8,297 research outputs found
Optimal Controller and Filter Realisations using Finite-precision, Floating- point Arithmetic.
The problem of reducing the fragility of digital controllers and filters
implemented using finite-precision, floating-point arithmetic is considered.
Floating-point arithmetic parameter uncertainty is multiplicative, unlike
parameter uncertainty resulting from fixed-point arithmetic. Based on first-
order eigenvalue sensitivity analysis, an upper bound on the eigenvalue
perturbations is derived. Consequently, open-loop and closed-loop eigenvalue
sensitivity measures are proposed. These measures are dependent upon the filter/
controller realization. Problems of obtaining the optimal realization with
respect to both the open-loop and the closed-loop eigenvalue sensitivity
measures are posed. The problem for the open-loop case is completely solved.
Solutions for the closed-loop case are obtained using non-linear programming.
The problems are illustrated with a numerical example
Efficient Inexact Proximal Gradient Algorithm for Nonconvex Problems
The proximal gradient algorithm has been popularly used for convex
optimization. Recently, it has also been extended for nonconvex problems, and
the current state-of-the-art is the nonmonotone accelerated proximal gradient
algorithm. However, it typically requires two exact proximal steps in each
iteration, and can be inefficient when the proximal step is expensive. In this
paper, we propose an efficient proximal gradient algorithm that requires only
one inexact (and thus less expensive) proximal step in each iteration.
Convergence to a critical point %of the nonconvex problem is still guaranteed
and has a convergence rate, which is the best rate for nonconvex
problems with first-order methods. Experiments on a number of problems
demonstrate that the proposed algorithm has comparable performance as the
state-of-the-art, but is much faster
ET-AL: Entropy-Targeted Active Learning for Bias Mitigation in Materials Data
Growing materials data and data-driven informatics drastically promote the
discovery and design of materials. While there are significant advancements in
data-driven models, the quality of data resources is less studied despite its
huge impact on model performance. In this work, we focus on data bias arising
from uneven coverage of materials families in existing knowledge. Observing
different diversities among crystal systems in common materials databases, we
propose an information entropy-based metric for measuring this bias. To
mitigate the bias, we develop an entropy-targeted active learning (ET-AL)
framework, which guides the acquisition of new data to improve the diversity of
underrepresented crystal systems. We demonstrate the capability of ET-AL for
bias mitigation and the resulting improvement in downstream machine learning
models. This approach is broadly applicable to data-driven materials discovery,
including autonomous data acquisition and dataset trimming to reduce bias, as
well as data-driven informatics in other scientific domains.Comment: 35 pages, 13 figures, under revie
Biometrics in ABC: counter-spoofing research
Automated border control (ABC) is concerned with fast and secure processing for intelligence-led identification. The
FastPass project aims to build a harmonised, modular reference system for future European ABC. When biometrics is taken on
board as identity, spoofing attacks become a concern. This paper presents current research in algorithm development for
counter-spoofing attacks in biometrics. Focussing on three biometric traits, face, fingerprint, and iris, it examines possible types
of spoofing attacks, and reviews existing algorithms reported in relevant academic papers in the area of countering measures to
biometric spoofing attacks. It indicates that the new developing trend is fusion of multiple biometrics against spoofing attacks
Leptons from Dark Matter Annihilation in Milky Way Subhalos
Numerical simulations of dark matter collapse and structure formation show
that in addition to a large halo surrounding the baryonic component of our
galaxy, there also exists a significant number of subhalos that extend hundreds
of kiloparsecs beyond the edge of the observable Milky Way. We find that for
dark matter (DM) annihilation models, galactic subhalos can significantly
modify the spectrum of electrons and positrons as measured at our galactic
position. Using data from the recent Via Lactea II simulation we include the
subhalo contribution of electrons and positrons as boundary source terms for
simulations of high energy cosmic ray propagation with a modified version of
the publicly available GALPROP code. Focusing on the DM DM -> 4e annihilation
channel, we show that including subhalos leads to a better fit to both the
Fermi and PAMELA data. The best fit gives a dark matter particle mass of 1.2
TeV, for boost factors of 90 in the main halo and 1950-3800 in the subhalos
(depending on assumptions about the background), in contrast to the 0.85 TeV
mass that gives the best fit in the main halo-only scenario. These fits suggest
that at least a third of the observed electron cosmic rays from DM annihilation
could come from subhalos, opening up the possibility of a relaxation of recent
stringent constraints from inverse Compton gamma rays originating from the
high-energy leptons.Comment: 8 pages, 13 figures; added referenc
An experimental approach to quantify strain transfer efficiency of fibre bragg grating sensors to host structures
This paper developed a method to evaluate the strain transfer efficiency of
fibre Bragg grating sensors to host structures. Various coatings were applied to
fibre Bragg grating sensors after being fabricated. They were epoxy, silane
agent and polypropylene, representing different surface properties. A neat epoxy
resin plate was used as the host in which the coated fibre sensors were embedded
in the central layer. The tensile strain output from the FBGs was compared with
that obtained from electrical strain gauges which were attached on the surface
of the specimen. A calculating method based on the measured strains was
developed to quantify the strain transfer function of different surface
coatings. The strain transfer coefficient obtained from the proposed method
provided a direct indicator to evaluate the strain transfer efficiency of
different coatings used on the FBG sensors, under either short or long-term
loading. The results demonstrated that the fibre sensor without any coating
possessed the best strain transfer, whereas, the worst strain transfer was
created by polypropylene coating. Coatings play a most influential role in
strain measurements using FBG sensors
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