基于梯度提升决策树的情境感知推荐模型     

郭静娟 《情报探索》2020,(4):58-63

[目的/意义]旨在深入研究情境信息对用户偏好的影响,提高情境感知推荐的准确性。[方法/过程]提出了基于梯度提升决策树的情境感知推荐模型,根据梯度提升决策树计算情境属性权重,将其与传统协同过滤算法相融合,生成情境感知推荐结果。[结果/结论]该模型可以识别影响用户偏好的重要情景属性,为用户提供个性化推荐服务。  相似文献   

Robust sulfonated poly (ether ether ketone) nanochannels for high-performance osmotic energy conversion     

Yuanyuan Zhao  Jin Wang  Xiang-Yu Kong  Weiwen Xin  Teng Zhou  Yongchao Qian  Linsen Yang  Jinhui Pang  Lei Jiang  Liping Wen 《国家科学评论(英文版)》2020,7(8):1349

The membrane-based reverse electrodialysis (RED) technique has a fundamental role in harvesting clean and sustainable osmotic energy existing in the salinity gradient. However, the current designs of membranes cannot cope with the high output power density and robustness. Here, we construct a sulfonated poly (ether ether ketone) (SPEEK) nanochannel membrane with numerous nanochannels for a membrane-based osmotic power generator. The parallel nanochannels with high space charges show excellent cation-selectivity, which could further be improved by adjusting the length and charge density of nanochannels. Based on numerical simulation, the system with space charge shows better conductivity and selectivity than those of a surface-charged nanochannel. The output power density of our proposed membrane-based device reaches up to 5.8 W/m² by mixing artificial seawater and river water. Additionally, the SPEEK membranes exhibit good mechanical properties, endowing the possibility of creating a high-endurance scale-up membrane-based generator system. We believe that this work provides useful insights into material design and fluid transport for the power generator in osmotic energy conversion.  相似文献   

基于VAR-SSM模型的突发事件舆情圈层扩散内生影响研究     

阳长征 《现代情报》2021,40(12):36

[目的/意义] 为了探索位势梯度、情感共轭与圈层扩散之间动态影响机制,对网络空间中的信息进行分类和定级,实现危机信息的差异化监控与治理。[方法/过程] 本文采用向量自回归、状态空间模型及时间序列模型对位势梯度、情感共轭及圈层扩散之间关系进行分析。[结果/结论] 研究发现：1）位势梯度及情感共轭的每次冲击对圈层扩散产生滞后性影响,在整个过程中呈现右偏态分布特征。2）位势梯度及情感共轭对圈层扩散波动的贡献率均较大。3）位势梯度与情感共轭对圈层扩散的边际影响变化呈倒U形抛物线特征,且均较大。4）位势梯度、情感共轭与圈层扩散之间的相互影响效应在不同人口统计学群体间存在差异。  相似文献   

陕西省优秀跆拳道运动员髋关节屈伸肌群等速测试与研究     

石新燕 《山东体育科技》2011,33(6)

采用ISOMED2000获得陕西省优秀跆拳道运动员髋关节等速收缩的生物力学特征。右髋关节屈肌群等速离心收缩峰值力矩出现时的关节角度在133．7°-140．20之间,伸肌群等速离心收缩峰值力矩出现时的关节角度在121．2°-106．30之间;髋关节屈伸肌群向心收缩、离心收缩速度在240°／s时相对力矩梯度达到最大。  相似文献   

Diversity change of microbial communities responding to zinc and arsenic pollution in a river of northeastern China     

Jun Zhao  Xin Zhao  Lei Chao  Wei Zhang  Tao You  Jie Zhang 《Journal of Zhejiang University. Science. B》2014,15(7):670-680

Pollution discharge disturbs the natural functions of water systems. The environmental microbial community composition and diversity are sensitive key indicators to the impact of water pollutant on the microbial ecology system over time. It is meaningful to develop a way to identify the microbial diversity related to heavy metal effects in evaluating river pollution. Water and sediment samples were collected from eight sections along the Tiaozi River where wastewater and sewage were discharged from Siping City in northeastern China. The main pollutants contents and microbial communities were analyzed. As the primary metal pollutants, zinc (Zn) and arsenic (As) were recorded at the maximum concentrations of 420 and 5.72 μg/L in the water, and 1704 and 1.92 mg/kg in the sediment, respectively. These pollutants posed a threat to the microbial community diversity as only a few species of bacteria and eukaryotes with strong resistance were detected through denaturing gradient gel electrophoresis (DGGE). Acinetobacter johnsonii, Clostridium cellulovorans, and Trichococcus pasteurii were the dominant bacteria in the severely polluted areas. The massive reproduction of Limnodrilus hoffmeisteri almost depleted the dissolved oxygen (DO) and resulted in the decline of the aerobic bacteria. It was noted that the pollution reduced the microbial diversity but the L. hoffmeisteri mass increased as the dominant community, which led to the overconsuming of DO and anaerobic stinking water bodies. Water quality, concentrations of heavy metals, and the spatial distribution of microbial populations have obvious consistencies, which mean that the heavy metals in the river pose a serious stress on the microorganisms.  相似文献   

基于精明增长理念的昆明城市建设用地梯度开发研究     

李嘉佳  熊理然  王锦 《蒙自师范高等专科学校学报》2014,(6):111-115

昆明作为云贵高原上重要的湖泊城市,近年来随着经济的快速增长而不断扩张,但其城市建设用地的扩展受一定资源环境约束,且城市用地的快速扩张也引发一系列问题。该篇研究结合地理学和经济学的研究方法,运用精明增长和梯度开发理念对其空间扩展进行研究,并基于时序性和集约性提出有效建议,其研究结论有助于加深对昆明城市规划方案的解读与思考,为昆明城市规划方案的后续实施提供建议,并可以为其他城市的空间扩展提供有效参考。  相似文献   

物流管理专业“3455”人才培养模式研究与实践     

曹家谋  薄斌  新夫 《江苏广播电视大学学报》2013,(6):32-37

从物流产业链发展和相关背景出发,确定城市商贸物流专业定位和“一专多能”的复合型人才培养目标,通过校企行合作研究,探索和实践了“3455”（校企行三方合作、四梯度培养过程、五融合实践模式、五主体质量评价）人才培养模式。该模式注重高职教育的开放性和职业性,突出实践育人,在培养高素质、精技能的复合型商贸物流人才上获得有益经验和明显效果。  相似文献   

禽肉在储存过程中菌群结构变化研究     

周晓锋  张珍 《南京晓庄学院学报》2013,(3):39-41

研究禽肉储存过程中菌群的变化,为其长期贮存奠定理论基础.采用酚氯仿异戊醇法提取禽肉中菌群基因组DNA,并通过PCR扩增及DGGE电泳技术探讨其随保存时间延长,菌群结构变化情况.结果表明,成功扩增了菌群基因组DNA,为230bp.DGGE电泳结果发现,DGGE分子指纹图谱上条带存在显著的差异,用bionumberics软件分析DGGE结果,发现第一天和第二天样本的相似度最高为0.75,第三天与第一天相比,相似度为0.47,第四天与第三天相比,相似度又下降为0.16,表明禽肉在储存过程中不断有新的菌种出现,但是具体是什么菌种有待于高通量测序分析.  相似文献   

图像局部自交干扰排除的渐变优化算法研究     

刘淑青 《科技通报》2013,(9)

在二维平面图形渐变算法中,但是对于较为复杂的图形,由于传统算法本身存在的不足,图形渐变过程中有时会出现一些局部自交现象,影响图形的渐变效果。为了避免上述缺陷,提出了一种图像局部自交干扰排除的渐变优化算法。利用小波对图像的边沿像素进行变换,提取图像边沿的纹理特征,利用K均值聚类方法,对边沿纹理像素设置分类阀指,消除图像局部自交干扰。实验结果表明,利用本文算法下的图像渐变过程得到了优化,取得了令人满意的效果。  相似文献   

“梯度”在中国生态学中的使用考辨     

崔骁勇  杨以宁 《中国科学院大学学报》2019,36(6):760-765

科学交流需要清晰的概念。"梯度"一词是中国生态学迅猛发展过程中引入的新概念，其含义与在其他学科中有所不同，导致了使用上的混乱。对该术语的原意、在中国生态学中的引入和误用进行系统分析，剖析造成误用的原因，并提出解决的方案。  相似文献