Pattern orientation

Abstract: The ability of honeybees (Apis mellifera) to discriminate pattern orientation was evaluated by examining their choice behaviour in a twin-choice Y-maze apparatus which offered two differently oriented patterns, one of which was associated with a reward. The distinctive feature of this experimental arrangement was that it forced the freely flying bees to choose between the two patterns at a distance, thus preventing the bees from fixating the patterns and discriminating between them on the basis of an eidetic (`photographic') image. Training and testing experiments using a number of different pairs of patterns, such as gratings, stripes and plaids, led to the following results: (i) bees perform well at discriminating the orientation of unidirectional patterns, such as single stripes or gratings; (ii) trained bees learn to prefer the orientation that is associated with the reward, as well as to avoid the unrewarded orientation; (iii) bees perform poorly at discriminating the orientation of right-angled crosses or plaids, but well at discriminating the orientation of 45 degrees crosses or plaids; and (iv) orientation discrimination appears to be mediated primarily by signals from the green-receptor channel of the bee's visual system. These findings, together with recent work (Srinivasan et al. Nature, Lond. 362, 539-540 (1993)), suggest that the honeybee's visual system analyses orientation in much the same manner as the mammalian cortex. Our data suggest the participation of at least three orientation-sensitive channels with different preferred orientations, and broad tuning curves with half-widths of ca. 90 degrees.

Abstract: This article is a review of the chemical and physical nature of patternable block copolymers and their use as templates for functional nanostructures. The patternability of block copolymers, that is, the ability to make complex, arbitrarily shaped submicron structures in block copolymer films, results from both their ability to self-assemble into microdomains, the "bottom-up" approach, and the manipulation of these patterns by a variety of physical and chemical means including "top-down" lithographic techniques. Procedures for achieving long-range control of microdomain pattern orientation as well as the combination of top-down and bottom-up patterning to give multilevel control of block copolymer films are extensively discussed. The level of control over patterning block copolymers that these strategies afford has enabled recent developments in nanofabrication including template nanolithography, template nanoparticle patterning, nanoporous as well as nanoreplicated materials.