Uncertainties and shortcomings of ground surface temperature histories derived from inversion of temperature logs

Analysing borehole temperature data in terms of ground surface history can add useful information to reconstructions of past climates. Therefore, a rigorous assessment of uncertainties and error sources is a necessary prerequisite for the meaningful interpretation of such ground surface temperature histories. This study analyses the most prominent sources of uncertainty. The diffusive nature of the process makes the inversion relatively robust against incomplete knowledge of the thermal diffusivity. Similarly the influence of heat production is small. It turns out that for investigations of the last 1000 to 100000 years the maximum depth of the temperature log is crucial. More than 3000 m are required for an optimal inversion. Reconstructions of the last one or two millennia require only modestly deep logs (>300 m) but suffer severely from noisy data.Comment: 28 pages, 18 figure, 3 table

The Dependence of Star Formation Efficiency on Gas Surface Density

Studies by Lada (2010) and Heiderman (2010) have suggested that star formation mostly occurs above a threshold in gas surface density Sigma of Sigma_c = 120 Msun pc^{-2} (A_K = 0.8). Heiderman infer a threshold by combining low-mass star-forming regions, which show a steep increase in the star formation rate per unit area Sigma_SFR with increasing Sigma, and massive cores forming luminous stars which show a linear relation. We argue that these observations do not require a particular density threshold. The steep dependence of Sigma_SFR, approaching unity at protostellar core densities, is a natural result of the increasing importance of self-gravity at high densities along with the corresponding decrease in evolutionary timescales. The linear behavior of Sigma_SFR vs. Sigma in massive cores is consistent with probing dense gas in gravitational collapse, forming stars at a characteristic free-fall timescale given by the use of a particular molecular tracer. The low-mass and high-mass regions show different correlations between gas surface density and the area A spanned at that density, with A=Sigma^{-3} for low-mass regions and A=Sigma^{-1} for the massive cores; this difference, along with the use of differing techniques to measure gas surface density and star formation, suggests that connecting the low-mass regions with massive cores is problematic. We show that the approximately linear relationship between dense gas mass and stellar mass used by Lada similarly does not demand a particular threshold for star formation, and requires continuing formation of dense gas. Our results are consistent with molecular clouds forming by galactic hydrodynamic flows with subsequent gravitational collapse.Comment: 15 pages, 11 figures, ApJ, in pres

Tourette Syndrome Research Highlights from 2017 [version 1; referees: 3 approved]

This is the fourth yearly article in the Tourette Syndrome Research Highlights series, summarizing research from 2017 relevant to Tourette syndrome and other tic disorders. The authors briefly summarize reports they consider most important or interesting. The highlights from 2018 article is being drafted on the Authorea online authoring platform, and readers are encouraged to add references or give feedback on our selections using the comments feature on that page. After the calendar year ends, the article is submitted as the annual update for the Tics collection on F1000Research

Promoting learner autonomy through multiliteracy skills development in cross-institutional exchanges

This contribution presents findings from two empirical case studies, which followed a task-based telecollaborative learning format. Participants included student teacher trainees, tutors, and language learners from colleges/universities in Germany, Poland, the United Kingdom, and the United States. The projects aimed at promoting learner autonomy through awareness raising of modes and meaning-making online and multiliteracy skills development based on hands-on analysis of web resources and social networking tools. It was hoped that this awareness would foster the teachers' own autonomy in virtual learning environments and enable them to design tasks which—in turn—would promote learner autonomy as understood by Palfreyman (2006): the informed use of a range of interacting resources in context. We argue that this awareness is reflected in enhanced multimodal communicative competence, i.e., “the ability to understand the combined potential of various modes for making meaning” (Royce, 2002, p. 92), and multiliteracy, with the latter allowing teachers and learners to realize the potential of blended and online only settings for language acquisition purposes. Ideally then, while becoming gradually more versed in multimodality and multiliteracy, learners can also take over more control and self-direct their own learning when working online (Benson, 2001) which are also characteristics of autonomy