99,836 research outputs found
Measurable cardinals and good -wellorderings
We study the influence of the existence of large cardinals on the existence
of wellorderings of power sets of infinite cardinals with the property
that the collection of all initial segments of the wellordering is definable by
a -formula with parameter . A short argument shows that the
existence of a measurable cardinal implies that such wellorderings do
not exist at -inaccessible cardinals of cofinality not equal to
and their successors. In contrast, our main result shows that these
wellorderings exist at all other uncountable cardinals in the minimal model
containing a measurable cardinal. In addition, we show that measurability is
the smallest large cardinal property that interferes with the existence of such
wellorderings at uncountable cardinals and we generalize the above result to
the minimal model containing two measurable cardinals.Comment: 14 page
Improving Retrieval Results with discipline-specific Query Expansion
Choosing the right terms to describe an information need is becoming more
difficult as the amount of available information increases.
Search-Term-Recommendation (STR) systems can help to overcome these problems.
This paper evaluates the benefits that may be gained from the use of STRs in
Query Expansion (QE). We create 17 STRs, 16 based on specific disciplines and
one giving general recommendations, and compare the retrieval performance of
these STRs. The main findings are: (1) QE with specific STRs leads to
significantly better results than QE with a general STR, (2) QE with specific
STRs selected by a heuristic mechanism of topic classification leads to better
results than the general STR, however (3) selecting the best matching specific
STR in an automatic way is a major challenge of this process.Comment: 6 pages; to be published in Proceedings of Theory and Practice of
Digital Libraries 2012 (TPDL 2012
The Hurewicz dichotomy for generalized Baire spaces
By classical results of Hurewicz, Kechris and Saint-Raymond, an analytic
subset of a Polish space is covered by a subset of if and
only if it does not contain a closed-in- subset homeomorphic to the Baire
space . We consider the analogous statement (which we call
Hurewicz dichotomy) for subsets of the generalized Baire space
for a given uncountable cardinal with
, and show how to force it to be true in a cardinal
and cofinality preserving extension of the ground model. Moreover, we show that
if the Generalized Continuum Hypothesis (GCH) holds, then there is a cardinal
preserving class-forcing extension in which the Hurewicz dichotomy for
subsets of holds at all uncountable regular
cardinals , while strongly unfoldable and supercompact cardinals are
preserved. On the other hand, in the constructible universe L the dichotomy for
sets fails at all uncountable regular cardinals, and the same
happens in any generic extension obtained by adding a Cohen real to a model of
GCH. We also discuss connections with some regularity properties, like the
-perfect set property, the -Miller measurability, and the
-Sacks measurability.Comment: 33 pages, final versio
Expectation Propagation on the Maximum of Correlated Normal Variables
Many inference problems involving questions of optimality ask for the maximum
or the minimum of a finite set of unknown quantities. This technical report
derives the first two posterior moments of the maximum of two correlated
Gaussian variables and the first two posterior moments of the two generating
variables (corresponding to Gaussian approximations minimizing relative
entropy). It is shown how this can be used to build a heuristic approximation
to the maximum relationship over a finite set of Gaussian variables, allowing
approximate inference by Expectation Propagation on such quantities.Comment: 11 pages, 7 figure
Discursive Killings: Intertextuality, Aestheticization, and Death in Nabokov's Lolita
This essay argues that Nabokov's Lolita is suffused with a rhetoric of death. Humbert Humbert's discursive constructions of Lolita trap her in a semantic web of death that conjures up her literal death in childbed at the age of seventeen. My reading of Lolita traces the fibres of that web in the more sinister implications of Humbert's intertextual references, his persistent gestures of aestheticization and his reflections on the nature of nymphets
A quantum cluster algebra of Kronecker type and the dual canonical basis
The article concerns the dual of Lusztig's canonical basis of a subalgebra of
the positive part U_q(n) of the universal enveloping algebra of a Kac-Moody Lie
algebra of type A_1^{(1)}. The examined subalgebra is associated with a
terminal module M over the path algebra of the Kronecker quiver via an Weyl
group element w of length four.
Geiss-Leclerc-Schroeer attached to M a category C_M of nilpotent modules over
the preprojective algebra of the Kronecker quiver together with an acyclic
cluster algebra A(C_M). The dual semicanonical basis contains all cluster
monomials. By construction, the cluster algebra A(C_M) is a subalgebra of the
graded dual of the (non-quantized) universal enveloping algebra U(n).
We transfer to the quantized setup. Following Lusztig we attach to w a
subalgebra U_q^+(w) of U_q(n). The subalgebra is generated by four elements
that satisfy straightening relations; it degenerates to a commutative algebra
in the classical limit q=1. The algebra U_q^+(w) possesses four bases, a PBW
basis, a canonical basis, and their duals. We prove recursions for dual
canonical basis elements. The recursions imply that every cluster variable in
A(C_M) is the specialization of the dual of an appropriate canonical basis
element. Therefore, U_q^+(w) is a quantum cluster algebra in the sense of
Berenstein-Zelevinsky. Furthermore, we give explicit formulae for the quantized
cluster variables and for expansions of products of dual canonical basis
elements.Comment: 32 page
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