Interactive tag maps and tag clouds for the multiscale exploration of large spatio-temporal datasets

'Tag clouds' and 'tag maps' are introduced to represent geographically referenced text. In combination, these aspatial and spatial views are used to explore a large structured spatio-temporal data set by providing overviews and filtering by text and geography. Prototypes are implemented using freely available technologies including Google Earth and Yahoo! 's Tag Map applet. The interactive tag map and tag cloud techniques and the rapid prototyping method used are informally evaluated through successes and limitations encountered. Preliminary evaluation suggests that the techniques may be useful for generating insights when visualizing large data sets containing geo-referenced text strings. The rapid prototyping approach enabled the technique to be developed and evaluated, leading to geovisualization through which a number of ideas were generated. Limitations of this approach are reflected upon. Tag placement, generalisation and prominence at different scales are issues which have come to light in this study that warrant further work

Developmental changes in the membrane current pattern, K+ buffer capacity, and morphology of glial cells in the corpus callosum slice

Recent studies indicated that glial cells in tissue culture can express a variety of different voltage-gated channels, while little is known about the presence of such channels in glial cells in vivo. We used a mouse corpus callosum slice preparation, in which after postnatal day 5 (P5) more than 99% of all perikarya belong to glial cells (Sturrock, 1976), to study the current patterns of glial cells during their development in situ. We combined the patch-clamp technique with intracellular labeling using Lucifer yellow (LY) and subsequent ultrastructural characterization. In slices of mice from P6 to P8, we predominantly found cells expressing delayed-rectifier K+ currents. They were similar to those described for cultured glial precursor cells (Sontheimer et al., 1989). A-type K+ currents or Na+ currents were not or only rarely observed, in contrast to cultured glial precursors. LY labeling revealed that numerous thin processes extended radially from the perikaryon of these cells, and ultrastructural observations suggested that they resemble immature glial cells. In slices of older mice (P10-13), when myelination of the corpus callosum has already commenced, many cells were characterized by an almost linear current-voltage relationship. This current pattern was similar to cultured oligodendrocytes (Sontheimer et al., 1989). Most processes of LY-filled cells with such a current profile extended parallel to each other. Electron microscopy showed that these processes surround thick, unmyelinated axons. We suggest that cells with oligodendrocyte-type electrophysiology are promyelinating oligodendrocytes. In contrast to cultured oligodendrocytes, membrane currents of promyelinating oligodendrocytes in the slice decayed during the voltage command. This decay was due not to inactivation, but to a marked change in the potassium equilibrium potential within the voltage jump. This implies that, in the more mature corpus callosum, small membrane polarizations in a physiological range can lead to extensive changes in the K+ gradient across the glial membrane within a few milliseconds

Construction of a Pragmatic Base Line for Journal Classifications and Maps Based on Aggregated Journal-Journal Citation Relations

A number of journal classification systems have been developed in bibliometrics since the launch of the Citation Indices by the Institute of Scientific Information (ISI) in the 1960s. These systems are used to normalize citation counts with respect to field-specific citation patterns. The best known system is the so-called "Web-of-Science Subject Categories" (WCs). In other systems papers are classified by algorithmic solutions. Using the Journal Citation Reports 2014 of the Science Citation Index and the Social Science Citation Index (n of journals = 11,149), we examine options for developing a new system based on journal classifications into subject categories using aggregated journal-journal citation data. Combining routines in VOSviewer and Pajek, a tree-like classification is developed. At each level one can generate a map of science for all the journals subsumed under a category. Nine major fields are distinguished at the top level. Further decomposition of the social sciences is pursued for the sake of example with a focus on journals in information science (LIS) and science studies (STS). The new classification system improves on alternative options by avoiding the problem of randomness in each run that has made algorithmic solutions hitherto irreproducible. Limitations of the new system are discussed (e.g. the classification of multi-disciplinary journals). The system's usefulness for field-normalization in bibliometrics should be explored in future studies.Comment: accepted for publication in the Journal of Informetrics, 20 July 201

Unterstützung des Editierens von Graphen in Visuellen Repräsentationen

The goal of this thesis is to provide solutions for supporting the direct editing of graphs in visual representations for analyzing graphs. For that, a conceptual view on the user's tasks is established first. On this basis, several novel approaches to "visually edit" the different data aspects of graphs - the graph's structure and associated attribute values - are introduced. Thereby, different visual graph representations suitable for communicating the data are considered.Das Ziel der vorliegenden Dissertation ist, Lösungen zur Unterstützung des direkten Editierens von Graphen in visuellen Repräsentationen zur Analyse von Graphen bereitzustellen. Dafür wird zunächst eine konzeptuelle Sicht auf die Aufgaben des Nutzers entwickelt. Auf dieser Basis werden anschließend mehrere neue Verfahren eingeführt, welche das "visuelle Editieren" der verschiedenen Datenaspekte von Graphen - der Struktur sowie dazu assoziierte Attributwerte - ermöglichen. Dabei werden verschiedene visuelle Graphrepräsentationen berücksichtigt, welche die Daten in geeigneter Form kommunizieren

Cabinet Tree: an orthogonal enclosure approach to visualizing and exploring big data

Treemaps are well-known for visualizing hierarchical data. Most related approaches have been focused on layout algorithms and paid little attention to other display properties and interactions. Furthermore, the structural information in conventional Treemaps is too implicit for viewers to perceive. This paper presents Cabinet Tree, an approach that: i) draws branches explicitly to show relational structures, ii) adapts a space-optimized layout for leaves and maximizes the space utilization, iii) uses coloring and labeling strategies to clearly reveal patterns and contrast different attributes intuitively. We also apply the continuous node selection and detail window techniques to support user interaction with different levels of the hierarchies. Our quantitative evaluations demonstrate that Cabinet Tree achieves good scalability for increased resolutions and big datasets