共查询到20条相似文献，搜索用时 546 毫秒
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随着体系尺寸减小到纳米级以及维度的降低,表面效应、量子限域效应、尺寸效应以及量子隧穿效应越来越显著,因而低维纳米材料通常表现出不同于普通块体材料的理化性质.第一性原理计算方法具有准确、高效、便捷以及低成本等优势,借助第一性原理计算方法,可以在原子与分子层面上设计、计算和分析新材料,在材料结构与性能计算相关领域,则可以准确预估各类材料的基本物性.因此第一性原理计算方法成为了除理论方法与实验方法外可以独立开展材料物性研究的第三种方法. 相似文献
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对爱因斯坦关于“时间”“空间”论证的理论基础的正确性、论据(数据)的有效性、论证过程的规范性、在“环球航行原子钟实验”中选择定量与定性分析的依据问题、空间弯曲示意图的真伪性、日全食星星偏移照片的有效性等问题提出了相应的疑问,并提出了“不同纬度时钟实验”和“等效日全食实验”,作为验证爱因斯坦“时、空”观点的验证新方法。 相似文献
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采用一阶剪切变形的Mindlin板理论研究了考虑表面效应的压电纳米板的振动问题。表面效应包括表面弹性、表面应力和表面的压电效应。基于此理论模型建立了考虑表面效应和压电效应的纳米板的修正模型,并建立了相应的控制方程。研究了四边简支压电纳米板的振动行为,并推导出了相应的频率特征方程。研究了表面效应、压电效应和剪切变形对振动频率的影响。 相似文献
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《国家科学评论(英文版)》2015,(2)
Catalysis, as a key and enabling technology, plays an increasingly important role in ields ranging from energy, environment and agriculture to health care. Rational design and synthesis of highly eicient catalysts has become the ultimate goal of catalysis research. hanks to the rapid development of nanoscience and nanotechnology, and in particular a theoretical understanding of the tuning of electronic structure in nanoscale systems, this element of design is becoming possible via precise control of nanoparticles' composition, morphology, structure and electronic states. At the same time, it is important to develop tools for in situ characterization of nanocatalysts under realistic reaction conditions, and for monitoring the dynamics of catalysis with high spatial, temporal and energy resolution. In this review, we discuss coninement efects in nanocatalysis, a concept that our group has put forward and developed over several years. Taking the conined catalytic systems of carbon nanotubes, metal-conined nano-oxides and 2D layered nanocatalysts as examples, we summarize and analyze the fundamental concepts, the research methods and some of the key scientiic issues involved in nanocatalysis. Moreover, we present a perspective on the challenges and opportunities in future research on nanocatalysis from the aspects of:(1) controlled synthesis of nanocatalysts and rational design of catalytically active centers;(2) in situ characterization of nanocatalysts and dynamics of catalytic processes;(3) computational chemistry with a complexity approximating that of experiments; and (4) scale-up and commercialization of nanocatalysts. 相似文献
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概念是科学教学中的重要内容之一,本文基于科学教育的研究视角,通过梳理概念和科学概念经典定义,对两者进行了进一步诠释;介绍构成概念的五个要素及其在科学教育中的作用,希望能为自然科学概念教学提供一定理论参考。 相似文献
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概念是科学教学中的重要内容之一,本文基于科学教育的研究视角,通过梳理概念和科学概念经典定义,对两者进行了进一步诠释;介绍构成概念的五个要素及其在科学教育中的作用,希望能为自然科学概念教学提供一定理论参考。 相似文献
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论信息管理学的概念与概念体系 总被引：11，自引：0，他引：11
基本概念的研究是否深入、定义是否准确,是一门学科的理论基础是否坚实的基本保证,也是检验一门学科是否成熟的首要标准。重要概念和相关概念的准确定义也至关重要。理论界许多低水平的重复研究和长期争论而无结果的现象,多半是相关概念定义不规范、不准确的结果。为避免信息管理学在初创时期便陷入这一局面,本文对信息管理学的基本概念、重要概念和相关学科的相关概念以及这些概念之间的内在联系和区别作一系统的梳理和探讨。对争议较大的概念和相关理论提出了信息管理学的定义和观点。 相似文献
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本体集成相关的基本概念研究 总被引：1，自引：0，他引：1
本文通过综合研究国内外典型观点.分析了本体匹配、本体映射、本体联结、本体融合、本体集成以及本体协同等概念的含义,详细描述了相似概念的区别与关系,并提出了易混淆概念的较为合适的中文译名,给出了重要概念的较为准确的定义. 相似文献
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The fundamental idea of the work reported here is to extract index phrases from texts with the help of a single word concept dictionary and a thesaurus containing relations among concepts. The work is based on the fact, that, within every phrase, the single words the phrase is composed of are related in a certain well denned manner, the type of relations holding between concepts depending only on the concepts themselves. Therefore relations can be stored in a semantic network. The algorithm described extracts single word concepts from texts and combines them to phrases using the semantic relations between these concepts, which are stored in the network. The results obtained show that phrase extraction from texts by this semantic method is possible and offers many advantages over other (purely syntactic or statistic) methods concerning preciseness and completeness of the meaning representation of the text. But the results show, too, that some syntactic and morphologic “filtering” should be included for effectivity reasons. 相似文献
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刘志坚 《科学．经济．社会》2005,23(1):89-92,96
行政与行政法是行政法学上两个最具基础性的，同时也是存在一定学术争议的概念范畴。论文在分析了行政法学界对行政特别是行政法的定义方面所存在问题的基础上，提出了对行政与行政法的新的定义观：行政是根据法律并为了执行法律而运用国家行政权，对国家事务和社会公共事务进行组织与管理的活动；行政法则是调整国家行政主体在行使国家行政权，对国家与社会公共事务进行组织和管理的活动过程中所发生的重要的社会关系的法律规定的总和。 相似文献
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We propose a new query reformulation approach, using a set of query concepts that are introduced to precisely denote the user’s information need. Since a document collection is considered to be a domain which includes latent primitive concepts, we identify those concepts through a local pattern discovery and a global modeling using data mining techniques. For a new query, we select its most associated primitive concepts and choose the most probable interpretations as query concepts. We discuss the issue of constructing the primitive concepts from either the whole corpus or from the retrieved set of documents. Our experiments are performed on the TREC8 collection. The experimental evaluation shows that our approach is as good as current query reformulation approaches, while being particularly effective for poorly performing queries. Moreover, we find that the approach using the primitive concepts generated from the set of retrieved documents leads to the most effective performance. 相似文献
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Seungji Yang Sang Kyun Kim Kyong Sok Seo Yong Man Ro Ji-Yeon Kim Yang Suk Seo 《Information processing & management》2007
In this paper, a semantic categorization method in generic home photos is proposed. In recent years, the semantic categorization of image has been a challenge due to the proliferation of digital home photos. Our approach is to detect semantically meaningful concepts contained in a photo. The proposed method incorporates an intermediate level of concepts, called local concept, so that it catches well semantic meaning of local regions of image as bridging the semantic gap of the low-level features and high-level category concepts. To detect the local concepts from the home photo, region segmentation by photographic region template and concept merging is also proposed. The efficacy of the proposed semantic categorization method was demonstrated with 3828 general home photos. The experiment results showed the proposed categorization method would be useful to detect multiple semantic meaning of the home photos. 相似文献
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We argue that the quality of a summary can be evaluated based on how many concepts in the original document(s) that can be preserved after summarization. Here, a concept refers to an abstract or concrete entity or its action often expressed by diverse terms in text. Summary generation can thus be considered as an optimization problem of selecting a set of sentences with minimal answer loss. In this paper, we propose a document concept lattice that indexes the hierarchy of local topics tied to a set of frequent concepts and the corresponding sentences containing these topics. The local topics will specify the promising sub-spaces related to the selected concepts and sentences. Based on this lattice, the summary is an optimized selection of a set of distinct and salient local topics that lead to maximal coverage of concepts with the given number of sentences. Our summarizer based on the concept lattice has demonstrated competitive performance in Document Understanding Conference 2005 and 2006 evaluations as well as follow-on tests. 相似文献