65,774 research outputs found
Separation of Synchronous Sources
This thesis studies the Separation of Synchronous Sources (SSS) problem, which deals with the separation of signals resulting from a linear mixing of sources whose phases are synchronous. While this study is made in a form independent of the application, a motivation from a neuroscience perspective is presented. Traditional methods for Blind Source Separation, such as Independent Component Analysis (ICA), cannot address this problem because synchronous sources are highly dependent. We provide sufficient conditions for SSS to be an identifiable problem, and quantify the effect of prewhitening on the difficulty of SSS. We also present two algorithms to solve SSS. Extensive studies on simulated data illustrate that these algorithms yield substantially better results when compared with ICA methods. We conclude that these algorithms can successfully perform SSS in varying configurations (number of sources, number of sensors, level of additive noise, phase lag between sources, among others). Theoretical properties of one of these algorithms are also presented. Future work is discussed extensively, showing that this area of study is far from resolved and still presents interesting challenges
Speech Separation Using Partially Asynchronous Microphone Arrays Without Resampling
We consider the problem of separating speech sources captured by multiple
spatially separated devices, each of which has multiple microphones and samples
its signals at a slightly different rate. Most asynchronous array processing
methods rely on sample rate offset estimation and resampling, but these offsets
can be difficult to estimate if the sources or microphones are moving. We
propose a source separation method that does not require offset estimation or
signal resampling. Instead, we divide the distributed array into several
synchronous subarrays. All arrays are used jointly to estimate the time-varying
signal statistics, and those statistics are used to design separate
time-varying spatial filters in each array. We demonstrate the method for
speech mixtures recorded on both stationary and moving microphone arrays.Comment: To appear at the International Workshop on Acoustic Signal
Enhancement (IWAENC 2018
A newly conceived cylinder measuring machine and methods that eliminate the spindle errors
Advanced manufacturing processes require improving dimensional metrology applications to reach a nanometric accuracy level. Such measurements may be carried out using conventional highly accurate roundness measuring machines. On these machines, the metrology loop goes through the probing and the mechanical guiding elements. Hence, external forces, strain and thermal expansion are transmitted to the metrological structure through the supporting structure, thereby reducing measurement quality. The obtained measurement also combines both the motion error of the guiding system and the form error of the artifact. Detailed uncertainty budgeting might be improved, using error separation methods (multi-step, reversal and multi-probe error separation methods, etc), enabling identification of the systematic (synchronous or repeatable) guiding system motion errors as well as form error of the artifact. Nevertheless, the performance of this kind of machine is limited by the repeatability level of the mechanical guiding elements, which usually exceeds 25 nm (in the case of an air bearing spindle and a linear bearing). In order to guarantee a 5 nm measurement uncertainty level, LNE is currently developing an original machine dedicated to form measurement on cylindrical and spherical artifacts with an ultra-high level of accuracy. The architecture of this machine is based on the ‘dissociated metrological technique’ principle and contains reference probes and cylinder. The form errors of both cylindrical artifact and reference cylinder are obtained after a mathematical combination between the information given by the probe sensing the artifact and the information given by the probe sensing the reference cylinder by applying the modified multi-step separation method.Thèse CIFR
Self-stabilising Byzantine Clock Synchronisation is Almost as Easy as Consensus
We give fault-tolerant algorithms for establishing synchrony in distributed
systems in which each of the nodes has its own clock. Our algorithms
operate in a very strong fault model: we require self-stabilisation, i.e., the
initial state of the system may be arbitrary, and there can be up to
ongoing Byzantine faults, i.e., nodes that deviate from the protocol in an
arbitrary manner. Furthermore, we assume that the local clocks of the nodes may
progress at different speeds (clock drift) and communication has bounded delay.
In this model, we study the pulse synchronisation problem, where the task is to
guarantee that eventually all correct nodes generate well-separated local pulse
events (i.e., unlabelled logical clock ticks) in a synchronised manner.
Compared to prior work, we achieve exponential improvements in stabilisation
time and the number of communicated bits, and give the first sublinear-time
algorithm for the problem:
- In the deterministic setting, the state-of-the-art solutions stabilise in
time and have each node broadcast bits per time
unit. We exponentially reduce the number of bits broadcasted per time unit to
while retaining the same stabilisation time.
- In the randomised setting, the state-of-the-art solutions stabilise in time
and have each node broadcast bits per time unit. We
exponentially reduce the stabilisation time to while each node
broadcasts bits per time unit.
These results are obtained by means of a recursive approach reducing the
above task of self-stabilising pulse synchronisation in the bounded-delay model
to non-self-stabilising binary consensus in the synchronous model. In general,
our approach introduces at most logarithmic overheads in terms of stabilisation
time and broadcasted bits over the underlying consensus routine.Comment: 54 pages. To appear in JACM, preliminary version of this work has
appeared in DISC 201
Radiation from Violently Accelerated Bodies
A determination is made of the radiation emitted by a linearly uniformly
accelerated uncharged dipole transmitter. It is found that, first of all, the
radiation rate is given by the familiar Larmor formula, but it is augmented by
an amount which becomes dominant for sufficiently high acceleration. For an
accelerated dipole oscillator, the criterion is that the center of mass motion
become relativistic within one oscillation period. The augmented formula and
the measurements which it summarizes presuppose an expanding inertial
observation frame. A static inertial reference frame will not do. Secondly, it
is found that the radiation measured in the expanding inertial frame is
received with 100% fidelity. There is no blueshift or redshift due to the
accelerative motion of the transmitter. Finally, it is found that a pair of
coherently radiating oscillators accelerating (into opposite directions) in
their respective causally disjoint Rindler-coordinatized sectors produces an
interference pattern in the expanding inertial frame. Like the pattern of a
Young double slit interferometer, this Rindler interferometer pattern has a
fringe spacing which is inversely proportional to the proper separation and the
proper frequency of the accelerated sources. The interferometer, as well as the
augmented Larmor formula, provide a unifying perspective. It joins adjacent
Rindler-coordinatized neighborhoods into a single spacetime arena for
scattering and radiation from accelerated bodies.Comment: 29 pages, 1 figure, Revte
Magnetic Interaction in Ultra-compact Binary Systems
This article reviews the current works on ultra-compact double-degenerate
binaries in the presence of magnetic interaction, in particular, unipolar
induction. The orbital dynamics and evolution of compact white-dwarf pairs are
discussed in detail. Models and predictions of electron cyclotron masers from
unipolar-inductor compact binaries and unipolar-inductor white-dwarf planetary
systems are presented. Einstein-Laub effects in compact binaries are briefly
discussed.Comment: invited review, accepted for publication in Research in Astronomy and
Astrophysics (RAA
Large-Scale Structure Observables in General Relativity
We review recent studies that rigorously define several key observables of
the large-scale structure of the Universe in a general relativistic context.
Specifically, we consider i) redshift perturbation of cosmic clock events; ii)
distortion of cosmic rulers, including weak lensing shear and magnification;
iii) observed number density of tracers of the large-scale structure. We
provide covariant and gauge-invariant expressions of these observables. Our
expressions are given for a linearly perturbed flat Friedmann-Robertson-Walker
metric including scalar, vector, and tensor metric perturbations. While we
restrict ourselves to linear order in perturbation theory, the approach can be
straightforwardly generalized to higher order.Comment: 24 pages, 3 figures. A review article submitted to CQG focus issue
"Relativistic Effects in Cosmology". arXiv admin note: substantial text
overlap with arXiv:1204.3625, v2: correct one missing referenc
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