A finite element model for wave propagation in an inhomogeneous material including experimental validation

A finite element model was developed to solve for the acoustic pressure field in a nonhomogeneous region. The derivations from the governing equations assumed that the material properties could vary with position resulting in a nonhomogeneous variable property two-dimensional wave equation. This eliminated the necessity of finding the boundary conditions between the different materials. For a two media region consisting of part air (in the duct) and part bulk absorber (in the wall), a model was used to describe the bulk absorber properties in two directions. An experiment to verify the numerical theory was conducted in a rectangular duct with no flow and absorbing material mounted on one wall. Changes in the sound field, consisting of planar waves was measured on the wall opposite the absorbing material. As a function of distance along the duct, fairly good agreement was found in the standing wave pattern upstream of the absorber and in the decay of pressure level opposite the absorber

AN EMPIRICAL ANALYSIS OF MINNEAPOLIS-ST. PAUL SUBURBAN HOUSING STARTS

Public Economics,

ImMApp: An immersive database of sound art

The ImMApp (Immersive Mapping Application) thesis addresses contemporary and historical sound art from a position informed by, on one hand, post-structural critical theory, and on the other, a practice-based exploration of contemporary digital technologies (MySQL, XML, XSLT, X3D). It proposes a critical ontological schema derived from Michel Foucault's Archaeology of Knowledge (1972) and applies this to pre-existing information resources dealing with sound art. Firstly an analysis of print-based discourses (Sound by Artists. Lander and Lexier (1990), Noise, Water, Meat. Kahn (2001) and Background Noise: Perspectives on Sound Art. LaBelle (2006» is carried out according to Foucauldian notions of genealogy, subject positions, the statement, institutional affordances and the productive nature of discursive formation. The discursive field (the archive) presented by these major canonical texts is then contrasted with a formulation derived from Giles Deleuze and Felix Guattari: that of a 'minor' history of sound art practices. This is then extended by media theory (McLuhan, Kittler, Manovich) into a critique of two digital sound art resources (The Australian Sound Design Project (Bandt and Paine (2005) and soundtoys.net Stanza (1998). The divergences between the two forms of information technologies (print vs. digital) are discussed. The means by which such digitised methodologies may enhance Foucauldian discourse analysis points onwards towards the two practice-based elements of the thesis. Surface, the first iterative part, is a web-browser based database built on an Apache/MySQIlXML architecture. It is the most extensive mapping of sound art undertaken to date and extends the theoretical framework discussed above into the digital domain. Immersion, the second part, is a re-presentation of this material in an immersive digital environment, following the transformation of the source material via XSL-T into X3D. Immersion is a real-time, large format video, surround sound (5.ln.l) installation and the thesis concludes with a discussion of how this outcome has articulated Foucauldian archaeological method and unframed pre-existing notions of the nature of sound art

Effects of fiber motion on the acoustic behavior of an anisotropic, flexible fibrous material

The acoustic behavior of a flexible fibrous material was studied experimentally. The material consisted of cylindrically shaped fibers arranged in a batting with the fibers primarily aligned parallel to the face of the batting. This type of material was considered anisotropic, with the acoustic propagation constant depending on whether the dirction of sound propagation was parallel or normal to the fiber arrangement. Normal incidence sound absorption measurements were taken for both fiber orientations over the frequency range 140 to 1500 Hz and with bulk densities ranging from 4.6 to 67 kg/cu m. When the sound propagated in a direction normal to the fiber alignment, the measured sound absorption showed the occurrence of a strong resonance, which increased absorption above that attributed to viscous and thermal effects. When the sound propagated in a direction parallel to the fiber alignment, indications of strong resonances in the data were not present. The resonance in the data for fibers normal to the direction of sound propagation is attributed to fiber motion. An analytical model was developed for the acoustic behavior of the material displaying the same fiber motion characteristics shown in the measurements

Modularity and community structure in networks

Many networks of interest in the sciences, including a variety of social and biological networks, are found to divide naturally into communities or modules. The problem of detecting and characterizing this community structure has attracted considerable recent attention. One of the most sensitive detection methods is optimization of the quality function known as "modularity" over the possible divisions of a network, but direct application of this method using, for instance, simulated annealing is computationally costly. Here we show that the modularity can be reformulated in terms of the eigenvectors of a new characteristic matrix for the network, which we call the modularity matrix, and that this reformulation leads to a spectral algorithm for community detection that returns results of better quality than competing methods in noticeably shorter running times. We demonstrate the algorithm with applications to several network data sets.Comment: 7 pages, 3 figure

Synchronization of dynamical hypernetworks: dimensionality reduction through simultaneous block-diagonalization of matrices

We present a general framework to study stability of the synchronous solution for a hypernetwork of coupled dynamical systems. We are able to reduce the dimensionality of the problem by using simultaneous block-diagonalization of matrices. We obtain necessary and sufficient conditions for stability of the synchronous solution in terms of a set of lower-dimensional problems and test the predictions of our low-dimensional analysis through numerical simulations. Under certain conditions, this technique may yield a substantial reduction of the dimensionality of the problem. For example, for a class of dynamical hypernetworks analyzed in the paper, we discover that arbitrarily large networks can be reduced to a collection of subsystems of dimensionality no more than 2. We apply our reduction techique to a number of different examples, including a class of undirected unweighted hypermotifs of three nodes.Comment: 9 pages, 6 figures, accepted for publication in Phys. Rev.