1,600 research outputs found
BACCHUS-3D/SP A computer programme for the three-dimensional description of sodium single-phase flow in bundle geometry
Analytical pre-test support of boil-down test QUENCH-11
Analytische UnterstĂŒtzung zur Vorbereitung des Ausdampf-Versuchs QUENCH-11
Im QUENCH-Vorhaben des Forschungszentrums Karlsruhe soll das Fluten eines teilweise zerstörten Kerns untersucht werden. Der zweite LACOMERA Versuch Q-L2 (QUENCH-11) beginnt mit einer Ausdampfphase des BĂŒndels, bis der Wasserspiegel das untere BĂŒndelÂŹende erreicht hat. Ein derartiger Versuch wurde bislang noch nicht in der QUENCH-Anlage durchgefĂŒhrt, so dass mit SCDAP/RELAP5 mod3.2.irs eine Machbarkeitsstudie erforderlich war. Die Ergebnisse zeigen, dass eine Zusatzheizung im unteren Plenum notwendig ist, um den Wasserstand und die Verdampfungsrate (Dampfmassenstrom in der Ausdampfphase) unabhĂ€ngig von der angestrebten Maximaltemperatur im BĂŒndel zu regeln. FĂŒr eine verlĂ€ssÂŹliche Versuchsplanung sowie zur Erstellung der Energiebilanz muss die Zusatzheizung inÂŹnerhalb des unteren Plenums unterhalb der WasseroberflĂ€che installiert werden, damit die Heizleistung vollstĂ€ndig in das Wasser eingekoppelt wird. Um die Verdampfungsrate ĂŒber lĂ€ngere Zeit aufrecht zu erhalten, muss zusĂ€tzlich Wasser in das untere Plenum eingespeist werden.
Anhand dieser Rechnungen wird der Testablauf im Detail diskutiert. Eine entsprechende Studie zeigte die DurchfĂŒhrbarkeit eines solchen Ausdampftests und war die Grundlage fĂŒr die oben erwĂ€hnten Ănderungen in der Anlage und der Versuchs-DurchfĂŒhrung gegenĂŒber frĂŒheren Tests. Eine Reihe von Vorversuche wurde durchgefĂŒhrt, um die Brauchbarkeit der Ănderungen an der Anlage und der geplanten VersuchsfĂŒhrung zu prĂŒfen und um Daten fĂŒr das thermohydraulische Verhalten der Anlage zu bekommen, an denen die Code-Modelle fĂŒr die Voraus- und Nachrechnungen von QUENCH-11 getestet werden können. Im Anschluss an die Vorversuche wurden wie bei frĂŒheren QUENCH-Tests detaillierte Vorausrechnungen mit verschiedenen Codes zu Versuchsablauf und -steuerung durchgefĂŒhrt. Drei ForschungsÂŹeinrichtungen in der EU waren beteiligt. Die berechneten Ergebnisse reagieren empfindlich auf Ănderungen der Versuchsparameter wie das anfĂ€ngliche axiale Temperaturprofil und die eingespeiste elektrische Leistung, wie es auch fĂŒr die untersuchten physikalischen BedinÂŹgungen im Versuch erwartet werden kann
Barriers to effective climate change policy development and implementation in West Africa
This Info Note explores major barriers for effective climate change policy implementation in Ghana, Mali and Senegal with a particular focus on agriculture and food systems. It aims to provide insights to researchers, policy makers and development practitioners working on climate change issues and activities as to what hampers successful climate policy implementation in West Africa and how identified barriers could be over-come
Indigenous knowledges and development: a postcolonial caution
As a result of the failure of formal top-down development, there has recently been increased interest in the possibilities of drawing upon the indigenous knowledges of those in the communities involved, in an attempt to produce more effective development strategies. The concept of indigenous knowledge calls for the inclusion of local voices and priorities, and promises empowerment through ownership of the process. However, there has been little critical examination of the ways in which indigenous knowledges have been included in the development process. Drawing upon postcolonial theory, this article suggests that indigenous knowledges are often drawn into development by both theorists and development institutions in a very limited way, failing to engage with other ways of perceiving development, and thus missing the possibility of devising more challenging alternatives
Explicit kinetic heterogeneity: mechanistic models for interpretation of labeling data of heterogeneous cell populations
Estimation of division and death rates of lymphocytes in different conditions
is vital for quantitative understanding of the immune system. Deuterium, in the
form of deuterated glucose or heavy water, can be used to measure rates of
proliferation and death of lymphocytes in vivo. Inferring these rates from
labeling and delabeling curves has been subject to considerable debate with
different groups suggesting different mathematical models for that purpose. We
show that the three models that are most commonly used are in fact
mathematically identical and differ only in their interpretation of the
estimated parameters. By extending these previous models, we here propose a
more mechanistic approach for the analysis of data from deuterium labeling
experiments. We construct a model of "kinetic heterogeneity" in which the total
cell population consists of many sub-populations with different rates of cell
turnover. In this model, for a given distribution of the rates of turnover, the
predicted fraction of labeled DNA accumulated and lost can be calculated. Our
model reproduces several previously made experimental observations, such as a
negative correlation between the length of the labeling period and the rate at
which labeled DNA is lost after label cessation. We demonstrate the reliability
of the new explicit kinetic heterogeneity model by applying it to artificially
generated datasets, and illustrate its usefulness by fitting experimental data.
In contrast to previous models, the explicit kinetic heterogeneity model 1)
provides a mechanistic way of interpreting labeling data; 2) allows for a
non-exponential loss of labeled cells during delabeling, and 3) can be used to
describe data with variable labeling length
Coupling of morphological instability and kinetic instability: Chemical waves in hydrogen oxidation on a bimetallic Ni/Rh(111) surface
The oxidation and reduction of a bimetallic Ni/Rh model catalyst during the water forming O2+H2 reaction is studied with low-energy electron microscopy, microspot-low-energy electron diffraction, and x-ray photoemission electron microscopy. Oxidation of a submonolayer Ni film results in the formation of three-dimensional (3D) NiO nanoparticles. Reduction of 3D-NiO in H2 produces a dispersed two-dimensional film of metallic Ni. Chemical waves during the O2+H2 reaction involve a cyclic transformation between 3D-NiO and 2D-NiO
Towards Endogenous Livestock Development: Borana Pastoralistsâ Responses to Environmental and Institutional Changes
Borana pastoralists in southern Ethiopia are faced with the challenge of developing more efficient and sustainable use of natural resources. In past decades poorly adapted development interventions and inadequate land-use policies aggravated by population growth have weakened pastoral rangeland management. Ignoring pastoralistsâ technical and organizational capacities has contributed to progressive land degradation, the erosion of social structures and poverty. The Endogenous Livestock Development concept recognises pastoralistsâ indigenous knowledge-based strategies and priorities, and uses them as the bases for further development of their production system and social relations, to be utilized, improved and combined with modern technologies. This paper explores the Borana pastoralistsâ adaptive strategies for improved utilization of natural resources and the manner in which they respond to environmental risk and external influences such as water development and new formal administration. The adaptive responses include controlled integration of crop production and protection of grazing reserves, as well as changing cattle breeding priorities and the adoption of camel husbandry. The pastoralists have started negotiations with the administration to regain control of land utilization by strengthening directives for settlements, land use pattern and extraction rates. To support these initiatives the study recommends that pastoralists and other stakeholders enter into an institutionalized process of negotiation that builds on indigenous knowledge and organizational structures and facilitates validation and implementation of newly generated knowledg
Short-term salivary acetaldehyde increase due to direct exposure to alcoholic beverages as an additional cancer risk factor beyond ethanol metabolism
<p>Abstract</p> <p>Background</p> <p>An increasing body of evidence now implicates acetaldehyde as a major underlying factor for the carcinogenicity of alcoholic beverages and especially for oesophageal and oral cancer. Acetaldehyde associated with alcohol consumption is regarded as 'carcinogenic to humans' (IARC Group 1), with sufficient evidence available for the oesophagus, head and neck as sites of carcinogenicity. At present, research into the mechanistic aspects of acetaldehyde-related oral cancer has been focused on salivary acetaldehyde that is formed either from ethanol metabolism in the epithelia or from microbial oxidation of ethanol by the oral microflora. This study was conducted to evaluate the role of the acetaldehyde that is found as a component of alcoholic beverages as an additional factor in the aetiology of oral cancer.</p> <p>Methods</p> <p>Salivary acetaldehyde levels were determined in the context of sensory analysis of different alcoholic beverages (beer, cider, wine, sherry, vodka, calvados, grape marc spirit, tequila, cherry spirit), without swallowing, to exclude systemic ethanol metabolism.</p> <p>Results</p> <p>The rinsing of the mouth for 30 seconds with an alcoholic beverage is able to increase salivary acetaldehyde above levels previously judged to be carcinogenic in vitro, with levels up to 1000 ÎŒM in cases of beverages with extreme acetaldehyde content. In general, the highest salivary acetaldehyde concentration was found in all cases in the saliva 30 sec after using the beverages (average 353 ÎŒM). The average concentration then decreased at the 2-min (156 ÎŒM), 5-min (76 ÎŒM) and 10-min (40 ÎŒM) sampling points. The salivary acetaldehyde concentration depends primarily on the direct ingestion of acetaldehyde contained in the beverages at the 30-sec sampling, while the influence of the metabolic formation from ethanol becomes the major factor at the 2-min sampling point.</p> <p>Conclusions</p> <p>This study offers a plausible mechanism to explain the increased risk for oral cancer associated with high acetaldehyde concentrations in certain beverages.</p
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