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- Callaghan, Terry V., et al.
(författare)
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Biodiversity, distributions and adaptations of arctic species in the context of environmental change
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - : Royal Swedish Academy of Sciences. - 0044-7447. ; 33:7, s. 404-417
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Forskningsöversikt (refereegranskat)abstract
- The individual of a species is the basic unit which responds to climate and UV-B changes, and it responds over a wide range of time scales. The diversity of animal, plant and microbial species appears to be low in the Arctic, and decreases from the boreal forests to the polar deserts of the extreme North but primitive species are particularly abundant. This latitudinal decline is associated with an increase in super-dominant species that occupy a wide range of habitats. Climate warming is expected to reduce the abundance and restrict the ranges of such species and to affect species at their northern range boundaries more than in the South: some Arctic animal and plant specialists could face extinction. Species most likely to expand into tundra are boreal species that currently exist as outlier populations in the Arctic. Many plant species have characteristics that allow them to survive short snow-free growing seasons, low solar angles, permafrost and low soil temperatures, low nutrient availability and physical disturbance. Many of these characteristics are likely to limit species responses to climate warming, but mainly because of poor competitive ability compared with potential immigrant species. Terrestrial Arctic animals possess many adaptations that enable them to persist under a wide range of temperatures in the Arctic. Many escape unfavorable weather and resource shortage by winter dormancy or by migration. The biotic environment of Arctic animal species is relatively simple with few enemies, competitors, diseases, parasites and available food resources. Terrestrial Arctic animals are likely to be most vulnerable to warmer and drier summers, climatic changes that interfere with migration routes and staging areas, altered snow conditions and freeze-thaw cycles in winter, climate-induced disruption of the seasonal timing of reproduction and development, and influx of new competitors, predators, parasites and diseases. Arctic microorganisms are also well adapted to the Arctics climate: some can metabolize at temperatures down to -39degreesC. Cyanobacteria and algae have a wide range of adaptive strategies that allow them to avoid, or at least minimize UV injury. Microorganisms can tolerate most environmental conditions and they have short generation times which can facilitate rapid adaptation to new environments. In contrast, Arctic plant and animal species are very likely to change their distributions rather than evolve significantly in response to warming.
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| 3. |
- Callaghan, Terry V., et al.
(författare)
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Responses to projected changes in climate and UV-B at the species level
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - : Royal Swedish Academy of Sciences. - 0044-7447. ; 33:7, s. 418-435
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Forskningsöversikt (refereegranskat)abstract
- Environmental manipulation experiments showed that species respond individualistically to each environmental-change variable. The greatest responses of plants were generally to nutrient, particularly nitrogen, addition. Summer warming experiments showed that woody plant responses were dominant and that mosses and lichens became less abundant. Responses to warming were controlled by moisture availability and snow cover. Many invertebrates increased population growth in response to summer warming, as long as desiccation was not induced. CO2 and UV-B enrichment experiments showed that plant and animal responses were small. However, some microorganisms and species of fungi were sensitive to increased UV-B and some intensive mutagenic actions could, perhaps, lead to unexpected epidemic outbreaks. Tundra soil heating, CO 2 enrichment and amendment with mineral nutrients generally accelerated microbial activity. Algae are likely to dominate cyanobacteria in milder climates. Expected increases in winter freeze-thaw cycles leading to ice-crust formation are likely to severely reduce winter survival rate and disrupt the population dynamics of many terrestrial animals. A deeper snow cover is likely to restrict access to winter pastures by reindeer/caribou and their ability to flee from predators while any earlier onset of the snow-free period is likely to stimulate increased plant growth. Initial species responses to climate change might occur at the sub-species level: an Arctic plant or animal species with high genetic/racial diversity has proved an ability to adapt to different environmental conditions in the past and is likely to do so also in the future. Indigenous knowledge, air photographs, satellite images and monitoring show that changes in the distributions of some species are already occurring: Arctic vegetation is becoming more shrubby and more productive, there have been recent changes in the ranges of caribou, and "new" species of insects and birds previously associated with areas south of the treeline have been recorded. In contrast, almost all Arctic breeding bird species are declining and models predict further quite dramatic reductions of the populations of tundra birds due to warming. Species-climate response surface models predict potential future ranges of current Arctic species that are often markedly reduced and displaced northwards in response to warming. In contrast, invertebrates and microorganisms are very likely to quickly expand their ranges northwards into the Arctic.
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| 7. |
- Laine, T. A., et al.
(författare)
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Canonical perturbative approach to nonlinear systems with application to optical waves in layered Kerr media
- 2000
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 61:6, s. 7098-7109
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Tidskriftsartikel (refereegranskat)abstract
- We investigate electromagnetic wave reflection and propagation in layered Kerr structures by introducing a method based on the application of canonical perturbation theory to fields in nonlinear media. Via the Hamilton-Jacobi formalism of classical mechanics, the waves in linear layers are expressed with constant canonical variables. The nonlinearity is treated as a small perturbation that modifies the constant invariants. We explicitly evaluate the nonlinear fields correct to first order by perturbation and compare the results to a rigorous nonlinear thin-layer model. Both polarizations, TE and TM, are considered separately. An exact quadrature solution of the nonlinear field in TM polarization is derived. We show that with weak nonlinearities the perturbative technique yields simple and accurate analytical expressions for the nonlinear fields. The results give physical insight into the use of nonlinear media for controlling the scattered fields in layered structures.
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| 9. |
- Laine, T. A., et al.
(författare)
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Self-guided waves and exact solutions of the nonlinear Helmholtz equation
- 2000
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 17:5, s. 751-757
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Tidskriftsartikel (refereegranskat)abstract
- The paraxial wave theory is known to lead to inaccurate predictions in self-focusing of optical beams. The nonlinear Helmholtz equation describes more accurately wave propagation in dispersive, spatially local, Kerr-type media. We derive rigorous bright and dark solutions to the nonlinear Helmholtz equation in a full three-dimensional form. These expressions are new and unique. The solutions are obtained with a multidimensional extension of the (paraxial) nonlinear Schrodinger equation. We also establish energy conservation laws for both nonlinear wave equations in terms of spatial currents. Our results give insight, for example, into the diffraction and breakup of tightly confined nonlinear fields.
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| 10. |
- Laine, T. A., et al.
(författare)
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Thin-layer theory of nonlinear fields
- 2000
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 17:10, s. 1711-1715
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Tidskriftsartikel (refereegranskat)abstract
- We derive a local nonlinear thin-layer theory for electromagnetic fields that propagate in layered structures of isotropic, dispersive, and spatially local Kerr media. By use of an ansatz of plane waves together with a thin-layer approximation, the two-dimensional Kerr-Maxwell equation is rigorously solved within a very thin slab, and the characteristic matrix of the nonlinear medium is determined. The theory makes use of periodicity and allows a direct calculation of the nonlinear field throughout the structure on the basis of the transmitted field. The method is applied in the two polarizations, TE and TM, and is illustrated with a numerical example. The nonlinear thin-layer technique provides a simple and accurate analytical theory that includes multiple plane-wave incident fields and takes rigorously into account all nonlinear interactions of these waves.
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| 11. |
- Laine, T. A., et al.
(författare)
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Variational analysis and angular bistability in layered nonlinear Kerr media with phase conjugation
- 2000
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 17:6, s. 977-984
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Tidskriftsartikel (refereegranskat)abstract
- The calculus of variations is applied to electromagnetic fields in a layered nonlinear structure supporting a guided wave. The system also includes a phase-conjugate mirror (PCM). By introducing a variational dimension and using a collection of plane waves as a trial function, we approximate the exact solution of the nonlinear Kerr-Maxwell equation. The formalism is new, and it involves the nonlinear interference of multiple plane waves. A simple analytical expression for the nonlinear field in the presence of the PCM is derived, and the fact that the scattered intensities may become bistable when the angle of incidence is varied is demonstrated. In particular, our theory predicts the angular bistability in the backscattering direction, where the effect of the guided waves is subtle. Our numerical results are also in good agreement with other theoretical approaches and with the experimental data.
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| 12. |
- Osterberg, M., et al.
(författare)
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Forces between xylan-coated surfaces : Effect of polymer charge density and background electrolyte
- 2001
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 242:1, s. 59-66
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Tidskriftsartikel (refereegranskat)abstract
- The forces between xylan-coated mica surfaces at pH 10 have been studied using the interferometric surface force apparatus. Xylan is a polysaccharide that is composed of (1,4)-linked beta -D-xylopyranose units, which are partially substituted at C2 with 4-O-methyl-alpha -D-glucuronic acid units and at C3 with alpha -L-arabinosyl units. Two different xylans were studied, one with 0.5% and one with 9% of the segments containing a carboxylic acid group. It was found that both xylans adsorbed onto the negatively charged mica surface despite their negative charge. The interactions between the xylan-coated surfaces were dependent on the charge density of the polymer. The xylan with higher charge density adsorbed in a more extended conformation leading to more long-range repulsion. The shapes of the force curves were consistent with the forces expected for anchored polyelectrolyte brushes. After compression the length of the protruding chains decreased. An increase in background electrolyte concentration led to a decrease in the range of the repulsion. This effect was, as expected, more pronounced for the high charge density xylan. In the presence of CaCl2 not only the long-range forces but also the layer thickness at high compressive load decreased.
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