分类: 地球科学 >> 地理学 提交时间: 2022-10-14 合作期刊: 《干旱区科学》
摘要:Estimating the snow cover change in alpine mountainous areas (in which meteorological stations are typically lacking) is crucial for managing local water resources and constitutes the first step in evaluating the contribution of snowmelt to runoff and the water cycle. In this paper, taking the Jingou River Basin on the northern slope of the Tianshan Mountains, China as an example, we combined a new moderate-resolution imaging spectroradiometer (MODIS) snow cover extent product over China spanning from 2000 to 2020 with digital elevation model (DEM) data to study the change in snow cover and the hydrological response of runoff to snow cover change in the Jingou River Basin under the background of climate change through trend analysis, sensitivity analysis and other methods. The results indicate that from 2000 to 2020, the annual average temperature and annual precipitation in the study area increased and snow cover fraction (SCF) showed obvious signs of periodicity. Furthermore, there were significant regional differences in the spatial distribution of snow cover days (SCDs), which were numerous in the south of the basin and sparse in the central of the basin. Factors affecting the change in snow cover mainly included temperature, precipitation, elevation, slope and aspect. Compared to precipitation, temperature had a greater impact on SCF. The annual variation in SCF was limited above the elevation of 4200 m, but it fluctuated greatly below the elevation of 4200 m. These results can be used to establish prediction models of snowmelt and runoff for alpine mountainous areas with limited hydrological data, which can provide a scientific basis for the management and protection of water resources in alpine mountainous areas.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: A lithium-assisted approach has been developed for the exfoliation of pristine graphite, which allows the large-scale preparation of few-layer graphene nanosheets. The process involves an unexpected physical insertion and exfoliation, and the graphene nanosheets prepared by this method reveal undisturbed sp2-hybridized structures. A possible two-step mechanism, which involves the negative charge being trapped around the edges of the graphite layers and a subsequent lithiation process, is proposed to explain the insertion of lithium inside the graphite interlayers. If necessary, the present exfoliation can be repeated and thinner (single or 2–3 layer) graphene can be achieved on a large scale. This simple process provides an efficient process for the exfoliation of pristine graphite, which might promote the future applications of graphene.