We present differential optical reflectivity and null transmission ellipsometry data from several mixtures of MHPBC enantiomers. From this data, we have determined the chiral smectic phase sequence as a function of enantiomeric excess. The data suggest a change in the structure of the smectic-C(*)(alpha) phase and the surface tilt state as the enantiomeric excess is reduced. The results also show that the intermediate phases, smectic C(*)(FI2), smectic C(*)(FI1), and smectic C(*)(alpha), disappear sequentially on reducing the net chirality.
Null transmission ellipsometry was employed to study the temperature evolution of the helical structure of the smectic-$C$${}_{\ensuremath{\alpha}}^{*}$ phase. Free-standing films with thickness ranging from 31 to more than 400 layers were prepared and studied. The experimental results show a reduced twisting power in thin films. A simple model was constructed to explain the results. Surface effects were found to be the key reason for this phenomenon. Our findings are consistent with the theoretical studies of helically ordered magnetic films.
We describe a simple method and device design that enables fast in-plane electro-optic modulation in conventional nematic liquid crystal (NLC) devices. When combined with optimized NLC materials, this approach yields rotational speeds of 1°/μs (independent of rotation angle, over a wide range) at a moderately low voltage. The observed rotational dynamics indicate that even these high speeds may not represent fundamental physical limits. We demonstrate these ideas in a compact tunable NLC waveplate that uses microelectrodes patterned directly on the tips of optical fibers. These devices offer fast, continuously tunable optic axis with low insertion loss and good performance in the near infrared. Modulators that use this design have promising potential applications for polarization control and analysis in optical communication systems.
This letter describes classes of tunable microfluidic fiber (μFF) devices that use specially designed long-period gratings in which the phase matching condition is satisfied over a wide spectral range. Dynamic tuning is achieved by electrowetting-based pumping of microfluidic plugs back and forth over the gratings. As specific examples, we demonstrate dynamically tunable broadband attenuators and filters with adjustable profiles by using fluids with different refractive indices. These devices have attractive features that include in-fiber design and polarization-independent behavior together with low-power, nonmechanical, fully reversible, and latchable tuning.
Resonant x-ray diffraction was carried out at the Se K edge in thick free-standing films of a selenophene liquid crystalline material, revealing detail of the structure of the ferro-, ferri-, and antiferroelectric phases. The ferrielectric phase was shown to have a three-layer superlattice. Moreover, the structure of a lower temperature hexatic phase was established. For the antiferroelectric phase, investigations were also carried out in a planar device configuration. The device allowed resonant scattering experiments to be carried out with and without the application of an electric field and resonant data are compared with electro-optic measurements carried out on the same device.
We have developed a simple, inexpensive, and easily incorporated technique for positioning point defects in free-standing smectic films, simplifying the study of defect structures in the moderate temperature window through probes such as depolarized reflected light microscopy. The technique exploits thermal flow in the smectic films to position and hold a point defect in place. We present details of the experimental design as well as measurements of the thermal flow induced by the device.
Null transmission ellipsometry has been employed to study the molecular arrangements in freestanding films of two no-layer-shrinkage liquid crystal homologous compounds above the bulk smectic $A$--smectic ${C}^{*}$ (Sm ${C}^{*}$) transition temperature. An unusual nonplanar-parallel or nonplanar-antiparallel-parallel transition has been observed in both compounds under a proper electric field. With the addition of one ${\mathrm{CH}}_{2}$ group, while the $\mathrm{Sm}{C}^{*}$ phase is more stable thermally, the magnitude of the critical field needed to induce a parallel-antiparallel transition decreases dramatically.
A detailed scaling argument is used to derive an expression for the thermal diffusivity in terms of the heat capacity, correlation length, and susceptibility. This simple model gives good fits to our experimental data near the smectic-A--hexatic-B transition of one liquid-crystal compound and the smectic-A--smectic-C transition of another. The critical dynamics of both transitions is assumed to be described by the conventional theory.
Abnormality of bone mineral metabolism is a common complication in chronic liver disease and/or chronic renal disease patients. We designed this study to evaluate the relationship between chronic hepatitis B infection and bone mineral metabolism in peritoneal dialysis patients.Serum calcium[adj], phosphorus, calcium and phosphorus product (Ca x P), along with intact parathyroid hormone (iPTH) levels were compared in peritoneal dialysis patients with and without chronic hepatitis B infection.A total of 220 patients (142 female, 78 male) with a mean age of 56.30 +/- 14.28 (range 19 - 86) years old were recruited, 23 showed chronic hepatitis B infection and 197 showed none. No statistically significant difference in serum calcium[adj] levels (9.90 +/- 0.85 mg/dl vs. 10.08 +/- 0.80 mg/dl, p = 0.354), phosphorus levels (5.26 +/- 1.58 mg/dl vs. 5.21 +/- 1.35 mg/dl, p = 0.879) and calcium and phosphorus product (Ca x P) (52.23 +/- 17.54 mg(2)/dl(2) vs. 52.42 +/- 14.16 mg(2)/dl(2), p = 0.960) between groups with and without chronic hepatitis B infection was observed. Serum iPTH levels were significantly lower in chronic hepatitis B patients (median 143 pg/ml, range 3.42 - 889) than in the control group (median 235 pg/ml, range 3 - 2381) (p = 0.035). As analyzed by multi-variable linear regression, chronic hepatitis B was a predictor of lower serum iPTH levels (beta = -0.271; p = 0.030) after adjustments for age, gender, serum calcium and phosphorus levels and diabetes.No significant difference in serum calcium[adj]), phosphorus and calcium and phosphorus product (Ca x P) levels appeared between peritoneal dialysis patients with and without chronic hepatitis B infection. Serum iPTH levels proved to be definitely lower in chronic hepatitis B infection patients.
Motivated by the defect-mediated two-stage melting theory, extensive experiments have been concluded on free-standing films of a liquid-crystal sample which exhibits the isotropic-smectic-A–hexatic B-crystal-B bulk phase sequence. For a two-layer film, which is virtually two-dimensional, our calorimetric measurement shows an apparently divergent anomaly near the smectic-A-hexatic-B transition. Its anomaly has a dominant fluctuation contribution and can be fitted to a power law with an exponent α≈0.37±0.05, in disagreement with the theoretical prediction. Thicker films exhibit surface-initiated layer-by-layer (LBL) wetting transition upon cooling. Moreover, these films also exhibit interesting LBL thinning transitions above the bulk clearing temperature.
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