A companion to Grillet's Theorem on maximal chains and antichains

It is shown that ifP is a poset containing noN, then every minimal cutset inP is an antichain, that the converse also holds whenP is finite, and that this converse fails in general.Research supported by NSERC Grant A-8054.     

Exploiting the Structural Metamorphosis of Polymers to ‘Wrap’ Micron-Sized Spherical Objects

There is growing interest in developing methods to ‘wrap’ nano- and micron-sized biological objects within films that may offer protection, enhance their stability or improve performance. We describe the successful ‘wrapping’ of lectin-decorated microspheres, which serve as appealing model micron-sized objects, within cross-linked polymer film. This approach utilizes polymer chains able to undergo a structural metamorphosis, from being intramolecularly cross-linked to intermolecularly cross-linked, a process that is triggered by polymer concentration upon the particle surface. Experiments demonstrate that both complementary molecular recognition and the dynamic covalent nature of the crosslinker are required for successful ‘wrapping’ to occur. This work is significant as it suggests that nano- and micron-sized biological objects such as virus-like particles, bacteria or mammalian cells—all of which may benefit from additional environmental protection or stabilization in emerging applications—may also be ‘wrapped’ by this approach.     

Audition in sciaenid fishes with different swim bladder-inner ear configurations

We investigated how morphological differences in the auditory periphery of teleost fishes may relate to hearing capabilities. Two species of western Atlantic sciaenids were examined: weakfish (Cynoscion regalis, Block and Schneider) and spot (Leiostomus xanthurus, Lacepede). These species differ in the anatomical relationship between the swim bladder and the inner ear. In weakfish, the swim bladder has a pair of anterior horns that terminate close to the ear, while there are no extensions of the swim bladder in spot. Thus, the swim bladder in spot terminates at a greater distance from the ear when compared to weakfish. With the use of the auditory brainstem response technique, Cynoscion regalis were found to detect frequencies up to 2000 Hz, while Leiostomus xanthurus detected up to 700 Hz. There were, however, no significant interspecific differences in auditory sensitivity for stimuli between 200 and 700 Hz. These data support the hypothesis that the swim bladder can potentially expand the frequency range of detection.     

Antimicrobial components of the red alga Laurencia hybrida (Rhodophyta,Rhodomelaceae)

Two unstable antimicrobial metabolites have been isolated from aqueous methanolic extracts of fresh samples of the red alga Laurencia hybrida. The molecules have been identified as 11-formyl-undeca-5(Z), 8(E), 10(E)-trienoic acid and 9-hydroxyeicosa-2(Z), 5(Z), 7(E), 11(Z), 14(Z)-pentaenoic acid.     

Measurement, modelling and simulation of defects in as-grown Czochralski silicon

Defects in as-grown and heat-treated 150 and 200 mm Czochralski silicon crystals are investigated for different crystal pulling conditions and thermal treatments. First results are presented using noncontact carrier recombination imaging for detection of electrically active defects. The defect densities and sizes are compared with the results of computer modelling, suggesting that the observed defects in as-grown material are most likely large voids, possibly partially filled with silicon oxide. In contrast, the defects observed after prolonged heat treatments are silicon oxide precipitates with a density which is several orders of magnitude larger. The voids nucleate at temperatures above 1100°C by a homogeneous nucleation process and grow further to the observed size during further cooling of the crystal. They are responsible for the midfield breakdown of 10–50 nm gate oxides.