an r-module m is called epi-retractable if every submodule of mr is a homomorphic image of m. it is shown that if r is a right perfect ring, then every projective slightly compressible module mr is epi-retractable. if r is a noetherian ring, then every epi-retractable right r-module has direct sum of uniform submodules. if endomorphism ring of a module mr is von-neumann regular, then m is semi-...

In the (covariant) topos approach to quantum theory by Heunen, Landsman and Spitters, one associates to each unital C*-algebra A a topos T (A) of sheaves on a locale and a commutative C*-algebra A within that topos. The Gelfand spectrum of A is a locale Σ in this topos, which is equivalent to a bundle over the base locale. We further develop this external presentation of the locale Σ, by noting...

The concept of semi-regular sets of matrices was introduced by J. Seberry in "A new construction for Williamson-type matrices", Graphs and Combinatorics, 2(1986), 81-87. A regular s-set of matrices of order m was first discovered by J. Seberry and A. L. Whiteman in "New Hadamard matrices and conference matrices obtained via Mathon's construction", Graphs and Combinatorics, 4(1988), 355-377. In ...

Period-luminosity sequences have been shown to exist among the Semi-Regular Variables (SRVs) in the Magellanic Clouds (Wood et al, 1999), the Bulge of the Milky Way galaxy (Glass & Schultheis, 2003) and elsewhere. Using modern period and revised Hipparcos parallax data, this paper demonstrates that they also appear among the M-giant SRVs of the Solar Neighbourhood. Their distribution in the K, ...

There are many functions of the degree sequence of a graph which give lower bounds on the independence number of the graph. In particular, for every graph G, α(G) ≥ R(d(G)), where R is the residue of the degree sequence of G. We consider the precision of this estimate when it is applied to semi-regular degree sequences. We show that the residue nearly always gives the best possible estimate on ...

Electric field pulse bursts generated by lightning flashes are considered as sources of high radio frequencies. In this study, an analysis of pulse bursts in electric field records of 30 negative cloud to ground lightning flashes recorded in the southern coastal area of Sri Lanka is presented. Sixty-four percent (64%) of pulse bursts are typical chaotic pulse trains (CPT). Twenty-four percent (...