Observation of a re-entrant isotropic phase in a pure disc-like liquid crystal

We report the observation of an optically isotropic phase in the new disc-like mesogen 2,3,7,8,12,13-hexa(octadecanoyloxy)truxene. On cooling, this optically isotropic phase goes over into a nematic phase, while on heating a columnar phase grows in. To our knowledge this is the first example of a pure discotic mesogen exhibiting an isotropic phase below the temperature existence of a columnar phase. Our findings are supported by refractive index measurements of this compound as a function of temperature.     

Comparative decay characteristics of the light generated free radical in chromatophores and chloroplasts

Abstract— Chromatophores of Rhodospirillum rubrum when illuminated exhibit a free radical which ordinarily shows a biphasic decay. When chromatophores are dehydrated at room temperature the time course of the appearance of the light-induced free radical is unaffected, but the decay pattern has been altered. Only the fast component remains, the slow component is no longer evident. Scanning the magnetic field reveals the presence of a dark signal which is stable as long as the preparation remains dehydrated. This signal has the same peak-to-peak line width of ? 10 G and the same g factor as the signal evident in the light. The amplitude of this signal is equal to the amplitude of the slow decay component seen in aqueous chromatophore suspensions. Chromatophores frozen in an aqueous medium at —150°C exhibit a behavior identical with dehydrated preparations. The effects produced by lyophilization or by freezing at low temperatures are entirely reversible. When a lyophilized preparation is re-hydrated, the stabilized portion of the signal now decays in the dark; the same is observed when preparations frozen at —150°C are thawed. When such thawed or re-hydrated preparations are illuminated again, they exhibit the usual light-induced ESR signal showing a biphasic dark decay. A comparison was made between the behavior of the light-induced ESR signal of chromatophores and that of system I of chloroplasts. This comparison revealed that there is a greater similarity in some of the decay characteristics of these signals than had been recognized previously. In chloroplasts, temperature insensitive, non-enzymatic back-reactions of the light-induced free radical appear to be nil, and in chromatophores a distinct portion of the light-induced free radicals exhibit the same characteristics. Another portion of the chromatophore free radicals must be able to back-react by electron tunneling, a mechanism which appears to be absent in the chloroplast system.     

Behaviour of leading infra-red divergences of QCD in the axial gauge

We identify in the axial gauge a simple set of diagrams which yield the exponential of leading infra-red corrections to massive quark scattering in QCD. The relevance of the Ward identities is pointed out.     

Evaluation of emulsion stability by thermogravimetric analysis (tg)

A rapid and simplified method for the determination of phase inversion temperature (PIT) and the stability of oil in water emulsions, stabilized by nonionic emulsifiers, is described. The method is based on the use of any thermogravimetric apparatus from which the rate of loss of water can be measured as a function of linear increase in the emulsion temperature. A DTG peak is obtained at the PIT: the emulsion in which the lowest PIT is observed is also the less stable one.     

High-performance liquid chromatographic separation of cobalamins

Physiological cobalamins were separated by means of high-performance liquid chromatography (HPLC). Optimal conditions for elution of methylcobalamin, adenosylcobalamin, hydroxycobalamin and cyanocobalamin were determined. Excellent separation and resolution of these physiological cobalamins by HPLC were achieved. In addition, several cobalamin analogues were also studied and shown to be separable from the physiological forms. HPLC provides a rapid, sensitive, reproducible means of characterizing physiological cobalamins.     

Infra-red behaviour in non-abelian gauge theories

The leading infra-red divergent corrections to massive quark scattering in quantum chromodynamics are very simple to fourth order. A simple dependence on the effective coupling constant is conjectured to hold to all orders.     

Molecular dynamics calculations on the time dependence of simple,anisotropic potentials in dense argon

Molecular dynamics calculations on the time dependence of the anisotropic potential experienced by a probe molecule in argon, are presented. The calculations were performed for Ar densities of 100, 300, 500 and 784 amagat and T = 160 K. Collective motions clearly manifest themselves at higher densities, in particular in the power-spectrum of the part of the anisotropic potential that transforms as an irreducible tensor of rank 1. The relation between time-dependent local anisotropy and a number of experiments is discussed.     

Theoretische Untersuchung des Prozesses der Bildung von Kondensationspolymeren — Polvamidsäuren

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