Single fibre action potentials in skeletal muscle related to recording distances

Single muscle fibre action potentials (SFAPs) are considered to be functions of a bioelectrical source and electrical conductivity parameters of the medium. In most model studies SFAPs are computed as a convolution of the bioelectrical source with a transfer function. Calculated peak-to-peak amplitudes of SFAPs decrease with increasing recording distances. In this paper an experimental validation of model results is presented. Experiments were carried out on the m. extensor digitorum longus (EDL) of the rat. Using a method including fluorescent labelling of the active fibre, the distance between the active fibre and the recording electrode was derived. With another method, the decline of the peak-to-peak amplitude of SFAPs detected along a multi-electrode was obtained. With both experimental methods, in general peak-to-peak amplitudes of SFAPs decreased with increasing recording distances, as was found in model results with present volume conduction theory. However, this behaviour was not found in all experiments. The rate of decline of the peak-to-peak amplitudes with recording distance was always less than in models

The categorisation of speech sounds by adults and children: a study of the categorical perception hypothesis and the development weighting of acoustic speech cues

This thesis investigates the way adults and children perceive speech. With adult listeners, the question was whether speech is perceived categorically (categorical speech perception). With children, the question was whether there are age-related differences between the weights assigned to acoustic cues that specify certain speech contrasts (cue-weighting). One goal of this thesis was to test the categorical perception hypothesis. According to this hypothesis, the acquisition of the native phonological system changes listeners perception in such a way that they find it difficult to detect small differences between different realisations of the same phoneme, but relatively easy to detect equally small differences between realisations of two different phonemes. Several discrimination and classification experiments are described involving stimulus continua between vowels and between stop consonants. It is shown that categorical perception results are far from robust and that the degree of categorical perception is influenced by the discrimination task, the interstimulus interval, the listener, and the stimulus. Evidence is provided that listeners are perfectly capable of hearing small within-phoneme-category differences and thus that the acquisition of the phonological system does not have negative effects on the detection of differences between speech signals. A second goal was to study the development of the perceptual integration of speech cues that specify a certain phoneme category. It was tested whether children of 4, 6, and 9 years old weight certain acoustic cues for stop consonants, fricatives, and vowels differently from adults. The results confirm earlier findings that children, especially the 4-year-olds, weigh certain speech cues more heavily, and other cues less heavily, than adults do. Children s ability to adjust the weighting of specific cues in the variable acoustic signal provides further evidence against the idea that acoustic detail in the signal becomes less detectable as language develops. This study is of interest to phoneticians and psycholinguists, as well as to researchers working in the field of experimental speech and language development

Tomography of photon-number resolving continuous-output detectors

We report a comprehensive approach to analysing continuous-output photon detectors. We employ principal component analysis to maximise the information extracted, followed by a novel noise-tolerant parameterised approach to the tomography of PNRDs. We further propose a measure for rigorously quantifying a detector's photon-number-resolving capability. Our approach applies to all detectors with continuous-output signals. We illustrate our methods by applying them to experimental data obtained from a transition-edge sensor (TES) detector.Comment: 5 pages, 3 figures, also includes supplementary informatio

Cryogenic scintillation properties of n-type GaAs for the direct detection of MeV/c2 dark matter

This paper is the first report of n-type GaAs as a cryogenic scintillation radiation detector for the detection of electron recoils from interacting dark matter (DM) particles in the poorly explored MeV/c2 mass range. Seven GaAs samples from two commercial suppliers and with different silicon and boron concentrations were studied for their low temperature optical and scintillation properties. All samples are n-type even at low temperatures and exhibit emission between silicon donors and boron acceptors that peaks at 1.33 eV (930 nm). The lowest excitation band peaks at 1.44 eV (860 nm), and the overlap between the emission and excitation bands is small. The X-ray excited luminosities range from 7 to 43 photons/keV. Thermally stimulated luminescence measurements show that n-type GaAs does not accumulate metastable radiative states that could cause afterglow. Further development and use with cryogenic photodetectors promises a remarkable combination of large target size, ultra-low backgrounds, and a sensitivity to electron recoils of a few eV that would be produced by DM particles as light as a few MeV/c2