10,227 research outputs found

    Increasing optimism and demand uncertainty

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    By allowing the initial prior over market size to be a mixture of distributions, this paper extends the model of irreversible investment under uncertainty proposed by Rob (1991). We find that capacity expansion fuels investors' optimism. It is shown in the paper that the crash is always preceded by a boom when the initial prior is a mixture of exponential distributions.Learning Investment Uncertainty

    The Wrong Kind of Transparency

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    In a model of career concerns for experts, when is the principal hurt from observing more information about her agent? This paper introduces a distinction between information on the consequence of the agent's action and information directly on the agent's action. It is the latter kind that can hurt the principal by engendering conformism, which worsens both discipline and sorting. The paper identifies a necessary and sufficient condition on the agent signal structure under which transparency on action is detrimental to the principal. The paper also shows the existence of complementarities between transparency on action and transparency on consequence. The results are used to interpret existing disclosure policies in politics, corporate governance, and delegated portfolio management.Transparency, career concerns, expert agents.

    Shear mixing in stellar radiative zones I. Effect of thermal diffusion and chemical stratification

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    Turbulent transport of chemical elements in radiative zones of stars is considered in current stellar evolution codes thanks to phenomenologically derived diffusion coefficients. Recent local numerical simulations (Prat & Ligni\`eres 2013, A&A, 551, L3) suggest that the coefficient for radial turbulent diffusion due to radial differential rotation satisfies Dt≃0.058κ/RiD_{\rm t}\simeq0.058\kappa/Ri, in qualitative agreement with Zahn's model. However, this model does not apply when differential rotation is strong with respect to stable thermal stratification or when chemical stratification has a significant dynamical effect, a situation encountered at the outer boundary of nuclear-burning convective cores. We extend our numerical study to consider the effects of chemical stratification and of strong shear, and compare the results with prescriptions used in stellar evolution codes. We performed local, direct numerical simulations of stably stratified, homogeneous, sheared turbulence in the Boussinesq approximation. The regime of high thermal diffusivities, typical of stellar radiative zones, is reached thanks to the so-called small-P\'eclet-number approximation, which is an asymptotic development of the Boussinesq equations in this regime. The dependence of the diffusion coefficient on chemical stratification was explored in this approximation. Maeder's extension of Zahn's model in the strong-shear regime is not supported by our results, which are better described by a model found in the geophysical literature. As regards the effect of chemical stratification, our quantitative estimate of the diffusion coefficient as a function of the mean gradient of mean molecular weight leads to the formula Dt≃0.45κ(0.12−Riμ)/RiD_{\rm t}\simeq 0.45\kappa(0.12-Ri_\mu)/Ri, which is compatible in the weak-shear regime with the model of Maeder & Meynet (1996, A&A, 313, 140).Comment: 10 pages, 9 figures, accepted in A&

    A one dimensional model for the prediction of extraction yields in a two phases modified twin-screw extruder

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    Solid/liquid extraction is performed on raw plant substrate with a modified twin-screw extruder (TSE) used as a thermo-mecanochemical reactor. Visual observations and experimental residence time distributions (RTD) are used to develop a solid transport model based on classical chemical engineering method. Modeled and experimental residence times are compared. The transport model is then coupled with a reactive extraction model in order to predict extraction yields

    Vertical integration or specialisation: producing and commercialising cotton goods (1815-1913)

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    This article describes the ways in which cotton goods were commercialised during the nineteenth century and the first third of the twentieth. Several national cases are analysed: Britain, as the Workshop of the World; France, Germany, Switzerland and the US, as core economies; and Italy and Spain as countries on the European periphery. The main question that we address is why some cotton industries vertically integrated their production and commercialisation processes, but others did not. We present a model that combines industrial district size and product differentiation to explain why vertical integration was present in most cases and why there was vertical specialisation in Lancashire and Lowell.vertical specialisation, industrial revolution, commercialisation, vertical integration, industrial organization, cotton industry, transaction costs

    Nonuniversal conductivity exponents in continuum percolating Gaussian fractures

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    We study the electrical and hydraulic conductivity percolation exponents in a Gaussian fracture using the method proposed in Plouraboué et al. [Phys. Rev. E 73, 036305, 2006]. Nonuniversal conductivity percolation exponents are found: they differ from the theoretical predictions for infinite system size for frozen power-law distributions of local conductivities, as with their finite size corrections. In the hydraulic case, we also find that the probability density function of the conductivity follows a power-law distribution near the percolation threshold
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