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SynopsisPolyhydroxybutyrate (PHB) is a bacterially produced thermoplastic. Meltcast PHB sheets are usually quite brittle. We show that this brittleness is due to cracks within the spherulites. These cracks, which may be either radial or circumferential within the spherulites, depending on the crystallization temperature, form under conditions of no externally applied stress. When the material is strained the cracks grow and join together, leading to brittle failure.It is possible to produce ductile PHB sheets in two ways: first, the cracks may be "healed" by a cold rolling process; second, special crystallization conditions can be used to produce ductile sheets consisting entirely of crack-free spherulites. The relevance of this work to the ductility of crystalline thermoplastic in general is discussed.

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Per Møller was educated in physics and mathematics at the University of Copenhagen (M.Sc.). He later received his M.A. degree in Psychology and Ph.D. degree in Cognitive Science from the University of Rochester, Rochester, NY.. He works on psychological and neurological problems of the senses using psychophysical and neurophysiological methods. Among other problems he works on relationships between the senses, reward, and appetite.

ABSTRACT:The morphology and structure of the bacterial plastics of poly(p-hydroxybutyrate-P-hydroxyvalerate) P(HB-HV) were studied as well as the reference homopolymer, poly(p-hydroxybutyrate) (PHB). Because of bacterial origins they are exceptionally pure. Crystallization behavior of them is expected to be almost ideal, so that we can easily infer how the minor component (HV) acts within the major component (HB). The solution-grown single crystals of PHB and P(HB-HV) showed linear increase in melting points and hyperbolic increase in long spacings as the crystallization temperature increased. The HV component in the polymer chain was inclined to be excluded outwards as much as possible from the crystal of HB component during the crystallization. A small part of the HV component included in the HB component crystal acts as a defect, by which small expansion of the a-parameter of the unit cell is mainly caused with increasing HV content. The severe effect of the HV component was observed on crystallization characteristics and morphological changes.

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Population trends of African penguins Spheniscus demersus in the Western Cape, South Africa, and their breeding success have been linked to the abundance of their main prey, sardine Sardinops sagax and anchovy Engraulis encrasicolus. During the late 1990s and early 2000s, both fish species increased markedly in abundance, but after 2004, sardine biomass decreased to below average levels. In addition, adults of both stocks were principally located to the east of Cape Agulhas from 2001 to 2009 and were thus distant from seabird colonies on South Africa's West Coast. The number of African penguin pairs counted at Robben Island from 2001 to 2009 and the fledging period of chicks from successful nests increased and decreased in apparent response to the biomass of sardine prior to each breeding season, possibly linked through adult condition at the onset of breeding. Breeding success and chick-fledging rates increased during the study period and showed positive relationships with local food availability, indexed through the annual industrial catch of anchovy made within 56 km (30 nautical miles) of the colony. In addition, chick-fledging rates were depressed in 2-chick broods during years when anchovy contributed < 75% by mass to the diet of breeding birds. Previously reported relationships between the overall abundance of forage fish in South Africa and penguin breeding success were not supported. Taken together, these results highlight the combined importance of ensuring adequate local food availability for seabirds during the reproductive cycle and safeguarding regional prey abundance during the non-breeding season.