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strong
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Posted: Fri Nov 05, 2010 1:58 am |
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Joined: Wed May 17, 2006 7:02 am Posts: 285 Location: MPE Garching
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tomassetti
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Posted: Wed Nov 17, 2010 5:02 am |
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Joined: Mon Jan 19, 2009 9:48 am Posts: 19 Location: INFN Perugia
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Results on the propagation parameters are given in terms of Best-Fit (i.e. from Chi^2 minimization) and Posterior-Mean (i.e. expectation values of the posterior pdf's). In some cases they differ a lot. So...stupid question: which one really "matters"? What's the "ultimate" set of CR propagation parameter that can be determined (with Galprop) at best of our knowledge on the basis of existing data? BestFit (as I'd guess) or PosteriorMean ? Why have you quoted both...do I miss some relevant physical differences/complementarity in the two?
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strong
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Posted: Wed Nov 17, 2010 5:07 am |
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Joined: Wed May 17, 2006 7:02 am Posts: 285 Location: MPE Garching
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(NB they are not chi^2 but probabilities) The posterior mean is definitely the one to use since it takes account of the full posterior, whereas the maximum posterior could be a local maximum or a narrow peak with little probability content. Why we quote both: to illustrate the difference. There is no 'ultimate' parameter set since we only considered a particular class of models, and did not include e.g. convection and other effects, or some other types of data which will give more constraints e.g. pbar (but we intend to in future).
_________________ Andy Strong, MPE
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tomassetti
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Posted: Wed Nov 17, 2010 5:22 am |
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Joined: Mon Jan 19, 2009 9:48 am Posts: 19 Location: INFN Perugia
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So.. the fact that the best-fit parameters are within the uncertainty band of the posterior pdfs is to be taken as a remarkable/untrivial result. Is that correct?
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strong
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Posted: Wed Nov 17, 2010 5:27 am |
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Joined: Wed May 17, 2006 7:02 am Posts: 285 Location: MPE Garching
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not at all remarkable, this happens in well-behaved distributions, which we have here.
_________________ Andy Strong, MPE
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tomassetti
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Posted: Wed Nov 17, 2010 6:30 am |
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Joined: Mon Jan 19, 2009 9:48 am Posts: 19 Location: INFN Perugia
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Ok... thank you very much.
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tomassetti
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Posted: Sun Nov 21, 2010 11:08 am |
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Joined: Mon Jan 19, 2009 9:48 am Posts: 19 Location: INFN Perugia
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Another point. In that paper, the fragmentation chain starts from Max_Z = 14 (silicon). So I deduce that the quantities under study (B/C, 10Be/9Be, pbar/p) are not significantly affected by the presence of Z>14 nuclei... correct? If yes... can you quantify "not significantly" with some number? 1%?
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strong
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Posted: Sun Nov 21, 2010 11:13 am |
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Joined: Wed May 17, 2006 7:02 am Posts: 285 Location: MPE Garching
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It is completely negligible, certainly below 1%
_________________ Andy Strong, MPE
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avladim
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Posted: Mon Nov 22, 2010 1:09 am |
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Joined: Wed Oct 21, 2009 6:30 pm Posts: 47 Location: Stanford U.
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I recently tested it by making several runs in WebRun with different max_Z. I was using the "Conventional Model" example. I also stopped at max_Z=14, because the spectra in QuickPlots for B/C and 10Be/9Bebecame indistinguishable from higher max_Z at this point. Certainly well within the uncertainty in the experimental data.
_________________ Andrey Vladimirov http://galprop.stanford.edu/
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