A novel mesophase formed by top-shaped molecules in the bulk and unsupported thin films: a molecular dynamics study

We have used molecular dynamics simulations to investigate the ordering of top-shaped molecules in bulk phases and in unsupported thin films. Each rigid anisotropic molecule was composed of 11 Lennard-Jones interaction centers (beads). In an attempt to enhance the nematic stability in preference to smectic, the three central beads were assigned a larger Lennard-Jones diameter than the tail beads, giving the molecule a shape resembling a top. The molecular model was found to exhibit an unusual bulk mesophase with long-range orientational order and with molecular center-of-mass positions arranged in parallel interdigitated layers, with layer spacing smaller than half the length of the long axis of a molecule. However, despite the toplike molecular shape, no nematic phase was observed in the pressure range studied. Unsupported films of the isotropic liquid were cooled in order to locate a triple point between the novel mesophase, vapor, and isotropic liquid. At temperatures slightly above the triple point, enhanced surface ordering of molecules was found to occur in the unsupported film. At temperatures slightly below the triple point, the preferred molecular alignment in the unsupported film was parallel to the interface, in violation of arguments that have been proposed based on the relative enthalpies of various cleavage planes for close-packed structures.     

Practical adaptive synchronization of a class of uncertain chaotic systems

This paper studies the practical adaptive synchronization of a class of uncertain chaotic systems in the drive-response framework. An adaptive response system is designed to practically synchronize a given drive chaotic system with uncertainties. An improved adaptation law on the upper bound of uncertainties is proposed to guarantee the boundedness of both the synchronization error and the estimated feedback coupling gains. The efficiency and effectiveness of the proposed approach is illustrated by computer simulation.     

Pseudopotential calculations using the FSGO Method: Application to first-row hydrides

Various pseudopotential schemes are examined in floating spherical Gaussian orbital (FSGO) calculations on the first row hydrides to help determine which pseudopotential scheme, if any, would be most useful in the FSGO method.     

Symbolic derivation of finite difference approximations for the three-dimensional Poisson equation

A symbolic procedure for deriving various finite difference approximations for the three-dimensional Poisson equation is described. Based on the software package Mathematica, we utilize for the formulation local solutions of the differential equation and obtain the standard second-order scheme (7-point), three fourth-order finite difference schemes (15-point, 19-point, 21-point), and one sixth-order scheme (27-point). The symbolic method is simple and can be used to obtain the finite difference approximations for other partial differential equations. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 593–606, 1998     

Highly branched radial block copolymers via dendritic initiation of aliphatic polyesters

Living ring opening polymerization of ε-caprolactone initiated from the numerous chain-end hydroxymethyl groups of the analogous dendrimeric and hyperbranched polyesters derived from 2,2-bis(hydroxymethyl) propionic acid is described. By controlling the size of the dendritic macromolecule and the molar ratio of ε-caprolactone, a variety of highly branched radial block copolymers are obtained. Comparison of the results obtained for the dendrimeric and hyperbranched initiators demonstrates that the reactivity of the chain-end hydroxymethyl groups in the dendrimer are significantly greater than in the isomeric hyperbranched case. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2793–2798, 1998     

Den Einfluss des arabischen Gummis auf gewisse Reactionen

Ohne Zusammenfassung     

Mesophase behaviour and thermal stability of octa-alkoxy substituted phthalocyaninatocobalt (II) complexes

Cobalt (II) phthalocyanines substituted with eight alkoxy chains in the peripheral (2, 3, 9, 10, 16, 17, 23, 24) positions were prepared. The alkoxy chain length was varied between n-butyloxy (C₄H₉O) and n-octadecyloxy (C₁₈H₃₇O). Studies by polarizing optical microscopy and high temperature X-ray diffraction revealed that all the complexes are liquid crystalline and that they exhibit a hexagonal columnar mesophase (Col_h). Transition enthalpies were determined by differential scanning calorimetry. The clearing point could only be observed for compounds with a chain length longer than C₁₃H₂₇O. Both the melting and clearing points decrease with increasing chain length. The transition temperatures of these discotic metallomesogens are higher than those of the corresponding metal-free phthalocyanines, but are comparable with those of the corresponding copper (II) compounds. The thermal decomposition of the compounds was studied by thermogravimetry.     

Relative de Morgan lattices

Let L be a finite distributive lattice. It is shown that every interval of L is a de Morgan lattice if and only if L contains no interval isomorphic to 2²⊕1 or to 1⊕2². Other characterizations of such lattices are also provided.