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   

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   

An Entity Theory of Intelligence Predicts Higher Cortisol Levels When High School Grades Are Declining     

Hae Yeon Lee  Jeremy P. Jamieson  Adriana S. Miu  Robert A. Josephs  David S. Yeager 《Child development》2019,90(6):e849-e867

Grades often decline during the high school transition, creating stress. The present research integrates the biopsychosocial model of challenge and threat with the implicit theories model to understand who shows maladaptive stress responses. A diary study measured declines in grades in the first few months of high school: salivary cortisol (N = 360 students, N = 3,045 observations) and daily stress appraisals (N = 499 students, N = 3,854 observations). Students who reported an entity theory of intelligence (i.e., the belief that intelligence is fixed) showed higher cortisol when grades were declining. Moreover, daily academic stressors showed a different lingering effect on the next day's cortisol for those with different implicit theories. Findings support a process model through which beliefs affect biological stress responses during difficult adolescent transitions.  相似文献   

Development as education for social justice     

Yoo  Sung-Sang  Mosrur  Ridwanul  Lee  Eunhye  Andrea  Diego Toca 《Asia Pacific Education Review》2019,20(2):259-272

Asia Pacific Education Review - The correlation between education and development, with time, went through many changes along with the changes of perspectives. Since both of these concepts...  相似文献   

Proposing an Effective Action Learning Process Model: Introducing the PAIR Model     

Yeol Huh  Dabae Lee 《Performance Improvement》2015,54(10):22-29

Action learning differentiates itself from other inquiry‐based learning approaches in that it requires learners to take actions based on project outcomes. While implementing their plans and reflecting on consequences of their actions, learners are given more and varied learning opportunities. Despite the apparent benefits of action learning, it entails a more complex process and a higher level of involvement from top management than do ordinary training programs. This article seeks to identify benefits and limitations of action learning and proposes a process model that enhances its benefits and helps to overcome its limitations. Thirty‐one research studies from academic journals were reviewed to identify espoused benefits and limitations of action learning. Those findings were used as the foundation for development of the PAIR model.  相似文献