Turbulent ‘stopping plumes’ and plume pinch-off in uniform surroundings

Observations of turbulent convection in the environment are of variously sus- tained plume-like flows or intermittent thermal-like flows. At different times of the day the prevailing conditions may change and consequently the observed flow regimes may change. Understanding the link between these flows is of practical importance meteorologically, and here we focus our interest upon plume-like regimes that break up to form thermal-like regimes. It has been shown that when a plume rises from a boundary with low conductivity, such as arable land, the inability to maintain a rapid enough supply of buoyancy to the plume source can result in the turbulent base of the plume separating and rising away from the source. This plume ‘pinch-off’ marks the onset of the intermittent thermal-like behavior. The dynamics of turbulent plumes in a uniform environment are explored in order to investigate the phenomenon of plume pinch-off. The special case of a turbulent plume having its source completely removed, a ‘stopping plume’, is considered in particular. The effects of forcing a plume to pinch-off, by rapidly reducing the source buoyancy flux to zero, are shown experi- mentally. We release saline solution into a tank filled with fresh water generating downward propagating steady turbulent plumes. By rapidly closing the plume nozzle, the plumes are forced to pinch-off. The plumes are then observed to detach from the source and descend into the ambient. The unsteady buoyant region produced after pinch-off, cannot be described by the power-law behavior of either classical plumes or thermals, and so the terminology ‘stopping plume’ (analogous to a ‘starting plume’) is adopted for this type of flow. The propagation of the stopping plume is shown to be approximately linearly dependent on time, and we speculate therefore that the closure of the nozzle introduces some vorticity into the ambient, that may roll up to form a vortex ring dominating the dynamics of the base of a stopping plume

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1.

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field

Educational research, culturally distinctive epistemologies and the decline of truth

The assumptions underlying this contribution are, first, that educational research, like research in other fields, is expected to yield knowledge. This is rather uncontroversial. It is only when it comes to the definition of knowledge, the kinds of knowledge sought and to questions as to whose knowledge counts, that the debate characteristically becomes more heated. Second, and perhaps more controversially, a discussion of the nature and purposes of educational research will, at some stage, have to engage with the notion of truth. Despite having traditionally been a serious philosophical subject, the idea of truth has in recent times become rather unpopular, an idea non grata. The reconceptualisation of knowledge and the decline of truth are due in no small part to the increased popularity of certain kinds of postcolonial theory, postmodernism, constructivism and feminist thought, the rise of subaltern science and alternative epistemologies in academia. This article critically examines current trends in the theory of educational research: the case against ‘crypto-positivism’ and ‘hyperrationality’, and the trend in favour of ‘epistemological diversity’ and ‘critical constructivist epistemology’, especially against the backdrop of the decline of truth as a significant subject and yardstick that is currently exercising and restraining us, as educational researchers, philosophers and as persons

“Epistemologische Vielfalt” – Bildungstheoretische Überlegungen

Besonders in den letzten Jahren ist auf die Begriffe der epistemologischen Vielfalt und der unterschiedlichen Epistemologien zunehmend Aufmerksamkeit gelenkt worden. Kritisch betrachtet bedeutet “epistemologische Vielfalt” allerdings weder eine Vielzahl von Wahrheiten noch eine “Alles-ist-erlaubt”-Auffassung von Rechtfertigung und Wissen, sondern die an gewisse soziale und geografische Orte geknüpften unterschiedlichen Erfahrungen, bzw. die verschiedenartigen sozialen Bahnen zum Wissen. In diesem Sinne ist der Verweis auf “Epistemologien”, wie auch auf “pluralische Wissenssysteme” oder subalterne, indigene oder lokale Wissensformen, nicht nur wenig hilfreich, sondern auch irreführend. Das Versprechen einer Sozialepistemologie für das wirkliche Leben hat teilweise mit Kontext und Örtlichkeit zu tun, aber nicht im Sinne einer ausschließenden Nichteinmischungspolitik. Es ist eher anzunehmen und auch vertretbar, dass die besonderen historischen, geografischen und soziokulturellen Erfahrungen von Menschen und Gruppen zu bestimmten Prioritäten führen, die ihre epistemologische Theorie und Praxis gestalten – und dabei erkenntnistheoretische Werkzeuge hervorbringen, welche die Erkenntnistheorie im Ganzen zu bereichern in der Lage sind

Water-rock interactions: An investigation of the relationships between mineralogy and groundwater composition and flow in a subtropical basalt aquifer

A holistic study of the composition of the basalt groundwaters of the Atherton Tablelands region in Queensland, Australia was undertaken to elucidate possible mechanisms for the evolution of these very low salinity, silica- and bicarbonate-rich groundwaters. It is proposed that aluminosilicate mineral weathering is the major contributing process to the overall composition of the basalt groundwaters. The groundwaters approach equilibrium with respect to the primary minerals with increasing pH and are mostly in equilibrium with the major secondary minerals (kaolinite and smectite), and other secondary phases such as goethite, hematite, and gibbsite, which are common accessory minerals in the Atherton basalts. The mineralogy of the basalt rocks, which has been examined using X-ray diffraction and whole rock geochemistry methods, supports the proposed model for the hydrogeochemical evolution of these groundwaters: precipitation + CO 2 (atmospheric + soil) + pyroxene + feldspars + olivine yields H 4SiO 4, HCO 3 -, Mg 2+, Na +, Ca 2+ + kaolinite and smectite clays + amorphous or crystalline silica + accessory minerals (hematite, goethite, gibbsite, carbonates, zeolites, and pyrite). The variations in the mineralogical content of these basalts also provide insights into the controls on groundwater storage and movement in this aquifer system. The fresh and weathered vesicular basalts are considered to be important in terms of zones of groundwater occurrence, while the fractures in the massive basalt are important pathways for groundwater movement