175 research outputs found
Error analysis of energy-conservative BDF2-FE scheme for the 2D Navier-Stokes equations with variable density
In this paper, we present an error estimate of a second-order linearized
finite element (FE) method for the 2D Navier-Stokes equations with variable
density. In order to get error estimates, we first introduce an equivalent form
of the original system. Later, we propose a general BDF2-FE method for solving
this equivalent form, where the Taylor-Hood FE space is used for discretizing
the Navier-Stokes equations and conforming FE space is used for discretizing
density equation. We show that our scheme ensures discrete energy dissipation.
Under the assumption of sufficient smoothness of strong solutions, an error
estimate is presented for our numerical scheme for variable density
incompressible flow in two dimensions. Finally, some numerical examples are
provided to confirm our theoretical results.Comment: 22 pages, 1 figure
SSformer: A Lightweight Transformer for Semantic Segmentation
It is well believed that Transformer performs better in semantic segmentation
compared to convolutional neural networks. Nevertheless, the original Vision
Transformer may lack of inductive biases of local neighborhoods and possess a
high time complexity. Recently, Swin Transformer sets a new record in various
vision tasks by using hierarchical architecture and shifted windows while being
more efficient. However, as Swin Transformer is specifically designed for image
classification, it may achieve suboptimal performance on dense prediction-based
segmentation task. Further, simply combing Swin Transformer with existing
methods would lead to the boost of model size and parameters for the final
segmentation model. In this paper, we rethink the Swin Transformer for semantic
segmentation, and design a lightweight yet effective transformer model, called
SSformer. In this model, considering the inherent hierarchical design of Swin
Transformer, we propose a decoder to aggregate information from different
layers, thus obtaining both local and global attentions. Experimental results
show the proposed SSformer yields comparable mIoU performance with
state-of-the-art models, while maintaining a smaller model size and lower
compute
UperFormer: A Multi-scale Transformer-based Decoder for Semantic Segmentation
While a large number of recent works on semantic segmentation focus on
designing and incorporating a transformer-based encoder, much less attention
and vigor have been devoted to transformer-based decoders. For such a task
whose hallmark quest is pixel-accurate prediction, we argue that the decoder
stage is just as crucial as that of the encoder in achieving superior
segmentation performance, by disentangling and refining the high-level cues and
working out object boundaries with pixel-level precision. In this paper, we
propose a novel transformer-based decoder called UperFormer, which is
plug-and-play for hierarchical encoders and attains high quality segmentation
results regardless of encoder architecture. UperFormer is equipped with
carefully designed multi-head skip attention units and novel upsampling
operations. Multi-head skip attention is able to fuse multi-scale features from
backbones with those in decoders. The upsampling operation, which incorporates
feature from encoder, can be more friendly for object localization. It brings a
0.4% to 3.2% increase compared with traditional upsampling methods. By
combining UperFormer with Swin Transformer (Swin-T), a fully transformer-based
symmetric network is formed for semantic segmentation tasks. Extensive
experiments show that our proposed approach is highly effective and
computationally efficient. On Cityscapes dataset, we achieve state-of-the-art
performance. On the more challenging ADE20K dataset, our best model yields a
single-scale mIoU of 50.18, and a multi-scale mIoU of 51.8, which is on-par
with the current state-of-art model, while we drastically cut the number of
FLOPs by 53.5%. Our source code and models are publicly available at:
https://github.com/shiwt03/UperForme
Human-machine Interactive Tissue Prototype Learning for Label-efficient Histopathology Image Segmentation
Recently, deep neural networks have greatly advanced histopathology image
segmentation but usually require abundant annotated data. However, due to the
gigapixel scale of whole slide images and pathologists' heavy daily workload,
obtaining pixel-level labels for supervised learning in clinical practice is
often infeasible. Alternatively, weakly-supervised segmentation methods have
been explored with less laborious image-level labels, but their performance is
unsatisfactory due to the lack of dense supervision. Inspired by the recent
success of self-supervised learning methods, we present a label-efficient
tissue prototype dictionary building pipeline and propose to use the obtained
prototypes to guide histopathology image segmentation. Particularly, taking
advantage of self-supervised contrastive learning, an encoder is trained to
project the unlabeled histopathology image patches into a discriminative
embedding space where these patches are clustered to identify the tissue
prototypes by efficient pathologists' visual examination. Then, the encoder is
used to map the images into the embedding space and generate pixel-level pseudo
tissue masks by querying the tissue prototype dictionary. Finally, the pseudo
masks are used to train a segmentation network with dense supervision for
better performance. Experiments on two public datasets demonstrate that our
human-machine interactive tissue prototype learning method can achieve
comparable segmentation performance as the fully-supervised baselines with less
annotation burden and outperform other weakly-supervised methods. Codes will be
available upon publication.Comment: IPMI2023 camera read
PHTrans: Parallelly Aggregating Global and Local Representations for Medical Image Segmentation
The success of Transformer in computer vision has attracted increasing
attention in the medical imaging community. Especially for medical image
segmentation, many excellent hybrid architectures based on convolutional neural
networks (CNNs) and Transformer have been presented and achieve impressive
performance. However, most of these methods, which embed modular Transformer
into CNNs, struggle to reach their full potential. In this paper, we propose a
novel hybrid architecture for medical image segmentation called PHTrans, which
parallelly hybridizes Transformer and CNN in main building blocks to produce
hierarchical representations from global and local features and adaptively
aggregate them, aiming to fully exploit their strengths to obtain better
segmentation performance. Specifically, PHTrans follows the U-shaped
encoder-decoder design and introduces the parallel hybird module in deep
stages, where convolution blocks and the modified 3D Swin Transformer learn
local features and global dependencies separately, then a sequence-to-volume
operation unifies the dimensions of the outputs to achieve feature aggregation.
Extensive experimental results on both Multi-Atlas Labeling Beyond the Cranial
Vault and Automated Cardiac Diagnosis Challeng datasets corroborate its
effectiveness, consistently outperforming state-of-the-art methods. The code is
available at: https://github.com/lseventeen/PHTrans.Comment: 10 pages, 3 figure
Earth’s changing global atmospheric energy cycle in response to climate change
The Lorenz energy cycle is widely used to investigate atmospheres and climates on planets. However, the long-term temporal variations of such an energy cycle have not yet been explored. Here we use three independent meteorological data sets from the modern satellite era, to examine the temporal characteristics of the Lorenz energy cycle of Earth’s global atmosphere in response to climate change. The total mechanical energy of the global atmosphere basically remains constant with time, but the global-average eddy energies show significant positive trends. The spatial investigations suggest that these positive trends are concentrated in the Southern Hemisphere. Significant positive trends are also found in the conversion, generation and dissipation rates of energies. The positive trends in the dissipation rates of kinetic energies suggest that the efficiency of the global atmosphere as a heat engine increased during the modern satellite era
ICG fluorescence imaging technology in laparoscopic liver resection for primary liver cancer: A meta-analysis
Objective:
To study the value of ICG molecular fluorescence imaging in laparoscopic hepatectomy for PLC.
Methods:
CNKI, WD, VIP.com, PM, CL and WOS databases were selected to search for literature on precise and traditional hepatectomy for the treatment of PLC.
Results:
A total of 33 articles were used, including 3987 patients, 2102 in precision and 1885 in traditional. Meta showed that the operation time of precision was longer, while IBV, HS, PLFI, ALT, TBil, ALB, PCR, PROSIM, RMR and 1-year SR had advantages.
Conclusion:
Hepatectomy with the concept of PS is a safe and effective method of PLC that can reduce the amount of IB, reduce surgery, reduce PC and improve prognosis and quality of life
A systematic review of the effectiveness of online learning in higher education during the COVID-19 pandemic period
BackgroundThe effectiveness of online learning in higher education during the COVID-19 pandemic period is a debated topic but a systematic review on this topic is absent.MethodsThe present study implemented a systematic review of 25 selected articles to comprehensively evaluate online learning effectiveness during the pandemic period and identify factors that influence such effectiveness.ResultsIt was concluded that past studies failed to achieve a consensus over online learning effectiveness and research results are largely by how learning effectiveness was assessed, e.g., self-reported online learning effectiveness, longitudinal comparison, and RCT. Meanwhile, a set of factors that positively or negatively influence the effectiveness of online learning were identified, including infrastructure factors, instructional factors, the lack of social interaction, negative emotions, flexibility, and convenience.DiscussionAlthough it is debated over the effectiveness of online learning during the pandemic period, it is generally believed that the pandemic brings a lot of challenges and difficulties to higher education and these challenges and difficulties are more prominent in developing countries. In addition, this review critically assesses limitations in past research, develops pedagogical implications, and proposes recommendations for future research
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