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Wednesday, December 30, 2009

Dec. 27 - Simulating the Cosmic Web‏


Dear Friends,

Everything is interconnected ;-) Paste the link if you don't receive the images.

http://www.technologyreview.com/blog/arxiv/24558/

Be Well.

David

Simulating the Cosmic Web

The beautiful tapestry of filaments, sheets and voids in the Cosmic Web is proving harder to model than anybody thought

The idea that stars clump together in "island universes" is relatively new to astronomy. It was only in the 1920s and 30s that astronomers agreed among themselves that "galaxies" must be separated by vast distances.

But only in the last ten years or so have astronomers discovered that galaxies themselves form into a far larger structure. The 100 billion galaxies that we know about are woven into a wispy web-like arrangement consisting of dense compact clusters, elongated filaments and sheet-like walls, amid large near-empty void regions.

This structure has become known as the Cosmic Web and one of the great challenges in modern cosmology is to accurately model and simulate it.

That's turning out to be tricky.

One of the important features of the Cosmic Web is that its structures range over many orders of magnitude. And since the largest structures, such as the wall-like features, are formed out of the smaller ones such as filaments and clusters, it's crucial that any model can handle the relationship between them at all these scales.

That's easier said than done. One way to imagine the problem is to think about zooming out from a particular cluster of galaxies to show the larger structures, rather in the manner of the famous Powers of Ten movie made in the 1970s.

As the small scale structures become too small to resolve, most computer models apply some kind of statistical smoothing process to make the large scale calculations easier.

But if you zoom back in again, there is no way to retrieve the information that is lost by the smoothing process, other than to rebuild the picture again from the original data.

That's OK if all you want is a 3D model of the universe. But it's a problem if you want to simulate how the large scale structures form from smaller structures and how, in turn, the shape of the large structures influences the way smaller structures evolve.

This kind of feedback process is impossible to model when the smoothing process between different scales essentially destroys any meaningful links between them.

Enter Rien van de Weygaert and Willem Schaap at the University of Groningen in the Netherlands. These guys have developed a way of modeling structures over many scales without the unnatural smoothing that other approaches use.

Their trick is to think of galaxies as points in 3D space and to fill the space between them with tetrahedra. These tetrahedra must be constructed in such a way that, if a sphere were inflated inside each one until it touched the sides, there would be no galaxies inside each sphere.

This is known as a Delauney tessellation. What's special about Delauney tessellations is that as the scale gets larger, there are rules for combining the tetrahedra into larger ones. These rules are special because they are reversible, meaning that the important features of the original structure can be reconstructed when you zoom in again.

That makes it much easier to simualte the feedback between structures on various scales.

So it's no surprise that astronomers are excited about the potential of the so-called Delaunay Tessellation Field Estimator (DTFE). If you want to know more, de Weygaert and a few mates give a comprehensive outline of the idea on the arXiv today.

It should mean that we'll have a much better model of the large scale structure of the Universe.

It should also mean that we can update the Powers of Ten movie which, understandably given its age, shows no detail in the Universe beyond our local cluster of galaxies.

Ref: arxiv.org/abs/0912.3448: Geometry and Morphology of the Cosmic Web: Analyzing Spatial Patterns in the Universe

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How to Digitally Record/Video a UFO sighting:


Como registar digitalmente ou gravar um vídeo de um avistamento de um UFO:




Stabilize the camera on a tripod. If there is no tripod, then set it on top of a stable, flat surface. If that is not possible lean against a wall to stabilize your body and prevent the camera from filming in a shaky, unsteady manner.

Estabilize a camera com um tripé. Se não tiver um tripé, então coloque-a em cima de uma superfície estável. Se não for possível, então encoste-se a uma parede para estabilizar o corpo e evitar que a camera registe de maneira tremida e instável.

Provide visual reference points for comparison. This includes the horizon, treetops, lampposts, houses, and geographical landmarks (i.e., Horsetooth Reservoir, Mt. Adams, etc.) Provide this in the video whenever is appropriate and doesn’t detract from what your focus is, the UFO.

Forneça pontos visuais de referência para comparação. Isso inclui o horizonte, cimo das árvores, postes de iluminação, pontos de referência geográficos (como o Reservatório de Horsetooth, Mone Adams, etc) Forneça esses pontos no vídeo sempre que for apropriado e não se distraia do que é o seu foco, o UFO/a Nave.

Narrate your videotape. Provide details of the date, time, location, and direction (N,S,E,W) you are looking in. Provide your observations on the weather, including approximate temperature, windspeed, any visible cloud cover or noticeable weather anomalies or events. Narrate on the shape, size, color, movements, approximate altitude of the UFO, etc and what it appears to be doing. Also include any unusual physical, psychological or emotional sensations you might have. Narrate any visual reference points on camera so they correlate with what the viewer will see, and thereby will be better able to understand.

Faça a narração do vídeo. Forneça pormenores sobre a data, hora, local e direcção (Norte, Sul, Este, Oeste) que está a observar. Faça observações sobre as condições atmosféricas, incluindo a temperatura aproximada, velocidade do vento, quantidade de nuvens, anomalias ou acontecimentos meteorológicos evidentes. Descreva a forma, o tamanho, a cor, os movimentos, a altitude aproximada onde se encontra o UFO/nave, etc e o que aparenta estar a fazer. Inclua também quaisquer aspectos pouco habituais de sensações físicas, psicológicas ou emocionais que possa ter. Faça a narração de todos os pontos de referência visual que o espectador irá ver e que, deste modo, será capaz de compreender melhor.

Be persistent and consistent. Return to the scene to videotape and record at this same location. If you have been successful once, the UFO sightings may be occurring in this region regularly, perhaps for specific reasons unknown, and you may be successful again. You may also wish to return to the same location at a different time of day (daylight hours) for better orientation and reference. Film just a minute or two under “normal” circumstances for comparison. Write down what you remember immediately after. As soon as you are done recording the experience/event, immediately write down your impressions, memories, thoughts, emotions, etc. so it is on the record in writing. If there were other witnesses, have them independently record their own impressions, thoughts, etc. Include in this exercise any drawings, sketches, or diagrams. Make sure you date and sign your documentation.

Seja persistente e não contraditório. Volte ao local da cena e registe o mesmo local. Se foi bem sucedido uma vez, pode ser que nessa região ocorram avistamentos de UFOs/naves com regularidade, talvez por razões específicas desconhecidas, e talvez possa ser novamente bem sucedido. Pode também desejar voltar ao mesmo lugar a horas diferentes do dia (durante as horas de luz)para ter uma orientação e referência melhor. Filme apenas um ,inuto ou dois em circunstâncias “normais” para ter um termo de comparação. Escreva tudo o que viu imediatamente após o acontecimento. Logo após ter feito o registo da experiência/acontecimento, escreva imediatamente as impressões, memórias, pensamentos, emoções, etc para que fiquem registadas por escrito. Se houver outras testemunhas, peça-lhes para registar independentemente as suas próprias impressões, pensamentos, etc. Inclua quaisquer desenhos, esbolos, diagramas. Certifique-se que data e assina o seu documento/testemunho.

Always be prepared. Have a digital camera or better yet a video camera with you, charged and ready to go, at all times. Make sure you know how to use your camera (and your cell phone video/photo camera) quickly and properly. These events can occur suddenly, unexpectedly, and often quite randomly, so you will need to be prepared.

Esteja sempre preparado, Tenha sempre uma camera digital, melhor ainda, uma camera vídeo consigo, carregada e pronta a usar sempre que necessário. Certifique-se que sabe como lidar com a sua camera (ou com o seu celular/camera fotográfica) rápida e adequadamente. Esses acontecimentos podem acontecer súbita e inesperadamente e, por vezes, acidentalmente, por isso, necessita estar preparado.

Look up. Be prepared. Report. Share.

Olhe para cima, Esteja preparado, Relate, Partilhe.

MUFON.COM

ESOTERIC



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