210 research outputs found
Fabrication of binder-free ultrafine WC-6CO composites by coupled multi-physical fields activation technology
A novel sintering method, named as coupled multi-physical fields activation technology, has been introduced for the forming of various material powder systems. Compared with the conventional ones, this technique presents more advantages: lower sintering temperature, shorter forming time, and remarkable inhibition of the grains coarsening. In the study, the cylinders of Φ4.0mm×4.0mm had been formed with ultrafine WC-6Co powders. The relative properties of sintered WC-6Co cemented carbides, such as hardness and the microstructures, had been obtained. The study has shown that a relative density, 97.80%, of the formed samples, could been achieved when the case of temperature 850℃, heating rate 50℃/s, pressure 75MPa and Electro-heating loop 6 times, were used. More importantly, the circumscription for the growth of grain size of WC, attributed to the effect of electrical field, renders coupled multi-physical fields activation technology applicable for getting WC-6Co cemented carbides with fine grain size and good properties
A new densification mechanism of copper powder sintered under an electrical field
A new sintering mechanism is revealed for copper powder sintered under the influence of an electrical field and a force field during the formation of microcomponents. Analysis of the microstructure and grain boundary evolution of the sintered samples showed that the disappearance of the interface at contact areas between particles is a continuous process which involves new grain formation and grain refinement during this innovative microsintering process. The densification process is therefore different from what is known in a conventional powder sintering process
Robust Quantitative Susceptibility Mapping via Approximate Message Passing
Purpose: It is challenging to recover magnetic susceptibility in the presence
of phase errors, which may be caused by noise or strong local-susceptibility
shifts in cases of brain hemorrhage and calcification. We propose a Bayesian
formulation for quantitative susceptibility mapping (QSM) where a customized
Gaussian-mixture distribution is used to model the long-tailed noise
distribution.
Theory: Complex exponential functions of the phase are used as nonlinear
measurements. Wavelet coefficients of the susceptibility map are modeled by the
Laplace distribution. Measurement noise is modeled by a two-component
Gaussian-mixture distribution, where the second component is reserved to model
the noise outliers. The susceptibility map and distribution parameters are
jointly recovered using approximate message passing (AMP).
Methods: The proposed AMP with built-in parameter estimation (AMP-PE) is
compared with the state-of-the-art nonlinear L1-QSM and MEDI approaches that
adopt the L1-norm and L2-norm data-fidelity terms respectively. They are tested
on the simulated and in vivo datasets.
Results: On the simulated Sim2Snr1 dataset, AMP-PE achieved the lowest NRMSE
and SSIM, MEDI achieved the lowest HFEN. On the in vivo datasets, AMP-PE is
more robust and better at preserving structural details and removing streaking
artifacts in the hemorrhage cases than L1-QSM and MEDI.
Conclusion: By leveraging a customized Gaussian-mixture noise prior, AMP-PE
achieves better performance in challenging cases of brain hemorrhage and
calcification. It is equipped with built-in parameter estimation, which avoids
subjective bias from the usual visual-tuning step of in vivo reconstruction.Comment: Keywords: Approximate message passing, Compressive sensing, Parameter
estimation, QS
Model-based T1, T2* and Proton Density Mapping Using a Bayesian Approach with Parameter Estimation and Complementary Undersampling Patterns
Purpose: To achieve automatic hyperparameter estimation for the joint
recovery of quantitative MR images, we propose a Bayesian formulation of the
reconstruction problem that incorporates the signal model. Additionally, we
investigate the use of complementary undersampling patterns to determine
optimal undersampling schemes for quantitative MRI.
Theory: We introduce a novel nonlinear approximate message passing framework,
referred to as ``AMP-PE'', that enables the simultaneous recovery of
distribution parameters and quantitative maps.
Methods: We employed the variable flip angle multi-echo (VFA-ME) method to
acquire measurements. Both retrospective and prospective undersampling
approaches were utilized to obtain Fourier measurements using variable-density
and Poisson-disk patterns. Furthermore, we extensively explored various
undersampling schemes, incorporating complementary patterns across different
flip angles and/or echo times.
Results: AMP-PE adopts a model-based joint recovery strategy, it outperforms
the -norm minimization approach that follows a decoupled recovery
strategy. A comparison with an existing joint-recovery approach further
demonstrates the advantageous outcomes of AMP-PE. For quantitative
mapping using VFA-ME, employing identical k-space sampling patterns across
different echo times produced the best performance. Whereas for and
proton density mappings, using complementary sampling patterns across different
flip angles yielded the best performance.
Conclusion: AMP-PE is equipped with built-in parameter estimation, and works
naturally in clinical settings with varying acquisition protocols and scanners.
It also achieves improved performance by combining information from the MR
signal model and the sparse prior on images
Volatile Component Analysis of Michelia alba Leaves and Their Effect on Fumigation Activity and Worker Behavior of Solenopsis invicta
Volatile compounds from mashed (fresh, fallen, and dried) leaves ofMichelia alba were collected via solid-phase microextraction and werethen identified via gas chromatography-mass spectrometry. The resultsshowed that linalool was the dominant component in different leaves,together with caryophyllene, β-elemene, and selinene, the contents ofwhich vary across the samples. The fumigation bioassay results showedthat the volatiles from M. alba leaves exhibited insecticidal activity againstred imported fire ant workers, and the mortality of workers could reachup to 100% after the fallen leaves were treated for 16 h. Mashed freshleaves could effectively reduce the aggregation and drinking ability ofworkers. The volatile substances released from the mashed leaves mightkill the ants, or affect their behavior and weaken the activity by interferingtransmit information between ants. A comprehensive consideration ofthe economic and ecological value of M. alba shows that fallen leavesmight be a good resource to control red imported fire ant
Attention Where It Matters: Rethinking Visual Document Understanding with Selective Region Concentration
We propose a novel end-to-end document understanding model called SeRum
(SElective Region Understanding Model) for extracting meaningful information
from document images, including document analysis, retrieval, and office
automation.
Unlike state-of-the-art approaches that rely on multi-stage technical schemes
and are computationally expensive,
SeRum converts document image understanding and recognition tasks into a
local decoding process of the visual tokens of interest, using a content-aware
token merge module.
This mechanism enables the model to pay more attention to regions of interest
generated by the query decoder, improving the model's effectiveness and
speeding up the decoding speed of the generative scheme.
We also designed several pre-training tasks to enhance the understanding and
local awareness of the model.
Experimental results demonstrate that SeRum achieves state-of-the-art
performance on document understanding tasks and competitive results on text
spotting tasks.
SeRum represents a substantial advancement towards enabling efficient and
effective end-to-end document understanding.Comment: Accepted to ICCV 2023 main conferenc
Identification of Plk4 interacting partners and establishment of Plk4 stable cell lines.
<p>Each error bar is one standard error. CK, control; NN, ambient CO<sub>2</sub> with N fertilizer; CC, elevated CO<sub>2</sub> without N fertilizer; CN, elevated CO<sub>2</sub> with N fertilizer. (a-c) <i>A</i>. <i>acuminatissima</i>; (d-f) <i>S</i>. <i>hancei</i>; (g-i) <i>C</i>. <i>hystrix</i>; (j-l) <i>O</i>. <i>pinnata</i>; (m-o) <i>S</i>. <i>superba</i>.</p
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