Temperature crossover of decoherence rates in chaotic and regular bath dynamics

The effect of chaotic bath dynamics on the decoherence of a quantum system is examined for the vibrational degrees of freedom of a diatomic molecule in a realistic, constant temperature collisional bath. As an example, the specific case of I$_2$ in liquid xenon is examined as a function of temperature, and the results compared with an integrable xenon bath. A crossover in behavior is found: the integrable bath induces more decoherence at low bath temperatures than does the chaotic bath, whereas the opposite is the case at the higher bath temperatures. These results, verifying a conjecture due to Wilkie, shed light on the differing views of the effect of chaotic dynamics on system decoherence.Comment: 7 pages, 3 figure

Geometrically derived difference formulae for the numerical integration of trajectory problems

The term 'trajectory problem' is taken to include problems that can arise, for instance, in connection with contour plotting, or in the application of continuation methods, or during phase-plane analysis. Geometrical techniques are used to construct difference methods for these problems to produce in turn explicit and implicit circularly exact formulae. Based on these formulae, a predictor-corrector method is derived which, when compared with a closely related standard method, shows improved performance. It is found that this latter method produces spurious limit cycles, and this behavior is partly analyzed. Finally, a simple variable-step algorithm is constructed and tested

International briefing 34: training and development in Spain

© 2016 John Wiley & Sons Ltd This article locates training and development in Spain within the country's socio-economic context. It maps the major changes which have been introduced into the training and development system since the briefing by Escardíbul and Llinas-Audet published in this journal in 2010. It relates those changes to the ongoing economic crisis which began in 2009 and the growing emphasis on employers’ demands in the design of the training system. Finally, it identifies the challenges presented to Spanish policy-makers by a number of weaknesses in the current system. The Spanish experience is particularly relevant for countries in which social partner involvement and a significant small and medium-sized enterprise (SME) presence are important issues in the development of their training system. It is also particularly useful for those countries in Latin America whose training systems have been influenced by the Spanish model

Symplectic algorithm for constant-pressure molecular dynamics using a Nose-Poincare thermostat

We present a new algorithm for isothermal-isobaric molecular-dynamics simulation. The method uses an extended Hamiltonian with an Andersen piston combined with the Nos'e-Poincar'e thermostat, recently developed by Bond, Leimkuhler and Laird [J. Comp. Phys., 151, (1999)]. This Nos'e-Poincar'e-Andersen (NPA) formulation has advantages over the Nos'e-Hoover-Andersen approach in that the NPA is Hamiltonian and can take advantage of symplectic integration schemes, which lead to enhanced stability for long-time simulations. The equations of motion are integrated using a Generalized Leapfrog Algorithm and the method is easy to implement, symplectic, explicit and time reversible. To demonstrate the stability of the method we show results for test simulations using a model for aluminum.Comment: 7 page

Puertas y murallas

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201