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Träfflista för sökning "WFRF:(Witzel T.) "

Sökning: WFRF:(Witzel T.)

  • Resultat 1-9 av 9
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1.
  • Ferizi, Uran, et al. (författare)
  • Diffusion MRI microstructure models with in vivo human brain Connectome data : Results from a multi-group comparison
  • 2017
  • Ingår i: NMR in Biomedicine. - : John Wiley and Sons. - 0952-3480 .- 1099-1492. ; 30:9
  • Tidskriftsartikel (refereegranskat)abstract
    • A large number of mathematical models have been proposed to describe the measured signal in diffusion-weighted (DW) magnetic resonance imaging (MRI). However, model comparison to date focuses only on specific subclasses, e.g. compartment models or signal models, and little or no information is available in the literature on how performance varies among the different types of models. To address this deficiency, we organized the 'White Matter Modeling Challenge' during the International Symposium on Biomedical Imaging (ISBI) 2015 conference. This competition aimed to compare a range of different kinds of models in their ability to explain a large range of measurable in vivo DW human brain data. Specifically, we assessed the ability of models to predict the DW signal accurately for new diffusion gradients and b values. We did not evaluate the accuracy of estimated model parameters, as a ground truth is hard to obtain. We used the Connectome scanner at the Massachusetts General Hospital, using gradient strengths of up to 300mT/m and a broad set of diffusion times. We focused on assessing the DW signal prediction in two regions: the genu in the corpus callosum, where the fibres are relatively straight and parallel, and the fornix, where the configuration of fibres is more complex. The challenge participants had access to three-quarters of the dataset and their models were ranked on their ability to predict the remaining unseen quarter of the data. The challenge provided a unique opportunity for a quantitative comparison of diverse methods from multiple groups worldwide. The comparison of the challenge entries reveals interesting trends that could potentially influence the next generation of diffusion-based quantitative MRI techniques. The first is that signal models do not necessarily outperform tissue models; in fact, of those tested, tissue models rank highest on average. The second is that assuming a non-Gaussian (rather than purely Gaussian) noise model provides little improvement in prediction of unseen data, although it is possible that this may still have a beneficial effect on estimated parameter values. The third is that preprocessing the training data, here by omitting signal outliers, and using signal-predicting strategies, such as bootstrapping or cross-validation, could benefit the model fitting. The analysis in this study provides a benchmark for other models and the data remain available to build up a more complete comparison in the future.
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2.
  • Rantakyrö, F.T., et al. (författare)
  • 50 μas resolution VLBI images of AGN’s at λ3 mm
  • 1998
  • Ingår i: Astronomy and Astrophysics. - Berlin : Springer-Verlag. - 0004-6361 .- 1432-0746. ; 131, s. 451-467
  • Tidskriftsartikel (refereegranskat)abstract
    • We present 15 images from the global mm-VLBI sessions in 1990 April at 100 GHz and 1993 April at 86 GHz. These observations probe the central engines of the 16 observed AGN's with up to 50 mu as resolution. Among other sources previously observed with lambda 3 mm VLBI we present the first lambda 3 mm maps of 0735+178, 0748+126, 1055+018, 2145+067, and CTA102, in total we have been able to image 13 out of the 16 observed sources. 6 out of the 13 imaged sources observed exhibit curvature and rapid structural changes, although the low dynamic range in two thirds of the maps limits the detection of weak features. Most of the sources have unresolved cores even at this high resolution. There is substantial evidence that the observed sources can be grouped into two general groups: A misaligned population with parsec scale jets in the form of low pitch helices and an aligned population with straight jets with small changes in PA due to intrinsic bends.
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3.
  • Marcaide, J. M., et al. (författare)
  • Discovery of shell-like radio-structure in SN1993J
  • 1995
  • Ingår i: Nature. - London : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 373:6509, s. 44-45
  • Tidskriftsartikel (refereegranskat)abstract
    • SUPERNOVA explosions are poorly understood, partly because of difficulties in modelling them theoretically(1), and partly because there have been no supernovae observed in our Galaxy since the invention of the telescope. But the recent discovery(2) of supernova SN1993J in the nearby galaxy M81 offers an opportunity to investigate the evolution of the remnant, and its interaction with the surrounding interstellar medium, at high resolution. Here we present radio observations of SN1993J, made using very-long-baseline interferometry, which show the development of a shell structure. This 8-month-old radio shell is the youngest ever discovered in a supernova. The data suggest that the supernova explosion and the expanding shell of the remnant have nearly spherical symmetry, with small deviations where some parts of the shell are brighter than others. If these deviations arise because of variations in the density of the shell, this may reconcile earlier reports of symmetric radio emission(3) with the observed optical asymmetry(4,5), as the density variations could easily cause the latter. We infer that the radio emission is generated at the interface(6-9), where the surrounding gas is shocked by the ejecta.
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4.
  • Pagels, A., et al. (författare)
  • Millimetre VLBI monitoring of AGN with sub-milliarcsecond resolution
  • 2004
  • Ingår i: in "Proceedings of the 7th European VLBI Network Symposium", Oct. 2004, Toledo, eds. R. Bachiller, F. Colomer, J.F. Desmurs, P. de Vicente, Obs. Astronómico Nacional, Alcala de Henares, Spain. ; , s. 7-10
  • Konferensbidrag (övrigt vetenskapligt)
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5.
  • Aschemann-Witzel, J., et al. (författare)
  • The who, where and why of choosing suboptimal foods : Consequences for tackling food waste in store
  • 2019
  • Ingår i: Journal of Cleaner Production. - : Elsevier Ltd. - 0959-6526 .- 1879-1786. ; 236
  • Tidskriftsartikel (refereegranskat)abstract
    • Food stores have begun to tackle food waste at the point of sale. They do so by selling ‘suboptimal’ food before it is wasted, typically with a price reduction. However, efficiency of this food waste avoidance action can be improved by knowing for which product category, which store type, which accompanying communication, and which consumer characteristics this action works best. This study uses an experimental online survey conducted in five North western European countries to investigate the effect of communication appealing to either self- or others-centred motives in either supermarkets or farmers' markets, for packaged and for fresh food. It is found that both messages – communicating budget saving or an emotional appeal - are effective in increasing choice likelihood. Store type affects choice likelihood of suboptimal packaged, while others-centred values and trust in the store affects choice likelihood for suboptimal fresh food. Communication improves quality perception of suboptimal fresh food. Findings imply that fresh suboptimal foods lend themselves more to be promoted with others-centred messages, or to be targeted at consumers with others-centred values. Sales of suboptimal food in the store should be accompanied by communication, and such efforts to tackle food waste in the store should focus on fresh food in particular.
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9.
  • Standke, K. J., et al. (författare)
  • High Sensitivity VLBI at 86 GHz : First Fringes with the 100 m Radio Telescope at Effelsberg
  • 1993
  • Ingår i: VLBI Technology. - Tokyo : Terra Scientific. - 4887041128 ; , s. 75-85
  • Bokkapitel (refereegranskat)abstract
    • Inclusion of large and sensitive antennas is of essential importance to further improve the imaging capabilities of VLBI at 3.5 mm wavelength. The combination of the 100 m radio telescope at Effelsberg (illuminated diameter ~60 m at lambda = 3.5 mm) with the 30 m radio telescope at Pico Veleta presently allows the detection of compact flux down to a level of 0.2 Jy (for τ=360 seconds integration time). Fringes have been found for 23 radio sources many of them not observed previously with VLBI at 86 GHz. On European baselines to Effelsberg the SNR typically was 10 to 30 (and ranged up to 107 for 3C279), facilitating model fitting for the brightest sources. Even in spite of chaning weather conditions during the observations (coherence times ranged between 10 to 100 seconds) and a still non-optimum pointing model for the 100 m antenna for observations at high frequencies, these results demonstrate that the 100 m radio telescope can be successfully incorporated in global VLBI experiments at 3.5 mm wavelength.
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  • Resultat 1-9 av 9

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