Numerical study of the shape and integral parameters of a dendrite

We present a numerical study of sidebranching of a solidifying dendrite by means of a phase--field model. Special attention is paid to the regions far from the tip of the dendrite, where linear theories are no longer valid. Two regions have been distinguished outside the linear region: a first one in which sidebranching is in a competition process and a second one further down where branches behave as independent of each other. The shape of the dendrite and integral parameters characterizing the whole dendrite (contour length and area of the dendrite) have been computed and related to the characteristic tip radius for both surface tension and kinetic dominated dendrites. Conclusions about the different behaviors observed and comparison with available experiments and theoretical predictions are presented.Comment: 10 pages, 7 figures, Accepted for publication in Phys. Rev.

Room temperature ferromagnetic-like behavior in Mn-implanted and post-annealed InAs layers deposited by Molecular Beam Epitaxy

We report on the magnetic and structural properties of Ar and Mn implanted InAs epitaxial films grown on GaAs (100) by Molecular Beam Epitaxy (MBE) and the effect of Rapid Thermal Annealing (RTA) for 30 seconds at 750C. Channeling Particle Induced X- ray Emission (PIXE) experiments reveal that after Mn implantation almost all Mn atoms are subsbtitutional in the In-site of the InAs lattice, like in a diluted magnetic semiconductor (DMS). All of these samples show diamagnetic behavior. But, after RTA treatment the Mn-InAs films exhibit room-temperature magnetism. According to PIXE measurements the Mn atoms are no longer substitutional. When the same set of experiments were performed with As as implantation ion all of the layers present diamagnetism without exception. This indicates that the appearance of room-temperature ferromagnetic-like behavior in the Mn-InAs-RTA layer is not related to lattice disorder produce during implantation, but to a Mn reaction produced after a short thermal treatment. X-ray diffraction patterns (XRD) and Rutherford Back Scattering (RBS) measurements evidence the segregation of an oxygen deficient-MnO2 phase (nominally MnO1.94) in the Mn-InAs-RTA epitaxial layers which might be on the origin of room temperature ferromagnetic-like response observed.Comment: 16 pages, 5 figures. Acepted in J. Appl. Phy

Data Augmentation in the Bayesian Multivariate Probit Model

This paper is concerned with the Bayesian estimation of a Multivariate Probit model. In particular, this paper provides an algorithm that obtains draws with low correlation much faster than a pure Gibbs sampling algorithm. The algorithm consists in sampling some characteristics of slope and variance parameters marginally on the latent data. Estimations with simulated datasets illustrate that the proposed algorithm can be much faster than a pure Gibbs sampling algorithm. For some datasets, the algorithm is also much faster than the efficient algorithm proposed by Liu and Wu (1999) in the context of the univariate Probit model

Structural Changes in the Transmission Mechanism of Monetary Policy in Mexico: A Non-linear VAR Approach

In this paper we present a first approach to the study of the transformation in the transmission mechanism of monetary policy that has taken place in Mexico in recent years. For this purpose, we use a non-linear VAR model that allows for regime shifts. The comparison of the different regimes identified leads to the following main findings: a) there was a major structural change in the transmission mechanism around January 2001, date that coincides with the formal adoption of the inflation targeting framework; b) after this change, fluctuations in the real exchange rate have had smaller effects on the process of price formation, the formation of inflation expectations and the nominal interest rate; c) also, there have been stronger reactions of the nominal interest rate to increases in the output gap and the rate of inflation; and d) the movements of the nominal interest rate have a more effective influence on the real exchange rate and the rate of inflation.Monetary policy, Mexico, Monetary transmission mechanism

Uncertainty about the Persistence of Cost-Push Shocks and the Optimal Reaction of the Monetary Authority.

In this paper we formalize the uncertainty about the persistence of cost-push shocks using an open economy optimal control model with Markov regime-switching and robust control. The latter is used in only one of the regimes producing relatively more persistent cost-push shocks in that regime. Conditional on being in the regime with relatively less persistence, we obtain two main results: a) underestimating the probability of switching to the regime with relatively more persistent cost-push shocks causes higher welfare losses than its overestimation; and b) the welfare losses associated with either underestimation or overestimation of such probability increase with the size of the penalty on inflation deviations from its target. Keywords: Model uncertainty, Robustness, Markov regime-switching, Monetary policy, Inflation targeting.Model uncertainty, Robustness, Markov regime-switching, Monetary policy, Inflation targeting

Free Fermionic Elliptic Reflection Matrices and Quantum Group Invariance

Elliptic diagonal solutions for the reflection matrices associated to the elliptic $R$ matrix of the eight vertex free fermion model are presented. They lead through the second derivative of the open chain transfer matrix to an XY hamiltonian in a magnetic field which is invariant under a quantum deformed Clifford--Hopf algebra.Comment: 9 pages, Late

THE METHOD OF SIMULATED MAXIMUM LIKELIHOOD FOR THE ESTIMATON OF DYNAMIC ORDERED PROBIT: AN APPLICATION TO COUNTRY-RISK FOR NON-DEVELOPED COUNTRIES

This paper aims to give a detailed explanation of the econometric methodology necessary to estimate dynamic probit models with ordinal dependent variables. A typology of cases are established which appear when considering different choices of individual heterogeneity along with time correlation. To be able to estimate by maximum likelihood the models which come out of the different alternatives proposed, simulation techniques are used and put into practice by the GHK simulator and, in this way, estimators by simulated maximum likelihood are obtained. Finally, all the models described are used to measure and determine the macroeconomic factors which explain the ratings of country-risk in non-developed countries.Country risk, panel data, external debt, dynamic ordered probit

Impact of Electric Fields on Highly Excited Rovibrational States of Polar Dimers

We study the effect of a strong static homogeneous electric field on the highly excited rovibrational levels of the LiCs dimer in its electronic ground state. Our full rovibrational investigation of the system includes the interaction with the field due to the permanent electric dipole moment and the polarizability of the molecule. We explore the evolution of the states next to the dissociation threshold as the field strength is increased. The rotational and vibrational dynamics are influenced by the field; effects such as orientation, angular motion hybridization and squeezing of the vibrational motion are demonstrated and analyzed. The field also induces avoided crossings causing a strong mixing of the electrically dressed rovibrational states. Importantly, we show how some of these highly excited levels can be shifted to the continuum as the field strength is increased, and reversely how two atoms in the continuum can be brought into a bound state by lowering the electric field strength.Comment: 10 pages, 4 figure

Quaternary glacial evolution in the Central Cantabrian Mountains (Northern Spain)

Peer reviewedPostprin