Has climate change driven spatio-temporal changes of cropland in northern China since the 1970s?

Improving the understanding of cropland change and its driving factors is a current focus for policy decision-makers in China. The datasets of cropland and cropland changes from the 1970s to the 2000s were used to explore whether climate change has produced spatio-temporal changes to cropland in northern China since the 1970s. Two representative indicators of heat and water resources, which are important determinants of crop growth and productivity, were considered to track climate change, including active accumulated temperatures ≥10 °C (AAT10) and the standardized precipitation evapotranspiration index (SPEI). Our results showed that rapid cropland change has occurred in northern China since the 1970s, and the area of cropland reclamation (10.23 million ha) was much greater than that of abandoned cropland (2.94 million ha). In the 2000s, the area of cropland with AAT10 higher than 3,000 °C·d increased, while the area of cropland with an SPEI greater than 0.25 decreased compared to the 1970s, 1980s and 1990s. It appears that climate warming has provided thermal conditions that have aided rapid cropland reclamation in northern China since the 1970s, and drier climatic conditions did not become a limiting factor for cropland reclamation, especially from the 1990s to the 2000s. Approximately 70 % of cropland reclamation areas were located in warmer but drier regions from the 1990s to the 2000s, and approximately 40 % of cropland abandonment occurred in warmer and wetter conditions that were suitable for agriculture during the periods from the 1970s to the 1980s and the 1990s to the 2000s. Our results suggest that climate change can be considered a driving factor of cropland change in the past several decades in northern China, in addition to socioeconomic factors.     

地理过程的时间性 ——关于地理教学中"点、线、面"问题的再认识

地理过程是地理学的重要概念,它是塑造地理景观格局的重要机制。作为地理过程的重要特征,时间性是厘清地理过程概念、把握地理过程走向的关键。地理过程的时间性包括作为某一地理过程在特定时间存在的特定状态的时间截面,由多个时间截面联结而成的时间脉络,以及在同一时间截面上由不同地理过程相互交织而成的时间叠置等三个方面。认识地理过程的时间性,是地理综合思维动态发展必不可少的内容。     

Mineralogical study of spinel-lherzolite inclusions from basalts in southern and eastern China

Ten spinel-lherzolite inclusions and one olivine-websterite inclusion, which were collected from Fujian, Jiangsu, Hebei and Yunnan Provinces, consist of olivine (FΦ_87.7–91.2), enstatite (En_87.3–89.7), Cr-diopside and spinel. According to the Mg/(Mg+Fe²⁺) ratios in the rocks and their mineralogies, they are designated to the Cr-diopside type. The websterite is composed of bronzite (En_71.9) and augite, while the gabbro-norite consists of hypersthene (En_68.9) and augite, belonging to the Al-augite type. The geothermos of spinel-lherzolites were calculated with four geothermometric methods, giving a temperature range of 925°–1,072°C. However, according to P. R. A. Wells' method, temperatures range from 845δ to 1,014°C, and by D. H. Lindsly's approach, from 716°–974°C. Pressures range from 15.1 to 19.8 kb. Genetically, Spinel-lherzolites and olivine-websterite are thought to have been derived from residual mantle material by partial melting at approximately 1,000°C and at a depth of about 50–70 km. Websterite and gabbro-norite may be products of the crystallization-differentiation of alkali basaltic magma.     

广清高速公路改扩建工程岩溶塌陷主要影响因素分析

岩溶塌陷对工程建设的影响不容小视。为了研究广清高速公路改扩建工程中影响岩溶塌陷的两个主要因素冲击荷载作用和地下水下降对塌陷的影响程度,在资料收集和现场调研的基础上,统计工程区12处岩溶塌陷的基本情况,总结塌陷特征并分析影响塌陷的主要因素,建立与实际覆盖层结构相符的塌陷地质模型-砂土+粉质黏土+灰岩地质模型。根据极限平衡理论,分别在冲击荷载和水位下降两种力学作用下对塌陷地质模型进行稳定性计算。通过计算得出,最大冲击荷载的作用在一定程度上会影响覆盖层的稳定性,但不是导致地面塌陷的主要因素,而地下水位下降对工程区岩溶塌陷起到了决定性的作用。通过进一步分析水位下降对塌陷的影响程度,确定水位降幅4m为警戒值, 6m为危险值,为保证施工的安全性提供一定的理论依据。     

矿山边坡稳定性研究的回顾与展望

本文阐述了露天矿边坡工程的特点, 回顾了露天矿边坡稳定性研究及其取得的理论成果和进展, 指出露天矿边坡稳定性研究的特点, 提出相应的研究技术路线与方法。     

对GPS接收机测试评估的探讨

随着GPS的广泛应用和GPS产业的迅速发展，GPS厂家众多，生产的接收机类型更是数以百计，整个GPS接收机市场可以说是鱼目混珠，识别困难；大多数购买者只能听信厂家的技术指标，如何对GPS接收机的性能进行测试评估的意义显得很重要，本文基于此对GPS接收机测试评估展开探讨和研究。