Shape-univ

shape-univ@cosmo.torun.pl

176 discussions

Re: Re:
by Rae Hathaway 04 Jun '06

04 Jun '06

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loose thoughts on topology and nongaussianity
by blew 22 May '06

22 May '06

Hi Boud, I've just had such a though. If we assumed some multiply-connected space-time within some model (eg. dodecahedral) then my question is whether is leads to nongaussian (NG) features in CMB. I think it definitely should. Such spacetime, gives a modified power spectrum of fluctuations, limited to fundamental domain size and there should be repercusions of this size in harmonic modes that are natural multiple of that size. Then given a feature at one length scale should automatically give features at other scales - hence vialation of gaussianity. This could be investigated by bi- or tri-spectrum optimalized for these particular perturbation modes that come from the model. Given NG simulations one could estimate the sensityvity of this approach. This is also a test of the multiply connected space hypothesis. Is that right ? What I would need is to have a full fourier space of perturbations with topology encoded in it. pozdr. Bartek

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Cosmo/LicMagTematy
by Boud Roukema 13 Mar '06

13 Mar '06

Witam Andrzej, wszystkich, Andrzej Strobel asked for licencjat/magisterki themes. So i've slightly updated http://cosmo.torun.pl/cgi-bin/twiki/view/Cosmo/LicMagTematy Andrzej: below is my proposed text. pozdr boud ---------------------------------------------------------------------- Observational Cosmology Masters/Licencjat Project - General Outline Description: There are many possible projects which could be done as a master's thesis project, in using publicly available archival data from observational surveys to constrain one or more of the local or global cosmological parameters, either those related to shape (curvature, topology) or maybe also those unrelated to shape ("dark energy" or "dark matter"). The precise projects would be chosen in discussion with the masters/licencjat students. Please see http://cosmo.torun.pl/cgi-bin/twiki/view/Cosmo/CosmoProjects for projects that the cosmology group is working on and http://cosmo.torun.pl/cgi-bin/twiki/view/Cosmo/CosmoNews for ideas on the hottest topics in cosmology research - any of these would be appropriate if the student is sufficiently interested. Some examples are on http://cosmo.torun.pl/cgi-bin/twiki/view/Cosmo/LicMagTematy. General Requirements: * basic knowledge in astronomy, physics, mathematics, computing skills * desire to measure something about the shape of the Universe and/or dark matter or dark energy or other observational cosmology * willingness both to learn from and to teach others interested in observational cosmology at TCfA * willingness to learn the following practical skills: touch-typing, emacs, \LaTeX, usage of wikis and/or mailing lists for communication, GPL compatible programming * participation in the "Shape of the Universe" monograph course and/or Bronek Rudak's semester 9 "Kosmologia" course: o http://cosmo.torun.pl/cgi-bin/twiki/view/Cosmo/MonographCosmo o http://www.ncac.torun.pl/~bronek/KOS.html * Nie ma problemu jeśli student magistera lub licjencacki (jeszcze) nie dobrze mówi po angielsku, ale potrzeba znać czytać i rozumieć angielskie tekst, np na http://arXiv.org/ ----------------------------------------------------------------------

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moge byc spozniony jutro (czwartek 26.01.06) dla wykladu
by Boud Roukema 25 Jan '06

25 Jan '06

Cześć wszystkim (którzy uczestniczą w wykładzie tym semestr :) Pani z Działu Nauki w Rektoracie prosiła o poprawki (proste) do naszego wniosku o grant więc muszę rano iść przed wykładem jeszcze raz do Rektoratu... Mam nadzieje, że nie będę zapóźno, chyba z autobusem 10.00 tzn ok. 10.40 @Piwnice będzie ok. W czasie czekanie, mogłybyście tłumaczyć do sceptyków (humanistów?), że treść tu: http://pl.wikipedia.org/wiki/Kszta%C5%82t_Wszech%C5%9Bwiata jest dobra, lub to poprawić... Dyskusja jest (w zasadzie) tu: http://pl.wikipedia.org/wiki/Dyskusja:Kszta%C5%82t_Wszech%C5%9Bwiata Prośba o usunięcie strony jest tu: http://pl.wikipedia.org/wiki/Wikipedia:SDU/Kszta%C5%82t_Wszech%C5%9Bwiata Też lepiej rejestrować się (na góry, na prawo) przed edycji. do jutra boud

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ksztalt_Wszechswiata na pl.wikipedii: Strona do usuniecia!!!!!
by Boud Roukema 24 Jan '06

24 Jan '06

Witam shape-univ, Jest walka na wikipedii dotyczączy: http://pl.wikipedia.org/wiki/Kszta%C5%82t_Wszech%C5%9Bwiata Jest procedura glosowania do *usunięcia* strona!!!! http://pl.wikipedia.org/wiki/Wikipedia:SDU/Kszta%C5%82t_Wszech%C5%9Bwiata Dla głosować, musisz mieć minimum 100 edycji na pl.wikipedii - termin 31.01.2006. Dla dyskutować, nie musisz mieć żadnego ,,kredyt" edycyjnego. Wiem, że prawie wszysce jest zajęty z sesji, ale jeśli chcesz, że strona nie jest usunięta, proponuję, że uczestniczyć... Nie mówiłem tam że jestem dr.hab., bo to jest tylko ,,argument od autorytetu" zamiast argument naukowy. Dobry aspekt tego sprawy, jest, że więcej osoby w Polsce będą coś uczyć się o kosmologii... pod warunkiem, że zaangużujemy się w poprawkach... pozdr boud

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mirror matter debate
by Boud Roukema 03 Jan '06

03 Jan '06

Witam shape-univ, There are a few arguments here about "mirror matter (Foot et al.)" on the wikipedia: http://en.wikipedia.org/wiki/Talk:Mirror_matter i haven't gone into them deeply, but editing this page, or the article itself, might be one way to have more confidence in understanding the issue, since any changes or comments you make may be read by anyone else with internet access... A few comments *against* the Foot interpretation are at the level of what we might call "scientists' gossip" or rough intuition. The only serious response is to understand what Foot et al. says and also try to understand the comments. pozdr boud

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reading matter - nonbaryonic dark matter
by Boud Roukema 30 Nov '05

30 Nov '05

Witam wszystkim na shape-univ, Mamy ktoś nowy, który interesuje się w kosmologii :) - Łukasz zaczyna licencjat o ciemnej materii - witam Łukasz :). Dodawałem nową sekcję do twiki: http://adjani.astro.uni.torun.pl/cgi-bin/twiki/view/Cosmo/NonBaryonicDarkMa… Proszę popraw błędy, albo daj lepszy artykułow, itd. pozdr boud Review/Introduction papers on Non-Baryonic Dark Matter problem big-bang nucleosynthesis (BBN), e.g. Steigmann AstroPh:0511534 \Rightarrow \Omega_{nonbaryonic} \sim 0.25 WIMPS * AstroPh:0402045 Martin Rees - recent, quick and short * AstroPh:0506676 pages 5,6,7 Paul Frampton - recent, quantified, quick, short summary * AstroPh:0403064 Paul Gondolo - recent, in-depth introduction MACHOS * recent MACHO articles: http://arxiv.org/find/astro-ph/1/ti:+machos/0/1/0/all/0/1 * MACHO debate: are the MW microlensing events only due to known stellar populations? o Evans & Belokurov, 2004, RIP: The Macho Era (1974-2004) AstroPh:0411222 vs o Griest & Thomas 2004 Contamination in the MACHO dataset and the puzzle of LMC Microlensing AstroPh:0412443 brown dwarfs * brown dwarfs are baryonic: they cannot explain \Rightarrow \Omega_{nonbaryonic} \sim 0.25 pierwotny czarny dziury - primordial black holes * Afshordi et al. AstroPh:0302035 Primordial Black Holes as Dark Matter: The Power Spectrum and Evaporation of Early Structures

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bede kilka minuty spozniony dzis
by Boud Roukema 25 Nov '05

25 Nov '05

Przepraszam, trochę zadużo spałem dziś - idę do Piwnic z autobusem o 10.00g - tzn będę wykład od ok. 10.40g. pozdr boud

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CosmoPl meeting Jan/Feb 2006
by Boud Roukema 22 Nov '05

22 Nov '05

Cześć cosmo-spotka, Marek Biesiada from Katowice is interested in helping organise a small, informal 2-day cosmology meeting in Jan/Feb 2006. The main idea is to get together the different Polish cosmology people from Szczecin, Toruń, Kraków, Katowice, Lublin, Warsaw and hopefully maybe also some visitors from Czechy, Potsdam, Estonia, ... Anyway, here's the twiki page: http://cosmo.torun.pl/cgi-bin/twiki/view/Cosmo/CosmPlMeeting2006 Please join cosmo-spotka@ http://cosmo.torun.pl/mailman/listinfo/cosmo-spotka or else read the twiki page regularly if you're interested in helping organise (scientifically + locally) or participate in this meeting. Some time soon, we should send an invitation out to cosmo-pl@ - but IMHO we should keep cosmo-pl@ as a low volume list (many people are subscribed). Anyone interested in this meeting should join cosmo-spotka. pozdr boud

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couple of comments on the pixelization schemes
by Bartosz Lew 10 Nov '05

10 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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