土地资源禀赋对农业转移人口进城落户意愿的影响研究

提高农业转移人口的进城落户意愿是推动户籍人口城镇化发展的重要途径。然而,当下各地农业转移人口进城落户积极性不高,提升户籍人口城镇化率并不乐观。基于推拉理论,利用中国流动人口动态监测调查数据(CMDS),采用二元 Logit 模型与中介效应模型,分析土地资源禀赋对农业转移人口进城落户意愿的影响,探讨两者间的作用机制。结果表明,农业转移人口进城落户意愿总体较低,占比为48.91%,农业转移人口拥有承包地与宅基地的比例分别为61.40%和71.71%。土地资源禀赋显著抑制了农业转移人口的进城落户意愿,农业转移人口的身份认同、社会交往状况在土地资源禀赋影响进城落户意愿的过程中发挥着中介效应,社会保障状况发挥着显著的负向调节效应。进一步研究发现,土地流转将会提高农业转移人口的进城落户意愿。因此,一方面要加快农村土地制度改革与农民土地权益保障机制设计,消除阻碍农业转移人口进城落户的体制障碍;另一方面也要通过土地为农业转移人口留条退路,增强社会结构的弹性,维护社会稳定。     

应用中值融合模型的条件植被温度指数降尺度转换研究

为获得基于Landsat卫星遥感数据更为精确的定量化干旱监测结果,以陕西省关中平原为研究区域,基于Aqua MODIS数据反演的1 km空间分辨率的条件植被温度指数(VTCI)的定量化干旱监测结果(MODIS-VTCI)和Landsat OLI/TIRS数据反演的30 m空间分辨率的VTCI相对干湿监测结果(Landsat-VTCI),应用降尺度的中值融合模型(MFM)将基于MODIS数据反演的VTCI降尺度至30 m空间分辨率的VTCI定量化干旱监测,并对其结果进行验证。结果表明,应用降尺度的中值融合模型转换的VTCI定量化干旱监测结果(MFM-VTCI)与Landsat-VTCI的空间分布及纹理特征相似,两者间的相关系数和结构相似度均较大,均方根误差、差值影像及差值频数分布图所呈现的结果与定量化干旱监测结果和相对干湿监测结果间的系统误差相符,表明Landsat-VTCI与MFM-VTCI间的可比性较强。MFM-VTCI与累计降水间的相关性和MODIS-VTCI与累计降水间的相关性相近,均大于Landsat-VTCI与累计降水间的相关性,表明MFM-VTCI是定量化的干旱监测结果。     

A universal grain-size distribution of soil with scaling invariance

Soils are composed of wide-ranged grains and grain size distribution (GSD) is the fundamental characteristic determining the physical and hydraulic properties. Previously we have proposed a GSD function for various soils. However, the remarkable discrepancy in the distribution occurs in some soils, which not only limits the applicability of the function but also raises doubt as to the possibility of a universal GSD function. In this study we modify the GSD function to a general form of P(D) ~ D^−μexp(−D/D_c)ⁿ, which introduces a new exponent n for the grain size scale. It turns out that this modification has eliminated the discrepancies and universally applies to a great variety of soils from around the world (hence to be a universal GSD function, UGSD). The exponent n is proved to be a scaling factor of grain size in log-scale and divides soils into three categories of n < 1 n > 1, and n = 1. Furthermore, soils of surface processes (e.g., erosion, tillage, desertification, landslides, avalanches, deposition, and sediment transportation) remain in the same category and preserve the UGSD function. Thus, the UGSD not only provides parameters μ and D_c as synthetic indices for soil properties (e.g., as indices for spatial heterogeneity or variables for pedotransfer functions), but also describes texture changes in dynamic processes. The UGSD function represents a ‘conservative law’ underlying soil genesis and processes, which fills the knowledge gaps related to the lack of universally applicable indices for soil properties, and thus has universal applications in soil classification, spatial variability, as well as dynamical processes.