A spectral sequence to compute L2-Betti numbers of groups and groupoids

We construct a spectral sequence for L2-type cohomology groups of discrete measured groupoids. Based on the spectral sequence, we prove the Hopf-Singer conjecture for aspherical manifolds with poly-surface fundamental groups. More generally, we obtain a permanence result for the Hopf-Singer conjecture under taking fiber bundles whose base space is an aspherical manifold with poly-surface fundamental group. As further sample applications of the spectral sequence, we obtain new vanishing theorems and explicit computations of L2-Betti numbers of groups and manifolds and obstructions to the existence of normal subrelations in measured equivalence relations.Comment: added remark 4.9 about applying spectral sequence in a non-ergodic situation; minor correction

The fidelity of prototype and testing environment in usability tests

This doctoral thesis investigated what setup of a usability test can best support valid test outcomes. Several aspects of contextual fidelity were manipulated in experimental usability studies, to examine their impact on test results. The first study demonstrated that the medium of prototype presentation has effects on test outcomes, which have not been found in previous research. Using a more hypothesis-driven approach, it was shown that participants exhibited more reading activity when using a paper-based as compared to a computer prototype presented on screen. This resulted in better performance, if task success required reading a short paragraph of text. Consequently, the medium of prototype presentation needs to be considered to avoid that respective usability problems go undetected. A second study demonstrated that additional observers may cause stress for test participants, which can be measured at the physiological level. Some performance indicators were affected, but only in interaction with perceived developmental stage of the test system. A third study investigated the effects of a work or leisure context on the outcome of a usability test. No effects were found for the type of usage context, but even short response time delays proved to be relevant for performance and emotions. Relevant factors for the validity of usability test outcomes were identified and theoretical and practical implications are discussed. Keywords: Usability test; paper prototype; fidelity; observer presence; work and leisure domain; system response time; heart rate variability; validity

Visual aesthetics and user experience: a multiple-session experiment

The article reports a longitudinal lab experiment, in which the influence of product aesthetics and inherent product usability was examined over a period of 7 weeks. Using a 2 × 2 × 7 mixed design, visual aesthetics (high vs. low) and usability (high vs. low) were manipulated as between-subjects variables whereas exposure time was used as a repeated-measures variable. One hundred and ten participants took part in the study, during which they carried out typical tasks of operating a fully automated coffee machine. We measured user experience by using the following outcome variables: perceived usability, perceived attractiveness, performance, affect, workload and perceived coffee quality (gustatory aesthetics). We found no effect of visual aesthetics on user experience (including perceived usability as the chief outcome variable), which is in contrast to a considerable number of previous studies. The absence of such an effect might be associated with influencing factors that have not yet been given sufficient attention (e.g., user identification with product, sensory dominance, characteristics of specific products)

Celebrating 30 years of Innovation System research : what you need to know about Innovation Systems

On the occasion of the 30th anniversary of Innovation System research, this paper presents an extensive literature review on this large field of innovation research. Building on an analytical basis of the commonalities system and innovation, the authors analyze the four main Innovation System approaches: National Innovation Systems (NIS), Regional Innovation Systems (RIS), Sectoral Innovation Systems (SIS) and Technological Innovation Systems (TIS). The analysis is structured systematically along ten comprehensive criteria. Starting with the founder(s) of each theory and the research program within each Innovation System approach was developed (1), the basic thoughts of each Innovation System approach are explained (2). For five case studies most cited (3), spatial boundaries are examined (4) and units of analyses are derived (5). By comparing the underlying theoretical concept and empirical results, the authors show patterns in the evolution of Innovation System research overall. By studying the basic components (6) and a functional analysis (7), each Innovation System approach is broken down into structural pieces and functional processes. If available, the authors present one or several taxonomies (8) for each Innovation System approach and summarize similar approaches (9), in order to classify and integrate the approaches into the ongoing innovation research. The identification of further research (10) shows which steps will need to be taken in the next years in order to evolve Innovation System research further and deeper. After the conclusion, the extensive table of comparison is presented which can serve as a guideline for academics and practitioners from basic and applied science, industry or policy that need to understand which Innovation System approach may be best for their specific analytical purposes

The Influence of Product Aesthetics and Usability over the Course of Time: A Longitudinal Field Experiment

A longitudinal field experiment was carried out over a period of two weeks to examine the influence of product aesthetics and inherent product usability. A 2 x 2 x 3 mixed design was used in the study, with product aesthetics (high / low) and usability (high / low) being manipulated as between-subjects variables and exposure time as a repeated-measures variable (3 levels). A sample of 60 mobile phone users was tested during a multiple-session usability test. A range of outcome variables was measured, including performance, perceived usability, perceived aesthetics, and emotion. A major finding was that the positive effect of an aesthetically appealing product on perceived usability, reported in many previous studies, began to wane with increasing exposure time. The data provided similar evidence for emotion, which also showed changes as a function of exposure time. The study has methodological implications for the future design of usability tests, notably suggesting the need for longitudinal approaches in usability research

RESPECTING THE HETEROGENEITY OF THE NATIVES: ANTECEDENTS AND CONSEQUENCES OF INDIVIDUALS´ DIGITAL NATIVENESS

The Internet and digital media have forced many individuals to change their attitudes and behaviours in nearly all aspects of life, including work and consumption. Other individuals, often younger, have grown up with digital media and seem not to have undergone changes in attitudes and behaviours. This research suggests, however, that age should not be used as the criterion to differentiate between individuals´ attitudes and behaviours towards digital media. Rather, we suggest utilizing a construct that we call digital nativeness which we characterize as an individual\u27s propensity to use and have a positive attitude towards digital media. Both a qualitative and a quantitative study investigate digital nativeness as well as its antecedents and consequnces. Results show that digital nativeness consists of three dimensions: Expertise in digital media, sophisticated digital media use and sophisticated mobile media use. The studies suggest that early and ubiquitous access to digital media influnce an individual´s level of digital nativeness, while, importantly, age does not have such an influnce. A high level of digital nativeness positively affects individuals´ attitude towards online social network communication, preference for online advertising, learning by doing, and media multitasking. Important implications for scholars and managers can be derived from this research