5,798 research outputs found
Transport through a vibrating quantum dot: Polaronic effects
We present a Green's function based treatment of the effects of
electron-phonon coupling on transport through a molecular quantum dot in the
quantum limit. Thereby we combine an incomplete variational Lang-Firsov
approach with a perturbative calculation of the electron-phonon self energy in
the framework of generalised Matsubara Green functions and a Landauer-type
transport description. Calculating the ground-state energy, the dot
single-particle spectral function and the linear conductance at finite carrier
density, we study the low-temperature transport properties of the vibrating
quantum dot sandwiched between metallic leads in the whole electron-phonon
coupling strength regime. We discuss corrections to the concept of an
anti-adiabatic dot polaron and show how a deformable quantum dot can act as a
molecular switch.Comment: 10 pages, 8 figures, Proceedings of "Progress in Nonequilibrium
Green's Function IV" Conference, Glasgow 200
Thermoplastic matrix composite processing model
The effects the processing parameters pressure, temperature, and time have on the quality of continuous graphite fiber reinforced thermoplastic matrix composites were quantitatively accessed by defining the extent to which intimate contact and bond formation has occurred at successive ply interfaces. Two models are presented predicting the extents to which the ply interfaces have achieved intimate contact and cohesive strength. The models are based on experimental observation of compression molded laminates and neat resin conditions, respectively. Identified as the mechanism explaining the phenomenon by which the plies bond to themselves is the theory of autohesion (or self diffusion). Theoretical predictions from the Reptation Theory between autohesive strength and contact time are used to explain the effects of the processing parameters on the observed experimental strengths. The application of a time-temperature relationship for autohesive strength predictions is evaluated. A viscoelastic compression molding model of a tow was developed to explain the phenomenon by which the prepreg ply interfaces develop intimate contact
Carrier-density effects in many-polaron systems
Many-polaron systems with finite charge-carrier density are often encountered
experimentally. However, until recently, no satisfactory theoretical
description of these systems was available even in the framework of simple
models such as the one-dimensional spinless Holstein model considered here. In
this work, previous results obtained using numerical as well as analytical
approaches are reviewed from a unified perspective, focussing on spectral
properties which reveal the nature of the quasiparticles in the system. In the
adiabatic regime and for intermediate electron-phonon coupling, a
carrier-density driven crossover from a polaronic to a rather metallic system
takes place. Further insight into the effects due to changes in density is
gained by calculating the phonon spectral function, and the fermion-fermion and
fermion-lattice correlation functions. Finally, we provide strong evidence
against the possibility of phase separation.Comment: 13 pages, 6 figures, accepted for publication in J. Phys.: Condens.
Matter; final versio
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