supplement or even replace labels based on best TF-IDF terms by coredocuments representation. A further advantage of this method is that coredocuments proved to express centrality as has shown in the context of hybrid journal clustering (cf. Zhang et al
of ‘coredocuments’ has been extended to a hybrid approach using bibliographic coupling and term frequencies . We will recall this method in brief. The notion of a ‘core’ of literature has its roots in co-citation analysis (Small 1973 ). The
The notion of a ‘core’ of literature has its roots in co-citation analysis. ‘Coredocuments’ have originally introduced in the sense of co-cited core papers, i.e., papers in a core formed by the most (co
A method to identify core documents within a given subject domain has been developed by the author. The method builds on the
concept of polyrepresentation by using different search rationales in several databases and isolating the overlaps between
them. This paper delineates the ideas behind the method and describes the study done to measure its effectiveness.
In an earlier study the authors have shown that bibliographic coupling techniques can be used to identify hot research topics. The methodology is based on appropriate thresholds for both number of related documentsand the strength of bibliographic links. Those papers are calledcore documents that have more than 9 links of at least the strength 0.25 according toSalton's measure, provided they are articles, notes or reviews. This choice resulted in a selection of nearly one per cent of all papers of the above types recorded in the 1992 annual cumulation of the SCI.Core documents proved important nodes in the network of documented science communication.In the present study, the set ofcore documents is analysed by journals, subfields and corporate addresses. The latter analysis is conducted on both national and regional-institutional level. First all countries which have published at least 20 core documents in 1992 are investigated in terms of their research profiles, their international collaboration patterns and their citation impact. Finally, those eight members of the European Union which have published at least 20 core documents in 1992 are analysed in respect of regional and institutional distribution of core documents.
The dynamic mapping of science using the data in theScience Citation Index was put on the research agenda of science studies byDe Solla Price in the mid 1960s. Recently, proponents of co-citation cluster analysis have claimed that in principle their methodology makes such mapping possible. The study examines this claim, both methodologically and theoretically, in relation to other means of mapping science. A detailed study of a co-citation map, its core documents' citation patterns and the related journal structures, is presented. At these three levels of possible study of aggregates of citations, an analysis is pursued for the years 1978 to 1984. The many different statistical methods which are in use for the analysis of the respective datamatrices—such as cluster analysis, factor analysis and multidimensional scalling—are assessed with a view to their potential to contribute to a better undérstanding of the dynamics at the different levels in relation to each other. This will lead to some recommendations about methods to use and to avoid when we aim at a comprehensive mapping of science. Although the study is pursued at a formal and analytical level, in the conclusions an attempt is made to reflect on the results in terms of further substantial questions for the study of the dynamics of science.
The role of remote sensing is well known and can be successfully applied as an initial step in surface geologic exploration. The aim of this study, by means of Landsat TM 7 image interpretation, is to assist photogeologic map compiling, which will serve as a core document for an upcoming field mapping exercise. The mathematical background and the wide variety of math-method possibilities offered by a satellite image interpretation software were used for this purpose. In this way the requested preliminary photogeologic map was compiled, based on the spectral properties of the surface geologic formations. Fortunately the areas of interest were in a desert area (Central Libya), so there was no limitation by vegetation coverage to hinder the application of spectral properties to geologic formations. After the geocoding of the images the display of different compositions of the Landsat TM 7 registration channels was begun. Contrast enhancement and histogram fitting were applied, and further operations to highlight some hidden properties of the original dataset were performed. Thus, some filters from the set offered by the software, some edge enhancement and finally the two types of classification (unsupervised and supervised), were applied.
important characteristic of within-specialty co-citations. A related issue is how close together co-citations occur in texts. 35 papers co-citing only two coredocuments were examined to determine whether the items were cited in the same sentence (which
unsupervised solution has been proposed by Thijs and Glänzel ( 2010 ). It makes use of coredocuments to bridge clustering results issued from different time periods. The coredocuments are defined as the documents that combine high bibliographic coupling and
(source items) or if they are only indexed as cited documents (non-source publications) in the database used (Åström 2007 ). The intellectual base is constituted by the coredocuments of a field; the documents that you should have read or cited, or the