19,552 research outputs found
Corporate Hierarchies and the Size of Nations: Theory and Evidence
Corporate organization varies within a country and across countries with country size. The paper starts by establishing some facts about corporate organization based on unique data of 660 Austrian and German corporations. The larger country (Germany) has larger firms with flatter more decentral corporate hierarchies compared to the smaller country (Austria). Firms in the larger country change their organization less fast than firms in the smaller country. Over time firms have been introducing less hierarchical organizations by delegating power to lower levels of the corporation. We develop a theory which explains these facts and which links these features to the trade environment that countries and firms face. We introduce firms with internal hierarchies in a Krugman (1980) model of trade. We show that international trade and the toughness of competition in international markets induce a power struggle in firms which eventually leads to decentralized corporate hierarchies. We offer econometric evidence which is consistent with the models predictions
X-ray polarimetric signatures induced by spectral variability in the framework of the receding torus model
Obscuring circumnuclear dust is a well-established constituent of active
galactic nuclei (AGN). Traditionally referred to as the receding dusty torus,
its inner radius and angular extension should depend on the photo-ionizing
luminosity of the central source. Using a Monte Carlo approach, we simulate the
radiative transfer between the multiple components of an AGN adopting model
constraints from the bright Seyfert galaxy NGC 4151. We compare our model
results to the observed near-IR to UV polarization of the source and predict
its X-ray polarization. We find that the 2-8 keV polarization fraction of a
standard AGN model varies from less then a few percent along polar viewing
angles up to tens of percent at equatorial inclinations. At viewing angles
around the type-1/type-2 transition the X-ray polarization variability differs
between a static or a receding torus scenario. In the former case, the expected
2-8 keV polarization of NGC 4151 is found to be 1.21% +/- 0.34% with a constant
polarization position angle, while in the later scenario it varies from 0.1% to
6% depending on the photon index of the primary radiation. Additionally, an
orthogonal rotation of the polarization position angle with photon energy
appears for very soft primary spectra. Future X-ray polarimetry missions will
be able to test if the receding model is valid for Seyfert galaxies seen at a
viewing angle close to the torus horizon. The overall stability of the
polarization position angle for photon indexes softer than {\Gamma} = 1.5
ensures that reliable measurements of X-ray polarization are possible. We
derive a long-term observational strategy for NGC 4151 assuming observations
with a small to medium-size X-ray polarimetry satellite.Comment: 10 pages, 8 Figures, accepted for publication in A&
Heat Fluctuations in Brownian Transducers
Heat fluctuation probability distribution function in Brownian transducers
operating between two heat reservoirs is studied. We find, both analytically
and numerically, that the recently proposed Fluctuation Theorem for Heat
Exchange [C. Jarzynski and D. K. Wojcik, Phys. Rev. Lett. 92, 230602 (2004)]
has to be modified when the coupling mechanism between both baths is
considered. We also extend such relation when external work is present. Our
work fixes the domain of applicability of the theorem in more realistic
operating systems.Comment: Comments are welcom
Enhanced van der Waals interaction at interfaces
Using a recently obtained (general) formula for the interaction energy
between an excited and a ground-state atom (Sherkunov Y 2007 Phys. Rev. A 75
012705), we consider the interaction energy between two such atoms near the
interface between two media. We demonstrate that under the circumstances of the
resonant coupling of the excited atom to the surface polariton mode of a
vacuum-medium system the nonretarded atom*-atom interaction energy can be
enhanced by (several) orders of magnitude in comparison with the van der Waals
interaction energy of the two isolated atoms.Comment: 8 pages, 5 figures, local-field corrections included and improved
presentatio
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