Consistent Approximations to Impulsive Optimal Control Problems

We analyse the theory of consistent approximations given by Polak and we use it in an impulsive optimal control problem. We reparametrize the original system and build consistent approximations for this new reparametrized problem. So, we prove that if a sequence of solution of the consistent approximations is converging, it will converge to a solution of the reparametrized problem, and, finally, we show that from a solution of the reparametrized problem we can find a solution of the original one

The strong coupling regime of twelve flavors QCD

We summarize the results recently reported in Ref.[1] [A. Deuzeman, M.P. Lombardo, T. Nunes da Silva and E. Pallante,"The bulk transition of QCD with twelve flavors and the role of improvement"] for the SU(3) gauge theory with Nf=12 fundamental flavors, and we add some numerical evidence and theoretical discussion. In particular, we study the nature of the bulk transition that separates a chirally broken phase at strong coupling from a chirally restored phase at weak coupling. When a non-improved action is used, a rapid crossover is observed at small bare quark masses. Our results confirm a first order nature for this transition, in agreement with previous results we obtained using an improved action. As shown in Ref.[1], when improvement of the action is used, the transition is preceded by a second rapid crossover at weaker coupling and an exotic phase emerges, where chiral symmetry is not yet broken. This can be explained [1] by the non hermiticity of the improved lattice Transfer matrix, arising from the competition of nearest-neighbor and non-nearest neighbor interactions, the latter introduced by improvement and becoming increasingly relevant at strong coupling and coarse lattices. We further comment on how improvement may generally affect any lattice system at strong coupling, be it graphene or non abelian gauge theories inside or slightly below the conformal window.Comment: 7 pages, 7 figures, Proceedings of the 30th International Symposium on Lattice Field Theory, June 24 - 29, 2012, Cairns, Australi

Latin American foreign exchange intervention - Updated

We examine Latin American foreign exchange intervention in a framework where the exchange rate regime is endogenous and there exists an inefficient, equilibrium foreign exchange intervention bias. The model suggests that greater central bank independence is associated with lesser intervention in the foreign exchange market, and also with leaning-against-the-wind intervention. Both results are confirmed by data from 13 Latin American countries.foreign exchange intervention; exchange rates; Latin America

Rational bubbles in emerging stockmarkets

We detected rational bubbles in 22 emerging stockmarkets using both standard and threshold cointegration. Eighteen stockmarkets experienced explosive bubbles (and some of them periodically collapsing bubbles as well). The remaining four markets experienced periodically collapsing bubbles only.bubbles; stockmarkets; emerging markets

Foreign exchange intervention and central bank independence: The Latin American experience

Employing data from 13 Latin American countries, we find that greater central bank independence is associated with lesser intervention in the foreign exchange market, and also with leaning-against-the-wind intervention. We also find that the structural reforms that occurred in Latin America mostly in the 1990s helped to reduce the need for foreign exchange intervention.central bank independence; foreign exchange intervention; Latin America

Explosive and periodically collapsing bubbles in emerging stockmarkets

We detected bubbles in 22 emerging stockmarkets using both standard and threshold cointegration. Eighteen stockmarkets experienced explosive bubbles (and some of them periodically collapsing bubbles as well). The remaining four markets experienced periodically collapsing bubbles only.Periodically collapsing bubbles

Complex evolution of the electronic structure from polycrystalline to monocrystalline graphene: generation of a new Dirac point

First principles calculations, employed to address the properties of polycrystalline graphene, indicate that the electronic structure of tilt grain boundaries in this system displays a rather complex evolution towards graphene bulk, as the tilt angle decreases, with the generation of a new Dirac point at the Fermi level, and an anisotropic Dirac cone of low energy excitations. Moreover, the usual Dirac point at the {\bf K} point falls below the Fermi level, and rises towards it as the tilt angle decreases. Further, our calculations indicate that the grain-boundary formation energy behaves non-monotonically with the tilt angle, due to a change in the the spatial distribution and relative contributions of the bond-stretching and bond-bending deformations associated with the formation of the defect.Comment: 4 pages (+ a few references on 5th page). Contains text (.tex) file + 4 figures + pdf fil

Conformal or Confining

We present a lattice study of the phase transitions at zero and nonzero temperature for the $SU(3)$ gauge theory with a varying number of flavours $N_f$ in the fundamental representation of the gauge group. We show that all results are consistent with a lower edge of the conformal window between $N_f=8$ and $N_f=6$. A lower edge in this interval is in remarkable agreement with perturbation theory and recent large-$N$ arguments. .Comment: 5 pages, 5 figures. New results added, conclusions strengthened. Scalar glueball now treated in a separate articl