4,581 research outputs found

    Statistical mechanics of strings with Y-junctions

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    We investigate the Hagedorn transitions of string networks with Y-junctions as may occur, for example, with (p,q) cosmic superstrings. In a simplified model with three different types of string, the partition function reduces to three generalised coupled XY models. We calculate the phase diagram and show that, as the system is heated, the lightest strings first undergo the Hagedorn transition despite the junctions. There is then a second, higher, critical temperature above which infinite strings of all tensions, and junctions, exist. Conversely, on cooling to low temperatures, only the lightest strings remain, but they collapse into small loops

    Synthesis and Structures of Co Bis-Trifluoromethylpyrazolate Complexes

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    Reactions of Co(PMe3)(3)Cl or CoCl2 with 3,5-(CF3)(2)-PzNa in hexane give Co(PMe3)(3)(3,5-(CF3)(2)-Pz) (1) and Co(PMe3)(3)(3,5-(CF3)(2)-Pz)(2) (2) respectively (3,5-(CF3)(2)-PzNa = sodium bis-trifluoromethylpyrazolate). Reaction of (3,5-(CF3)(2)-PzH) with Co(PMe3)(4) produces the unusual complex [cis-Co(PMe3)(4)H-2][Co(PMe3)(3,5-( CF3)(2)-Pz)(3)] (3) which formally contains a [Co(III)](+)[Co(II)](-) complex ion pair. Reaction of 3,5-(CF3)(2)-PzLi with an oxygenated suspension of CoCl2 and 3 equivalents of PMe3 gives (3,5-(CF3)(2)-Pz)(2)Co(mu-3,5-(CF3)(2)Pz)(mu-OPMe3)Li(OPMe3)(2) (4), while 2 reacts with LiOH to give [(PMe3)Co(mu-3,5-(CF3)(2)-Pz)(2)(mu(3)-OH)Li](2) (5). Both 2 and 3 react with O-2 in toluene solution to give Co(OPMe3)(2)(3,5-(CF3)(2)-Pz)(2) (6). All compounds have been characterized spectroscopically and by single crystal X-ray diffraction studies.Welch Foundation F-816Petroleum Research Fund 47014-ACSNSF 0741973Chemistr

    Africa and Technology in Higher Education: Trends, Challenges, and Promise

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    Showing that technology in higher education in African countries is lagging behind the developed world and also that Internet connectivity is on the rise in African nations, this paper describes and analyzes trends in the use of ICTs as well as the impact that the shortage in technological use and capacity has on Africa, particularly that needed to address the changing demands within the higher education sector. Challenges to the proposed widespread implementation of technology exist, particularly because most institutions of higher education have very limited technological capacity and basic resources, such as electricity, equipment, and funding; brain drain, improper use of ICT, and the colonial mindset are also factors. It is suggested that ICT be integrated into education with a purpose and within the context of postcolonial theory and a critical pedagogy perspective. Key uses of ICT in education, including mobile technology, are access, support, and communication, making learning available to anyone anywhere and enhancing learning as an interactive process, with much potential for collaboration and problem-solving. Four salient components related to incorporating ICTs into higher education are discussed: (a) teacher education; (b) curriculum; (c) distance learning; and (d) educational policy, planning, and management. Examples of technological initiatives in higher education as well as recommendations are given. Ghana, Kenya, and Tanzania, representative of other African nations to varying degrees, are highlighted in regard to ICT infrastructure and its relevancy to higher education. It is concluded that African higher education has high potential for catching up in the technological race

    2013-2 Are Exporters More Productive than Non-Exporters?

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    Book Reviews: Alien Phenomenology, or What It’s Like to Be a Thing by Ian Bogost, Jet Plane: How It Works by David Macaulay, andVibrant Matter: A Political Ecology of Things by Jane Bennett

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    In this review essay, I review Ian Bogost’s Alien Phenomenology, or What It’s Like to Be a Thing (2012) and Jane Bennett’s Vibrant Matter: A Political Ecology of Things (2010) alongside David MacAuley’s Jet Plane: How It Works (2012), which is devoted to a child’s experience of airplanes. While composed for different audiences in traditionally discrete contexts, all three books do critical, speculative work in providing explicit articulations and implicit performances of alternative ontologies from which Critical Air Studies might benefit
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