| 1. |
- Demaziere, Christophe, 1973, et al.
(författare)
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Multi-fractal analysis of chaotic flashing-induced instabilities
- 2007
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Ingår i: Proc. 12th Int. Topl. Mtg. Nuclear Reactor Thermal Hydraulics (NURETH-12). - 0894480588
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Konferensbidrag (refereegranskat)abstract
- In this paper, two-phase flow oscillations at the low pressure, low power, natural circulation CIRCUS test facility (Delft University of Technology) are investigated in a two-riser configuration. These oscillations are driven by flashing (and to some extent by geysering). For given temperatures at the inlet of the heated channels, the dynamics of the flow oscillations exhibits an a-periocal behaviour, which is attributed to deterministic chaos. This is proven by performing a Continuous Wavelet Transform of the measured time series of the primary flow rate. Any hidden self-similarity in the measurement is seen in the corresponding scale-space plane. The novelty of the present investigation lies within the multi-fractal approach used for characterizing the chaos. Both non-linear time series analysis (Higuchi’s method and Detrended Fluctuation Analysis) and wavelet-based analysis (Wavelet-Transform Modulus-Maxima) methods show that the dynamics of the flow oscillations has a multi-fractal structure. The strange attractor corresponding to the dynamics of the system can thus be described as a set of interwoven mono-fractal objects. The global singular properties of the measured time series is then fully characterized by a spectrum of singularities f(alpha), which is the Hausdorff dimension of the set of points where the multi-fractal object has singularities of strength (or Hölder exponents of) alpha. Whereas Higuchi’s method and Detrended Fluctuation Analysis allow easily determining whether the deterministic chaos has a mono- or multi-fractal hierarchy, the Wavelet-Transform Modulus-Maxima has the advantage of giving a quantitative estimation of the fractal spectrum.
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| 2. |
- Demaziere, Christophe, 1973, et al.
(författare)
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Multi-fractal analysis of chaotic flashing-induced instabilities in boiling channels in the natural circulation CIRCUS facility
- 2008
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Ingår i: Nuclear Science and Engineering. - 0029-5639 .- 1943-748X. ; 158:2, s. 164-193
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, two-phase flow oscillations at the natural circulation CIRCUS test facility are investigated in a two-riser configuration. These oscillations are driven by flashing (and to some extent by geysering). For a given range of operating conditions of the facility, the oscillations exhibit an erratic behaviour. This study demonstrates that this behaviour can be attributed to deterministic chaos. This is proven by performing a Continuous Wavelet Transform of the measured time series. Any hidden self-similarity in the measurement is seen in the corresponding scale-space plane. The novelty of the present investigation lies with the multi-fractal approach used for characterizing the chaos. Both non-linear time series analysis and wavelet-based analysis methods show that the dynamics of the flow oscillations has a multi-fractal structure. For the former, both Higuchi’s method and Detrended Fluctuation Analysis were used, whereas for the latter, the Wavelet-Transform Modulus-Maxima method was used. The strange attractor corresponding to the dynamics of the system can thus be described as a set of interwoven mono-fractal objects. The global singular properties of the measured time series is then fully characterized by a spectrum of singularities f(alpha), which is the Hausdorff dimension of the set of points where the multi-fractal object has singularities of strength (or Hölder exponents of) alpha. Whereas Higuchi’s method and Detrended Fluctuation Analysis allow easily determining whether the deterministic chaos has a mono- or multi-fractal hierarchy, the Wavelet-Transform Modulus-Maxima has the advantage of giving a quantitative estimation of the fractal spectrum. The time-modelling of such a behaviour of the facility is therefore difficult since there is sensitive dependence on initial conditions. From a regulatory point-of-view, such a behaviour of natural circulation systems in a multiple riser configuration has thus to be avoided.
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| 3. |
- Elsik, Christine G., et al.
(författare)
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The Genome Sequence of Taurine Cattle : A Window to Ruminant Biology and Evolution
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 324:5926, s. 522-528
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Tidskriftsartikel (refereegranskat)abstract
- To understand the biology and evolution of ruminants, the cattle genome was sequenced to about sevenfold coverage. The cattle genome contains a minimum of 22,000 genes, with a core set of 14,345 orthologs shared among seven mammalian species of which 1217 are absent or undetected in noneutherian (marsupial or monotreme) genomes. Cattle-specific evolutionary breakpoint regions in chromosomes have a higher density of segmental duplications, enrichment of repetitive elements, and species-specific variations in genes associated with lactation and immune responsiveness. Genes involved in metabolism are generally highly conserved, although five metabolic genes are deleted or extensively diverged from their human orthologs. The cattle genome sequence thus provides a resource for understanding mammalian evolution and accelerating livestock genetic improvement for milk and meat production.
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| 4. |
- Meier, Holger A., et al.
(författare)
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Visualization of Particle Interactions in Granular Media
- 2008
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Ingår i: IEEE Transactions on Visualization & Computer Graphics. - : IEEE Computer Society. - 1077-2626. ; 14:5, s. 1110-1125
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Tidskriftsartikel (refereegranskat)abstract
- Interaction between particles in so-called granular media, such as soil and sand, plays an important role in the context of geomechanical phenomena and numerous industrial applications. A two scale homogenization approach based on a micro and a macro scale level is briefly introduced in this paper. Computation of granular material in such a way gives a deeper insight into the context of discontinuous materials and at the same time reduces the computational costs. However, the description and the understanding of the phenomena in granular materials are not yet satisfactory. A sophisticated problem-specific visualization technique would significantly help to illustrate failure phenomena on the microscopic level. As main contribution, we present a novel 2D approach for the visualization of simulation data, based on the above outlined homogenization technique. Our visualization tool supports visualization on micro scale level as well as on macro scale level. The tool shows both aspects closely arranged in form of multiple coordinated views to give users the possibility to analyze the particle behavior effectively. A novel type of interactive rose diagrams was developed to represent the dynamic contact networks on the micro scale level in a condensed and efficient way.
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