| 31. |
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| 32. |
- Callaghan, Terry V., et al.
(författare)
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A new climate era in the sub-Arctic : Accelerating climate changes and multiple impacts
- 2010
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 37:14, s. L14705-
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Tidskriftsartikel (refereegranskat)abstract
- Climate warming in the Swedish sub-Arctic since 2000 has reached a level at which statistical analysis shows for the first time that current warming has exceeded that in the late 1930' s and early 1940' s, and has significantly crossed the 0 degrees C mean annual temperature threshold which causes many cryospheric and ecological impacts. The accelerating temperature increase trend has driven similar trends in the century-long increase in snow thickness, loss of lake ice, increases in active layer thickness, lake water TOC (total organic carbon) concentrations and the assemblages of diatoms, and changes in tree-line location and plant community structure. Some of these impacts were not evident in the first warm period of the 20th Century. Changes in climate are associated with reduced temperature variability, particularly loss of cold winters and cool summers, and an increase in extreme precipitation events that cause mountain slope instability and infrastructure failure. The long term records of multiple, local environmental factors compiled here for the first time provide detailed information for adaptation strategy development while dramatic changes in an environment particularly vulnerable to climate change highlight the need to adopt global mitigation strategies.
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| 33. |
- Carey, V, et al.
(författare)
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Blockwise adaptivity for time dependent problems based on coarse scale adjoint solutions
- 2010
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Ingår i: SIAM Journal on Scientific Computing. - : Society for Industrial and Applied Mathematics. - 1064-8275 .- 1095-7197. ; 32:4, s. 2121-2145
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Tidskriftsartikel (refereegranskat)abstract
- We describe and test an adaptive algorithm for evolution problems that employs a sequence of "blocks" consisting of fixed, though non-uniform, space meshes. This approach offers the advantages of adaptive mesh refinement but with reduced overhead costs associated with load balancing, re-meshing, matrix reassembly, and the solution of adjoint problems used to estimate discretization error and the effects of mesh changes. A major issue whith a blockadaptive approach is determining block discretizations from coarse scale solution information that achieve the desired accuracy. We describe several strategies to achieve this goal using adjoint-based a posteriori error estimates and we demonstrate the behavior of the proposed algorithms as well as several technical issues in a set of examples.
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| 34. |
- Dimarogonas, Dimos V., et al.
(författare)
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Bounded control of network connectivity in multi-agent systems
- 2010
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Ingår i: IET Control Theory & Applications. - : Institution of Engineering and Technology (IET). - 1751-8644 .- 1751-8652. ; 4:8, s. 1330-1338
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Tidskriftsartikel (refereegranskat)abstract
- A distributed control law that guarantees connectivity maintenance in a network of multiple mobile agents is presented. The control law, which lets the agents perform formation manoeuvres, respects sensor limitations by allowing each agent to only take into account agents within its sensing radius. In contrast to previous approaches to the problem, the proposed control law does not attain infinite values whenever an edge of the communication graph tends to be lost. This is achieved via the use of decentralised navigation functions, which are bounded potential fields. The navigation functions are defined to take into account the connectivity maintenance objective. The authors first treat the case of connectivity maintenance for a static communication graph and then extend the result to the case of dynamic graphs. The results are illustrated on a formation control problem.
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| 35. |
- Dimarogonas, Dimos V., et al.
(författare)
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Distributed self-triggered control for multi-agent systems
- 2010
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Konferensbidrag (refereegranskat)abstract
- It is desirable to limit the amount of communication and computation generated by each agent in a large multi-agent system. Event- and self-triggered control strategies have been recently proposed as alternatives to traditional time-triggered periodic sampling for feedback control systems. In this paper we consider self-triggered control applied to a multi-agent system with an agreement objective. Each agent computes its next update time instance at the previous time. This formulation extends considerably our recent work on event-based control, because in the self-triggered setting the agents do not have to keep track of the state error that triggers the actuation between consecutive update instants. Both a centralized and a distributed self-triggered control architecture are presented and shown to achieve the agreement objective. The results are illustrated through simulated examples.
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| 36. |
- Dimarogonas, Dimos V., et al.
(författare)
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Stability analysis for multi-agent systems using the incidence matrix : Quantized communication and formation control
- 2010
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 46:4, s. 695-700
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Tidskriftsartikel (refereegranskat)abstract
- The spectral properties of the incidence matrix of the communication graph are exploited to provide solutions to two multi-agent control problems. In particular, we consider the problem of state agreement with quantized communication and the problem of distance-based formation control. In both cases, stabilizing control laws are provided when the communication graph is a tree. It is shown how the relation between tree graphs and the null space of the corresponding incidence matrix encode fundamental properties for these two multi-agent control problems.
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| 37. |
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| 38. |
- Hansson, Gunnar C., 1951, et al.
(författare)
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The inner of the two Muc2 mucin-dependent mucus layers in colon is devoid of bacteria.
- 2010
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Ingår i: Gut microbes. - : Informa UK Limited. - 1949-0984 .- 1949-0976. ; 1:1, s. 51-54
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Forskningsöversikt (refereegranskat)abstract
- We have recently shown that the colon is protected by an inner mucus layer that efficiently separates the bacteria in the outer mucus from the epithelial cells. The inner mucus is impervious for bacteria and built by a network formed by the MUC2 mucin. Lack or defects in this inner mucus layer allow bacteria to reach the epithelia, something that triggers colon inflammation.
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| 39. |
- Holomb, R., et al.
(författare)
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Boson peak in low-frequency Raman spectra of AsxS100-x glasses: nanocluster contribution
- 2010
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Ingår i: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley. - 1610-1642 .- 1862-6351. ; 7:3-4, s. 885-888
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Tidskriftsartikel (refereegranskat)abstract
- The origin of the Boson peak was investigated using Raman spectroscopy and ab initio calculations. Low frequency Raman active vibrational modes of different branchy-, ring- and cage-like AsmSn nanoclusters were calculated and compared to experimentally determined Raman spectra of AsxS100-x glasses with different compositon. A good correlation was found between the spectral features and the calculated Raman modes. The possible structural nature of the Boson peak in arsenic chalcogenides is proposed and discussed.
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| 40. |
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