169 research outputs found
Large traveling capillary-gravity waves for Darcy flow
We study capillary-gravity and capillary surface waves for fluid flows
governed by Darcy's law. This includes flows in vertical Hele-Shaw cells and in
porous media (the one-phase Muskat problem) with finite or infinite depth. The
free boundary is acted upon by an external pressure posited to be in traveling
wave form with an arbitrary periodic profile and an amplitude parameter. For
any given wave speed, we first prove that there exists a unique local curve of
small periodic traveling waves corresponding to small values of the parameter.
Then we prove that as the parameter increases but could possibly be bounded,
the curve belongs to a connected set of traveling waves. The set
contains traveling waves that either have arbitrarily large
gradients or are arbitrarily close to the rigid bottom in the finite depth
case. To the best of our knowledge, this is the first construction of large
traveling surface waves for a viscous free boundary problem.Comment: 25 page
Traveling wave solutions to the one-phase Muskat problem: existence and stability
We study the Muskat problem for one fluid in arbitrary dimension, bounded
below by a flat bed and above by a free boundary given as a graph. In addition
to a fixed uniform gravitational field, the fluid is acted upon by a generic
force field in the bulk and an external pressure on the free boundary, both of
which are posited to be in traveling wave form. We prove that for sufficiently
small force and pressure data in Sobolev spaces, there exists a locally unique
traveling wave solution in Sobolev-type spaces. The free boundary of the
traveling wave solutions is either periodic or asymptotically flat at spatial
infinity. Moreover, we prove that small periodic traveling wave solutions
induced by external pressure only are asymptotically stable. These results
provide the first class of nontrivial stable solutions for the problem.Comment: Funding source for H. Q. N. correcte
Enhancing Few-shot Image Classification with Cosine Transformer
This paper addresses the few-shot image classification problem, where the
classification task is performed on unlabeled query samples given a small
amount of labeled support samples only. One major challenge of the few-shot
learning problem is the large variety of object visual appearances that
prevents the support samples to represent that object comprehensively. This
might result in a significant difference between support and query samples,
therefore undermining the performance of few-shot algorithms. In this paper, we
tackle the problem by proposing Few-shot Cosine Transformer (FS-CT), where the
relational map between supports and queries is effectively obtained for the
few-shot tasks. The FS-CT consists of two parts, a learnable prototypical
embedding network to obtain categorical representations from support samples
with hard cases, and a transformer encoder to effectively achieve the
relational map from two different support and query samples. We introduce
Cosine Attention, a more robust and stable attention module that enhances the
transformer module significantly and therefore improves FS-CT performance from
5% to over 20% in accuracy compared to the default scaled dot-product
mechanism. Our method performs competitive results in mini-ImageNet, CUB-200,
and CIFAR-FS on 1-shot learning and 5-shot learning tasks across backbones and
few-shot configurations. We also developed a custom few-shot dataset for Yoga
pose recognition to demonstrate the potential of our algorithm for practical
application. Our FS-CT with cosine attention is a lightweight, simple few-shot
algorithm that can be applied for a wide range of applications, such as
healthcare, medical, and security surveillance. The official implementation
code of our Few-shot Cosine Transformer is available at
https://github.com/vinuni-vishc/Few-Shot-Cosine-Transforme
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