... Three energetic mechanisms are considered: multiple supernova explosions (SNe), a hypernova explosion associated with a gamma ray burst (GRB), and the vertical impact of a high velocity cloud (HVC). ... As a consequence, multiple SNe form rings with a high ring-to-center contrast K < 100 in the HI column density, whereas single hypernova explosions form rings with K < 10. ... Our simulations show (see Fig. 6) that both multiple SNe and single hypernovae may form rings of up to 2 kpc in diameter. ...

... A rough estimation is that in the United States there is one planetarium per 100,000 population, ranging in size from the Hayden Planetarium's 20-meter dome seating 430 people, to three-meter inflatable portable domes where children sit on the floor. ... Together dblo associates make a huge impact in the architecture, interior design and development arena in London. ... With the holidays around the corner what better way to spoil your family than with your very own private home cinema. ...