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阻燃黄麻纤维/聚酯纤维复合材料的紫外老化性能 被引量:2
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作者 胡晓兰 自雅娴 +3 位作者 兰茜 刘国忠 张熙明 陈红武 《高分子材料科学与工程》 EI CAS CSCD 北大核心 2022年第2期109-114,共6页
利用聚酯纤维的皮芯结构实现黏接制备了黄麻纤维/聚酯纤维复合材料,通过磷系复配阻燃剂对黄麻纤维/聚酯纤维进行阻燃处理,应用紫外光辐照对复合材料进行加速老化,表征了复合材料老化过程中的力学性能及微观形貌。结果发现,复合材料的拉... 利用聚酯纤维的皮芯结构实现黏接制备了黄麻纤维/聚酯纤维复合材料,通过磷系复配阻燃剂对黄麻纤维/聚酯纤维进行阻燃处理,应用紫外光辐照对复合材料进行加速老化,表征了复合材料老化过程中的力学性能及微观形貌。结果发现,复合材料的拉伸强度和拉伸模量在紫外光照射的前10 d逐渐上升,之后逐渐下降;阻燃黄麻纤维/聚酯纤维复合无纺布的拉伸强度和拉伸模量比未阻燃处理的复合无纺布的更高,但紫外照射10 d后,阻燃复合无纺布的力学性能下降速度比未阻燃的复合无纺布更快。微观形貌结果显示,老化过程中,黄麻纤维结构逐渐变得疏松、产生了横向裂纹;聚酯纤维出现大量横向裂纹。阻燃处理加速了黄麻纤维/聚酯纤维复合材料的老化。 展开更多
关键词 黄麻纤维:聚酯纤维 老化性能 阻燃 复合材料
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Effects of deficit irrigation on daily and seasonal variations of trunk sap flow and its growth in Calligonum arborescens 被引量:7
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作者 LiShan SHAN Yi LI +1 位作者 RuiFeng ZHAO ximing zhang 《Journal of Arid Land》 SCIE CSCD 2013年第2期233-243,共11页
Water deficit in arid and semiarid regions affects whole-plant sap flow and leaf-level water relations. The objectives of this study were to clarify how sap flow of Calligonum arborescens responds to different drought... Water deficit in arid and semiarid regions affects whole-plant sap flow and leaf-level water relations. The objectives of this study were to clarify how sap flow of Calligonum arborescens responds to different drought stress conditions and to understand its acclimation mechanism to drought environments. A field experiment was conducted for C. arborescens during the growing season to evaluate the effects of deficit irrigation on the daily and seasonal variations of trunk sap flow in the shelterbelt along the Tarim Desert Highway, Xinjiang, China. Three dif- ferent water regimes (2,380, 1,960 and 1,225 m3/hm2) were applied at different stages of plant growth. From 1 May to 30 October 2007, a heat-balance stem flow gauge was used to monitor the sap flow dynamics of C. arborescens under different water regimes. Atmospheric evaporation demand and soil moisture conditions for differentially irri- gated C. arborescens were also monitored. The result showed that sap flow exhibited a clear diurnal pattern re- gardless of treatments; the diurnal patterns of sap flow and vapour pressure deficit were very similar under different water regimes and growing seasons, while the slope of the linear regression of this correlation confirmed an in- creasing water regime. The sap flow decreased under reduced water regimes and there was nocturnal sap flow regardless of water regimes, which was mainly contributed to nocturnal transpiration and water recharge. The sap flow peaked before midnight and dropped afterwards with obviously higher values in summer than in other seasons. It is speculated that the water consumption of C. arborescens during the day can be supplemented through the sap flow at night, which increased with increasing irrigation amount. Net radiation was the most significant correlated factor that influenced sap flow velocity and transpiration under different water regimes (R2〉0.719). Compared with the commonly practiced water regime, the growth of C. arborescens was significantly slower in the stress deficit irrigation, but not significantly different from that in the moderate deficit irrigation. The moderate deficit irrigation would not affect the stability of the shelterbelt and was a more efficient use of water resources compared with the current watering amount. 展开更多
关键词 Calligonum arborescens sap flow environmental factor growth parameter Tarim Desert Highway
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O2O迭代式项目学习的设计与应用——基于首要教学原理视角 被引量:4
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作者 熊邦忠 张希明 《中国远程教育》 CSSCI 北大核心 2020年第4期36-42,57,76,77,共10页
针对传统项目学习存在周期长、自由度大等问题,O2O迭代式项目学习引入了"O2O迭代"为新型学习脚手架。它将复杂项目分解成前后知识相关的多个功能小项目,串接起线上线下的迭代学习和知识运用,螺旋式发展学习者融合知识解决复... 针对传统项目学习存在周期长、自由度大等问题,O2O迭代式项目学习引入了"O2O迭代"为新型学习脚手架。它将复杂项目分解成前后知识相关的多个功能小项目,串接起线上线下的迭代学习和知识运用,螺旋式发展学习者融合知识解决复杂项目问题的能力。以首要教学原理为处方科学指导,它聚焦复杂项目增量式的解决,在O2O空间环境和协同机制的配合下,通过"结构、指导、辅导和反思"的过程,衔接"教与学"成为统一整体,服务于学习者在线上"需要知道"和线下"需要做"之间反复迭代的学习。在以开放教育"信息技术应用"课程为应用案例的实证研究中,样本统计显示,它能尽早发现和控制项目学习的过程变异,促进学习最终成果的绩效交付,一定程度上解决了传统项目学习容易遭遇过程障碍的难题。 展开更多
关键词 项目学习 项目迭代 O2O 首要教学原理 学习设计 绩效交付 开放教育
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Regulation of the water status in three co-occurring phreatophytes at the southern fringe of the Taklamakan Desert 被引量:13
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作者 Frank M.Thomas Andrea Foetzki +4 位作者 Dirk Gries Helge Bruelheide Xiangyi Li Fanjiang Zeng ximing zhang 《Journal of Plant Ecology》 SCIE 2008年第4期227-235,共9页
Aims We investigated the regulation of the water status in three predominant perennial C3 phreatophytes(Alhagi sparsifolia,Populus euphratica,Tamarix ramosissima)at typical sites of their occurrence at the southern fr... Aims We investigated the regulation of the water status in three predominant perennial C3 phreatophytes(Alhagi sparsifolia,Populus euphratica,Tamarix ramosissima)at typical sites of their occurrence at the southern fringe of the hyperarid Taklamakan Desert(north-west China).Methods In the foreland of the river oasis of Qira(Cele),we determined meteorological variables,plant biomass production,plant water potentials(WL)and the water flux through the plants.We calculated the hydraulic conductance on the flow path from the soil to the leaves(kSL)and tested the effects of kSL,WL and the leaf-to-air difference in the partial pressure of water vapour(Dw)on stomatal regulation using regression analyses.Important Findings Despite high values of plant water potential at the point of turgor loss,all plants sustained WL at levels that were high enough to maintain transpiration throughout the growing season.In A.sparsifolia,stomatal resistance(rs;related to leaf area or leaf mass)was most closely correlated with kSL;whereas in P.euphratica,~70%of the variation in rs was explained by Dw.In T.ramosissima,leaf area-related rs was significantly correlated with WL and kSL.The regulation mechanisms are in accordance with the growth patterns and the occurrence of the species in relation to their distance to the ground water. 展开更多
关键词 aboveground growth extreme aridity stomatal conductance transpirational demand vapour pressure deficit
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Stand structure and productivity of Populus euphratica along a gradient of groundwater distances at the tarim River(NW china) 被引量:5
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作者 Frank M.Thomas Michael Jeschke +1 位作者 ximing zhang Petra Lang 《Journal of Plant Ecology》 SCIE CSCD 2017年第5期753-764,共12页
Aims Along central-Asian rivers in arid regions,lowering of the ground-water level constitutes a major threat to the riparian forests,whose tree layers are dominated by Euphrates poplar(Populus euphratica).Some of the... Aims Along central-Asian rivers in arid regions,lowering of the ground-water level constitutes a major threat to the riparian forests,whose tree layers are dominated by Euphrates poplar(Populus euphratica).Some of these fragile ecosystems are supplied with additional(‘eco-logical’)water for protection and conservation.We investigated interrelationships among groundwater distance,stand structure and above-ground wood production(at the tree and the stand level)in P.euphratica stands along a groundwater gradient(distances of 2.0-12.0 m)that also included a plot supplied with‘ecological water’.Methods We measured the height,diameter at breast height and basal area of poplar trees and determined the annual above-ground wood production for the three most recent years on the basis of tree-ring analyses and allometric regressions at three sites at the upper,mid-dle and lower reaches of the tarim River,Xinjiang,NW china.Important Findingsthe distribution of age classes differed significantly among the plots:in accordance with their life histories,stands growing at a larger distance to the groundwater harboured a larger fraction of old trees(>80 years)and,in most cases,a smaller fraction of young trees(≤20 years).the annual above-ground wood production per ha was highest on a plot with a short groundwater distance(2.0 m;maxi-mum of the 3-year investigation period:3.0 t ha−1 a−1)and lowest,at a plot with a large distance to the water table(6.6 m;minimum:0.23 t ha^(−1)a^(−1)).However,the plot located close to the groundwater(and to the river)at the middle reaches exhibited a relatively large interannual variation in above-ground wood production,which can be attributed to interannual variations in the river discharge.At the middle and the lower reaches,these interannual variations on plots with the most favourable water supply were even more obvious at the tree level.For the fraction of mature trees(60-99 years old),no significant differences in above-ground wood production were found between the plots with the most and the least favourable water supply.Overall,the productivity at the stand level was most closely correlated with the stand density(number of trees per ha,tree cover percentage).Productivity was negatively related to tree age,whereas groundwater distance alone was not a good predictor of above-ground wood production.In conclusion,vigorous growth of P.euphratica is possible at sites with groundwater distances of up to 12 m.Supply with‘ecological water’may be beneficial to trees growing at groundwater distances not larger than~6 m.However,allocation of water should focus on stands with a short distance to the groundwater because only under these conditions,natural gen-erative reproduction of the poplars is possible. 展开更多
关键词 ALLOMETRY ground water life history tree-age distribution tugai forest
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