| 1. |
- Arulraj, A, et al.
(författare)
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Shear strain in Nd0.5Ca0.5MnO3 at high pressures
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 94:16, s. 29-31
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Tidskriftsartikel (refereegranskat)abstract
- High-pressure x-ray powder diffraction has been measured on the half doped rare earth manganite Nd0.5Ca0.5MnO3 up to a pressure of 15 GPa. We report the presence of a quantifiable amount of shear distortion of the MnO6 octahedra in Nd0.5Ca0.5MnO3 at high pressures. The lattice strain of Nd0.5Ca0.5MnO3 is minimal at a crossover pressure of p*similar to 7 GPa, with the same lattice strain above and below this pressure achieved by shear and Jahn-Teller-type distortions, respectively. The increase in shear strain with increasing pressure provides a mechanism for the insulating behavior of manganites at high pressures that has not been considered before.
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| 2. |
- Arulraj, Anthony, et al.
(författare)
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Strain effects in perovskite manganites
- 2007
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Ingår i: Progress in Solid State Chemistry. - : Elsevier BV. - 1873-1643 .- 0079-6786. ; 35:2-4, s. 367-377
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Tidskriftsartikel (refereegranskat)abstract
- Colossal magnetoresistance (CMR) - the dramatic reduction of electrical resistivity in a magnetic field and charge ordering (CO) in rare earth manganites of the type Ln(1-x)A(x)MnO(3) [Ln: rare earth, A: divalent cation] are manifestations of the intricate relation between orbital, spin, charge and lattice degrees of freedom. Recent studies indicate that the inhomogeneous state of mixed-valence manganites - evidenced by the presence of texture and multiple phase coexistence - is important for the CMR property of manganites. Theoretical models that explain the multiphase coexistence are based on quenched disorder or strain. Here we show that lattice strain due to the Jahn-Teller (IT) distortions of MnO6 octahedra and their tilt rotations are not sufficient to provide a unique structure-property relation. We present evidence that the science of manganites should take into account shear distortions of the MnO6 octahedra as well. Pressure evolution of the lattice strain of Nd0.5Ca0.5MnO3 shows a minimum around 7 GPa, with the same lattice strain above and below this pressure achieved by shear- and JT-type distortions, respectively. In general, a particular lattice strain of manganites can be achieved by different combinations of JT-type and shear-type distortions of the MnO6 octahedra, together with their tilts, which suggest a plausible description of the inhomogeneous state in manganites as one where phases with differently distorted states having the same lattice strain are preserved. (C) 2007 Published by Elsevier Ltd.
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| 3. |
- Axelsson, Magnus, et al.
(författare)
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Measuring energy dependent polarization in soft γ-rays using Compton scattering in PoGOLite
- 2007
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Ingår i: Astroparticle Physics. - : Elsevier BV. - 0927-6505. ; 28:3, s. 327-337
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Tidskriftsartikel (refereegranskat)abstract
- Linear polarization in X- and γ-rays is an important diagnostic of many astrophysical sources, foremost giving information about their geometry, magnetic fields, and radiation mechanisms. However, very few X-ray polarization measurements have been made, and then only mono-energetic detections, whilst several objects are assumed to have energy dependent polarization signatures. In this paper, we investigate whether detection of energy dependent polarization from cosmic sources is possible using the Compton technique, in particular with the proposed PoGOLite balloon-experiment, in the 25–100 keV range. We use Geant4 simulations of a PoGOLite model and input photon spectra based on Cygnus X-1 and accreting magnetic pulsars (100 mCrab). Effective observing times of 6 and 35 h were simulated, corresponding to a standard and a long duration flight, respectively. Both smooth and sharp energy variations of the polarization are investigated and compared to constant polarization signals using chi-square statistics. We can reject constant polarization, with energy, for the Cygnus X-1 spectrum (in the hard state), if the reflected component is assumed to be completely polarized, whereas the distinction cannot be made for weaker polarization. For the accreting pulsar, constant polarization can be rejected in the case of polarization in a narrow energy band with at least 50% polarization, and similarly for a negative step distribution from 30% to 0% polarization.
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| 4. |
- Azeria, Ermias T., et al.
(författare)
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Biogeographic patterns of the East African coastal forest vertebrate fauna
- 2007
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Ingår i: Biodiversity and Conservation. - : Springer Science and Business Media LLC. - 0960-3115 .- 1572-9710. ; 16:4, s. 883-912
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Tidskriftsartikel (refereegranskat)abstract
- The archipelago-like coastal forest of East Africa is one of the highest priority ecosystems for biodiversity conservation worldwide. Here we investigate patterns of species richness and biogeographic distribution among birds, mammals and reptiles of these forests, using distribution data obtained from recently published reviews and information collated by the WWF Eastern Africa Coastal Forest Ecoregion Programme. Birds and mammals species were divided into forest specialists and generalists, and forest specialist reptiles into 'coastal' and 'forest' endemics. The species richness of birds and generalist mammals increased with area, and is probably a result of area-dependent extinction. Only in birds, however, species richness increased with decreasing isolation, suggesting possible isolation-dependent colonization. Forest diversity, associated to altitudinal range, is important for specialist birds and mammals, whose species richness increased with wider altitudinal range. The number of relict coastal endemic and forest endemic reptiles was higher in forests with wider altitudinal ranges and on relatively higher altitude, respectively. Such forests have probably provided a suitable (and perhaps stable) environment for these species through time, thus increasing their persistence. Parsimony analysis of distributions (PAD) and cluster analyses showed geographical distance and general ecological similarity among forests as a determinant factor in bird distribution patterns, with compositional similarity decreasing with increasing inter-forest distance. Compositional similarity patterns of mammals among the forests did not show a strong geographical correspondence or a significant correlation with inter-forest distance, and those of reptiles were not resolved, with very low similarity levels among forest faunas. Our results suggest that the relative importance (and causal relationship) of forest attributes affecting the distribution of the East African coastal forest vertebrate fauna varies depending on life history traits such as dispersal ability and forest specialization. The groupings in PAD are partly congruent with some of the previous classifications of areas of endemism for this region, supporting the 'naturalness' of these regions.
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| 5. |
- Bring, Torun, et al.
(författare)
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Selenium : molybdenum-based coloration of alkali silicate glasses
- 2007
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Ingår i: Glass Technology. - : Society of Glass Technology. - 0017-1050. ; 48:5, s. 213-221
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between selenium and molybdenum in reduced alkali silicate melts, resulting in red glasses has been studied. The oxidation state of Mo is Mo(VI) as evidenced by XANES and ESCA results. Selenium is present in a reduced state, as indicated by ultraviolet/visible spectroscopy and XANES. The colour is described by ultraviolet/visible spectra and CIE colour coordinates. The main absorption peaks are at 450 and 540 nm. Similar bands are reported for MoOSe32−. Several commonly used glass components must be avoided in the batch, as they prevent formation of the red colour.
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| 6. |
- Carlson, Ola, 1955, et al.
(författare)
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Integration of Wind Power by DC-Power Systems
- 2005
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The world climate changing is driving the electric power production towards renewable energy sources. The development of wind turbines has reached the power level of 5 MW and wind farms up to 1000 MW are planned. Investigations have shown that the cost for production of wind energy is in the same level as coal and gas. The large amount of hydro power in the Nordic countries can be used tocompensate for the irregularity of producing wind power in Europe. High voltage direct current connections between Sweden and Germany, with a wind farm between can be a solution in the future.
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