1,748 research outputs found
Revisit of directed flow in relativistic heavy-ion collisions from a multiphase transport model
We have revisited several interesting questions on how the rapidity-odd
directed flow is developed in relativistic Au+Au collisions at
= 200 and 39 GeV based on a multiphase transport model. As the
partonic phase evolves with time, the slope of the parton directed flow at
midrapidity region changes from negative to positive as a result of the later
dynamics at 200 GeV, while it remains negative at 39 GeV due to the shorter
life time of the partonic phase. The directed flow splitting for various quark
species due to their different initial eccentricities is observed at 39 GeV,
while the splitting is very small at 200 GeV. From a dynamical coalescence
algorithm with Wigner functions, we found that the directed flow of hadrons is
a result of competition between the coalescence in momentum and coordinate
space as well as further modifications by the hadronic rescatterings.Comment: 8 pages, 8 figures, version after major revisio
Cluster-guided Asymmetric Contrastive Learning for Unsupervised Person Re-Identification
Unsupervised person re-identification (Re-ID) aims to match pedestrian images
from different camera views in unsupervised setting. Existing methods for
unsupervised person Re-ID are usually built upon the pseudo labels from
clustering. However, the quality of clustering depends heavily on the quality
of the learned features, which are overwhelmingly dominated by the colors in
images especially in the unsupervised setting. In this paper, we propose a
Cluster-guided Asymmetric Contrastive Learning (CACL) approach for unsupervised
person Re-ID, in which cluster structure is leveraged to guide the feature
learning in a properly designed asymmetric contrastive learning framework. To
be specific, we propose a novel cluster-level contrastive loss to help the
siamese network effectively mine the invariance in feature learning with
respect to the cluster structure within and between different data augmentation
views, respectively. Extensive experiments conducted on three benchmark
datasets demonstrate superior performance of our proposal
MaskCL: Semantic Mask-Driven Contrastive Learning for Unsupervised Person Re-Identification with Clothes Change
This paper considers a novel and challenging problem: unsupervised long-term
person re-identification with clothes change. Unfortunately, conventional
unsupervised person re-id methods are designed for short-term cases and thus
fail to perceive clothes-independent patterns due to simply being driven by RGB
prompt. To tackle with such a bottleneck, we propose a semantic mask-driven
contrastive learning approach, in which silhouette masks are embedded into
contrastive learning framework as the semantic prompts and cross-clothes
invariance is learnt from hierarchically semantic neighbor structure by
combining both RGB and semantic features in a two-branches network. Since such
a challenging re-id task setting is investigated for the first time, we
conducted extensive experiments to evaluate state-of-the-art unsupervised
short-term person re-id methods on five widely-used clothes-change re-id
datasets. Experimental results verify that our approach outperforms the
unsupervised re-id competitors by a clear margin, remaining a narrow gap to the
supervised baselines
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