149 research outputs found
Convolution, Rotation, and Data Fusion with Orthogonal Expansions
This dissertation investigates certain special function classes, namely Hermite and
Bessel functions, and uncovers some useful properties relating multiplication, convolution,
rotation, and coordinate conversion. These mathematical operations are performed
on the underlying basis functions and are thus continuous in nature, lending
itself to higher accuracy and computational speed. Some integral transformations involving
these special functions (e.g. Abel transform, 3h integrals, 3J integrals) possess
recurrence relations, and so given a nite set of analytic starting conditions, higher
order forms of these integrals can be obtained quickly. It will be shown how these
integrals and the aforementioned special function properties are used in engineering
applications including data fusion, deconvolution, continuum normal mode analysis,
cryo-electron microscopy (cryo-EM) and small angle X-ray scattering (SAXS)
Quantum field theory of photons with orbital angular momentum
A quantum-field-theory approach is put forward to generalize the concept of classical spatial light beams carrying orbital angular momentum to the single-photon level. This quantization framework is carried out both in the paraxial and nonparaxial regimes. Upon extension to the optical phase space, closed-form expressions are found for a photon Wigner representation describing transformations on the orbital Poincaré sphere of unitarily related families of paraxial spatial modes
Predicting blur visual discomfort for natural scenes by the loss of positional information
The perception of blur due to accommodation failures, insufficient optical correction or imperfect image reproduction is a common source of visual discomfort, usually attributed to an anomalous and annoying distribution of the image spectrum in the spatial frequency domain. In the present paper, this discomfort is related to a loss of the localization accuracy of the observed patterns. It is assumed, as a starting perceptual principle, that the visual system is optimally adapted to pattern localization in a natural environment. Thus, since the best possible accuracy of the image patterns localization is indicated by the positional Fisher Information, it is argued that blur discomfort is strictly related to a loss of this information. Following this concept, a receptive field functional model is adopted to predict the visual discomfort. It is a complex-valued operator, orientation-selective both in the space domain and in the spatial frequency domain. Starting from the case of Gaussian blur, the analysis is extended to a generic type of blur by applying a positional Fisher Information equivalence criterion. Out-of-focus blur and astigmatic blur are presented as significant examples. The validity of the proposed model is verified by comparing its predictions with subjective ratings. The model fits linearly with the experiments reported in independent databases, based on different protocols and settings
Clifford wavelets for fetal ECG extraction
Analysis of the fetal heart rate during pregnancy is essential for monitoring
the proper development of the fetus. Current fetal heart monitoring techniques
lack the accuracy in fetal heart rate monitoring and features acquisition,
resulting in diagnostic medical issues. The challenge lies in the extraction of
the fetal ECG from the mother's ECG during pregnancy. This approach has the
advantage of being a reliable and non-invasive technique. For this aim, we
propose in this paper a wavelet/multi-wavelet method allowing to extract
perfectly the feta ECG parameters from the abdominal mother ECG. The method is
essentially due to the exploitation of Clifford wavelets as recent variants in
the field. We prove that these wavelets are more efficient and performing
against classical ones. The experimental results are therefore due to two basic
classes of wavelets and multi-wavelets. A first-class is the classical Haar
Schauder, and a second one is due to Clifford valued wavelets and
multi-wavelets. These results showed that wavelets/multiwavelets are already
good bases for the FECG processing, provided that Clifford ones are the best.Comment: 21 pages, 8 figures, 1 tabl
Predicting the Blur Visual Discomfort for Natural Scenes by the Loss of Positional Information
The perception of the blur due to accommodation failures, insufficient
optical correction or imperfect image reproduction is a common source of visual
discomfort, usually attributed to an anomalous and annoying distribution of the
image spectrum in the spatial frequency domain. In the present paper, this
discomfort is attributed to a loss of the localization accuracy of the observed
patterns. It is assumed, as a starting perceptual principle, that the visual
system is optimally adapted to pattern localization in a natural environment.
Thus, since the best possible accuracy of the image patterns localization is
indicated by the positional Fisher Information, it is argued that the blur
discomfort is strictly related to a loss of this information. Following this
concept, a receptive field functional model, tuned to common features of
natural scenes, is adopted to predict the visual discomfort. It is a
complex-valued operator, orientation-selective both in the space domain and in
the spatial frequency domain. Starting from the case of Gaussian blur, the
analysis is extended to a generic type of blur by applying a positional Fisher
Information equivalence criterion. Out-of-focus blur and astigmatic blur are
presented as significant examples. The validity of the proposed model is
verified by comparing its predictions with subjective ratings. The model fits
linearly with the experiments reported in independent databases, based on
different protocols and settings.Comment: 12 pages, 8 figures, article submitted to Vision Research (Elsevier)
Journal in July 202
Wave Front Sensing and Correction Using Spatial Modulation and Digitally Enhanced Heterodyne Interferometry
This thesis is about light. Specifically it explores a new way
sensing the spatial distribution
of amplitude and phase across the wavefront of a propagating
laser. It uses spatial
light modulators to tag spatially distinct regions of the beam, a
single diode to collect
the resulting light and digitally enhanced heterodyne
interferometry to decode the phase
and amplitude information across the wavefront. It also
demonstrates how using these
methods can be used to maximise the transmission of light through
a cavity and shows
how minor aberrations in the beam can be corrected in real time.
Finally it demonstrate
the preferential transmission of higher order modes.
Wavefront sensing is becoming increasingly important as the
demands on modern interferometers
increase. Land based systems such as the Laser Interferometer
Gravitational-Wave
Observatory (LIGO) use it to maximise the amount of power in the
arm cavities during
operation and reduce noise, while space based missions such as
the Laser Interferometer
Space Antenna (LISA) will use it to align distant partner
satellites and ensure that the
maximum amount of signal is exchanged. Conventionally wavefront
sensing is accomplished
using either Hartmann Sensors or multi-element diodes. These are
well proven
and very effective techniques but bring with them a number of
well understood limitations.
Critically, while they can map a wavefront in detail, they are
strictly sensors and
can do nothing to correct it.
Our new technique is based on a single-element photo-diode and
the spatial modulation
of the local oscillator beam. We encode orthogonal codes
spatially onto this light and use
these to separate the phases and amplitudes of different parts of
the signal beam in post
processing. This technique shifts complexity from the optical
hardware into deterministic
digital signal processing. Notably, the use of a single analogue
channel (photo-diode,
connections and analogue to digital converter) avoids some
low-frequency error sources.
The technique can also sense the wavefront phase at many points,
limited only by the
number of actuators on the spatial light modulator in contrast to
the standard 4 points
from a quadrant photo-diode. For ground-based systems, our
technique could be used to
identify and eliminate higher-order modes, while, for space-based
systems, it provides a
measure of wavefront tilt which is less susceptible to low
frequency noise.
In the future it may be possible to couple the technique with an
artificial intelligence
engine to automate more of the beam alignment process in
arrangements involving multiple
cavities, preferentially select (or reject) specific higher order
modes and start to reduce
the burgeoning requirements for human control of these complex
instruments
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