Low-level otoacoustic emissions may predict susceptibility to noise-induced hearing loss

In a longitudinal study with 338 volunteers, audiometric thresholds and otoacoustic emissions were measured before and after 6 months of noise exposure on an aircraft carrier. While the average amplitudes of the otoacoustic emissions decreased significantly, the average audiometric thresholds did not change. Furthermore, there were no significant correlations between changes in audiometric thresholds and changes in otoacoustic emissions. Changes in transient-evoked otoacoustic emissions and distortion-product otoacoustic emissions were moderately correlated. Eighteen ears acquired permanent audiometric threshold shifts. Only one-third of those ears showed significant otoacoustic emission shifts that mirrored their permanent threshold shifts. A Bayesian analysis indicated that permanent threshold shift status following a deployment was predicted by baseline low-level or absent otoacoustic emissions. The best predictor was transient-evoked otoacoustic emission amplitude in the 4-kHz half-octave frequency band, with risk increasing more than sixfold from approximately 3% to 20% as the emission amplitude decreased. It is possible that the otoacoustic emissions indicated noise-induced changes in the inner ear, undetected by audiometric tests. Otoacoustic emissions may therefore be a diagnostic predictor for noise-induced-hearing-loss risk.     

Coordination complexes bearing potentially tetradentate phenoxyamine ligands

A series of metal complexes containing potentially tetradentate phenoxyamine ligands is described. The ligands are found to bind to main-group metals and first-row transition-metal centres with variable denticity depending upon the requirements of the particular metal centre. Bidentate [Al(III)], tridentate [Mg(II), Ca(II), Zn(II)] and tetradentate [K(I), Cr(III), Fe(II), Co(II)] binding modes have been established unambiguously through single-crystal X-ray structure determinations.     

Synthesis, structural characterization and the first electroluminescent properties of tris- and bis-cycloiridiated complexes of sterically hindered electron-poor 2-(3,5-bis(trifluoromethyl)phenyl)-4-trifluoromethylpyridine

An application of the new sterically hindered electron-poor 2-(3,5-bis(trifluoromethyl)phenyl)-4-trifluoromethylpyridine [HC--N] (1) in the one-step high temperature cyclometalation by Ir(III)Cl3 in the presence of Ag(I)OC(O)CF3 resulted in the synthesis of tris-cyclometalated complexes [C--N]2Ir[C--C] (3) and [C--N]3Ir (5). A neutral silver cluster with a repeating unit of hexa-silver groups in an infinite chain of (2) was isolated from the above reaction as well. When this cyclometalation was carried out in trimethylphosphate at lower temperature, bis-cyclometalated derivatives [C--N]2Ir(mu-Cl)2Ir[CN]2 (6), [C--N]2Ir[eta2-(O(C((t)Bu))2CH] (7), and [C--N]2Ir(mu-O-P(OMe)2-O)2Ir[C--N]2 (8) were synthesized. According to X-ray analyses complex (3), while trivalent, contains four cyclometalated single Ir-C bonds. One of the Ir-C bonds, next to the nitrogen atom of the CC pyridinium ligand, was found to be the shortest to date (1.977(4) angstroms) for a single bond between iridium and carbon atoms. The coordination of the C--C ligand in (3) to iridium has a decidedly interesting bonding pattern and can be explained by various formulations. The first one is considering this ligand as a monoanionic chelating ligand, in which the second coordination site arises from a carbene or azomethine ylide. Overall the best single picture may be a dianionic ligand making two normal Ir-C bonds, in which the ligand just happens to contain a pyridinium function that compensates for one negative charge on the iridium. LEDs constructed with compounds (7) and (8) give blue-green emission with peak electroluminescent efficiency of 15 and 2 cd A(-1), respectively. An LED constructed with compound (5) gives a yellowish emission with peak electroluminescent efficiency of 5.5 cd A(-1).     

Dissociative electron transfer in donor-peptide-acceptor systems: results for kinetic parameters from a density functional/polarizable continuum model

The main structural and electronic factors playing a role in intramolecular dissociative electron transfer of a simple donor-peptide-acceptor (D-peptide-A) model have been investigated by an integrated computational protocol based on the density functional theory, its time-dependent extension, and the polarizable continuum model. Our results allow us to elucidate the electronic states involved in the process and how they are perturbed by the orientation of the donor and the acceptor with respect to the peptide chain and by the presence of the solvent. We also report a semiquantitative estimation of the rate constant governing electron transfer obtained by a direct quantum mechanical evaluation of all the terms entering the kinetic expressions based on the Marcus theory and its extensions.     

Synthesis of a bistetrahydrofuran C17-C32 fragment of the polyether antibiotic ionomycin

A Zn-initiated triepoxide cascade cyclization reaction was employed for the synthesis of the bistetrahydrofuran core segment of the polyether ionophore antibiotic ionomycin.     

Lower bounds for a polynomial in terms of its coefficients

We determine new sufficient conditions in terms of the coefficients for a polynomial ${f\in \mathbb{R}[\underline{X}]}We determine new sufficient conditions in terms of the coefficients for a polynomial f ? \mathbbR[X]{f\in \mathbb{R}[\underline{X}]} of degree 2d (d ≥ 1) in n ≥ 1 variables to be a sum of squares of polynomials, thereby strengthening results of Fidalgo and Kovacec (Math. Zeitschrift, to appear) and of Lasserre (Arch. Math. 89 (2007) 390–398). Exploiting these results, we determine, for any polynomial f ? \mathbbR[X]{f\in \mathbb{R}[\underline{X}]} of degree 2d whose highest degree term is an interior point in the cone of sums of squares of forms of degree d, a real number r such that f − r is a sum of squares of polynomials. The existence of such a number r was proved earlier by Marshall (Canad. J. Math. 61 (2009) 205–221), but no estimates for r were given. We also determine a lower bound for any polynomial f whose highest degree term is positive definite.     

Boundary kernels for adaptive density estimators on regions with irregular boundaries

In some applications of kernel density estimation the data may have a highly non-uniform distribution and be confined to a compact region. Standard fixed bandwidth density estimates can struggle to cope with the spatially variable smoothing requirements, and will be subject to excessive bias at the boundary of the region. While adaptive kernel estimators can address the first of these issues, the study of boundary kernel methods has been restricted to the fixed bandwidth context. We propose a new linear boundary kernel which reduces the asymptotic order of the bias of an adaptive density estimator at the boundary, and is simple to implement even on an irregular boundary. The properties of this adaptive boundary kernel are examined theoretically. In particular, we demonstrate that the asymptotic performance of the density estimator is maintained when the adaptive bandwidth is defined in terms of a pilot estimate rather than the true underlying density. We examine the performance for finite sample sizes numerically through analysis of simulated and real data sets.     

High finesse opto-mechanical cavity with a movable thirty-micron-size mirror

We report on the demonstration of a high finesse micro-optomechanical system and identify potential applications ranging from optical cooling to weak force detection to massive quantum superpositions. The system consists of a high quality diameter flat dielectric mirror cut from a larger substrate with a focused ion beam and attached to an atomic force microscope cantilever. Cavity ring-down measurements performed on a 25 mm long Fabry-Pérot cavity with the 30 microm mirror at one end show an optical finesse of 2100. Numerical calculations show that the finesse is not diffraction limited and that orders of magnitude higher finesse should be possible. A mechanical quality factor of more than 10(5) at pressures below 10(-3) mbar is demonstrated for the cantilever with a mirror attached.     

Using dynamic graphs to reveal student reasoning

Using dynamic graphs, future secondary mathematics teachers were able to represent and communicate their understanding of a brief mathematical investigation in a way that a symbolic proof of the problem could not. Four different student work samples are discussed.