The fate of sandstone during impact cratering: shock compaction, cataclastic flow, and granular fluidization

Impact of solid bodies is the most fundamental of all processes that have taken place on the terrestrial planets in our Solar system (Shoemaker 1977). On Earth, impact cratering was the dominant geologic process during the period of the early heavy bombardment until 3.8Ga. A constant asteroid impact flux exists since that time. Although deformation of the crust by meteorite impacts is now subordinate with respect to tectonics, it represents an important, but often underestimated fraction of the bulk crustal deformation. Short-term deformation during hypervelocity impact events differs in many respects from standard tectonics: Unique conditions exist at pressures above the so-called Hugoniot elastic limit (HEL) of a particular mineral or rock. This state of compression is reached in a shock wave that propagates from the point of impact. Shock waves travel at supersonic velocity, heat and irreversibly deform the rock, and cause a residual motion of the material they have passed, which ultimately leads to the formation of parabolically shaped crater cavity of much larger extent than the projectile diameter. At pressure above the HEL minerals are subjected to shock metamorphism...conferenc

Structural record of an oblique impact: the central uplift of the Upheaval Dome impact structure, Utah, USA

Most asteroids strike their target at an oblique angle (Pierazzo & Melosh 2000). The common criterion for identifying craters formed by an oblique impact is the pattern of the ejecta blanket. On Earth, however, ejecta blankets are rarely preserved and morphological, structural, geophysical as well as depositional criteria were used to infer an oblique impact (e.g. for Chicxulub, Schultz & D’Hondt 1996, Ries- Steinheim, Stöffler et al. 2003, Mjölnir & Tsikalas 2005). However, the significance of such criteria in predicting impact angle or direction is a matter of debate (c.f. Schultz & Anderson, 1996, Ekholm & Melosh 2001). Particularly, it is not yet known whether there is an influence of the impact angle on the displacement field during the collapse of large transient cavities, and thus, the final crater. For most impact angles, the shape of the final crater is controlled by its size. At a critical diameter (ca. 2–5 km on Earth), simple bowl shaped craters are getting gravitationally unstable and collapse to form complex craters, with a flat floor and a terraced rim (Melosh 1989). During collapse, the crater floor rises to form a central uplift, that may or may not be visible as a central peak, or, when the peak in turn collapses, as a peak ring at yet larger diameters.conferenc

Older care-home residents as collaborators or advisors in research: a systematic review

Background: patient and public involvement (PPI) in research can enhance its relevance. Older care-home residents are often not involved in research processes even when studies are care-home focused. Objective: to conduct a systematic review to find out to what extent and how older care-home residents have been involved in research as collaborators or advisors. Methods: a systematic literature search of 12 databases, covering the period from 1990-September 2014 was conducted. A lateral search was also carried out. Standardised inclusion criteria were used and checked independently by two researchers. Results: 19 reports and papers were identified relating to 11 different studies. Care-home residents had been involved in the research process in multiple ways. Two key themes were identified: (i) the differences in residents’ involvement in small-scale and large-scale studies, (ii) the barriers to and facilitators of involvement. Conclusions: small-scale studies involved residents as collaborators in participatory action research, whereas larger studies involved residents as consultants in advisory roles. There are multiple facilitators of and barriers to involving residents as PPI members. The reporting of PPI varies. While it is difficult to evaluate the impact of involving care-home residents on the research outcomes, impact has been demonstrated from more inclusive research processes with care-home residents. The review shows that older care-home residents can be successfully involved in the research process

Lasteaiaõpetajaks õppivate üliõpilaste erialased õigusalased teadmised

https://www.ester.ee/record=b5508226*es

Long-term erosion rates as a function of climate derived from the impact crater inventory

Worldwide erosion rates seem to have increased strongly since the beginning of the Quaternary, but there is still discussion about the role of glaciation as a potential driver and even whether the increase is real at all or an artifact due to losses in the long-term sedimentary record. In this study we derive estimates of average erosion rates on the timescale of some tens of millions of years from the terrestrial impact crater inventory. This approach is completely independent from all other methods to infer erosion rates such as river loads, preserved sediments, cosmogenic nuclides, and thermochronometry. Our approach yields average erosion rates as a function of present-day topography and climate. The results confirm that topography accounts for the main part of the huge variation in erosion on Earth, but also identifies a significant systematic dependence on climate in contrast to several previous studies. We found a 5-fold increase in erosional efficacy from the cold regimes to the tropical zone and that temperate and arid climates are very similar in this context. Combining our results into a worldwide mean erosion rate, we found that erosion rates on the timescale of some tens of millions of years are at least as high as present-day rates and suggest that glaciation has a rather regional effect with a limited impact at the continental scale.</p

Frühe Zeugnisse über den Holocaust: die Befragungen von Kindern in Polen nach der Befreiung von der deutschen Herrschaft

Über die Interviewprotokolle wird die kindliche Erinnerung festgehalten und der älteren Generation übermittelt. Die Dynamik des Vernichtungsprozesses wird auf diese Weise aus der Perspektive des Kindes festgehalten. Ein Hauptziel der Interviewer war es, neben der faktischen Überlebensgeschichte vor allem die Ausgestaltung des Alltags im Überleben sowie die Erfahrungen und die Gefühle der Kinder zum Ausdruck zu bringen. Es ging weniger um die präzise detailgetreue Rekonstruktion der einzelnen Überlebensgeschichten als vielmehr um die Frage, wie die Kinder die Verfolgung wahrgenommen hatten, wie sie reagiert und was sie empfunden hatten. Im Zentrum der Befragungen standen individuelle Erlebnisse, subjektive Wahrnehmungen und Gefühle. Diese Binnenperspektive findet sich in den Protokollen wieder. Sie stellen dadurch dichte Quellen dar, die einen alltags- und erfahrungsgeschichtlichen Zugang zu den nationalsozialistischen Verbrechen ermöglichen. Sie lassen die Schwächsten unter den Verfolgten sichtbar werden. Indem sie auf Befragungen zurückgehen, gehören die Gesprächsprotokolle in methodischer Hinsicht zur Geschichtsschreibung durch mündliche Überlieferung. Das Unterfangen der Zentralen Jüdischen Historischen Kommission, Holocaust-Überlebende in großer Anzahl zu befragen, ist ein sehr frühes und ambitioniertes Vorhaben der Oral History. Es gab schon in unmittelbarer Nachkriegszeit den Kindern unter den Verfolgten eine Stimme, die ansonsten kaum wahrzunehmen gewesen wäre. Die Befragungen wurden nicht aufgezeichnet und anschließend transkribiert, wie in anderen Interviews mit Holocaust-Überlebenden auch damals mancherorts schon verfahren wurde und wie es heute in lebensgeschichtlichen Interviews Standard ist. Ihr Inhalt wurde von einer dritten Person zusammengefasst und schriftlich festgehalten. Gerade wenn Gesprächsprotokolle in der Ich-Form abgefasst, aber tatsächlich von einem Interviewer niedergeschrieben wurden, ist dieser Entstehungsprozess nicht zu vergessen. Bei den Interviewprotokollen handelt es sich um schriftliche Quellen zeitgeschichtlicher Vergangenheit, die auf einer mündlichen Befragung beruhten und diese in hohem Maße integrierten. (ICF2

Dynamic Compressive Strength and Fragmentation in Felsic Crystalline Rocks

Brittle deformation in rocks depends upon loading rate; with increasing rates, typically greater than ~102 s‐1, rocks become significantly stronger and undergo increasingly severe fragmentation. Dynamic conditions required for rate‐dependent brittle failure may be reached during impact events, seismogenic rupture, and landslides. Material characteristics and fragment characterization of specific geomaterials from dynamic loading are only approximately known. Here we determine the characteristic strain rate for dynamic behavior in felsic crystalline rocks, including anisotropy, and describe the resulting fragments. Regardless of the type of felsic crystalline rock or anisotropy, the characteristic strain rate is the same within uncertainties for all tested materials, with an average value of 229 ± 81 s‐1. Despite the lack of variation of the critical strain rate with lithology, we find that the degree of fragmentation as a function of strain rate varies depending on material. Scaled or not, the fragmentation results are inconsistent with current theoretical models of fragmentation. Additionally, we demonstrate that conditions during impact cratering, where the impactor diameter is less than ~100 m, are analogous to the experiments carried out here, and therefore that dynamic strengthening and compressive fragmentation should be considered as important processes during impact cratering

The complex impact structure Serra da Cangalha, Tocantins State, Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Serra da Cangalha is a complex impact structure with a crater diameter of 13,700 m and a central uplift diameter of 5800 m. New findings of shatter cones, planar fractures, feather features, and possible planar deformation features are presented. Several ring-like features that are visible on remote sensing imagery are caused by selective erosion of tilted strata. The target at Serra da Cangalha is composed of Devonian to Permian sedimentary rocks, mainly sandstones that are interlayered with siltstone and claystones. NNE-SSW and WNW-ESE-striking joint sets were present prior to the impact and also overprinted the structure after its formation. As preferred zones of weakness, these joint sets partly controlled the shape of the outer perimeter of the structure and, in particular, affected the deformation within the central uplift. Joints in radial orientation to the impact center did not undergo a change in orientation during tilting of strata when the central uplift was formed. These planes were used as major displacement zones. The asymmetry of the central uplift, with preferred overturning of strata in the northern to western sector, may suggest a moderately oblique impact from a southerly direction. Buckle folding of tilted strata, as well as strata overturning, indicates that the central uplift became gravitationally unstable at the end of crater formation.466875889German Research Foundation (DFG) [Re 528/9-1, Re 528/11-1]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Ph.D. grantGerman Academic Exchange Service (DAAD)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)German Research Foundation (DFG) [Re 528/9-1, Re 528/11-1]FAPESP [2008/53588-7]CNPq [30334/2009-0