| 1. |
- Belyazid, Salim, et al.
(författare)
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A Sustainability Assessment of the Urban Rehabilitation Project of the Medina of Fez, Morocco
- 2003
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Ingår i: Proceedings of the 21st International Conference of the System Dynamics Society. - 9780967291482
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Konferensbidrag (refereegranskat)abstract
- The old city of Fez, Morocco, classified as Heritage of Humankind by the UNESCO, is subject to an integrated rehabilitation plan running over 15 years. The plan aims at restoring and preserving the economy, cultural value, and social heritage of the old city. The study follows a system dynamics approach to describe and analyze the rehabilitation plan in order to identify the strengths and defects of the plan. This study shows that while the plan is giving relatively satisfying results over the short and medium terms, it is unlikely to attain long term sustainability.
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| 2. |
- Fogel, Nina Ya. 1938, et al.
(författare)
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Interfacial superconductivity in semiconducting monochalcogenide superlattices
- 2002
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 66:17, s. 174513(11pp.)-
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Tidskriftsartikel (refereegranskat)abstract
- Superconducting and structural properties of superconducting semiconducting multilayers are investigated. These layered systems are obtained by epitaxial growth of the isomorphic monochalcogenides of Pb, Sn, and rare-earth elements on a KCl substrate. Some of these compounds are narrow-gap semiconductors (PbTe, PbS, PbSe, SnTe). Layered structures containing one or two narrow-gap semiconductors have a metallic type of conductivity and a transition to a superconducting state at temperatures in the range of 2.56 K. Structures containing only wide-gap semiconductors (YbS, EuS, EuSe) do not demonstrate such properties. All superconducting layered systems are type-II superconductors. The critical magnetic fields and the resistive behavior in the mixed state reveal features characteristic of other layered superconductors. However, data obtained in magnetic fields testify that the period of the superstructure corresponds to half of that obtained from x-ray-diffractometry investigations. This is evidence that the superconducting layers in these samples are confined to the interfaces between two semiconductors. Electron microscopy studies reveal that in the case of epitaxial growth the interfaces contain regular grids of misfit dislocations covering all the interface area. These samples appear to undergo a superconducting transition if they have a metallic type of conductivity in the normal state. Samples with island-type dislocation grids only reveal partial superconducting transitions. The correlations between the appearance of superconductivity and the presence of dislocations, which have been found experimentally, lead to the conclusion that the normal metallic conductivity as well as the superconductivity are induced by the elastic deformation fields created by the misfit dislocation grids. A theoretical model is proposed for the description of the narrow-gap semiconductor metallization, which is due to a band inversion effect and the appearance of electron- or hole-type inversion layers near the interfaces. For different combinations of the semiconductors, such inversion layers in the superlattices can have different shapes and topology. In particular, they can form multiply connected periodic nets having a repetition period coinciding with that of the dislocation grids. Numerical estimates show that such a scenario for the appearance of superconductivity is quite likely. It is shown that the new type of metallic and superconducting nanoscale two-dimensional structures with unusual properties may be obtained from monochalcogenide semiconductors.
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