2,200 research outputs found
HMM-Based Speech Enhancement Using Sub-Word Models and Noise Adaptation
This work proposes a method of speech enhancement that uses a network of HMMs to first decode noisy speech and to then synthesise a set of features that enables a clean speech signal to be reconstructed. Different choices of acoustic model (whole-word, monophone and triphone) and grammars (highly constrained to no constraints) are considered and the effects of introducing or relaxing acoustic and grammar constraints investigated. For robust operation in noisy conditions it is necessary for the HMMs to model noisy speech and consequently noise adaptation is investigated along with its effect on the reconstructed speech. Speech quality and intelligibility analysis find triphone models with no grammar, combined with noise adaptation, gives highest performance that outperforms conventional methods of enhancement at low signal-to-noise ratios
Audio-to-Visual Speech Conversion using Deep Neural Networks
We study the problem of mapping from acoustic to visual speech with the goal of generating accurate, perceptually natural speech animation automatically from an audio speech signal. We present a sliding window deep neural network that learns a mapping from a window of acoustic features to a window of visual features from a large audio-visual speech dataset. Overlapping visual predictions are averaged to generate continuous, smoothly varying speech animation. We outperform a baseline HMM inversion approach in both objective and subjective evaluations and perform a thorough analysis of our results
Classification of the conditionally observable spectra exhibiting central symmetry
We show how in PT-symmetric 2J-level quantum systems the assumption of an
upside-down symmetry (or duality) of their spectra simplifies their
classification based on the non-equivalent pairwise mergers of the energy
levels.Comment: 10 pp. 3 figure
Time-Dependent Pseudo-Hermitian Hamiltonians Defining a Unitary Quantum System and Uniqueness of the Metric Operator
The quantum measurement axiom dictates that physical observables and in
particular the Hamiltonian must be diagonalizable and have a real spectrum. For
a time-independent Hamiltonian (with a discrete spectrum) these conditions
ensure the existence of a positive-definite inner product that renders the
Hamiltonian self-adjoint. Unlike for a time-independent Hamiltonian, this does
not imply the unitarity of the Schroedinger time-evolution for a general
time-dependent Hamiltonian. We give an additional necessary and sufficient
condition for the unitarity of time-evolution. In particular, we obtain the
general form of a two-level Hamiltonian that fulfils this condition. We show
that this condition is geometrical in nature and that it implies the reality of
the adiabatic geometric phases. We also address the problem of the uniqueness
of the metric operator.Comment: 11 pages, published versio
Inoue surfaces and the Chern-Ricci flow
We investigate the Chern-Ricci flow, an evolution equation of Hermitian
metrics, on Inoue surfaces. These are non-Kahler compact complex surfaces of
type Class VII. We show that, after an initial conformal change, the flow
always collapses the Inoue surface to a circle at infinite time, in the sense
of Gromov-Hausdorff.Comment: 23 page
NASA Task Load Index (TLX) for IOS: an Essential Workload Measure in the Human Performance Toolbox
no abstract availabl
Aftershocks driven by afterslip and fluid pressure sweeping through a fault‐fracture mesh
A variety of physical mechanisms are thought to be responsible for the triggering and spatiotemporal evolution of aftershocks. Here we analyze a vigorous aftershock sequence and postseismic geodetic strain that occurred in the Yuha Desert following the 2010 Mw 7.2 El Mayor‐Cucapah earthquake. About 155,000 detected aftershocks occurred in a network of orthogonal faults and exhibit features of two distinct mechanisms for aftershock triggering. The earliest aftershocks were likely driven by afterslip that spread away from the main shock with the logarithm of time. A later pulse of aftershocks swept again across the Yuha Desert with square root time dependence and swarm‐like behavior; together with local geological evidence for hydrothermalism, these features suggest that the events were driven by fluid diffusion. The observations illustrate how multiple driving mechanisms and the underlying fault structure jointly control the evolution of an aftershock sequence
Perron vector optimization applied to search engines
In the last years, Google's PageRank optimization problems have been
extensively studied. In that case, the ranking is given by the invariant
measure of a stochastic matrix. In this paper, we consider the more general
situation in which the ranking is determined by the Perron eigenvector of a
nonnegative, but not necessarily stochastic, matrix, in order to cover
Kleinberg's HITS algorithm. We also give some results for Tomlin's HOTS
algorithm. The problem consists then in finding an optimal outlink strategy
subject to design constraints and for a given search engine.
We study the relaxed versions of these problems, which means that we should
accept weighted hyperlinks. We provide an efficient algorithm for the
computation of the matrix of partial derivatives of the criterion, that uses
the low rank property of this matrix. We give a scalable algorithm that couples
gradient and power iterations and gives a local minimum of the Perron vector
optimization problem. We prove convergence by considering it as an approximate
gradient method.
We then show that optimal linkage stategies of HITS and HOTS optimization
problems verify a threshold property. We report numerical results on fragments
of the real web graph for these search engine optimization problems.Comment: 28 pages, 5 figure
Slow rupture of frictional interfaces
The failure of frictional interfaces and the spatiotemporal structures that
accompany it are central to a wide range of geophysical, physical and
engineering systems. Recent geophysical and laboratory observations indicated
that interfacial failure can be mediated by slow slip rupture phenomena which
are distinct from ordinary, earthquake-like, fast rupture. These discoveries
have influenced the way we think about frictional motion, yet the nature and
properties of slow rupture are not completely understood. We show that slow
rupture is an intrinsic and robust property of simple non-monotonic
rate-and-state friction laws. It is associated with a new velocity scale
, determined by the friction law, below which steady state rupture
cannot propagate. We further show that rupture can occur in a continuum of
states, spanning a wide range of velocities from to elastic
wave-speeds, and predict different properties for slow rupture and ordinary
fast rupture. Our results are qualitatively consistent with recent
high-resolution laboratory experiments and may provide a theoretical framework
for understanding slow rupture phenomena along frictional interfaces.Comment: 6 pages, 4 figures, 1 table (Supplementary material: 5 pages, 2
figures
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