Dynamics of a turbulent buoyant plume in a stratified fluid : an idealized model of subglacial discharge in Greenland fjords

Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 2611-2630, doi:10.1175/JPO-D-16-0259.1.This study reports the results of large-eddy simulations of an axisymmetric turbulent buoyant plume in a stratified fluid. The configuration used is an idealized model of the plume generated by a subglacial discharge at the base of a tidewater glacier with an ambient stratification typical of Greenland fjords. The plume is discharged from a round source of various diameters and characteristic stratifications for summer and winter are considered. The classical theory for the integral parameters of a turbulent plume in a homogeneous fluid gives accurate predictions in the weakly stratified lower layer up to the pycnocline, and the plume dynamics are not sensitive to changes in the source diameter. In winter, when the stratification is similar to an idealized two-layer case, turbulent entrainment and generation of internal waves by the plume top are in agreement with the theoretical and numerical results obtained for turbulent jets in a two-layer stratification. In summer, instead, the stratification is more complex and turbulent entrainment by the plume top is significantly reduced. The subsurface layer in summer is characterized by a strong density gradient and the oscillating plume generates internal waves that might serve as an indicator of submerged plumes not penetrating to the surface.This work was supported by Linné FLOW Centre at KTH and the Academy of Finland Centre of Excellence program (Grant 307331) (E. E.) and VR Swedish Research Council, Outstanding Young Researcher Award, Grant VR 2014-5001 (L. B.). Support to C. C. was given by the NSF Project OCE-1434041.2018-04-2

Dynamics of three-dimensional turbulent wall plumes and implications for estimates of submarine glacier melting

Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018):1941-1950, doi:10.1175/JPO-D-17-0194.1.Subglacial discharges have been observed to generate buoyant plumes along the ice face of Greenland tidewater glaciers. These plumes have been traditionally modeled using classical plume theory, and their characteristic parameters (e.g., velocity) are employed in the widely used three-equation melt parameterization. However, the applicability of plume theory for three-dimensional turbulent wall plumes is questionable because of the complex near-wall plume dynamics. In this study, corrections to the classical plume theory are introduced to account for the presence of a wall. In particular, the drag and entrainment coefficients are quantified for a three-dimensional turbulent wall plume using data from direct numerical simulations. The drag coefficient is found to be an order of magnitude larger than that for a boundary layer flow over a flat plate at a similar Reynolds number. This result suggests a significant increase in the melting estimates by the current parameterization. However, the volume flux in a wall plume is found to be one-half that of a conical plume that has 2 times the buoyancy flux. This finding suggests that the total entrainment (per unit area) of ambient water is the same and that the plume scalar characteristics (i.e., temperature and salinity) can be predicted reasonably well using classical plume theory.This work was supported by the Linné FLOW Centre at KTH and the Academy of Finland Center of Excellence Programme Grant 307331 (author Ezhova) and by VR Swedish Research Council GrantVR2014-5001 (author Brandt). Support to author Cenedese was given by NSF Project OCE-1434041.2019-02-2

Interaction between a vertical turbulent jet and a thermocline

Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 3415-3427, doi:10.1175/JPO-D-16-0035.1.The behavior of an axisymmetric vertical turbulent jet in an unconfined stratified environment is studied by means of well-resolved, large-eddy simulations. The stratification is two uniform layers separated by a thermocline. This study considers two cases: when the thermocline thickness is small and on the order of the jet diameter at the thermocline entrance. The Froude number of the jet at the thermocline varies from 0.6 to 1.9, corresponding to the class of weak fountains. The mean jet penetration, stratified turbulent entrainment, jet oscillations, and the generation of internal waves are examined. The mean jet penetration is predicted well by a simple model based on the conservation of the source energy in the thermocline. The entrainment coefficient for the thin thermocline is consistent with the theoretical model for a two-layer stratification with a sharp interface, while for the thick thermocline entrainment is larger at low Froude numbers. The data reveal the presence of a secondary horizontal flow in the upper part of the thick thermocline, resulting in the entrainment of fluid from the thermocline rather than from the upper stratification layer. The spectra of the jet oscillations in the thermocline display two peaks, at the same frequencies for both stratifications at fixed Froude number. For the thick thermocline, internal waves are generated only at the lower frequency, since the higher peak exceeds the maximal buoyancy frequency. For the thin thermocline, conversely, the spectra of the internal waves show the two peaks at low Froude numbers, whereas only one peak at the lower frequency is observed at higher Froude numbers.This work was supported by the Linné FLOW Centre at KTH (E. E.), the European Research Council Grant ERC-2013-CoG-616186, TRITOS (L. B.), and the Swedish Research Council (VR), Outstanding Young Researcher Award (L. B.). Support to C. C. was given by the NSF Project OCE-1434041.2017-05-1

Imaging markers of disability in aquaporin-4 immunoglobulin G seropositive neuromyelitis optica: a graph theory study

Neuromyelitis optica spectrum disorders lack imaging biomarkers associated with disease course and supporting prognosis. This complex and heterogeneous set of disorders affects many regions of the central nervous system, including the spinal cord and visual pathway. Here, we use graph theory-based multimodal network analysis to investigate hypothesis-free mixed networks and associations between clinical disease with neuroimaging markers in 40 aquaporin-4-immunoglobulin G antibody seropositive patients (age = 48.16 ± 14.3 years, female:male = 36:4) and 31 healthy controls (age = 45.92 ± 13.3 years, female:male = 24:7). Magnetic resonance imaging measures included total brain and deep grey matter volumes, cortical thickness and spinal cord atrophy. Optical coherence tomography measures of the retina and clinical measures comprised of clinical attack types and expanded disability status scale were also utilized. For multimodal network analysis, all measures were introduced as nodes and tested for directed connectivity from clinical attack types and disease duration to systematic imaging and clinical disability measures. Analysis of variance, with group interactions, gave weights and significance for each nodal association (hyperedges). Connectivity matrices from 80% and 95% F-distribution networks were analyzed and revealed the number of combined attack types and disease duration as the most connected nodes, directly affecting changes in several regions of the central nervous system. Subsequent multivariable regression models, including interaction effects with clinical parameters, identified associations between decreased nucleus accumbens (β = −0.85, P = 0.021) and caudate nucleus (β = −0.61, P = 0.011) volumes with higher combined attack type count and longer disease duration, respectively. We also confirmed previously reported associations between spinal cord atrophy with increased number of clinical myelitis attacks. Age was the most important factor associated with normalized brain volume, pallidum volume, cortical thickness and the expanded disability status scale score. The identified imaging biomarker candidates warrant further investigation in larger-scale studies. Graph theory-based multimodal networks allow for connectivity and interaction analysis, where this method may be applied in other complex heterogeneous disease investigations with different outcome measures

The effects of phrasing on the answer likelihood in multiple choice based examinations : a case study in microbiology

Multiple choice (MC)-Klausuren sind im deutschen Medizinstudium trotz weitgehend fehlender Daten zur Validität dieser Prüfungsform zur Regelprüfung geworden. Darüber hinaus ist unklar, in welchem Ausmaß die Studierenden - auch solche mit guten Prüfungsergebnissen - den geprüften Lernstoff tatsächlich beherrschen. Am Fachbereich Medizin der Johann-Wolfgang-Goethe-Universität Frankfurt wurde am Ende des SS 2003 im Fach Mikrobiologie für die Studierenden des 2. klinischen Semesters eine MC-basierte Abschlussprüfung geschrieben. Die Studierenden des 1. klinischen Semesters hatten - bedingt durch Umstellungen des Curriculums - eine identische Ausbildung. Diese wurde durch eine inhaltlich weitgehend identische, im Format aber andere Klausur abgeschlossen, in der sowohl offene Fragen enthalten waren als auch Fragen, bei denen die Studierenden jede Aussage einzeln auf Korrektheit bewerten mussten. Der Vergleich der Ergebnisse für inhaltlich gleiche Fragen zeigt, dass die Studierenden im MC-Format eine hohe Quote richtiger Antworten erzielen, diese jedoch durch ein geändertes Fragenformat stark reduziert wird. So erreichten nur 20 - 30% der Studierenden ein vollständig richtiges Ergebnis, wenn jede Aussage einzeln bewertet werden musste, während die inhaltlich gleiche Frage im MC-Format 80 - 90% richtige Ergebnisse erzielte. In freien Fragen konnten nur 30 - 40% der Studierenden die richtige Antwort aktiv niederschreiben, während 90 -99% der Studierenden die richtige Lösung passiv erkannten. Wir interpretieren diese Ergebnisse dahin, dass der Entscheidungszwang in MC-basierten Fragen einen starken Einfluss auf die Quote richtiger Antworten hat, und die Prüfungsergebnisse damit wesentlich durch das Format beeinflusst werden, das Wissen dagegen nicht beherrscht wird. Die Ergebnisse dieser Studie legen nahe, Sorgfalt bei der Auswahl des Prüfungsverfahrens walten zu lassen und der Steuerung des studentischen Lernverhaltens durch das Prüfungsformat wesentlich mehr Aufmerksamkeit zu widmen als bisher.Multiple choice(MC) questions have become the mainstay medical examinations in Germany, although there are currently few data available to show their validity. It also remains unclear, whether or not students master the knowledge tested, even those students with good test results. Students of the second clinical semester at the Medical Faculty of the Johann Wolfgang Goethe-University in Frankfurt have written an MC-based examination in microbiology. Due to changes in their curriculum students of the first clinical semester took the identical class in microbiology. This class was concluded by an examination identical in content, however in a different format including open questions as well as questions consisting of statements that had to be judged individually whether or not they are true. A comparison of test results between these two groups showed that only 20 - 30% of the students were able to correctly assess five statements, whereas the identical question presented in MC-format yielded 80 - 90% correct answers. For open questions only 30 - 40% of the students were able to actively answer the question correctly whereas 90 - 99% of the students passively recognized the correct answer. These results indicate that the need to choose one among five options as it is inherent for MC-based questions has a strong influence on the ratio of correct answers, and examination results are strongly depended upon the format of the test, while the knowledge presumed to be tested is not necessarily available. Our results suggest that care should be taken when selecting the mode of an examination. Moreover, the faculty should be more aware of the impact of the test format on the students learning behaviour

What skills do agricultural professionals need in the transition towards a sustainable agriculture? A qualitative literature review

Agriculture is facing mounting challenges across the globe and must move towards more sustainable practices to combat climate change and meet changed production requirements. Education has been acknowledged as highly important in a sustainable transition, but there is no clear agreement about what skills are needed for professionals in the agricultural system. The purpose of this paper is to identify and analyse skills needed for professionals in the agricultural system to engage in the transition towards sustainable agriculture and elaborate on the implications of this for a transition towards sustainable agriculture. The review is based on a qualitative semi-systematic literature review of 20 peer-reviewed articles concerned with sustainability, skills, and agriculture. Five categories of skills were identified and analysed, including systems perspective, lifelong learning, knowledge integration, building and maintaining networks and learning communities, and technical and subject-specific knowledge and technology. As the identified categories of skills have emerged from different contextual settings and a diverse group of actors, these five categories encourage a broad and inclusive understanding of skills that can be translated into different contextual settings, scales, and professions within the agricultural system. The article concludes that professionals engaged in the transition towards sustainable agriculture need skills that encourage a perspective that moves beyond generic discipline-based skills and instead builds on heterogeneity, inclusion, and use of different actors’ knowledge, practices, and experiences, and the ability to respond and be proactive in a constantly changing world

Übertragung von Kontaminationen durch Umluftbetrieb sowie Leckagen in zentralen und dezentralen Lüftungsanlagen

Durch den Einsatz von Raumlufttechnischen (RLT) Anlagen lassen sich Schadstoffkonzentrationen in Räumen effektiv reduzieren. Dies gilt grundsätzlich auch für die Konzentration von luftgetragenen Krankheitserregern. Es existieren Anlagentypen, die aufgrund ihrer Konfiguration ein Risikopotential bieten. Hierbei kann kontaminierte Abluft über die RLT-Anlage in nicht kontaminierte Bereiche verteilt werden. In dieser Studie wurde betrachtet, wie hoch die Übertragung derartiger Kontaminationen durch den Umluftbetrieb sowie durch eventuell vorhandene interne Leckagen in zentralen und dezentralen Lüftungsanlagen ist. Hierfür wurden verschiedene Fälle ausgewählt und die Verdünnung der Konzentration bestimmt. Neben einer dezentralen Lüftung für einen einzelnen Raum wurden zentrale Lüftungssysteme mit einer unterschiedlichen Anzahl angeschlossener Räume und damit verschiedenen Gesamtvolumenströmen betrachtet. Bei dem dezentralen Fall und einem Umluftanteil von 40 % am Zuluftvolumenstrom liegt die Verdünnung bei 60 %. Da ein dezentrales System typischerweise raumweise arbeitet, ist eine Übertragung in andere Räume über die raumlufttechnische Anlage ausgeschlossen. Bei einem zentralen System erhöht sie sich mit steigender Anzahl der versorgten Räume auf 80 – ca. 95 % unter der Annahme einer einzigen Kontaminationsquelle in nur einem der Räume. Die Versorgung mehrerer Räume führt gleichzeitig zu einem höheren Gesamtzuluftvolumenstrom im Vergleich zu dem dezentralen Fall. Die Verdünnung vergrößert sich je geringer der Leckage- bzw. Umluftanteil am Zuluftvolumenstrom ist. Im nächsten Schritt wurde für ein kleines Büro ein Vergleich der Belastung pro m3 Raumvolumen als Maß für die Kontamination mit vier verschiedenen Lüftungsszenarien (unbelüftet sowie nach DIN EN 16798-1 Kategorie I bis III) vorgenommen. Abschließend wurden für drei Bürogrößen Belastungen für die Fälle mit Umluftanteilen von 20 % und von 40 % berechnet und mit Luftvolumenströmen nach Kategorie II und III verglichen. Außerdem wurde für eine Anlage ohne Umluft betrachtet, wie sich interne Leckagen (bspw. durch Wärmerückgewinnungssysteme selbst oder den Einbau dieser) von 5% auswirken. Es ist zu erkennen, dass sich die Luftqualität bei der Nutzung einer dezentralen Lüftungsanlage und einem Umluftanteil von 40 % um eine Kategorie verschlechtert. Zu beachten ist, dass es sich um eine vereinfachte Rechnung des ungünstigsten Falls handelt, bei der die Wirkung von Filtern nicht betrachtet wurde. Bei Einbeziehung von Filterleistungen in die Berechnung ist mit einer Verringerung der Belastung zu rechnen [1]. Insgesamt ist zu bemerken, dass durch den Einsatz von Umluft in zentralen Lüftungssystemen das Risiko der Übertragungen von Kontaminationen aus der Abluft in die Zuluft nur sehr gering erhöht wird. Das Vorhandensein von Leckagen (Annahme 5%) durch Wärmerückgewinnungssysteme führt zu einem unerheblichen Einfluss. Dennoch sollte stets der Außenluftluftanteil möglichst hoch sein, um die Raumlufthygiene auf einem hohen Standard zu halten.BMWI, 03EN1038, EnOB: MinInfekt - Notwendige Luftmengen zur Minderung des Infektionsrisikos über Aerosole effektiv und energieeffizient bereitstelle

What Skills Do Agricultural Professionals Need in the Transition towards a Sustainable Agriculture? A Qualitative Literature Review

Agriculture is facing mounting challenges across the globe and must move towards more sustainable practices to combat climate change and meet changed production requirements. Education has been acknowledged as highly important in a sustainable transition, but there is no clear agreement about what skills are needed for professionals in the agricultural system. The purpose of this paper is to identify and analyse skills needed for professionals in the agricultural system to engage in the transition towards sustainable agriculture and elaborate on the implications of this for a transition towards sustainable agriculture. The review is based on a qualitative semi-systematic literature review of 20 peer-reviewed articles concerned with sustainability, skills, and agriculture. Five categories of skills were identified and analysed, including systems perspective, lifelong learning, knowledge integration, building and maintaining networks and learning communities, and technical and subject-specific knowledge and technology. As the identified categories of skills have emerged from different contextual settings and a diverse group of actors, these five categories encourage a broad and inclusive understanding of skills that can be translated into different contextual settings, scales, and professions within the agricultural system. The article concludes that professionals engaged in the transition towards sustainable agriculture need skills that encourage a perspective that moves beyond generic discipline-based skills and instead builds on heterogeneity, inclusion, and use of different actors' knowledge, practices, and experiences, and the ability to respond and be proactive in a constantly changing world

Smoking and Colorectal Cancer Risk, Overall and by Molecular Subtypes:A Meta-Analysis

The aim of this study was to provide the most comprehensive and up-to-date evidence on the association between cigarette smoking and colorectal cancer (CRC) risk