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Simo A.,Network-1 | Simo A.,University of the Western Cape | Mwakikunga B.,National Center for Nanostructured Materials | Sone B.T.,Network-1 | And 4 more authors.
International Journal of Hydrogen Energy | Year: 2014

Mott-type VO2 oxide nanobelts are demonstrated to be effective hydrogen gas sensors at room temperature. These nanobelts, synthesized by hydrothermal process and exhibiting the VO2 (A) crystallographic phase, display room temperature H2 sensitivity as low as 0.17 ppm. The nanobelts (ultralong belt-like) nanostructures could be an ideal system for fully understanding dimensionally confined transport phenomena in functional oxides and for building functional devices based on individual nanobelts. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Mavundla S.E.,National Center for Nanostructured Materials | Mavundla S.E.,University of the Western Cape | Malgas G.F.,National Center for Nanostructured Materials | Motaung D.E.,National Center for Nanostructured Materials | And 2 more authors.
Journal of Materials Science | Year: 2010

Copolymers of aniline and pyrrole have been prepared by chemical oxidative-polymerization of aniline and pyrrole using ammonium per sulphate and ferric chloride as oxidants. The structural and morphological properties were studied by X-ray diffraction and scanning electron microscopy. Both copolymers showed an amorphous behaviour compared to their homopolymers. SEM micrographs of poly(aniline-pyrrole) copolymer showed agglomerated spherical structures where as poly(2,5-dimethoxyaniline-pyrrole) showed disordered structures of spherical agglomerates. The copolymers showed improved UV-Vis absorption with the broad peak from 450 to 850 nm. The copolymers exhibited a lower conductivity compared to the homopolymers due to the unsuccessful complex between PANI and PPy, induced by the use of APS as the oxidant. © 2010 Springer Science+Business Media, LLC.

Wesley-Smith J.,University of KwaZulu - Natal | Wesley-Smith J.,National Center for Nanostructured Materials | Berjak P.,University of KwaZulu - Natal | Pammenter N.W.,University of KwaZulu - Natal | Walters C.,U.S. Department of Agriculture
Annals of Botany | Year: 2014

Background and Aims Cryopreservation is the only long-term conservation strategy available for germplasm of recalcitrant-seeded species. Efforts to cryopreserve this form of germplasm are hampered by potentially lethal intracellular freezing events; thus, it is important to understand the relationships among cryo-exposure techniques, water content, structure and survival. Methods Undried embryonic axes of Acer saccharinum and those rapidly dried to two different water contents were cooled at three rates and re-warmed at two rates. Ultrastructural observations were carried out on radicle and shoot tips prepared by freeze-fracture and freeze-substitution to assess immediate (i.e. pre-thaw) responses to cooling treatments. Survival of axes was assessed in vitro. Key Results Intracellular ice formation was not necessarily lethal. Embryo cells survived when crystal diameter was between 0·2 and 0·4 μm and fewer than 20 crystals were distributed per μm 2 in the cytoplasm. Ice was not uniformly distributed within the cells. In fully hydrated axes cooled at an intermediate rate, the interiors of many organelles were apparently ice-free; this may have prevented the disruption of vital intracellular machinery. Intracytoplasmic ice formation did not apparently impact the integrity of the plasmalemma. The maximum number of ice crystals was far greater in shoot apices, which were more sensitive than radicles to cryo-exposure. Conclusions The findings challenge the accepted paradigm that intracellular ice formation is always lethal, as the results show that cells can survive intracellular ice if crystals are small and localized in the cytoplasm. Further understanding of the interactions among water content, cooling rate, cell structure and ice structure is required to optimize cryopreservation treatments without undue reliance on empirical approaches. © 2013 Published by Oxford University Press on behalf of the Annals of Botany Company.

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