Chaos in Time Dependent Variational Approximations to Quantum Dynamics

Dynamical chaos has recently been shown to exist in the Gaussian approximation in quantum mechanics and in the self-consistent mean field approach to studying the dynamics of quantum fields. In this study, we first show that any variational approximation to the dynamics of a quantum system based on the Dirac action principle leads to a classical Hamiltonian dynamics for the variational parameters. Since this Hamiltonian is generically nonlinear and nonintegrable, the dynamics thus generated can be chaotic, in distinction to the exact quantum evolution. We then restrict attention to a system of two biquadratically coupled quantum oscillators and study two variational schemes, the leading order large N (four canonical variables) and Hartree (six canonical variables) approximations. The chaos seen in the approximate dynamics is an artifact of the approximations: this is demonstrated by the fact that its onset occurs on the same characteristic time scale as the breakdown of the approximations when compared to numerical solutions of the time-dependent Schrodinger equation.Comment: 10 pages (12 figures), RevTeX (plus macro), uses epsf, minor typos correcte

Effect of solar fraction on the economic performance of a solar air conditioning by an adsorption chiller / F. Basrawi et al.

Solar cooling is a promising way for a sustainable air-conditioning system. However, since solar has intermittent output, it is usually backed-up by a conventional heater. Thus, it still needs electricity or fossil fuel to operate stabily. This study presents the effect of ratio of heat delivered by solar to the total heat delivered to an adsorption chiller (solar fraction) on the economic performance of a solar cooling system. This cooling system need covers cooling demand for an office building in a tropical region (Kuala Lumpur). Cooling demand was simulated using well-known energy analysis software for building, Equest. Flat-plate collectors and an adsorption chiller were the main component of the cooling system. Flat-plate collecters were simulated using another software, Watsun, and the adsorption chiller was based on our simulation model that is comparable with other studies. Economic performance was analyzed by life cycle cost analysis. Solar fraction of 0.33, 0.74 and 0.98 were studied. It was found that none of the solar fraction studied can generate Net Profit under subsidized electricity. It was also found that a natural gas boiler is a better solution than an electric heater as an auxiliary heater in term of economic. For a natural gas boiler, Net Profit increased when solar fraction decreased; the highest one was solar fraction of 0.33 with US$15,600. However, since more energy is used for the auxiliary heater in lower solar fraction, more emissions is expected to be released. Thus, emissions for all solar fraction need to be considered and studied further

Out of Equilibrium Non-perturbative Quantum Field Dynamics in Homogeneous External Fields

The quantum dynamics of the symmetry broken lambda (Phi^2)^2 scalar field theory in the presence of an homogeneous external field is investigated in the large N limit. We choose as initial state the ground state for a constant external field J .The sign of the external field is suddenly flipped from J to - J at a given time and the subsequent quantum dynamics calculated. Spinodal instabilities and parametric resonances produce large quantum fluctuations in the field components transverse to the external field. This allows the order parameter to turn around the maximum of the potential for intermediate times. Subsequently, the order parameter starts to oscillate near the global minimum for external field - J, entering a novel quasi-periodic regime.Comment: LaTex, 30 pages, 12 .ps figures, improved version to appear in Phys Rev