Growth of graphene on cylindrical copper conductors as an anticorrosion coating: a microscopic study.

We have successfully grown graphene film on the surface of cylindrical copper conductors by chemical vapour deposition. The quality and number of graphene layers have been investigated using Raman spectroscopy, Raman mapping and scanning electron microscopy, as a function of methane gas flow rate and of growth temperature. Transmission electron microscopy analysis has been performed to verify the number of graphene layers, confirming the results obtained by Raman spectroscopy. The results open up the possibility of using graphene as an anticorrosion coating for copper cables and earth grids.

The perceptual tone/noise ratio of merged iterated rippled noises.

Iterated rippled noise (IRN) is constructed by delaying a random noise by d ms, adding it back to the same noise, and repeating the process iteratively. When two IRNs with the same power but slightly different delays are added together, the perceptual tone/noise ratio of the "merged" IRN is markedly reduced with respect to that of either of the component IRNs. In this paper, the reduction in the perceptual tone/noise ratio is measured for IRNs in which one of the delays is always 16 ms and the other is either 16 +/- 0.1 ms or 16 +/- 1.1 ms. The component IRNs have the same number of iterations, and the number varies across conditions from 4 to 256. The perceptual tone/noise ratio is measured using a discrimination matching procedure developed for single IRNs; each merged IRN is compared with a range of "standard" stimuli having varying proportions of a complex tone and a broadband noise [Patterson et al., J. Acoust. Soc. Am. 100, 3286-3294 (1996)]. For single IRNs, the function relating the signal-to-noise ratio of the matching standard to the number of iterations in the IRN was found to be essentially straight. This relationship was explained in terms of the height of the first peak in the autocorrelation of the stimulus wave, or by the first peak in the summary autocorrelogram produced by a time-domain auditory model. For the merged IRNs in the current experiment, the matching-point functions are found to have pronounced downward curvature, in addition to being well below the function for single IRNs. To account for the reduction in the perceptual tone/noise ratio of merged IRNs, the autocorrelation model was extended to include a simple rule for combining adjacent peaks in the autocorrelation function of the wave, and the autocorrelogram model was revised to improve the simulation of the "loss of phase locking" at higher frequencies in the autocorrelogram.

Excitation produced by Schroeder-phase complexes: evidence for fast-acting compression in the auditory system.

A series of experiments compared the excitation produced in an auditory filter centered on 1100 Hz by two complexes, both of which consisted of harmonics 2-20 of a 100-Hz fundamental. When the components had a level of 69 dB SPL each, summing them in positive Schroeder phase produced substantially less forward masking of an 1100-Hz signal than when the components were summed in negative Schroeder phase. This difference decreased with decreases in overall masker level. Listeners also reported that the components of the positive-phase masker close to 1100 Hz were quieter than the corresponding components in the negative-phase masker. The data are explained using Kohlrausch and Sander's [J. Acoust. Soc. Am. 97, 1817-1829 (1995)] finding that the response of an 1100-Hz auditory filter to the positive-phase complex shows marked peaks and dips, whereas that to the negative-phase complex does not. It is argued that the peaks in the response to the positive-phase masker are attenuated by fast-acting compression in the auditory system, thereby reducing the excitation produced by that sound. It is also argued that, compared to the power functions commonly used to model "excess masking" and the growth of loudness, the present data reflect greater compression at high levels but less compression at low levels.

Masking period patterns of Schroeder-phase complexes: effects of level, number of components, and phase of flanking components.

Masking period patterns (MPPs) were obtained for maskers consisting of harmonics 2-20 of a 100-Hz fundamental. The signal was always a 5-ms 1100-Hz sinusoid presented 152, 154, 156, 158, or 160 ms after the start of a 400-ms masker. Experiment 1 replicated the finding that, for a masker level of 69 dB component, the shape of the MPP depended strongly on the phases of the components: Summing them in positive Schroeder phase led to a threshold variation of about 18 dB across the MPP, but summing them in negative Schroeder phase produced a flat MPP [A. Kohlrausch and A. Sander, J. Acoust. Soc. Am. 97, 1817-1829 (1995)]. Reducing the level of the positive-phase masker resulted in a systematic flattening of the MPP, whereas the negative-phase MPPs were flat both at high and at low levels. Experiment 2 showed that removing all components of a positive-phase masker except those close to the signal raised thresholds at the minimum of the MPP. In contrast, a similar manipulation applied to the negative-phase masker produced a uniform elevation of the MPP. Experiment 3 showed that an analogous effect could be obtained by manipulating the phases of masker components remote from the signal. It is shown that several features of the data can be simulated using a nonlinear model of the auditory periphery [C. Giguère and P.C. Woodland, J. Acoust. Soc. Am. 95, 331-342 (1994)].