4,723 research outputs found
Efficient Correlated Topic Modeling with Topic Embedding
Correlated topic modeling has been limited to small model and problem sizes
due to their high computational cost and poor scaling. In this paper, we
propose a new model which learns compact topic embeddings and captures topic
correlations through the closeness between the topic vectors. Our method
enables efficient inference in the low-dimensional embedding space, reducing
previous cubic or quadratic time complexity to linear w.r.t the topic size. We
further speedup variational inference with a fast sampler to exploit sparsity
of topic occurrence. Extensive experiments show that our approach is capable of
handling model and data scales which are several orders of magnitude larger
than existing correlation results, without sacrificing modeling quality by
providing competitive or superior performance in document classification and
retrieval.Comment: KDD 2017 oral. The first two authors contributed equall
Transient analysis of proton electrolyte membrane fuel cells (PEMFC) at start-up and failure
A two-dimensional, transient, single-phase computational model, incorporating water transport in the membrane and the flow and transport of species in porous gas diffusion electrodes is developed to evaluate the transient performance of a PEMFC with interdigitated gas distributors. The co-flow and counter-flow of the anode and cathode reactants are discussed to address their effects on PEMFC performance and transients. The important role of water transport in the membrane on the transients is demonstrated. The membrane’s water intake or outtake determines the duration of the transients. The effect of the operating conditions on steady state and transient performances is outlined. Overshoots and undershoots are observed in the average current density, due to a step change in the cell voltage and the cathode pressure under start-up conditions. Simulation results are used to address the role of auxiliary components in the failure modes of the PEMFC
Learning-based Ensemble Average Propagator Estimation
By capturing the anisotropic water diffusion in tissue, diffusion magnetic
resonance imaging (dMRI) provides a unique tool for noninvasively probing the
tissue microstructure and orientation in the human brain. The diffusion profile
can be described by the ensemble average propagator (EAP), which is inferred
from observed diffusion signals. However, accurate EAP estimation using the
number of diffusion gradients that is clinically practical can be challenging.
In this work, we propose a deep learning algorithm for EAP estimation, which is
named learning-based ensemble average propagator estimation (LEAPE). The EAP is
commonly represented by a basis and its associated coefficients, and here we
choose the SHORE basis and design a deep network to estimate the coefficients.
The network comprises two cascaded components. The first component is a
multiple layer perceptron (MLP) that simultaneously predicts the unknown
coefficients. However, typical training loss functions, such as mean squared
errors, may not properly represent the geometry of the possibly non-Euclidean
space of the coefficients, which in particular causes problems for the
extraction of directional information from the EAP. Therefore, to regularize
the training, in the second component we compute an auxiliary output of
approximated fiber orientation (FO) errors with the aid of a second MLP that is
trained separately. We performed experiments using dMRI data that resemble
clinically achievable -space sampling, and observed promising results
compared with the conventional EAP estimation method.Comment: Accepted by MICCAI 201
A combined SEM, CV and EIS study of multi-layered porous ceramic reactors for flue gas purification
The effect of sintering temperature of 12-layered porous ceramic reactors (comprising 5 cells) was studied using scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The difference in microstructures of the reactors was evaluated by SEM. Additional information on the influence of sintering temperature on the properties of the reactors could be gained by the use of EIS. The present work has provided the first set of fundamental electrochemical data and their interpretation in terms of fabrication conditions, for the multi-layered porous ceramic reactors
A Surprisingly Effective Fix for Deep Latent Variable Modeling of Text
When trained effectively, the Variational Autoencoder (VAE) is both a
powerful language model and an effective representation learning framework. In
practice, however, VAEs are trained with the evidence lower bound (ELBO) as a
surrogate objective to the intractable marginal data likelihood. This approach
to training yields unstable results, frequently leading to a disastrous local
optimum known as posterior collapse. In this paper, we investigate a simple fix
for posterior collapse which yields surprisingly effective results. The
combination of two known heuristics, previously considered only in isolation,
substantially improves held-out likelihood, reconstruction, and latent
representation learning when compared with previous state-of-the-art methods.
More interestingly, while our experiments demonstrate superiority on these
principle evaluations, our method obtains a worse ELBO. We use these results to
argue that the typical surrogate objective for VAEs may not be sufficient or
necessarily appropriate for balancing the goals of representation learning and
data distribution modeling.Comment: EMNLP 2019 short paper. The first two authors contributed equall
Optimizing the Performance of Porous Electrochemical Cells for Flue Gas Purification using the DOE method
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