Braid groups and Kleinian singularities

We establish faithfulness of braid group actions generated by twists along an ADE configuration of $2$-spherical objects in a derived category. Our major tool is the Garside structure on braid groups of type ADE. This faithfulness result provides the missing ingredient in Bridgeland's description of a space of stability conditions associated to a Kleinian singularity.Comment: Section 4 from versions 1 and 2 has been deleted due to an error in the proof of Theorem 2. Renamed the paper and rewrote the other sections to reflect this chang

Erfolgreiche Arbeit in Gruppen

Die Effekte von Gruppenarbeit wurden in einer schriftliche Umfragestudie mit dem Produktionspersonal (n = 754) in acht schwedischen Industrieunternehmen untersucht. Unterschiede in der Gruppengröße, der alters- und geschlechtermässigen Zusammensetzung der Gruppen als auch dem Motivationsbild der einzelnen Gruppenmitglieder wurden untersucht, um deren Bedeutung für Effekte von Gruppenarbeit auf Unternehmens-, Gruppen- und Individualebene zu zeigen. Gruppenmitglieder mit einem aktiven Motivationsbild gaben mehr positive Effekte an als solche, die über weniger solcher Möglichkeiten verfügten. Bei der Implementierung von Gruppenarbeit ist es wichtiger, solche beeinflussbaren Aspekte, wie der Möglichkeit zum Lernen in der Arbeit und zur Nutzung eigener Kompetenz, Autonomie und Arbeits(un)zufriedenheit der Gruppenmitglieder zu ermitteln, als sich auf einfache Daumenregeln zur Gruppengröße und Geschlechter- und Alterszusammensetzung zu stützen.The aim of the study is to illuminate the relationship between group composition (group size; gender, age, and motivation of group members) and the effects of group working. The results are based on a questionnaire distributed to workers within eight Swedish industries (n=754). The results suggest that aspects which are possible for management to influence and develop when group work is implemented like motivation (here measured as use of group members aptitudes and skills, autonomy and job satisfaction) has a positive impact on the effects of working in groups. Group composition according to gender and age contributes little to our understanding of what makes group work effective

Recent advances in research on hedge fund activism: Value creation and identification

Hedge fund activism has emerged as a major force of corporate governance since the 2000s. By the mid-2000s, there were between 150–200 activist hedge funds in action each year, advocating for changes in 200–300 publicly listed companies in the U.S. In this paper, we review the evolution and major characteristics of hedge fund activism, as well as the short- and long-term impact of such activities on the performance and governance of the targeted companies. Though most of the analyses are based on a comprehensive sample of over 2,000 activism events in the U.S. from 1994 to 2011, hand-collected by the authors from regulatory filings and news searches, this paper covers all major studies on the topic, including those on non-U.S. markets

Stability conditions and quantum dilogarithm identities for Dynkin quivers

We study fundamental group of the exchange graphs for the bounded derived category D(Q) of a Dynkin quiver Q and the finite-dimensional derived category D(\Gamma_N Q) of the Calabi-Yau-N Ginzburg algebra associated to Q. In the case of D(Q), we prove that its space of stability conditions (in the sense of Bridgeland) is simply connected; as applications, we show that its Donanldson-Thomas invariant can be calculated via a quantum dilogarithm function on exchange graphs. In the case of D(\Gamma_N Q), we show that faithfulness of the Seidel-Thomas braid group action (which is known for Q of type A or N = 2) implies the simply connectedness of its space of stability conditions.Comment: Journal (almost) equivalent versio