Transient Turbulence in Taylor-Couette Flow

Recent studies have brought into question the view that at sufficiently high Reynolds number turbulence is an asymptotic state. We present the first direct observation of the decay of turbulent states in Taylor-Couette flow with lifetimes spanning five orders of magnitude. We also show that there is a regime where Taylor-Couette flow shares many of the decay characteristics observed in other shear flows, including Poisson statistics and the coexistence of laminar and turbulent patches. Our data suggest that characteristic decay times increase super-exponentially with increasing Reynolds number but remain bounded in agreement with the most recent data from pipe flow and with a recent theoretical model. This suggests that, contrary to the prevailing view, turbulence in linearly stable shear flows may be generically transient.Comment: 4 pages, 4 figures v2: Addressed referee comments for PRE. Made some cosmetic changes. Added inset to Fig.

Archaeological dating of colluvial and lacustrine deposits in a GIS environment investigating the multi-period site Gortz 1 on Oberer Beetzsee, Brandenburg

From the mid-14th century CE onwards, extensive soil erosion, caused by intensive agricultural practices, has led to the destruction of landscape structures in Central Europe. In 2016, the University of Applied Sciences in Berlin investigated the colluvial deposits at the site of Gortz in western Brandenburg (Germany), which had accumulated on the lower slopes and were caused by the processes just mentioned. The mapping of each individual archaeological find made it possible to project all finds onto one profile running along the slope. Transformation of the finds' coordinates from profile view to plan view enabled the visualization in a Geographical Information System (GIS). The combination of adjacent strata into larger units using a pedological and sedimentological approach enabled an improved dating of colluvial deposits. In addition, the method facilitated the dating of historical water levels in the Beetzsee chain of lakes, which are part of the Havel river system. As a result, it could be demonstrated that substantial anthropogenic activity, such as clay quarrying and bank straightening, took place during the Late Slavic Period. An interlocking horizon of colluvial and lacustrine deposits indicates that the water level of the lake Oberer Beetzsee rose from a value under 29.4 m above sea level (a.s.l.) in the 11th/12th century CE to approximately 29.8 m a.s.l. in the 13th century CE. However, isolated flooding events during the 13th century CE can be recorded up to a height of 30.5 m a.s.l. A modern colluvial deposit of 1 m in thickness indicates an acute endangerment of the archaeological site by modern agriculture.Flächenhafte Bodenerosion, ausgelöst durch intensive landwirtschaftliche Nutzung, führte ab Mitte des 14. Jahrhunderts u.Z. zur Zerstörung von Landschaftsstrukturen und in Mitteleuropa. Kolluvien, welche durch diese Prozesse entstanden und am Unterhang akkumulierten, wurden auf dem Fundplatz Gortz (westliches Brandenburg, Deutschland) durch die Hochschule für Technik und Wirtschaft Berlin im Jahr 2016 untersucht. Konsequente Einzelfundeinmessung ermöglichte die Projizierung aller Funde auf eines der längs zum Hang verlaufenden Profile. Koordinatentransformation der Funde von der Profilansicht in die Draufsicht, ermöglichte die Visualisierung in einem GIS. Die Zusammenfassung benachbarter Schichten auf Basis der bodenkundlich-sedimentologischen Ansprache ermöglichte eine verbesserte Datierung der Kolluvien. Zusätzlich ermöglichte diese Methode die Datierung historischer Pegelstände der Beetzseekette, eines Teils des Flusssystems der Havel. Im Ergebnis ließen sich für die spätslawische Zeit starke anthropogene Aktivitäten wie Mergelabbau und eine Uferbegradigung nachweisen. Über einen Verzahnungshorizont limnischer und kolluvialer Sedimente. ließ sich ein Pegelanstieg des Oberen Beetzsees von einem Wert unterhalb von 29.4 m Normalhöhennull (NHN) im 11./12. Jahrhundert u.Z. auf etwa 29.8 m NHN im 13. Jahrhundert u.Z. feststellen. Es lassen sich für das 13. Jahrhundert u.Z. jedoch auch vereinzelte Überschwemmungsereignisse bis in eine Höhe von 30.5 m NHN fassen. Ein modernes Kolluvium von einem Meter Mächtigkeit zeigt die akute Gefährdung des Bodendenkmals durch die moderne Landwirtschaft

Improving Quality: Current Evidence on What Affects the Quality of Commissioned Evaluations

With the increase in resources that organisations are dedicating to evaluation the issue of evaluation quality has risen up the agenda and a growing number of commissioners are now looking at how to ensure the studies they commission are of sufficient quality. While a plethora of evaluation quality standards exist that identify the factors that shape quality, most are experiential rather than based on research evidence. Particularly in the context of commissioning and implementing evaluation in bilateral donors, there has been limited empirical research on identifying the factors that underlie evaluation quality. Drawing on the findings of two recent studies into the quality of evaluations and other recent work in this area, this CDI Practice Paper by Rob Lloyd and Florian Schatz starts to fill this gap in evidence. The paper argues that the current debate on evaluation quality has become fixated on the issue of methodology to the neglect of other equally important issues. While methodological rigour is important, a singular focus on this issue is unwise. Considerations of quality need to permeate all stages of the evaluation process and evaluation quality needs to be recognised as a product of the capacities of the evaluation commissioner and evaluation team, the relationship between them, and the wider institutional environment in which the evaluation is being conducted.UK Department for International Developmen