109,429 research outputs found
Chern class identities from tadpole matching in type IIB and F-theory
In light of Sen's weak coupling limit of F-theory as a type IIB orientifold,
the compatibility of the tadpole conditions leads to a non-trivial identity
relating the Euler characteristics of an elliptically fibered Calabi-Yau
fourfold and of certain related surfaces. We present the physical argument
leading to the identity, and a mathematical derivation of a Chern class
identity which confirms it, after taking into account singularities of the
relevant loci. This identity of Chern classes holds in arbitrary dimension, and
for varieties that are not necessarily Calabi-Yau. Singularities are essential
in both the physics and the mathematics arguments: the tadpole relation may be
interpreted as an identity involving stringy invariants of a singular
hypersurface, and corrections for the presence of pinch-points. The
mathematical discussion is streamlined by the use of Chern-Schwartz-MacPherson
classes of singular varieties. We also show how the main identity may be
obtained by applying `Verdier specialization' to suitable constructible
functions.Comment: 26 pages, 1 figure, references added, typos correcte
ERBlox: Combining Matching Dependencies with Machine Learning for Entity Resolution
Entity resolution (ER), an important and common data cleaning problem, is
about detecting data duplicate representations for the same external entities,
and merging them into single representations. Relatively recently, declarative
rules called matching dependencies (MDs) have been proposed for specifying
similarity conditions under which attribute values in database records are
merged. In this work we show the process and the benefits of integrating three
components of ER: (a) Classifiers for duplicate/non-duplicate record pairs
built using machine learning (ML) techniques, (b) MDs for supporting both the
blocking phase of ML and the merge itself; and (c) The use of the declarative
language LogiQL -an extended form of Datalog supported by the LogicBlox
platform- for data processing, and the specification and enforcement of MDs.Comment: To appear in Proc. SUM, 201
Comparing knowledge sources for nominal anaphora resolution
We compare two ways of obtaining lexical knowledge for antecedent selection in other-anaphora
and definite noun phrase coreference. Specifically, we compare an algorithm that relies on links
encoded in the manually created lexical hierarchy WordNet and an algorithm that mines corpora
by means of shallow lexico-semantic patterns. As corpora we use the British National
Corpus (BNC), as well as the Web, which has not been previously used for this task. Our
results show that (a) the knowledge encoded in WordNet is often insufficient, especially for
anaphor-antecedent relations that exploit subjective or context-dependent knowledge; (b) for
other-anaphora, the Web-based method outperforms the WordNet-based method; (c) for definite
NP coreference, the Web-based method yields results comparable to those obtained using
WordNet over the whole dataset and outperforms the WordNet-based method on subsets of the
dataset; (d) in both case studies, the BNC-based method is worse than the other methods because
of data sparseness. Thus, in our studies, the Web-based method alleviated the lexical knowledge
gap often encountered in anaphora resolution, and handled examples with context-dependent relations
between anaphor and antecedent. Because it is inexpensive and needs no hand-modelling
of lexical knowledge, it is a promising knowledge source to integrate in anaphora resolution systems
Cocycle Properties of String Theories on Orbifolds
We study cocycle properties of vertex operators and present an operator
representation of cocycle operators, which are attached to vertex operators to
ensure the duality of amplitudes. It is shown that this analysis makes it
possible to obtain the general class of consistent string theories on
orbifolds.Comment: 40 pages (Talk given at Workshop on ``Recent Developments in String
and Field theory", Kyoto, Japan on September 9-12, 1991.
First Order Semiclassical Thermal String in the AdS Spacetime
We formulate the finite temperature theory for the free thermal excitations
of the bosonic string in the anti-de Sitter (AdS) spacetime in the Thermo Field
Dynamics (TFD) approach. The spacetime metric is treated exactly while the
string and the thermal reservoir are semiclassically quantized at the first
order perturbation theory with respect to the dimensionless parameter \epsilon
= \a ' H^{-2}. In the conformal black-hole AdS background the
quantization is exact. The method can be extended to the arbitrary AdS
spacetime only in the first order perturbation. This approximation is taken in
the center of mass reference frame and it is justified by the fact that at the
first order the string dynamics is determined only by the interaction between
the {\em free} string oscillation modes and the {\em exact} background. The
first order thermal string is obtained by thermalization of the system
carried on by the TFD Bogoliubov operator. We determine the free thermal string
states and compute the local entropy and free energy in the center of mass
reference frame.Comment: Minor typos corrected. Two references added. LATeX file, 19 page
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