| 11. |
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| 12. |
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| 13. |
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| 14. |
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| 15. |
- Bergman Ärlebäck, Jonas, 1972-
(författare)
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Matematisk modellering i svenska gymnasieskolans kursplaner i matematik 1965-2000
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Denna rapport studerar hur begreppen matematisk modell och matematisk modellering behandlats i kursplanerna i matematik för motsvarande svenska gymnasieskolans naturvetenskapliga program mellan åren 1965 och 2000. En översikt över sex kursplaners olika form och innehåll ges och tre olika analyser på tre olika nivåer genomförs; en innehållsanalys, en kvalitativ analys, och en analys som beaktar relationen mellan begreppen modellering, tillämpningar och problemlösning. Analysen visar att matematiska modeller och modellering förekommit implicit sedan kursplanen från 1965, men att begreppen främst i de två senaste kursplanerna lyfts fram explicit och fått en central position i kursplanerna. I den nuvarande kursplanen Gy2000 framgår att matematiska modeller kan tolkas både som ett undervisningsmål i sig och som ett didaktiskt hjälpmedel att lära matematik.
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| 16. |
- Bergsten, Christer, 1949-
(författare)
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Symbolic computing and mathematics education
- 1994
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A lab sequence with the computer algebra system Maple was integrated in one of the analysis courses for beginning engineering students. The students appreciated the labs, but questionned their value for the learning of analysis. There was a significant shift over time toward a higher appreciation of the labs, and most students wanted Maple in the course. No significant differences were found in mathematical achievement or attitudes between the lab and control groups. The plotting function of Maple was valued for learning and understanding analysis. Data indicate, however, that the symbolic computational feature of a computer algebra system will not be fully appreciated until students are familiar with the computations. It thus seems necessary, when planning to use a computer algebra system as a learning tool, to explicate the intended learning paradigm, how the computational facilities of the system are to be used, and what kind of mathematical competence students develop and get out of the course. A conclusion from this study is that the use in education of thus type of technology is appreciated by the students, but that early in an analysis course it should be used mainly as a support to imagery, and that only later in the course automated algebraic computations should be used for example as a problem solving tool.
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| 17. |
- Berntsson, Fredrik, et al.
(författare)
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A Data Assimilation Approach to Coefficient Identification
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The thermal conductivity properties of a material can be determined experimentally by using temperature measurements taken at specified locations inside the material. We examine a situation where the properties of a (previously known) material changed locally. Mathematically we aim to find the coefficient k(x) in the stationary heat equation (kTx)x = 0;under the assumption that the function k(x) can be parametrized using only a few degrees of freedom. The coefficient identification problem is solved using a least squares approach; where the (non-linear) control functional is weighted according to the distribution of the measurement locations. Though we only discuss the 1D case the ideas extend naturally to 2D or 3D. Experimentsdemonstrate that the proposed method works well.
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| 18. |
- Berntsson, Fredrik, 1971-, et al.
(författare)
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A Modification to the Kirchhoff Conditions at a Bifurcation and Loss Coefficients
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- One dimensional models for fluid flow in tubes are frequently used tomodel complex systems, such as the arterial tree where a large numberof vessels are linked together at bifurcations. At the junctions transmission conditions are needed. One popular option is the classic Kirchhoffconditions which means conservation of mass at the bifurcation andprescribes a continuous pressure at the joint.In reality the boundary layer phenomena predicts fast local changesto both velocity and pressure inside the bifurcation. Thus it is not appropriate for a one dimensional model to assume a continuous pressure. In this work we present a modification to the classic Kirchhoff condi-tions, with a symmetric pressure drop matrix, that is more suitable forone dimensional flow models. An asymptotic analysis, that has beencarried out previously shows that the new transmission conditions hasen exponentially small error.The modified transmission conditions take the geometry of the bifurcation into account and can treat two outlets differently. The conditions can also be written in a form that is suitable for implementationin a finite difference solver. Also, by appropriate choice of the pressuredrop matrix we show that the new transmission conditions can producehead loss coefficients similar to experimentally obtained ones.
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| 19. |
- Berntsson, Fredrik
(författare)
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Boundary identification for an elliptic equation
- 2001
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We consider an inverse problem for the two dimensional steady state heat equation. More precisely, the heat equation is valid in a domain Ω, that is a subset of the unit square, temperature and heat-flux measurements are available on the line y = 0, and the sides x = 0 and x = 1 are assumed to be insulated. From these we wish to determine the temperature in the domain Ω. Furthermore, a part of the boundry ∂Ω is considered to be unknown, and must also be determined.The problem is ill-posed in the sense that the solution does not depend continuously on the data. We stabilize the computations by replacing the x-derivative in the heat equation by an operator, representing differentiation of least squares cubic splines. We discretize in the x-coordinate, and obtain an initial value problem for a system of ordinary differential equation, which can be solved using standard numerical methods.The inverse problem, that we consider in this paper, arises in iron production, where the walls of a melting furnace are subject to physical and chemical wear. In order to avoid a situation where molten metal breaks out the remaining thickness of the walls should constantly be monitored. This is done by recording the temperature at several locations inside the walls. The shape of the interface boundary between the molten iron and the walls of the furnace can then be determined by solving an invers heat conduction problem.
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| 20. |
- Berntsson, Fredrik, 1971-, et al.
(författare)
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More on Estimation of Banded and Banded Toeplitz Covariance Matrices
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we consider two different linear covariance structures, e.g., banded and bended Toeplitz, and how to estimate them using different methods, e.g., by minimizing different norms.One way to estimate the parameters in a linear covariance structure is to use tapering, which has been shown to be the solution to a universal least squares problem. We know that tapering not always guarantee the positive definite constraints on the estimated covariance matrix and may not be a suitable method. We propose some new methods which preserves the positive definiteness and still give the correct structure.More specific we consider the problem of estimating parameters of a multivariate normal p–dimensional random vector for (i) a banded covariance structure reflecting m–dependence, and (ii) a banded Toeplitz covariance structure.
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