Effect of current stimulus on in vivo cochlear mechanics

In this paper, the influence of direct current stimulation on the acoustic impulse response of the basilar membrane (BM) is studied. A positive current applied in the scala vestibuli relative to a ground electrode in the scala tympani is found to enhance gain and increase the best frequency at a given location on the BM. An opposite effect is found for a negative current. Also, the amplitude of low-frequency cochlear microphonic at high sound levels is found to change with the concurrent application of direct current stimulus. BM vibrations in response to pure tone acoustic excitation are found to possess harmonics whose levels relative to the fundamental increase with the application of positive current and decrease with the application of negative current. A model for outer hair cell activity that couples changes in length and stiffness to transmembrane potential is used to interpret the results of these experiments and others in the literature. The importance of the in vivo mechanical and electrical loading is emphasized. Simulation results show the somewhat paradoxical finding that for outer hair cells under tension, hyperpolarization causes shortening of the cell length due to the dominance of voltage dependent stiffness changes.     

A state space model for cochlear mechanics

The stability of a linear model of the active cochlea is difficult to determine from its calculated frequency response alone. A state space model of the cochlea is presented, which includes a discretized set of general micromechanical elements coupled via the cochlear fluid. The stability of this time domain model can be easily determined in the linear case, and the same framework used to simulate the time domain response of nonlinear models. Examples of stable and unstable behavior are illustrated using the active micromechanical model of Neely and Kim. The stability of this active cochlea is extremely sensitive to abrupt spatial inhomogeneities, while smoother inhomogeneities are less likely to cause instability. The model is a convenient tool for investigating the presence of instabilities due to random spatial inhomogeneities. The number of unstable poles is found to rise sharply with the relative amplitude of the inhomogeneities up to a few percent, but to be significantly reduced if the spatial variation is smoothed. In a saturating nonlinear model, such instabilities generate limit cycles that are thought to produce spontaneous otoacoustic emissions. An illustrative time domain simulation is presented, which shows how an unstable model evolves into a limit cycle, distributed along the cochlea.     

Invariance principles for cochlear mechanics: hearing phases

A functional model of the cochlea is devised on the basis of the results from classical experiments. The basilar membrane filter is investigated in detail. Its phase is close to linear in the region around the peak of the amplification. On one side this has consequences for the time analysis and on the other side this has led to a prediction on phase perception for very simple combinations of tones, a prediction which is now confirmed by experiments. Equivariance under the dilation group permits one to describe the model by a wavelet transform [Daubechies, Ten Lectures on Wavelets (SIAM, Philadelphia, 1992)]. The wavelet is discussed in reference to the phase analysis of the basilar membrane filter.     

No sharpening? a challenge for cochlear mechanics

Recent data on mechanical movements of the basilar membrane (BM) suggest that the part played in cochlear physiology by a sharpening mechanism is much less important than hitherto has been thought. In an extreme view, one could dispense with a sharpening mechanism completely and assume that (near the threshold) hair-cell excitation is proportional to BM velocity, or a very simple linear transform of it. In the present paper the consequences of this idea are worked out. A theoretical cochlear movement pattern is constructed that shows the same frequency selectivity as an average reverse-correlation function of an auditory nerve fiber. This response is called a revcor-spectrumlike response. Cochlear mechanics is then simplified to a pure shortwave model. It is shown that, if the cochlea model should present a revcor-spectrumlike response, this can only be achieved when the resistance component of the BM impedance is negative over a part of the length of the cochlea. This result is refined in several respects, and it is shown that a model equipped with the right kind of BM impedance function can have a response of the required type. It remains difficult to conceive of a physiological mechanism that would cause the desired effect on the BM impedance.     

Some observations on degenerate metrics

There are some polynomial formulations of Einstein's equations in which the metric is allowed to become degenerate. We examine some known exact solutions to see whether they may be smoothly joined to solutions with degenerate metrics. If one uses a lapse function which is a spatial scalar, this is very easy. If the lapse function has a small and negative tensor density weight, the joining together may take place across the horizons in the Schwarzschild and Kerr solutions. For large and negative weights, we have been unable to find any examples.     

Some remarks concerning Nambu mechanics

The quantum probability flux of a particle integrated over time and a distant surface gives the probability for the particle crossing that surface at some time. We prove the free flux-across-surfaces theorem, which was conjectured by Combes, Newton and Shtokhamer (Phys. Rev. D. 11 (1975), 366), and which relates the integrated quantum flux to the usual quantum mechanical formula for the cross-section. The integrated quantum flux is equal to the probability of outward crossings of surfaces by Bohmian trajectories in the scattering regime.     

Modeling cochlear dynamics: interrelation between cochlea mechanics and psychoacoustics

A model of the cochlea was used to bridge the gap between model approaches commonly used to investigate phenomena related to otoacoustic emissions and more filter-based model approaches often used in psychoacoustics. In the present study, a nonlinear and active one-dimensional transmission line model was developed that accounts for several aspects of physiological data with a single fixed parameter set. The model shows plausible excitation patterns and an input-output function similar to the linear-compressive-linear function as hypothesized in psychoacoustics. The model shows realistic results in a two-tone suppression paradigm and a plausible growth function of the 2f(1)-f(2) component of distortion product otoacoustic emissions. Finestructure was found in simulated stimulus-frequency otoacoustic emissions (SFOAE) with realistic levels and rapid phase rotation. A plausible "threshold in quiet" including finestructure and spontaneous otoacoustic emissions (SOAE) could be simulated. It is further shown that psychoacoustical data of modulation detection near threshold can be explained by the mechanical dynamics of the modeled healthy cochlea. It is discussed that such a model can be used to investigate the representation of acoustic signals in healthy and impaired cochleae at this early stage of the auditory pathway for both, physiological as well as psychoacoustical paradigms.     

Some remarks on classical representations of quantum mechanics

It is shown that, to a certain extent, the statistical framework of Hilbert-space quantum mechanics can be reformulated in classical terms.     

Some observations on models of absorption spectra

The question of models of absorption spectra as applied to the problems which arise in investigations of the propagation of infrared radiation in the atmosphere is discussed. The general and asymptotic formulas for the absorption function of individual lines, models of equidistant lines of equal intensity and statistical models are considered successively. Certain new formulas are introduced without mathematical derivation. Inaccuracies and errors in the literature are corrected, and the square-toot law is considered critically. The general conclusions resulting from the investigations into spectral models are analyzed.     

教学研究:介绍量子力学几个基本概念——兼答《关于量子几何相位的评注》中的几个主要问题

介绍了量子绝热定理的物理含义及成立的条件，认为有关主要献（Aharonov-Anandan,Bohm，孙昌璞等）的表述是正确的，而《关于量子几何相位的评注》^[1]（以下简称《评注》）相应的表述不完全正确。在此基础上，认为这些献和教材（R.Shankar)得出的涉及Berry绝热相位的一些论述（不含Berry绝热相因子的瞬时能量本征态不满足含时Schroedinger方程等）也是正确的，而《评注》的论述与此相反。《评注》认为只有γn(C)才是Berry相位。本作则倾向于把γn（t）叫做Berry绝热相位，而把γn（C）=γn（T）-γn（0）叫做几何相位（geometric phase)^[2]。     

Some aspects of gravitational quantum mechanics

String theory, quantum geometry, loop quantum gravity and black hole physics all indicate the existence of a minimal observable length on the order of Planck length. This feature leads to a modification of Heisenberg uncertainty principle. Such a modified Heisenberg uncertainty principle is referred as gravitational uncertainty principle(GUP) in literatures. This proposal has some novel implications on various domains of theoretical physics. Here, we study some consequences of GUP in the spirit of Quantum mechanics. We consider two problem: a particle in an one-dimensional box and free particle wave function. In each case we will solve corresponding perturbational equations and compare the results with ordinary solutions.     

Some a priori estimates in mechanics

The scope for quantitative a priori estimators is considered and some of the input data are of probabilistic type subject to given constraints. Corresponding estimates are given for the stability of a rod with initial imperfections on pulsed loading, boundary-value problems for a planar potential, and topics in planar elasticity; these relate the constraints imposed on the initial data to certain solution characteristics. Methods are given for determining the coefficients in the corresponding inequalities.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 114–120, August, 1992.     

Some remarks on a model of supersymmetric quantum mechanics

We develop a recently proposed model within supersymmetric quantum mechanics that puts a group structure on the creation and annihilation operators. We apply the scheme to a variety of quantum mechanical problems and work out a two-term energy recursion equation when the overall group structure isU(1, 1).     

Some observations on the development of anticipatory coarticulation

The influence of vocalic context on various temporal and spectral properties of preceding acoustic segments was investigated in utterances containing [schwa No. CV] sequences produced by two girls aged 4;8 and 9;5 years and by their father. The younger (but not the older) child's speech showed a systematic lowering of [s] noise and [th] release burst spectra before [u] as compared to [i] and [ae]. The older child's speech, on the other hand, showed an orderly relationship of the second-formant frequency in [] to the transconsonantal vowel. Both children tended to produce longer [s] noises and voice onset times as well as higher second-formant peaks at constriction noise offset before [i] than before [u] and [ae]. All effects except the first were shown by the adult who, in addition, produced first-formant frequencies in [] that anticipated the transconsonantal vowel. These observations suggest that different forms of anticipatory coarticulation may have different causes and may follow different developmental patterns. A strategy for future research is suggested.