土壤金属污染源的定位研究     

李玉梅  向阳  张娟  杨志明  唐文璐 《怀化学院学报》2011,30(11):25-27

对某城市工业区土壤汞（Hg）、镉（Cd）、铅（Pb）、砷（As）、铜（Cu）、铬（Cr）、镍（Ni）、锌（Zn）八种重金属元素含量的数据进行统计分析,研究了它们的分布特征．定义了一个随机变量X表示采样点状态,它描述了各金属浓度在该采样点所占比例,具有分布P（X=i）=xiμg／1g=Pi．给出了自然区的熵H=-∑Pil...  相似文献   

知识元的本质、结构与运动机制研究     

戎军涛  李兰 《情报理论与实践》2020,43(1):42-46,41

[目的/意义]关于知识元的基本理论问题研究是开展知识组织、知识检索、知识发现等知识管理活动的基础。[方法/过程]首先界定了知识元内涵的理论边界,确定了研究的逻辑起点。通过考察知识和人类思维的映射关系,阐明了知识元的本质属性。依据知识元承载的内容语义依存关系,抽象出了知识元的内部结构及其特征。最后演绎推论出知识元的运动机制。[结果/结论]通过对知识元基本理论问题的梳理和研究,进一步明晰了知识元的内涵、本质属性、结构和运动机制,为以知识元为基础的知识组织与服务实践提供了坚实的理论基础。  相似文献   

面向区域新业态的地方高校金属材料工程专业改造升级路径研究     

艾建平  向军淮  胡丽玲  杨文  李文魁 《科教文汇》2020,(12):90-91

本文从适应地方新业态的金属材料工程专业改造和升级路径出发,探索对接产业需求的人才培养模式,形成与信息技术深度融合兼有学科交叉特点的课程体系,探索具有新工科特色的专业人才培养质量评价体系,以期实现地方应用型高校传统工科专业的改造升级和跨越式发展。  相似文献   

Enabling Mg metal anodes rechargeable in conventional electrolytes by fast ionic transport interphase     

Ruijing Lv  Xuze Guan  Jiahua Zhang  Yongyao Xia  Jiayan Luo 《国家科学评论(英文版)》2020,7(2):333

Rechargeable magnesium batteries have received extensive attention as the Mg anodes possess twice the volumetric capacity of their lithium counterparts and are dendrite-free. However, Mg anodes suffer from surface passivation film in most glyme-based conventional electrolytes, leading to irreversible plating/stripping behavior of Mg. Here we report a facile and safe method to obtain a modified Mg metal anode with a Sn-based artificial layer via ion-exchange and alloying reactions. In the artificial coating layer, Mg₂Sn alloy composites offer a channel for fast ion transport and insulating MgCl₂/SnCl₂ bestows the necessary potential gradient to prevent deposition on the surface. Significant improved ion conductivity of the solid electrolyte interfaces and decreased overpotential of Mg symmetric cells in Mg(TFSI)₂/DME electrolyte are obtained. The coated Mg anodes can sustain a stable plating/stripping process over 4000 cycles at a high current density of 6 mA cm⁻². This finding provides an avenue to facilitate fast ion diffusion kinetics of Mg metal anodes in conventional electrolytes.  相似文献   

A highly alkaline-stable metal oxide@metal–organic framework composite for high-performance electrochemical energy storage     

Shasha Zheng  Qing Li  Huaiguo Xue  Huan Pang  Qiang Xu 《国家科学评论(英文版)》2020,7(2):305

Most metal–organic frameworks (MOFs) hardly maintain their physical and chemical properties after exposure to alkaline aqueous solutions, thus precluding their use as potential electrode materials for electrochemical energy storage devices. Here, we present the design and synthesis of a highly alkaline-stable metal oxide@MOF composite, Co₃O₄ nanocube@Co-MOF (Co₃O₄@Co-MOF), via a controllable and facile one-pot hydrothermal method under highly alkaline conditions. The obtained composite possesses exceptional alkaline stability, retaining its original structure in 3.0 M KOH for at least 15 days. Benefitting from the exceptional alkaline stability, unique structure, and larger surface area, the Co₃O₄@Co-MOF composite shows a specific capacitance as high as 1020 F g⁻¹ at 0.5 A  g⁻¹ and a high cycling stability with only 3.3% decay after 5000 cycles at 5 A g⁻¹. The as-constructed solid-state flexible device exhibits a maximum energy density of 21.6 mWh cm⁻³.  相似文献   

Encapsulating metal organic framework into hollow mesoporous carbon sphere as efficient oxygen bifunctional electrocatalyst     

Wanfeng Xiong  Hongfang Li  Hanhui You  Minna Cao  Rong Cao 《国家科学评论(英文版)》2020,7(3):609

Applying metal organic frameworks (MOFs) in electrochemical systems is a currently emerging field owing to the rich metal nodes and highly specific surface area of MOFs. However, the problems for MOFs that need to be solved urgently are poor electrical conductivity and low ion transport. Here we present a facile in situ growth method for the rational synthesis of MOFs@hollow mesoporous carbon spheres (HMCS) yolk–shell-structured hybrid material for the first time. The size of the encapsulated Zeolitic Imidazolate Framework-67 (ZIF-67) is well controlled to 100 nm due to the spatial confinement effect of HMCS, and the electrical conductivity of ZIF-67 is also increased significantly. The ZIF@HMCS-25% hybrid material obtained exhibits a highly efficient oxygen reduction reaction activity with 0.823 V (vs. reversible hydrogen electrode) half-wave potential and an even higher kinetic current density (J_K = 13.8 mA cm⁻²) than commercial Pt/C. ZIF@HMCS-25% also displays excellent oxygen evolution reaction performance and the overpotential of ZIF@HMCS-25% at 10 mA cm⁻² is 407 mV. In addition, ZIF@HMCS-25% is further employed as an air electrode for a rechargeable Zn–air battery, exhibiting a high power density (120.2 mW cm⁻² at 171.4 mA cm⁻²) and long-term charge/discharge stability (80 h at 5 mA cm⁻²). This MOFs@HMCS yolk–shell design provides a versatile method for the application of MOFs as electrocatalysts directly.  相似文献   

2000—2015年中国铜废碎料贸易及效益风险分析     

郝敏  陈伟强  马梓洁  张超  甘建邦 《资源科学》2020,42(8):1515-1526

铜是具有重要战略意义的关键金属。中国长期以来进口“六类废杂铜”和“七类废杂铜”两种废碎料来冶炼再生铜。本文基于海关贸易和有色金属工业统计数据,利用物质流分析和生命周期评价方法研究了铜废碎料贸易的资源、环境和经济效益以及环境与健康风险。结果显示：①2000—2015年,中国累计进口铜废碎料实物量6680万t,其中含金属铜约2000万t,占同期国内再生铜累计产量的56%;②相比利用铜矿石生产精炼铜,利用进口铜废碎料生产再生铜在非生物性资源消耗、温室效应和人体毒性等方面减少了一系列环境影响,同时累计节约铜矿山投资成本约580亿美元。然而,进口的“七类废杂铜”在带来资源效益的同时也造成严重的区域性环境与健康风险：一是进口低品位铜废碎料中夹杂大量有机物,在拆解和熔炼过程中容易产生二恶英等有毒有害物质;二是部分工业园区和小企业在工艺、技术、空间布局和生产管理等方面的落后引发了局部地区较为严重的环境和健康危害。因此,建议辩证和全面地认识铜废碎料进口带来的效益和风险,在坚决禁止进口“以回收铜为主的废电机、电线、电缆和五金电器”这些“七类废杂铜”的同时,继续利用进口“六类废杂铜”作为重要的铜资源,以降低中国对原生铜矿石的依赖以及造成的采矿和原矿冶炼阶段的环境影响。  相似文献   

《鬼妈妈》恐怖元素与作用探析     

程橙  崔醒群 《山西广播电视大学学报》2012,(4):96-98

随着制作观念的开放,新的青少年儿童文艺形式不断衍生,融入了恐怖元素的作品大量涌现,影片《鬼妈妈》就是一部成功之作。儿童片与恐怖因素并非势不两立,合理适度的运用恐怖因素有利于激发青少年儿童的想象力,培养他们分辨是非的能力和勇于挑战的精神。少儿文艺影视作品的恐怖元素也会对青少年儿童带来不良影响,在其应用于儿童片时应以禁止滥用、避免危害少年儿童为原则。  相似文献   

国家图书馆中文名称规范的探讨   总被引：2，自引：0，他引：2  

曹玉强 《图书馆建设》2007,(3):46-48

本文回顾了国图中文名称规范的历史,并指出个人名称标目学科附加成分存在的问题,提出个人名称非规范标目附加成分的重要性,分析虚拟团体名称,最后对中文名称规范工作提出4点建议。  相似文献   

中文文本知识元的构建及其现实意义   总被引：4，自引：3，他引：4       下载免费PDF全文

文庭孝  侯经川  龚蛟腾  刘晓英  汪全莉 《中国图书馆学报》2007,33(6)

中文文本知识元的构建是解决汉语自动分词问题,实现对中文自然语言理解,并对知识内容进行操作、管理之基础。应当以汉语主题词为基础,构建中文文本知识元,建立知识元数据库,完成对知识内容的自由操作和管理。图1。参考文献26。  相似文献