13,122 research outputs found
Performance evaluation of the Hilbert–Huang transform for respiratory sound analysis and its application to continuous adventitious sound characterization
© 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The use of the Hilbert–Huang transform in the analysis of biomedical signals has increased during the past few years, but its use for respiratory sound (RS) analysis is still limited. The technique includes two steps: empirical mode decomposition (EMD) and instantaneous frequency (IF) estimation. Although the mode mixing (MM) problem of EMD has been widely discussed, this technique continues to be used in many RS analysis algorithms.
In this study, we analyzed the MM effect in RS signals recorded from 30 asthmatic patients, and studied the performance of ensemble EMD (EEMD) and noise-assisted multivariate EMD (NA-MEMD) as means for preventing this effect. We propose quantitative parameters for measuring the size, reduction of MM, and residual noise level of each method. These parameters showed that EEMD is a good solution for MM, thus outperforming NA-MEMD. After testing different IF estimators, we propose Kay¿s method to calculate an EEMD-Kay-based Hilbert spectrum that offers high energy concentrations and high time and high frequency resolutions. We also propose an algorithm for the automatic characterization of continuous adventitious sounds (CAS). The tests performed showed that the proposed EEMD-Kay-based Hilbert spectrum makes it possible to determine CAS more precisely than other conventional time-frequency techniques.Postprint (author's final draft
Algebraic and algorithmic frameworks for optimized quantum measurements
Von Neumann projections are the main operations by which information can be
extracted from the quantum to the classical realm. They are however static
processes that do not adapt to the states they measure. Advances in the field
of adaptive measurement have shown that this limitation can be overcome by
"wrapping" the von Neumann projectors in a higher-dimensional circuit which
exploits the interplay between measurement outcomes and measurement settings.
Unfortunately, the design of adaptive measurement has often been ad hoc and
setup-specific. We shall here develop a unified framework for designing
optimized measurements. Our approach is two-fold: The first is algebraic and
formulates the problem of measurement as a simple matrix diagonalization
problem. The second is algorithmic and models the optimal interaction between
measurement outcomes and measurement settings as a cascaded network of
conditional probabilities. Finally, we demonstrate that several figures of
merit, such as Bell factors, can be improved by optimized measurements. This
leads us to the promising observation that measurement detectors which---taken
individually---have a low quantum efficiency can be be arranged into circuits
where, collectively, the limitations of inefficiency are compensated for
Holographic duality from random tensor networks
Tensor networks provide a natural framework for exploring holographic duality
because they obey entanglement area laws. They have been used to construct
explicit toy models realizing many interesting structural features of the
AdS/CFT correspondence, including the non-uniqueness of bulk operator
reconstruction in the boundary theory. In this article, we explore the
holographic properties of networks of random tensors. We find that our models
naturally incorporate many features that are analogous to those of the AdS/CFT
correspondence. When the bond dimension of the tensors is large, we show that
the entanglement entropy of boundary regions, whether connected or not, obey
the Ryu-Takayanagi entropy formula, a fact closely related to known properties
of the multipartite entanglement of assistance. Moreover, we find that each
boundary region faithfully encodes the physics of the entire bulk entanglement
wedge. Our method is to interpret the average over random tensors as the
partition function of a classical ferromagnetic Ising model, so that the
minimal surfaces of Ryu-Takayanagi appear as domain walls. Upon including the
analog of a bulk field, we find that our model reproduces the expected
corrections to the Ryu-Takayanagi formula: the minimal surface is displaced and
the entropy is augmented by the entanglement of the bulk field. Increasing the
entanglement of the bulk field ultimately changes the minimal surface
topologically in a way similar to creation of a black hole. Extrapolating bulk
correlation functions to the boundary permits the calculation of the scaling
dimensions of boundary operators, which exhibit a large gap between a small
number of low-dimension operators and the rest. While we are primarily
motivated by AdS/CFT duality, our main results define a more general form of
bulk-boundary correspondence which could be useful for extending holography to
other spacetimes.Comment: 57 pages, 13 figure
Nomadic input on mobile devices: the influence of touch input technique and walking speed on performance and offset modeling
In everyday life people use their mobile phones on-the-go with different walking speeds and with different touch input techniques. Unfortunately, much of the published research in mobile interaction does not quantify the influence of these variables. In this paper, we analyze the influence of walking speed, gait pattern and input techniques on commonly used performance parameters like error rate, accuracy and tapping speed, and we compare the results to the static condition. We examine the influence of these factors on the machine learned offset model used to correct user input and we make design recommendations. The results show that all performance parameters degraded when the subject started to move, for all input techniques. Index finger pointing techniques demonstrated overall better performance compared to thumb-pointing techniques. The influence of gait phase on tap event likelihood and accuracy was demonstrated for all input techniques and all walking speeds. Finally, it was shown that the offset model built on static data did not perform as well as models inferred from dynamic data, which indicates the speed-specific nature of the models. Also, models identified using specific input techniques did not perform well when tested in other conditions, demonstrating the limited validity of offset models to a particular input technique. The model was therefore calibrated using data recorded with the appropriate input technique, at 75% of preferred walking speed, which is the speed to which users spontaneously slow down when they use a mobile device and which presents a tradeoff between accuracy and usability. This led to an increase in accuracy compared to models built on static data. The error rate was reduced between 0.05% and 5.3% for landscape-based methods and between 5.3% and 11.9% for portrait-based methods
Measurements in two bases are sufficient for certifying high-dimensional entanglement
High-dimensional encoding of quantum information provides a promising method
of transcending current limitations in quantum communication. One of the
central challenges in the pursuit of such an approach is the certification of
high-dimensional entanglement. In particular, it is desirable to do so without
resorting to inefficient full state tomography. Here, we show how carefully
constructed measurements in two bases (one of which is not orthonormal) can be
used to faithfully and efficiently certify bipartite high-dimensional states
and their entanglement for any physical platform. To showcase the practicality
of this approach under realistic conditions, we put it to the test for photons
entangled in their orbital angular momentum. In our experimental setup, we are
able to verify 9-dimensional entanglement for a pair of photons on a
11-dimensional subspace each, at present the highest amount certified without
any assumptions on the state.Comment: 11+14 pages, 2+7 figure
- …