1,117 research outputs found
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 < 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 rĂ©gimes de RetraitĂ©s (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 individualâs 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'équivalent patrimonial des droits à retraite ?
Depuis 1993, la France a enregistrĂ© plusieurs rĂ©formes de son systĂšme de retraites, visant avant tout Ă en assurer la soutenabilitĂ©. Cette contribution a pour objectif dâĂ©valuer lâimpact de la rĂ©forme de 1993 sur lâĂ©quivalent patrimonial des droits individuels Ă la retraite (EPDR), c\u27est-Ă -dire la somme actuarielle probable des pensions Ă recevoir, de la date de liquidation des droits jusquâau dĂ©cĂšs. Plus prĂ©cisĂ©ment, nous mesurons lâimpact de cette rĂ©forme sur lâEPDR des mono-pensionnĂ©s du rĂ©gime gĂ©nĂ©ral, Ă lâaide des donnĂ©es de lâEchantillon InterrĂ©gimes de RetraitĂ©s 2008. Parmi les mesures phares de la rĂ©forme de 1993 figure lâaugmentation progressive de la durĂ©e de cotisation nĂ©cessaire pour obtenir une retraite Ă taux plein au rĂ©gime gĂ©nĂ©ral. Cette augmentation est susceptible dâengendrer deux effets opposĂ©s : un effet de report de lâĂąge de liquidation pour conserver un EPDR adĂ©quat pour ses vieux jours (voire lâaugmenter) ou un effet de dĂ©cote, si lâassurĂ©-e ne souhaite, ou ne peut, pas prolonger son activitĂ© et subit donc une dĂ©cote sur sa pension, et partant sur son EPDR. Pour tester les effets nets de la rĂ©forme de 1993 sur lâEPDR, nous procĂ©dons Ă des estimations Ă©conomĂ©triques en diffĂ©rences premiĂšres et en doubles diffĂ©rences, ainsi quâĂ des estimations par quantiles pour mesurer les impacts le long de la distribution de lâEPDR. Nos estimations montrent des rĂ©sultats diffĂ©rents selon que les individus partent avant ou aprĂšs 2004, date dâentrĂ©e en vigueur de la rĂ©forme. Ainsi, toutes choses Ă©gales par ailleurs, un dĂ©part en retraite avant 2004 plutĂŽt que postĂ©rieurement, augmente lâEPDR des retraitĂ©s concernĂ©s. Toutefois, lâinteraction avec les autres variables nuance cette conclusion. Dâune part, reporter son dĂ©part en retraite rĂ©duit lâEPDR moyen dâenviron 20% : le report permet dâaccumuler des droits supplĂ©mentaires, mais sur une pĂ©riode rĂ©duite. Dâautre part, lâeffet de la dĂ©cote est nĂ©gatif, mais son intensitĂ© est rĂ©duite quand les retraitĂ©s reportent leur dĂ©part. En outre, comme les gĂ©nĂ©rations 1934-1943 ont subi conjointement les rĂ©formes de 1993 et 2003, nos estimations en double diffĂ©rence permettent dâisoler lâeffet « pur » de la rĂ©forme de 1993 : lorsque les affiliĂ©s ont subi une dĂ©cote, sans avoir reportĂ© leur dĂ©part en retraite pour lâattĂ©nuer, la liquidation des droits aux conditions de 2003 par rapport aux conditions de 1993 est la plus dĂ©favorable. Enfin, les estimations par quantiles montrent que ces effets sâintensifient dans la premiĂšre moitiĂ© de la distribution, et sâattĂ©nuent au-delĂ
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
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