| 1. |
- Löfdahl, Lennart, 1948, et al.
(author)
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Determination of Derivative Moments using Two Slanted Hot-Wires and a Spectral method
- 1993
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In: Experiments in Fluids. ; 15, s. 393-400
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Journal article (peer-reviewed)abstract
- A method to determine derivative moments using slanted hot-wires and a spectral method has been developed. The general idea is to minimize measuring volume by using only two hot-wires, and a post-processing of the measurement data. It is shown that the spectral method is equivalent to conventional determinations of correlations. The method developed has been tested in the self-preserving region of a plane wake by computing profiles of the Reynolds stresses as well as the derivative moments in the expression for the total energy dissipation. One term in this expression, which with conventional methods requires two triple-wires or four cross-wires, has been determined using the spectral method.
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| 2. |
- Löfdahl, Lennart, 1948, et al.
(author)
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Measurement of the Enstrophy and the Vorticity Vector in a Plane Cylinder Wake using a Spectral Method
- 1994
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In: Fifth European Turbulence Conference in Siena, Italy, July 5-8 1994..
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Conference paper (peer-reviewed)abstract
- A method to determine derivative moments using only two slanted hot-wires and a spectral method has been employed for a complete determination of the enstrophy and the vorticity vector. The general idea behind the method is to minimize the measuring volume by use of only two hot-wires and to post-process the measured data. All measurements were conducted in the far wake of a cylinder at a Reynolds number of 1840. Comparisons between the spectral method and conventional measuring techniques are made, and the results justifies the approximation between enstrophy and dissipation. For the vorticity vector it was found that the components of the normal and lateral directions were considerably larger than the stream-wise ones.
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| 3. |
- Bergh, Jöran, 1941, et al.
(author)
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Siciak's homogeneous extremal functions, holomorphic extension and a generalization of Helgason's support theorem
- 2019
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In: Annales Polonici Mathematici. - : Institute of Mathematics, Polish Academy of Sciences. - 0066-2216 .- 1730-6272. ; 123:1, s. 61-70
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Journal article (peer-reviewed)abstract
- The main result of the present paper is that a function defined on a union of lines CE through the origin in C-n with directional vectors in E subset of C-n and holomorphic of fixed finite order and finite type along each of these lines can be extended to an entire function of the same order and finite type provided that CE is not pluripolar and all directional derivatives along the lines satisfy a necessary compatibility condition at the origin. We are able to estimate the indicator function of the extension in terms of Siciak's weighted homogeneous extremal function, where the weight is a function of the type of the given function on each given line. As an application we prove a generalization of Helgason's support theorem by showing how the support of a continuous function with rapid decrease at infinity can be located from partial information about the support of its Radon transform.
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| 4. |
- Romeo, Alessandro, 1961, et al.
(author)
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A wavelet add-on code for new-generation N-body simulations and data de-noising (JOFILUREN)
- 2004
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 354:4, s. 1208-1222
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Journal article (peer-reviewed)abstract
- Wavelets are a new and powerful mathematical tool, whose most celebrated applications are data compression and de‐noising. In a previous paper, we have shown that wavelets can be used for removing noise efficiently from cosmological, galaxy and plasma N‐body simulations. The expected two‐orders‐of‐magnitude higher performance means, in terms of the well‐known Moore's law, an advance of more than one decade in the future. In this paper, we describe a wavelet add‐on code designed for such an application. Our code can be included in common grid‐based N‐body codes, is written in fortran, is portable and is available on request from the first author. The code can also be applied for removing noise from standard data, such as signals and images.
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| 5. |
- Romeo, Alessandro, 1961, et al.
(author)
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N-body simulations with two-orders-of-magnitude higher performance using wavelets
- 2003
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In: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 342:2, s. 337-344
-
Journal article (peer-reviewed)abstract
- Noise is a problem of major concern for N-body simulations of structure formation in the early Universe, and of galaxies and plasmas. Here for the first time we use wavelets to remove noise from N-body simulations of disc galaxies, and show that they become equivalent to simulations with two orders of magnitude more particles. We expect a comparable improvement in performance for cosmological and plasma simulations. Our wavelet code will be described in a following paper, and will then be available on request.
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