On the geometry of the smallest circle enclosing a finite set of points     

Lance D. Drager  Jeffrey M. Lee 《Journal of The Franklin Institute》2007,344(7):929-940

A number of numerical codes have been written for the problem of finding the circle of smallest radius in the Euclidean plane that encloses a finite set P of points, but these do not give much insight into the geometry of this circle. We investigate geometric properties of the minimal circle that may be useful in the theoretical analysis of applications. We show that a circle C enclosing P is minimal if and only if it is rigid in the sense that it cannot be translated while still enclosing P. We show that the center of the minimal circle is in the convex hull of P. We use this rigidity result and an analysis of the case of three points to find sharp estimates on the diameter of the minimal circle in terms of the diameter of P.  相似文献   

国产十种乌头的染色体研究   总被引：1，自引：0，他引：1  

商效民  李正理 《中国科学院研究生院学报》1984,22(5):378-385

本文描述了我国产毛茛科乌头属的10个种的染色体数目和形态。  根据该属染色体基 数为8(x＝8)，可将这些种归为二倍体、四倍体、六倍体和八倍体种。  10种乌头的染色体在数目、大小、结构上表现出相关性。其中具根状茎而多年生的种多为二倍体，染色体形态较大，第3-7号多为近端着丝点(st)染色体, 具块茎而二年生的种多为多倍体，染色体形态较小，第3-7号多为近中着丝点(sm)染色体。染色体演化方向可能是二倍体→多倍体、大→ 小、st→sm。这进一步证明根状茎种较块茎种原始。根据染色体数目和形态，又可将这些种的染色体分为两类。这进一步支持了目前分类学上的牛扁亚属和乌头亚属的划分。本文还讨论了这些种的有关分类问题。  相似文献   

Unsupervised word sense disambiguation for Korean through the acyclic weighted digraph using corpus and dictionary     

Yeohoon Yoon  Choong-Nyoung Seon  Songwook Lee  Jungyun Seo 《Information processing & management》2006

Word sense disambiguation (WSD) is meant to assign the most appropriate sense to a polysemous word according to its context. We present a method for automatic WSD using only two resources: a raw text corpus and a machine-readable dictionary (MRD). The system learns the similarity matrix between word pairs from the unlabeled corpus, and it uses the vector representations of sense definitions from MRD, which are derived based on the similarity matrix. In order to disambiguate all occurrences of polysemous words in a sentence, the system separately constructs the acyclic weighted digraph (AWD) for every occurrence of polysemous words in a sentence. The AWD is structured based on consideration of the senses of context words which occur with a target word in a sentence. After building the AWD per each polysemous word, we can search the optimal path of the AWD using the Viterbi algorithm. We assign the most appropriate sense to the target word in sentences with the sense on the optimal path in the AWD. By experiments, our system shows 76.4% accuracy for the semantically ambiguous Korean words.  相似文献   

Optimization of some factors affecting the performance of query expansion     

Young Mee Chung  Jae Yun Lee 《Information processing & management》2004,40(6):29

This paper examines the factors affecting the performance of global query expansion based on term co-occurrence data and suggests a way to maximize the retrieval effectiveness. Major parameters to be optimized through experiments are term similarity measure and the weighting scheme of additional terms. The evaluation of four similarity measures tested in query expansion reveal that mutual information and Yule's Y, which emphasize low frequency terms, achieve better performance than cosine and Jaccard coefficients that have the reverse tendency. In the evaluation of three weighting schemes, similarity weight performs well only with short queries, whereas fixed weights of approximately 0.5 and similarity rank weights were effective with queries of any length. Furthermore, the optimal similarity rank weight achieving the best overall performance seems to be the least affected by test collections and the number of additional terms. For the efficiency of retrieval, the number of additional terms needs not exceed 70 in our test collections, but the optimal number may vary according to the characteristics of the similarity measure employed.  相似文献   

Parsimonious translation models for information retrieval     

Seung-Hoon Na  In-Su KangJong-Hyeok Lee 《Information processing & management》2007

In the KL divergence framework, the extended language modeling approach has a critical problem of estimating a query model, which is the probabilistic model that encodes the user’s information need. For query expansion in initial retrieval, the translation model had been proposed to involve term co-occurrence statistics. However, the translation model was difficult to apply, because the term co-occurrence statistics must be constructed in the offline time. Especially in a large collection, constructing such a large matrix of term co-occurrences statistics prohibitively increases time and space complexity. In addition, reliable retrieval performance cannot be guaranteed because the translation model may comprise noisy non-topical terms in documents. To resolve these problems, this paper investigates an effective method to construct co-occurrence statistics and eliminate noisy terms by employing a parsimonious translation model. The parsimonious translation model is a compact version of a translation model that can reduce the number of terms containing non-zero probabilities by eliminating non-topical terms in documents. Through experimentation on seven different test collections, we show that the query model estimated from the parsimonious translation model significantly outperforms not only the baseline language modeling, but also the non-parsimonious models.  相似文献   

An empirical study of query expansion and cluster-based retrieval in language modeling approach     

Seung-Hoon Na  In-Su Kang  Ji-Eun Roh  Jong-Hyeok Lee 《Information processing & management》2007

The term mismatch problem in information retrieval is a critical problem, and several techniques have been developed, such as query expansion, cluster-based retrieval and dimensionality reduction to resolve this issue. Of these techniques, this paper performs an empirical study on query expansion and cluster-based retrieval. We examine the effect of using parsimony in query expansion and the effect of clustering algorithms in cluster-based retrieval. In addition, query expansion and cluster-based retrieval are compared, and their combinations are evaluated in terms of retrieval performance by performing experimentations on seven test collections of NTCIR and TREC.  相似文献   

The Book Industry Study Group, Inc., Book Industry Trends 2006: Comprehensive Coverage of Book Sales by Publishers, Including Dollar and Unit Sales Figures for the Years 2004–2010 and Insights from Interviews with Leaders in Major Sectors of the Book Publishing Industry     

Peter W. Adams 《Publishing Research Quarterly》2007,23(1):89-91

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The historical context of science and education at the American Museum of Natural History     

Jennifer D. Adams 《Cultural Studies of Science Education》2007,2(2):393-440

In this article I critically examine the historical context of science education in a natural history museum and its relevance to using museum resources to teach science today. I begin with a discussion of the historical display of race and its relevance to my practice of using the Museum’s resources to teach science. I continue with a critical review of the history of the education department in a natural history museum to demonstrate the historical constitution of current practices of the education department. Using sociocultural constructs around identity formation and transformation, I move to the present with a case study of a teacher who transforms the structure of science education in her classroom and school as a result of her identity transformation and association with a museum-based professional education program.

Jennifer D. AdamsEmail:

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Doing the right thing: infants' selection of actions to imitate from observed event sequences     

Brugger A  Lariviere LA  Mumme DL  Bushnell EW 《Child development》2007,78(3):806-824

Two studies were conducted to investigate how 14- to 16-month-old infants select actions to imitate from the stream of events. In each study, an experimenter demonstrated two actions leading to an interesting effect. Aspects of the first action were manipulated and whether infants performed this action when given the objects was observed. In both studies, infants were more likely to imitate the first action when it was physically necessary to generate the effect, and in Study 2 they were also more likely to imitate the action when it was socially cued. It seems that infants' own knowledge of space and causality as well as their sensitivity to others' social signals both contribute to their tendency to imitate actions.  相似文献   

Religious Development in African American Adolescents: Growth Patterns That Offer Protection     

Daniel B. Lee  Enrique W. Neblett 《Child development》2019,90(1):245-259

Although religiosity promotes resilient outcomes in African American (AA) adolescents, there is a lack of research that examines the protective role of religious development in the context of stressful life events (SLEs). In 1,595 AA adolescents, a cohort-sequential design was used from ages 12 to 18 to examine subtypes of religiosity, as well as distinct developmental patterns within subtypes. The protective role of religious development was also examined in the context of SLEs. The study findings indicated two subtypes of religiosity—extrinsic and intrinsic religiosity—as well as low and high developmental patterns in the identified subtypes. Furthermore, the protective influence of extrinsic and intrinsic religiosity gradually diminished from age 12 to 18 in the context of SLEs.  相似文献