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- Chaloupka, Milani, et al.
(författare)
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Encouraging outlook for recovery of a once severely exploited marine megaherbivore
- 2008
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Ingår i: Global Ecology and Biogeography. - : Wiley. - 1466-8238 .- 1466-822X. ; 17:2, s. 297-304
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Tidskriftsartikel (refereegranskat)abstract
- Aim To critically review the status of the green sea turtle (Chelonia mydas) using the best available scientific studies as there is a prevailing view that this species is globally endangered and its marine ecosystem functions compromised. Location Ogasawara (Japan), Hawaii (USA), Great Barrier Reef (Australia), Florida (USA), Tortuguero (Costa Rica). Methods We compiled seasonal nesting activity data from all reliable continuous long-term studies (> 25 years), which comprised data series for six of the world's major green turtle rookeries. We estimated the underlying time-specific trend in these six rookery-specific nester or nest abundance series using a generalized smoothing spline regression approach. Results Estimated rates of nesting population increase ranged from c. 4-14% per annum over the past two to three decades. These rates varied considerably among the rookeries, reflecting the level of historical exploitation. Similar increases in nesting population were also evident for many other green turtle stocks that have been monitored for shorter durations than the long-term studies presented here. Main conclusions We show that six of the major green turtle nesting populations in the world have been increasing over the past two to three decades following protection from human hazards such as exploitation of eggs and turtles. This population recovery or rebound capacity is encouraging and suggests that the green turtle is not on the brink of global extinction even though some stocks have been seriously depleted and are still below historical abundance levels. This demonstrates that relatively simple conservation strategies can have a profound effect on the recovery of once-depleted green turtle stocks and presumably the restoration of their ecological function as major marine consumers.
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| 2. |
- Etz, Corina, et al.
(författare)
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Magnetic properties of FeCo nanoclusters on Cu(100 : Ab initio calculations
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:24
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Tidskriftsartikel (refereegranskat)abstract
- We present ab initio calculations of the magnetic moments and magnetic anisotropy energies of small FeCo clusters of varying composition on top of a Cu(100) substrate. Three different cluster layouts have been considered, namely, 2×2, 3×3, and crosslike pentamer clusters. The ratio of Co atoms with respect to the total number in a chosen cluster ("concentration") was varied and all possible arrangements of the atomic species were taken into account. Calculations have been performed fully relativistic using the embedded-cluster technique in conjunction with the screened Korringa-Kohn- Rostoker method and the magnetocrystalline anisotropy energy (MAE) has been evaluated by means of the magnetic force theorem. A central result of the investigations is that the size of the magnetic moments of the individual Fe and Co atoms and their contributions to the anisotropy energy depend on the position they occupy in a particular cluster and on the type and the number of nearest neighbors. The MAE for the 2×2 and 3×3 clusters varies with respect to the concentration of Co atoms in the same manner as the corresponding monolayer case, whereas the pentamer clusters show a slightly different behavior. Furthermore, for the clusters with an easy axis along a direction in the surface plane, the MAE shows a significant angular dependence.
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