Discrete-Time Dynamic Principal-Agent Models:Contraction Mapping Theorem and Computational Treatment

We consider discrete-time dynamic principal--agent problems with continuous choice sets and potentially multiple agents. We prove the existence of a unique solution for the principal's value function only assuming continuity of the functions and compactness of the choice sets. We do this by a contraction mapping theorem and so we also obtain a convergence result for the value function iteration. To numerically compute a solution for the problem, we have to solve a collection of static principal--agent problems at each iteration. As a result, in the discrete-time setting solving the static problem is the difficult step. If the agent's expected utility is a rational function of his action, then we can transform the bi-level optimization problem into a standard nonlinear program. The final results of our solution method are numerical approximations of the policy and value functions for the dynamic principal--agent model. We illustrate our solution method by solving variations of two prominent social planning models from the economics literature

Leading-order hadronic contribution to the anomalous magnetic moment of the muon from N_f=2+1+1 twisted mass fermions

We present results for the leading order QCD correction to the anomalous magnetic moment of the muon including the first two generations of quarks as dynamical degrees of freedom. Several light quark masses are examined in order to yield a controlled extrapolation to the physical pion mass. We analyse ensembles for three different lattice spacings and several volumes in order to investigate lattice artefacts and finite-size effects, respectively. We also provide preliminary results for this quantity for two flavours of mass-degenerate quarks at the physical value of the pion mass.Comment: 7 pages, 7 figures, presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German

Four-Flavour Leading-Order Hadronic Contribution To The Muon Anomalous Magnetic Moment

We present a four-flavour lattice calculation of the leading-order hadronic vacuum polarisation contribution to the anomalous magnetic moment of the muon, $a_\mathrm{\mu}^{\rm hvp}$, arising from quark-connected Feynman graphs. It is based on ensembles featuring $N_f=2+1+1$ dynamical twisted mass fermions generated by the European Twisted Mass Collaboration (ETMC). Several light quark masses are used in order to yield a controlled extrapolation to the physical pion mass. We employ three lattice spacings to examine lattice artefacts and several different volumes to check for finite-size effects. Incorporating the complete first two generations of quarks allows for a direct comparison with phenomenological determinations of $a_\mathrm{\mu}^{\rm hvp}$. Our final result including an estimate of the systematic uncertainty $$a_{\mathrm{\mu}}^{\rm hvp} = 6.74(21)(18) \cdot 10^{-8}$$ shows a good overall agreement with these computations.Comment: 24 pages, 11 figures, accepted for publication in JHE

Individual and Organizational Factors in Coping With COVID-19 in Soldier Students

The COVID-19 pandemic has posed significant burden across different industrial sectors. Generally, an increase in psychological stress experiences has been reported, while the stress and coping responses of specific, potentially burdened populations have received less attention thus far. Thus, the present study investigated relations between individual (i.e., extraversion, neuroticism, conscientiousness) and organizational (i.e., organizational commitment and study satisfaction) factors, indicators of psychological health (i.e., loneliness, life satisfaction, COVID-19-related stress), and possible mediating effects of four broad coping dimensions (active coping, avoidant coping, social support, positive cognitive restructuring) in a specific sample of soldier students who engage in a double-role being military affiliates and students of non-military subjects. To this end, we assessed data of soldier students at two measurement points (N = 106 at t1 and N = 63 at t2) shortly after the second national lockdown in Germany (20. May 2021 to 11. July 2021) during the COVID-19 pandemic. Personality traits showed expected associations with indicators of psychological health, i.e., positive relations between neuroticism and social loneliness, between extraversion and COVID-19 stress, and negative relations between neuroticism and life satisfaction. Remarkably, organizational variables showed effects above and beyond personality traits on loneliness and life satisfaction. Neither individual, nor organizational factors could predict change in psychological health over time. We found evidence for mediation effects through active coping, avoidant coping, and the use of social support, but not through positive cognitive restructuring. Findings highlight the relative importance of organizational factors besides personality traits for psychological health in a military student sample, holding important implications for designing efficient support systems in the military

Expansion der Ratgeber- und Lebenshilfeformate im Fernsehen. Quantitative und qualitative Untersuchung zu Sendungen im deutschen TV-Programm

Das Programmsegment der Ratgeber- und Lebenshilfeformate hat in den letzten Jahren zugenommen. Das zeigt sich insbesondere, wenn man aktuelle Zahlen mit den Ergebnissen einer Programmbeobachtung der Ratgebersendungen im Jahr 1979 vergleicht. Dabei ist klar zu erkennen, dass für die Zunahme des Sendevolumens die Entwicklung von neuen Formaten entscheidend war, die nicht mehr einmal die Woche, sondern täglich ausgestrahlt werden. Die neuen Formate entstanden nicht durch eine thematische Ausdifferenzierung wie im Zeitschriftensektor, sondern durch unterschiedliche Ausdifferenzierungen der kommunikativen Handlung „einen Rat geben“, die das Grundschema aller Ratgeber- und Lebenshilfeformate bildet. Weitere Faktoren sind die Einbeziehung von Unterhaltungselementen und die fernsehspezifische Umsetzung der einzelnen Sendekonzepte als Studio-, Film- oder Magazinformate. Eine Schlüsselrolle kommt den Online-Auftritten zu, die alle Ratgeberformate eingerichtet haben. Mithilfe des Internets wurden neue Formen der medialen Beratung möglich, was die Entwicklung neuer Ratgeberformate erleichterte. EnglishKarl N. Renner: Expansion of advising and counselling TV programs in Germany. A quantitative und qualitative analysis The segment of advising and counselling TV programs got a remarkable increase during the last years. This becomes obvious, if one compares the actual volume of these programs with the volume of 1979, the last period before the release of private TV programs in Germany. It’s also obvious that this increase was only made possi- ble with the creation of new TV formats which could be broadcasted every day and not only once a week. These new formats didn’t emerge by topical differentiation like newspaper journals, but by differentia- tion of the communicative act „to advise“, which is the fundamental procedure of all advising and counselling formats. Further factors are the influence of entertaining elements and the particular concepts TV-specific transformation as a studio-, film- or magazine-format. The advising formats’ online presence which they created in the course of media convergence got a key function for this expansion. As the TV formats’ new internet modules enabled new kinds of medial advising and thus fostered the evolution of new advising formats.

Journalistische Wirklichkeitserzählungen und fotografische Bilder

Photos are, like texts, a core means of representation in print as well as in online-journalism. Photos can already indicate a narration. Because of this fact they can be combined with texts to develop complex narrative structures. However, problems arise when there are no photos available of the event itself. In these cases metonymic and metaphoric relations between text and photo are established and used. Looking at the story (histoire), the following essay argues that in the first case narrative structures are established bottom-up and in the second case top-down. Considering the level of discourse, metonymic text-photo relations show an affinity to the communicative act of reporting, whereas meta¬phoric relations lean towards the communicative act of storytelling

Journalismus aus erzähltheoretischer Perspektive

The essay demonstrates how the narratological theories developed in the field of literary studies can accomplish a better comprehension of journalistic narratives. As they have to accommodate the principles of journalism, these narratives have to be true, topical and impartial. From this point of view storytelling and the inverted-pyramid principle prove themselves as two complementary approaches of journalistic narration, whose stories are all constructed on the basis of real world occurrences and the ideologies of the diverse societies. Storytelling is enabling the communication of individual experience and the inverted-pyramid principle is supporting the narrative construction of future-open macro stories. Der Aufsatz zeigt am Beispiel der Zeitungsberichterstattung über die Guttenberg-Affäre 2011, wie die literaturwissenschaftliche Erzähltheorie zum besseren Verständnis des journalistischen Erzählens beitragen kann. Da dieses Erzählen den Anforderungen des Journalismus Rechnung tragen muss, müssen journalistische Erzählungen wahr, aktuell und unparteiisch sein. In diesem Zusammenhang erweisen sich Storytelling und Leadprinzip als zwei komplementäre Verfahren des journalistischen Erzählens, dessen Geschichten ausgehend von den Geschehnissen der realen Welt und den Weltbildern der jeweiligen Gesellschaften konstruiert werden. Dabei unterstützen das Storytelling die Vermittlung individueller Erfahrungen und das Leadprinzip die Erzählung zukunftsoffener Makrogeschichten

Narrative Darstellungsweisen im Journalismus: Die Kommunikationswissenschaftler Werner Früh und Felix Frey untersuchen die Wirkungen des journalistischen Storytellings

Werner Früh / Felix Frey: Narration und Storytelling. Theorie und empirische Befunde. Mit einem Beitrag von Jette Blümler. Köln: Herbert von Halem Verlag 2014 (= Unterhaltungsforschung 10). 412 S. EUR 36,00. ISBN 978-3-86962-083-

Dynamic Principal–Agent Models

This paper contributes to the theoretical and numerical analysis of discrete time dynamic principal-agent problems with continuous choice sets. We first provide a new and simplified proof for the recursive reformulation of the sequential dynamic principal-agent relationship. Next we prove the existence of a unique solution for the principal's value function, which solves the dynamic programming problem in the recursive formulation. By showing that the Bellman operator is a contraction mapping, we also obtain a convergence result for the value function iteration. To compute a solution for the problem, we have to solve a collection of static principal{agent problems at each iteration. Under the assumption that the agent's expected utility is a rational function of his action, we can transform the bi-level optimization problem into a standard nonlinear program. The final results of our solution method are numerical approximations of the policy and value functions for the dynamic principal-agent model. We illustrate our solution method by solving variations of two prominent social planning models from the economics literature