1,414 research outputs found
Detection of Pristine Gas Two Billion Years after the Big Bang
In the current cosmological model, only the three lightest elements were
created in the first few minutes after the Big Bang; all other elements were
produced later in stars. To date, however, heavy elements have been observed in
all astrophysical environments. We report the detection of two gas clouds with
no discernible elements heavier than hydrogen. These systems exhibit the lowest
heavy-element abundance in the early universe and thus are potential fuel for
the most metal poor halo stars. The detection of deuterium in one system at the
level predicted by primordial nucleosynthesis provides a direct confirmation of
the standard cosmological model. The composition of these clouds further
implies that the transport of heavy elements from galaxies to their
surroundings is highly inhomogeneous.Comment: 32 pages, 11 figures, SOM included. To appear in Scienc
Book Review: Archytas of Tarentum. Pythagorean, Philosopher and Mathematician King: Huffman(C.A.) Archytas of Tarentum. Pythagorean, Philosopher and Mathematician King. Pp. xvi + 665. Cambridge: Cambridge University Press, 2005. Cased, £95, US$175. ISBN: 0-521-83746-4
Growth curves for algebras
This paper studies matrix representations of algebras (over a field) using countably-infinite matrices which are both row and column finite, and in which the
bandwidth growth is controlled. The ideas lead naturally to a concept of "growth of
an algebra", somewhat analogous to the growth associated with GK-dimension. They
also lead in a similar way to a dimension function on general algebras, which we term
bandwidth dimension. For each real number r ∈ [0,1], we construct an algebra having
bandwidth dimension precisely r. Since the free algebra turns out to have bandwidth
dimension 0, our new dimension promises to distinguish among algebras of infinite
GK-dimension
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