4,528 research outputs found

    Design rules for technical-biological bank protection on non-tidal, navigable waterways

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    Duality symmetry in four-dimensional string actions

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    We reduce the dual version of D=10D=10, N=1N=1 supergravity coupled to nn vector fields to four dimensions, and derive the SL(2,R)×O(6,6+n)SL(2,R)\times O(6,6+n) transformations which leave the equations of motion invariant. For n=0n=0 SL(2,R)SL(2,R) is also a symmetry of the action, but for n>0n>0 only those SL(2,R)SL(2,R) transformations which act linearly on all fields leave the action invariant. The resulting four-dimensional theory is related to the bosonic part of the usual formulation of N=4N=4 supergravity coupled to matter by a duality transformation.Comment: 9 pages, Latex fil

    De Sitter in Extended Supergravity

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    We show that known de Sitter solutions in extended gauged supergravity theories are interrelated via a web of supersymmetry-breaking truncations. In particular, all N=8 models reduce to a subset of the N=4 possibilities. Furthermore, a different subset of the N=4 models can be truncated to stable de Sitter vacua in N=2 theories. In addition to relations between the known cases, we also find new (un)stable models.Comment: 16 page

    Dual versions of extended supergravities

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    Recently, using the model of N=2 supergravity -- vector multiplets interaction with the scalar field geometry SU(1,m)/SU(m)⊗U(1)SU(1,m)/SU(m)\otimes U(1) as an example, we have shown that even when the scalar field geometry is fixed, one can have a whole family of the Lagrangians, which differ by vector field duality transformation. In this paper we carry out the construction of such families for the case of N=3 and N=4 supergravities, the scalar field geometry being SU(3,m)/SU(3)⊗SU(m)⊗U(1)SU(3,m)/SU(3)\otimes SU(m)\otimes U(1) and SU(1,1)/U(1)⊗O(6,m)/O(6)⊗O(m)SU(1,1)/U(1)\otimes O(6,m)/O(6)\otimes O(m), correspondingly. Moreover, it turns out that these families contain, as a partial case, the models describing the interaction of arbitrary number of vector multiplets with our hidden sectors, admitting spontaneous supersymmetry breaking without a cosmological term.Comment: 9 pages, plain LaTeX, no figure

    The role, opportunities and challenges of 3D and geo-ICT in archaeology

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    Archaeology joins in the trend of three-dimensional (3D) data and geospatial information technology (geo-ICT). Currently, the spatial archaeological data acquired is 3D and mostly used to create realistic visualizations. Geographical information systems (GIS) are used for decades in archaeology. However, the integration of geo-ICT with 3D data still poses some problems. Therefore, this paper clarifies the current role of 3D, and the opportunities and challenges for 3D and geo-ICT in the domain of archaeology. The paper is concluded with a proposal to integrate both trends and tackle the outlined challenges. To provide a clear illustration of the current practices and the advantages and difficulties of 3D and geo-ICT in the specific case of archaeology, a limited case study is presented of two structures in the Altay Mountains

    Good Governance of land and natural resources : Balancing local and global interests

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    This report presents the results of a seminar on ‘good governance of land and natural resources; balancing local and global interests’. Three case studies were presented on large-scale land acquisitions, biofuels – fuelling development in Brazil and governance of the mineral sector in Eastern DRC. Participants identified 6 important challenges for improving land and natural resource governance and concluded that: more research and information sharing is needed; collaborative voluntary and legally binding initiatives are needed at international level to balance local and global interests; accountability arrangements need to be set up that enable stakeholders to hold each other accountable; capacity building of all actors is needed and that each actor has its own contributions to make to good governance
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