Magnetic ordering in GaAlAs:Mn double well structure

The magnetic order in the diluted magnetic semiconductor barrier of double AlAs/GaAs: Mn quantum well structures is investigated by Monte Carlo simulations. A confinement adapted RKKY mechanism is implemented for indirect exchange between Mn ions mediated by holes. It is shown that, depending on the barrier width and the hole concentration a ferromagnetic or a spin-glass order can be established.Comment: 3 figure

A dynamical point of view of Quantum Information: Wigner measures

We analyze a known version of the discrete Wigner function and some connections with Quantum Iterated Funcion Systems. This paper is a follow up of "A dynamical point of view of Quantum Information: entropy and pressure" by the same authors

Melting of polymer blends and concomitant morphology development in single screw extruders

The current understanding of the melting stage in single screw extruders results from pioneering research efforts that were initiated in the fifties and continued for more than thirty years. Most of these theoretical and experimental studies used homopolymers as model systems, whereas in industrial practice there has been a considerable evolution in terms of the complexity of the materials being extruded. This work reports an attempt to monitor the melting sequence and the morphology development of immiscible physical and chemically compatibilized PA6/PP blends. A hybrid melting mechanism, incorporating elements of the Tadmor and of the Dispersive melting mechanisms seems to develop; the early stages of morphology development seem to be similar to those observed in the Haake mixer and Twin-screw extruder

Melting of immiscible physical and compatibilized polymer blends in single screw extruders

Melting is a major step in plasticating single screw extrusion, but most of the existing phenomenological know how was gathered by performing Maddock-type experiments with homopolymers. Given the current widespread industrial use of polymer blends, it is worth determining whether the same mechanisms and mathematical models apply, or whether different sequences develop. This work reports the results of Maddock-type experiments using a PA6/PP blend, both in its immiscible and compatibilized varieties. A melting mechanism combining the features of the classical Tadmor mechanism and of the dispersed melting mechanism, also previously reported in the literature, was observed

Morphology development of immiscible polymer blends during melting in single-screw extruders : effect of composition and compatibilization

Melting in single screw extruders began to be studied in the fifties, based on the pioneering work of Maddock. Most theoretical and experimental studies used homopolymers as model systems. However, in practice, there has been a considerable evolution in terms of the complexity of the materials being extruded. In the case of polymer blends, the morphology developed during melting should determine the final blend properties. Therefore, this work aims at investigating the morphology evolution during the melting stage of immiscible physical and chemically compatibilized PA6/PP blends. In general, the sequence of steps of morphology evolution reported for twin screw extruders and batch mixers was observed, though adapted to the flow kinematics along a helical single screw channel. The global morphological development is not affected by blend composition, but distinct domains seem to be formed when in situ reactive compatibilization takes place

Spin-polarized transport in ferromagnetic multilayered semiconductor nanostructures

The occurrence of inhomogeneous spin-density distribution in multilayered ferromagnetic diluted magnetic semiconductor nanostructures leads to strong dependence of the spin-polarized transport properties on these systems. The spin-dependent mobility, conductivity and resistivity in (Ga,Mn)As/GaAs,(Ga,Mn)N/GaN, and (Si,Mn)/Si multilayers are calculated as a function of temperature, scaled by the average magnetization of the diluted magnetic semiconductor layers. An increase of the resistivity near the transition temperature is obtained. We observed that the spin-polarized transport properties changes strongly among the three materials.Comment: 3 pages, 4 figure

Asymptotic Entanglement Dynamics and Geometry of Quantum States

A given dynamics for a composite quantum system can exhibit several distinct properties for the asymptotic entanglement behavior, like entanglement sudden death, asymptotic death of entanglement, sudden birth of entanglement, etc. A classification of the possible situations was given in [M. O. Terra Cunha, {\emph{New J. Phys}} {\bf{9}}, 237 (2007)] but for some classes there were no known examples. In this work we give a better classification for the possibile relaxing dynamics at the light of the geometry of their set of asymptotic states and give explicit examples for all the classes. Although the classification is completely general, in the search of examples it is sufficient to use two qubits with dynamics given by differential equations in Lindblad form (some of them non-autonomous). We also investigate, in each case, the probabilities to find each possible behavior for random initial states.Comment: 9 pages, 2 figures; revised version accepted for publication in J. Phys. A: Math. Theo

Driven flow with exclusion and transport in graphene-like structures

The totally asymmetric simple exclusion process (TASEP), a well-known model in its strictly one-dimensional (chain) version, is generalized to cylinder (nanotube) and ribbon (nanoribbon) geometries. A mean-field theoretical description is given for very narrow ribbons ("necklaces"), and nanotubes. For specific configurations of bond transmissivity rates, and for a variety of boundary conditions, theory predicts equivalent steady state behavior between (sublattices on) these structures and chains. This is verified by numerical simulations, to excellent accuracy, by evaluating steady-state currents. We also numerically treat ribbons of general width. We examine the adequacy of this model to the description of electronic transport in carbon nanotubes and nanoribbons, or specifically-designed quantum dot arrays.Comment: RevTeX, 13 pages, 9 figures (published version