721 research outputs found
Isometric endomorphisms of free groups
An arbitrary homomorphism between groups is nonincreasing for stable
commutator length, and there are infinitely many (injective) homomorphisms
between free groups which strictly decrease the stable commutator length of
some elements. However, we show in this paper that a random homomorphism
between free groups is almost surely an isometry for stable commutator length
for every element; in particular, the unit ball in the scl norm of a free group
admits an enormous number of exotic isometries.
Using similar methods, we show that a random fatgraph in a free group is
extremal (i.e. is an absolute minimizer for relative Gromov norm) for its
boundary; this implies, for instance, that a random element of a free group
with commutator length at most n has commutator length exactly n and stable
commutator length exactly n-1/2. Our methods also let us construct explicit
(and computable) quasimorphisms which certify these facts.Comment: 26 pages, 6 figures; minor typographical edits for final published
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Automatic Detection of Abnormal Behavior in Computing Systems
I present RAACD, a software suite that detects misbehaving computers in large computing systems and presents information about those machines to the system administrator. I build this system using preexisting anomaly detection techniques. I evaluate my methods using simple synthesized data, real data containing coerced abnormal behavior, and real data containing naturally occurring abnormal behavior. I find that the system adequately detects abnormal behavior and significantly reduces the amount of uninteresting computer health data presented to a system administrator
Weighted dependency graphs
The theory of dependency graphs is a powerful toolbox to prove asymptotic
normality of sums of random variables. In this article, we introduce a more
general notion of weighted dependency graphs and give normality criteria in
this context. We also provide generic tools to prove that some weighted graph
is a weighted dependency graph for a given family of random variables.
To illustrate the power of the theory, we give applications to the following
objects: uniform random pair partitions, the random graph model ,
uniform random permutations, the symmetric simple exclusion process and
multilinear statistics on Markov chains. The application to random permutations
gives a bivariate extension of a functional central limit theorem of Janson and
Barbour. On Markov chains, we answer positively an open question of Bourdon and
Vall\'ee on the asymptotic normality of subword counts in random texts
generated by a Markovian source.Comment: 57 pages. Third version: minor modifications, after review proces
Spoken content retrieval: A survey of techniques and technologies
Speech media, that is, digital audio and video containing spoken content, has blossomed in recent years. Large collections are accruing on the Internet as well as in private and enterprise settings. This growth has motivated extensive research on techniques and technologies that facilitate reliable indexing and retrieval. Spoken content retrieval (SCR) requires the combination of audio and speech processing technologies with methods from information retrieval (IR). SCR research initially investigated planned speech structured in document-like units, but has subsequently shifted focus to more informal spoken content produced spontaneously, outside of the studio and in conversational settings. This survey provides an overview of the field of SCR encompassing component technologies, the relationship of SCR to text IR and automatic speech recognition and user interaction issues. It is aimed at researchers with backgrounds in speech technology or IR who are seeking deeper insight on how these fields are integrated to support research and development, thus addressing the core challenges of SCR
Siirto-oppiminen kielimalleilla luokitteluongelmille
Neural network based modern language models can reach state of the art performance on wide range of natural language tasks. Their success is based on capability to learn from large unlabeled data by pretraining, using transfer learning to learn strong representations for the language and transferring the learned into new domains and tasks.
I look at how language models produce transfer learning for NLP. Especially from the viewpoint of classification. How transfer learning can be formally defined? I compare different LM implementations in theory and also use two example data sets for empirically testing their performance on very small labeled training data
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