MHD numerical simulations of colliding winds in massive binary systems - I. Thermal versus non-thermal radio emission

In the past few decades detailed observations of radio and X-ray emission from massive binary systems revealed a whole new physics present in such systems. Both thermal and non-thermal components of this emission indicate that most of the radiation at these bands originates in shocks. O and B-type stars and WolfRayet (WR) stars present supersonic and massive winds that, when colliding, emit largely due to the freefree radiation. The non-thermal radio and X-ray emissions are due to synchrotron and inverse Compton processes, respectively. In this case, magnetic fields are expected to play an important role in the emission distribution. In the past few years the modelling of the freefree and synchrotron emissions from massive binary systems have been based on purely hydrodynamical simulations, and ad hoc assumptions regarding the distribution of magnetic energy and the field geometry. In this work we provide the first full magnetohydrodynamic numerical simulations of windwind collision in massive binary systems. We study the freefree emission characterizing its dependence on the stellar and orbital parameters. We also study self-consistently the evolution of the magnetic field at the shock region, obtaining also the synchrotron energy distribution integrated along different lines of sight. We show that the magnetic field in the shocks is larger than that obtained when the proportionality between B and the plasma density is assumed. Also, we show that the role of the synchrotron emission relative to the total radio emission has been underestimated.

Constitutive models for biodegradable thermoplastic ropes for ligament repair

The concept behind a biodegradable ligament device is to temporarily replace the biomechanical functions of the ruptured ligament, while it progressively regenerates its capacities. However, there is a lack of methods to predict the mechanical behaviour evolution of the biodegradable devices during degradation, which is an important aspect of the project. In this work, a hyper elastic constitutive model will be used to predict the mechanical behaviour of a biodegradable rope made of aliphatic polyesters. A numerical approach using ABAQUS is presented, where the material parameters of the model proposal are automatically updated in correspondence to the degradation time, by means of a script in PYTHON. In this method we also use a User Material subroutine (UMAT) to apply a failure criterion base on the strength that decreases according to a first order differential equation. The parameterization of the material model proposal for different degradation times were achieved by fitting the theoretical curves with the experimental data of tensile tests on fibres. To model all the rope behaviour we had considered one step of homogenisation considering the fibres architectures in an elementary volume. (C) 2012 Elsevier Ltd. All rights reserved.

Evolution of a dense neutrino gas in matter and electromagnetic field

We describe the system of massive Weyl fields propagating in a background matter and interacting with an external electromagnetic field. The interaction with an electromagnetic field is due to the presence of anomalous magnetic moments. To canonically quantize this system first we develop the classical field theory treatment of Weyl spinors in frames of the Hamilton formalism which accounts for the external fields. Then, on the basis of the exact solution of the wave equation for a massive Weyl field in a background matter we obtain the effective Hamiltonian for the description of spin-flavor oscillations of Majorana neutrinos in matter and a magnetic field. Finally, we incorporate in our analysis the neutrino self-interaction which is essential when the neutrino density is sufficiently high. We also discuss the applicability of our results for the studies of collective effects in spin-flavor oscillations of supernova neutrinos in a dense matter and a strong magnetic field. (C) 2011 Elsevier B.V. All rights reserved.