The potential role of formal structural optimization was investigated for designing foldable and deployable structures in this work.Shape-sizing nested optimization is a challenging design problem.Shape,represented by...The potential role of formal structural optimization was investigated for designing foldable and deployable structures in this work.Shape-sizing nested optimization is a challenging design problem.Shape,represented by the lengths and relative angles of elements,is critical to achieving smooth deployment to a desired span,while the section profiles of each element must satisfy structural dynamic performances in each deploying state.Dynamic characteristics of deployable structures in the initial state,the final state and also the middle deploying states are all crucial to the structural dynamic performances.The shape was represented by the nodal coordinates and the profiles of cross sections were represented by the diameters and thicknesses.SQP(sequential quadratic programming) method was used to explore the design space and identify the minimum mass solutions that satisfy kinematic and structural dynamic constraints.The optimization model and methodology were tested on the case-study of a deployable pantograph.This strategy can be easily extended to design a wide range of deployable structures,including deployable antenna structures,foldable solar sails,expandable bridges and retractable gymnasium roofs.展开更多
Aims Harsh environmental conditions in alpine ecosystems shape vegetation structure into patches,where many different plant species cluster and grow together.Yet,which factors are important for the structure and dynam...Aims Harsh environmental conditions in alpine ecosystems shape vegetation structure into patches,where many different plant species cluster and grow together.Yet,which factors are important for the structure and dynamics of such plant–patch networks remains poorly understood.We aim to assess which and how environmental and biotic factors predict the assembly of plant–patch networks along a mountain range.Methods We examined the distribution of plant species in more than 5500 vegetation patches in 37 Mediterranean alpine grasslands distributed along a 500 m altitudinal gradient(National Park of Sierra Guadarrama,Spain).We established a plant–patch network for each grassland community and analyzed how nestedness and modularity vary with environmental(altitude,insolation and soil conditions)and biotic factors(number of species per plot,mean patch area and total pasture area).Important Findings Plant–patch networks showed consistent,non-random patterns characterized by a nested,but not modular,structure,which suggests that positive associations among co-occurring specialists promote their growth within patches as subsets of a pool with more generalist species.Both nestedness and modularity of plant–patch networks varied among grasslands.Specifically,nestedness decreased with increasing species per plot and increased with mean patch area,while it was independent of environmental variables;modularity increased with increasing pasture area and species per plot.The negative relationship between species per plot and nested patterns may be linked to the restricted number of species that can coexist within the same patch at a given size.Moreover,the positive relationship between patch size and nestedness indicates that the growth of rare plant species within vegetation patches occupied by more abundant species is facilitated in bigger rather than smaller patches.Furthermore,these results indicate that the nested assembly of vegetation patches may be independent of abiotic conditions.These findings suggest that large and unfragmented vegetation patches are fundamental for the maintenance of plant diversity in alpine grasslands.Looking at species distribution at fine spatial scales may shed new light on the biotic processes underlying plant network assembly and provide novel ways for conserving biodiversity.展开更多
基金Project(030103) supported by the Weaponry Equipment Pre-Research Key Foundation of ChinaProject(69982009) supported by the National Natural Science Foundation of China
文摘The potential role of formal structural optimization was investigated for designing foldable and deployable structures in this work.Shape-sizing nested optimization is a challenging design problem.Shape,represented by the lengths and relative angles of elements,is critical to achieving smooth deployment to a desired span,while the section profiles of each element must satisfy structural dynamic performances in each deploying state.Dynamic characteristics of deployable structures in the initial state,the final state and also the middle deploying states are all crucial to the structural dynamic performances.The shape was represented by the nodal coordinates and the profiles of cross sections were represented by the diameters and thicknesses.SQP(sequential quadratic programming) method was used to explore the design space and identify the minimum mass solutions that satisfy kinematic and structural dynamic constraints.The optimization model and methodology were tested on the case-study of a deployable pantograph.This strategy can be easily extended to design a wide range of deployable structures,including deployable antenna structures,foldable solar sails,expandable bridges and retractable gymnasium roofs.
基金supported by the Madrid Regional Government(grant REMEDINAL TE-CM-S2018/EMT-4338)the Ministry of Economy and Competitiveness of Spain,(grants ROOTs-CGL2015-66809-P-)and AdAptA-CGL2012-33528)partially by the Swiss National Science Foundation to GL(grants IZSEZ0_180195 and P2ZHP3_187938).
文摘Aims Harsh environmental conditions in alpine ecosystems shape vegetation structure into patches,where many different plant species cluster and grow together.Yet,which factors are important for the structure and dynamics of such plant–patch networks remains poorly understood.We aim to assess which and how environmental and biotic factors predict the assembly of plant–patch networks along a mountain range.Methods We examined the distribution of plant species in more than 5500 vegetation patches in 37 Mediterranean alpine grasslands distributed along a 500 m altitudinal gradient(National Park of Sierra Guadarrama,Spain).We established a plant–patch network for each grassland community and analyzed how nestedness and modularity vary with environmental(altitude,insolation and soil conditions)and biotic factors(number of species per plot,mean patch area and total pasture area).Important Findings Plant–patch networks showed consistent,non-random patterns characterized by a nested,but not modular,structure,which suggests that positive associations among co-occurring specialists promote their growth within patches as subsets of a pool with more generalist species.Both nestedness and modularity of plant–patch networks varied among grasslands.Specifically,nestedness decreased with increasing species per plot and increased with mean patch area,while it was independent of environmental variables;modularity increased with increasing pasture area and species per plot.The negative relationship between species per plot and nested patterns may be linked to the restricted number of species that can coexist within the same patch at a given size.Moreover,the positive relationship between patch size and nestedness indicates that the growth of rare plant species within vegetation patches occupied by more abundant species is facilitated in bigger rather than smaller patches.Furthermore,these results indicate that the nested assembly of vegetation patches may be independent of abiotic conditions.These findings suggest that large and unfragmented vegetation patches are fundamental for the maintenance of plant diversity in alpine grasslands.Looking at species distribution at fine spatial scales may shed new light on the biotic processes underlying plant network assembly and provide novel ways for conserving biodiversity.
