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AbstractWe show that immigrant managers are substantially more likely to hire immigrants than are native managers. The finding holds when comparing establishments in the same 5-digit industry and location, when comparing different establishments within the same firm, when analyzing establishments that change management over time, and when accounting for within-establishment trends in recruitment patterns. The effects are largest for small and owner-managed establishments in the for-profit sector. Separations are more frequent when workers and managers have dissimilar origin, but only before workers become protected by EPL. We also find that native managers are unbiased in their recruitments of former co-workers, suggesting that information deficiencies are important. We find no effects on entry wages. Our findings suggest that a low frequency of immigrant managers may contribute to the observed disadvantages of immigrant workers.Do you want to read the rest of this article?Request full-text
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Conductive and Radiative Heat Transfer in Ceramic and Metal Foams at Fire Temperatures | SpringerLink
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Conductive and Radiative Heat Transfer in Ceramic and Metal Foams at Fire TemperaturesContribution to the Special Issue “Materials in Fire” Guest Editor K. Ghazi WakiliRémi CoquardDenis RochaisDominique BaillisArticle
In addition to the multiple actual or possible applications of metal and ceramic foams in various technological fields, their thermal properties make them a good candidate for utilization as fire barriers. Several studies have shown experimentally their exceptional fire retardance due to their low apparent thermal conductivity. However, while the thermal properties of this porous material have been widely studied at ambient temperature and are, at present, well-known, their thermal behaviour at fire temperatures remains relatively unexplored. Indeed, at such temperatures, the major difficulties are not only due to the fact that thermal measurements are rendered fussy since heavy equipments are required but also stem from the fact that a significant part of the heat transfer occurs by thermal radiation which is much more difficult to evaluate than conductive heat transfer. Therefore, the present chapter is written with a view to report progress on the knowledge of heat transfer in open cell foams and to enlighten the reader on the mechanisms of heat transfer at high temperatures. A first part is devoted to the review of the prior published works on the experimental or theoretical characterisations of radiative and conductive heat transfers from ambient to high temperatures. By taking inspiration from the concepts and models presented in these previous works, we propose, in a second part, a model of prediction of the conductive and radiative contributions to heat transfer at fire temperatures. This analytical model is based on numerical simulations applied to real foams and takes into account the structure of the foam and the optical and thermal properties of the constituents. In a third part, we propose an innovative experimental technique of characterization of heat transfer in foams at high temperatures which permit to evaluate independently the radiative and conductive contributions from a unique and simple measurement. The experimental results obtained on several metal and ceramic foams are compared to the results predicted by our numerical model. The good adequacy between experimental and theoretical results show the consistency of both approaches.Metal foams High temperatures Heat conduction Thermal radiation aLength of cell struts (m)ACharacteristic size of particles interacting with radiation (m)dThickness of cell struts (m)DCharacteristic size of cell lumps (m)DcellCell diameter (m)Ec, EhEmissivities of the hot and cold boundariesfsFraction of solid phase in struts (-)fv = 1 - εSolid fraction (-)kThermal conductivity (W/m/K)kcEffective thermal conductivity (W/m/K)kequEquivalent thermal conductivity (W/m/K)kradRadiative conductivity (W/m/K)KRRosseland extinction coefficient (m-1)IλSpectral radiative intensity (W/m2/Sr)Iλ0(T)Spectral radiative intensity of the black body at temperature T (W/m2/Sr)LThickness of the foam slice (m)LoptOptical thickness of the foam slice (-)MFoam density (kg/m3)Pλ(μ′ → μ)Scattering phase function (-)\( \dot{Q} \)Heat flux density (W/m2)qr, qc, qtRadiative, conductive and total heat flux densities (W/m2)\( \vec{r} \)Position vectorspSpecularity parameter (-)TTemperature (K)Thot, TcoldTemperatures of the hot and cold boundaries (K)V1, V2Volume of struts and lumps (m3)x = πA/λSize parameter (-)z1D coordinate (m)β, σ, κExtinction, scattering and absorption coefficients (m-1)β*Weighted extinction coefficient (m-1)\( \vec{\Updelta } \)Direction vectorεPorosity (-)μDirecting cosine of the radiant intensity (-)θScattering angle (rad)ρReflectivity (-)λWavelength (m)σ = 5.67 × 10-8Stefan–Boltzmann constant (W/m2/K-4)ωScattering albedo (-)fluid, solidRelative to the fluid/solid phasesDOM, ROSSCalculated by the DOM or the Rosseland Approximation⊥, //Relative to perpendicular or parallel polarizationdif, specRelative to diffuse or specular reflectionradRadiativeThis is a preview of subscription content,
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PhD thesis, Institut National des Sciences Appliquées (INSA) de Lyon, Villeurbanne, France, 2008Rémi Coquard1Denis Rochais2Dominique Baillis341.Société <> (EC2MS)Villeurbanne CedexFrance2.Commissariat à l’Energie Atomique (CEA)/Le RipaultMontsFrance3.Université de Lyon, CNRS, INSA-Lyon, CETHIL, UMR5008VilleurbanneFrance4.Université Lyon 1VilleurbanneFrance
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