2,899 research outputs found
Emergent localized states at the interface of a twofold -symmetric lattice
We consider the role of non-triviality resulting from a non-Hermitian
Hamiltonian that conserves twofold PT-symmetry assembled by interconnections
between a PT-symmetric lattice and its time reversal partner. Twofold
PT-symmetry in the lattice produces additional surface exceptional points that
play the role of new critical points, along with the bulk exceptional point. We
show that there are two distinct regimes possessing symmetry-protected
localized states, of which localization lengths are robust against external
gain and loss. The states are demonstrated by numerical calculation of a
quasi-1D ladder lattice and a 2D bilayered square lattice.Comment: 10 pages, 7 figure
Task complexity interacts with state-space uncertainty in the arbitration between model-based and model-free learning
It has previously been shown that the relative reliability of model-based and model-free reinforcement-learning (RL) systems plays a role in the allocation of behavioral control between them. However, the role of task complexity in the arbitration between these two strategies remains largely unknown. Here, using a combination of novel task design, computational modelling, and model-based fMRI analysis, we examined the role of task complexity alongside state-space uncertainty in the arbitration process. Participants tended to increase model-based RL control in response to increasing task complexity. However, they resorted to model-free RL when both uncertainty and task complexity were high, suggesting that these two variables interact during the arbitration process. Computational fMRI revealed that task complexity interacts with neural representations of the reliability of the two systems in the inferior prefrontal cortex
F^2-Softmax: Diversifying Neural Text Generation via Frequency Factorized Softmax
Despite recent advances in neural text generation, encoding the rich
diversity in human language remains elusive. We argue that the sub-optimal text
generation is mainly attributable to the imbalanced token distribution, which
particularly misdirects the learning model when trained with the
maximum-likelihood objective. As a simple yet effective remedy, we propose two
novel methods, F^2-Softmax and MefMax, for a balanced training even with the
skewed frequency distribution. MefMax assigns tokens uniquely to frequency
classes, trying to group tokens with similar frequencies and equalize frequency
mass between the classes. F^2-Softmax then decomposes a probability
distribution of the target token into a product of two conditional
probabilities of (i) frequency class, and (ii) token from the target frequency
class. Models learn more uniform probability distributions because they are
confined to subsets of vocabularies. Significant performance gains on seven
relevant metrics suggest the supremacy of our approach in improving not only
the diversity but also the quality of generated texts.Comment: EMNLP 202
Self-supervised debiasing using low rank regularization
Spurious correlations can cause strong biases in deep neural networks,
impairing generalization ability. While most existing debiasing methods require
full supervision on either spurious attributes or target labels, training a
debiased model from a limited amount of both annotations is still an open
question. To address this issue, we investigate an interesting phenomenon using
the spectral analysis of latent representations: spuriously correlated
attributes make neural networks inductively biased towards encoding lower
effective rank representations. We also show that a rank regularization can
amplify this bias in a way that encourages highly correlated features.
Leveraging these findings, we propose a self-supervised debiasing framework
potentially compatible with unlabeled samples. Specifically, we first pretrain
a biased encoder in a self-supervised manner with the rank regularization,
serving as a semantic bottleneck to enforce the encoder to learn the spuriously
correlated attributes. This biased encoder is then used to discover and
upweight bias-conflicting samples in a downstream task, serving as a boosting
to effectively debias the main model. Remarkably, the proposed debiasing
framework significantly improves the generalization performance of
self-supervised learning baselines and, in some cases, even outperforms
state-of-the-art supervised debiasing approaches
Small intestinal model for electrically propelled capsule endoscopy
The aim of this research is to propose a small intestine model for electrically propelled capsule endoscopy. The electrical stimulus can cause contraction of the small intestine and propel the capsule along the lumen. The proposed model considered the drag and friction from the small intestine using a thin walled model and Stokes' drag equation. Further, contraction force from the small intestine was modeled by using regression analysis. From the proposed model, the acceleration and velocity of various exterior shapes of capsule were calculated, and two exterior shapes of capsules were proposed based on the internal volume of the capsules. The proposed capsules were fabricated and animal experiments were conducted. One of the proposed capsules showed an average (SD) velocity in forward direction of 2.91 ± 0.99 mm/s and 2.23 ± 0.78 mm/s in the backward direction, which was 5.2 times faster than that obtained in previous research. The proposed model can predict locomotion of the capsule based on various exterior shapes of the capsule
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