Effect Of Amplitude Fluctuations Research Articles

Effect of amplitude fluctuations on the loudness of low-frequency sounds

The loudness of two-tone complexes (TTCs) with center frequencies (fc ) of 40, 63, 80, and 1000 Hz was matched with that of unmodulated tones (UTs). Frequency differences between the TTC components, corresponding to beat frequencies, fb , were 1, 2, 5, and 12 Hz. To compensate for the steep decline in hearing sensitivity below 100 Hz, prior to the loudness match, subjects adjusted the relative levels (ΔL) of the TTC components to give maximum beat perception. Twenty-four normal-hearing subjects were tested. The values of ΔL giving best beats were well predicted from the transfer function of the middle ear and the estimated shapes of the auditory filters, assuming that the auditory filter whose output dominated the beat percept was centered somewhat above fc . At the same root-mean-square level and independent of fc , TTCs were perceived as louder than UTs for fb ≤ 2 Hz, had roughly equal loudness to UTs for fb = 5 Hz, and were less loud than UTs for fb = 12 Hz. The similar pattern observed across fc suggests that the dependence of loudness on amplitude-fluctuation rate is determined by processes occurring at higher stages of the auditory system than the cochlea.The loudness of two-tone complexes (TTCs) with center frequencies (fc ) of 40, 63, 80, and 1000 Hz was matched with that of unmodulated tones (UTs). Frequency differences between the TTC components, corresponding to beat frequencies, fb , were 1, 2, 5, and 12 Hz. To compensate for the steep decline in hearing sensitivity below 100 Hz, prior to the loudness match, subjects adjusted the relative levels (ΔL) of the TTC components to give maximum beat perception. Twenty-four normal-hearing subjects were tested. The values of ΔL giving best beats were well predicted from the transfer function of the middle ear and the estimated shapes of the auditory filters, assuming that the auditory filter whose output dominated the beat percept was centered somewhat above fc . At the same root-mean-square level and independent of fc , TTCs were perceived as louder than UTs for fb ≤ 2 Hz, had roughly equal loudness to UTs for fb = 5 Hz, and were less loud than UTs for fb = 12 Hz. The similar pattern observed across fc s...

Spectral properties of a resonator driven by a superconducting single-electron transistor

We analyze the spectral properties of a resonator coupled to a superconducting single electron transistor (SSET) close to the Josephson quasiparticle resonance. Focussing on the regime where the resonator is driven into a limit-cycle state by the SSET, we investigate the behavior of the resonator linewidth and the energy relaxation rate which control the widths of the main features in the resonator spectra. We find that the linewidth becomes very narrow in the limit-cycle regime, where it is dominated by a slow phase diffusion process, as in a laser. The overall phase diffusion rate is determined by a combination of direct phase diffusion and the effect of amplitude fluctuations which affect the phase because the resonator frequency is amplitude dependent. For sufficiently strong couplings we find that a regime emerges where the phase diffusion is no longer minimized when the average resonator energy is maximized. Finally we show that the current noise of the SSET provides a way of measuring both the linewidth and energy relaxation rate.

Signal amplitude effects on reflectometer studies of density turbulence in tokamaks

The effect of amplitude fluctuations on reflectometer measurements of density turbulence has been investigated through comparison of reflectometry and Langmuir probes on the CCT and DIII-D tokamaks. Power spectra, turbulent radial correlation lengths, and root-mean square magnitude variations (at the H-mode transition) of the homodyne reflectometer signal (given by , which depends strongly on the amplitude E and nonlinearly on the phase ), show good agreement with Langmuir probes. The homodyne signal is found to be dominated by the amplitude fluctuations and not by the phase for high density fluctuation levels. Correspondingly, power spectra and correlation lengths deduced from the phase data alone show agreement with the homodyne signal only at low density fluctuation levels. It is concluded that for these plasma parameters the homodyne signal is closely representative of the density fluctuation behaviour and that this response is related to the reflectometer amplitude E. This correspondence of the homodyne signal and density fluctuations is in contrast to most theoretical/modelling work which has typically concentrated on the phase. A one-dimensional simulation of resonance absorption effects upon the amplitude and phase of a reflectometer is presented as an example of how amplitude fluctuations might arise due to processes internal to the plasma. The implications of these results and the connection to theory are discussed.

Mutual coherence function of a wave front corrected by zonal adaptive optics

The mutual coherence function (MCF) of a wave propagated through atmospheric turbulence and corrected by zonal adaptive optics is derived for a segmented corrector with either piston only or piston with a local tilt fit. We begin with an intuitive approach which is based on replacing the outer scale of turbulence in the uncorrected MCF with a quantity proportional to the segment size. This approach is especially useful in deriving asymptotes. A rigorous approach provides the full curves, and reduces to a single curve for piston only and a single curve for piston with tilt, after proper parametrization. The effect of amplitude fluctuations is also considered, since scintillation limits the ultimate degree of correction as the segment size goes to zero. Although the analysis is for a segmented corrector, the results apply fairly well to continuous corrector with actuator spacing equal to d/√3, where d is the segment diameter.

Non-Gaussian fluctuations in electromagnetic radiation scattered by a random phase screen. II. Application to dynamic scattering in liquid crystal

For pt.I see ibid., vol.8, 369 (1975). The authors have studied experimentally the statistical, spatial coherence and temporal coherence properties of non-Gaussian fluctuations in light scattered by a thin layer of liquid crystal (MBBA) in its dynamic scattering state. The results are consistent with the deep phase-screen theory developed in the previous paper. With 20 V applied to the sample, experimental values of the parameters of the model are: mean square phase deviation phi 2=45.6+or-8.0 rad2, phase correlation length xi =2.63+or-0.24 mu m and phase coherence time 2.2+or-0.2s. Indications are found that, while phase fluctuations in the emergent wave-front are probably dominant, amplitude fluctuations are not entirely negligible. It is argued, however, that the effects of amplitude fluctuations on the values of the above parameters are probably quite small. Taking a broader view, the results confirm that, in many scattering experiments, detailed information concerning the scattering process can be obtained from measurements in the non-Gaussian regime.

Precision Coaxial VSWR Measurements by Coupled Sliding-Load Technique

The method described employs a slotted line for VSWR measurement and a precision coaxial line as an impedance standard. A sliding load terminates the standard line during the process of transforming the impedance of the slotted line to that of the standard line. This load is coupled mechanically to the slotted-line probe so that the two move together. The VSWR seen by the probe is then, to first approximation, only that due to the reflection from the junction of the two lines. It is simple, therefore, to tune out the residual reflection without requiring a perfect load. The slotted line is then effectively transformed to the impedance of the standard line, and subsequent measurements made with it at the same frequency indicate VSWR with respect to the standard line. In order to minimize the effect of amplitude fluctuations of the RF source and to expand the scale, the detected probe output is compared with the detected output of a directional coupler monitoring the incident power. The difference is recorded with a strip recorder; the paper transport of the recorder is synchronized with the probe travel. In describing the method, considerable background material is presented on other precision impedance-measuring methods and techniques and on the general state-of-the-art. Theory, accuracy, system details, and results are given. The system appears capable of making absolute impedance measurements on a low VSWR termination to a maximum possible error in reflection coefficient of 0.0012.