Experimental implementation of a low-frequency global sound equalization method based on free field propagation

An experimental implementation of a global sound equalization method in a rectangular room using active control is described in this paper. The main purpose of the work has been to provide experimental evidence that sound can be equalized in a continuous three-dimensional region, the listening zone, which occupies a considerable part of the complete volume of the room. The equalization method, based on the simulation of a progressive plane wave, was implemented in a room with inner dimensions of 2.70 m × 2.74 m × 2.40 m. With this method, the sound was reproduced by a matrix of 4 × 5 loudspeakers in one of the walls. After traveling through the room, the sound wave was absorbed on the opposite wall, which had a similar arrangement of loudspeakers, by means of active control. A set of 40 digital FIR filters was used to modify the original input signal before it was fed to the loudspeakers, one filter for each transducer. The optimal arrangement of the loudspeakers and the maximum frequency that can be equalized is analyzed theoretically in this paper. The presented experimental results show that sound equalization was possible from 10 Hz to approximately 425 Hz in the listening zone. A flat frequency response with deviations within ±5 decibels from the desired value was achieved. A higher demanding performance with deviations within ±1.5 decibels from a flat frequency response was attained in the interval between 20 Hz and 280 Hz. At the same time, the impulse response was quite well approximated to a delayed delta function in the listening zone. Examples of the spatial distribution of the sound field are also shown.     

An inertia-capacitance beam substructure formulation based on the bond graph method with application to rotating beams

In this paper, a novel inertia-capacitance (IC) beam substructure formulation based on the IC-field presentation from the bond graph method is developed. The IC beam provides a modular, systematic and graphical approach to beam modeling. These features allow the modeler to focus more on the modeling and less on the mathematics. As such, the IC beam is proposed as an alternative to the many existing types of beam models available in the literature. The IC beam is formulated in the center of mass body fixed coordinate system allowing for easy interfacing in a multibody system setting. This floating frame approach is also computationally cheap. Elastic deformations in the IC beam are assumed to be small and described by modal superposition. The formulation couples rigid body and elastic deformations in a nonlinear fashion. The formulation is also compact and efficient. Detailed derivations for a two-dimensional planar IC beam with bending modes are presented. A modal acceleration method based on the decoupling of bending modes is proposed for use in the IC beam. The rotating beam spin-up maneuver problem is solved. The Karnopp-Margolis method is applied to ensure complete integral causality for an efficient numerical system. Geometric substructuring technique is applied to model large deflections. The IC beam is shown to be capable of solving the rotating beam problem accurately and efficiently.     

Global Existence and Blowup for a Parabolic Equation with a Non-Local Source and Absorption

In this paper we consider a double fronts free boundary problem for a parabolic equation with a non-local source and absorption. The long time behaviors of the solutions are given and the properties of the free boundaries are discussed. Our results show that if the initial value is sufficiently large, then the solution blows up in finite time, while the global fast solution exists for sufficiently small initial data, and the intermediate case with suitably large initial data gives the existence of the global slow solution.     

Synthesis of crystalline Ge nanoclusters in PE-CVD-deposited SiO2 films

The synthesis of evenly distributed Ge nanoclusters in plasma-enhanced chemical-vapour-deposited (PE-CVD) SiO₂ thin films containing 8 at. % Ge is reported. This is of importance for the application of nanoclusters in semiconductor technology. The average diameter of the Ge nanoclusters can be controlled in the range of 3–6 nm by variation of the annealing parameters. Using a combination of transmission electron microscopy and Raman-scattering spectroscopy, the nanoclusters were shown to be crystalline. However, photoluminescence measurements showed no light emission that could be definitively correlated to the presence of the nanoclusters. PACS 61.82.Rx; 78.67.Bf; 81.07.Bc     

Quantitation of pressure-sensitive film using digital image scanning

An experimental technique is presented for measurement of contact stress distribution using Fuji Pressensor film. The development of packets of Pressensor disks for use in small areas or surfaces of complex curvature is explained. A digital-image-scanning procedure has been developed to substantially increase the spatial resolution with which stress distributions can be constructed from stained Fuji Pressensor film. The technique is developed for small, discrete disks as well as for larger, continuous sheets of Pressensor. As an illustration, sealed packets of small Pressensor disks are used to measure the stress distribution across a cadaveric juvenile femoral head under load.     

Enhanced Catalytic Activity of Cobalt Porphyrin in CO2 Electroreduction upon Immobilization on Carbon Materials

In a comparative study of the electrocatalytic CO₂ reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO₂ becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO₂. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone.     

Synthesis of the core structure of the lipoteichoic acid of Streptococcus pneumoniae

Streptococcus pneumoniae LTA is a highly complex glycophospholipid that consists of nine carbohydrate residues: three glucose, two galactosamine and two 2‐acetamino‐4‐amino‐2,4,6‐trideoxygalactose (AATDgal) residues that are each differently linked, one ribitol and one diacylated glycerol (DAG) residue. Suitable building blocks for the glucose and the AATDgal residues were designed and their synthesis is described in this paper. These building blocks permitted the successful synthesis of the core structure Glcβ(1‐3)AATDgalβ(1‐3)Glcα(1‐O)DAG in a suitably protected form for further chain extension ( 1 b , 1 c ) and as unprotected glycolipid ( 1 a ) that was employed in biological studies. These studies revealed that 1 a as well as 1 lead to interleukin‐8 release, however not via TLR2 or TLR4 as receptor.     

Atomic forces for geometry‐dependent point multipole and Gaussian multipole models

In standard treatments of atomic multipole models, interaction energies, total molecular forces, and total molecular torques are given for multipolar interactions between rigid molecules. However, if the molecules are assumed to be flexible, two additional multipolar atomic forces arise because of (1) the transfer of torque between neighboring atoms and (2) the dependence of multipole moment on internal geometry (bond lengths, bond angles, etc.) for geometry‐dependent multipole models. In this study, atomic force expressions for geometry‐dependent multipoles are presented for use in simulations of flexible molecules. The atomic forces are derived by first proposing a new general expression for Wigner function derivatives . The force equations can be applied to electrostatic models based on atomic point multipoles or Gaussian multipole charge density. Hydrogen‐bonded dimers are used to test the intermolecular electrostatic energies and atomic forces calculated by geometry‐dependent multipoles fit to the ab initio electrostatic potential. The electrostatic energies and forces are compared with their reference ab initio values. It is shown that both static and geometry‐dependent multipole models are able to reproduce total molecular forces and torques with respect to ab initio, whereas geometry‐dependent multipoles are needed to reproduce ab initio atomic forces. The expressions for atomic force can be used in simulations of flexible molecules with atomic multipoles. In addition, the results presented in this work should lead to further development of next generation force fields composed of geometry‐dependent multipole models. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Psychophysical tuning curves for frequencies below 100 Hz

Psychophysical tuning curves (PTCs) were measured for sinusoidal signals with frequency f(s)?= 31.5, 40, 50, 63, and 80 Hz, using sinusoidal and narrowband-noise maskers. For the former, conditions were included where a pair of beating tones was added to reduce the use of cues related to beats. Estimates of each subject's middle-ear transfer function (METF) were obtained from equal-loudness contours measured from 20 to 160 Hz. With decreasing f(s), the PTCs became progressively broadened and markedly asymmetrical, with shallow upper skirts and steep lower skirts. For the sinusoidal maskers, the tips were more irregular than for narrowband-noise maskers or when beating tones were added. For f(s)?= 31.5 and 40 Hz, the tips of the PTCs always fell above f(s). Allowing for the METF so as to infer underlying filter shapes resulted in flatter lower skirts, especially below 40 Hz, and reduced the frequency at the tips for f(s) between 31.5 and 50 Hz; however, the tips did not fall below 40 to 50 Hz. The bandwidths of the PTCs increased with decreasing f(s) below 80 Hz. However, bandwidths remained roughly constant if the METF was included as part of auditory filtering for frequencies below 40 Hz.     

Low-frequency noise from large wind turbines

As wind turbines get larger, worries have emerged that the turbine noise would move down in frequency and that the low-frequency noise would cause annoyance for the neighbors. The noise emission from 48 wind turbines with nominal electric power up to 3.6 MW is analyzed and discussed. The relative amount of low-frequency noise is higher for large turbines (2.3-3.6 MW) than for small turbines (≤ 2 MW), and the difference is statistically significant. The difference can also be expressed as a downward shift of the spectrum of approximately one-third of an octave. A further shift of similar size is suggested for future turbines in the 10-MW range. Due to the air absorption, the higher low-frequency content becomes even more pronounced, when sound pressure levels in relevant neighbor distances are considered. Even when A-weighted levels are considered, a substantial part of the noise is at low frequencies, and for several of the investigated large turbines, the one-third-octave band with the highest level is at or below 250 Hz. It is thus beyond any doubt that the low-frequency part of the spectrum plays an important role in the noise at the neighbors.