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Ståhl, Fredrik
Publications (9 of 9) Show all publications
Skytt, T., Nielsen, S. N., Ståhl, F., Jonsson, A., Grönlund, E., Carlman, I. & Fröling, M. (2015). A strategic tool to find out regional sustainability methodologies helpingindividuals to make long term decisions. In: Proceedings of Global Cleaner Production and Sustainable Consumption, Barcelona Sitges, November 1-4, 2015: . Paper presented at Global Cleaner Production and Sustainable Consumption, Barcelona Sitges, Novmenber 1-4, 2015.
Open this publication in new window or tab >>A strategic tool to find out regional sustainability methodologies helpingindividuals to make long term decisions
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2015 (English)In: Proceedings of Global Cleaner Production and Sustainable Consumption, Barcelona Sitges, November 1-4, 2015, 2015Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

There is a variety of definitions of the concept ‘sustainable’ to be found, and many interestingideas how to measure and evaluate what can be regarded as ‘sustainability’. Meanwhile,whatever the definition is used it must have a strong physical background. There is also acontinuous flow of information and a general awareness about the necessity of taking action,thereby reducing the negative anthropocentric contribution to global warming and ecologicalsystems depletion. A number of visions about (for example) future emission values typically 15-30 years from today are often presented. At the same time there is a continuous political debateabout the balance between individual freedom vs political regulations. The typical individual -standing in the intersection of all this - still seldom gets practical guidelines on how to act in thedaily life to meet future visions. This paper argues that it is necessary to simplify the indicatorsused to evaluate sustainability and at the same time ensure clear instructions of action therebyincreasing the communicability. This is believed to be possible through the application of aholistic approach based upon a detailed mapping, thus making it possible to find out an over-allstrategy and then transform it into specific guidelines for the individual to apply, taking anentrance point in a realistic description of individual everyday life. The regional level is chosenas the most suitable level to work with to keep in touch with the individual level without losingthe strategic possibilities and over-all view when attacking the problem. Without a deep andcommon understanding of the ‘daily life’ in the region, visions and guidelines might show to becounterproductive.For the Swedish region Jämtland, a sparsely populated area with large forests, a lot of hydropower, and one major city (Östersund with about 60.000 inhabitants), some industries and skiresorts (the largest being Åre), the method developed by Nielsen and Jørgensen for the minorisland named Samsø in Denmark has been chosen. By building a model for evaluating thecarbon balance and the work energy balances we are able to focus the strategies and make aguideline for individuals. It seems necessary to accept some usage of fossil fuels also in thefuture but we need to see how this usage can be steered to applications where non-fossilalternatives are less realistic. By working with sectors, built together, we are able to work withsub-models without having to compromise on either lower or higher level of societal activities.Compared to the Samsø case, Jämtland is more complex and also much larger (127.000inhabitants compared to Samsø’s 4.000 and with an area about 20% larger than theNetherlands). The sectors chosen are Industry (Businesses other than those covered in othersectors), Agriculture, Forestry, Tourism, Nature, Public, Private (households), Reindeerherding, Wastes and Energy. The budget of each sector is mapped in terms of carbon and workenergy balances as a sub-model of an over-all model of Jämtland. By finding out the limits(constrains) from simulations carried out on the region it is possible to set for example carbonand energy budgets as basis for personal guidelines for the citizens of the region.The major idea is that most citizens of the region will understand and adapt to such guidelinesto an extent that may induce a change of individual behavioral patterns thus turning the regiontowards sustainability. Jämtland has a specific “culture” which can be used to create proudnessand interest for the sustainability aims. It is important to arrange a platform that serves to shapea fruitful dialogue between all stakeholders – from individual to groups – that will make itpossible to create a common plan for measurements to be implemented, i.e. a concertedgovernance which ensure and guarantee a future of optimal existence for ecosystems as wellas human beings.

Keywords
Sustainability evaluation, Carbon balance, Work energy, Societal transition
National Category
Environmental Sciences Environmental Engineering
Identifiers
urn:nbn:se:miun:diva-26231 (URN)
Conference
Global Cleaner Production and Sustainable Consumption, Barcelona Sitges, Novmenber 1-4, 2015
Available from: 2015-11-08 Created: 2015-11-08 Last updated: 2015-11-11Bibliographically approved
Skytt, T., Nielsen, S. N., Grönlund, E., Ståhl, F., Jonsson, A., Carlman, I. & Fröling, M. (2015). Interdisciplinary Cooperation And System Modelling As Means To Govern The Anthropocene. In: Proceedings of the 59th Annual Meeting of the International Society for the Systems Sciences: . Paper presented at 59th Annual Meeting of the International Society for the Systems Sciences; Scandic Berlin Potsdamer PlatzBerlin; Germany; 2 August 2015 through 7 August 2015; Code 121844. international society for the systems sciences (ISSS)
Open this publication in new window or tab >>Interdisciplinary Cooperation And System Modelling As Means To Govern The Anthropocene
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2015 (English)In: Proceedings of the 59th Annual Meeting of the International Society for the Systems Sciences, international society for the systems sciences (ISSS) , 2015Conference paper, Published paper (Other academic)
Abstract [en]

The global development has now come to a critical state where humanity act as a new geological force and it is obvious that there are numerous of environmental problems which arise from the present geosphere-biosphere-anthroposphere interactions which urgently need to be addressed. This paper argues that systems analysis and modelling of environmental systems is one necessary part in successful governing of societies towards sustainability. In the 1960th many observations and data made it evident that the environment in most countries was in a bad state. To get a holistic view of the complex problems and to clarify the relationships of structure and function, systems thinking was applied e.g. modelling, cybernetics, systems analysis, life cycle assessment and energy and material flow analysis. Such tools used collectively, conceptualized as ‘integrated assessment’, can help to communicate fundamental knowledge, and to support decision-making when identifying, developing and implementing precautionary measures and solutions. There are good examples demonstrating the strength of such approaches; Solutions to the ozone depletion by replacing CFC’s with more chemically reactive compounds that are degraded within the troposphere. Acidification of European low buffer soils and lakes, sensitive to acid rain, has decreased due to concerted action on Sulphur emission control in large parts of Europe. The handling and recycling of solid waste has resulted in a considerable reduction of deposits in large parts of the world. This basically natural scientific knowledge has also influenced the development within e.g. economy and jurisprudence and today ecological economy and environmental law assume ecological systems as fundamental.

The complexity of ecosystems and environmental issues can only be understood by use of advanced scientific tools such as modelling as a base for establishing interdisciplinary co-operation. Each component of such models will of course be an approximation, but validation and verification of the models will serve to make them useful. An ongoing research project at Mid Sweden University aims at building a complete carbon and energy balance model of an entire Swedish region, based on the Danish Samsø-model. Such models will make it possible to refer to a robust scientific base, thereby making it easier to argue for appropriate measures and actions. At the same time it will be clear what data these actions rest upon thereby making it easier to identify possible errors or limitations.

Systems analysis and subsequent modes are constructs. According to systems theory and model development they are strategies as the best representations of nature, we can make. At the same time it must be assured, that a continuous adaptation and improvement in a studied area is possible - i.e. that model outcomes are matched with phenomenological observations and that empirical work also is carried out. Model development can therefore be characterized as a dynamic and iterative process.

Governance in the Anthropocene must be based on an understanding of the problem picture at hand, and learning how to appropriately address increasingly complex issues. For identifying potential solutions and consequences of policy implementation, systems modelling on relevant levels will be one necessary tool. The current project developing an environmental regional model, illustrates how modelling can provide decision support for the county of Jämtland regarding management of energy resources and planning of future infrastructure, as well as serving regional and national information purposes.

Place, publisher, year, edition, pages
international society for the systems sciences (ISSS), 2015
Keywords
Integrated Assessment, Regional sustainability, Governing Anthropocene, Ecological modelling, Interdisciplinary cooperation
National Category
Other Engineering and Technologies Other Environmental Engineering
Identifiers
urn:nbn:se:miun:diva-25797 (URN)2-s2.0-84976466711 (Scopus ID)
Conference
59th Annual Meeting of the International Society for the Systems Sciences; Scandic Berlin Potsdamer PlatzBerlin; Germany; 2 August 2015 through 7 August 2015; Code 121844
Available from: 2015-08-27 Created: 2015-08-27 Last updated: 2018-11-16Bibliographically approved
Sundström, D., Carlsson, P., Ståhl, F. & Tinnsten, M. (2013). Numerical optimization of pacing strategy in cross-country skiing. Structural and multidisciplinary optimization (Print), 47(6), 943-950
Open this publication in new window or tab >>Numerical optimization of pacing strategy in cross-country skiing
2013 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 47, no 6, p. 943-950Article in journal (Refereed) Published
Abstract [en]

When studying events involving locomotive exercise,such as cross-country skiing, one generally assumesthat pacing strategies (i.e. power distributions) have a significantimpact on performance. In order to better understandthe importance of pacing strategies, a program isdeveloped for numerical simulation and optimization of thepacing strategy in cross-country ski racing. This programcomputes the optimal pacing strategy for an arbitrary athleteskiing on a delineated course. The locomotion of theskier is described by introducing the equations of motionfor cross-country skiing. A transformation of the motionequations is carried out in order to improve the simulation. Furthermore, a nonlinear optimization routine is connectedto the simulation program. Simulation and optimization areperformed on a fictional male skier. Results show that it ispossible to attain an optimal pacing strategy by simulatingcross-country skiing while connecting nonlinear optimizationroutines to the simulation. It is also shown that an optimalpacing strategy is characterized by minor variations inspeed. In our opinion, this kind of optimization could serveas essential preparations before important competitions.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2013
Keywords
Optimization, Numerical simulation, Cross-country skiing, Pacing strategy, Power distribution
National Category
Applied Mechanics
Identifiers
urn:nbn:se:miun:diva-17529 (URN)10.1007/s00158-012-0856-7 (DOI)000318624100012 ()2-s2.0-84879103889 (Scopus ID)
Projects
Sportstech 2
Available from: 2012-12-04 Created: 2012-11-30 Last updated: 2017-12-07Bibliographically approved
Lund, M., Ståhl, F. & Gulliksson, M. (2008). Regularity Aspects in Inverse Musculoskeletal Biomechanics. In: Simos, TE; Psihoyios, G; Tsitouras, C (Ed.), NUMERICAL ANALYSIS AND APPLIED MATHEMATICS: . Paper presented at International Conference on Numerical Analysis and Applied Mathematics, Sep 16-20, 2008, Psalidi, Greece (pp. 368-371). American Institute of Physics (AIP)
Open this publication in new window or tab >>Regularity Aspects in Inverse Musculoskeletal Biomechanics
2008 (English)In: NUMERICAL ANALYSIS AND APPLIED MATHEMATICS / [ed] Simos, TE; Psihoyios, G; Tsitouras, C, American Institute of Physics (AIP), 2008, p. 368-371Conference paper, Published paper (Refereed)
Abstract [en]

Inverse simulations of musculoskeletal models computes the internal forces such as muscle and joint reaction forces, which are hard to measure, using the more easily measured motion and external forces as input data. Because of the difficulties of measuring muscle forces and joint reactions, simulations are hard to validate. One way of reducing errors for the simulations is to ensure that the mathematical problem is well-posed. This paper presents a study of regularity aspects for an inverse simulation method, often called forward dynamics or dynamical optimization, that takes into account both measurement errors and muscle dynamics. Regularity is examined for a test problem around the optimum using the approximated quadratic problem. The results shows improved rank by including a regularization term in the objective that handles the mechanical over-determinancy. Using the 3-element Hill muscle model the chosen regularization term is the norm of the activation. To make the problem full-rank only the excitation bounds should be included in the constraints. However, this results in small negative values of the activation which indicates that muscles are pushing and not pulling, which is unrealistic but the error maybe small enough to be accepted for specific applications. These results are a start to ensure better results of inverse musculoskeletal simulations from a numerical point of view.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2008
Series
AIP conference proceedings, ISSN 0094-243X ; 1048
Keywords
Least Squares Problem; Optimization; Inverse problem; Forward dynamics
National Category
Computational Mathematics
Identifiers
urn:nbn:se:miun:diva-9938 (URN)10.1063/1.2990935 (DOI)000259567000087 ()2-s2.0-54049098396 (Scopus ID)978-0-7354-0576-9 (ISBN)
Conference
International Conference on Numerical Analysis and Applied Mathematics, Sep 16-20, 2008, Psalidi, Greece
Available from: 2009-09-29 Created: 2009-09-29 Last updated: 2016-09-23Bibliographically approved
Rendall, A. & Ståhl, F. (2008). Shock Waves in Plane Symmetric Spacetimes. Communications in Partial Differential Equations, 33(11), 2020-2039
Open this publication in new window or tab >>Shock Waves in Plane Symmetric Spacetimes
2008 (English)In: Communications in Partial Differential Equations, ISSN 0360-5302, E-ISSN 1532-4133, Vol. 33, no 11, p. 2020-2039Article in journal (Refereed) Published
Abstract [en]

We consider Einstein's equations coupled to the Euler equations in plane symmetry, with compact spatial slices and constant mean curvature time. We show that for a wide variety of equations of state and a large class of initial data, classical solutions break down in finite time. The key mathematical result is a new theorem on the breakdown of solutions of systems of balance laws. We also show that an extension of the solution is possible if the spatial derivatives of the energy density and the velocity are bounded, indicating that the breakdown is really due to the formation of shock waves.

National Category
Mathematics Natural Sciences
Identifiers
urn:nbn:se:miun:diva-8302 (URN)10.1080/03605300802421948 (DOI)000260833800005 ()2-s2.0-56049117658 (Scopus ID)
Note
VR-MathematicsAvailable from: 2009-01-18 Created: 2009-01-18 Last updated: 2017-12-14Bibliographically approved
Ståhl, F. (2002). Fuchsian analysis of S^2 x S^1 and S^3 Gowdy spacetimes. Classical and Quantum Gravity, 19(17), 4483-4504
Open this publication in new window or tab >>Fuchsian analysis of S^2 x S^1 and S^3 Gowdy spacetimes
2002 (English)In: Classical and Quantum Gravity, ISSN 0264-9381, Vol. 19, no 17, p. 4483-4504Article in journal (Refereed) Published
Abstract [en]

The Gowdy spacetimes are vacuum solutions of Einstein's equations with two commuting Killing vectors having compact spacelike orbits with T^3, S^2 x S^1 or S^3 topology. In the case of T^3 topology, Kichenassamy and Rendall have found a family of singular solutions which are asymptotically velocity dominated by construction. In the case when the velocity is between zero and one, the solutions depend on the maximal number of free functions. We consider the similar case with S^2 x S^1 or S^3 topology, where the main complication is the presence of symmetry axes. The results for T^3 may be applied locally except at the axes, where one of the Killing vectors degenerate. We use Fuchsian techniques to show the existence of singular solutions similar to the T^3 case. We first solve the analytic case and then generalise to the smooth case by approximating smooth data with a sequence of analytic data. However, for the metric to be smooth at the axes, the velocity must be -1 or 3 there, which is outside the range where the constructed solutions depend on the full number of free functions. A plausible explanation is that in general a spiky feature may develop at the axis, a situation which is unsuitable for a direct treatment by Fuchsian methods.

Keywords
general relativity, cosmology, differential equations, wave map, Fuchsian analysis, singularity, asymptotic expansion
National Category
Natural Sciences Mathematics
Identifiers
urn:nbn:se:miun:diva-1744 (URN)10.1088/0264-9381/19/17/301 (DOI)422 (Local ID)422 (Archive number)422 (OAI)
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2011-01-10Bibliographically approved
Ståhl, F. (2000). At the edge of space and time - exploring the b-boundary in general relativity. (Doctoral dissertation). Umeå: Umeå universitet
Open this publication in new window or tab >>At the edge of space and time - exploring the b-boundary in general relativity
2000 (English)Doctoral thesis, monograph (Other academic)
Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2000. p. 30
Series
Doctoral thesis - University of Umeå, Department of Mathematics, ISSN 1102-8300 ; 19
Keywords
general relativity, b-boundary, singularity, non-Hausdorff topology
National Category
Natural Sciences Mathematics
Identifiers
urn:nbn:se:miun:diva-5527 (URN)421 (Local ID)91-7191-844-2 (ISBN)421 (Archive number)421 (OAI)
Public defence
(English)
Available from: 2008-09-30 Created: 2009-07-09Bibliographically approved
Ståhl, F. (1999). Degeneracy of the b-boundary in General Relativity. Communications in Mathematical Physics, 208(1999), 331-353
Open this publication in new window or tab >>Degeneracy of the b-boundary in General Relativity
1999 (English)In: Communications in Mathematical Physics, ISSN 0010-3616, Vol. 208, no 1999, p. 331-353Article in journal (Refereed) Published
Abstract [en]

The b-boundary construction by B. Schmidt is a general way of providing a boundary to a manifold with connection. It has been shown to have undesirable topological properties however. C. J. S. Clarke gave a result showing that for space-times, non-Hausdorffness is to be expected in general, but the argument contains some errors. We show that under somewhat different conditions on the curvature, the b-boundary will be non-Hausdorff, and illustrate the degeneracy by applying the conditions to some well known exact solutions of general relativity.

Keywords
general relativity, b-boundary, singularity, singular holonomy, non-Hausdorff
National Category
Mathematics Natural Sciences
Identifiers
urn:nbn:se:miun:diva-1595 (URN)10.1007/s002200050761 (DOI)420 (Local ID)420 (Archive number)420 (OAI)
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2011-04-19Bibliographically approved
Ståhl, F. (1997). A local variational theory for the Schmidt metric. Journal of Mathematical Physics, 38(8), 3347-3357
Open this publication in new window or tab >>A local variational theory for the Schmidt metric
1997 (English)In: Journal of Mathematical Physics, ISSN 0022-2488, Vol. 38, no 8, p. 3347-3357Article in journal (Refereed) Published
Abstract [en]

We study local variations of causal curves in a space-time with respect to b-length (or generalized affine parameter length). In a convex normal neighbourhood, causal curves of maximal metric length are geodesics. Using variational arguments, we show that causal curves of minimal b-length in sufficiently small globally hyperbolic sets are geodesics. As an application we obtain a generalization of a theorem by Schmidt, showing that the cluster curve of a partially future imprisoned, future inextendible and future b-incomplete curve must be a null geodesic. We give examples which illustrate that the cluster curve does not have to be closed or incomplete. The theory of variations developed in this work provides a starting point for a Morse theory of b-length.

Keywords
general relativity, variational calculus, arc length, b-boundary, Morse theory
National Category
Mathematics Natural Sciences
Identifiers
urn:nbn:se:miun:diva-1594 (URN)10.1063/1.532047 (DOI)418 (Local ID)418 (Archive number)418 (OAI)
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2011-01-10Bibliographically approved
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