A kinematic subgrid scale model for large-eddy simulation of turbulence generated sound

In the hybrid approach of large-eddy simulation (LES) and Lighthill’s acoustic analogy for turbulence-generated sound, the turbulence source fields are obtained using an LES and the turbulence-generated sound at far fields is calculated from Lighthill’s acoustic analogy. As only the velocity fields at resolved scales are available from the LES, the Lighthill stress tensor, serving as a source term in Lighthill’s acoustic equation, has to be evaluated from the resolved velocity fields. As a result, the contribution from the unresolved velocity fields is missing in the conventional LES. The sound of missing scales is shown to be important and hence needs to be modeled. The present study proposes a kinematic subgrid-scale (SGS) model which recasts the unresolved velocity fields into Lighthill’s stress tensors. A kinematic simulation is used to construct the unresolved velocity fields with the imposed temporal statistics, which is consistent with the random sweeping hypothesis. The kinematic SGS model is used to calculate sound power spectra from isotropic turbulence and yields an improved result: the missing portion of the sound power spectra is approximately recovered in the LES.

Telemetric recordings of single neuron activity and visual scenes in monkeys walking in an open field

This paper describes a portable recording system and methods for obtaining chronic recordings of single units and tracking rhesus monkey behavior in an open field. The integrated system consists of four major components: (1) microelectrode assembly; (2) h

Neurophysiological recordings in freely moving monkeys

Recordings of neuronal activity in freely moving rats are common in experiments where electrical signals are transmitted using cables. Such techniques are not common in monkeys because their prehensile abilities are thought to preclude such techniques. Ho

Influence of physical parameters of sound on the sensory gating effects of N40 in rats

Sensory gating is the ability of the brain to modulate its sensitivity to incoming stimuli. The N40 component of the auditory evoked potential, evaluated with the paired click paradigm, was used to probe the gating effect in rats. The physical characteris

A micromachined SiO2/silicon probe for neural signal recordings

The development of an implantable five channel microelectrode array is presented for neural signal recordings. The detailed fabrication process is outlined with four masked used. The SEM images show that the probe shank is 1.2mm long, 100 mu m wide and 30 mu m thick with the recording sites spaced 200 mu m apart for good signal isolation. The plot of the single recording site impedance versus frequency is shown by test in vitro and the ompedence declines with the increasing frequency. Experiment in vivo using this probe is under way.

Simulation of a monolithically integrated CMOS bioamplifier for EEG recordings

A monolithically integrated CMOS bioamplifier is presented in this paper for EEG recording applications. The capacitive-coupled circuit input structure is utilized to eliminate the large and random DC offsets existing in the electrode-tissue interface. Diode-connected NMOS transistors with negative voltage between gate and source are candidates for large resistors necessary to the bioamplifier. A passive BEF (Band Eliminator Filter) can reduce 50 Hz noise disturbance strength by more than 60 dB. A novel analysis approach is given to help determine the noise power spectral density. Simulation results show that the two-stage CMOS bioamplifier in a closed-loop capacitive feedback configuration,provides an AC in-band gain of 39.6 dB, a DC gain of zero, and an input-referred noise of 87 nVrms integrated from 0.01 Hz to 100 Hz.

Simulation of a Monolithic Integrated CMOS Preamplifier for Neural Recordings

A monolithic integrated CMOS preamplifier is presented for neural recording applications. Two AC-coupied capacitors are used to eliminate the large and random DC offsets existing in the electrode-electrolyte interface. Diode-connected nMOS transistors with a negative voltage between the gate and source are candidates for the large resistors necessary for the preamplifier. A novel analysis is given to determine the noise power spectral density. Simulation results show that the two-stage CMOS preamplifier in a closed-loop capacitive feedback configuration provides an AC in-band gain of 38.8dB,a DC gain of 0,and an input-referred noise of 277nVmax, integrated from 0. 1Hz to 1kHz. The preamplifier can eliminate the DC offset voltage and has low input-referred noise by novel circuit configuration and theoretical analysis.

Spatial and temporal variations of sound speed at the PN section

Gridded sound speed data were calculated using Del Grosso's formulation from the temperature and salinity data at the PN section in the East China Sea covering 92 cruises between February 1978 and October 2000. The vertical gradients of sound speed are mainly related to the seasonal variations, and the strong horizontal gradients are mainly related to the Kuroshio and the upwelling. The standard deviations show that great variations of sound speed exist in the upper layer and in the slope zone. Empirical orthogonal function analysis shows that contributions of surface heating and the Kuroshio to sound speed variance are almost equivalent.