Michael Heinz

Collaboration and distances between German immunological institutes – a trend analysis

BackgroundThe hypothesis that distance matters but that in recent years geographical proximity has become less important for research collaboration was tested. We have chosen a sample–authors at German immunological institutes–that is relatively homogeneous with regard to research field, language and culture, which beside distance are other possible factors influencing the willingness to co-operate. We analyse yearly distributions of co-authorship links between institutes and compare them with the yearly distributions of distances of all institutes producing papers in journals indexed in the Science Citation Index, editions 1992 till 2002. We weight both types of distributions properly with paper numbers.ResultsOne interesting result is that place matters but if a researcher has to leave the home town to find a collaborator distance does not matter any longer. This result holds for all years considered, but is statistically most significant in 2002. The tendency to leave the own town for collaborators has slightly increased in the sample. In addition, yearly productivity distributions of institutes have been found to be lognormal.ConclusionThe Internet did not change much the collaboration patterns between German immunological institutes.

Firm-like behavior of journals? Scaling properties of their output and impact growth dynamics

In the study of growth dynamics of artificial and natural systems, the scaling properties of fluctuations can exhibit information on the underlying processes responsible for the observed macroscopic behavior according to H.E. Stanley and colleagues (Lee, Amaral, Canning, Meyer, & Stanley, 1998; Plerou, Amaral, Gopikrishnan, Meyer, & Stanley, 1999; Stanley et al., 1996). With such an approach, they examined the growth dynamics of firms, of national economies, and of university research fundings and paper output. We investigated the scaling properties of journal output and impact according to the Journal Citation Reports (JCR; ISI - Institute for Scientific Information - , Philadelphia, PA) and find distributions of paper output and of citations near to lognormality. Growth rate distributions are near to Laplace tents, however with a better fit to Subbotin distributions. The width of fluctuations decays with size according to a power law. The form of growth rate distributions seems not to depend on journal size, and conditional probability densities of the growth rates can thus be scaled onto one graph. To some extent even quantitatively, all our results are in agreement with the observations of Stanley and others. Further on, a Matthew effect of journal citations is confirmed. If journals behave like business firms, a better understanding of Bradfords Law as a result of competition among publishing houses, journals, and topics suggests itself.

Identifying Overlapping and Hierarchical Thematic Structures in Networks of Scholarly Papers: A Comparison of Three Approaches

The aim of this paper is to introduce and assess three algorithms for the identification of overlapping thematic structures in networks of papers. We implemented three recently proposed approaches to the identification of overlapping and hierarchical substructures in graphs and applied the corresponding algorithms to a network of 492 information-science papers coupled via their cited sources. The thematic substructures obtained and overlaps produced by the three hierarchical cluster algorithms were compared to a content-based categorisation, which we based on the interpretation of titles, abstracts, and keywords. We defined sets of papers dealing with three topics located on different levels of aggregation: h-index, webometrics, and bibliometrics. We identified these topics with branches in the dendrograms produced by the three cluster algorithms and compared the overlapping topics they detected with one another and with the three predefined paper sets. We discuss the advantages and drawbacks of applying the three approaches to paper networks in research fields.

Structural similarities between science growth dynamics in China and in western countries

SummaryTo compare science growth of different countries is both, of theoretical and of pragmatic interest. Using methods for the analysis of complex growth processes introduced by H. E. Stanley and others, we exhibit quantitative features of Chinese science growth from 1986 to 1999 and compare them with corresponding features of western countries. Patterns of growth dynamics of Chinese universities publication output do not differ significantly from those found in the case of western countries. The same is valid for Chinese journals when compared to international journals. In nearly all cases the size distribution of output over universities or journals is near to a lognormal one, the growth rate distribution is Laplace-like, and the standard deviations of the corresponding conditional distributions with regard to size decay according to a power law. This means that regarding some structural-dynamical properties Chinas recent science system cannot be distinguished from a western one - despite different prehistory and different political and economic environment.

Memetic search for overlapping topics based on a local evaluation of link communities

In spite of recent advances in field delineation methods, bibliometricians still don’t know the extent to which their topic detection algorithms reconstruct ‘ground truths’, i.e., thematic structures in the scientific literature. In this paper, we demonstrate a new approach to the delineation of thematic structures that attempts to match the algorithm to theoretically derived and empirically observed properties all thematic structures have in common. We cluster citation links rather than publication nodes, use predominantly local information and search for communities of links starting from seed subgraphs in order to allow for pervasive overlaps of topics. We evaluate sets of links with a new cost function and assume that local minima in the cost landscape correspond to link communities. Because this cost landscape has many local minima we define a valid community as the community with the lowest minimum within a certain range. Since finding all valid communities is impossible for large networks, we designed a memetic algorithm that combines probabilistic evolutionary strategies with deterministic local searches. We apply our approach to a network of about 15,000 Astronomy and Astrophysics papers published 2010 and their cited sources, and to a network of about 100,000 Astronomy and Astrophysics papers (published 2003–2010) which are linked through direct citations.

Growth dynamics of German university enrolments and of scientific disciplines in the 19th century: Scaling behaviour under weak competitive pressure

According to authors like H. E. Stanley and others, growth dynamics of university research displays a quantitative behaviour similar to the growth dynamics of firms acting under competitive pressure. Features of such behaviour are probability distributions of annual growth rates or the standard deviation of growth rates. We show that a similar statistical behaviour can be observed in the growth dynamics of German university enrolments or in the growth dynamics of physics and mathematics, both for the 19th century. Since competitive pressure was generally weak at that time, interpretations of statistical similarities as to pointing to a “firm-like behaviour” are questionable.