462 research outputs found
Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds
Half-Heusler (HH) alloys have attracted considerable interest as promising
thermoelectric (TE) materials in the temperature range around 700 K and above,
which is close to the temperature range of most industrial waste heat sources.
The past few years have seen nanostructuing play an important role in
significantly enhancing the TE performance of several HH alloys. In this
article, we briefly review the recent progress and advances in these HH
nanocomposites. We begin by presenting the structure of HH alloys and the
different strategies that have been utilized for improving the TE properties of
HH alloys. Next, we review the details of HH nanocomposites as obtained by
different techniques. Finally, the review closes by highlighting several
promising strategies for further research directions in these very promising TE
materials.Comment: 34 pages, 22 figure
CtxMIM: Context-Enhanced Masked Image Modeling for Remote Sensing Image Understanding
Learning representations through self-supervision on unlabeled data has
proven highly effective for understanding diverse images. However, remote
sensing images often have complex and densely populated scenes with multiple
land objects and no clear foreground objects. This intrinsic property generates
high object density, resulting in false positive pairs or missing contextual
information in self-supervised learning. To address these problems, we propose
a context-enhanced masked image modeling method (CtxMIM), a simple yet
efficient MIM-based self-supervised learning for remote sensing image
understanding. CtxMIM formulates original image patches as a reconstructive
template and employs a Siamese framework to operate on two sets of image
patches. A context-enhanced generative branch is introduced to provide
contextual information through context consistency constraints in the
reconstruction. With the simple and elegant design, CtxMIM encourages the
pre-training model to learn object-level or pixel-level features on a
large-scale dataset without specific temporal or geographical constraints.
Finally, extensive experiments show that features learned by CtxMIM outperform
fully supervised and state-of-the-art self-supervised learning methods on
various downstream tasks, including land cover classification, semantic
segmentation, object detection, and instance segmentation. These results
demonstrate that CtxMIM learns impressive remote sensing representations with
high generalization and transferability. Code and data will be made public
available
SA-BEV: Generating Semantic-Aware Bird's-Eye-View Feature for Multi-view 3D Object Detection
Recently, the pure camera-based Bird's-Eye-View (BEV) perception provides a
feasible solution for economical autonomous driving. However, the existing
BEV-based multi-view 3D detectors generally transform all image features into
BEV features, without considering the problem that the large proportion of
background information may submerge the object information. In this paper, we
propose Semantic-Aware BEV Pooling (SA-BEVPool), which can filter out
background information according to the semantic segmentation of image features
and transform image features into semantic-aware BEV features. Accordingly, we
propose BEV-Paste, an effective data augmentation strategy that closely matches
with semantic-aware BEV feature. In addition, we design a Multi-Scale
Cross-Task (MSCT) head, which combines task-specific and cross-task information
to predict depth distribution and semantic segmentation more accurately,
further improving the quality of semantic-aware BEV feature. Finally, we
integrate the above modules into a novel multi-view 3D object detection
framework, namely SA-BEV. Experiments on nuScenes show that SA-BEV achieves
state-of-the-art performance. Code has been available at
https://github.com/mengtan00/SA-BEV.git
MOMENT AND LONGITUDINAL RESISTANCE FOR COMPOSITE BEAMS BASED ON STRAIN LIMITED DESIGN METHOD
The bending and longitudinal shear design of composite beams of steel and concrete
follows often the plastic design method, which is a simplification based on rectangle
stress blocks. The application of the plastic design method requires cross-section to have
enough rotation capacity allowing most parts of the critical cross-section reach plastic
at failure. There are different types of compact composite beams, such as the slim-floor
beams. For them, the neutral axis position often gets deeper at failure, which reduces
the rotation capacity and brings questions to the bending resistance and longitudinal
shear design according to the plastic design resistance.
For a composite beam with deep neutral axis position, advanced numerical methods
such as strain-limited design and FEM simulations can provide more accurate results than
the plastic cross-section resistance. However, they are challenging to perform for general
design engineers. In this work, simplified non-linear strain-limited design approaches,
a strain-limited design software "SL.com" and an Abaqus add-in "CivilLab" have been
developed to simplify the numerical calculations. They have also been applied in other
chapters of this work to check the conventional plastic design results and to provide
simplified design rules through parametric studies.
With full shear connection, a deep neutral axis position in composite beam under
sagging bending may cause an important part of the steel section not to reach plastic at
concrete failure. In this case, plastic bending resistance calculated based on rectangle
stress blocks can result in an overestimation of the resistance and therefore leads to
unsafe design. Thus, according to EN1994-1-1 [22], a reduction factor β on plastic
bending resistance (Mpl,Rd) needs to be applied for cross-sections with steel grade S420
and S460 and the relative compression zone height (zpl/h) is over 0.15. However, with the
developments in industry as well as the second generation of Eurocode, this reduction
factor still needs to be updated to consider new types of composite beams and wider
ranges of steel grades.
While the conventional plastic design method has its limitations and only applicable
when the beam cross-section has enough rotation capacity to allow full plastic development, the more advanced strain-limited numerical calculation and FEM can be used
for a much wider range regardless of the position of the neutral axis. The investigations
in this dissertation through comparing the plastic bending resistance with advanced
numerical calculation results, have confirmed that besides the cross-sections with high
steel grades (S420, S460), also certain cross-sections with lower steel grades can have an
overestimated plastic bending moment resistance. At least this effect is more important
for compact cross-section types such as slim-floor sections or composite beams with
asymmetrical structural steel profiles or with a small concrete slab effective width. Therefore vast amount of parametric studies based on strain-limited method and FEM have
been developed to check the topics, such as limitation of plastic design methods for
different types of composite beams. Furthermore new reduction β functions on Mpl,Rd for
engineering practice considering much wider variates of composite beam cross-sections
have been deviated.
For the design with partial shear connection, the partial shear diagram developed based
on plastic analysis has been widely used. As discussed above, the plastic design may
not be suitable when the position of neutral axis is too deep, similar problems can occur
for the partial shear diagram. This problem is especially significant for slim-floor beams,
for which due to the compact cross-section, the relative compression zone height (zpl/h) is usually much higher than conventional composite beams. Thus the limitation of using
the partial shear diagram for slim-floor beams is provided, and additional simplified
engineering design rules are proposed.
Plastic development inside the cross-section increases the longitudinal shear force in the
plastic zones, furthermore with ductile shear connectors and respecting the minimum
degree of shear connection, the non-linear redistribution of longitudinal shear force
allows equal distance arrangement of shear connectors by the conventional design.
For which, the full plastic development of the cross-section allowing plastic bending
moment resistance and ductile shear connectors allowing non-linear longitudinal shear
force distribution are the two fundamental conditions. The deep neutral axis position
brings questions directly to the first assumption, as full plastic development of crosssection may not be able to reach. Thus the impact of a deep neutral axis position in the
composite beams on longitudinal shear force distribution has been analysed. For which,
the influence of plastic development inside beam cross-sections on longitudinal shear
force with full shear interaction is theoretically explained. The different stages of nonlinear distribution of longitudinal shear force due to shear connectors are investigated
through FEM parametric studies. Based on the theoretical and numerical calculation,
the design suggestions of composite beams with deep neutral axis position are given
Iterative Geometry-Aware Cross Guidance Network for Stereo Image Inpainting
Currently, single image inpainting has achieved promising results based on
deep convolutional neural networks. However, inpainting on stereo images with
missing regions has not been explored thoroughly, which is also a significant
but different problem. One crucial requirement for stereo image inpainting is
stereo consistency. To achieve it, we propose an Iterative Geometry-Aware Cross
Guidance Network (IGGNet). The IGGNet contains two key ingredients, i.e., a
Geometry-Aware Attention (GAA) module and an Iterative Cross Guidance (ICG)
strategy. The GAA module relies on the epipolar geometry cues and learns the
geometry-aware guidance from one view to another, which is beneficial to make
the corresponding regions in two views consistent. However, learning guidance
from co-existing missing regions is challenging. To address this issue, the ICG
strategy is proposed, which can alternately narrow down the missing regions of
the two views in an iterative manner. Experimental results demonstrate that our
proposed network outperforms the latest stereo image inpainting model and
state-of-the-art single image inpainting models.Comment: Accepted by IJCAI 202
Reaction characteristics of waste coffee grounds chemical-looping gasification
Coffee grounds in chemical-looping gasification is an innovative handling approach of waste coffee grounds which couple the coffee grounds gasification and chemical looping technology together. By sol-gel method, the Fe4ATP6K1 compound oxygen carrier (OC) modified by KNO3 were prepared with Fe2O3 as an active component, natural attapugite (ATP) as an inert support. The effects of reaction temperature, steam flow as well as O/C molar ratio on coffee grounds in chemical looping gasification (CLG) were investigated in a fluidized bed using steam as gasification agent. It indicated that the Fe4ATP6K1 oxygen carrier could enhance the conversion of coffee grounds. Compared with SiO2 as bed material, the carbon conversion increased in CLG from 71.38% to 86.25%. The optimized conditions were presented as follows: the reaction temperature was 900°C, the water flow was 0.23 g·min-1, the O/C molar ratio was 1. Under these conditions, it was found that the average concentration of H2 reached a maximum value 52.75%, with the syngas production of 1.30 m3·kg-1 and H2 production of 83.79 g·kg-1, respectively. 20 redox cycles demonstrated that the Fe4ATP6K1 oxygen carrier has an excellent cyclic stability, the carbon conversion and cold gas efficiency were both above 75%, while the average gas concentration of gases were nearly stable
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