High-Quality Seizure-Like Activity from Acute Brain Slices Using a Complementary Metal-Oxide-Semiconductor High-Density Microelectrode Array System.

Complementary metal-oxide-semiconductor high-density microelectrode array (CMOS-HD-MEA) systems can record neurophysiological activity from cell cultures and ex vivo brain slices in unprecedented electrophysiological detail. CMOS-HD-MEAs were first optimized to record high-quality neuronal unit activity from cell cultures but have also been shown to produce quality data from acute retinal and cerebellar slices. Researchers have recently used CMOS-HD-MEAs to record local field potentials (LFPs) from acute, cortical rodent brain slices.

Increased modal damping of undamped single and multiscale acoustic black hole panels.

The acoustic black hole (ABH) effect has been shown to increase damping of structures by focusing energy into a tapered-thickness region with added damping material. This paper illustrates that enhanced damping can be achieved without the use of damping material. Three panels were designed with different ABH grid patterns and parameters and compared to a baseline panel.

A simple model for the spatial correlation of turbulence-induced pressures.

The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.

Directional characteristics of two gamelan gongs.

The distinctive geometry and structural characteristics of Balinese gamelan gongs lead to the instrument's unique sound and musical style. This work presents high-resolution directivity measurements of two types of gamelan gongs to quantify and better understand their acoustic behavior. The measured instruments' structural modes clearly impact their far-field directivity patterns, with the number of directional lobes corresponding to the associated structural mode shapes.

Optimization of an acoustic black hole vibration absorber at the end of a cantilever beam.

Structures whose thickness follow a power law profile exhibit the "acoustic black hole" (ABH) effect and can be used for effective vibration reduction. However, it is difficult to know a priori what constitutes the best design. A new block matrix formulation of the transfer matrix method is developed for use in the optimization of an ABH vibration absorber at the end of a cantilever beam.

Transient finite element/equivalent sources using direct coupling and treating the acoustic coupling matrix as sparse.

Transient structural-acoustic problems can be solved using time stepping procedures with the structure and fluid modeled using finite elements and equivalent sources, respectively. Limitations on the time step size for stable solutions have led to the current popularity of iterative coupling to enforce the boundary conditions at the fluid-structure interface, which also helps to alleviate difficulties caused by the fully populated acoustic coupling matrix. The research presented here examines a monolithic approach using a stabilized equivalent source formulation where the acoustic coupling matrix is either fully diagonal or treated as sparse.

Quieting a rib-framed honeycomb core sandwich panel for a rotorcraft roof.

A rotorcraft roof composite sandwich panel has been redesigned to optimize sound power transmission loss (TL) and minimize structure-borne sound for frequencies between 1 and 4 kHz where gear meshing noise from the transmission has the most impact on speech intelligibility. The roof section, framed by a grid of ribs, was originally constructed of a single honeycomb core/composite facesheet sandwich panel. The original panel has acoustic coincidence frequencies near 600 Hz, leading to poor TL across the frequency range of 1 to 4 kHz.

Multi-objective optimization of acoustic black hole vibration absorbers.

Structures with power law tapers exhibit the acoustic black hole (ABH) effect and can be used for vibration reduction. However, the design of ABHs for vibration reduction requires consideration of the underlying theory and its regions of validity. To address the competing nature of the best ABH design for vibration reduction and the underlying theoretical assumptions, a multi-objective approach is used to find the lowest frequency where both criteria are sufficiently met.

A hybrid approach for simulating fluid loading effects on structures using experimental modal analysis and the boundary element method.

Many structural acoustics problems involve a vibrating structure in a heavy fluid. However, obtaining fluid-loaded natural frequencies and damping experimentally can be difficult and expensive. This paper presents a hybrid experimental-numerical approach to determine the heavy-fluid-loaded resonance frequencies and damping of a structure from in-air measurements.

Experimental evidence of modal wavenumber relation to zeros in the wavenumber spectrum of a simply supported plate.

The modal wavenumber of rectangular, simply supported, isotropic thin plates was theoretically shown to be related to the zeros in the wavenumber spectrum and not to the peaks, resulting in an error between the actual modal wavenumber and location of the wavenumber spectrum peak for low mode orders. This theoretical proof is confirmed by experimental results reported in this letter.

The effects of wood variability on the free vibration of an acoustic guitar top plate.

A finite element model of a bare top plate with braces and a bridge plate was created using orthotropic material properties. The natural variation of the wood properties including dependence on moisture content was also determined. The simulated modes were then compared to experimentally obtained modes from top plate prototypes.

Minimizing the acoustic power radiated by a fluid-loaded curved panel excited by turbulent boundary layer flow.

In order to address noise control problems in the design stage, structural-acoustic optimization procedures can be used to find the optimal design for reduced noise or vibration. However, most structural-acoustic optimization procedures are not general enough to include both heavy fluid loading and complex forcing functions. Additionally, it can be difficult to determine and assess trade-offs between weight and sound radiation.

Comment on plate modal wavenumber transforms in Sound and structural vibration [Academic Press (1987, 2007)] (L).

The wavenumber transform for rectangular, simply supported, isotropic thin plates has been rederived to correct a technical error found in the text Sound and Structural Vibration (Academic Press, 1985/2007) by Fahy/Fahy and Gardonio. The text states that the modal wavenumber corresponds to the peak of the wavenumber spectrum. While this is approximately true for higher-order modes, it does not hold for lower-order modes due to coupling between positive and negative wavenumber energy.

Evolution of statistical properties for a nonlinearly propagating sinusoid.

The nonlinear propagation of a pure sinusoid is considered using time domain statistics. The probability density function, standard deviation, skewness, kurtosis, and crest factor are computed for both the amplitude and amplitude time derivatives as a function of distance. The amplitude statistics vary only in the postshock realm, while the amplitude derivative statistics vary rapidly in the preshock realm.

Bicoherence analysis of model-scale jet noise.

Bicoherence analysis has been used to characterize nonlinear effects in the propagation of noise from a model-scale, Mach-2.0, unheated jet. Nonlinear propagation effects are predominantly limited to regions near the peak directivity angle for this jet source and propagation range.

Short-range shock formation and coalescence in numerical simulation of broadband noise propagation.

The number of jet and rocket noise studies has increased in recent years as researchers have sought to better understand aeroacoustic source and radiation characteristics. Although jet and rocket noise is finite-amplitude in nature, little is known about the existence of shock formation and coalescence close to the source. A numerical experiment is performed to propagate finite-amplitude noise and determine the extent of the nonlinearity over short distances with spherical spreading.