6,949 research outputs found
Improving Sparsity in Kernel Adaptive Filters Using a Unit-Norm Dictionary
Kernel adaptive filters, a class of adaptive nonlinear time-series models,
are known by their ability to learn expressive autoregressive patterns from
sequential data. However, for trivial monotonic signals, they struggle to
perform accurate predictions and at the same time keep computational complexity
within desired boundaries. This is because new observations are incorporated to
the dictionary when they are far from what the algorithm has seen in the past.
We propose a novel approach to kernel adaptive filtering that compares new
observations against dictionary samples in terms of their unit-norm
(normalised) versions, meaning that new observations that look like previous
samples but have a different magnitude are not added to the dictionary. We
achieve this by proposing the unit-norm Gaussian kernel and define a
sparsification criterion for this novel kernel. This new methodology is
validated on two real-world datasets against standard KAF in terms of the
normalised mean square error and the dictionary size.Comment: Accepted at the IEEE Digital Signal Processing conference 201
Global Representation of the Fine Structure Constant and its Variation
The fine structure constant, alpha, is shown to be proportional to the ratio
of the quanta of electric and magnetic flux of force of the electron, and
provides a new representation, which is global across all unit systems.
Consequently, a variation in alpha was shown to manifest due to a differential
change in the fraction of the quanta of electric and magnetic flux of force,
while a variation in hcross.c was shown to manifest due to the common mode
change. The representation is discussed with respect to the running of the fine
structure constant at high energies (small distances), and a putative temporal
drift. It is shown that the running of the fine structure constant is due to
equal components of electric screening (polarization of vacuum) and magnetic
anti-screening (magnetization of vacuum), which cause the perceived quanta of
electric charge to increase at small distances, while the magnetic flux quanta
decreases. This introduces the concept of the bare magnetic flux quanta as well
as the bare electric charge. With regards to temporal drift, it is confirmed
that it is impossible to determine which fundamental constant is varying if
alpha varies.Comment: Final accepted version for Metrologia. This version includes a proof
that the representation of the fine structure constant is global across all
unit systems, using Jackson's global representation of Maxwell's equations
(which is also valid for all unit systems). The version is shorter than the
previous, thus the discussion throughout is more brie
Gravitational Wave Detection with High Frequency Phonon Trapping Acoustic Cavities
There are a number of theoretical predictions for astrophysical and
cosmological objects, which emit high frequency (~Hz) Gravitation
Waves (GW) or contribute somehow to the stochastic high frequency GW
background. Here we propose a new sensitive detector in this frequency band,
which is based on existing cryogenic ultra-high quality factor quartz Bulk
Acoustic Wave cavity technology, coupled to near-quantum-limited SQUID
amplifiers at ~mK. We show that spectral strain sensitivities reaching
per per mode is possible, which in principle can
cover the frequency range with multiple () modes with quality factors
varying between allowing wide bandwidth detection. Due to its
compactness and well established manufacturing process, the system is easily
scalable into arrays and distributed networks that can also impact the overall
sensitivity and introduce coincidence analysis to ensure no false detections.Comment: appears in Phys. Rev. D, (2014
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