Cosmo-torun

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328 discussions

couple of comments on the pixelization schemes
by Bartosz Lew 09 Nov '05

09 Nov '05

Hi Boud, I've been wondering about the optimal pixelization scheme of the sphere a couple of weeks ago and since I've send to you my own implementation of the Healpix pixelization scheme written (generally) in C (according to astro-ph/0409533) but compatible with GNU c++ compiler here I'd like to comment on some comments that can be found in the source code. And since you don't like private, closed conversations I also cc this letter to shape-univ. 1) First of all healpix is not stupid :)))) - it's cool because pixels have the same area which is not always the case (e.g.. quad-cube pixelization used with COBE data), because it's hierarchical and isolatitude of course, however the first and the last features are also common in other pixelization schemes. 1.1) But also very important thing is that it is more less "equi-angular" - i.e. the angular distance from pixel to pixel is more less constant. But obviously the exact "equi-angular" solution does not exist. 2) Now the my CPEDS library for doing useful stuff - and especially the pixelization.c has more useful functions so probably I should update the version I've send to you. i.e. - conversions from RING to NESTED and vice versa - calculation of ring given pixel and vice versa (in both nested and ring orderings) - estimated pixel size (maybe not that useful) since it may be probably just as well estimated from 4PI/N_pix. 3) The main point I wanted to come up with the new idea for pixelization scheme was the thing I addressed in point 1.1. But also the following 3 drawbacks of this scheme, namely: 3.1) the pixel shape dramatically varies from pixel to pixel. this is what I didn't like because of e.g. CMB lensing studies where the morphology at small scales would be very important - but of course this can be overcome with sufficiently oversampling the pixelization by increasing the Nside parameter to meet the Nyquist conditions. 3.2) the number of pixels in a ring does NOT gradually rises with increasing \theta (in spherical system definition consistent with HEALPIX - i.e. theta = 0 at North pole). Instead it only rises in the top (bottom) part of the north (south) polar region. This is certainly unnatural thing. since all the latitudes in equatorial (roughly from 41 deg to 180-41 deg regions are represented by the same amount of pixels in longitude) !! This is not the case e.g.. in he GLESP (Gauss-Legendre) or Igloo pixelization schemes. 3.3) It has an axial symmetry (since it has a poles equator, rings, etc). And why the CMB sky should know anything about the symmetry ? In particular why should it have an axial symmetry ? So naturally the solution would evolve into direction of platonic forms like tetrahedron, cube, ... oops it ends at icosahedron. And since we need a pixelization with number of pixels something like few Mpixels the 20 pixels of icosahedron is not enough. My idea of tetrahedron based pixelization system was just driven from this point of view that there should be no preferred directions in the sky. The system would gain higher resolution by looking for directions equally separated from neighboring directions (initially defined by axis of tetrahedron). This concept fails, of course because such a solution does not exist. Max Tegmark also went in this direction inventing the icosahedron pixelization system which is the next step after the quad-cube system, but each triangle is divided in other way. Anyway, at this time I see no point of terrible importance to force the idea of the tetrahedron pixelization system so I drop this case. rather it would be interesting to implement other pixelizations systems into the isolat packet. pozdr, Bartek

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Why continue "Topologia Wszechswiata" research?
by Boud Roukema 21 Oct '05

21 Oct '05

Witam "Why continue funding for cosmic topology research?" ----------------------------------------------------------------------- The topology of the Universe (as an observational question) is one of the most fundamental questions of observational cosmology: it concerns the shape of the whole space-time that we live in. The Universe is clearly as important as any object inside the Universe. Knowing the "shape" of atoms, molecules, cells, mountains and continents is one of the basic steps in understanding any of these. At the moment, all that we are confident about regarding the shape of the Universe is a local property: it is "nearly" flat on the horizon scale; we do not know its global properties, such as its topology. Since the Toruń cosmology group is one of the most active groups in this field, funding this research topic is clearly a top priority. ----------------------------------------------------------------------- Staszek Krawczyk asked me to write why "Topologia Wszechswiata" is an important research topic which is "worth continuing", in 5 sentences, within the next 10 minutes or so (and the 10 minutes are already up). So that's what the above statement is about. (This is related to some funding request. i've wasted enough time in KBN requests with zero positive results, so if someone else is doing the admin/political work, i guess i won't complain...) Probably any feedback from cosmo-torun subscribers will be too late, but here it is anyway. pozdr boud

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physics spam (but interesting anyway :P) Spacetime 100 Years Later (fwd)
by Boud Roukema 30 Sep '05

30 Sep '05

witam cosmo-torun, IOP to nie firma, która ewidentnie popiera otwarty dostęp do informacji, raczej ma tradycję zamkniętą. Jest dlaczego dla mnie, jest to raczej ,,spam". Jednakże, artykuły mogą być interesujący - dla osoby nie chętny do szukiwanie w arxiv.org. Np, raczej lubię artykuł Ashtekar'a: są dwa rodzaju ,,approaches" do grawitacji kwantowej - jeden w czymś jest m.in. teoria struń (jest teoria ,,perturbative", - drugi w czymś jest m.in. ,,loop quantum gravity" (związany z Ashtekarem) Ashtekar uważa, że z loop quantum gravity, nie ma osobliwość na a(t) = 0, bo zwykly czas-przestrzeń tam już nie ma. Więc, tu jest info ta. pozdr boud > ---------- Forwarded message ---------- > Date: Thu, 29 Sep 2005 15:18:21 +0100 (BST) > From: New Journal of Physics <njp at iop.org> > To: boud at astro.uni.torun.pl > Subject: Spacetime 100 Years Later > > Dear Dr Roukema > > You may be interested to know that New Journal of Physics > (http://www.njp.org) has just published the third of its three > celebratory Focus Issues to appear this year in connection with the > World Year of Physics. > All contributions to 'Spacetime 100 Years Later', edited by Richard > Price and Jorge Pullin, are permanently free to read at > http://www.njp.org/focus/spacetime. Each review article is also > listed below with a direct link. > Please don't hesitate to contact me with any comments or queries you > may have about this issue or NJP in general. > With best regards, > > Tim Smith > > Dr Tim Smith > Publisher, New Journal of Physics > E-mail: njp at iop.org > WWW: http://www.njp.org > Tel: +44 (0)117 930 1204 > Fax: +44 (0)117 920 0948 > > NJP 2004 Impact Factor = 3.095 > > > FOCUS ON SPACETIME 100 YEARS LATER > > Gravity and the quantum > A Ashtekar > http://stacks.iop.org/1367-2630/7/198 > > Black holes in astrophysics > R Narayan > http://stacks.iop.org/1367-2630/7/199 > > A most useful manifestation of relativity: gravitational lenses > E E Falco > http://stacks.iop.org/1367-2630/7/200 > > Spacetime in string theory > G T Horowitz > http://stacks.iop.org/1367-2630/7/201 > > Gravitational wave detectors > P Aufmuth and K Danzmann > http://stacks.iop.org/1367-2630/7/202 > > Hawking radiation and black hole thermodynamics > D N Page > http://stacks.iop.org/1367-2630/7/203 > > The basics of gravitational wave theory > E E Flanagan and S A Hughes > http://stacks.iop.org/1367-2630/7/204 > > Laboratory tests of gravity > J H Gundlach > http://stacks.iop.org/1367-2630/7/205 > _________________ > *Data Protection* > If you would prefer not to receive updates on our journals in future, please reply to this e-mail, entering the word 'Unsubscribe' in the body of your e-mail (please leave the subject line). > > IOP Publishing Limited is the data controller (data.protection at iop.org). > We will take all reasonable measures to prevent unauthorised or unlawful processing. >

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Structured abstracts - A&A recommendation
by Andrzej Marecki 22 Sep '05

22 Sep '05

The Editors of A&A published the following recommendation to the authors. http://publish.edpsciences.org/articles/aa/pdf/2005/37/aa441100f.pdf -- a.

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healpix goes GPL :)))))))
by Boud Roukema 05 Sep '05

05 Sep '05

witam healpix goes GPL :)))))))) http://cosmocoffee.info/viewtopic.php?p=972 pozdr boud

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phd candidate(s) for cosmology starting 2005/2006 ?
by Boud Roukema 11 Jul '05

11 Jul '05

Witam, We have at least one candidate to do a PhD in cosmology at TCfA. :) Because the details include personal data, IMHO i should not send any personal stuff on public lists - but anyone who feels they have a right to participate (to some extent) in informal decision-making related to PhD candidates can contact me (or Andrzej Marecki/Kus) offlist for more details. (AFAIK the formal decision is made by a committee of Wydzia³ Fizyki AiIS). pozdr boud

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CMB person - few days visit, nov/dev/jan - Jacques Delabrouille
by Boud Roukema 18 Mar '05

18 Mar '05

Witam, Jacques Delabrouille is likely to come to TCfA for a visit of a few days sometime during the next few months. He's a CMB cosmologist from Paris (College de France). You can see the CMB stuff he does here: http://de.arxiv.org/find/astro-ph/1/delabrouille/0/1/0/all/3/0 You can email him directly at delabrouille at cdf.in2p3.fr pozdr boud

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http://cosmocoffee.info Witamy :)
by Boud Roukema 25 Feb '05

25 Feb '05

Witam, W kosmologii, ju� u�ywamy astro-ph od dawno, i prawie ka�dy artyku� powa�ny w kosmo jest na astro-ph. Jednak�e, gdzie rozmawia� z kolegami o najostatnich artyku�y? Na twiki na adjani, jest *technicznie* mo�liwe zrobi� fajne rozmowy, tylko w tej chwili jeszcze nie ma spo�ecze�stwo - jest mniej-wi�cej tylko boud ;). Wi�c... teraz jest: http://cosmocoffee.info Jest forum phpBB o artyku��w astro-ph - szczeg�lowie kosmo, oczywi�cie. Te� o software jak cmbfast itd itd itd. Formalnie, jest otwarty tylko dla autor�w astro-ph ,,i studenci" - tzn raczej doktoranci, ale je�li m�odsze studenci robi� konstruktywne komentarze tam, nie wierz� �e b�d� ich cenzurowane... By� autorem A&A/ApJ/MNRAS, chyba to nie wystarczy, musisz istnie� elektronicznie ;). boud

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(fwd) Crisis in Cosmology
by Andrzej Marecki 15 Feb '05

15 Feb '05

-- forwarded message -- Path: news.man.torun.pl!newsfeed.pionier.net.pl!news-fra1.dfn.de!newsfeed.hanau.net!newsfeed01.sul.t-online.de!t-online.de!newsfeed.stueberl.de!ecngs!feeder.ecngs.de!195.40.0.165.MISMATCH!easynet-monga!easynet.net!feed4.jnfs.ja.net!feed2.jnfs.ja.net!jnfs.ja.net!gemini.csx.cam.ac.uk!news.cam.ac.uk!not-for-mail From: bda(a)fisica.uminho.pt Newsgroups: sci.astro.research Subject: Crisis in Cosmology Date: Mon, 14 Feb 05 17:55:41 GMT Organization: http://groups.google.com Lines: 6 Approved: sci.astro.research-request(a)slimy.greenend.org.uk (mjh) Message-ID: <mt2.0-21535-1108403741(a)hercules.herts.ac.uk> NNTP-Posting-Host: rapun.sel.cam.ac.uk X-Posting-Tool: modtool v2.0 Originator: mjh(a)hercules.herts.ac.uk ([147.197.230.144]) Xref: news.man.torun.pl sci.astro.research:5284 This is an announcement for the 1st Crisis in Cosmology Conference (CCC-I) which will be held in Portugal in the period 23-25 June 2005. All information can be obtained from http://www.cosmology.info Best regards, Jose B. Almeida -- end of forwarded message -- -- ----------------------------------------------------------------------------- Andrzej Marecki | Torun Centre for Astronomy | e-mail: amr(a)astro.uni.torun.pl N. Copernicus University | WWW: http://www.astro.uni.torun.pl ul. Gagarina 11 | tel: +48 56 6113032 PL-87-100 Torun, POLAND | fax: +48 56 6113009 ----------------------------------------------------------------------------- "If Bill Gates actually had to admin his own stuff, he'd shoot himself." -----------------------------------------------------------------------------

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CARTIER PIAGET - Just Like the Real Thing - Logines Louis Vuitton Omega - 592049
by Kathryn Small 04 Feb '05

04 Feb '05

K798SI88 PIAGET CARTIER - Expensive Look Not Expensive Price - Louis Vuitton Omega Logines - 025154 You don't want to miss this - http://marquee.icfbingknd.com/?btdJJgIEfMOjGbbmillenarian no more - http://intrepid.akefbahj.com/chateaux?NzjjjmieRSopghhannulling g488D752

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