Laboratory studies of ice-particle collisions in Saturn's dense rings

In this work, we report on microgravity studies of particle ensembles simulating ice-particle collisions in Saturn's dense main rings. We have developed an experimental method to study the energy dissipation in a many-body system consisting of approx. one hundred cm-sized glass spheres. The temporal development of the mean particle velocity, ranging from ~10 cm/s (at the beginning) to ~0.35 cm/s (after 9s of experiment duration), can be explained by a constant coefficient of restitution of 0.64. A comparison to values obtained for pure water-ice bodies shows that future cryogenic ice-collision experiments can achieve collision velocities of ~0.1 cm/s, and thus will very well simulate the conditions in Saturn's main rings.Comment: Accepted by "Proc. Powders and Grains 2009", Publisher AI

Microgravity experiments on the collisional behavior of Saturnian ring particles

In this paper we present results of two novel experimental methods to investigate the collisional behavior of individual macroscopic icy bodies. The experiments reported here were conducted in the microgravity environments of parabolic flights and the Bremen drop tower facility. Using a cryogenic parabolic-flight setup, we were able to capture 41 near-central collisions of 1.5-cm-sized ice spheres at relative velocities between 6 and $22 \mathrm{cm s^{-1}}$. The analysis of the image sequences provides a uniform distribution of coefficients of restitution with a mean value of $\overline{\varepsilon} = 0.45$ and values ranging from $\varepsilon = 0.06$ to 0.84. Additionally, we designed a prototype drop tower experiment for collisions within an ensemble of up to one hundred cm-sized projectiles and performed the first experiments with solid glass beads. We were able to statistically analyze the development of the kinetic energy of the entire system, which can be well explained by assuming a granular `fluid' following Haff's law with a constant coefficient of restitution of $\varepsilon = 0.64$. We could also show that the setup is suitable for studying collisions at velocities of $< 5 \mathrm{mm s^{-1}}$ appropriate for collisions between particles in Saturn's dense main rings.Comment: Accepted for publication in the Icarus Special Issue "Cassini at Saturn

Agenda-setting effects during times of social disruption: the influence of mass media and personal experiences on societal concerns

Using an 8-wave panel survey of German citizens, the present study investigates the media’s agenda-setting power in the context of the disruptive coronavirus pandemic. By examining how societal concerns are influenced by mass media and personal experiences, this study shows differences regarding the health, political, and economic dimensions of the crisis. Only health-related societal concerns were influenced by the perceived issue salience in the media. Societal concerns regarding the economy were shaped by individuals’ evaluation of the adequacy of the perceived issue salience in the media and thus not by the media agenda per se. In contrast, societal concerns regarding restrictions on fundamental rights were strongly influenced by people’s personal experiences. Variations in the role of mass media and personal experiences over the course of the pandemic can be traced back to changes in the severity of the crisis and its different phases

Nichts wird meine Welt verändern - oder helfen journalistische Richtigstellungen gegen Gerüchte?

In the current digitalized media landscape, communicators and recipients are struggling to produce and identify reliable information in order to cope with rumors, misconceptions, and fake news. In the face of this, the popularity and relevance of factchecking services have increased in recent years. Nevertheless, not much is known about the effectiveness of these journalistic entities. This study proposes a theoretical framework that systemizes possible influencing factors. An online survey of 607 German media users was conducted, measuring the effectiveness of several clarifications in adjusting recipients’ misperceptions about six current controversial issues in Germany. The results indicate that journalistic clarifications are in fact capable of causing an adjustment process. Regression analyses show that, contrary to expectations, the users’ attitudes that go against the message of the clarification had only a small effect on the adjustment process. Media reliance had positive effects on only one issue, as well, and cognitive mobilization on two issues. A positive evaluation of the quality of the clarification showed effects in four cases, but not always as expected. Evaluations of the credibility of the communicator delivered no effects.In der heutigen digitalisierten Medienwelt ist es sowohl für Kommunikatoren als auch für Rezipienten schwierig, die Verlässlichkeit von Informationen zu beurteilen sowie Gerüchte und Falschmeldungen zu identifizieren. Vor diesem Hintergrund hat die journalistische Faktenprüfung in den letzten Jahren an Relevanz gewonnen und zahlreiche Redaktionen, die sich auf diese Aufgabe spezialisierten haben, wurden eingerichtet. Bislang ist aber wenig darüber bekannt, wie erfolgreich deren Arbeit ist und unter welchen Bedingungen es gelingt, durch Falschmeldungen hervorgerufene Fehlvorstellungen der Rezipienten zu korrigieren. In dem vorliegenden Beitrag wurde daher ein Modell entwickelt, das die möglichen Einflussfaktoren systematisiert. Es wurde eine Online-Umfrage unter 607 deutschen Mediennutzern durchgeführt, in der die Wirksamkeit einer Reihe von Richtigstellungen gemessen wurde. Die Ergebnisse zeigen, dass journalistische Richtigstellungen tatsächlich die Korrektur falscher Vorstellungen bewirken können. Anders als erwartet, haben aber weder eine dissonante Einstellung der Rezipienten zur Botschaft der Richtigstellung noch die Glaubwürdigkeit des Kommunikators oder die habitualisierte Nutzung der Informationsquelle einen nennenswerten Effekt auf die Wirksamkeit der Richtigstellungen. Hingegen erweisen sich die kognitive Mobilisierung der Rezipienten und vor allem die wahrgenommene Qualität der Richtigstellungen als Faktoren, die die Wirksamkeit der Richtigstellungen tendenziell begünstigten