Universality of ac-conduction in anisotropic disordered systems: An effective medium approximation study

Anisotropic disordered system are studied in this work within the random barrier model. In such systems the transition probabilities in different directions have different probability density functions. The frequency-dependent conductivity at low temperatures is obtained using an effective medium approximation. It is shown that the isotropic universal ac-conduction law, $\sigma \ln \sigma=u$, is recovered if properly scaled conductivity ($\sigma$) and frequency ($u$) variables are used.Comment: 5 pages, no figures, final form (with corrected equations

Guardianship of Adults With Mental Retardation: Towards A Presumption of Competence

Statutes should be revised so that people with varying levels of mental retardation are allowed to live as independently as they are able. To achieve this goal, legislators and members of the legal community must become aware of the nature of mental retardation, consider the individual personhood of one having this condition, and devise a legal framework with enough flexibility to accommodate both the individual and society. Ohio\u27s guardianship laws and their relationship to adults with mental retardation require analysis. Although progress has been made in Ohio towards the goal of facilitating maximum enjoyment of independence, the present guardianship laws still allow for the unnecessary removal of guaranteed rights. The purpose of this comment is to explore the advantages of a more limited form of guardianship as a means of determining a balance between the freedom of the adult with mental retardation and the duties and responsibilities of the state

No L1 privilege in talker adaptation

As a rule, listening is easier in first (L1) than second languages (L2); difficult L2 listening can challenge even highly proficient users. We here examine one particular listening function, adaptation to novel talkers, in such a high-proficiency population: Dutch emigrants to Australia, predominantly using English outside the family, but all also retaining L1 proficiency. Using lexically-guided perceptual learning (Norris, McQueen & Cutler, 2003), we investigated these listeners’ adaptation to an ambiguous speech sound, in parallel experiments in both their L1 and their L2. A control study established that perceptual learning outcomes were unaffected by the procedural measures required for this double comparison. The emigrants showed equivalent proficiency in tests in both languages, robust perceptual adaptation in their L2, English, but no adaptation in L1. We propose that adaptation to novel talkers is a language-specific skill requiring regular novel practice; a limited set of known (family) interlocutors cannot meet this requirement

Listener adjustment of stress cue use to fit language vocabulary structure

In lexical stress languages, phonemically identical syllables can differ suprasegmentally (in duration, amplitude, F0). Such stress cues allow listeners to speed spoken-word recognition by rejecting mismatching competitors (e.g., unstressed set- in settee rules out stressed set- in setting, setter, settle). Such processing effects have indeed been observed in Spanish, Dutch and German, but English listeners are known to largely ignore stress cues. Dutch and German listeners even outdo English listeners in distinguishing stressed versus unstressed English syllables. This has been attributed to the relative frequency across the stress languages of unstressed syllables with full vowels; in English most unstressed syllables contain schwa, instead, and stress cues on full vowels are thus least often informative in this language. If only informativeness matters, would English listeners who encounter situations where such cues would pay off for them (e.g., learning one of those other stress languages) then shift to using stress cues? Likewise, would stress cue users with English as L2, if mainly using English, shift away from using the cues in English? Here we report tests of these two questions, with each receiving a yes answer. We propose that English listeners’ disregard of stress cues is purely pragmatic

Effective Elastic Moduli in Solids with High Crack Density

We investigate the weakening of elastic materials through randomly distributed circles and cracks numerically and compare the results to predictions from homogenization theories. We find a good agreement for the case of randomly oriented cracks of equal length in an isotropic plane-strain medium for lower crack densities; for higher densities the material is weaker than predicted due to precursors of percolation. For a parallel alignment of cracks, where percolation does not occur, we analytically predict a power law decay of the effective elastic constants for high crack densities, and confirm this result numerically.Comment: 8 page

Anisotropic dielectric function in polar nano-regions of relaxor ferroelectrics

The paper suggests to treat the infrared reflectivity spectra of single crystal perovskite relaxors as fine-grained ferroelectric ceramics: locally frozen polarization makes the dielectric function strongly anisotropic in the phonon frequency range and the random orientation of the polarization at nano-scopic scale requires to take into account the inhomogeneous depolarization field. Employing a simple effective medium approximation (Bruggeman symmetrical formula) to dielectric function describing the polar optic modes as damped harmonic oscillators turns out to be sufficient for reproducing all principal features of room temperature reflectivity of PMN. One of the reflectivity bands is identified as a geometrical resonance entirely related to the nanoscale polarization inhomogeneity. The approach provides a general guide for systematic determination of the polar mode frequencies split by the inhomogeneous polarization at nanometer scale.Comment: 5 pages, 2 figure

Optical conductivity of a granular metal at not very low temperatures

We study the finite-temperature optical conductivity, sigma(omega,T), of a granular metal using a simple model consisting of a array of spherical metallic grains. It is necessary to include quantum tunneling and Coulomb blockade effects to obtain the correct temperature dependence of sigma(omega, T), and to consider polarization oscillations to obtain the correct frequency dependence. We have therefore generalized the Ambegaokar-Eckern-Schoen (AES) model for granular metals to obtain an effective field theory incorporating the polarization fluctuations of the individual metallic grains. In contrast to the DC conductivity, which is determined by inter-grain charge transfer and obeys an Arrhenius law at low temperature, the AC conductivity is dominated by a resonance peak for intra-grain polarization oscillations, which has a power-law tail at low frequencies. More importantly, although the resonance frequency agrees with the classical prediction, the resonance width depends on intergrain quantum tunneling and Coulomb blockade parameters, in addition to the classical Drude relaxation within the grain. This additional damping is due to inelastic cotunneling of polarization fluctuations to neighbouring grains and it qualitatively differs from the DC conductivity in its temperature dependence quite unlike the expectation from Drude theory.Comment: Added figures, published version, 16 pages, REVTe

The dynamics of lexical activation and competition in bilinguals’ first versus second language

Speech input causes listeners to activate multiple candidate words which then compete with one another. These include onset competitors, that share a beginning (bumper, butter), but also, counterintuitively, rhyme competitors, sharing an ending (bumper, jumper). In L1, competition is typically stronger for onset than for rhyme. In L2, onset competition has been attested but rhyme competition has heretofore remained largely unexamined. We assessed L1 (Dutch) and L2 (English) word recognition by the same late-bilingual individuals. In each language, eye gaze was recorded as listeners heard sentences and viewed sets of drawings: three unrelated, one depicting an onset or rhyme competitor of a word in the input. Activation patterns revealed substantial onset competition but no significant rhyme competition in either L1 or L2. Rhyme competition may thus be a “luxury” feature of maximally efficient listening, to be abandoned when resources are scarcer, as in listening by late bilinguals, in either language