3,199 research outputs found

    Synthesis and characterisation of new layered oxychalcogenide materials

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    Chapter one describes oxychalcogenide phases found in the literature with layered and three- dimensional structures. An attempt is made to systematise the structures of a range of materials to help understand their structural chemistry. Synthetic details and physical properties are also reported. Potential applications of these materials are discussed, with emphasis placed on compounds similar to those discussed in later chapters. Chapter Two gives full details of the synthetic methods, characterisation techniques and physical property measurements employed in the work described in the following chapters. Chapter Three contains the results of experiments on ԼaշՕՅMշՏBշ (M = Μn, Co) materials, including synthesis, room temperature structure and thermal behaviour by powder X-ray and neutron diffraction, magnetic and conductivity properties. The low temperature magnetic structures of both compounds have been determined and reveal antiferromagnetic ordering of spins within MշՕ layers. Chapter Four reports the synthesis and room temperature structure of the AշMCսշՕշXշ (A = Sr, Ba; M = Μn, Co, Ni, Zn; χ = s, Se) family of compounds. The results of variable temperature powder X-ray diffraction, magnetometry and conductivity experiments on these compounds are also discussed. They show smooth thermal expansion properties except BaշCoCuշՕշՏշ and SrշNiCuշOշSeշ, which show deviations between 100 and 200 K, indicative of structural/magnetic phase transitions at low temperature. Varying magnetic properties are found and a number of the compounds are found to be semiconductors. Chapter Five discusses attempts to prepare the Aշ MOշ Lnշ Oշ Xշ (A = Sr, Ba; M = Co, Mn, Fe; Ln = La, Y, Gd; X = S, Se) family of compounds. The potential stability of such compounds is investigated using bond valence calculations. Chapter Six outlines the work done in indexing, solving and refining the crystal structure of an α,α thiophene tin tetramer from powder X-ray diffraction data

    Green spines, back story: delving into the early history of Virago reprints and modern classics

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    While the iconic green spines of Virago Modern Classics have become a fixture in the literary imagination, D-M Withers looks into the early history of feminist publisher Virago Press to explore how the decision to publish a fiction reprint list represented a significant change in the publishing strategy of a company whose main activity had been non-fiction, in new or reprint form

    Generation of internal stress and its effects

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    Internal stresses may be generated continually in many polycrystalline materials. Their existence is manifested by changes in crystal defect concentration and arrangement, by surface observations, by macroscopic shape changes and particularly by alteration of mechanical properties when external stresses are simultaneously imposed

    Macrofauna Associate with Ungrounded Prop Roots of Rhizophora mangle in Veracruz and Quintana Roo, Mexico

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    The prop roots of the red mangrove (Rhizophora mangle) provide a solid substrate for diverse assemblages of marine organisms in areas typically characterized by soft bottoms (Bingham 1992, Farnsworth and Ellison 1996). Macrobenthic communities of mangroves have received little attention compared with other components of the ecosystem, largely due to sampling difficulties (Lee 2008). Mangrove root epifauna are likely used by predatory fish, especially juveniles. Thus, these organisms have the potential of being important links between mangroves and adjacent ecosystems. The fauna associated with red mangrove prop roots along Mexican Gulf of Mexico (GOM) and Caribbean shorelines has not been well described. The infauna of red mangrove associated sediments has been studied in GOM sites in the Río Carrizal Estuary, Tamaulipas, Mexico (Rabalais et al. 1989), Laguna de Términos, Veracruz, Mexico (Hernández-Alcántara and V. Solís-Weiss 1995) and Rookery Bay, Florida (Sheridan 1997). Red mangrove root epifauna in the GOM has been described only in Laguna de Tamiahua (Fajardo M. 1990). Although red mangrove root faunas have been described in some areas of the Caribbean, such as Puerto Rico (Mattox 1949, Kolehmainen and Wildner 1975) and Bahia de Buche, Venezuela (Sutherland 1980), in the northwestern Caribbean the mangrove root epifauna has only been described in Belize (Ellison and Farnsworth 1992, Farnsworth and Ellison 1996). The objective of this study was to describe macrofaunal community composition of ungrounded red mangrove prop roots in the southwestern GOM and the northwestern Caribbean, on the Yucatan Peninsula. The communities we describe are compared to others in Mexico, Central America and the wider Caribbean to address factors that may explain similarities and differences
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