Honeycomb Texture Research Articles

Glial fibrillary acidic protein (GFAP) in oligodendroglial tumors: gliofibrillary oligodendroglioma and transitional oligoastrocytoma as subtypes of oligodendroglioma.

Immuno-reactivity to glial fibrillary acidic protein (GFAP) is mainly regarded as a sign of astroglial histogenesis and/or differentiation. The presence of astrocytes in oligodendrogliomas is a well known phenomenon; in addition, GFAP-positive neoplastic oligodendrocytes have also been described but have not yet been studied systematically. Using an anti-GFAP serum in the peroxidase-antiperoxidase antiperoxidase (PAP) technique, 50 oligodendrogliomas and 16 mixed oligodendrocytomas were investigated; they had been diagnosed by routine histological stains. In half of all oligodendrogliomas, and only in a few (12%) of the mixed oligoastrocytomas, GFAP-positive oligodendrocytes were found in some areas of the classical honey-comb texture with a prominent vascular stroma. The term 'gliofibrillary oligodendrocyte' (gfoc) is proposed for these immuno-reactive cells. The existence of a tumour cell combining morphological characteristics of oligodendroglia with GFAP production in its cytoplasm may be considered analogous to transient GFAP expression by myelin-forming glia during normal development (Choi and Kim 1984), thus suggesting the return to a foetal behaviour by some neoplastic oligodendrocytes. Three tumours of the present series consisted largely of gfocs and, therefore, may be termed gliofibrillary oligodendrogliomas. In about 32% of all oligodendrogliomas, but only once in the mixed tumour group, a gradual morphological transition from gfocs to gemistocytic astrocytes was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Melting kinetics of a plagioclase feldspar

Partial melting experiments on plagioclase feldspar have been carried out to investigate textures and kinetics of the melting. A labradorite single crystal was heated at one atmosphere pressure and temperatures within its melting interval as a function of time. So called honeycomb, fingerprint, or sieve textures were produced except for the runs just below the liquidus. The melting was initiated by heterogeneous nucleation of melt at the surface and/or interior (cracks and possively dislocations) of the crystal. The pattern of the melt is dendritic with a few μm arm spacing. After the melt develops throughout the crystal, the volumes of melt and residual crystal become larger and smaller, respectively, without changing the arm spacings. The melt is homogeneous and has the approximate temperature dependent liquidus composition irrespective of the time. There are compositional gradients in the residual crystal after short periods of melting. The An content of the crystals increases with increasing time until it finally reaches equilibrium with the melt after several thousands minutes of heating. It is concluded that the enlargement of the melt, the main process of the melting, is controlled by diffusion in the crystal. The fact that partial melts have the composition of the equilibrium liquidus even from the first several minutes strongly suggests that the local equilibrium at the crystal-liquid interface is satisfied during the melting. Some of the honeycomb, fingerprint, and sieve textures found in xenoliths and phenocrysts of sodic plagioclase in volcanic rocks would be caused by heating events (such as magma mixing) during which temperatures of magmas were temporarily higher than the solidus of some of the minerals.

Growth of a smectic A from a bent nematic phase and the smectic light valve

We show that for certain liquid crystals, characterized by very small nematic/smectic−A latent heats, the transition from a nematic phase, held firmly in a bent state, to a smectic−A phase takes place via an intermediate state which is stable in a given temperature range and which we have called ’’striped texture’’. This state consists of a corrugated layer of bent nematic which is sandwiched between two smectic−A layers whose planes are oriented in two different directions. As the temperature of the sample is further decreased, the ’’striped texture’’ becomes unstable. The corrugated layer undergoes axial buckling leading to the final smectic−A ’’honeycomb texture’’. This texture is the scattering phase of Kahn’s smectic light valve. We explain the occurrences of these phenomena on the basis of elastic and surface energy considerations.