349 research outputs found
Periodic solutions for a porous medium equation
In this paper, we study with a periodic porous medium equation with nonlinear convection terms and weakly nonlinear sources under Dirichlet boundary conditions. Based on the theory of Leray-Shauder fixed point theorem, we establish the existence of periodic solutions
Coherence-Assisted Superradiant Laser with Hz Linewidth and W Power
The superradiant laser, based on the clock transition between the electric
ground state S and the metastable state P of fermionic
alkaline-earth(-like) atoms, has been proposed to be a new promising light
source with linewidth being the order of millihertz. However, due to the small
S-to-P transition strength, the steady-state power in that
system is relatively low (W). In this work, we propose an
alternative superradiant laser scheme based on a Raman-transition-induced
coupling between the P and P states in bosonic
alkaline-earth(-like) atoms, and achieve a laser with linewidth Hz and power W ( photons in steady
state) at a small pumping cost. The Raman beams play two significant roles in
our scheme. First, the coherence between the dark and bright states induced by
the Raman beams produce a new local minimum in the pumping-linewidth curve with
pumping rate lower than kHz, which is beneficial for continuous
output. Second, the Raman beams mix the long-lived P state into the
lasing state and thus reduce the linewidth. Our work greatly improves the
output performance of the superradiant laser system with coherence induced by
Raman transitions and may offer a firm foundation for its practical use in
future
Image Denoising via Nonlinear Hybrid Diffusion
A nonlinear anisotropic hybrid diffusion equation is discussed for image denoising, which is a combination of mean curvature smoothing and Gaussian heat diffusion. First, we propose a new edge detection indicator, that is, the diffusivity function. Based on this diffusivity function, the new diffusion is nonlinear anisotropic and forward-backward. Unlike the Perona-Malik (PM) diffusion, the new forward-backward diffusion is adjustable and under control. Then, the existence, uniqueness, and long-time behavior of the new regularization equation of the model are established. Finally, using the explicit difference scheme (PM scheme) and implicit difference scheme (AOS scheme), we do numerical experiments for different images, respectively. Experimental results illustrate the effectiveness of the new model with respect to other known models
SaaFormer: Spectral-spatial Axial Aggregation Transformer for Hyperspectral Image Classification
Hyperspectral images (HSI) captured from earth observing satellites and
aircraft is becoming increasingly important for applications in agriculture,
environmental monitoring, mining, etc. Due to the limited available
hyperspectral datasets, the pixel-wise random sampling is the most commonly
used training-test dataset partition approach, which has significant overlap
between samples in training and test datasets. Furthermore, our experimental
observations indicates that regions with larger overlap often exhibit higher
classification accuracy. Consequently, the pixel-wise random sampling approach
poses a risk of data leakage. Thus, we propose a block-wise sampling method to
minimize the potential for data leakage. Our experimental findings also confirm
the presence of data leakage in models such as 2DCNN. Further, We propose a
spectral-spatial axial aggregation transformer model, namely SaaFormer, to
address the challenges associated with hyperspectral image classifier that
considers HSI as long sequential three-dimensional images. The model comprises
two primary components: axial aggregation attention and multi-level
spectral-spatial extraction. The axial aggregation attention mechanism
effectively exploits the continuity and correlation among spectral bands at
each pixel position in hyperspectral images, while aggregating spatial
dimension features. This enables SaaFormer to maintain high precision even
under block-wise sampling. The multi-level spectral-spatial extraction
structure is designed to capture the sensitivity of different material
components to specific spectral bands, allowing the model to focus on a broader
range of spectral details. The results on six publicly available datasets
demonstrate that our model exhibits comparable performance when using random
sampling, while significantly outperforming other methods when employing
block-wise sampling partition.Comment: arXiv admin note: text overlap with arXiv:2107.02988 by other author
The Position and Function of Macroscopic Analysis in the Failure Analysis of Railway Fasteners
Macroscopic analysis plays an important role in failure analysis, which cannot be replaced by other analyzing methods. In recent years, with the development of characterization techniques, more and more engineers and technicians rely on the advanced analytical testing methods in the process of failure analysis, ignoring the methods and means of macroscopic analysis. This can easily lead to some wrong judgments. Therefore, this chapter will combine with the cases to explain the position and role of macroanalysis in the failure analysis of rail fastening clips and to offer references for engineers and technicians in relevant fields
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