Planetesimal formation by sweep-up: How the bouncing barrier can be beneficial to growth

The formation of planetesimals is often accredited to collisional sticking of dust grains. The exact process is unknown, as collisions between larger aggregates tend to lead to fragmentation or bouncing rather than sticking. Recent laboratory experiments have however made great progress in the understanding and mapping of the complex physics involved in dust collisions. We want to study the possibility of planetesimal formation using the results from the latest laboratory experiments, particularly by including the fragmentation with mass transfer effect, which might lead to growth even at high impact velocities. We present a new experimentally and physically motivated dust collision model capable of predicting the outcome of a collision between two particles of arbitrary masses and velocities. It is used together with a continuum dust-size evolution code that is both fast in terms of execution time and able to resolve the dust well at all sizes, allowing for all types of interactions to be studied without biases. We find that for the general dust population, bouncing collisions prevent the growth above millimeter-sizes. However, if a small number of cm-sized particles are introduced, for example due to vertical mixing or radial drift, they can act as a catalyst and start to sweep up the smaller particles. At a distance of 3 AU, 100-meter-sized bodies are formed on a timescale of 1 Myr. We conclude that direct growth of planetesimals might be a possibility thanks to a combination of the existence of a bouncing barrier and the fragmentation with mass transfer effect. The bouncing barrier is here even beneficial, as it prevents the growth of too many large particles that would otherwise only fragment among each other, and creates a reservoir of small particles that can be swept up by larger bodies. However, for this process to work, a few seeds of cm in size or larger have to be introduced.Comment: 17 pages, 13 figures. Accepted for publication in Astronomy and Astrophysic

Effects of short- and long-term unemployment on health satisfaction: evidence from German data

The purpose of this study is to analyse the effects of short- and long-term unemployment on health satisfaction. The data source used for the analysis is the German Socio-Economic Panel (GSOEP) which, given its longitudinal structure, allows one to better overcome the problem of endogeneity. Three different models are used in order to assess the effect of short and long-term unemployment and reemployment on health satisfaction. The results show that short-term unemployment has only a significant (and negative) effect for men, while for women short-term unemployment does not have a significant effect on health satisfaction. Being unemployed for a long period has a significant and negative effect for both men and women. Finally, it can be also concluded from the empirical analysis that reemployment has a significant and positive effect on health satisfaction for both unemployed men and women, independent of how long individuals have been unemployed.

Explaining Income Nonresponse – A Case Study by means of the British Household Panel Study (BHPS)

interviewer effects, item-nonresponse, multilevel modeling, panel analysis, respondent behavior, C81,

Das Sozio-oekonomische Panel (SOEP): Multidisziplinäres Haushaltspanel und Kohortenstudie für Deutschland – Eine Einführung (für neue Datennutzer) mit einem Ausblick (für erfahrene Anwender)

SOEP, Biographische Erhebung, Haushaltspanel, Paneldesign, Kohortenstudie, Lebensverlauf, Stichprobenziehung, Hochrechnung, Datenstruktur, Service, SOEP, Biographical survey, Household panel, Panel design, Cohort study, Life course, Life span, Sampling procedure, Weighting, Data structure, Service,