Subjects: Psychology >> Psychological Measurement submitted time 2019-02-19
Abstract： 基于推荐系统中协同过滤推荐的思想，提出两种可以利用已有答题者数据的CAT选题策略：直接基于答题者推荐（DEBR）和间接基于答题者推荐（IEBR）。通过两个模拟研究，在不同题库和不同长度的测验中，比较了两种推荐选题策略与两种传统选题策略（FMI和BAS）在测量精度和对题目曝光率控制上的表现，以及影响推荐选题策略表现的因素。结果发现：两种推荐选题策略对题目曝光率的控制优于两种传统选题策略，测量精度不亚于BAS方法，其中DEBR侧重选题精度，IEBR对题目曝光率控制最好。已有答题者数据的特点和质量是影响推荐选题策略表现的主要因素。
Subjects: Agriculture, Forestry,Livestock & Aquatic Products Science >> Basic Disciplines of Agriculture submitted time 2017-11-09 Cooperative journals: 《中国生态农业学报》
Abstract：华北地区淡水资源短缺, 其不能承载小麦-玉米一年两作的生产, 在过去几十年中为追求高产进行灌溉严重超采地下水引发了一系列的环境问题。发展一年1 作的春玉米种植是减少地下水超采的主要途径。但在春玉米生产中存在耐密宜机收品种缺乏、机械化程度低及配套农机农艺关键技术不完善导致的春玉米生产效率低等问题。因此, 开展华北春玉米高水效、耐密植宜机收品种筛选及不同管理措施下品种资源高效利用技术研究, 是保障区域粮食安全和水安全的迫切需求。
Subjects: Geosciences >> Geography submitted time 2020-12-17 Cooperative journals: 《干旱区研究》
Abstract：冰川物质平衡作为表征气候变化的重要指标，通常被用来评估冰川对径流及海平面上升的贡献。本文采用世界冰川监测服务处（World Glacier Monitoring Service, WGMS）最新公布的物质平衡、平衡线高度及积累区面积比率资料，以北极地区具有长时间观测序列的23条冰川为研究对象，分析了北极山地冰川物质平衡状况及物质平衡与平衡线高度和积累区比率的关系。分析表明：（1）1960—2017年北极冰川厚度平均减薄14.8 m，俄罗斯北极减薄最小，为4.3 m，阿拉斯加地区减薄最严重，为27.7 m；（2）23条冰川中，仅Engabreen冰川平均物质平衡为正值，Kongsvegen冰川保持微弱的负平衡，其他21条冰川的物质平衡均处于较强的负平衡状态，北极冰川整体物质损失严重；（3）过去60 a，北极冰川物质平衡整体呈负平衡，20世纪90年代后期开始，冰川开始加速消融，损失速率从-128.2 mm·a-1上升至-594 mm·a-1；（4）物质平衡与平衡线高度呈负相关，与积累区比率呈正相关，相关性显著；（5）北极气温升高是冰川物质消融的主要原因，90年代之后气温大幅度升高造成同期冰川物质大量流失，降水量对物质平衡影响较小
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology submitted time 2021-01-25 Cooperative journals: 《干旱区研究》
Abstract：基于天山乌鲁木齐河源1号冰川区1980—2016年的水文和气象资料，对冰川区径流在月、日和时尺度的变化特征及其原因进行了分析。结果表明：（1）1980—2016年该区消融期（5—9月）径流总体呈上升趋势，倾向率为3.44×104 m3·a-1，其中6—8月上升趋势较为显著；37 a来8月对径流增多贡献率最大，其次为6月和7月，5月和9月最低；消融期径流在1993年显著增加，5—8月径流均在20世纪90年代发生突变。（2）日径流量自1980s、1990s至2000s显著增加，而2010—2016年径流量有所减少；日径流峰值出现时间在1980s—1990s有明显提前趋势，但在2010—2016年，日径流峰值出现日期趋于稳定。（3）2011—2016年7月和8月昼夜流量变化较为显著；日流量曲线呈现“峰-谷”的日变化特征，且7月和8月峰值出现时间小于6月和9月。（4）1980—2016年，该流域消融期气温和降水均呈上升趋势；相关分析表明6—8月径流与气温均呈显著正相关。总体上冰川区年内径流与气温、降水在月、日尺度上表现出较好的同步性，表明其变化主要受控于同期的气温与降水量状况。
Subjects: Other Disciplines >> Synthetic discipline submitted time 2023-03-19 Cooperative journals: 《中国科学院院刊》
Abstract： China has 48 571 glaciers with a total area of 5.18×104 km2, which accounts for 11%–14.5% of the total area of mountain glaciers in the world. These glaciers constitute a vital source of water for more than 100 million people and for wildlife ecosystems in this vast arid and semi-arid land in northwestern China. Urumqi Glacier No. 1, the best monitored glacier in China, is located at the headwaters of the Urumqi River in eastern Tianshan and is within the core area of central Asia. To implement the long term monitoring of Urumqi Glacier No. 1, the Tianshan Glaciological Station (TGS) was established by Chinese Academy of Sciences (CAS) in 1959. Since then, Urumqi Glacier No. 1 has been the subject of extensive studies. Internationally, it has been one of the ten referential glaciers in the World Glacier Monitoring Service (WGMS), and considered to be of great importance because of its special geographical position. The Urumqi Glacier No. 1 complements similar long-term monitoring programs covering more maritime-type glaciers and glaciers in transitional climates in polar, temperate, and tropical regions. Over the past 60 years, the TGS has served as a research and training base for domestic and overseas scientists and graduate students. It plays a central role in central Asian climatological, hydrological and glaciological research. As such, it is well known and highly regarded by the international scientific community. As a permanent year-round glacier station among glaciers in central Asia, it is the benchmark to which other relevant studies can make reference.
Subjects: Geosciences >> Geography submitted time 2024-03-01 Cooperative journals: 《干旱区研究》
Abstract： Debris-covered glaciers are widely distributed in Western China. Their ablation areas are covered byvarying degrees of rock debris, and consequently, their melting statuses differ greatly when compared to debrisfreeglaciers. There is currently a need for melting simulations to better understand debris- covered glaciers. Inthis paper, driven by field meteorological data, an energy balance model for debris- covered glaciers has beenused to simulate the energy and ablation in debris-covered areas of Qingbingtan Glacier No. 72 in Mt. Tomor,Tianshan. Based on the heat conduction process and the energy balance equation, the model calculates the debrissurface temperature and the internal temperature of the debris, then estimates the subdebris melt using the internaldebris temperature. The results showed that the modeled ablation was 0.39 m w.e. in the summer of 2008, and thesimulation accuracy (R2 = 0.92, RMSE = ± 0.03 m w.e.) was higher when compared with the field data. Thesimulated debris temperatures at the surface and a depth of 10 cm inside the debris were also found to fit wellwith the measured data (R2 = 0.91 and 0.60, respectively). During energy exchange in the debris area, netshortwave radiation was the only energy income item, and sensible heat flux was the largest energy expenditureitem (49.7%), followed by the heat conduction flux (ablation heat consumption) (25.8%), net longwave radiation(19.8%), and latent heat flux (4.6%), while precipitation heat was <1%. Cloud cover had a significant impact onthe meteorological and energy characteristics of the debris area. Under overcast conditions, the incomingshortwave radiation in the debris area decreased from 854 W·m- 2 on sunny days to 587 W·m− 2, while thedownward longwave radiation and relative humidity increased, and the average ablation decreased by 12%, whencompared with sunny days. In addition, the sensitivity analysis of the key parameters for debris shows that thesimulated ablation is most sensitive to the changes in thermal conductivity, and the changes in albedo and surfaceroughness cannot be ignored.
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