Turbulent Flows and Pollution Dispersion around Tall Buildings Using Adaptive Large Eddy Simulation (LES)

The motivation for this work stems from the increased number of high-rise buildings/skyscrapers all over the world, and in London, UK, and hence the necessity to see their effect on the local environment. We concentrate on the mean velocities, Reynolds stresses, turbulent kinetic energies (TKEs) and tracer concentrations. We look at their variations with height at two main locations within the building area, and downstream the buildings. The pollution source is placed at the top of the central building, representing an emission from a Combined Heat and Power (CHP) plant. We see how a tall building may have a positive effect at the lower levels, but a negative one at the higher levels in terms of pollution levels. Mean velocities at the higher levels (over 60 m in real life) are reduced at both locations (within the building area and downstream it), whilst Reynolds stresses and TKEs increase. However, despite the observed enhanced turbulence at the higher levels, mean concentrations increase, indicating that the mean flow has a greater influence on the dispersion. At the lower levels (Z < 60 m), the presence of a tall building enhanced dispersion (hence lower concentrations) for many of the configurations

Effect of the lattice misfit on the equilibrium shape of strained islands in Volmer-Weber growth

We have studied the effect of the misfit on the equilibrium shape of three-dimensional pyramidal islands grown on a foreign substrate in the case of incomplete wetting (Volmer-Weber mode of growth). We have found that tensile islands have smaller aspect ratios compared with compressed islands owing to its better adhesion to the substrate. The average strains of consecutive layers decrease faster with thickness in compressed than in tensile islands. The strains decrease rapidly with thickness, with the consequence that above a certain height, the upper layers of the pyramid become practically unstrained and does not contribute to a further reduction in the upper base. As a result, the truncated pyramids are not expected to transform into full pyramids. Our results are in good agreement with experimental observations in different systems.Comment: 6 pages, 7 figures. Accepted version, minor change

Azathioprine and 6-Mercaptopurine use in the Swiss IBD cohort : adverse effects, causes of discontinuation and risk of "flares" according to 6-TG levels

Background: To characterize and analyze in the Swiss IBD Cohort: a) reported Azathioprine (AZA) and 6-Mercaptopurine (6-MP) adverse effects (AE), b) causes of discontinuation and c) response to therapy according to gastroenterologists' clinical judgment, d) whether level of 6-TGN &lt; 235pmol/8 x108 red blood cells (RBC) is associated with a higher risk of "flare" occurrence. Methods: Retrospective statistical description, Cox model and Kaplan-Meier survival estimation. Results: 1499 patients with Crohn's Disease (CD) and 1066 with Ulcerative colitis (UC)

Enhancing CFD-LES air pollution prediction accuracy using data assimilation

It is recognised worldwide that air pollution is the cause of premature deaths daily, thus necessitating the development of more reliable and accurate numerical tools. The present study implements a three dimensional Variational (3DVar) data assimilation (DA) approach to reduce the discrepancy between predicted pollution concentrations based on Computational Fluid Dynamics (CFD) with the ones measured in a wind tunnel experiment. The methodology is implemented on a wind tunnel test case which represents a localised neighbourhood environment. The improved accuracy of the CFD simulation using DA is discussed in terms of absolute error, mean squared error and scatter plots for the pollution concentration. It is shown that the difference between CFD results and wind tunnel data, computed by the mean squared error, can be reduced by up to three order of magnitudes when using DA. This reduction in error is preserved in the CFD results and its benefit can be seen through several time steps after re-running the CFD simulation. Subsequently an optimal sensors positioning is proposed. There is a trade-off between the accuracy and the number of sensors. It was found that the accuracy was improved when placing/considering the sensors which were near the pollution source or in regions where pollution concentrations were high. This demonstrated that only 14% of the wind tunnel data was needed, reducing the mean squared error by one order of magnitude

Que valent les engagements des régimes de retraite envers les retraités en France ?

Using the "Echantillon Inter régimes des Retraités" (EIR) 2008 and 2012 panel data, we calculate retirees\u27 pension wealth (consumed and residual) at an aggregated level, and provide in-depth results by type of pension scheme and by managing organism. We put an emphasis on direct pensions already perceived by retirees and to be paid in the future, without taking into account current contributors\u27 future retirement. We find that the overall pension wealth is not very sensitive to the discount rate, but this result does not hold if we concentrate on the future pension wealth. From this point of view, it must be noted that some of the organisms have a high proportion of pension still to be paid. Moreover, whatever the type of pension wealth calculated, the results show a rapid increase from 2008 to 2012 (except for the basic scheme of farmers). Finally, spread indicators and Gini index of pension wealth are relatively higher than those found in the distribution of labor income by other studies. We find that there are more inequalities in the private sector than in the public, particularly in the private sector for complementary pension schemes

Pension Wealth in France: An Assessment on Panel Data

This contribution proposes a measure of pension wealth in the French public PAYG schemes (first and second pillar schemes) and of its distribution among the population of retirees in 2008 using the Echantillon Inter régimes de Retraités (EIR) panel data. We show that aggregate pension wealth amounts to around 4765 billion Euros assuming a 2 percent discount rate. There are significant differences in the amount of individual’s pension wealth between the pension schemes of the private and public sector. Moreover, there is more inequality in the distribution of pension wealth among private sector retirees than public sectorones

La réforme des retraites de 1993 : quel impact sur l&#039;équivalent patrimonial des droits à retraite ?

Depuis 1993, la France a enregistré plusieurs réformes de son système de retraites, visant avant tout à en assurer la soutenabilité. Cette contribution a pour objectif d’évaluer l’impact de la réforme de 1993 sur l’équivalent patrimonial des droits individuels à la retraite (EPDR), c\u27est-à-dire la somme actuarielle probable des pensions à recevoir, de la date de liquidation des droits jusqu’au décès. Plus précisément, nous mesurons l’impact de cette réforme sur l’EPDR des mono-pensionnés du régime général, à l’aide des données de l’Echantillon Interrégimes de Retraités 2008. Parmi les mesures phares de la réforme de 1993 figure l’augmentation progressive de la durée de cotisation nécessaire pour obtenir une retraite à taux plein au régime général. Cette augmentation est susceptible d’engendrer deux effets opposés : un effet de report de l’âge de liquidation pour conserver un EPDR adéquat pour ses vieux jours (voire l’augmenter) ou un effet de décote, si l’assuré-e ne souhaite, ou ne peut, pas prolonger son activité et subit donc une décote sur sa pension, et partant sur son EPDR. Pour tester les effets nets de la réforme de 1993 sur l’EPDR, nous procédons à des estimations économétriques en différences premières et en doubles différences, ainsi qu’à des estimations par quantiles pour mesurer les impacts le long de la distribution de l’EPDR. Nos estimations montrent des résultats différents selon que les individus partent avant ou après 2004, date d’entrée en vigueur de la réforme. Ainsi, toutes choses égales par ailleurs, un départ en retraite avant 2004 plutôt que postérieurement, augmente l’EPDR des retraités concernés. Toutefois, l’interaction avec les autres variables nuance cette conclusion. D’une part, reporter son départ en retraite réduit l’EPDR moyen d’environ 20% : le report permet d’accumuler des droits supplémentaires, mais sur une période réduite. D’autre part, l’effet de la décote est négatif, mais son intensité est réduite quand les retraités reportent leur départ. En outre, comme les générations 1934-1943 ont subi conjointement les réformes de 1993 et 2003, nos estimations en double différence permettent d’isoler l’effet « pur » de la réforme de 1993 : lorsque les affiliés ont subi une décote, sans avoir reporté leur départ en retraite pour l’atténuer, la liquidation des droits aux conditions de 2003 par rapport aux conditions de 1993 est la plus défavorable. Enfin, les estimations par quantiles montrent que ces effets s’intensifient dans la première moitié de la distribution, et s’atténuent au-delà

Charge redistribution at Pd surfaces: ab initio grounds for tight-binding interatomic potentials

A simplified tight-binding description of the electronic structure is often necessary for complex studies of surfaces of transition metal compounds. This requires a self-consistent parametrization of the charge redistribution, which is not obvious for late transition series elements (such as Pd, Cu, Au), for which not only d but also s-p electrons have to be taken into account. We show here, with the help of an ab initio FP-LMTO approach, that for these elements the electronic charge is unchanged from bulk to the surface, not only per site but also per orbital. This implies different level shifts for each orbital in order to achieve this orbital neutrality rule. Our results invalidate any neutrality rule which would allow charge redistribution between orbitals to ensure a common rigid shift for all of them. Moreover, in the case of Pd, the power law which governs the variation of band energy with respect to coordination number, is found to differ significantly from the usual tight-binding square root.Comment: 6 pages, 2 figures, Latex; Phys.Rev. B 56 (1997