| 1. |
- Agåker, Marcus, et al.
(author)
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Spectroscopy in the vacuum-ultraviolet
- 2011
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In: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 5:5, s. 248-248
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Journal article (peer-reviewed)
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| 2. |
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| 3. |
- Andersson, C, et al.
(author)
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Triple specificity of ZnT8 autoantibodies in relation to HLA and other islet autoantibodies in childhood and adolescent type 1 diabetes
- 2013
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In: Pediatric Diabetes. - : Wiley-Blackwell. - 1399-543X .- 1399-5448. ; 14:2, s. 97-105
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Journal article (peer-reviewed)abstract
- Andersson C, Vaziri-Sani F, Delli AJ, Lindblad B, Carlsson A, Forsander G, Ludvigsson J, Marcus C, Samuelsson U, Ivarsson SA, Lernmark A, Elding Larsson H, the BDD Study group. Triple specificity of ZnT8 autoantibodies in relation to HLA and other islet autoantibodies in childhood and adolescent type 1 diabetes. Pediatric Diabetes 2013: 14: 97-105. Objective To establish the diagnostic sensitivity of and the relationships between autoantibodies to all three Zinc transporter 8 (Zinc transporter 8 autoantibody to either one, two, or all three amino acid variants at position 325, ZnT8A) variants to human leukocyte antigen (HLA)-DQ and to autoantibodies to glutamic acid decarboxylase (GADA), insulinoma-associated protein 2 (IA-2A), and insulin (IAA). Methods We analyzed 3165 patients with type 1 diabetes (T1D) in the Better Diabetes Diagnosis study for HLA-DQ genotypes and all six autoantibodies (ZnT8RA, arginine 325 Zinc transporter 8 autoantibody; ZnT8WA, tryptophan 325 Zinc transporter 8 autoantibody; ZnT8QA, glutamine 325 Zinc transporter 8 autoantibody; GADA, IA-2A, and IAA). Results ZnT8A was found in 65% of the patients and as many as 108 of 3165 (3.4%) had 13 ZnT8A alone. None had ZnT8QA alone. Together with GADA (56%), IA-2A (73%), and IAA (33%), 93% of the T1D patients were autoantibody positive. All three ZnT8A were less frequent in children below 2 yr of age (pandlt;0.0001). All three ZnT8A were associated with DQA1-B1*X-0604 (DQ6.4) and DQA1-B1*03-0302 (DQ8). ZnT8WA and ZnT8QA were negatively associated with DQA1-B1*05-02 (DQ2). Conclusions Analysis of ZnT8A increased the diagnostic sensitivity of islet autoantibodies for T1D as only 7% remained islet autoantibody negative. The association between DQ6.4 and all three ZnT8A may be related to ZnT8 antigen presentation by the DQ6.4 heterodimer.
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| 4. |
- Andersson, Erik, 1966, et al.
(author)
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Konsumtionens finansialisering
- 2014
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In: Konsumtionsrapporten 2014. - Göteborg : University of Gothenburg. ; , s. 35-39
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Book chapter (other academic/artistic)
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| 5. |
- Andersson, Fredrik, et al.
(author)
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A New Frequency Estimation Method for Equally and Unequally Spaced Data
- 2014
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In: IEEE Transactions on Signal Processing. - 1053-587X. ; 62:21, s. 5761-5774
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Journal article (peer-reviewed)abstract
- Spectral estimation is an important classical problem that has received considerable attention in the signal processing literature. In this contribution, we propose a novel method for estimating the parameters of sums of complex exponentials embedded in additive noise from regularly or irregularly spaced samples. The method relies on Kronecker's theorem for Hankel operators, which enables us to formulate the nonlinear least squares problem associated with the spectral estimation problem in terms of a rank constraint on an appropriate Hankel matrix. This matrix is generated by sequences approximating the underlying sum of complex exponentials. Unequally spaced sampling is accounted for through a proper choice of interpolation matrices. The resulting optimization problem is then cast in a form that is suitable for using the alternating direction method of multipliers (ADMM). The method can easily include either a nuclear norm or a finite rank constraint for limiting the number of complex exponentials. The usage of a finite rank constraint makes, in contrast to the nuclear norm constraint, the method heuristic in the sense that the problem is non-convex and convergence to a global minimum can not be guaranteed. However, we provide a large set of numerical experiments that indicate that usage of the finite rank constraint nevertheless makes the method converge to minima close to the global minimum for reasonably high signal to noise ratios, hence essentially yielding maximum-likelihood parameter estimates. Moreover, the method does not seem to be particularly sensitive to initialization and performs substantially better than standard subspace-based methods.
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| 6. |
- Andersson, Fredrik, et al.
(author)
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Alternating Projections on Nontangential Manifolds
- 2013
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In: Constructive Approximation. - : Springer Science and Business Media LLC. - 0176-4276 .- 1432-0940. ; 38:3, s. 489-525
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Journal article (peer-reviewed)abstract
- We consider sequences of points obtained by projecting a given point B=B (0) back and forth between two manifolds and , and give conditions guaranteeing that the sequence converges to a limit . Our motivation is the study of algorithms based on finding the limit of such sequences, which have proved useful in a number of areas. The intersection is typically a set with desirable properties but for which there is no efficient method for finding the closest point B (opt) in . Under appropriate conditions, we prove not only that the sequence of alternating projections converges, but that the limit point is fairly close to B (opt) , in a manner relative to the distance ayenB (0)-B (opt) ayen, thereby significantly improving earlier results in the field.
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| 7. |
- Andersson, Fredrik, et al.
(author)
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Frequency Estimation Based on Hankel Matrices and the Alternating Direction Method of Multipliers
- 2013
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In: 2013 Proceedings of the 21st European Signal Processing Conference (Eusipco).
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Conference paper (peer-reviewed)abstract
- We develop a parametric high-resolution method for the estimation of the frequency nodes of linear combinations of complex exponentials with exponential damping. We use Kronecker's theorem to formulate the associated nonlinear least squares problem as an optimization problem in the space of vectors generating Hankel matrices of fixed rank. Approximate solutions to this problem are obtained by using the alternating direction method of multipliers. Finally, we extract the frequency estimates from the con-eigenvectors of the solution Hankel matrix. The resulting algorithm is simple, easy to implement and can be applied to data with equally spaced samples with approximation weights, which for instance allows cases of missing data samples. By means of numerical simulations, we analyze and illustrate the excellent performance of the method, attaining the Cramer-Rao bound.
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| 8. |
- Andersson, Fredrik, et al.
(author)
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Frequency Extrapolation through Sparse Sums of Lorentzians
- 2014
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In: Journal of Earth Science. - : Springer Science and Business Media LLC. - 1867-111X .- 1674-487X. ; 25:1, s. 117-125
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Journal article (peer-reviewed)abstract
- Sparse sums of Lorentzians can give good approximations to functions consisting of linear combination of piecewise continuous functions. To each Lorentzian, two parameters are assigned: translation and scale. These parameters can be found by using a method for complex frequency detection in the frequency domain. This method is based on an alternating projection scheme between Hankel matrices and finite rank operators, and have the advantage that it can be done in weighted spaces. The weighted spaces can be used to partially revoke the effect of finite band-width filters. Apart from frequency extrapolation the method provides a way of estimating discontinuity locations.
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| 9. |
- Andersson, Fredrik, et al.
(author)
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Nonlinear approximation of functions in two dimensions by sums of exponential functions
- 2010
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In: Applied and Computational Harmonic Analysis. - : Elsevier BV. - 1096-603X .- 1063-5203. ; 29:2, s. 156-181
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Journal article (peer-reviewed)abstract
- We consider the problem of approximating a given function in two dimensions by a sum of exponential functions, with complex-valued exponents and coefficients. In contrast to Fourier representations where the exponentials are fixed, we consider the nonlinear problem of choosing both the exponents and coefficients. In this way we obtain accurate approximations with only few terms. Our approach is built on recent work done by G. Beylkin and L Monzon in the one-dimensional case. We provide constructive methods for how to find the exponents and the coefficients, and provide error estimates. We also provide numerical simulations where the method produces sparse approximations with substantially fewer terms than what a Fourier representation produces for the same accuracy. (c) 2009 Elsevier Inc. All rights reserved.
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| 10. |
- Andersson, Fredrik, et al.
(author)
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Nonlinear approximation of functions in two dimensions by sums of wave packets
- 2010
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In: Applied and Computational Harmonic Analysis. - : Elsevier BV. - 1096-603X .- 1063-5203. ; 29:2, s. 198-213
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Journal article (peer-reviewed)abstract
- We consider the problem of approximating functions that arise in wave-equation imaging by sums of wave packets. Our objective is to find sparse decompositions of image functions, over a finite range of scales. We also address the naturally connected task of numerically approximating the wavefront set. We present an approximation where we use the dyadic parabolic decomposition, but the approach is not limited to only this type. The approach makes use of expansions in terms of exponentials, while developing an algebraic structure associated with the decomposition of functions into wave packets. (c) 2009 Elsevier Inc. All rights reserved.
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