{ We analyse the Schlieren textures formed by the nematic director in a thermotropic main-chain liquid crystalline polymer. After an initial coarsening, the textures reach a stable time-independent state which appears to be an equilibrium function of temperature and material parameters, with a characteristic length scale of order 2 m. In particular, we study the evolution of this domain size when the temperature approaches the nematic-isotropic transition Tni. The texture size increases towards Tni, but decreases reversibly when the temperature decreases back into the nematic phase. We discuss possible theoretical models that may explain such an equilibrium polydomain state of nematic director and the dependence of its size on the nematic order parameter.

SUMMARYThe Tauher trap was subjected to tests in the controlled waterflow of a flume to assess its sampling efliciency for a range of pollen types and varying speeds of flow. The equipment and procedures of pollen preparation are described, and the method of trap efficiency calculation is explained. Results indicating numerical differences in amounts of pollen caught by two sizes of trap are attributed to scaling factors on the traps used, and the increased flow velocity near tht floor of the flume. Similar pollen proportions from these traps in each experiment are obtained, indicating an even distribution of pollen within the flow. Collection efliciency for individual tasa are found to vary both according to size and weight of the grains and to velocity of flow. Within one experiment, other factors being constant, smaller grains are trapped less efficiently than those larger. The total experimental evidence suggests that, with increasing water speed, differences in grain characteristics have less effect, though the overall trappmg efficiency is lowered. Factors of weight rather than density are proposed as determining the final catch from water by this particular design of trap. The significance of under-and over-representation of grains at low flow velocities is discussed in relation to the potential use of the trap as a pollen sampling mechanism in the field.

In a polydisperse thermotropic main-chain liquid crystalline polymer, we observe the process of thermally induced nematic−nematic phase separation between short and long polymer chains. We study the dynamical features of this system, in particular the evolution of Schlieren textures formed by disclinations surrounding areas of relatively uniform director. We analyze the dependence of domain size ξ on temperature and the nematic order parameter, and the evolution of textures with the waiting time at a temperature well below the nematic transition T ni. We find that before phase separation the coarsening proceeds toward the uniform state, with characteristic size of the texture increasing as ξ ∼ t 1/4. When the system is phase-separated, the texture in the regions with long chains is frozen at an equilibrium value ξ, a reversible function of temperature, while in the short-chain regions the coarsening accelerates. This behavior is interpreted in terms of a miscibility gap that is proportional to the degree of nematic order, which is different for the different lengths of the nematic polymers.

SUMMARY Laboratory tests were made on three absolute pollen preparation techniques previously published by Davis (1965, 1966), Matthews (1969) and Jørgensen (1967), and on an additional weighing method (Modified Jørgensen) using both standard pollen suspensions and fossil minerogenic samples. Laboratory procedure is described and the following results include an investigation of grain distribution within slides prepared by the Jørgensen and Matthews methods, a discussion of the statistical reliability of the Jørgensen method, and a test of the variability attributable to preparation methods, using the coefficient of variation (C.V.) as the basis of comparision. The relation between grain loss (bias) during the preparation procedure, the methods employed, and the sediment type used is explored, and some practical aspects of the various techniques are considered. It is concluded that for detailed palynological work, particularly in conjunction with 14C dating, the extra time needed in the preparation of the Davis or the Modified Jørgensen methods is balanced by a greater reliability of result. The Matthews and Jørgensen techniques are shown to be adequate for determination of large scale changes in pollen concentration, though all methods would benefit through the addition of an ‘exotic’ pollen type in order to detect losses during preparation.