冻结细砂剪切蠕变的若干特性   总被引：2，自引：2，他引：2  

米海珍  吴紫汪 《冰川冻土》1993,15(3):492-497

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1990年以来4个时期四川省湿地的面积、景见旨数及其变化     

李娜娜  高飞  黄从德 《湿地科学》2020,18(1):110-114

以1990年、2000年、2010年和2015年的Landsat TM/ETM+/OLI影像为数据源,在遥感和地理信息系统技术的支持下,研究了4个时期四川省湿地的面积、景观指数及其变化。研究结果表明,与1990年相比,2015年四川省的湿地总面积减少了29 744.84 hm^2,其中,沼泽湿地面积减少了63 619.19 hm^2,河流湿地面积减少了27 742.60 hm^2;人工湿地面积增加了63 249.19 hm^2;四川省的湿地主要分布在川西北高原湿地区,最主要的湿地类型是沼泽湿地。随着时间的推移,4个时期四川省的湿地斑块数量、斑块密度和香农多样性指数在波动增大,而最大斑块指数在波动减小,面积加权平均斑块分维数变化不大;四川省的湿地向斑块破碎化、形状规则化和类型多样化方向发展。  相似文献   

ATP系统位置回路搜索扫描控制算法设计     

陆从德  傅汝霖 《物探化探计算技术》1999,21(4):354-357

本文对ＡＴＰ系统位置回路搜索扫描的控制算法进行了比较详细的讨论,并给出了校正算法的差分方程。该算法在实践中得到了验证和应用。  相似文献   

气象因子对2002年小麦生产的利弊浅析     

苏永贵  李崇德  程永福  石振水 《山西气象》2002,(4):18-20

2002年小麦生育期间，气候反常，出现了多年罕见的暖冬暖春现象，致使小麦生育期提前；生育中期降水偏少，旱象严重，株高降低，分薛成穗率小；穗分化中后期遭受2次晚霜冻害，小穗数数明显减少，灌浆初期阴雨连绵，光照不足，小穗成粒小，灌浆后期光照充足，日较差大，干热风出现迟，强度弱，对粒重增加十分有利。  相似文献   

Evaluation of hydraulic conductivity of gap-graded granular soils based on equivalent void ratio concept     

Shi  X. S.  Zeng  Yiwen  Shi  Congde  Ma  Zhanguo  Chen  Wenbo 《Acta Geotechnica》2022,17(9):3839-3854

Gap-graded granular soils are used as construction materials worldwide, and their hydraulic conductivity depends on their relative content of coarse and fine grains, initial conditions, and particle shape. In this study, a series of constant head hydraulic conductivity tests were performed on gap-graded granular soils with different initial relative densities, fine contents, and particle shapes. The test results show that the hydraulic conductivity decreases with an increase in fine fraction and then remains approximately constant beyond the “transitional fine content.” The role of the structural effect on the hydraulic conductivity is different from that on the mechanical properties (such as stiffness and shear strength). This can be attributed to the degree of filling within inter-aggregate voids, disturbance of soil structure, and densified fine bridges between coarse aggregates. The equivalent void ratio concept was introduced into the Kozeny–Carman formula to capture the effect of fines (aggregates) on the “coarse-dominated” (“fine-dominated”) structure, and a simple model is proposed to capture the change of hydraulic conductivity of gap-granular soils. The model incorporates a structural variable to capture the effect of fines on “coarse-dominated” structure and coarse aggregates on “fine-dominated” structure. The performance of the model was verified with experimental data from this study and previously reported data compiled from the literature. The results reveal that the proposed model is simple yet effective at capturing the hydraulic conductivity of gap-graded granular soils with a wide range of fine contents, initial conditions, and particle shapes.

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