10,126 research outputs found
Machine learning in solar physics
The application of machine learning in solar physics has the potential to
greatly enhance our understanding of the complex processes that take place in
the atmosphere of the Sun. By using techniques such as deep learning, we are
now in the position to analyze large amounts of data from solar observations
and identify patterns and trends that may not have been apparent using
traditional methods. This can help us improve our understanding of explosive
events like solar flares, which can have a strong effect on the Earth
environment. Predicting hazardous events on Earth becomes crucial for our
technological society. Machine learning can also improve our understanding of
the inner workings of the sun itself by allowing us to go deeper into the data
and to propose more complex models to explain them. Additionally, the use of
machine learning can help to automate the analysis of solar data, reducing the
need for manual labor and increasing the efficiency of research in this field.Comment: 100 pages, 13 figures, 286 references, accepted for publication as a
Living Review in Solar Physics (LRSP
A DeepONet multi-fidelity approach for residual learning in reduced order modeling
In the present work, we introduce a novel approach to enhance the precision
of reduced order models by exploiting a multi-fidelity perspective and
DeepONets. Reduced models provide a real-time numerical approximation by
simplifying the original model. The error introduced by the such operation is
usually neglected and sacrificed in order to reach a fast computation. We
propose to couple the model reduction to a machine learning residual learning,
such that the above-mentioned error can be learned by a neural network and
inferred for new predictions. We emphasize that the framework maximizes the
exploitation of high-fidelity information, using it for building the reduced
order model and for learning the residual. In this work, we explore the
integration of proper orthogonal decomposition (POD), and gappy POD for sensors
data, with the recent DeepONet architecture. Numerical investigations for a
parametric benchmark function and a nonlinear parametric Navier-Stokes problem
are presented
ParGANDA: Making Synthetic Pedestrians A Reality For Object Detection
Object detection is the key technique to a number of Computer Vision
applications, but it often requires large amounts of annotated data to achieve
decent results. Moreover, for pedestrian detection specifically, the collected
data might contain some personally identifiable information (PII), which is
highly restricted in many countries. This label intensive and privacy
concerning task has recently led to an increasing interest in training the
detection models using synthetically generated pedestrian datasets collected
with a photo-realistic video game engine. The engine is able to generate
unlimited amounts of data with precise and consistent annotations, which gives
potential for significant gains in the real-world applications. However, the
use of synthetic data for training introduces a synthetic-to-real domain shift
aggravating the final performance. To close the gap between the real and
synthetic data, we propose to use a Generative Adversarial Network (GAN), which
performsparameterized unpaired image-to-image translation to generate more
realistic images. The key benefit of using the GAN is its intrinsic preference
of low-level changes to geometric ones, which means annotations of a given
synthetic image remain accurate even after domain translation is performed thus
eliminating the need for labeling real data. We extensively experimented with
the proposed method using MOTSynth dataset to train and MOT17 and MOT20
detection datasets to test, with experimental results demonstrating the
effectiveness of this method. Our approach not only produces visually plausible
samples but also does not require any labels of the real domain thus making it
applicable to the variety of downstream tasks
Generalizability of Functional Forms for Interatomic Potential Models Discovered by Symbolic Regression
In recent years there has been great progress in the use of machine learning
algorithms to develop interatomic potential models. Machine-learned potential
models are typically orders of magnitude faster than density functional theory
but also orders of magnitude slower than physics-derived models such as the
embedded atom method. In our previous work, we used symbolic regression to
develop fast, accurate and transferrable interatomic potential models for
copper with novel functional forms that resemble those of the embedded atom
method. To determine the extent to which the success of these forms was
specific to copper, here we explore the generalizability of these models to
other face-centered cubic transition metals and analyze their out-of-sample
performance on several material properties. We found that these forms work
particularly well on elements that are chemically similar to copper. When
compared to optimized Sutton-Chen models, which have similar complexity, the
functional forms discovered using symbolic regression perform better across all
elements considered except gold where they have a similar performance. They
perform similarly to a moderately more complex embedded atom form on properties
on which they were trained, and they are more accurate on average on other
properties. We attribute this improved generalized accuracy to the relative
simplicity of the models discovered using symbolic regression. The genetic
programming models are found to outperform other models from the literature
about 50% of the time in a variety of property predictions, with about 1/10th
the model complexity on average. We discuss the implications of these results
to the broader application of symbolic regression to the development of new
potentials and highlight how models discovered for one element can be used to
seed new searches for different elements
A Hamilton-Jacobi-based Proximal Operator
First-order optimization algorithms are widely used today. Two standard
building blocks in these algorithms are proximal operators (proximals) and
gradients. Although gradients can be computed for a wide array of functions,
explicit proximal formulas are only known for limited classes of functions. We
provide an algorithm, HJ-Prox, for accurately approximating such proximals.
This is derived from a collection of relations between proximals, Moreau
envelopes, Hamilton-Jacobi (HJ) equations, heat equations, and Monte Carlo
sampling. In particular, HJ-Prox smoothly approximates the Moreau envelope and
its gradient. The smoothness can be adjusted to act as a denoiser. Our approach
applies even when functions are only accessible by (possibly noisy) blackbox
samples. We show HJ-Prox is effective numerically via several examples
Discovering the hidden structure of financial markets through bayesian modelling
Understanding what is driving the price of a financial asset is a question that is currently mostly unanswered. In this work we go beyond the classic one step ahead prediction and instead construct models that create new information on the behaviour of these time series. Our aim is to get a better understanding of the hidden structures that drive the moves of each financial time series and thus the market as a whole.
We propose a tool to decompose multiple time series into economically-meaningful variables to explain the endogenous and exogenous factors driving their underlying variability. The methodology we introduce goes beyond the direct model forecast. Indeed, since our model continuously adapts its variables and coefficients, we can study the time series of coefficients and selected variables. We also present a model to construct the causal graph of relations between these time series and include them in the exogenous factors.
Hence, we obtain a model able to explain what is driving the move of both each specific time series and the market as a whole. In addition, the obtained graph of the time series provides new information on the underlying risk structure of this environment. With this deeper understanding of the hidden structure we propose novel ways to detect and forecast risks in the market. We investigate our results with inferences up to one month into the future using stocks, FX futures and ETF futures, demonstrating its superior performance according to accuracy of large moves, longer-term prediction and consistency over time. We also go in more details on the economic interpretation of the new variables and discuss the created graph structure of the market.Open Acces
Differential Models, Numerical Simulations and Applications
This Special Issue includes 12 high-quality articles containing original research findings in the fields of differential and integro-differential models, numerical methods and efficient algorithms for parameter estimation in inverse problems, with applications to biology, biomedicine, land degradation, traffic flows problems, and manufacturing systems
Mathematical Modeling of Biological Systems
Mathematical modeling is a powerful approach supporting the investigation of open problems in natural sciences, in particular physics, biology and medicine. Applied mathematics allows to translate the available information about real-world phenomena into mathematical objects and concepts. Mathematical models are useful descriptive tools that allow to gather the salient aspects of complex biological systems along with their fundamental governing laws, by elucidating the system behavior in time and space, also evidencing symmetry, or symmetry breaking, in geometry and morphology. Additionally, mathematical models are useful predictive tools able to reliably forecast the future system evolution or its response to specific inputs. More importantly, concerning biomedical systems, such models can even become prescriptive tools, allowing effective, sometimes optimal, intervention strategies for the treatment and control of pathological states to be planned. The application of mathematical physics, nonlinear analysis, systems and control theory to the study of biological and medical systems results in the formulation of new challenging problems for the scientific community. This Special Issue includes innovative contributions of experienced researchers in the field of mathematical modelling applied to biology and medicine
CITIES: Energetic Efficiency, Sustainability; Infrastructures, Energy and the Environment; Mobility and IoT; Governance and Citizenship
This book collects important contributions on smart cities. This book was created in collaboration with the ICSC-CITIES2020, held in San José (Costa Rica) in 2020. This book collects articles on: energetic efficiency and sustainability; infrastructures, energy and the environment; mobility and IoT; governance and citizenship
Recent Advances in Single-Particle Tracking: Experiment and Analysis
This Special Issue of Entropy, titled “Recent Advances in Single-Particle Tracking: Experiment and Analysis”, contains a collection of 13 papers concerning different aspects of single-particle tracking, a popular experimental technique that has deeply penetrated molecular biology and statistical and chemical physics. Presenting original research, yet written in an accessible style, this collection will be useful for both newcomers to the field and more experienced researchers looking for some reference. Several papers are written by authorities in the field, and the topics cover aspects of experimental setups, analytical methods of tracking data analysis, a machine learning approach to data and, finally, some more general issues related to diffusion
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