A technique has recently been proposed for determining the elastic constant ratio K22∕K11 in nematic liquid crystals [E. P. Raynes, C. V. Brown, and J. F. Strömer, Appl. Phys. Lett. 82, 13 (2003)]. This technique has been applied to five nematic materials that cover a range of K33∕K11 elastic constant ratio values. An unusually high value of K22∕K11 is found in one material. High values of the ratio K22∕K11 tended to occur in materials that also have high values of the ratio K33∕K11. The results are validated with independent measurements of K22 from cholesteric helix unwinding.

A technique has been developed for the measurement of the K22 twist elastic constant in nematic liquid crystal materials. This involves the measurement of the Freedericksz transition voltages in untwisted linear and π-twist regions in a wedge cell geometry. The method avoids the need for the accurate determination of the cell thickness and cholesteric pitch and is far more straightforward to implement than other methods in the literature. The validity of this method is demonstrated for the well-characterized material E7.

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The strong influence of the complex reverse flow phenomenon on the dynamic temperature behavior of vertically aligned liquid crystal displays (VA-LCDs) has been demonstrated. Good agreement was obtained between theoretical and experimental switching profiles over a wide temperature range (25–75°C). This was achieved using the Leslie–Ericksen theory in a one-dimensional model with material viscosity coefficients obtained from an improved estimation procedure. Such accurate numerical simulations can have a large impact on further improvements of VA-LCDs (e.g., the development of temperature-compensating driving schemes).

In this paper, we report on high critical current density (J c ) YBCO films deposited by pulsed laser deposition on CeO 2 buffered ABAD-YSZ/stainless steel templates with a thickness ranging from 0.7 μm up to 4.2 μm. In the thinnest sample, a transition temperature (T c ) of 90 K and a critical current density of 2.6 MA/cm 2 was reached at 77 K. With increasing thickness, T c drops as well as J c . The total critical current (I c ) increases strongly up to a thickness of 2.8 μm, reaching a value of almost 600 A/cm-width. In thicker films, no further increase in I c was observed. A higher surface roughness and misoriented YBCO grains were found in layer thicknesses above 2.8 μm and are assumed to be the main reason for the limitation of the current transport.

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Articles you may be interested inBound states for an induced electric dipole in the presence of an azimuthal magnetic field and a disclinationThe 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 -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.