Global instability of low-density jets

The global stability of laminar axisymmetric low-density jets is investigated in the low Mach number approximation. The linear modal dynamics is found to be characterised by two features: a stable arc branch of eigenmodes and an isolated eigenmode. Both features are studied in detail, revealing that, whereas the former is highly sensitive to numerical domain size and its existence can be linked to spurious feedback from the outflow boundary, the latter is the physical eigenmode that is responsible for the appearance of self-sustained oscillations in low-density jets observed in experiments at low Mach numbers. In contrast to previous local spatio-temporal stability analyses, the present global analysis permits, for the first time, the determination of the critical conditions for the onset of global instability, as well the frequency of the associated oscillations, without additional hypotheses, yielding predictions in fair agreement with previous experimental observations. It is shown that under the conditions of those experiments, viscosity variation with composition, as well as buoyancy, only have a small effect on the onset of instability

Towards an agent-based framework for online after-sales services

The multi-agent paradigm for building intelligent systems has gradually been accepted by researchers and practitioners in the research field of artificial intelligence. There are also attempts of adapting agents and agent-based systems for creating industrial applications and providing e-services. In this paper, we present an attempt to use agents for constructing an online after-sale services system. The system is decomposed into four major cooperative agents, and in which each agent concentrates on particular aspects in the system and expresses intelligence by using various techniques. The proposed agent-based framework for the system is presented at both the micro-level and the macro-level according to the Gaia methodology. UML notations are also used to represent some software design models. As the result of this, agents are implemented into a framework for which exploits Case-Based Reasoning (CBR) technique to fulfil real life on-line services' diagnoses and tasks

The effects of ability tracking of future primary school teachers on student performance

Because of the Dutch tracking system, primary school teachers in the Netherlands can have a vocational or a higher secondary background. Policymakers and school principles worry that teachers with vocational backgrounds are less capable to teach math and reading. This study therefore examines the effects of ability tracking of future primary school teachers on the students' math and reading performance. We exploit data of 91 schools for all primary school children in grades 3, 4 and 5 and identify the tracking effect by exploiting unique information on how teachers are assigned to classes based on their teaching abilities. The estimation results for math (reading) indicate that test scores are .2 (.12) of a standard deviation lower if their teacher had a vocational background. The results for reading are, however, not signicant at the 10% condence level and the tracking estimates appear to be less stable and precise

Money in monetary policy design: monetary cross-checking in the New-Keynesian model

In the New-Keynesian model, optimal interest rate policy under uncertainty is formulated without reference to monetary aggregates as long as certain standard assumptions on the distributions of unobservables are satisfied. The model has been criticized for failing to explain common trends in money growth and inflation, and that therefore money should be used as a cross-check in policy formulation (see Lucas (2007)). We show that the New-Keynesian model can explain such trends if one allows for the possibility of persistent central bank misperceptions. Such misperceptions motivate the search for policies that include additional robustness checks. In earlier work, we proposed an interest rate rule that is near-optimal in normal times but includes a cross-check with monetary information. In case of unusual monetary trends, interest rates are adjusted. In this paper, we show in detail how to derive the appropriate magnitude of the interest rate adjustment following a significant cross-check with monetary information, when the New-Keynesian model is the central bank’s preferred model. The cross-check is shown to be effective in offsetting persistent deviations of inflation due to central bank misperceptions. Keywords: Monetary Policy, New-Keynesian Model, Money, Quantity Theory, European Central Bank, Policy Under Uncertaint

Chemical vapor deposition and infiltration for the production of tungsten fiber reinforced tungsten composite material

Contribution submission to the conference Regensburg 2016Chemical vapor deposition and infiltration for the productionof tungsten fiber reinforced tungsten composite material —∙Martin Aumann1, Jan Willem Coenen1, Hanns Gietl2, TillHoeschen2, Johann Riesch2, Klaus Schmid2, Rudolf Neu2, andChristian Linsmeier1 — 1Forschungszentrum Juelich GmbH, Institutfür Energie- und Klimaforschung, 52425 Juelich — 2Max-Planck-Institut für Plasmaphysik, 85748 GarchingDue to its high melting point, high corrosion resistance and its preferableproperties in terms of hydrogen retention, tungsten is a promisingcandidate in future nuclear fusion devices. However, the mechanicalbehavior of tungsten is crucial, as it is inherently brittle at room temperature.As possibility to overcome this brittleness, a composite materialcan be formed, which shows pseudo-ductility and therefore avoidscatastrophic failure of the material. A possibility to produce such aWf/W-composite is chemical vapor deposition and chemical vapor infiltration,where tungsten is deposited on small tungsten wires throughthe reaction of WF6 and H2. With ongoing infiltration time, pores areformed between the fibers, which decrease in size through the chemicalreaction. For better process understanding, a pore model was established,which solves the mass balance inside the pore and the resultingpore diameter simultaneously. It shows a significant difference in diameterfor longer infiltration times. This behavior shall be proved inexperiments with an experimental pore, which is similar to the simulatedone. Furthermore also kinetic investigations on the chemicalsurface reaction are carried out to increase the process understanding.Part: MMType: Vortrag;TalkTopic: Transport (Diffusion, Leitfähigkeit,Wärme)/ Transport (Diffusion,conductivity, heat)Email: [email protected]