High-resolution x-ray study of the nematic - smectic-A and smectic-A - smectic-C transitions in 8barS5-aerosil gels

The effects of dispersed aerosil nanoparticles on two of the phase transitions of the thermotropic liquid crystal material 4-n-pentylphenylthiol-4'-n-octyloxybenzoate 8barS5 have been studied using high-resolution x-ray diffraction techniques. The aerosils hydrogen bond together to form a gel which imposes a weak quenched disorder on the liquid crystal. The smectic-A fluctuations are well characterized by a two-component line shape representing thermal and random-field contributions. An elaboration on this line shape is required to describe the fluctuations in the smectic-C phase; specifically the effect of the tilt on the wave-vector dependence of the thermal fluctuations must be explicitly taken into account. Both the magnitude and the temperature dependence of the smectic-C tilt order parameter are observed to be unaffected by the disorder. This may be a consequence of the large bare smectic correlation length in the direction of modulation for this transition. These results show that the understanding developed for the nematic to smectic-A transition for octylcyanobiphenyl (8CB) and octyloxycyanobiphenyl (8OCB) liquid crystals with quenched disorder can be extended to quite different materials and transitions.Comment: 7 pages, 8 figure

Regulation der TNF-#alpha#-Genexpression in humanen Tumorzellen

Available from TIB Hannover: DW 6828 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

TID 4500 16th ed

This report consists of the description, drawings, connections, and schematics of the various control elements that make up the control system of the Engineering Test Reactor Critical Facility (ETRC)

Surface zone-axis patterns

In electron diffraction from crystals, whether it be in reflection or transmission, the intensity of the emergent beams varies in a complex way with the angle that the incident beam makes with the crystal structure. The techniques for displaying this variation of intensity as a function of incident beam orientation have mostly been applied to zone-axis orientations, where the variation is particularly elaborate. The resulting patterns, known as zone-axis patterns or zaps, have become an important part of transmission electron microscopy.There are several techniques for obtaining zaps. The best known is convergent-beam diffraction but they can also be obtained in the form of bend-contour patterns and Tanaka patterns, and by rocking methods.</jats:p