Unified Description of Polarized and Unpolarized Quark Distributions in the Proton.

We propose a unified new approach to describe polarized and unpolarized quark distributions in the proton based on the gauge-gravity correspondence, light-front holography, and the generalized Veneziano model. We find that the spin-dependent quark distributions are uniquely determined in terms of the unpolarized distributions by chirality separation without the introduction of additional free parameters. The predictions are consistent with existing experimental data and agree with perturbative QCD constraints at large longitudinal momentum x. In particular, we predict the sign reversal of the polarized down-quark distribution in the proton at x=0.8±0.03, a key property of nucleon substructure which will be tested very soon in upcoming experiments.

Universality of Generalized Parton Distributions in Light-Front Holographic QCD.

The structure of generalized parton distributions is determined from light-front holographic QCD up to a universal reparametrization function w(x) which incorporates Regge behavior at small x and inclusive counting rules at x→1. A simple ansatz for w(x) that fulfills these physics constraints with a single-parameter results in precise descriptions of both the nucleon and the pion quark distribution functions in comparison with global fits. The analytic structure of the amplitudes leads to a connection with the Veneziano model and hence to a nontrivial connection with Regge theory and the hadron spectrum.

Language related differences of the sustained response evoked by natural speech sounds.

In tonal languages, such as Mandarin Chinese, the pitch contour of vowels discriminates lexical meaning, which is not the case in non-tonal languages such as German. Recent data provide evidence that pitch processing is influenced by language experience. However, there are still many open questions concerning the representation of such phonological and language-related differences at the level of the auditory cortex (AC). Using magnetoencephalography (MEG), we recorded transient and sustained auditory evoked fields (AEF) in native Chinese and German speakers to investigate language related phonological and semantic aspects in the processing of acoustic stimuli. AEF were elicited by spoken meaningful and meaningless syllables, by vowels, and by a French horn tone. Speech sounds were recorded from a native speaker and showed frequency-modulations according to the pitch-contours of Mandarin. The sustained field (SF) evoked by natural speech signals was significantly larger for Chinese than for German listeners. In contrast, the SF elicited by a horn tone was not significantly different between groups. Furthermore, the SF of Chinese subjects was larger when evoked by meaningful syllables compared to meaningless ones, but there was no significant difference regarding whether vowels were part of the Chinese phonological system or not. Moreover, the N100m gave subtle but clear evidence that for Chinese listeners other factors than purely physical properties play a role in processing meaningful signals. These findings show that the N100 and the SF generated in Heschl's gyrus are influenced by language experience, which suggests that AC activity related to specific pitch contours of vowels is influenced in a top-down fashion by higher, language related areas. Such interactions are in line with anatomical findings and neuroimaging data, as well as with the dual-stream model of language of Hickok and Poeppel that highlights the close and reciprocal interaction between superior temporal gyrus and sulcus.

Radiative feedback in Helmholtz resonators with more than one opening.

The resonance frequency of a Helmholtz resonator with several openings is derived, taking into account the radiation feedback between the different holes. This is done under the assumption that the distance between the openings is large as compared to their linear dimensions. The effect of a finite wall thickness of the resonator is also discussed. The radiation feedback can lead to a shift of the resonance position by more than 10%.

Latency effect of the pitch response due to variations of frequency and spectral envelope.

OBJECTIVE: A clear definition of pitch and timbre is still an open debate and often both terms are mixed up in investigations of tone height. However, fundamental frequency (f(0)) and spectral envelope of a sound play a major role in the perception of tone height. Recent electrophysiological experiments showed that one sub-component of the complex N 100-signal was found to be highly correlated to the perceived tone height. METHODS: Tone height was independently varied by both, a change of f(0) and spectral envelope in order to disentangle the influence of both parameters. Relative tone height was determined psychoacoustically. Neuromagnetic responses were evaluated using source-analysis. RESULTS: Perceived tone height increases with increasing f(0) or spectral envelope. Latency of the pitch change response (PCR) reacts oppositely for the two modi of tone height change. For increasing f(0) and fixed bandpass condition, tone height increases and the latency of the PCR decreases. In contrast, for increasing the center frequency of the bandpass with fixed f(0), tone height increases, but the latency of the PCR increases. CONCLUSIONS: The neuromagnetic pitch response is influenced by both, f(0) and spectral envelope. SIGNIFICANCE: Further investigations of the influence of pitch and timbre on neurophysiological pitch responses have to take into account that both, f(0) and spectral envelope, affect tone height and latency of the PCR.

Semirealistic models of the cochlea.

The aim of this paper is the introduction and comparison of consistent albeit passive mechanical models for the whole cochlea. A widely used transmission line filterbank, which hydrodynamically speaking is a long wave approximation (L model), suffers from a well-known inconsistency: its main modeling assumption is not valid within the resonance region, where most of the overall excitation takes place. In the present paper two approaches to overcome this inconsistency are discussed. One model is the average pressure (AP) model by Duifhuis, the other is obtained by a combination of a long and a short wave approximation (LS model). Considerable differences between the L and the LS model are observed. All models are compared by inserting them into the full integral equation obtained from the hydrodynamic equations and the boundary conditions. Here the LS model fares better than the AP model for small damping, whereas the opposite is true for higher damping. As expected, the L model fails badly in the resonance region.