210 research outputs found
Learning State-Space Models for Mapping Spatial Motion Patterns
Mapping the surrounding environment is essential for the successful operation
of autonomous robots. While extensive research has focused on mapping geometric
structures and static objects, the environment is also influenced by the
movement of dynamic objects. Incorporating information about spatial motion
patterns can allow mobile robots to navigate and operate successfully in
populated areas. In this paper, we propose a deep state-space model that learns
the map representations of spatial motion patterns and how they change over
time at a certain place. To evaluate our methods, we use two different
datasets: one generated dataset with specific motion patterns and another with
real-world pedestrian data. We test the performance of our model by evaluating
its learning ability, mapping quality, and application to downstream tasks. The
results demonstrate that our model can effectively learn the corresponding
motion pattern, and has the potential to be applied to robotic application
tasks.Comment: 6 pages, 5 figures, to be published in ECMR 2023 conference
proceeding
Provable Guarantees for Neural Networks via Gradient Feature Learning
Neural networks have achieved remarkable empirical performance, while the
current theoretical analysis is not adequate for understanding their success,
e.g., the Neural Tangent Kernel approach fails to capture their key feature
learning ability, while recent analyses on feature learning are typically
problem-specific. This work proposes a unified analysis framework for two-layer
networks trained by gradient descent. The framework is centered around the
principle of feature learning from gradients, and its effectiveness is
demonstrated by applications in several prototypical problems, such as mixtures
of Gaussians and parity functions. The framework also sheds light on
interesting network learning phenomena such as feature learning beyond kernels
and the lottery ticket hypothesis.Comment: NeurIPS 2023, 71 page
The Minimization of Piecewise Functions: Pseudo Stationarity
There are many significant applied contexts that require the solution of
discontinuous optimization problems in finite dimensions. Yet these problems
are very difficult, both computationally and analytically. With the functions
being discontinuous and a minimizer (local or global) of the problems, even if
it exists, being impossible to verifiably compute, a foremost question is what
kind of ''stationary solutions'' one can expect to obtain; these solutions
provide promising candidates for minimizers; i.e., their defining conditions
are necessary for optimality. Motivated by recent results on sparse
optimization, we introduce in this paper such a kind of solution, termed
''pseudo B- (for Bouligand) stationary solution'', for a broad class of
discontinuous piecewise continuous optimization problems with objective and
constraint defined by indicator functions of the positive real axis composite
with functions that are possibly nonsmooth. We present two approaches for
computing such a solution. One approach is based on lifting the problem to a
higher dimension via the epigraphical formulation of the indicator functions;
this requires the addition of some auxiliary variables. The other approach is
based on certain continuous (albeit not necessarily differentiable) piecewise
approximations of the indicator functions and the convergence to a pseudo
B-stationary solution of the original problem is established. The conditions
for convergence are discussed and illustrated by an example
Towards Few-Shot Adaptation of Foundation Models via Multitask Finetuning
Foundation models have emerged as a powerful tool for many AI problems.
Despite the tremendous success of foundation models, effective adaptation to
new tasks, particularly those with limited labels, remains an open question and
lacks theoretical understanding. An emerging solution with recent success in
vision and NLP involves finetuning a foundation model on a selection of
relevant tasks, before its adaptation to a target task with limited labeled
samples. In this paper, we study the theoretical justification of this
multitask finetuning approach. Our theoretical analysis reveals that with a
diverse set of related tasks, this multitask finetuning leads to reduced error
in the target task, in comparison to directly adapting the same pretrained
model. We quantify the relationship between finetuning tasks and target tasks
by diversity and consistency metrics, and further propose a practical task
selection algorithm. We substantiate our theoretical claims with extensive
empirical evidence. Further, we present results affirming our task selection
algorithm adeptly chooses related finetuning tasks, providing advantages to the
model performance on target tasks. We believe our study shed new light on the
effective adaptation of foundation models to new tasks that lack abundant
labels. Our code is available at
https://github.com/OliverXUZY/Foudation-Model_Multitask.Comment: Published at ICLR 2024. 54 page
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Fabrication of densified wood via synergy of chemical pretreatment, hot-pressing and post mechanical fixation
Article describes examination of the appearance, color, chemical composition, and physiology and mechanical properties of densified Abies wood before and after densification treatment using a colorimeter, FTIR and mechanical testing machine
Nonlinear Gossip Algorithms for Wireless Sensor Networks
We study some nonlinear gossip algorithms for wireless sensor networks. Firstly, two types of nonlinear single gossip algorithms are proposed. By using Lyapunov theory, Lagrange mean value theorem, and stochastic Lasalle’s invariance principle, we prove that the nonlinear single gossip algorithms can converge to the average of initial states with probability one. Secondly, two types of nonlinear multigossip algorithms are also presented and the convergence is proved by the same methods. Finally, computer simulation is also given to show the validity of the theoretical results
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In Situ TEM Study of the Degradation of PbSe Nanocrystals in Air
PbSe
nanocrystals have attracted widespread attention due to a
variety of potential applications. However, the practical utility
of these nanocrystals has been hindered by their poor air stability,
which induces undesired changes in the optical and electronic properties.
An understanding of the degradation of PbSe nanocrystals when they
are exposed to air is critical for improving the stability and enhancing
their applications. Here, we use in situ transmission electron microscopy
(TEM) with an environmental cell connected to air to study PbSe nanocrystal
degradation triggered by air exposure. We have also conducted a series
of complementary studies, including in situ environmental TEM study
of PbSe nanocrystals exposed to pure oxygen and PbSe nanocrystals
in H2O using a liquid cell, and ex situ experiments, such
as O2 plasma treatment and thermal heating of PbSe nanocrystals
under different air exposure. Our in situ observations reveal that
when PbSe nanocrystals are exposed to air (or oxygen) under electron
beam irradiation, they experience a series of changes, including shape
evolution of individual nanocrystals with the cuboid intermediates,
coalescence between nanocrystals, and formation of PbSe thin films
through drastic solid-state fusion. Further studies show that the
PbSe thin films transform into an amorphous Pb rich phase or eventually
pure Pb, which suggest that Se reacts with oxygen and can be evaporated
under electron beam illumination. These various in situ and ex situ
experimental results indicate that PbSe nanocrystal degradation in
air is initiated by the dissociation and removal of ligands from the
PbSe nanocrystal surface
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