| 1. |
- Arheimer, Berit, et al.
(författare)
-
Climate change impact on riverine nutrient load and land-based remedial measures of the Baltic sea action plan.
- 2012
-
Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 41:6, s. 600-612
-
Tidskriftsartikel (refereegranskat)abstract
- To reduce eutrophication of the Baltic Sea, all nine surrounding countries have agreed upon reduction targets in the HELCOM Baltic Sea Action Plan (BSAP). Yet, monitoring sites and model concepts for decision support are few. To provide one more tool for analysis of water and nutrient fluxes in the Baltic Sea basin, the HYPE model has been applied to the region (called Balt-HYPE). It was used here for experimenting with land-based remedial measures and future climate projections to quantify the impacts of these on water and nutrient loads to the sea. The results suggest that there is a possibility to reach the BSAP nutrient reduction targets by 2100, and that climate change may both aggravate and help in some aspects. Uncertainties in the model results are large, mainly due to the spread of the climate model projections, but also due to the hydrological model.
|
|
| 2. |
- Dahne, Joel, et al.
(författare)
-
A counterexample to Payne's nodal line conjecture with few holes
- 2021
-
Ingår i: Communications in nonlinear science & numerical simulation. - : Elsevier. - 1007-5704 .- 1878-7274. ; 103
-
Tidskriftsartikel (refereegranskat)abstract
- Payne conjectured in 1967 that the nodal line of the second Dirichlet eigenfunction must touch the boundary of the domain. In their 1997 breakthrough paper, Hoffmann-Ostenhof, Hoffmann-Ostenhof and Nadirashvili proved this to be false by constructing a counterexample in the plane with many holes and raised the question of the minimum number of holes a counterexample can have. In this paper we prove it is at most 6.
|
|
| 3. |
- Dahne, Joel, et al.
(författare)
-
Computation of Tight Enclosures for Laplacian Eigenvalues
- 2020
-
Ingår i: SIAM Journal on Scientific Computing. - 1064-8275 .- 1095-7197. ; 42:5, s. A3210-A3232
-
Tidskriftsartikel (refereegranskat)abstract
- Recently, there has been interest in high precision approximations of the first eigenvalue of the Laplace-Beltrami operator on spherical triangles for combinatorial purposes. We compute improved and certified enclosures to these eigenvalues. This is achieved by applying the method of particular solutions in high precision, the enclosure being obtained by a combination of interval arithmetic and Taylor models. The index of the eigenvalue is certified by exploiting the monotonicity of the eigenvalue with respect to the domain. The classically troublesome case of singular corners is handled by combining expansions at all corners and an expansion from an interior point. In particular, this allows us to compute 100 digits of the fundamental eigenvalue for the three-dimensional Kreweras model that has been the object of previous efforts.
|
|
| 4. |
|
|
| 5. |
- Dahne, Joel, 1994-
(författare)
-
Computer Assisted Studies in Fluid Mechanics and Spectral Geometry
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contains four papers in the area of partial differential equations. The first two papers are related to spectral geometry and the last two papers to fluid mechanics. A common theme of the papers is that they make use of computer assisted methods in the proofs.Paper I concerns the computation of very precise enclosures of eigenvalues of the Laplace-Beltrami operator on spherical triangles. The interest in these eigenvalues comes from a connection with the combinatorial problem of studying discrete random walks.Paper II gives a concrete counterexample to Payne's nodal line conjecture. The conjecture is concerned with the existence of bounded planar domains for which the second eigenfunction of the Dirichlet Laplacian has a nodal line that doesn't touch the boundary. The paper gives an explicit domain for which it is proved that the nodal line doesn't touch the boundary.Paper III and IV both prove the existence of a certain type of solution known as a highest cusped traveling wave. Paper III deals with the Burgers-Hilbert equation and Paper IV with a family of fractional Korteweg-de Vries equations. The existence is asserted by constructing an explicit approximation of the solution and proving the existence of an exact solution nearby with the use of a fixed point formulation. The proof not only establishes the existence, but also determines the precise asymptotic behavior of the waves near the cusp.
|
|
| 6. |
- Dahne, Joel, et al.
(författare)
-
Enclosing all zeros of a system of analytic functions
- 2019
-
Ingår i: Applied Mathematics and Computation. - : Elsevier. - 0096-3003 .- 1873-5649. ; 348, s. 513-522
-
Tidskriftsartikel (refereegranskat)abstract
- We present a rigorous numerical method for location of simple zeros of a system of two analytic functions in a rectangular cuboid domain based on the logarithmic integral. We compare this to a simpler, also rigorous, method based on bisection. The latter is determined to be more efficient in the examples considered. This is mainly due to inefficient methods for computing the logarithmic integral occurring in the former method. (C) 2018 Elsevier Inc. All rights reserved.
|
|
| 7. |
- Dahne, Joel, et al.
(författare)
-
Highest Cusped Waves for the Burgers-Hilbert Equation
- 2023
-
Ingår i: Archive for Rational Mechanics and Analysis. - : Springer. - 0003-9527 .- 1432-0673. ; 247:5
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we prove the existence of a periodic highest, cusped, traveling wave solution for the Burgers-Hilbert equation f(t )+ ff(x) = H[f ], and give its asymptotic behaviour at 0. The proof combines careful asymptotic analysis and a computer-assisted approach.
|
|
| 8. |
- Dahne, Joel
(författare)
-
Highest Cusped Waves for the Fractional KdV Equations
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we prove the existence of highest, cusped, traveling wave solutions for the fractional KdV equations $f_t + f f_x = |D|^{\alpha} f_x$ for all $\alpha \in (-1,0)$ and give their exact leading asymptotic behavior at zero. The proof combines careful asymptotic analysis and a computer-assisted approach.
|
|
| 9. |
- Hytteborn, Julia K., 1976-, et al.
(författare)
-
Patterns and predictability in the intra-annual organic carbon variability across the boreal and hemiboreal landscape
- 2015
-
Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 520, s. 260-269
-
Tidskriftsartikel (refereegranskat)abstract
- Factors affecting total organic carbon (TOC) concentrations in 215 watercourses across Sweden were investigated using parameter parsimonious regression approaches to explain spatial and temporal variabilities of the TOC water quality responses. We systematically quantified the effects of discharge, seasonality, and long-term trend as factors controlling intra-annual (among year) and inter-annual (within year) variabilities of TOC by evaluating the spatial variability in model coefficients and catchment characteristics (e.g. land cover, retention time, soil type).Catchment area (0.18–47,000 km2) and land cover types (forests, agriculture and alpine terrain) are typical for the boreal and hemiboreal zones across Fennoscandia. Watercourses had at least 6 years of monthly water quality observations between 1990 and 2010. Statistically significant models (p < 0.05) describing variation of TOC in streamflow were identified in 209 of 215 watercourses with a mean Nash-Sutcliffe efficiency index of 0.44. Increasing long-term trends were observed in 149 (70%) of the watercourses, and intra-annual variation in TOC far exceeded inter-annual variation. The average influences of the discharge and seasonality terms on intra-annual variations in daily TOC concentration were 1.4 and 1.3 mg l− 1 (13 and 12% of the mean annual TOC), respectively. The average increase in TOC was 0.17 mg l− 1 year− 1 (1.6% year− 1).Multivariate regression with over 90 different catchment characteristics explained 21% of the spatial variation in the linear trend coefficient, less than 20% of the variation in the discharge coefficient and 73% of the spatial variation in mean TOC. Specific discharge, water residence time, the variance of daily precipitation, and lake area, explained 45% of the spatial variation in the amplitude of the TOC seasonality.Because the main drivers of temporal variability in TOC are seasonality and discharge, first-order estimates of the influences of climatic variability and change on TOC concentration should be predictable if the studied catchments continue to respond similarly.
|
|
| 10. |
- Salas, Julián, et al.
(författare)
-
Swapping trajectories with a sufficient sanitizer
- 2020
-
Ingår i: Pattern Recognition Letters. - : Elsevier. - 0167-8655 .- 1872-7344. ; 131, s. 474-480
-
Tidskriftsartikel (refereegranskat)abstract
- Real-time mobility data is useful for several applications such as planning transports in metropolitan areas or localizing services in towns. However, if such data is collected without any privacy protection it may reveal sensible locations and pose safety risks to an individual associated to it. Thus, mobility data must be anonymized preferably at the time of collection. In this paper, we consider the SwapMob algorithm that mitigates privacy risks by swapping partial trajectories. We formalize the concept of sufficient sanitizer and show that the SwapMob algorithm is a sufficient sanitizer for various statistical decision problems. That is, it preserves the aggregate information of the spatial database in the form of sufficient statistics and also provides privacy to the individuals. This may be used for personalized assistants taking advantage of users’ locations, so they can ensure user privacy while providing accurate response to the user requirements. We measure the privacy provided by SwapMob as the Adversary Information Gain, which measures the capability of an adversary to leverage his knowledge of exact data points to infer a larger segment of the sanitized trajectory. We test the utility of the data obtained after applying SwapMob sanitization in terms of Origin-Destination matrices, a fundamental tool in transportation modelling.
|
|
