Condensed Matter Theory

Abstract:

The behavior of a disclination line in a Grandjean-Cano wedge is investigated under an electric field applied normal to the cell substrates. The focus of attention is the first disclination, separating the untwisted and the π -twisted area. This disclination line shows a field dependent migration process that was observed in the cholesteric mixture ZLI-1132/S811. The dynamics of this migration process is studied experimentally and is compared with two theoretical models. One model utilizes a two-dimensional lattice Boltzmann approach to predict the initial migration movement, whereas a one-dimensional continuum model allows a full analysis of the experimental results. © 2006 American Institute of Physics.

Abstract:

In a quantum dot with three leads, the transmission matrix t12 between two of these leads is a truncation of a unitary scattering matrix S, which we treat as random. As the number of channels in the third lead is increased, the constraints from the symmetry of S become less stringent and t12 becomes closer to a matrix of complex Gaussian random numbers with no constraints. We consider the distribution of the singular values of t12, which is related to a number of physical quantities.

Abstract:

Maximum trapping efficiency in optical tweezers occurs close to the coverslip because spherical aberration owing to a mismatch in the refractive indices of the specimen (water) and the immersion oil dramatically decreases the trap efficiency as the trap depth increases. Measuring the axial trap efficiency at various tube lengths by use of an oil-immersion objective has shown that such an aberration can be balanced by another source of spherical aberration, leading to a shift in the position of the maximum efficiency in the Z direction. For a 1.1 microm polystyrene bead we could achieve the maximal efficiency at a depth of 70 microm, whereas the trap was stable up to a depth of 100 microm.