61,265 research outputs found

    Stability and asymptotic behavior of periodic traveling wave solutions of viscous conservation laws in several dimensions

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    Under natural spectral stability assumptions motivated by previous investigations of the associated spectral stability problem, we determine sharp LpL^p estimates on the linearized solution operator about a multidimensional planar periodic wave of a system of conservation laws with viscosity, yielding linearized L1LpLpL^1\cap L^p\to L^p stability for all p2p \ge 2 and dimensions d1d \ge 1 and nonlinear L1HsLpHsL^1\cap H^s\to L^p\cap H^s stability and L2L^2-asymptotic behavior for p2p\ge 2 and d3d\ge 3. The behavior can in general be rather complicated, involving both convective (i.e., wave-like) and diffusive effects

    Chaotic cold accretion onto black holes

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    Using 3D AMR simulations, linking the 50 kpc to the sub-pc scales over the course of 40 Myr, we systematically relax the classic Bondi assumptions in a typical galaxy hosting a SMBH. In the realistic scenario, where the hot gas is cooling, while heated and stirred on large scales, the accretion rate is boosted up to two orders of magnitude compared with the Bondi prediction. The cause is the nonlinear growth of thermal instabilities, leading to the condensation of cold clouds and filaments when t_cool/t_ff < 10. Subsonic turbulence of just over 100 km/s (M > 0.2) induces the formation of thermal instabilities, even in the absence of heating, while in the transonic regime turbulent dissipation inhibits their growth (t_turb/t_cool < 1). When heating restores global thermodynamic balance, the formation of the multiphase medium is violent, and the mode of accretion is fully cold and chaotic. The recurrent collisions and tidal forces between clouds, filaments and the central clumpy torus promote angular momentum cancellation, hence boosting accretion. On sub-pc scales the clouds are channelled to the very centre via a funnel. A good approximation to the accretion rate is the cooling rate, which can be used as subgrid model, physically reproducing the boost factor of 100 required by cosmological simulations, while accounting for fluctuations. Chaotic cold accretion may be common in many systems, such as hot galactic halos, groups, and clusters, generating high-velocity clouds and strong variations of the AGN luminosity and jet orientation. In this mode, the black hole can quickly react to the state of the entire host galaxy, leading to efficient self-regulated AGN feedback and the symbiotic Magorrian relation. During phases of overheating, the hot mode becomes the single channel of accretion (with a different cuspy temperature profile), though strongly suppressed by turbulence.Comment: Accepted by MNRAS: added comments and references. Your feedback is welcom

    AGN Feedback and Bimodality in Cluster Core Entropy

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    We investigate a series of steady-state models of galaxy clusters, in which the hot intracluster gas is efficiently heated by active galactic nucleus (AGN) feedback and thermal conduction, and in which the mass accretion rates are highly reduced compared to those predicted by the standard cooling flow models. We perform a global Lagrangian stability analysis. We show for the first time that the global radial instability in cool core clusters can be suppressed by the AGN feedback mechanism, provided that the feedback efficiency exceeds a critical lower limit. Furthermore, our analysis naturally shows that the clusters can exist in two distinct forms. Globally stable clusters are expected to have either: 1) cool cores stabilized by both AGN feedback and conduction, or 2) non-cool cores stabilized primarily by conduction. Intermediate central temperatures typically lead to globally unstable solutions. This bimodality is consistent with the recently observed anticorrelation between the flatness of the temperature profiles and the AGN activity (Dunn & Fabian 2008) and the observation by Rafferty et al. (2008) that the shorter central cooling times tend to correspond to significantly younger AGN X-ray cavities.Comment: 4 pages, to appear in the proceedings of "The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", Eds. Sebastian Heinz, Eric Wilcots (AIP conference series

    Regional Multinationals and the Korean Comestics Industry

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    This paper analyzes the market penetration and expansion strategy of cosmetics and toiletries multinational enterprises (MNEs) in South Korea from the perspective of regional strategy as developed recently by Rugman. We find that MNEs have different market entry and expansion strategies in the home region and in the foreign region. Home region MNEs (Japanese MNEs in this case), in general, utilize their firm-specific advantages (FSAs) better than foreign region MNEs (European and MNEs from the Americas in this case). Due to differences in transaction costs, home region MNEs exploit downstream FSAs while foreign region MNEs develop upstream FSAs. Market similarity also leads to a greater incentive to operate in the home region rather than in foreign regions. The home region effect significantly increases the likelihood of entry into foreign markets as the host country’s “diamond” significantly affects the market entry strategies of MNEs.regional strategy, market penetration, cosmetics industry, double diamond, South Korea

    The Regional Sales of Multinationals in the World Cosmetics Industry

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    This paper analyzes the regional characteristics and strategies of multinational enterprises (MNEs) in the world cosmetics and toiletries industry, based on the new work by Rugman on regional strategy. We test the proposition that MNEs may asymmetrically develop their upstream and downstream firm specific advantages (FSAs). We find that the upstream activities of the MNEs in cosmetics are home region based but that downstream activities are less so. Further, the asymmetry of FSAs in the world cosmetics industry is mainly due to the atypical Asian entry strategies of North American and West European cosmetics MNEs. Two case studies confirm how variations in FSAs can affect regional strategy.regionalism, regional strategy, cosmetics industry, firm specific advantage, Avon, Gucci