Angular distributions of scattered excited muonic hydrogen atoms

Differential cross sections of the Coulomb deexcitation in the collisions of excited muonic hydrogen with the hydrogen atom have been studied for the first time. In the framework of the fully quantum-mechanical close-coupling approach both the differential cross sections for the $nl \to n'l'$ transitions and $l$-averaged differential cross sections have been calculated for exotic atom in the initial states with the principle quantum number $n=2 - 6$ at relative motion energies $E_{\rm {cm}}=0.01 - 15$ eV and at scattering angles $\theta_{\rm {cm}}=0 - 180^{\circ}$. The vacuum polarization shifts of the $ns$-states are taken into account. The calculated in the same approach differential cross sections of the elastic and Stark scattering are also presented. The main features of the calculated differential cross sections are discussed and a strong anisotropy of cross sections for the Coulomb deexcitation is predicted.Comment: 5 pages, 9 figure

Study of the one-dimensional off-lattice hot-monomer reaction model

Hot monomers are particles having a transient mobility (a ballistic flight) prior to being definitely absorbed on a surface. After arriving at a surface, the excess energy coming from the kinetic energy in the gas phase is dissipated through degrees of freedom parallel to the surface plane. In this paper we study the hot monomer-monomer adsorption-reaction process on a continuum (off-lattice) one-dimensional space by means of Monte Carlo simulations. The system exhibits second-order irreversible phase transition between a reactive and saturated (absorbing) phases which belong to the directed percolation (DP) universality class. This result is interpreted by means of a coarse-grained Langevin description which allows as to extend the DP conjecture to transitions occurring in continuous media.Comment: 13 pages, 5 figures, final version to appear in J. Phys.

Phonon-induced quadrupolar ordering of the magnetic superconductor TmNi2_2B2_2C

We present synchrotron x-ray diffraction studies revealing that the lattice of thulium borocarbide is distorted below T_Q = 13.5 K at zero field. T_Q increases and the amplitude of the displacements is drastically enhanced, by a factor of 10 at 60 kOe, when a magnetic field is applied along [100]. The distortion occurs at the same wave vector as the antiferromagnetic ordering induced by the a-axis field. A model is presented that accounts for the properties of the quadrupolar phase and explains the peculiar behavior of the antiferromagnetic ordering previously observed in this compound.Comment: submitted to PR

Dynamic Critical approach to Self-Organized Criticality

A dynamic scaling Ansatz for the approach to the Self-Organized Critical (SOC) regime is proposed and tested by means of extensive simulations applied to the Bak-Sneppen model (BS), which exhibits robust SOC behavior. Considering the short-time scaling behavior of the density of sites ($\rho(t)$) below the critical value, it is shown that i) starting the dynamics with configurations such that $\rho(t=0) \to 0$ one observes an {\it initial increase} of the density with exponent $\theta = 0.12(2)$; ii) using initial configurations with $\rho(t=0) \to 1$, the density decays with exponent $\delta = 0.47(2)$. It is also shown that he temporal autocorrelation decays with exponent $C_a = 0.35(2)$. Using these, dynamically determined, critical exponents and suitable scaling relationships, all known exponents of the BS model can be obtained, e.g. the dynamical exponent $z = 2.10(5)$, the mass dimension exponent $D = 2.42(5)$, and the exponent of all returns of the activity $\tau_{ALL} = 0.39(2)$, in excellent agreement with values already accepted and obtained within the SOC regime.Comment: Rapid Communication Physical Review E in press (4 pages, 5 figures

Sub-ballistic behavior in quantum systems with L\'evy noise

We investigate the quantum walk and the quantum kicked rotor in resonance subjected to noise with a L\'evy waiting time distribution. We find that both systems have a sub-ballistic wave function spreading as shown by a power-law tail of the standard deviation.Comment: 4 pages, 4 figure