Inter-channel Delay Research Articles

Effects of filtering and delays on the estimates of a nonlinear respiratory mechanics model

Estimation of mechanical properties of the respiratory system may be disturbed by instrumentation and physical set-up. The effects of lowpass filtering, filter mismatch and inter-channel delay in the digital converter are assessed on numerically simulated signals from a nonlinear model of the respiratory system. Large biases in model parameter estimates (up to about -300% for some parameters) were caused by these instrumental interferences and were reduced by including an inertance in the retrieved model. The results reinforce the importance of a careful evaluation of the instrumental set-up used in physiological measurements.

Quadrupole mass spectrometer operating in the electron-capture negative ion mode as detector for comprehensive two-dimensional gas chromatography

A recently introduced rapid-scanning quadrupole mass spectrometer (qMS) with an electron-capture negative ion (ECNI) option, the Perkin-Elmer Clarus 500, was tested as a detector for comprehensive two-dimensional gas chromatography (GC × GC). The parameters influencing the data acquisition rate in the scan mode, such as scan time and inter-scan delay, and in the selected ion monitoring mode, such as dwell time and inter-channel delay, were evaluated. In the scan mode, good-quality mass spectra covering a range of 300 Da can be obtained at an acquisition rate of 23 Hz; in selected ion monitoring, an acquisition rate of 90 Hz can be achieved when monitoring a single ion. Compared with electron ionisation, the use of electron-capture negative ionisation causes no extra peak broadening. As applications, mixtures of polychlorinated n-alkanes (PCAs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo- p-dioxins (PCDDs) and dibenzofurans (PCDFs) were analysed. The separation of PCAs based on their number of chlorine substituents was confirmed for the first time by using GC × GC–ECNI qMS in the scan mode and a significantly improved limit of detection was achieved for BDEs (10–150 fg injected) and CDD/Fs (10–700 fg injected) in the selected ion monitoring mode.

Detection of small across-channel timing differences by cochlear implantees

Five post-lingually deafened users of the LAURA cochlear implant were presented with two trains of biphasic pulses applied concurrently to two widely separated channels. They could all discriminate between stimuli where pulses on the two channels were nearly synchronous (inter-channel delay=0.1 ms) and those where there was a longer delay applied to one channel. All showed an asymmetry, being more sensitive when the longer delay was on either the more basal or, depending on the listener, the more apical channel. For four out of the five listeners this asymmetry could be at least partly attributed to one stimulus, with a 0.1-ms delay in either the apical (three listeners) or basal (one listener) channel, sounding markedly different from all other stimuli used in the experiment. Both the overall sensitivity of listeners and the general pattern of results survived the presentation of maskers on intermediate channels, and did not vary markedly with changes in the polarity of the pulses applied to one channel. Although the results varied substantially across listeners, it is concluded that they demonstrate a genuine sensitivity to the relative timing of stimulation applied to discrete populations of auditory nerve fibers.

On the advantages and drawbacks of using digital acquisition systems for the determination of magnetic properties of electrical steel sheet and strip

This paper focusses on the use of digital acquisition techniques when measuring the magnetic characteristics of electrical steel sheet and strip. Different aspects on accuracy and error sources caused by the use of such a setup are considered. As the main point, the importance of phase accuracy and interchannel delay compensation when using LabVIEW virtual instruments is shown.