4,868 research outputs found
Deformable Overset Grid for Multibody Unsteady Flow Simulation
A deformable overset grid method is proposed to simulate the unsteady aerodynamic problems with multiple flexible moving bodies. This method uses an unstructured overset grid coupled with local mesh deformation to achieve both robustness and efficiency. The overset grid hierarchically organizes the subgrids into clusters and layers, allowing for overlapping/embedding of different type meshes, in which the mesh quality and resolution can be independently controlled. At each time step, mesh deformation is locally applied to the subgrids associated with deforming bodies by an improved Delaunay graph mapping method that uses a very coarse Delaunay mesh as the background graph. The graph is moved and deformed by the spring analogy method according to the specified motion, and then the computational meshes are relocated by a simple one-to-one mapping. An efficient implicit hole-cutting and intergrid boundary definition procedure is implemented fully automatically for both cell-centered and cell-vertex schemes based on the wall distance and an alternative digital tree data search algorithm. This method is successfully applied to several complex multibody unsteady aerodynamic simulations, and the results demonstrate the robustness and efficiency of the proposed method for complex unsteady flow problems, particularly for those involving simultaneous large relative motion and self-deformation
A Diffusion model for POI recommendation
Next Point-of-Interest (POI) recommendation is a critical task in
location-based services that aim to provide personalized suggestions for the
user's next destination. Previous works on POI recommendation have laid focused
on modeling the user's spatial preference. However, existing works that
leverage spatial information are only based on the aggregation of users'
previous visited positions, which discourages the model from recommending POIs
in novel areas. This trait of position-based methods will harm the model's
performance in many situations. Additionally, incorporating sequential
information into the user's spatial preference remains a challenge. In this
paper, we propose Diff-POI: a Diffusion-based model that samples the user's
spatial preference for the next POI recommendation. Inspired by the wide
application of diffusion algorithm in sampling from distributions, Diff-POI
encodes the user's visiting sequence and spatial character with two
tailor-designed graph encoding modules, followed by a diffusion-based sampling
strategy to explore the user's spatial visiting trends. We leverage the
diffusion process and its reversed form to sample from the posterior
distribution and optimized the corresponding score function. We design a joint
training and inference framework to optimize and evaluate the proposed
Diff-POI. Extensive experiments on four real-world POI recommendation datasets
demonstrate the superiority of our Diff-POI over state-of-the-art baseline
methods. Further ablation and parameter studies on Diff-POI reveal the
functionality and effectiveness of the proposed diffusion-based sampling
strategy for addressing the limitations of existing methods
RAHNet: Retrieval Augmented Hybrid Network for Long-tailed Graph Classification
Graph classification is a crucial task in many real-world multimedia
applications, where graphs can represent various multimedia data types such as
images, videos, and social networks. Previous efforts have applied graph neural
networks (GNNs) in balanced situations where the class distribution is
balanced. However, real-world data typically exhibit long-tailed class
distributions, resulting in a bias towards the head classes when using GNNs and
limited generalization ability over the tail classes. Recent approaches mainly
focus on re-balancing different classes during model training, which fails to
explicitly introduce new knowledge and sacrifices the performance of the head
classes. To address these drawbacks, we propose a novel framework called
Retrieval Augmented Hybrid Network (RAHNet) to jointly learn a robust feature
extractor and an unbiased classifier in a decoupled manner. In the feature
extractor training stage, we develop a graph retrieval module to search for
relevant graphs that directly enrich the intra-class diversity for the tail
classes. Moreover, we innovatively optimize a category-centered supervised
contrastive loss to obtain discriminative representations, which is more
suitable for long-tailed scenarios. In the classifier fine-tuning stage, we
balance the classifier weights with two weight regularization techniques, i.e.,
Max-norm and weight decay. Experiments on various popular benchmarks verify the
superiority of the proposed method against state-of-the-art approaches.Comment: Accepted by the ACM International Conference on Multimedia (MM) 202
ALEX: Towards Effective Graph Transfer Learning with Noisy Labels
Graph Neural Networks (GNNs) have garnered considerable interest due to their
exceptional performance in a wide range of graph machine learning tasks.
Nevertheless, the majority of GNN-based approaches have been examined using
well-annotated benchmark datasets, leading to suboptimal performance in
real-world graph learning scenarios. To bridge this gap, the present paper
investigates the problem of graph transfer learning in the presence of label
noise, which transfers knowledge from a noisy source graph to an unlabeled
target graph. We introduce a novel technique termed Balance Alignment and
Information-aware Examination (ALEX) to address this challenge. ALEX first
employs singular value decomposition to generate different views with crucial
structural semantics, which help provide robust node representations using
graph contrastive learning. To mitigate both label shift and domain shift, we
estimate a prior distribution to build subgraphs with balanced label
distributions. Building on this foundation, an adversarial domain discriminator
is incorporated for the implicit domain alignment of complex multi-modal
distributions. Furthermore, we project node representations into a different
space, optimizing the mutual information between the projected features and
labels. Subsequently, the inconsistency of similarity structures is evaluated
to identify noisy samples with potential overfitting. Comprehensive experiments
on various benchmark datasets substantiate the outstanding superiority of the
proposed ALEX in different settings.Comment: Accepted by the ACM International Conference on Multimedia (MM) 202
Intermediate Levels of Hippocampal Activity Appear Optimal for Associative Memory Formation
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87971.pdf (publisher's version ) (Open Access
Kernel-based Substructure Exploration for Next POI Recommendation
Point-of-Interest (POI) recommendation, which benefits from the proliferation
of GPS-enabled devices and location-based social networks (LBSNs), plays an
increasingly important role in recommender systems. It aims to provide users
with the convenience to discover their interested places to visit based on
previous visits and current status. Most existing methods usually merely
leverage recurrent neural networks (RNNs) to explore sequential influences for
recommendation. Despite the effectiveness, these methods not only neglect
topological geographical influences among POIs, but also fail to model
high-order sequential substructures. To tackle the above issues, we propose a
Kernel-Based Graph Neural Network (KBGNN) for next POI recommendation, which
combines the characteristics of both geographical and sequential influences in
a collaborative way. KBGNN consists of a geographical module and a sequential
module. On the one hand, we construct a geographical graph and leverage a
message passing neural network to capture the topological geographical
influences. On the other hand, we explore high-order sequential substructures
in the user-aware sequential graph using a graph kernel neural network to
capture user preferences. Finally, a consistency learning framework is
introduced to jointly incorporate geographical and sequential information
extracted from two separate graphs. In this way, the two modules effectively
exchange knowledge to mutually enhance each other. Extensive experiments
conducted on two real-world LBSN datasets demonstrate the superior performance
of our proposed method over the state-of-the-arts. Our codes are available at
https://github.com/Fang6ang/KBGNN.Comment: Accepted by the IEEE International Conference on Data Mining (ICDM)
202
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