A thin cell dielectric spectroscopy method for liquid crystals

A thin cell method for dielectric time domain spectroscopy is described. The cell allows one to study the dielectric dispersion and absorption spectra for both components of the dielectric permittivity tensor of uniaxial systems like nematic and smectic A and B phases. Results are presented for 4-n-pentyl-4'-cyanobiphenyl in the isotropic phase and upon orientation in the nematic phase.     

Synthesis and characterization of sodium-tetramethylammonium decamolybdate

Sodium-tetramethylammonium decamolybdate in acidified solution has been crystallized. Chemical analysis, thermogravimetric and X-ray studies have been performed.     

Morphology of melt-pressed latex films examined by scanning and freeze-fracture electron microscopy

We report freeze-fracture transmission electron microscopy (FFTEM) and scanning electron microscopy (SEM) studies of films prepared by melt-pressing micrometer-size polystyrene (PS) and poly(methyl methacrylate) (PMMA) latex samples prepared by surfactant-free emulsion polymerization. Film samples were prepared in two ways intended to influence the nature of packing in the solid: slow evaporation of water at 40°C and 1 atm, or freezedrying. These powder samples were then gently pressed into transparent films using a Carver press. Samples prepared from freeze-dried latex are much less ordered then those from slowly dried dispersions. Two kinds of close packing, face-centered cubic (fcc) and body-centered cubic (bcc), may exist in different parts of an individual sample. An excellent example of bcc ordering was observed in a sample prepared by slowly drying a PMMA latex dispersion. Under very similar conditions, small regions of both fcc and bcc ordering were observed in PS samples. However, distortion of ideal bcc or fcc packing produces the same pattern of fracture. © 1994 John Wiley & Sons, Inc.     

Dynamics of the formation of excited hydrogen,H(n=2,3,4), during a pulse discharge in methane

The dynamics of the formation and decay of excited hydrogen during a pulse discharge in methane at a pressure of 200 Pa and energy density of 0.05 J/cm³ has been studied. The population of hydrogen in the n=2 state was monitored by the laser absorption method. The time constant of the decay of the excited hydrogen was measured to be 95±15 ns. The concentration of free electrons reached a maximum value of 7×10¹⁴ cm^–3, and the time constant of their recombination was 220±50 ns. The formation of appreciable amounts of atomic hydrogen in the ground state during the discharge, H(n=1)>10¹⁶ cm^–3, was estimated on the basis of a kinetic model.Notation absorption coefficient - wave number, cm^–1 - c velocity of light - e electron charge - m _e mass of electron - A _mn Einstein coefficient - F _mn collisional deexcitation rate constant - S _m ionization rate constant - f ₂₄ oscillator strength - n _e electron concentration - n _H(n=2,3,4) excited-state hydrogen concentration - v _e electron velocity - q _mn excitation cross-section - (q _mnve) excitation rate constants - T _e electron temperature - E (t) electrical field strength - j current density - t _ei ^–1 electron-ion collision frequency - _2,m two-body recombination rate constant - _3,m three-body recombination rate constant     

Non-covering in the interpretability lattice of equational theories

We prove a general theorem which implies that many members of the interpretability lattice — including the least element of the lattice, the element represented by the theory with one constant and no axioms, and the equational theory of semilattices — have no cover in the lattice.Presented by R. W. Quackenbush.Research supported by National Science Foundation Grant DMS 89 04014.     

PVT measurements on n -octyl-isothiocyanato-biphenyl (8BT) at elevated pressures

For the first time pressure-volume-temperature (PVT) measurements for the crystal-like smectic E phase have been performed. The phase diagram of 4'- n -octyl-4-isothiocyanatobiphenyl 8BT has been recently established using differential thermal analysis up to 250 MPa. 8BT exhibits a splitting of the clearing line above 170 MPa. PVT data have been measured in the same pressure range for temperatures between 313 and 393 K. Volume and enthalpy changes accompanying the clearing line of 8BT are also presented. The configurational part of the entropy change at the CrE-I transition of 8BT amounts to ≈60%. Using the PVT data and recently published dielectric relaxation results, the isochoric activation energy was calculated (giving ≈50% of the activation enthalpy); this is compared with analogous results for other liquid crystals.     

Lp-Spaces for UHF Algebras

We construct L^p-spaces for a UHFalgebra A with a faithful product state . We showthat the spaces obtained are isomorphic, as Banachspaces, to the Haagerup spaces L^p((A)).     

Benzotriazol-1-ylmethylammonium salts synthesis and reactivity

Benzotriazol-1-ylmethylamines on treatment with alkylating agents afford benzotriazol-1-ylmethylammoni-um salts, also available from reactions of chloromethylbenzotriazole with tertiary amines. In deuterated solvents under basic conditions the methylene protons of these salts exchange with deuterium. At elevated temperatures, an alkyl group substituent migrated from the ammonium center to the benzotriazolyl N-3. Reactions of the salts with Grignard reagents afforded various products arising from substitution of the ammonium moiety and/or from attack on the benzotriazolyl N-3 or on the benzenoid ring.