5,290 research outputs found
A non-ambiguous decomposition of regular languages and factorizing codes
AbstractGiven languages Z,L⊆Σ∗,Z is L-decomposable (finitely L-decomposable, resp.) if there exists a non-trivial pair of languages (finite languages, resp.) (A,B), such that Z=AL+B and the operations are non-ambiguous. We show that it is decidable whether Z is L-decomposable and whether Z is finitely L-decomposable, in the case Z and L are regular languages. The result in the case Z=L allows one to decide whether, given a finite language S⊆Σ∗, there exist finite languages C,P such that SC∗P=Σ∗ with non-ambiguous operations. This problem is related to Schützenberger's Factorization Conjecture on codes. We also construct an infinite family of factorizing codes
Heavy Quark Effective Theory beyond Perturbation Theory: Renormalons, the Pole Mass and the Residual Mass Term
We study the asymptotic behaviour of the perturbative series in the heavy
quark effective theory (HQET) using the expansion. We find that this
theory suffers from an {\it ultraviolet} renormalon problem, corresponding to a
non-Borel-summable behaviour of perturbation series in large orders, and
leading to a principal nonperturbative ambiguity in its definition. This
ambiguity is related to an {\it infrared} renormalon in the pole mass and can
be understood as the necessity to include the residual mass term in
the definition of HQET, which must be considered as ambiguous (and possibly
complex), and is required to cancel the ultraviolet renormalon singularity
generated by the perturbative expansion. The formal status of is
thus identical to that of condensates in the conventional short-distance
expansion of correlation functions in QCD. The status of the pole mass of a
heavy quark, the operator product expansion for inclusive decays, and QCD sum
rules in the HQET are discussed in this context.Comment: LATEX, 43 pages, 6 figures appended as uu-encoded file, MPI-PhT/94-9,
(Text as to appear in NPB, typing errors corrected [Eq.(3.24),(3.26)], some
statements in Sect.5 more precise
Direction of Arrival with One Microphone, a few LEGOs, and Non-Negative Matrix Factorization
Conventional approaches to sound source localization require at least two
microphones. It is known, however, that people with unilateral hearing loss can
also localize sounds. Monaural localization is possible thanks to the
scattering by the head, though it hinges on learning the spectra of the various
sources. We take inspiration from this human ability to propose algorithms for
accurate sound source localization using a single microphone embedded in an
arbitrary scattering structure. The structure modifies the frequency response
of the microphone in a direction-dependent way giving each direction a
signature. While knowing those signatures is sufficient to localize sources of
white noise, localizing speech is much more challenging: it is an ill-posed
inverse problem which we regularize by prior knowledge in the form of learned
non-negative dictionaries. We demonstrate a monaural speech localization
algorithm based on non-negative matrix factorization that does not depend on
sophisticated, designed scatterers. In fact, we show experimental results with
ad hoc scatterers made of LEGO bricks. Even with these rudimentary structures
we can accurately localize arbitrary speakers; that is, we do not need to learn
the dictionary for the particular speaker to be localized. Finally, we discuss
multi-source localization and the related limitations of our approach.Comment: This article has been accepted for publication in IEEE/ACM
Transactions on Audio, Speech, and Language processing (TASLP
Tachyon Condensation on the Elliptic Curve
We use the framework of matrix factorizations to study topological B-type
D-branes on the cubic curve. Specifically, we elucidate how the brane RR
charges are encoded in the matrix factors, by analyzing their structure in
terms of sections of vector bundles in conjunction with equivariant R-symmetry.
One particular advantage of matrix factorizations is that explicit moduli
dependence is built in, thus giving us full control over the open-string moduli
space. It allows one to study phenomena like discontinuous jumps of the
cohomology over the moduli space, as well as formation of bound states at
threshold. One interesting aspect is that certain gauge symmetries inherent to
the matrix formulation lead to a non-trivial global structure of the moduli
space. We also investigate topological tachyon condensation, which enables us
to construct, in a systematic fashion, higher-dimensional matrix factorizations
out of smaller ones; this amounts to obtaining branes with higher RR charges as
composites of ones with minimal charges. As an application, we explicitly
construct all rank-two matrix factorizations.Comment: 69p, 6 figs, harvmac; v2: minor change
Matrix Factorizations, D-Branes and their Deformations
We review in elementary, non-technical terms the description of topological
B-type of D-branes in terms of boundary Landau-Ginzburg theory, as well as some
applications.Comment: 20p, 5 figs, Proceedings of Cargese school on string theory, 200
Fitting DVCS at NLO and beyond
We outline the twist-two analysis of deeply virtual Compton scattering
(DVCS)within the conformal partial wave expansion of the amplitude, represented
as a Mellin--Barnes integral. The complete next-to-leading order results,
including evolution, are obtained in the MS and a conformal factorization
scheme. Within the latter, exploiting conformal symmetry, the radiative
corrections are evaluated up to next-to-next-to-leading order. Using a new
proposed parameterization for GPDs, we study the convergence of perturbation
theory and demonstrate for H1 and ZEUS measurements that our formalism is
suitable for a fitting procedure of DVCS observables. We comment on a recent
claim of a breakdown of collinear factorization and show that a Regge-inspired
Q^2 scaling law is ruled out by small x_Bj DVCS data.Comment: 15 pages, 4 figure
CESI: Canonicalizing Open Knowledge Bases using Embeddings and Side Information
Open Information Extraction (OpenIE) methods extract (noun phrase, relation
phrase, noun phrase) triples from text, resulting in the construction of large
Open Knowledge Bases (Open KBs). The noun phrases (NPs) and relation phrases in
such Open KBs are not canonicalized, leading to the storage of redundant and
ambiguous facts. Recent research has posed canonicalization of Open KBs as
clustering over manuallydefined feature spaces. Manual feature engineering is
expensive and often sub-optimal. In order to overcome this challenge, we
propose Canonicalization using Embeddings and Side Information (CESI) - a novel
approach which performs canonicalization over learned embeddings of Open KBs.
CESI extends recent advances in KB embedding by incorporating relevant NP and
relation phrase side information in a principled manner. Through extensive
experiments on multiple real-world datasets, we demonstrate CESI's
effectiveness.Comment: Accepted at WWW 201
- …