57,544 research outputs found
On Time-Reversal Imaging by Statistical Testing
This letter is focused on the design and analysis of computational wideband
time-reversal imaging algorithms, designed to be adaptive with respect to the
noise levels pertaining to the frequencies being employed for scene probing.
These algorithms are based on the concept of cell-by-cell processing and are
obtained as theoretically-founded decision statistics for testing the
hypothesis of single-scatterer presence (absence) at a specific location. These
statistics are also validated in comparison with the maximal invariant
statistic for the proposed problem.Comment: Reduced form accepted in IEEE Signal Processing Letter
Illumination strategies for intensity-only imaging
We propose a new strategy for narrow band, active array imaging of localized
scat- terers when only the intensities are recorded and measured at the array.
We consider a homogeneous medium so that wave propagation is fully coherent. We
show that imaging with intensity-only measurements can be carried out using the
time reversal operator of the imaging system, which can be obtained from
intensity measurements using an appropriate illumination strategy and the
polarization identity. Once the time reversal operator has been obtained, we
show that the images can be formed using its singular value decomposition
(SVD). We use two SVD-based methods to image the scatterers. The proposed
approach is simple and efficient. It does not need prior information about the
sought image, and guarantees exact recovery in the noise-free case.
Furthermore, it is robust with respect to additive noise. Detailed numerical
simulations illustrate the performance of the proposed imaging strategy when
only the intensities are captured
Investigating the effect of long-term musical experience on the auditory processing skills of young Maltese adults
Learning and practising a musical instrument has
recently been thought to âtrainâ the brain into processing sound
in a more refined manner.As a result, musicians experiencing
consistent exposure to musical practice have been suspected
to have superior auditory processing skills. This study aimed
to investigate this phenomenon within the Maltese context,
by testing two cohorts of young Maltese adults. Participants
in the musician cohort experienced consistent musical training
throughout their lifetime, while those in the non-musician
cohort did not have a history of musical training. A total of
24 Maltese speakers (14 musicians and 10 non-musicians) of
ages ranging between 19 and 31 years were tested for Frequency
Discrimination (FD), Duration Discrimination (DD), Temporal
Resolution (TR) and speech-in-noise recognition. The main
outcomes yielded by each cohort were compared and analysed
statistically. In comparison to the non-musician cohort, the
musicians performed in a slightly better manner throughout
testing. Statistical superiority was surprisingly only present in
the FD test. Although musicians displayed a degree of superiority
in performance on the other tests, differences in mean scores
were not statistically significant. The results yielded by this investigation
are to a degree coherent with implications of previous
research, in that the effect of long-term musical experience on
the trained cohort manifested itself in a slight superiority in performance
on auditory processing tasks. However, this difference
in scoring was not prominent enough to be statistically significant.peer-reviewe
Barry Truax Riverrun (1986/2004), a case study from the TaCEM project, exploring new approaches to techniques of analysis and re-synthesis in the study of concert electroacoustic works
At last yearâs EMS in Lisbon we introduced the TaCEM project (Technology and Creativity in Electroacoustic Music), a 30-month project funded by the UKâs Arts and Humanities Research Council, and demonstrated the generic TIAALS software being produced as part of this project. This year we present an update on the project, focusing particularly on the first of our case studies, Barry Truaxâs Riverrun.
Eight works have been selected for the project, taking into account criteria such as historical context, the nature of the synthesis techniques employed, and the aesthetics that have underpinned their realisation. Key considerations have included the accessibility of the technical resources and composing materials used in their production, and opportunities to pursue particular lines of enquiry with the composer concerned. In selecting the eight works for detailed study, a further consideration has been the extent to which the composers explored techniques that were already available at the time in ways that are unique and distinctive, or alternatively developed entirely new methods of synthesis in pursuit of their creative goals. The pioneering work of Barry Truax in terms of developing techniques of granular synthesis assign his achievements almost exclusively to the latter classification, and the composition of Riverrun (1986/2004) is a landmark achievement in this regard.
Truaxâs composing environment evolved from the early study of interactive real-time synthesis techniques at the Institute of Sonology, Utrecht 1971-73, exploring the possibilities of using Poisson-ordered distributions in the generation of microsound, to the emergence of entirely granular techniques at Simon Fraser University, British Columbia a decade later, culminating in the development of his program GSX designed specifically for waveform-based synthesis and first used to compose Riverrun, and its later extension, GSAMX, that extended these granular techniques to include the manipulation of previously sampled sound material.
At the time of composition conventional minicomputers still lacked the capacity to generate multiple voices of granulated sound material in real time, but for Truax the acquisition in 1982 of a high speed bit slice array processor, the DMX-1000, provided the enhancedprocessing power necessary for achieving such a goal. The unique characteristics of its special hardware and associated programming environment, managed in turn via a host PDP 11/23 computer, both empowered his creative objectives and also materially shaped and influenced the ways in which they could be practically achieved. The significance of such causal relationships in the evolution of the electroacoustic music repertory has yet to be widely understood, and this study of Riverrun corroborates the importance of such a line of investigation. In this case it has been possible to carry out a detailed study of the original system, still maintained in working order by Truax, leading to a reconstruction of key elements of Riverrun using a Max-based simulation of GSX, the authenticity of the results being assessed both subjectively by means of a direct aural comparison and also measured objectively using software.
Our presentation at this yearâs EMS in Berlin included a demonstration of examples of the software we have developed to enable readers to engage with Riverrun interactively, both by analysing the original recordings and by using our emulation of the GSX system to be able to recreate passages of the work and manipulate the techniques employed in order to learn more about them. We also gave examples of other materials we have collected in relation to this case study, including videos of the composer himself working with the GSX system and discussing the composition of Riverrun
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Moderating influence of dominant attentional style and exercise intensity on responses to asynchronous music
Copyright @ 2013 Human Kinetics as accepted for publication. This is the author's accepted manuscript. The final published article is available from the link below.We examined independent and combined influences of asynchronous music and dominant attentional style (DAS) on psychological and psychophysical variables during exercise using mixed methods. Participants (N = 34) were grouped according to DAS and completed treadmill runs at three intensities (low, moderate, high) crossed with three music conditions (motivational, oudeterous, no-music control). State attentional focus shifted from dissociative to associative with increasing intensity and was most aligned with DAS during moderate-intensity exercise. Both music conditions facilitated dissociation at low-to-moderate intensities. At high exercise intensity, both music conditions were associated with reduced RPE among participants with an associative DAS. Dissociators reported higher RPE overall during moderate and high intensities. Psychological responses were most positive in the motivational condition, followed by oudeterous and control. Findings illustrate the relevance of individual differences in DAS as well as task intensity and duration when selecting music for exercise
Tuning of Human Modulation Filters Is Carrier-Frequency Dependent
Licensed under the Creative Commons Attribution License
Array imaging of localized objects in homogeneous and heterogeneous media
We present a comprehensive study of the resolution and stability properties
of sparse promoting optimization theories applied to narrow band array imaging
of localized scatterers. We consider homogeneous and heterogeneous media, and
multiple and single scattering situations. When the media is homogeneous with
strong multiple scattering between scatterers, we give a non-iterative
formulation to find the locations and reflectivities of the scatterers from a
nonlinear inverse problem in two steps, using either single or multiple
illuminations. We further introduce an approach that uses the top singular
vectors of the response matrix as optimal illuminations, which improves the
robustness of sparse promoting optimization with respect to additive noise.
When multiple scattering is negligible, the optimization problem becomes linear
and can be reduced to a hybrid- method when optimal illuminations are
used. When the media is random, and the interaction with the unknown
inhomogeneities can be primarily modeled by wavefront distortions, we address
the statistical stability of these methods. We analyze the fluctuations of the
images obtained with the hybrid- method, and we show that it is stable
with respect to different realizations of the random medium provided the
imaging array is large enough. We compare the performance of the
hybrid- method in random media to the widely used Kirchhoff migration
and the multiple signal classification methods
Network Archaeology: Uncovering Ancient Networks from Present-day Interactions
Often questions arise about old or extinct networks. What proteins interacted
in a long-extinct ancestor species of yeast? Who were the central players in
the Last.fm social network 3 years ago? Our ability to answer such questions
has been limited by the unavailability of past versions of networks. To
overcome these limitations, we propose several algorithms for reconstructing a
network's history of growth given only the network as it exists today and a
generative model by which the network is believed to have evolved. Our
likelihood-based method finds a probable previous state of the network by
reversing the forward growth model. This approach retains node identities so
that the history of individual nodes can be tracked. We apply these algorithms
to uncover older, non-extant biological and social networks believed to have
grown via several models, including duplication-mutation with complementarity,
forest fire, and preferential attachment. Through experiments on both synthetic
and real-world data, we find that our algorithms can estimate node arrival
times, identify anchor nodes from which new nodes copy links, and can reveal
significant features of networks that have long since disappeared.Comment: 16 pages, 10 figure
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