| 1. |
|
|
| 2. |
- Yi, Chuixiang, et al.
(författare)
-
Climate control of terrestrial carbon exchange across biomes and continents
- 2010
-
Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 5:3
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid-and high-latitudes, (2) a strong function of dryness at mid-and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45 degrees N). The sensitivity of NEE to mean annual temperature breaks down at similar to 16 degrees C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence.
|
|
| 3. |
- Almeida, Cristiane G., et al.
(författare)
-
Photocatalytic hydrogen production with visible light over Mo and Cr-doped BiNb(Ta)O-4
- 2014
-
Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 39:3, s. 1220-1227
-
Tidskriftsartikel (refereegranskat)abstract
- In the present work, we prepared pure and Cr(III) and Mo(V)-doped BiNbO4 and BiTaO4 by the citrate method. Pure BiNbO4 and BiTaO4 were obtained in triclinic phase at 600 degrees C and 800 degrees C, respectively. The metal doping influenced strongly the crystal structure as well as the photocatalytic activity of the oxides. The XRD data could prove that the Mo(V) doping induces the orthorhombic phase, while the Cr(III) doping favors the triclinic phase for both oxides. Metal doping also modified the photosensitivity of the oxides, extending the absorption toward the visible light region. The photocatalytic activity in water splitting under visible light irradiation was evaluated by monitoring the H-2, CO2 and CO evolution. The results showed that Cr(III)-doped BiTaO4 and BiNbO4, in general, are more selective for hydrogen production, while Mo(V)-doped materials are more selective for CO2 generation. Comparing the photocatalytic activity of BiTaO4 and BiNbO4, the former shows higher activity for hydrogen production as well as for CO2 generation, specially when the concentration was 2% in Cr(III) and Mo(V), respectively. Those results are in agreement with the computational study to access the effect of doping on the electronic structure. For Mo(V)-doped materials a negligible change of conduction band minimum potential was found, indicating that there might be no improvement on the reduction power of the material following the substitutional doping. In Cr(III)-doped BiNbO4 there is a slight shift of the CBM potential increasing a little bit the reduction power. However, the effect is much stronger in the Cr(III)-doped BiTaO4.
|
|
| 4. |
- DeAngelis, Donald L., et al.
(författare)
-
The Effect of Travel Loss on Evolutionarily Stable Distributions of Populations in Space
- 2011
-
Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 178:1, s. 15-29
-
Tidskriftsartikel (refereegranskat)abstract
- A key assumption of the ideal free distribution (IFD) is that there are no costs in moving between habitat patches. However, because many populations exhibit more or less continuous population movement between patches and traveling cost is a frequent factor, it is important to determine the effects of costs on expected population movement patterns and spatial distributions. We consider a food chain (tritrophic or bitrophic) in which one species moves between patches, with energy cost or mortality risk in movement. In the two-patch case, assuming forced movement in one direction, an evolutionarily stable strategy requires bidirectional movement, even if costs during movement are high. In the N-patch case, assuming that at least one patch is linked bidirectionally to all other patches, optimal movement rates can lead to source-sink dynamics where patches with negative growth rates are maintained by other patches with positive growth rates. As well, dispersal between patches is not balanced (even in the two-patch case), leading to a deviation from the IFD. Our results indicate that cost-associated forced movement can have important consequences for spatial metapopulation dynamics. Relevance to marine reserve design and the study of stream communities subject to drift is discussed.
|
|
| 5. |
- Araújo, M.C., et al.
(författare)
-
Predicting the mechanical behavior of amorphous polymeric materials under strain through multi-scale simulation
- 2014
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 306, s. 37-46
-
Tidskriftsartikel (refereegranskat)abstract
- Polymeric materials have become the reference material for high reliability and performance applications. However, their performance in service conditions is difficult to predict, due in large part to their inherent complex morphology, which leads to non-linear and anisotropic behavior, highly dependent on the thermomechanical environment under which it is processed. In this work, a multiscale approach is proposed to investigate the mechanical properties of polymeric-based material under strain. To achieve a better understanding of phenomena occurring at the smaller scales, the coupling of a finite element method (FEM) and molecular dynamics (MD) modeling, in an iterative procedure, was employed, enabling the prediction of the macroscopic constitutive response. As the mechanical response can be related to the local microstructure, which in turn depends on the nano-scale structure, this multiscale approach computes the stress-strain relationship at every analysis point of the macro-structure by detailed modeling of the underlying micro- and meso-scale deformation phenomena. The proposed multiscale approach can enable prediction of properties at the macroscale while taking into consideration phenomena that occur at the mesoscale, thus offering an increased potential accuracy compared to traditional methods.
|
|
| 6. |
- Araujo, Rafael B., et al.
(författare)
-
First-principles investigation of Li ion diffusion in Li2FeSiO4
- 2013
-
Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738 .- 1872-7689. ; 247, s. 8-14
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the Li-ion migration and the electrochemical performance of Li2FeSiO4 in the monoclinic crystal structure with P2(1) symmetry and the related delithiated system LiFeSiO4. For this purpose, the framework of the density functional theory within the generalized gradient approximation in conjunction with the climbing image nudged elastic band method was used. Addition of the Hubbard term was also considered in the Kohn-Sham Hamiltonian to better model the d electrons of the metal ions in this material. The calculated activation energies for Li ion migration are found to decrease by around 20% with the Hubbard term inclusion in the chosen diffusion pathways of Li2FeSiO4. Regarding the delithiated structure, the activation energies were found to be sensitive to the Hubbard term addition, however no general behavior such as in the lithiated structure was found. Furthermore, the diffusion coefficients were calculated considering temperatures of 300 K, 500 K, and 700 K.
|
|
| 7. |
- Araujo, Rafael B., et al.
(författare)
-
Lithium transport investigation in LixFeSiO4 : A promising cathode material
- 2013
-
Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 173, s. 9-13
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we investigate lithium mobility in both Li 2FeSiO4 and its half-lithiated state LiFeSiO4 considering an orthorhombic crystal structure. We find that the calculated activation energy of Li+ ions hopping between adjacent equilibrium sites predicts two least hindered diffusion pathways in both materials. One of them is along the [100] direction characterizing an ionic diffusion in a straight line and the other follows a zig-zag way between the Fe-Si-O layers. We also show that diffusion of Li+ ions in the half-lithiated structure follows the same behavior as in the lithiated structure. As a whole, the activation energies for the investigated compounds present a greater value compared with the activation energies in currently used materials such as LiFePO4. The results were calculated in the framework of density functional theory in conjunction with the climbing image nudged elastic band method. The Hubbard term was added to the Kohn-Sham Hamiltonian to overcome the delocalization problem of d electrons. Furthermore, the diffusion coefficients were calculated for both structures considering temperatures ranging from 300 to 700 K.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
