3,857 research outputs found
Incommensurate magnetism in cuprate materials
In the low doping region an incommensurate magnetic phase is observed in
LSCO. By means of the composite operator method we show that the single-band 2D
Hubbard model describes the experimental situation. In the higher doping
region, where experiments are not available, the incommensurability is
depressed owing to the van Hove singularity near the Fermi level. A
proportionality between the incommensurability amplitude and the critical
temperature is predicted, suggesting a close relation between superconductivity
and incommensurate magnetism.Comment: 4 pages, 5 figures in one Postscript file, RevTe
Inverse modeling of European CH4 emissions: sensitivity to the observational network
Inverse modeling is widely employed to provide “top-down” emission estimates using atmospheric measurements. Here, we analyze the dependence of derived CH4 emissions on the sampling frequency and density of the observational surface network, using the TM5-4DVAR inverse modeling system and synthetic observations. This sensitivity study focuses on Europe. The synthetic observations are created by TM5 forward model simulations. The inversions of these synthetic observations are performed using virtually no knowledge on the a priori spatial and temporal distribution of emissions, i.e. the emissions are derived mainly from the atmospheric signal detected by the measurement network. Using the European network of stations for which continuous or weekly flask measurements are available for 2001, the synthetic experiments can retrieve the “true” annual total emissions for single countries such as France within 20%, and for all North West European countries together within ~5%. However, larger deviations are obtained for South and East European countries due to the scarcity of stations in the measurement network. Upgrading flask sites to stations with continuous measurements leads to an improvement for central Europe in emission estimates. For realistic emission estimates over the whole European domain, however, a major extension of the number of stations in the existing network is required. We demonstrate the potential of an extended network of a total of ~60 European stations to provide realistic emission estimates over the whole European domain
Valore aggiunto alle nostre strade
Si viene determinando l’esigenza di riflettere sulla necessità di decidere quale funzione assegnare ai diversi elementi dei patrimoni esistenti quando si pensi alla progettazione di nuove opere. La finalità che ci si prefigge, in attesa di Norme specifiche per
l’adeguamento di infrastrutture viarie esistenti, è formulare
proposte per l’adattamento della Normativa vigente al tema
progettuale in questione
The Hubbard model in the two-pole approximation
The two-dimensional Hubbard model is analyzed in the framework of the
two-pole expansion. It is demonstrated that several theoretical approaches,
when considered at their lowest level, are all equivalent and share the
property of satisfying the conservation of the first four spectral momenta. It
emerges that the various methods differ only in the way of fixing the internal
parameters and that it exists a unique way to preserve simultaneously the Pauli
principle and the particle-hole symmetry. A comprehensive comparison with
respect to some general symmetry properties and the data from quantum Monte
Carlo analysis shows the relevance of imposing the Pauli principle.Comment: 12 pages, 8 embedded Postscript figures, RevTeX, submitted to Int.
Jou. Mod. Phys.
Strategic R&D Investment under Information Revelation\u201d
R&D projects generally involve multiple phases with or without overlapping. Moreover, the investment is usually made in a phased manner, with the commencement of the subsequent phase being dependent on the successful completion of the preceding phase. The aim of this article is to analyze the equilibrium strategies of two firms competing for a two-stage sequential R&D investment, when a firm may infer a private signal from the strategy played by the other. Thus, firms must formulate their optimal strategies in a context of imperfect information. We evaluate the resulting compound option with information revelation as an American compound exchange option using Monte Carlo simulations. We then show that different equilibria may arise
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