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Scanning tunneling microscopy and first-principles atomic orbital based calculations have been used to study TiO 2 (110)1ϫ2. A structure is proposed that resolves the controversy surrounding the surface morphology. Our model is simple, in that it consists only of atoms in their bulk-terminated positions. Theoretical modeling of the images shows an agreement with the experimental data that cannot be achieved even qualitatively for the previously proposed models. Furthermore, a previously unobserved 1ϫ3 phase has been imaged that can be simply explained in terms of the model.

A finite-element model of liquid-crystal hydrodynamics based on the Qian and Sheng formulation has been developed. This formulation is a generalization of the Ericksen-Leslie theory to include variations in the order parameter, allowing for a proper description of disclinations. The present implementation is well suited to treat properly the various length scales necessary to model large regions yet resolve the rapid variations in the order parameter in proximity to disclinations.Index Terms-Finite elements, liquid-crystal (LC) modeling, variable order parameter.

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Abstract-Research on reducing material absorption in Terahertz (THz) waveguides has lead to development of guiding structures with transmission losses as low as 1 dB/m. Among waveguides that exhibit low loss at THz frequencies are the dielectriclined hollow cylindrical metallic waveguides. Loss reduction in this waveguide is attributed to an ideal profile of the dominant hybrid HE mode. This mode profile also results in relatively low dispersion and very high coupling efficiency. In this contribution we overview properties of dielectric-lined hollow cylindrical metallic waveguides for THz waves, their design principles and the fabrication process. The impact of the mode profile on losses and dispersion at THz frequencies is confirmed experimentally by THz near-field imaging and THz time-domain spectroscopy and numerically by the finite element method.