| 1. |
- Hoffman, Johan, et al.
(författare)
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A General Galerkin Finite Element Method for the Compressible Euler Equations
- 2008
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Ingår i: SIAM Journal on Scientific Computing. - 1064-8275 .- 1095-7197.
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a General Galerkin (G2) method for the compressible Euler equations, including turbulent ow. The G2 method presented in this paper is a nite element method with linear approximation in space and time, with componentwise stabilization in the form of streamline diusion and shock-capturing modi cations. The method conserves mass, momentum and energy, and we prove an a posteriori version of the 2nd Law of thermodynamics for the method. We illustrate the method for a laminar shock tube problem for which there exists an exact analytical solution, and also for a turbulent flow problem
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| 2. |
- Algesten, Grete, et al.
(författare)
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Organic carbon budget for the Gulf of Bothnia
- 2006
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 63:3-4, s. 155-161
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Tidskriftsartikel (refereegranskat)abstract
- We calculated input of organic carbon to the unproductive, brackish water basin of the Gulf of Bothnia from rivers, point sources and the atmosphere. We also calculated the net exchange of organic carbon between the Gulf of Bothnia and the adjacent marine system, the Baltic Proper. We compared the input with sinks for organic carbon; permanent incorporation in sediments and mineralization and subsequent evasion of CO2 to the atmosphere. The major fluxes were riverine input (1500 Gg C year(-1)), exchange with the Baltic Proper (depending on which of several possible DOC concentration differences between the basins that was used in the calculation, the flux varied between an outflow of 466 and an input of 950 Gg C year(-1)), sediment burial (1100 Gg C year) and evasion to the atmosphere (3610 Gg C year(-1)). The largest single net flux was the emission of CO2 to the atmosphere, mainly caused by bacterial mineralization of organic carbon. Input and output did not match in our budget which we ascribe uncertainties in the calculation of the exchange of organic carbon between the Gulf of Bothnia and the Baltic Proper, and the fact that CO2 emission, which in our calculation represented 1 year (2002) may have been overestimated in comparison with long-term means. We conclude that net heterotrophy of the Gulf of Bothnia was due to input of organic carbon from both the catchment and from the Baltic Proper and that the future degree of net heterotrophy will be sensible to both catchment export of organic carbon and to the ongoing eutrophication of the Baltic Proper.
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| 3. |
- Napieralski, Jacob, et al.
(författare)
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Towards a GIS assessment of numerical ice sheet model performance using geomorphological data
- 2007
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Ingår i: Journal of Glaciology. ; 53:180, s. 71-83
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Tidskriftsartikel (refereegranskat)abstract
- A major difficulty in assimilating geomorphological information with ice-sheet models is the lack of a consistent methodology to systematically compare model output and field data. As an initial step in establishing a quantitative comparison methodology, automated proximity and conformity analysis (APCA) and automated flow direction analysis (AFDA) have been developed to assess the level of correspondence between modelled ice extent and ice-marginal features such as end moraines, as well as between modelled basal flow directions and palaeo-flow direction indicators, such as glacial lineations. To illustrate the potential of such an approach, an ensemble suite of 40 numerical simulations of the Fennoscandian ice sheet were compared to end moraines of the Last Glacial Maximum and the Younger Dryas and to glacial lineations in northern Sweden using APCA and AFDA. Model experiments evaluated in this manner were ranked according to level of correspondence. Such an approach holds considerable promise for optimizing the parameter space and coherence of ice-flow models by automated, quantitative assessment of multiple ensemble experiments against a database of geological or glaciological evidence.
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| 4. |
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| 5. |
- Jansson, Johan, et al.
(författare)
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Algorithms and Data Structures for Multi-Adaptive Time-Stepping
- 2008
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Ingår i: ACM Transactions on Mathematical Software. - : Association for Computing Machinery (ACM). - 0098-3500 .- 1557-7295. ; 35:3
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Tidskriftsartikel (refereegranskat)abstract
- Multi-adaptive Galerkin methods are extensions of the standard continuous and discontinuous Galerkin methods for the numerical solution of initial value problems for ordinary or partial differential equations. In particular, the multi-adaptive methods allow individual and adaptive time steps to be used for different components or in different regions of space. We present algorithms for efficient multi-adaptive time-stepping, including the recursive construction of time slabs and adaptive time step selection. We also present data structures for efficient storage and interpolation of the multi-adaptive solution. The efficiency of the proposed algorithms and data structures is demonstrated for a series of benchmark problems.
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| 6. |
- Jansson, Johan, 1978, et al.
(författare)
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Computational modeling of dynamical systems
- 2005
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Ingår i: Mathematical Models and Methods in Applied Sciences. - 0218-2025. ; 15:3, s. 471-481
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Tidskriftsartikel (refereegranskat)abstract
- In this short note, we discuss the basic approach to computational modeling of dynamical systems. If a dynamical system contains multiple time scales, ranging from very fast to slow, computational solution of the dynamical system can be very costly. By resolving the fast time scales in a short time simulation, a model for the effect of the small time scale variation on large time scales can be determined, making solution possible on a long time interval. This process of computational modeling can be completely automated. Two examples are presented, including a simple model problem oscillating at a time scale of 10-9 computed over the time interval [0, 100], and a lattice consisting of large and small point masses. © World Scientific Publishing Company.
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| 7. |
- Jansson, Patrik, 1972, et al.
(författare)
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Testing Properties of Generic Functions
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Software testing is an important part of the software development process. Testing comes in many flavours: unit testing, property testing, regression testing, contract checking, etc. QuickCheck is probably one of the most advanced tools for testing properties of functional programs. It supports the definition of properties and random test-data generators in Haskell, and checks that a property passes the test cases. A datatype-generic function is parametrised by a type. Examples of generic functions are equality tests, maps and pretty printers. A generic function can be seen as a template algorithm that can be instantiated with (the structure of) a data type. Generic functions satisfy generic properties. This paper discusses testing properties of generic functions. It shows how generic properties can be formulated, and how QuickCheck can be used to test generic properties. Furthermore, it shows how to automatically generate QuickCheck generators using Generic Haskell.
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| 8. |
- Jansson, Patrik, 1972, et al.
(författare)
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Testing Properties of Generic Functions
- 2007
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Ingår i: LNCS, Proceedings of IFL 2006. ; 4449
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Konferensbidrag (refereegranskat)abstract
- A datatype-generic function is a family of functions indexed by (the structure of) a type. Examples include equality tests, maps and pretty printers. Property based testing tools like QuickCheck and Gast support the definition of properties and test-data generators, and they check if a monomorphic property is satisfied by the test cases. Generic functions satisfy generic properties and this paper discusses specifying and testing such properties. It shows how generic properties and generators can be expressed, and explains three bugs we found and corrected in the Generic Haskell library.
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| 9. |
- Nilsson, Christer, 1951-, et al.
(författare)
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Forecasting environmental responses to restoration of rivers used as log floatways : an interdisciplinary challenge
- 2005
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 8:7, s. 779-800
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Tidskriftsartikel (refereegranskat)abstract
- Log floating in the 19th to mid 20th centuries has profoundly changed the environmental conditions in many northern river systems of the world. Regulation of flow by dams, straightening and narrowing of channels by various piers and wing dams, and homogenization of bed structure are some of the major impacts. As a result, the conditions for many riverine organisms have been altered. Removing physical constructions and returning boulders to the channels can potentially restore conditions for these organisms. Here we describe the history of log driving, review its impact on physical and biological conditions and processes, and predict the responses to restoration. Reviewing the literature on comparable restoration efforts and building upon this knowledge, using boreal Swedish rivers as an example, we address the last point. We hypothesize that restoration measures will make rivers wider and more sinuous, and provide rougher bottoms, thus improving land-water interactions and increasing the retention capacity of water, sediment, organic matter and nutrients. The geomorphic and hydraulic/hydrologic alterations are supposed to favor production, diversity, migration and reproduction of riparian and aquatic organisms. The response rates are likely to vary according to the types of processes and organisms. Some habitat components, such as beds of very large boulders and bedrock outcrops, and availability of sediment and large woody debris are believed to be extremely difficult to restore. Monitoring and evaluation at several scales are needed to test our predictions.
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| 10. |
- Bylesjö, Max, et al.
(författare)
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LAMINA : a tool for rapid quantification of leaf size and shape parameters
- 2008
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Ingår i: BMC Plant Biology. - : BMC. - 1471-2229. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Background: An increased understanding of leaf area development is important in a number of fields: in food and non-food crops, for example short rotation forestry as a biofuels feedstock, leaf area is intricately linked to biomass productivity; in paleontology leaf shape characteristics are used to reconstruct paleoclimate history. Such fields require measurement of large collections of leaves, with resulting conclusions being highly influenced by the accuracy of the phenotypic measurement process.Results: We have developed LAMINA (Leaf shApe deterMINAtion), a new tool for the automated analysis of images of leaves. LAMINA has been designed to provide classical indicators of leaf shape (blade dimensions) and size (area), which are typically required for correlation analysis to biomass productivity, as well as measures that indicate asymmetry in leaf shape, leaf serration traits, and measures of herbivory damage (missing leaf area). In order to allow Principal Component Analysis (PCA) to be performed, the location of a chosen number of equally spaced boundary coordinates can optionally be returned.Conclusion: We demonstrate the use of the software on a set of 500 scanned images, each containing multiple leaves, collected from a common garden experiment containing 116 clones of Populus tremula (European trembling aspen) that are being used for association mapping, as well as examples of leaves from other species. We show that the software provides an efficient and accurate means of analysing leaf area in large datasets in an automated or semi-automated work flow.
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