51,251 research outputs found
Open Quantum Systems in Noninertial Frames
We study the effects of decoherence on the entanglement generated by Unruh
effect in noninertial frames by using bit flip, phase damping and depolarizing
channels. It is shown that decoherence strongly influences the initial state
entanglement. The entanglement sudden death can happens irrespective of the
acceleration of the noninertial frame under the action of phase flip and phase
damping channels. It is investigated that an early sudden death happens for
large acceleration under the depolarizing environment. Moreover, the
entanglement increases for a highly decohered phase flip channel.Comment: 11 pages, 6 eps figure
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The Dynamics of International R & D spillovers
Coe and Helpman (1995) among others report positive and equivalent R&D spillovers
across groups of countries. However, the nature of their econometric tests does not
address the heterogeneity of knowledge diffusion across countries. We empirically
examine these issues in a sample of 10 OECD countries by extending both the time
span and the coverage of R&D activities in the data set. We find that the elasticity of
total factor productivity with respect to domestic and foreign R&D stocks is
extremely heterogeneous across countries and that data cannot be pooled. Thus, panel
estimates conceal important cross-country differences. The US appears to be a net
loser in terms of international R&D spillovers. Our interpretation is that when
competitors ‘catch-up’ technologically, they challenge US market shares and
investments worldwide. This has implications for US productivity
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Are international R&D spillovers costly for the US?
Coe and Helpman (1995) and others report positive and equivalent R&D
spillovers across G7 countries. We argue that their homogeneity constraint on
spillovers across G7 countries is inappropriate, and show that it is rejected by the data.
Extending the data set and applying new empirical approaches, we find: (i) R&D
spillovers are extremely heterogeneous across G7 countries; (ii) panel estimates do
not correspond to country specific estimates and conceal important cross-country
differences in knowledge diffusion; and (iii) the US is a net loser in terms of
international R&D spillovers. Our interpretation is that when competitors ‘catch-up’
technologically, they challenge US market shares and investments worldwide and this
has implications for US productivity
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