Current Issue : April - June Volume : 2012 Issue Number : 2 Articles : 6 Articles
The purpose of this paper is to discuss a methodology for determining some modal parameters (frequencies, damping ratios, and\r\nseismic eigenvectors) and, under certain hypotheses, the physical matrices of a general structure with proportional damping and\r\nsubjected to seismic loads. The procedure is based on a time-domain state space formulation from which the modal parameters,\r\nincluding the seismic eigenvectors, and the complex eigenvectors of the system can be derived also in the case of a limited set\r\nof instrumentations. The conditions to normalize the eigenvectors are then illustrated and, finally, applied to derive the secondorder\r\nmatrices of the system. The proposed procedure is applied to some numerical examples also in the case of noise-polluted\r\nmeasurements and to an experimental investigation performed on a four-story steel frame subjected to earthquake excitations.\r\nAn optimization procedure to improve the prediction of the first-order modal parameters of the system is also discussed and\r\nexperimentally proved....
The present paper describes the use of microphone array technology and beamforming algorithms for the measurement and\r\nanalysis of noise generated by the interaction of a turbulent flow with the leading edge of an airfoil. Experiments were performed\r\nusing a setup in an aeroacoustic wind tunnel, where the turbulent inflow is provided by different grids. In order to exactly\r\nlocalize the aeroacoustic noise sources and, moreover, to separate airfoil leading edge noise from grid-generated noise, the\r\nselected deconvolution beamforming algorithm is extended to be used on a fully three-dimensional source region. The result\r\nof this extended beamforming are three-dimensional mappings of noise source locations. Besides acoustic measurements, the\r\ninvestigation of airfoil leading edge noise requires the measurement of parameters describing the incident turbulence, such as the\r\nintensity and a characteristic length scale or time scale. The method used for the determination of these parameters in the present\r\nstudy is explained in detail. To demonstrate the applicability of the extended beamforming algorithm and the experimental setup as\r\na whole, the noise generated at the leading edge of airfoils made of porous materials was measured and compared to that generated\r\nat the leading edge of a common nonporous airfoil....
The effect of underwater anthropogenic sound on marine mammals is of increasing concern. Here we show that humpback\r\nwhale (Megaptera novaeangliae) song in the Stellwagen Bank National Marine Sanctuary (SBNMS) was reduced, concurrent\r\nwith transmissions of an Ocean Acoustic Waveguide Remote Sensing (OAWRS) experiment approximately 200 km away. We\r\ndetected the OAWRS experiment in SBNMS during an 11 day period in autumn 2006. We compared the occurrence of song for\r\n11 days before, during and after the experiment with song over the same 33 calendar days in two later years. Using a quasi-\r\nPoisson generalized linear model (GLM), we demonstrate a significant difference in the number of minutes with detected song\r\nbetween periods and years. The lack of humpback whale song during the OAWRS experiment was the most substantial signal\r\nin the data. Our findings demonstrate the greatest published distance over which anthropogenic sound has been shown to\r\naffect vocalizing baleen whales, and the first time that active acoustic fisheries technology has been shown to have this effect.\r\nThe suitability of Ocean Acoustic Waveguide Remote Sensing technology for in-situ, long term monitoring of marine\r\necosystems should be considered, bearing in mind its possible effects on non-target species, in particular protected species....
In speech perception, a functional hierarchy has been proposed by recent functional neuroimaging studies: Core auditory\r\nareas on the dorsal plane of superior temporal gyrus (STG) are sensitive to basic acoustic characteristics, whereas\r\ndownstream regions, specifically the left superior temporal sulcus (STS) and middle temporal gyrus (MTG) ventral to Heschl�s\r\ngyrus (HG) are responsive to abstract phonological features. What is unclear so far is the relationship between the dorsal\r\nand ventral processes, especially with regard to whether low-level acoustic processing is modulated by high-level\r\nphonological processing. To address the issue, we assessed sensitivity of core auditory and downstream regions to acoustic\r\nand phonological variations by using within- and across-category lexical tonal continua with equal physical intervals. We\r\nfound that relative to within-category variation, across-category variation elicited stronger activation in the left middle MTG\r\n(mMTG), apparently reflecting the abstract phonological representations. At the same time, activation in the core auditory\r\nregion decreased, resulting from the top-down influences of phonological processing. These results support a hierarchical\r\norganization of the ventral acoustic-phonological processing stream, which originates in the right HG/STG and projects to\r\nthe left mMTG. Furthermore, our study provides direct evidence that low-level acoustic analysis is modulated by high-level\r\nphonological representations, revealing the cortical dynamics of acoustic and phonological processing in speech\r\nperception. Our findings confirm the existence of reciprocal progression projections in the auditory pathways and the roles\r\nof both feed-forward and feedback mechanisms in speech perception....
Biodiversity assessment remains one of the most difficult challenges encountered by ecologists and conservation biologists.\r\nThis task is becoming even more urgent with the current increase of habitat loss. Many methodsââ?¬â??from rapid biodiversity\r\nassessments (RBA) to all-taxa biodiversity inventories (ATBI)ââ?¬â??have been developed for decades to estimate local species\r\nrichness. However, these methods are costly and invasive. Several animalsââ?¬â??birds, mammals, amphibians, fishes and\r\narthropodsââ?¬â??produce sounds when moving, communicating or sensing their environment. Here we propose a new concept\r\nand method to describe biodiversity. We suggest to forego species or morphospecies identification used by ATBI and RBA\r\nrespectively but rather to tackle the problem at another evolutionary unit, the community level. We also propose that a part\r\nof diversity can be estimated and compared through a rapid acoustic analysis of the sound produced by animal\r\ncommunities. We produced a and b diversity indexes that we first tested with 540 simulated acoustic communities. The a\r\nindex, which measures acoustic entropy, shows a logarithmic correlation with the number of species within the acoustic\r\ncommunity. The b index, which estimates both temporal and spectral dissimilarities, is linearly linked to the number of\r\nunshared species between acoustic communities. We then applied both indexes to two closely spaced Tanzanian dry\r\nlowland coastal forests. Indexes reveal for this small sample a lower acoustic diversity for the most disturbed forest and\r\nacoustic dissimilarities between the two forests suggest that degradation could have significantly decreased and modified\r\ncommunity composition. Our results demonstrate for the first time that an indicator of biological diversity can be reliably\r\nobtained in a non-invasive way and with a limited sampling effort. This new approach may facilitate the appraisal of animal\r\ndiversity at large spatial and temporal scales....
Background: Vowel lenition and its link with coarticulation have been the subject of extensive debate in the literature. The\r\naims of the present paper are to demonstrate how vowel lenition and coarticulation are linked in Cypriot Greek (henceforth\r\nCG), to determine the nature of vowel lenition, and to illustrate how vowel lenition and coarticulation result from\r\naerodynamic phenomena.\r\nMethodology/Principal Findings: Eight speakers were recorded producing utterances ending in either /i/ or /u/. Acoustic\r\nmeasures such as V1F2 and stop duration were employed to determine whether lenition of the vowels results in\r\ncoarticulation with the preceding consonant. Results show that there is extensive stop-vowel coarticulation in CG and that\r\nstop production is as variable as vowel production, with full vowels never co-occurring with canonical consonants,\r\nindicating the existence of two routes to lenition in CG.\r\nConclusions/Significance: These findings suggest that lenition in the final syllable is a consequence of the supralaryngeal\r\narticulation coupled with a marginal glottal setting....
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