Phonon Rabi-assisted tunneling in diatomic molecules

We study electronic transport in diatomic molecules connected to metallic contacts in the regime where both electron-electron and electron-phonon interactions are important. We find that the competition between these interactions results in unique resonant conditions for interlevel transitions and polaron formation: the Coulomb repulsion requires additional energy when electrons attempt phonon-assisted interlevel jumps between fully or partially occupied levels. We apply the equations of motion approach to calculate the electronic Green's functions. The density of states and conductance through the system are shown to exhibit interesting Rabi-like splitting of Coulomb blockade peaks and strong temperature dependence under the it interacting resonant conditions.Comment: Updated version, 5 pages, 4 figures, to be published in Phys. Rev. B on 9/1

Optical Phonon Lasing in Semiconductor Double Quantum Dots

We propose optical phonon lasing for a double quantum dot (DQD) fabricated in a semiconductor substrate. We show that the DQD is weakly coupled to only two LO phonon modes that act as a natural cavity. The lasing occurs for pumping the DQD via electronic tunneling at rates much higher than the phonon decay rate, whereas an antibunching of phonon emission is observed in the opposite regime of slow tunneling. Both effects disappear with an effective thermalization induced by the Franck-Condon effect in a DQD fabricated in a carbon nanotube with a strong electron-phonon coupling.Comment: 8 pages, 4 figure

Manoeuvring and seakeeping aspects of pod-driven ships

An existing coupled non-linear six-degree-of-freedom model, which combines manoeuvring and seakeeping, is being enhanced for the simulation of motions of azimuthing pod-driven vessels. The equations of motions and modified numerical model for calculation of pod-induced propulsive and hull forces are presented. The modified numerical code has been verified using an extensive amount of experimental data for both conventional and pod-driven roll-on roll-off passenger ship/ferry (ROPAX) hull forms. Comparisons have been made between conventional and podded control using zigzag and pull-out manoeuvring tests and significant motion amplitudes in waves, with the aim of investigating the directional stability and course-keeping ability of pod-driven ships, as well as the effect of large pod-induced heel angles to the turning and ship motions in waves. The results showed satisfactory agreement with experiments for the enhanced model. In the light of this investigation, the importance of hydrodynamic optimization for the azimuthing pod-driven ship design to eliminate any stability and control problems caused by design modifications has been demonstrated by the use of numerical simulations. Finally the efficiency of the azimuthing podded drives, in terms of overall controllability and seakeeping characteristics of ships, is discussed and conclusions are drawn

A mixed finite-element finite-difference method for nonlinear fluid-structure interaction dynamics. I. Fluid-rigid structure interaction

A mixed finite-element finite-difference numerical method is developed to calculate nonlinear fluid-solid interaction problems. In this study, the structure is assumed to be rigid with large motion and the fluid flow is governed by nonlinear, viscous or non-viscous, field equations with nonlinear boundary conditions applied to the free surface and fluid-solid interaction interfaces. A moving coordinate system fixed at a point in the structure is used to describe the fluid flow, and for numerical analysis purposes, an arbitrary Lagrangian-Eulerian mesh system is constructed relative to this moving system. This provides a convenient method of overcoming the difficulties of matching fluid meshes with large solid motion. Nonlinear numerical equations describing nonlinear fluid-solid interaction dynamics are derived through a numerical discretization scheme of study. A coupling iteration process is used to solve these numerical equations. A selection of numerical examples illustrates the developed mathematical model and through numerical simulations it is shown that the proposed approach is practical and useful