107 research outputs found
Tackling Heavy-Tailed Rewards in Reinforcement Learning with Function Approximation: Minimax Optimal and Instance-Dependent Regret Bounds
While numerous works have focused on devising efficient algorithms for
reinforcement learning (RL) with uniformly bounded rewards, it remains an open
question whether sample or time-efficient algorithms for RL with large
state-action space exist when the rewards are \emph{heavy-tailed}, i.e., with
only finite -th moments for some . In this
work, we address the challenge of such rewards in RL with linear function
approximation. We first design an algorithm, \textsc{Heavy-OFUL}, for
heavy-tailed linear bandits, achieving an \emph{instance-dependent} -round
regret of , the
\emph{first} of this kind. Here, is the feature dimension, and
is the -th central moment of the reward at
the -th round. We further show the above bound is minimax optimal when
applied to the worst-case instances in stochastic and deterministic linear
bandits. We then extend this algorithm to the RL settings with linear function
approximation. Our algorithm, termed as \textsc{Heavy-LSVI-UCB}, achieves the
\emph{first} computationally efficient \emph{instance-dependent} -episode
regret of . Here, is length of the episode, and
are instance-dependent quantities scaling with
the central moment of reward and value functions, respectively. We also provide
a matching minimax lower bound to demonstrate the optimality of our algorithm in the worst
case. Our result is achieved via a novel robust self-normalized concentration
inequality that may be of independent interest in handling heavy-tailed noise
in general online regression problems.Comment: NeurIPS 202
An Empirical Study on the Holiday Effect of China's Time-Honored Companies
The stock segment of China's time-honored brand enterprises has an important
position in our securities stock market. The holiday effect is one of the
market anomalies that occur in the securities market, which refers to the
phenomenon that the stock market has significantly different returns than other
trading days around festivals. The study of the holiday effect of China's
time-honored brand enterprises can provide fresh ideas for the revitalization
of our time-honored brands and the revitalization of time-honored enterprises.
This paper takes listed companies of China's time-honored brand enterprises as
the research object and focuses on the impact of the holiday effect on listed
companies of China's time-honored brands with the help of the event study, and
empirically analyses the changes in the return of listed companies of China
time-honored brands during the Spring Festival period from 2012 to 2021. The
empirical results reveal that: the time-honored brand concept stocks have a
significant post-holiday effect during the Chinese New Year period, the
time-honored alcoholic beverage enterprises are more sensitive to the Chinese
New Year reflection, while the holiday effect of the time-honored
pharmaceutical manufacturing enterprises is not significant.Comment: 24page
Higher critical closing pressure is independently associated with enlarged basal ganglia perivascular spaces
ObjectiveThis study aimed to explore the association between cerebral hemodynamic parameters focused on the critical closing pressure (CCP) and enlarged perivascular spaces (EPVS).MethodsCerebral blood velocity in the middle cerebral artery (MCAv) and non-invasive continuous blood pressure (NIBP) were measured using a transcranial Doppler (TCD) and Finometer, followed by the calculation of cerebral hemodynamic parameters including CCP, resistance area product (RAP), pulsatility index (PI), and pulse pressure (PP). EPVS were graded separately in the basal ganglia (BG) and centrum semiovale (CSO), using a visual semiquantitative ordinal scale. Patients with EPVS >10 were classified into the severe BG-EPVS group and severe CSO-EPVS group, and the remainder into the mild BG-EPVS group and the mild CSO-EPVS group. Spearman’s correlation and binary logistic regression analysis were performed to analyze the relationship between hemodynamic parameters and BG-EPVS and CSO-EPVS, respectively.ResultsOverall, 107 patients were enrolled. The severe BG-EPVS group had higher CCP, mean arterial blood pressure (MABP), systolic blood pressure (SBP), and diastolic blood pressure (DBP) than that in the mild BG-EPVS group (p < 0.05). There was no statistical difference in hemodynamic parameters between the severe CSO-EPVS group and the mild CSO-EPVS group. Spearman’s correlation analysis showed that CCP was positively associated with BG-EPVS (rho = 0.331, p < 0.001) and CSO-EPVS (rho = 0.154, p = 0.044). The binary logistic regression analysis showed that CCP was independently associated with severe BG-EPVS (p < 0.05) and not with CSO-EPVS (p > 0.05) after adjusting for confounders.ConclusionCCP representing cerebrovascular tension was independently associated with BG-EPVS
Learning Audio-Visual Source Localization via False Negative Aware Contrastive Learning
Self-supervised audio-visual source localization aims to locate sound-source
objects in video frames without extra annotations. Recent methods often
approach this goal with the help of contrastive learning, which assumes only
the audio and visual contents from the same video are positive samples for each
other. However, this assumption would suffer from false negative samples in
real-world training. For example, for an audio sample, treating the frames from
the same audio class as negative samples may mislead the model and therefore
harm the learned representations e.g., the audio of a siren wailing may
reasonably correspond to the ambulances in multiple images). Based on this
observation, we propose a new learning strategy named False Negative Aware
Contrastive (FNAC) to mitigate the problem of misleading the training with such
false negative samples. Specifically, we utilize the intra-modal similarities
to identify potentially similar samples and construct corresponding adjacency
matrices to guide contrastive learning. Further, we propose to strengthen the
role of true negative samples by explicitly leveraging the visual features of
sound sources to facilitate the differentiation of authentic sounding source
regions. FNAC achieves state-of-the-art performances on Flickr-SoundNet,
VGG-Sound, and AVSBench, which demonstrates the effectiveness of our method in
mitigating the false negative issue. The code is available at
\url{https://github.com/OpenNLPLab/FNAC_AVL}.Comment: CVPR202
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Collaboration on evidence synthesis in Africa: a network study of growing research capacity
Background
Evidence-based practice in medicine and social policy relies heavily on evidence synthesis. To translate evidence into practical guidelines for low- and middle-income countries, local expertise is essential. The objectives of this study are to assess the change in capacity for conducting evidence synthesis in Africa and to identify key African institutions for regional capacity-building. We take on a network perspective, considering that the position of an institution in the African evidence ecosystem is one constituent of its research capacity.
Methods
We systematically identified 3548 evidence synthesis publications between 2008 and 2019 with at least one author in Africa from the Web of Science Core Collection. These articles involved 3769 institutions. Longitudinal institution-level collaboration network data were constructed based on co-authorship information. We used social network analysis to examine the institutions’ connectivity and tendency for intra- and interregional collaboration. We also identified the degree- and betweenness-central African institutions and explored the structure and composition of their local network neighbourhoods.
Results
The number of African institutions involved in evidence synthesis has increased substantially over the last decade, from 31 in 2008 to 521 in 2019, and so has the number of evidence synthesis publications with authors in Africa. African institutions in the evidence ecosystem have also become more connected during this period. Although the amount of intercontinental collaboration continues to exceed that of regional collaboration, the tendency for African institutions to collaborate with partners in Africa is increasing. We identified seven institutions—in South Africa, Egypt and Uganda—as central to the collaboration networks between 2008 and 2019, all of whom showed a tendency to collaborate across sectors.
Conclusion
The development of more regionally based network-building initiatives would help to foster communities of practice and inter-institutional collaboration, strengthening regional research capacity. Moreover, the analysis in this study adds depth beyond a simple bibliometric analysis and illustrates that network analysis could provide a useful tool to evaluate the effectiveness of capacity-building strategies and programmes in the future
Audio-Visual Segmentation
We propose to explore a new problem called audio-visual segmentation (AVS),
in which the goal is to output a pixel-level map of the object(s) that produce
sound at the time of the image frame. To facilitate this research, we construct
the first audio-visual segmentation benchmark (AVSBench), providing pixel-wise
annotations for the sounding objects in audible videos. Two settings are
studied with this benchmark: 1) semi-supervised audio-visual segmentation with
a single sound source and 2) fully-supervised audio-visual segmentation with
multiple sound sources. To deal with the AVS problem, we propose a novel method
that uses a temporal pixel-wise audio-visual interaction module to inject audio
semantics as guidance for the visual segmentation process. We also design a
regularization loss to encourage the audio-visual mapping during training.
Quantitative and qualitative experiments on the AVSBench compare our approach
to several existing methods from related tasks, demonstrating that the proposed
method is promising for building a bridge between the audio and pixel-wise
visual semantics. Code is available at https://github.com/OpenNLPLab/AVSBench.Comment: ECCV 2022; Correct the equation (3) and update the notation of the
evaluation metrics in the last arxiv version; Code is available at
https://github.com/OpenNLPLab/AVSBenc
Unlocking the enigma: unraveling multiple cognitive dysfunction linked to glymphatic impairment in early Alzheimer’s disease
BackgroundAlzheimer’s disease (AD) is one of the world’s well-known neurodegenerative diseases, which is related to the balance mechanism of production and clearance of two proteins (amyloid-β and tau) regulated by the glymphatic system. Latest studies have found that AD patients exhibit impairments to their glymphatic system. However, the alterations in the AD disease continuum, especially in the early stages, remain unclear. Moreover, the relationship between the glymphatic system and cognitive dysfunction is still worth exploring.MethodsA novel diffusion tensor image analysis method was applied to evaluate the activity of the glymphatic system by an index for diffusivity along the perivascular space (ALPS-index). Based on this method, the activity of the glymphatic system was noninvasively evaluated in 300 subjects, including 111 normal controls (NC), 120 subjects with mild cognitive impairment (MCI), and 69 subjects with AD. Partial correlation analysis was applied to explore the association between glymphatic system and cognitive impairment based on three domain-general scales and several domain-specific cognitive scales. Receiver operating characteristic curve analysis was used to evaluate the classification performance of ALPS-index along the AD continuum.ResultsALPS-index was significantly different among NC, MCI and AD groups, and ALPS-index decreased with cognitive decline. In addition, ALPS-index was significantly correlated with the scores of the clinical scales (p<0.05, FDR corrected), especially in left hemisphere. Furthermore, combination of ALPS and fractional anisotropy (FA) values achieved better classification results (NC vs. MCI: AUC = 0.6610, NC vs. AD: AUC = 0.8214).ConclusionHere, we show that the glymphatic system is closely associated with multiple cognitive dysfunctions, and ALPS-index can be used as a biomarker for alterations along the AD continuum. This may provide new targets and strategies for the treatment of AD, and has the potential to assist clinical diagnosis
Robust Multimodal Failure Detection for Microservice Systems
Proactive failure detection of instances is vitally essential to microservice
systems because an instance failure can propagate to the whole system and
degrade the system's performance. Over the years, many single-modal (i.e.,
metrics, logs, or traces) data-based nomaly detection methods have been
proposed. However, they tend to miss a large number of failures and generate
numerous false alarms because they ignore the correlation of multimodal data.
In this work, we propose AnoFusion, an unsupervised failure detection approach,
to proactively detect instance failures through multimodal data for
microservice systems. It applies a Graph Transformer Network (GTN) to learn the
correlation of the heterogeneous multimodal data and integrates a Graph
Attention Network (GAT) with Gated Recurrent Unit (GRU) to address the
challenges introduced by dynamically changing multimodal data. We evaluate the
performance of AnoFusion through two datasets, demonstrating that it achieves
the F1-score of 0.857 and 0.922, respectively, outperforming the
state-of-the-art failure detection approaches
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