Shake-up Processes in a Low-Density Two-Dimensional Electron Gas: Spin-Dependent Transitions to Higher Hole Landau Levels

A theory of shake-up processes in photoabsorption of an interacting low-density two-dimensional electron gas (2DEG) in strong magnetic fields is presented. In these processes, an incident photon creates an electron-hole pair and, because of Coulomb interactions, simultaneously excites one particle to higher Landau levels (LL's). In this work, the spectra of correlated charged spin-singlet and spin-triplet electron-hole states in the first hole LL and optical transitions to these states (i.e., shake-ups to the first hole LL) are studied. Our results indicate, in particular, the presence of optically-active three-particle quasi-discrete states in the exciton continuum that may give rise to surprisingly sharp Fano resonances in strong magnetic fields. The relation between shake-ups in photoabsorption of the 2DEG and in the 2D hole gas (2DHG), and shake-ups of isolated negative X^- and positive X^+ trions are discussed.Comment: 8 pages, 8 figures. References updated, one figure added (Fig. 6). Accepted in Phys. Rev.

Frame Theory for Signal Processing in Psychoacoustics

This review chapter aims to strengthen the link between frame theory and signal processing tasks in psychoacoustics. On the one side, the basic concepts of frame theory are presented and some proofs are provided to explain those concepts in some detail. The goal is to reveal to hearing scientists how this mathematical theory could be relevant for their research. In particular, we focus on frame theory in a filter bank approach, which is probably the most relevant view-point for audio signal processing. On the other side, basic psychoacoustic concepts are presented to stimulate mathematicians to apply their knowledge in this field

A revision of Zwicker's loudness model

Zwicker's loudness model has the following stages: (a) A fixed filter representing transfer through the outer and middle ear; (b) Calculation of an excitation pattern from the physical spectrum; (c) Transformation of the excitation pattern to a specific loudness pattern. The area under the specific loudness pattern is assumed to determine loudness. This paper presents some modifications and extensions to Zwicker's loudness model. Changes are made in: (a) The assumed transfer function for the outer and middle ear; (b) The way that excitation patterns are calculated; (c) The way that specific loudness is related to excitation for sounds in quiet and in noise. The revised model accounts more accurately than Zwicker's model for the way that equal-loudness contours change with level. It also provides a more satisfactory explanation of why the loudness of a sound of fixed intensity remains constant when the sound has a bandwidth less than the critical bandwidth (CB). Finally, the revised model is able to account for the loudness of partially masked sounds without the introduction of correction factors. The revised model has the advantage that the excitation patterns on which it is based are calculated from analytical formulae rather than by reference to charts or tables. This avoids discontinuities in the predicted values of loudness

Comparison of auditory filter shapes obtained with notched-noise and noise-tone maskers

The notched-noise method has been widely used to estimate the shape of the auditory filter. Results obtained using this method may be influenced by combination bands produced by the interaction of components within the upper band of noise in the notched-noise masker. To assess the possible effect of such combination bands, results were compared for two types of masker: A notched noise, as used in previous experiments; and a masker in which the upper band of noise was replaced by a sinusoid with a frequency corresponding to the lower edge frequency of that band. This is referred to as the noise-tone masker. The signal frequency was 2 kHz, and measurements were obtained for two different spectrum levels of the noise masker, 30 and 45 dB. Auditory filter shapes derived using the two maskers were similar on their low-frequency sides, as expected. The low-frequency sides were less steep at the higher masker level. The high-frequency sides of the auditory filters derived using the noise-tone masker were sometimes slightly steeper than those obtained using the notched-noise masker, but the effect was generally small. Changes with level on the high-frequency sides were not consistent across subjects. An analysis of the notched-noise data taking into account the effects of the combination bands suggests that the maximal spectrum level of the combination bands, in the region just below the lower spectral edge of the primary noise band, is about 20 to 30 dB below the spectrum level of the primary band. At this relative level, the combination bands have only a very small influence on the high-frequency sides of the derived auditory filters. The influence on the estimated equivalent rectangular bandwidths (ERBs) of the auditory filters is usually negligible