In order to improve the prediction precision of the safety performance function （SPF） of freeway basic segments, design and crash data of 640 segments are collected from different institutions. Three negative binomi...In order to improve the prediction precision of the safety performance function （SPF） of freeway basic segments, design and crash data of 640 segments are collected from different institutions. Three negative binomial （NB） regression models and three generalized negative binomial （GNB） regression models are built to prove that the interactive influence of explanatory variables plays an important role in fitting goodness. The effective use of the GNB model in analyzing the interactive influence of explanatory variables and predicting freeway basic segments is demonstrated. Among six models, the two models （one is the NB model and the other is the GNB model. ） which consider the interactive influence of the annual average daily traffic （AADT） and length are more reasonable for predicting results. Furthermore, a comprehensive study is carried out to prove that when considering the interactive influence, the NB and GNB models have almost the same fitting performance in estimating the crashes, among which the GNB model is slightly better for prediction performance.展开更多
Bare patches in alpine meadow are the main manifestation of its degradation.The change of bare patches in an alpine meadow in the Yellow River Source Zone during 2018-2019 was studied in relation to the disturbances c...Bare patches in alpine meadow are the main manifestation of its degradation.The change of bare patches in an alpine meadow in the Yellow River Source Zone during 2018-2019 was studied in relation to the disturbances caused by plateau pika(Ochotona curzoniae)population and simulated grazing via artificial mowing both independently and interactively.The disturbance was set at three levels of high,medium and no disturbance(control group).Bare patches were mapped by from unmanned aerial vehicle(UAV)images with fine resolution of 1 cm obtained in August 2018 and August 2019 in ArcGIS.The results showed that the total area of bare patches decreased by 112.05 m2 in sub-plots devoid of pika disturbance but increased by 126.37 m2 in other subplots.The highest rate of increase is 89.02%.The individual effect of pika exceeds the joint effect of pika and mowing disturbances.The sole effect of mowing is lower than the joint effect of pika disturbance and intensive mowing,but higher than the joint influence of pika disturbance and moderate mowing.Strong pika disturbance(14 per sub-plot)caused the influence of mowing from moderate to intensive to increase by five-fold.The area of bare patches treated with moderate mowing and no pika disturbance decreased at the highest pace(-37.22%).Intensive mowing and medium density pikas(100 pikas/ha)are considered the thresholds at which the bare patches start to expand.Even if the meadow is mowed at the medium and high intensity,the area of bare patches can be significantly reduced if plateau pika population is controlled to a low level.ANOVA analysis and longterm macro-scale satellite-derived results reveal that pika disturbance is more important in causing the bare patches to change than simulated grazing.Therefore,it is more important to control the number of pikas than to reduce grazing intensity to prevent the expansion of bare patches in the degraded alpine meadow in the study area.展开更多
The interaction mechanism and phase evolution of ammonium polyphosphate（APP）mixed with muscovite（APP/muscovite）were studied by TG,XRD and SEM,respectively,during heating.When the temperature is not higher than 300...The interaction mechanism and phase evolution of ammonium polyphosphate（APP）mixed with muscovite（APP/muscovite）were studied by TG,XRD and SEM,respectively,during heating.When the temperature is not higher than 300 ℃,muscovite has no effect on the thermaldecomposition of APP,and the initialdecomposition temperature of APP/muscovite at 283 ℃ is basically the same as the APP at 295 ℃,and the main thermaldecomposition products are polyphosphoric acid and NH_4H_2PO_4 at 300 ℃.The polyphosphoric acid,the decomposition products of APP,can enable K and Siout of muscovite and interact with muscovite chemically to generate Al_2O_3·2SiO_2,α-SiO_2 and phosphates（AlPO_4 and K_5P_3O_（10））compounds during 400 ℃-800 ℃,which own obvious adhesive phenomenon and porous structure with the apparent porosity of 58.4%.Further reactions between phosphates other than reactions among Al_2O_3·2SiO_2 and α-SiO_2 can generate KAlP_2O_7 at 1 000 ℃ and the density of residualproduct is improved by low melting point phosphate filling pore to form relatively dense structure and decrease the apparent porosity to 44.4%.The flame resistant and self-supported ceramic materials are expected to enhance the fire-retarding synergistic effect between APP and muscovite.展开更多
As high-grade magnesite and brucite resources(hereinafter referred to as magnesium-containing minerals)are decreasing annually,developing flotation separation technologies capable of efficiently and economically extra...As high-grade magnesite and brucite resources(hereinafter referred to as magnesium-containing minerals)are decreasing annually,developing flotation separation technologies capable of efficiently and economically extracting magnesium resources from low-grade magnesium-containing minerals is necessary.Although efficient flotation separation technologies for magnesium-containing minerals are well researched,related concepts are not yet clarified.Moreover,the industrial development of magnesium-containing mineral flotation technologies is limited by their low separation efficiency and environmental problems.This limitation has inhibited the full utilization of low-grade magnesium-containing minerals.This study comprehensively discusses the research progress of flotation separation technologies for magnesium-containing minerals,focusing on the crystal chemical and surface characteristics of magnesium-containing minerals and their gangue minerals,effect of inevitable ions on mineral flotation behavior,interaction effects of minerals,and research advancement of flotation reagents.The study aims to clarify the future development direction of the flotation separation of magnesium-containing minerals and provide theoretical support and technical references for an efficient separation.展开更多
Deeply integrated vulnerability and its evaluation framework provide a new perspective for the study ofsocio-ecological systems in metropolitan suburbs.A new vulnerability evaluation system of‘exposure-sensitivityada...Deeply integrated vulnerability and its evaluation framework provide a new perspective for the study ofsocio-ecological systems in metropolitan suburbs.A new vulnerability evaluation system of‘exposure-sensitivityadaptability’based on the socio-ecological system and vulnerability theory was constructed.Meanwhile,drawing onthe concept of‘spatial trap’,the concept of‘spatial vulnerability trap’was tried to put forward.The spatial-temporal interaction characteristics were analyzed,the existence of spatial vulnerability trap was tested and the interactionmechanism of vulnerability dynamic evolution was revealed using spatial-temporal exploration analysis method andgeographic detector for socio-ecological system vulnerability of 184 administrative villages in Qingpu District from theyear 1998 to 2018.The results showed that:(1)During the study period,the socio-ecological systems vulnerability ofQingpu District increased from 0.518 to 0.621,and the vulnerability level increased from low grade to medium grade.The spatial-temporal pattern showed the dynamic characteristics of first increase and then decrease and high in theEast and low in the west.(2)The relative length of the socio-ecological systems vulnerability temporal path movementin Qingpu District from 1998 to 2018 showed a trend of gradual decline from the central region to the surrounding area.The mobility curvature of the vulnerability time path was relatively small,showing the spatial pattern of low in the northand high in south,and the cohesion index of the spatial transition of vulnerability is 0.496.The spatial agglomerationstructure had relatively high transfer activity and low path locking.(3)No‘spatial vulnerability absolute trap’was detected during the study period,yet the‘spatial vulnerability relative trap’highlighted in the 11 administrative villagesmainly distributed around the administrative boundary in the north and south of the area.(4)Social capital factor,human capital factor,social factor,economic factor,ecological factor and financial capital factor are the main factorsinfluencing the vulnerability change,but the influence of each factor showed fluctuation and type difference.The maininteraction types of socio-ecological system vulnerability differentiation in urban suburbs are the cumulative type ofinternal and external coupling,the type of endogenous capacity constraint and the external environmental stress type.The results of the study are of great theoretical and practical significance to guide the suburban areas to prevent thevulnerability risk,promote regional coordination to reduce vulnerability and sustainable development.展开更多
The coefficient of static friction(SF),the coefficient of rolling friction(RF)for particles are two key parameters affecting the repose angle formation and flow characteristics.In this paper,the interaction effects of...The coefficient of static friction(SF),the coefficient of rolling friction(RF)for particles are two key parameters affecting the repose angle formation and flow characteristics.In this paper,the interaction effects of SF and RF on the formation process of corn repose angle was investigated by the discrete element method.Firstly,five shape kinds of corn models(horse tooth,spherical cone,spheroid,oblate,and irregular shape)were established.Secondly,aluminum cylinder and organic glass box were used to conduct the simulation experiments with taking SF and RF as independent factors and seeing the repose angle as dependent value.Based on simulation results the regression equations were established.Simulation results showed the relation between two factors and the rotational kinetic energy is not nonlinear,and SF does not significantly restrict the flow of corn models after increasing the flow direction,and the effect of SF on the contact number between corns and the bottom plate is remarkable,while the effect of RF on the contact number is not remarkable.Finally,the interaction effect of two factors on the repose angle was analyzed by variance analysis and results showed SF and RF all have a significant impact on the repose angle.Moreover,their interaction effect has an impact on the repose angle.展开更多
基金The National Natural Science Foundation of China(No.51408229,51278202)the Program of the Key Laboratory of Road and Traffic Engineering of the Ministry of Education,Tongji University(No.K201204)the Science and Technology Program of Guangdong Communication Department(No.2013-02-068)
文摘In order to improve the prediction precision of the safety performance function （SPF） of freeway basic segments, design and crash data of 640 segments are collected from different institutions. Three negative binomial （NB） regression models and three generalized negative binomial （GNB） regression models are built to prove that the interactive influence of explanatory variables plays an important role in fitting goodness. The effective use of the GNB model in analyzing the interactive influence of explanatory variables and predicting freeway basic segments is demonstrated. Among six models, the two models （one is the NB model and the other is the GNB model. ） which consider the interactive influence of the annual average daily traffic （AADT） and length are more reasonable for predicting results. Furthermore, a comprehensive study is carried out to prove that when considering the interactive influence, the NB and GNB models have almost the same fitting performance in estimating the crashes, among which the GNB model is slightly better for prediction performance.
基金financially supported by the National Natural Science Foundation of China(Grant No.31872999)Project of the Science and Technology Department of Qinghai Province(Grant No.2018-ZJ781)+2 种基金Discipline Innovation and Introducing Talents Program of Higher Education Institutions(the 111 Project)(Grant No.D18013)Changjiang Scholars and Innovation Team Development plan(Grant No.IRT17R62)China Scholarship Council(Grant No.201907660003)。
文摘Bare patches in alpine meadow are the main manifestation of its degradation.The change of bare patches in an alpine meadow in the Yellow River Source Zone during 2018-2019 was studied in relation to the disturbances caused by plateau pika(Ochotona curzoniae)population and simulated grazing via artificial mowing both independently and interactively.The disturbance was set at three levels of high,medium and no disturbance(control group).Bare patches were mapped by from unmanned aerial vehicle(UAV)images with fine resolution of 1 cm obtained in August 2018 and August 2019 in ArcGIS.The results showed that the total area of bare patches decreased by 112.05 m2 in sub-plots devoid of pika disturbance but increased by 126.37 m2 in other subplots.The highest rate of increase is 89.02%.The individual effect of pika exceeds the joint effect of pika and mowing disturbances.The sole effect of mowing is lower than the joint effect of pika disturbance and intensive mowing,but higher than the joint influence of pika disturbance and moderate mowing.Strong pika disturbance(14 per sub-plot)caused the influence of mowing from moderate to intensive to increase by five-fold.The area of bare patches treated with moderate mowing and no pika disturbance decreased at the highest pace(-37.22%).Intensive mowing and medium density pikas(100 pikas/ha)are considered the thresholds at which the bare patches start to expand.Even if the meadow is mowed at the medium and high intensity,the area of bare patches can be significantly reduced if plateau pika population is controlled to a low level.ANOVA analysis and longterm macro-scale satellite-derived results reveal that pika disturbance is more important in causing the bare patches to change than simulated grazing.Therefore,it is more important to control the number of pikas than to reduce grazing intensity to prevent the expansion of bare patches in the degraded alpine meadow in the study area.
基金Funded by the National Natural Science Foundation of China(No.51472188)
文摘The interaction mechanism and phase evolution of ammonium polyphosphate（APP）mixed with muscovite（APP/muscovite）were studied by TG,XRD and SEM,respectively,during heating.When the temperature is not higher than 300 ℃,muscovite has no effect on the thermaldecomposition of APP,and the initialdecomposition temperature of APP/muscovite at 283 ℃ is basically the same as the APP at 295 ℃,and the main thermaldecomposition products are polyphosphoric acid and NH_4H_2PO_4 at 300 ℃.The polyphosphoric acid,the decomposition products of APP,can enable K and Siout of muscovite and interact with muscovite chemically to generate Al_2O_3·2SiO_2,α-SiO_2 and phosphates（AlPO_4 and K_5P_3O_（10））compounds during 400 ℃-800 ℃,which own obvious adhesive phenomenon and porous structure with the apparent porosity of 58.4%.Further reactions between phosphates other than reactions among Al_2O_3·2SiO_2 and α-SiO_2 can generate KAlP_2O_7 at 1 000 ℃ and the density of residualproduct is improved by low melting point phosphate filling pore to form relatively dense structure and decrease the apparent porosity to 44.4%.The flame resistant and self-supported ceramic materials are expected to enhance the fire-retarding synergistic effect between APP and muscovite.
基金financially supported by the Open Foundation of State Key Laboratory of Mineral Processing (No.BGRIMM-KJSKL-2024-07)the Open Project of the Key Laboratory of Solid Waste Treatment and Resource Utilization of the Ministry of Education,China (No.23kfgk02)。
文摘As high-grade magnesite and brucite resources(hereinafter referred to as magnesium-containing minerals)are decreasing annually,developing flotation separation technologies capable of efficiently and economically extracting magnesium resources from low-grade magnesium-containing minerals is necessary.Although efficient flotation separation technologies for magnesium-containing minerals are well researched,related concepts are not yet clarified.Moreover,the industrial development of magnesium-containing mineral flotation technologies is limited by their low separation efficiency and environmental problems.This limitation has inhibited the full utilization of low-grade magnesium-containing minerals.This study comprehensively discusses the research progress of flotation separation technologies for magnesium-containing minerals,focusing on the crystal chemical and surface characteristics of magnesium-containing minerals and their gangue minerals,effect of inevitable ions on mineral flotation behavior,interaction effects of minerals,and research advancement of flotation reagents.The study aims to clarify the future development direction of the flotation separation of magnesium-containing minerals and provide theoretical support and technical references for an efficient separation.
基金The Social Science Foundation of Hunan Province(20JD011)The Natural Science Foundation of Hunan Province(2022JJ50273)+1 种基金The National Natural Science Foundation of China(42271105)The Key Laboratory of Key Technologies of Digital Urban-Rural Spatial Planning of Hunan Province(2018TP1042)。
文摘Deeply integrated vulnerability and its evaluation framework provide a new perspective for the study ofsocio-ecological systems in metropolitan suburbs.A new vulnerability evaluation system of‘exposure-sensitivityadaptability’based on the socio-ecological system and vulnerability theory was constructed.Meanwhile,drawing onthe concept of‘spatial trap’,the concept of‘spatial vulnerability trap’was tried to put forward.The spatial-temporal interaction characteristics were analyzed,the existence of spatial vulnerability trap was tested and the interactionmechanism of vulnerability dynamic evolution was revealed using spatial-temporal exploration analysis method andgeographic detector for socio-ecological system vulnerability of 184 administrative villages in Qingpu District from theyear 1998 to 2018.The results showed that:(1)During the study period,the socio-ecological systems vulnerability ofQingpu District increased from 0.518 to 0.621,and the vulnerability level increased from low grade to medium grade.The spatial-temporal pattern showed the dynamic characteristics of first increase and then decrease and high in theEast and low in the west.(2)The relative length of the socio-ecological systems vulnerability temporal path movementin Qingpu District from 1998 to 2018 showed a trend of gradual decline from the central region to the surrounding area.The mobility curvature of the vulnerability time path was relatively small,showing the spatial pattern of low in the northand high in south,and the cohesion index of the spatial transition of vulnerability is 0.496.The spatial agglomerationstructure had relatively high transfer activity and low path locking.(3)No‘spatial vulnerability absolute trap’was detected during the study period,yet the‘spatial vulnerability relative trap’highlighted in the 11 administrative villagesmainly distributed around the administrative boundary in the north and south of the area.(4)Social capital factor,human capital factor,social factor,economic factor,ecological factor and financial capital factor are the main factorsinfluencing the vulnerability change,but the influence of each factor showed fluctuation and type difference.The maininteraction types of socio-ecological system vulnerability differentiation in urban suburbs are the cumulative type ofinternal and external coupling,the type of endogenous capacity constraint and the external environmental stress type.The results of the study are of great theoretical and practical significance to guide the suburban areas to prevent thevulnerability risk,promote regional coordination to reduce vulnerability and sustainable development.
基金by the Excellent Ph.D.Dissertation of Gansu Agricultural University(YB2020003)the Chinese Natural Science Foundation(52065004).
文摘The coefficient of static friction(SF),the coefficient of rolling friction(RF)for particles are two key parameters affecting the repose angle formation and flow characteristics.In this paper,the interaction effects of SF and RF on the formation process of corn repose angle was investigated by the discrete element method.Firstly,five shape kinds of corn models(horse tooth,spherical cone,spheroid,oblate,and irregular shape)were established.Secondly,aluminum cylinder and organic glass box were used to conduct the simulation experiments with taking SF and RF as independent factors and seeing the repose angle as dependent value.Based on simulation results the regression equations were established.Simulation results showed the relation between two factors and the rotational kinetic energy is not nonlinear,and SF does not significantly restrict the flow of corn models after increasing the flow direction,and the effect of SF on the contact number between corns and the bottom plate is remarkable,while the effect of RF on the contact number is not remarkable.Finally,the interaction effect of two factors on the repose angle was analyzed by variance analysis and results showed SF and RF all have a significant impact on the repose angle.Moreover,their interaction effect has an impact on the repose angle.
