The size distribution of the broken top coal blocks is an important factor,affecting the recovery ratio and the efficiency of drawing top coal in longwall top coal caving(LTCC)mining panel.The standard deviation of to...The size distribution of the broken top coal blocks is an important factor,affecting the recovery ratio and the efficiency of drawing top coal in longwall top coal caving(LTCC)mining panel.The standard deviation of top coal block size(dt)is one of the main parameters to reflect the size distribution of top coal.To find the effect of dt on the caving mechanism,this study simulates experiments with 9 different dt by using discrete element software PFC.The dt is divided into two stages:uniform distribution stage(UDS)whose dt is less than 0.1(Schemes 1–5),and nonuniform distribution stage(NDS)whose dt is more than 0.1(Schemes 6–9).This research mainly investigates the variation of recovery ratio,drawing body shape,boundary of top coal,and contact force between particles in the two stages,respectively.The results showed that with the increasing dt,the recovery ratio of the panel increases first and then decreases in UDS.It is the largest in Scheme 3,which mainly increases the drawing volume at the side of starting drawing end.However,the recovery ratio decreases first and then increases quickly in NDS,and it is the largest in Scheme 9,where the drawing volume at the side of finishing drawing end are relatively higher.In UDS,the major size of top coal is basically medium,while in NDS,the size varies from medium to small,and then to large,with a distinct difference in shape and volume of the drawing body.When the major size of top coal is medium and small,the cross-section width of the initial boundary of top coal at each height is relatively small.Conversely,when the top coal size is large,the initial boundary of top coal has a larger opening range,the rotating angle of lower boundary is relatively small in the normal drawing stage,which is conducive to the development of drawing body and reduces the residual top coal,and the maximum particle velocity and the particles movement angle are both larger.This study lays a foundation for the prediction of recovery ratio,and suggests that the uniform top coal is more manageable and has a larger recovery ratio.展开更多
It is important to quantify and analyze forest spatial patterns for studying biological characteristics,population interaction and the relationship between the population and environment.In this study,the forest spati...It is important to quantify and analyze forest spatial patterns for studying biological characteristics,population interaction and the relationship between the population and environment.In this study,the forest spatial structure unit was generated based on the Delaunay triangulation model(DTM),and the weights were generated using the comprehensive values of the tree diameter at breast height,total height and crown width.The distance between neighbors determined by the DTM was weighted to transform the original coordinates of trees into logical coordinates.Then,a weighted spatial pattern(WSP)was developed.After weighting,the neighboring trees were replaced,the replacement ratio was 38.3%,and there was 57.4%of the central tree.Correlation analysis showed that the uniform angle index of the WSP was significantly correlated with the tree size standard deviation under uniformity(r=0.932)and randomness(r=0.711).The DTM method not only considers the spatial distance between trees,but also considers the non-spatial attributes of trees.By changing the spatial topological relation between trees,this method further improves the spatial structure measurement of forest.展开更多
Microplastics in terrestrial ecosystems are relatively understudied compared to microplastics in well-studied marine and freshwater ecosystems.It is well-documented that soil microplastics can profoundly influence agr...Microplastics in terrestrial ecosystems are relatively understudied compared to microplastics in well-studied marine and freshwater ecosystems.It is well-documented that soil microplastics can profoundly influence agricultural plant species;while terrestrial wild plants are primary producers and at the bottom of food chains,remarkably little is known about how microplastic abundances affect their growth and the related mechanisms.We selected 18 wild plant species,exposed them to an environmentally realistic microplastic gradient(ranging from 0 to 8000 items kg-1 soil)for one growing season,and measured soil pH,nutrients and microbes,leaf fluorescence,and plant biomass.We also used structural equation modeling to link the associations between variables.11%of the 18 wild plant species were inhibited by polypropylene(PP)microplastics,39%were facilitated,and 50%were unaffected.Across all the 18 species,PP microplastics had no negative impacts on their whole-plant growth,as measured by the standardized effect size;microplastic abundance impacts on whole-plant growth exhibited hump-shaped reaction norms,and the abundance thresholds for positive impacts approximately ranged from 2000 to 6000 items kg-1 soil.Soil pH played a key role in mediating microplastic impacts directly and indirectly by altering leaf chlorophyll and root nutrient uptake.These findings suggest that microplastic abundance thresholds could shape the whole-plant growth of terrestrial wild plants and microplastic abundance impacts might not rise consistently.Additionally,threshold effects highlight the importance of the full gamut of microplastic abundance gradients and provide insights into ecosystem management strategies.展开更多
基金supported by the National Key R&D Plan of China,China(Grant No.2018YFC0604501)the Natural Science Foundation of China,China(Grant Nos.51934008,51674264,51904305)the Research Fund of the State Key Laboratory of Coal Resources and Safe Mining,CUMT,China(Grant No.SKLCRSM19KF023).
文摘The size distribution of the broken top coal blocks is an important factor,affecting the recovery ratio and the efficiency of drawing top coal in longwall top coal caving(LTCC)mining panel.The standard deviation of top coal block size(dt)is one of the main parameters to reflect the size distribution of top coal.To find the effect of dt on the caving mechanism,this study simulates experiments with 9 different dt by using discrete element software PFC.The dt is divided into two stages:uniform distribution stage(UDS)whose dt is less than 0.1(Schemes 1–5),and nonuniform distribution stage(NDS)whose dt is more than 0.1(Schemes 6–9).This research mainly investigates the variation of recovery ratio,drawing body shape,boundary of top coal,and contact force between particles in the two stages,respectively.The results showed that with the increasing dt,the recovery ratio of the panel increases first and then decreases in UDS.It is the largest in Scheme 3,which mainly increases the drawing volume at the side of starting drawing end.However,the recovery ratio decreases first and then increases quickly in NDS,and it is the largest in Scheme 9,where the drawing volume at the side of finishing drawing end are relatively higher.In UDS,the major size of top coal is basically medium,while in NDS,the size varies from medium to small,and then to large,with a distinct difference in shape and volume of the drawing body.When the major size of top coal is medium and small,the cross-section width of the initial boundary of top coal at each height is relatively small.Conversely,when the top coal size is large,the initial boundary of top coal has a larger opening range,the rotating angle of lower boundary is relatively small in the normal drawing stage,which is conducive to the development of drawing body and reduces the residual top coal,and the maximum particle velocity and the particles movement angle are both larger.This study lays a foundation for the prediction of recovery ratio,and suggests that the uniform top coal is more manageable and has a larger recovery ratio.
基金funded by National Natural Science Foundation of China(31570627)Hunan Forestry Science and Technology Project(XLK201740)+1 种基金Hunan Science and Technology Innovation Platform and Talent Plan(2017TP1022)Hunan Science and Technology Plan Project(2015WK3017)。
文摘It is important to quantify and analyze forest spatial patterns for studying biological characteristics,population interaction and the relationship between the population and environment.In this study,the forest spatial structure unit was generated based on the Delaunay triangulation model(DTM),and the weights were generated using the comprehensive values of the tree diameter at breast height,total height and crown width.The distance between neighbors determined by the DTM was weighted to transform the original coordinates of trees into logical coordinates.Then,a weighted spatial pattern(WSP)was developed.After weighting,the neighboring trees were replaced,the replacement ratio was 38.3%,and there was 57.4%of the central tree.Correlation analysis showed that the uniform angle index of the WSP was significantly correlated with the tree size standard deviation under uniformity(r=0.932)and randomness(r=0.711).The DTM method not only considers the spatial distance between trees,but also considers the non-spatial attributes of trees.By changing the spatial topological relation between trees,this method further improves the spatial structure measurement of forest.
基金supported by the Hebei Agricultural University Talents Fund(grant number:YJ2022023).
文摘Microplastics in terrestrial ecosystems are relatively understudied compared to microplastics in well-studied marine and freshwater ecosystems.It is well-documented that soil microplastics can profoundly influence agricultural plant species;while terrestrial wild plants are primary producers and at the bottom of food chains,remarkably little is known about how microplastic abundances affect their growth and the related mechanisms.We selected 18 wild plant species,exposed them to an environmentally realistic microplastic gradient(ranging from 0 to 8000 items kg-1 soil)for one growing season,and measured soil pH,nutrients and microbes,leaf fluorescence,and plant biomass.We also used structural equation modeling to link the associations between variables.11%of the 18 wild plant species were inhibited by polypropylene(PP)microplastics,39%were facilitated,and 50%were unaffected.Across all the 18 species,PP microplastics had no negative impacts on their whole-plant growth,as measured by the standardized effect size;microplastic abundance impacts on whole-plant growth exhibited hump-shaped reaction norms,and the abundance thresholds for positive impacts approximately ranged from 2000 to 6000 items kg-1 soil.Soil pH played a key role in mediating microplastic impacts directly and indirectly by altering leaf chlorophyll and root nutrient uptake.These findings suggest that microplastic abundance thresholds could shape the whole-plant growth of terrestrial wild plants and microplastic abundance impacts might not rise consistently.Additionally,threshold effects highlight the importance of the full gamut of microplastic abundance gradients and provide insights into ecosystem management strategies.
