Measured acoustic properties of variable and low density bulk absorbers

Experimental data were taken to determine the acoustic absorbing properties of uniform low density and layered variable density samples using a bulk absober with a perforated plate facing to hold the material in place. In the layered variable density case, the bulk absorber was packed such that the lowest density layer began at the surface of the sample and progressed to higher density layers deeper inside. The samples were placed in a rectangular duct and measurements were taken using the two microphone method. The data were used to calculate specific acoustic impedances and normal incidence absorption coefficients. Results showed that for uniform density samples the absorption coefficient at low frequencies decreased with increasing density and resonances occurred in the absorption coefficient curve at lower densities. These results were confirmed by a model for uniform density bulk absorbers. Results from layered variable density samples showed that low frequency absorption was the highest when the lowest density possible was packed in the first layer near the exposed surface. The layers of increasing density within the sample had the effect of damping the resonances

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

Neural networks in geophysical applications

Neural networks are increasingly popular in geophysics. Because they are universal approximators, these tools can approximate any continuous function with an arbitrary precision. Hence, they may yield important contributions to finding solutions to a variety of geophysical applications. However, knowledge of many methods and techniques recently developed to increase the performance and to facilitate the use of neural networks does not seem to be widespread in the geophysical community. Therefore, the power of these tools has not yet been explored to their full extent. In this paper, techniques are described for faster training, better overall performance, i.e., generalization,and the automatic estimation of network size and architecture

On the concepts of radial and angular kinetic energies

We consider a general central-field system in D dimensions and show that the division of the kinetic energy into radial and angular parts proceeds differently in the wavefunction picture and the Weyl-Wigner phase-space picture. Thus, the radial and angular kinetic energies are different quantities in the two pictures, containing different physical information, but the relation between them is well defined. We discuss this relation and illustrate its nature by examples referring to a free particle and to a ground-state hydrogen atom.Comment: 10 pages, 2 figures, accepted by Phys. Rev.

Differential gaze behavior towards sexually preferred and non-preferred human figures

The gaze pattern associated with image exploration is a sensitive index of our attention, motivation and preference. To examine whether an individual’s gaze behavior can reflect his/her sexual interest, we compared gaze patterns of young heterosexual men and women (M = 19.94 years, SD = 1.05) while viewing photos of plain-clothed male and female figures aged from birth to sixty years old. Our analysis revealed a clear gender difference in viewing sexually preferred figure images. Men displayed a distinctive gaze pattern only when viewing twenty-year-old female images, with more fixations and longer viewing time dedicated to the upper body and waist-hip region. Women also directed more attention at the upper body on female images in comparison to male images, but this difference was not age-specific. Analysis of local image salience revealed that observers’ eye-scanning strategies could not be accounted for by low-level processes, such as analyzing local image contrast and structure, but were associated with attractiveness judgments. The results suggest that the difference in cognitive processing of sexually preferred and non-preferred figures can be manifested in gaze patterns associated with figure viewing. Thus, eye-tracking holds promise as a potential sensitive measure for sexual preference, particularly in men

Evolutionary Approaches to Optimization Problems in Chimera Topologies

Chimera graphs define the topology of one of the first commercially available quantum computers. A variety of optimization problems have been mapped to this topology to evaluate the behavior of quantum enhanced optimization heuristics in relation to other optimizers, being able to efficiently solve problems classically to use them as benchmarks for quantum machines. In this paper we investigate for the first time the use of Evolutionary Algorithms (EAs) on Ising spin glass instances defined on the Chimera topology. Three genetic algorithms (GAs) and three estimation of distribution algorithms (EDAs) are evaluated over $1000$ hard instances of the Ising spin glass constructed from Sidon sets. We focus on determining whether the information about the topology of the graph can be used to improve the results of EAs and on identifying the characteristics of the Ising instances that influence the success rate of GAs and EDAs.Comment: 8 pages, 5 figures, 3 table

Lake Erie 1993, Western, West Central and Eastern Basins: Change in Trophic Status, and Assessment of the Abundance, Biomass and Production of the Lower Trophic Levels

The western and west central basins were mesotrophic and the eastern basin was oligotrophic, based on many biological and chemical parameters measured in 1993. Gradients were observed for most parameters, with chlorophyll a, nitrogen, phosphorus, silica, and light extinction decreasing from west to east. In the western basin, phytoplankton biomass declined by 51% from 1983-85. Phytoplankton photosynthesis (g C·m-2), predicted from total phosphorus (TP) using a relationship developed in other offshore productivity studies in Lake Ontario, declined by 35% in 1993, without a corresponding decline in phosphorus (P) loading or TP. Diatoms decreased and there was a shift towards smaller phytoplankton species. These changes were attributed to zebra mussel filtration, but were not of sufficient magnitude to reduce zooplankton biomass. In the west central basin, the reductions in phytoplankton biomass were modest. Photosynthesis (g C·m-2) in 1993, was in line with that predicted by TP and the empirical relationship developed in other offshore studies. Limited mussel populations in the west central basin, resulting from low hypolimnetic oxygen concentrations, caused little change in the phytoplankton. There also were no reductions in mean biomass of zooplankton from 1984-87. In the eastern basin, phytoplankton biomass declined by 49% from 1983-85. Photosynthesis (g C·m-2) declined by 50% from the value predicted, from TP and the empirical relationship developed for other studies, for 1983-85, without a decline in P-leading. TP was lower in 1993 and was attributed to filtering by Dreissena and subsequent redirection of pelagic material to the sediments. Phytoplankton species indicative of eutrophy were reduced and there was an overall shift towards smaller species. Zooplankton biomass was also reduced. Mean zooplankton community size and the loss of Daphnia sp. suggest that predation by planktivores as well as a reduced food supply, affected zooplankton biomass in 1993. The Dreissena population also affected the benthic community structure as Diporeia were virtually eliminated from the eastern basin and Gammarus increased in all basins. Benthic biomass was 40% higher on average than in 1979. Dreissena dominated benthic production at all stations except offshore in the west-central basin

Dilaton-Axion hair for slowly rotating Kerr black holes

Campbell et al. demonstrated the existence of axion ``hair'' for Kerr black holes due to the non-trivial Lorentz Chern-Simons term and calculated it explicitly for the case of slow rotation. Here we consider the dilaton coupling to the axion field strength, consistent with low energy string theory and calculate the dilaton ``hair'' arising from this specific axion source.Comment: 13 pages + 1 fi