11,313 research outputs found
Comparing skew Schur functions: a quasisymmetric perspective
Reiner, Shaw and van Willigenburg showed that if two skew Schur functions s_A
and s_B are equal, then the skew shapes A and B must have the same "row overlap
partitions." Here we show that these row overlap equalities are also implied by
a much weaker condition than skew Schur equality: that s_A and s_B have the
same support when expanded in the fundamental quasisymmetric basis F.
Surprisingly, there is significant evidence supporting a conjecture that the
converse is also true.
In fact, we work in terms of inequalities, showing that if the F-support of
s_A contains that of s_B, then the row overlap partitions of A are dominated by
those of B, and again conjecture that the converse also holds. Our evidence in
favor of these conjectures includes their consistency with a complete
determination of all F-support containment relations for F-multiplicity-free
skew Schur functions. We conclude with a consideration of how some other
quasisymmetric bases fit into our framework.Comment: 26 pages, 7 figures. J. Combin., to appear. Version 2 includes a new
subsection (5.3) on a possible skew version of the Saturation Theore
Jet induced star formation in centrally dominant galaxies?
Using U-I CCD color maps of two centrally dominant cluster galaxies, we find unusual color structures which may be due to star formation which has been induced by their radio sources. These objects, located in the clusters A1795 and A2597, have blue central colors to radii of 20 kpc, spatially extended emission-line structures, and powerful radio sources. They reside at the centers of cooling flows with mass-accretion rates which are estimated to be approximately greater than 300 solar mass/yr. The regions of bluest local color are superposed on or along their radio-source structures. Our observations suggest that the radio sources associated with these objects may be inducing massive star formation in their central 20 kpc. The star formation may be the result of the radio plasma interacting with the warm emission-line gas and dense, x-ray emitting filaments similar to those recently discovered in two other clusters with the ROSAT Observatory. Since radio jets are likely to be transient, this may help to explain the scatter in the correlations between color and mass-accretion rate, although other factors may also contribute. Alternatively, scattered radiation from a hidden active nucleus or recent mergers may be responsible for the color structure. The color and radio properties of these objects are qualitatively similar but smaller in luminosity and spatial extent to those found in high redshift radio galaxies. Our observations of galaxies at z approximately = 0.06-0.1 show that processes similar to 'the alignment effect' found in high redshift radio galaxies occur at more recent epochs
On the topology of the permutation pattern poset
The set of all permutations, ordered by pattern containment, forms a poset.
This paper presents the first explicit major results on the topology of
intervals in this poset. We show that almost all (open) intervals in this poset
have a disconnected subinterval and are thus not shellable. Nevertheless, there
seem to be large classes of intervals that are shellable and thus have the
homotopy type of a wedge of spheres. We prove this to be the case for all
intervals of layered permutations that have no disconnected subintervals of
rank 3 or more. We also characterize in a simple way those intervals of layered
permutations that are disconnected. These results carry over to the poset of
generalized subword order when the ordering on the underlying alphabet is a
rooted forest. We conjecture that the same applies to intervals of separable
permutations, that is, that such an interval is shellable if and only if it has
no disconnected subinterval of rank 3 or more. We also present a simplified
version of the recursive formula for the M\"obius function of decomposable
permutations given by Burstein et al.Comment: 33 pages, 4 figures. Incorporates changes suggested by the referees;
new open problems in Subsection 9.4. To appear in JCT(A
The structure of the consecutive pattern poset
The consecutive pattern poset is the infinite partially ordered set of all
permutations where if has a subsequence of adjacent
entries in the same relative order as the entries of . We study the
structure of the intervals in this poset from topological, poset-theoretic, and
enumerative perspectives. In particular, we prove that all intervals are
rank-unimodal and strongly Sperner, and we characterize disconnected and
shellable intervals. We also show that most intervals are not shellable and
have M\"obius function equal to zero.Comment: 29 pages, 7 figures. To appear in IMR
The M\"obius function of generalized subword order
Let P be a poset and let P* be the set of all finite length words over P.
Generalized subword order is the partial order on P* obtained by letting u \leq
w if and only if there is a subword u' of w having the same length as u such
that each element of u is less than or equal to the corresponding element of u'
in the partial order on P. Classical subword order arises when P is an
antichain, while letting P be a chain gives an order on compositions. For any
finite poset P, we give a simple formula for the Mobius function of P* in terms
of the Mobius function of P. This permits us to rederive in a easy and uniform
manner previous results of Bjorner, Sagan and Vatter, and Tomie. We are also
able to determine the homotopy type of all intervals in P* for any finite P of
rank at most 1.Comment: 29 pages, 4 figures. Incorporates referees' suggestions; to appear in
Advances in Mathematic
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