1998—2014年阿克苏河流域耕地景观时空变化研究

以新疆阿克苏河流域为研究对象,利用遥感和GIS解译了研究区1998年、2002年、2006年、2010年、2014年5个时相的Landsat TM/ETM/OLI遥感影像数据。针对耕地信息,分别从耕地面积动态变化、耕地重心空间迁移、耕地景观格局变化等分析阿克苏河流域耕地近16年的变化过程,并从人口增长、社会经济增长、水利设施建设等方面分析这些因素对该流域耕地变化的影响。结果表明：整个流域耕地面积持续增加,上、中、下游耕地面积增加幅度有所不同,下游耕地面积增幅最大,上游次之,中游最小;流域上、中、下游耕地重心坐标在不同时段内分别向不同方向迁移,但总体表现为上游向东迁移,中游向南迁移,下游向北迁移;流域内耕地间逐渐聚拢,空间上接连成片,斑块面积不断增大,景观异质性降低;阿克苏地区人口和社会经济的持续增长是流域耕地面积持续扩张的重要原因,水利设施的配套建设保证了不断增加的耕地的用水灌溉。     

Estimating the variability of tillage forces on a chisel plough shank by modeling the variability of tillage system parameters

In this paper, a probabilistic approach is proposed for quantifying the variability of the tillage forces for the shank of a chisel plough with narrow tines and to estimate the failure probability. An existing three-dimensional analytical model of tool forces from McKyes was used to model the interaction between the tillage tools and the soil. The variability of tillage forces was modeled, taking into account the variability of soil engineering properties, tool design parameters and operational conditions. The variability of the soil engineering properties was modeled by means of experimental observations. The dispersion effect of each tillage system parameter on the tillage forces was determined by a sensitivity analysis. The results show that the variability of the horizontal and vertical forces follows a lognormal distribution (μ = 0.872, ξ = 0.449; μ = 0.004, ξ = 0.447) and the relationship between these forces is positive and quasi-linear (ρ(P_H, P_v) = 0.93).This lognormal variability was integrated into the estimation of the failure probability for the shank by using Monte Carlo simulation (MCS) and the first-order reliability method (FORM). The results obtained by these two methods, with the assumption of non-correlation between the horizontal and vertical forces, were almost identical. However, the FORM method was faster and simpler, compared to the MCS technique. Furthermore, the correlation between the horizontal and vertical forces has no significant effect on the failure probability, regardless of the correlation strength. Therefore, it is concluded that the FORM method can be used to estimate the failure probability without considering the correlation between horizontal and vertical forces.     

The integration of planted and natural forests in a regional landscape

The 10,700 km² region of northwestern Oregon, USA, is dominated by mountainous forested landscapes fringed by agricultural lands and rapidly expanding urban areas. The Douglas-fir/western-hemlock trees, admixed with other species, in the mild, moist regional climate with rich soils are among the most highly productive of temperate forests. Timber harvest has been the dominant land use for much of this century. Many current forest stands are planted, and have the potentials to be managed and shaped for a variety of traditional and evolving forestry objectives. The ages, resilience and productivity of these forests and mosaics of land ownerships permit a variety of future scenarios of forested landscapes, constrained largely by capacities of social organizations to plan and execute management for desired future conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

甘肃省建设用地结构演变及其驱动力分析

基于甘肃省1997~2004年统计资料和土地详查与变更调查数据,研究揭示了全省近八年来建设用地利用结构信息熵的时空变化,并在此基础上进一步探讨了土地利用结构动态变化的驱动机制。结果表明:自1997年以来,甘肃省建设用地利用结构信息熵呈上升趋势,即建设用地多样性程度提高,用地结构趋于均衡;通过驱动力分析发现造成建设用地结构演变的主要驱动力是人口增长和城镇化水平,而各经济发展指标次之。     

新疆耕地变化及驱动力分析

利用1949~2003年的统计和普查数据,分析探讨了新疆54年来耕地数量变化趋势、变化速度、区域差异及驱动因素。结果表明:新疆耕地数量经历了迅速上升→波动→下降→回升的变化历程;耕地变化区域差异显著;人口增长、经济发展和农业科技进步是影响新疆耕地动态变化的三类主要动因,政策因素是影响耕地变化的间接驱动力;通过模型计算,人类行为对耕地变化的影响尤其显著。并对研究结果应用GIS进行了空间表达。研究内容和分析结论对新疆农业可持续发展具有重要意义。     

中国退耕还林(草)驱动力的多尺度分析

退耕还林(草)作为当前生态建设的重要内容,其实质是通过调整土地利用方式,恢复重建地表自然覆盖,建立生态安全条件下的土地利用/覆盖格局。研究不同尺度下退耕还林(草)的驱动力,可以为构造典型区域土地可持续利用结构与优化模式提供依据。该文从国家-省区-县域-农户尺度上分析了中国退耕还林(草)的驱动力,国家尺度上驱动力是生态环境安全、粮食结构调整和西部大开发,以生态安全为主;省区驱动力分为产业结构调整、水源地保护、防洪、保护三峡工程、减少入黄泥沙和防治风蚀沙化6种类型,经济状况居于主导地位;县域驱动力归纳为12种类型,以产业结构调整、发展主导产业、增加农民收入和改善农业生产条件为主;农户的退耕还林(草)是国家政策满足农户需求,个体利益最佳化为主要驱动力。     

关中盆地用水结构变化及其驱动因子分析

用水结构的合理确定与科学预测是制定水资源发展利用规划的前提和基础,对于实现区域水资源合理配置、社会经济协调发展具有重要意义。文中分析了关中地区的农业、工业和生活用水的结构变化,并采用信息熵的方法分析了其用水结构的演变趋势。同时阐明了造成这种变化的主要驱动力因子,并针对各驱动因子提出了相应的节水措施,为关中地区水资源可持...     

西安市耕地变化驱动力研究

对西安市耕地资源的空间变化和 1 95 0年以来耕地面积变化过程进行分析 ,利用主成分分析方法定量分析西安市耕地动态变化的驱动力 ,建立了耕地面积与驱动因子之间的多元线形回归模型。     

云南省近10年耕地利用变化的驱动力研究

以高原山地地貌为主的云南省耕地利用作为研究对象,在收集历年与耕地利用相关数据的基础上,得出影响云南省耕地利用变化的影响因素,主要是人口、经济、社会以及政策等方面的因素,着重针对人文驱动中的可量化的因素指标,选用相应的指标体系,建立了耕地利用变化的人文驱动力分析模型和多元线性回归模型,结合区域自然因素指标对驱动力因素进行了综合的定量分析,得出了各指标之间的相关性以及总人口和经济因素是该区域耕地利用变化的主要驱动力,提出了耕地保护的相关建议。     

Relationship between the forces acting on the horse's back and the movements of rider and horse while walking on a treadmill

Reasons for performing study: The exact relationship between the saddle pressure pattern during one stride cycle and the movements of horse and rider at the walk are poorly understood and have never been investigated in detail. Hypothesis: The movements of rider and horse account for the force distribution pattern under the saddle. Method: Vertical ground reaction forces (GRF), kinematics of horse and rider as well as saddle forces (FS) were measured synchronously in 7 high level dressage horses while being ridden on an instrumented treadmill at walk. Discrete values of the total saddle forces (FStot) were determined for each stride and related to kinematics and GRF. The pressure sensitive mat was divided into halves and sixths to assess the force distribution over the horse's back in more detail. Differences were tested using a one sample t test (P<0.05). Results: FStot of all the horses showed 3 peaks (P1‐P3) and 3 minima (M1‐M3) in each half‐cycle, which were systematically related to the footfall sequence of the walk. Looking at the halves of the mat, force curves were 50% phase‐shifted. The analysis of the FS of the 6 sections showed a clear association to the rider's and horse's movements. Conclusion: The saddle force distribution during an entire stride cycle has a distinct pattern although the force fluctuations of the FStot are small. The forces in the front thirds were clearly related to the movement of the front limbs, those in the mid part to the lateral flexion of the horse's spine and the loading of the hind part was mainly influenced by the axial rotation and lateral bending of the back. Potential relevance: These data can be used as a reference for comparing different types of saddle fit.