Polarization field and orientational order in liquid crystals

Optical birefringence is a conveniently measurable quantity that is often used for determining the orientational order in uniaxial liquid crystals. The orientational order parameter is given by S = αe − α0/ α|| − α⊥ where αe and α0 are the polarizabilities of the medium corresponding to the extraordinary and ordinary refractive indices, α|| and α⊥ are the corresponding values for a perfectly oriented medium with S = 1

Metadata Architecture for Digital Libraries: Conceptual framework for Indian Digital Libraries

This paper describes approach of development of Metadata solution for digital library architecture for resource description and retrieval. This deals with the concept of Metadata [2], the different Metadata standards (Dublin core in particular [5]), Digital library environment, computer network capabilities etc. This paper also discusses two of the Digital Library architecture protocols, for resource description and retrieval. They are STARTS (Stanford Protocol Proposal for Internet Retrieval and Search) [8] and SODA (Smart Objects and Dump Archives)[13] architecture to arrive at a possible protocol that would help to build Indian Digital Libraries [5]. While proposing the new architecture the existing Indian environment with respect to information sources and user's query of the information sources [5.1], which are feasible for launch of this protocol for information processing and retrieval has been dealt with. This is a pilot study which the author has done while doing his Fulbright fellowship in the College of Library Information Studies, University of Maryland, College Park, MD during 1999-2000

Role of molecular dipoles in liquid crystals

A vast majority of compounds exhibiting liquid crystalline phases have polar molecules. The nematic director is apolar, even when the molecules have cyano or nitro end-groups, as neighbouring molecules tend to have an antiparallel short-range order. This leads to a partial bilayer structure in the smectic A phase of rod-like molecules as also many interesting phase transitions. The latter can be understood on the basis of a change over to a polar short-range order as the density of the medium is increased. If the molecules have bent-cores and cyano end-groups, a partial bilayer biaxial smectic A phase is also found, implying the formation of quartets with an apolar structure. Lateral dipolar components lead to a tilting of molecules in smectic phases. This can be understood on the basis of the off-axis locations of such dipoles. A mean field theory of smectic C liquid crystals based on this mechanism gives results which reflect experimental trends. In appropriate cases, the possibility of occurrence of a cone-phase consisting of double-tilt cylinders is also pointed out

Dynamics of cholesteric structures in an electric field

Motivated by Lehmann-like rotation phenomena in cholesteric drops we study the transverse drift of two types of cholesteric fingers, which form rotating spirals in thin layers of cholesteric liquid crystal in an ac or dc electric field. We show that electrohydrodynamic effects induced by Carr-Helfrich charge separation or flexoelectric charge generation can describe the drift of cholesteric fingers. We argue that the observed Lehmann-like phenomena can be understood on the same basis.Comment: 4 pages, 4 figures, submitted to PR

Efficient and high-​yielding protocol for the synthesis of nitriles from aldehydes

An operationally simple and high-​yielding procedure was developed for the conversion of aryl aldehydes into the corresponding nitriles using p-​toluenesulfonic acid as a mild catalyst under microwave irradn. The products were characterized by IR spectral anal. and by comparison of the melting and b.ps. with the reported values

Studies on high strength defects in nematic liquid crystals?

We recently reported the discovery of stable disclinations of strength ±3/2 and ±2 in mixtures of several nematogenic compounds with a non-mesomorphic compound having plate-like molecules. We describe here further detailed observations on these defects, particularly on pairs of high strength disclinations