834 research outputs found
Comparing Probabilistic Models for Melodic Sequences
Modelling the real world complexity of music is a challenge for machine
learning. We address the task of modeling melodic sequences from the same music
genre. We perform a comparative analysis of two probabilistic models; a
Dirichlet Variable Length Markov Model (Dirichlet-VMM) and a Time Convolutional
Restricted Boltzmann Machine (TC-RBM). We show that the TC-RBM learns
descriptive music features, such as underlying chords and typical melody
transitions and dynamics. We assess the models for future prediction and
compare their performance to a VMM, which is the current state of the art in
melody generation. We show that both models perform significantly better than
the VMM, with the Dirichlet-VMM marginally outperforming the TC-RBM. Finally,
we evaluate the short order statistics of the models, using the
Kullback-Leibler divergence between test sequences and model samples, and show
that our proposed methods match the statistics of the music genre significantly
better than the VMM.Comment: in Proceedings of the ECML-PKDD 2011. Lecture Notes in Computer
Science, vol. 6913, pp. 289-304. Springer (2011
Representation Learning: A Review and New Perspectives
The success of machine learning algorithms generally depends on data
representation, and we hypothesize that this is because different
representations can entangle and hide more or less the different explanatory
factors of variation behind the data. Although specific domain knowledge can be
used to help design representations, learning with generic priors can also be
used, and the quest for AI is motivating the design of more powerful
representation-learning algorithms implementing such priors. This paper reviews
recent work in the area of unsupervised feature learning and deep learning,
covering advances in probabilistic models, auto-encoders, manifold learning,
and deep networks. This motivates longer-term unanswered questions about the
appropriate objectives for learning good representations, for computing
representations (i.e., inference), and the geometrical connections between
representation learning, density estimation and manifold learning
Gamma rays and positrons from a decaying hidden gauge boson
We study a scenario that a hidden gauge boson constitutes the dominant
component of dark matter and decays into the standard model particles through a
gauge kinetic mixing. Interestingly, gamma rays and positrons produced from the
decay of hidden gauge boson can explain both the EGRET excess of diffuse gamma
rays and the HEAT anomaly in the positron fraction. The spectra of the gamma
rays and the positrons have distinctive features; the absence of line emission
of the gamma ray and a sharp peak in the positron fraction. Such features may
be observed by the GLAST and PAMELA satellites.Comment: 16 pages, 4 figures, adding PAMELA data, the version accepted by PL
Training Restricted Boltzmann Machines on Word Observations
The restricted Boltzmann machine (RBM) is a flexible tool for modeling
complex data, however there have been significant computational difficulties in
using RBMs to model high-dimensional multinomial observations. In natural
language processing applications, words are naturally modeled by K-ary discrete
distributions, where K is determined by the vocabulary size and can easily be
in the hundreds of thousands. The conventional approach to training RBMs on
word observations is limited because it requires sampling the states of K-way
softmax visible units during block Gibbs updates, an operation that takes time
linear in K. In this work, we address this issue by employing a more general
class of Markov chain Monte Carlo operators on the visible units, yielding
updates with computational complexity independent of K. We demonstrate the
success of our approach by training RBMs on hundreds of millions of word
n-grams using larger vocabularies than previously feasible and using the
learned features to improve performance on chunking and sentiment
classification tasks, achieving state-of-the-art results on the latter
Anomaly-Mediation and Sequestering from a Higher-Dimensional viewpoint
We study a five-dimensional supergravity model with boundary-localized
visible sector exhibiting anomaly-mediated supersymmetry breaking, in which the
central requirements of sequestering and radius stabilization are achieved
perturbatively. This makes it possible to understand these various mechanisms
in a more integrated and transparent fashion, mostly from the
higher-dimensional viewpoint. Local supersymmetry, in the presence of visible
sector quantum effects, is enforced by the formalism of the five-dimensional
superconformal tensor calculus. The construction results in only mild warping,
which allows a natural supersymmetry-breaking mediation mechanism of (finite)
boundary-to-boundary gravity loops to co-dominate with anomaly-mediation,
thereby solving the latter's tachyonic slepton problem. We make the non-trivial
check that this can occur while dangerous loops of stabilizing fields remain
highly suppressed. Our discussion is a well-controlled starting point for
considering other generalizations of anomaly-mediation, or for string theory
realizations.Comment: 33 pages, typos corrected, added references, version appearing in
JHE
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