Anthony M. J. Davis

Bio: Anthony M. J. Davis is an academic researcher from University of Alabama. The author has contributed to research in topics: Stokes flow & Boundary value problem. The author has an hindex of 13, co-authored 45 publications receiving 1146 citations. Previous affiliations of Anthony M. J. Davis include Worcester Polytechnic Institute.

The effect of transpiration on self-similar boundary layer flow over moving surfaces

Abstract: The simultaneous effects of normal transpiration through and tangential movement of a semi-infinite plate on self-similar boundary layer flow beneath a uniform free stream is considered. The flow is therefore governed by a plate velocity parameter λ and a transpiration parameter μ and the computed wall shear stress parameter is f″(0). Dual solutions are found for each value of μ in λ–f″(0) parameter space. It is shown that the range of known dual solutions for zero transpiration increases with suction and decreases with blowing. A stability analysis for this self-similar flow reveals that, for each value of μ, lower solution branches are unstable while upper solution branches are stable.

Flow at the interface of a model fibrous porous medium

Abstract: Planar flow in the interfacial region of an open porous medium is investigated by finding solutions for Stokes flow in a channel partially filled with an array of circular cylinders beside one wall. The cylinders are in a square array oriented across the flow and are widely spaced, so that the solid volume fraction ϕ is 0.1 or less. For this spacing, singularity methods are appropriate and so they are used to find solutions for both planar Couette flow and Poiseuille flow in the open portion of the channel. The solutions, accurate to O(ϕ), are used to calculate the apparent slip velocity at the interface, Us, and results obtained for Us are presented in terms of a dimensionless slip velocity. For shear-driven flow, this dimensionless quantity is found to depend only weakly on ϕ and to be independent of the height of the array relative to the height of the channel and independent of the cylinder size relative to the height of the channel. For pressure-driven flow, Us is found to be less than that under comparable shear-flow conditions, and dependent on cylinder size and filling fraction in this case. Calculations also show that the external flow penetrates the porous medium very little, even for sparse arrays, and that Us is about one quarter of the velocity predicted by the Brinkman model.

Long‐term memory for unfamiliar voices

Abstract: From a sample of young male Californians, ten speakers were selected whose voices were approximately normally distributed with respect to the ‘‘easy‐to‐remember’’ versus ‘‘hard‐to‐remember’’ judgments of a group of raters. A separate group of listeners each heard one of the voices, and, after delays of 1, 2, or 4 weeks, tried to identify the voice they had heard, using an open‐set, independent‐judgment task. Distributions of the results did not differ from the distributions expected under the hypothesis of independent judgments. For both ‘‘heard previously’’ and ‘‘not heard previously’’ responses, there was a trend toward increasing accuracy as a function of increasing listener certainty. Overall, heard previously responses were less accurate than not heard previously responses. For heard previously responses, there was a trend toward decreasing accuracy as a function of delay between hearing a voice and trying to identify it. Information‐theoretic analysis showed loss of information as a function of delay and provided means to quantify the effects of patterns of voice confusability. Signal‐detection analysis revealed the similarity of results from diverse experimental paradigms. A ‘‘prototype’’ model is advanced to explain the fact that certain voices are preferentially selected as having been heard previously. The model also unites several previously unconnected findings in the literature on voice recognition and makes testable predictions.

Radial stagnation flow on a rotating circular cylinder with uniform transpiration

Abstract: Radial stagnation flow of strain rate k impinging on a cylinder with uniform transpiration U0 and rotating at constant angular velocity ω is investigated. An exact reduction of the Navier-Stokes equations to a primary nonlinear equation for the meridional flow similar to that found by Wang [1] and a secondary linear equation for the azimuthal flow is obtained. The governing parameters are the stagnation-flow Reynolds number R = ka2/2v, the dimensionless transpiration S = U0/ka, and the dimensionless rotation rate ω = ω/k, where a is the cylinder radius and v is the kinematic viscosity of the fluid. The boundary-value problem is solved by numerical integration and by asymptotic analysis in certain limits. The results are succinctly summarized in plots of the axial and azimuthal shear-stress parameters as functions of R and S. Sample velocity profiles, meridional streamfunction plots, and projections of particle paths for both suction and blowing are given. An interesting double-layer structure in the azimuthal velocity profile, consisting of a removed free shear layer connected to a wall boundary layer, is observed at large values of blowing. This feature is consistent with results obtained from the asymptotic analysis.

Crocco variable formulation for uniform shear flow over a stretching surface with transpiration: Multiple solutions and stability

Abstract: The simultaneous effects of transpiration through and tangential movement of a semi-infinite flat plate on the self-similar boundary layer flow driven by uniform shear in the far field is considered. Difficulties with standard shooting techniques are overcome using Crocco variables which also serve to better elucidate the solution structure. The stabilities of dual, triple and even quadruple steady flow solutions encountered in different ranges of plate stretching and wall stress are determined using a linear temporal stability analysis for the self-similar flow.

Voice-selective areas in human auditory cortex

Abstract: The human voice contains in its acoustic structure a wealth of information on the speaker's identity and emotional state which we perceive with remarkable ease and accuracy. Although the perception of speaker-related features of voice plays a major role in human communication, little is known about its neural basis. Here we show, using functional magnetic resonance imaging in human volunteers, that voice-selective regions can be found bilaterally along the upper bank of the superior temporal sulcus (STS). These regions showed greater neuronal activity when subjects listened passively to vocal sounds, whether speech or non-speech, than to non-vocal environmental sounds. Central STS regions also displayed a high degree of selectivity by responding significantly more to vocal sounds than to matched control stimuli, including scrambled voices and amplitude-modulated noise. Moreover, their response to stimuli degraded by frequency filtering paralleled the subjects' behavioural performance in voice-perception tasks that used these stimuli. The voice-selective areas in the STS may represent the counterpart of the face-selective areas in human visual cortex; their existence sheds new light on the functional architecture of the human auditory cortex.

Echoes of echoes? An episodic theory of lexical access.

Abstract: In this article the author proposes an episodic theory of spoken word representation, perception, and production. By most theories, idiosyncratic aspects of speech (voice details, ambient noise, etc.) are considered noise and are filtered in perception. However, episodic theories suggest that perceptual details are stored in memory and are integral to later perception. In this research the author tested an episodic model (MINERVA 2; D. L. Hintzman, 1986) against speech production data from a word-shadowing task. The model predicted the shadowing-response-time patterns, and it correctly predicted a tendency for shadowers to spontaneously imitate the acoustic patterns of words and nonwords. It also correctly predicted imitation strength as a function of "abstract" stimulus properties, such as word frequency. Taken together, the data and theory suggest that detailed episodes constitute the basic substrate of the mental lexicon. Early in the 20th century, Semon (1909/1923) described a memory theory that anticipated many aspects of contemporary theories (Schacter, Eich, & Tulving, 1978). In modem parlance, this was an episodic (or exemplar) theory, which assumes that every experience, such as perceiving a spoken word, leaves a unique memory trace. On presentation of a new word, all stored traces are activated, each according to its similarity to the stimulus. The most activated traces connect the new word to stored knowledge, the essence of recognition. The multiple-trace assumption allowed Semon's theory to explain the apparent permanence of specific memories; the challenge was also to create

The discovery of spoken language

Abstract: Surveying the terrain a brief historical perspective on language acquisition research early research on speech perception how speech perception develops in the first year the role of memory and attentional processes in the development of speech perception how attention to sound properties may facilitate learning other elements of linguistic organization relating perception to production wrapping things up. Appendix - methodology used in studies of infant speech perception.

Thinking the voice: neural correlates of voice perception

Abstract: The human voice is the carrier of speech, but also an "auditory face" that conveys important affective and identity information. Little is known about the neural bases of our abilities to perceive such paralinguistic information in voice. Results from recent neuroimaging studies suggest that the different types of vocal information could be processed in partially dissociated functional pathways, and support a neurocognitive model of voice perception largely similar to that proposed for face perception.