, precipitation behavior, and strengthening mechanisms were systematically investigated, and the fracture mechanisms were analyzed via combination of impact fracture morphologies and deflection–load curves. The experimental results indicate that the transformed microstructure of experimental steel is all complex consisting of granular bainitic ferrite and bainitic ferrite with dispersed martensite/austenite(M/A) constituents in the matrix at cooling rates of 13, 21, and 29 °C/s. When the cooling rate increases, the grain of the steel is obviously refined. The sizes of the bainitic ferrite are 5.8, 4.7, and 3.1 lm under cooling rates of 13, 21, and 29 °C/s, respectively. The refinement of the bainitic ferrite plays a dominant role in strength increasing and also contributes to high crack propagation energy. However, the morphologies of M/A constituents obtained under different cooling rates contribute to different crack initiation energies and then affect the impact property.     

Control of coal and gas outbursts in Huainan mines in China: A review

Coal extraction in Huainan area is basically characterized by one of typical multi-seam mining conditions observed in China, where coal is mined in soft seams characterized by high gas content, high stress, low permeability and difficult geological conditions. The average mining depth in Huainan area is 875 m and continues to increase by 15-25 m annually. The rise in mining depth increases the risk of coal and gas outbursts and makes it more difficult to control outburst risk in Huainan coalmines. This paper reviews the main achievements(e.g. theories, technologies and equipment) in outburst control in Huainan, and tries to analyze some key challenging issues, and to present associated strategies to address these issues.It suggests that the outburst control in Huainan must take a combination approach of both regional and localized control in which the former plays a dominant role. Other outburst prevention principles include(1) non-outburst seams protecting outburst seams,(2) less outburst-prone seams protecting strong outburst-prone seams,(3) stress-releasing mining, and(4) the combination of ground and underground gas drainage(the model is dubbed as "walking on two legs"). The paper concludes that we should conduct fundamental researches on outburst mechanism, and develop outburst control technologies and equipment to ensure safe and efficient coal mining of deep coal resources in Huainan area.     

Animating turbulent water by vortex shedding in PIC/FLIP

In this paper,we present a hybrid method,which integrates PIC/FLIP and vortex particle methods into a unified framework,to efficiently simulate vortex shedding that happens when fluids flow around internal obstacles.To improve efficiency and reduce the numerical dissipations,we first solve the governing equations on a coarse grid using PIC/FLIP,and then interpolate the intermediate results to a finer grid to obtain the base flow.When the regular particles in PIC/FLIP enter the boundary layer,if the specified conditions are satisfied to cause vortex shedding,they are selected as vortex particles by assigning additional vorticity related attributes.The vortex particle dynamics are controlled by the vorticity form of NS equations,and several efficient methods are proposed to solve them on the finer grid.Finally,the obtained turbulence flow is added to the base flow.As a result,we are able to simulate turbulent water with rich wake details around the internal obstacles.     

Efficient polygonization of tree trunks modeled by convolution surfaces

We present an efficient polygonization approach for tree trunks modeled by line skeleton-based convolution surfaces.A quad-dominated non-convex bounding polyhedron is firstly created along the skeleton,which is then tetrahedralized and subdivided into the pre-defined resolution.After that,the iso-surface within each tetrahedron is extracted using marching tetrahedra.Our algorithm can generate polygons with adaptive edge lengths according to the thickness of the trunk.In addition,we present an efficient CUDA-based parallel algorithm utilizing the high parallelism of the tetrahedron subdivision,the potential field calculation,and the iso-surface extraction.     

Energy-efficient power allocation for non-regenerative OFDM relay links

We consider a two-hop non-regenerative (amplify-and-forward) relay link with one source, one destination and one relay, in which orthogonal frequency division multiplexing (OFDM) is used. The power allocation (PA) to maximize the energy efficiency for the whole link is investigated under quality of service (Qos) require- ment and separate power constraints. An approximation method with low complexity is first proposed to convert the PA problem into a quasi-concave problem, which can obtain a tight lower bound in high SNR region. Furthermore, a more accurate approximation method with higher complexity is raised, which can approach the actual performance both in the low SNR and high SNR regions. We also introduce subcarrier pairing scheme to further enhance the energy efficiency for the link. Simulation results are shown to compare the performance of the two proposed methods.     

Effect of deformation twinning on the evolution of texture in TWIP steels during cold-rolling

Texture evolution of high-manganese twining-induced plasticity (TWIP) steels (Fe-16Mn-0.6C) during cold-rolling is studied by means of quantitative orientation distribution function (ODF)analysis.Thickness reductions of the specimens during cold-rolling are 10%,20%,30%,50% and 65%,respectively.Evolution of texture is of the Brass type,which is typical for low-stacking fault energy (SFE) materials.The contribution of deformation twinning to the development of texture is clearly illustrated by the monotonic increase of the twinned Cu component.In the present study,the deformation twinning was identified as significantly contributing to deformation up to the maximum reduction applied.These results are useful for the prediction and control of the texture in TWIP steels.     

The Correlation between Density and Low-Temperature Creep Property of Asphalt

The density of asphalt was measured with the pycnometer and densitometer. Creep properties of the asphalt were investigated with the bending beam rheometer at temperatures ranging from 0 ℃ to -36 ℃. The asphalt density data used to correlate with the creep properties were calculated from the regression equation of density and temperature. The asphalt sample used to determine the creep property was aged by the standard RTFOT test and the PAV test. The test results showed that the asphalt density had a linear relationship with temperature changes. The logarithm of the creep stiffness and the slope of the logarithm of the stiffness at 60 seconds all demonstrated a linear relationship with the density, and the regression coefficient of these data was around 0.99. The creep stiffness and the slope of the creep stiffness can be calculated from the asphalt density at the same temperature.