Gap detection with sinusoids and noise in normal, impaired, and electrically stimulated ears

Thresholds for the detection of temporal gaps were measured using two types of signals to mark the gaps: bandpass-filtered noises and sinusoids. The first experiment used seven subjects with relatively flat unilateral moderate cochlear hearing loss. The normal ear of each subject was tested both at the same sound-pressure level (SPL) as the impaired ear, and at the same sensation level (SL). Background noise was used to mask spectral "splatter" associated with the gap. For the noise markers, gap thresholds tended to be larger for the impaired ears than for the normal ears when the comparison was made at equal SPL; the difference was reduced, but not eliminated, when the comparison was made at equal SL. Gap thresholds for both the normal and impaired ears decreased as the center frequency increased from 0.5 to 2.0 kHz. For the sinusoidal markers, gap thresholds were often similar for the normal and impaired ears when tested at equal SPL, and were larger for the normal ears when tested at equal SL. Gap thresholds did not change systematically with frequency. Gap thresholds using sinusoidal markers were smaller than those using noise markers. In the second experiment, three subjects with single-channel cochlear implants were tested. Gap thresholds for noise bands tended to increase with increasing center frequency when the noise bandwidth was fixed, and to decrease with increasing bandwidth when the center frequency was fixed. Gap thresholds for sinusoids did not change with center frequency, but decreased markedly with increasing level. Gap thresholds for sinusoids were considerably smaller than those for noise bands.(ABSTRACT TRUNCATED AT 250 WORDS)     

A subdeterminant inequality for normal matrices

Let A be an n × n normal matrix over $\text{C}$, and Q_m, _n be the set of strictly increasing integer sequences of length m chosen from 1,…,n. For α, β ? Q_m, _n denote by A[α|β] the submatrix obtained from A by using rows numbered α and columns numbered β. For k ? {0, 1,…, m} we write |α∩β| = k if there exists a rearrangement of 1,…, m, say i₁,…, i_k, i_k+1,…, i_m, such that α(i_j) = β(i_j), i = 1,…, k, and {α(i_k+1),…, α(i_m) } ∩ {β(i_k+1),…, β(i_m) } = ?. A new bound for |detA[α|β ]| is obtained in terms of the eigenvalues of A when 2m = n and |α∩β| = 0.Let $\text{U}$_n be the group of n × n unitary matrices. Define the nonnegative number

where | α ∩ β| = k. It is proved that

Let A be semidefinite hermitian. We conjecture that ρ₀(A) ? ρ₁(A) ? ··· ? ρ_m(A). These inequalities have been tested by machine calculations.     

Travelling wave solutions of multisymplectic discretizations of semi-linear wave equations

How well do multisymplectic discretisations preserve travelling wave solutions? To answer this question, the 5-point central difference scheme is applied to the semi-linear wave equation. A travelling wave ansatz leads to an ordinary difference equation whose solutions can be compared to travelling wave solutions of the PDE. For a discontinuous nonlinearity the difference equation is solved exactly. For continuous nonlinearities the difference equation is solved using a Fourier series, and resonances that depend on the grid-size are revealed for a smooth nonlinearity. In general, the infinite dimensional functional equation, which must be solved to get the travelling wave solutions, is intractable, but backward error analysis proves to be a powerful tool, as it provides a way to study the solutions of equation through a simple ODE that describes the behavior to arbitrarily high order. A general framework for using backward error analysis to analyze preservation of travelling waves for other equations and discretisations is presented. Then, the advantages that multisymplectic methods have over other methods are briefly highlighted.     

Engineered biosynthesis of antiprotealide and other unnatural salinosporamide proteasome inhibitors

A new shunt in the phenylalanine biosynthetic pathway to the nonproteinogenic amino acid L-3-cyclohex-2'-enylalanine was exploited in the marine bacterium Salinispora tropica by mutagenesis to allow for the genetic engineering of unnatural derivatives of the potent proteasome inhibitor salinosporamide A (2) such as antiprotealide (1).     

SERRS-based enzymatic probes for the detection of protease activity

Measurement of protease activity, for the first time using SERRS as a detection method, is reported herein. Synthetic introduction of phenylalanine to a benzotriazole azo dye allows the SERRS response to be "switched off" and subsequent exposure to protease restores the SERRS response. The substrates exhibit varying reactivity for a range of proteases and allow for in situ, real-time analysis of protease reactivity. A limit of detection for one protease, Subtilisin carlsberg, was investigated and was established to be 50 ng ml-1.     

Surface reactivity of the quinone/hydroquinone redox center tethered to gold: comparison of delocalized and saturated bridges

We found that when a quinone headgroup, present in a mixed self-assembled monolayer on gold, reacts with a nucleophile, dissolved in the bulk phase, the reaction rate widely depends on the chemical nature of the tether, being 7 times faster for quinones attached via a delocalized bridge as compared to a saturated alkane chain. Cyclic voltammetry (CV) of the quinone/hydroquinone redox couple was used to monitor the nucleophilic addition, while simulated CVs compared to experimental runs permitted the determination of rate constants. Analysis of CV data also suggests that the delocalized oligo(phenylene ethynylene) bridge facilitates the addition of two mercaptoethanol molecules as compared to the alkane bridge, where only one molecule is being added. The use of delocalized bridges for tethering quinones to electrodes is of great potential in electrochemically controlled "tuning" of surfaces needed in biosensor applications.     

A bioinspired construct that mimics the proton coupled electron transfer between P680*+ and the Tyr(Z)-His190 pair of photosystem II

A bioinspired hybrid system, composed of colloidal TiO2 nanoparticles surface modified with a photochemically active mimic of the PSII chlorophyll-Tyr-His complex, undergoes photoinduced stepwise electron transfer coupled to proton motion at the phenolic site. Low temperature electron paramagnetic resonance studies reveal that injected electrons are localized on TiO2 nanoparticles following photoexcitation. At 80 K, 95% of the resulting holes are localized on the phenol moiety and 5% are localized on the porphyrin. At 4.2 K, 52% of the holes remain trapped on the porphyrin. The anisotropic coupling tensors of the phenoxyl radical are resolved in the photoinduced D-band EPR spectra and are in good agreement with previously reported g-tensors of tyrosine radicals in photosystem II. The observed temperature dependence of the charge shift is attributed to restricted nuclear motion at low temperature and is reminiscent of the observation of a trapped high-energy state in the natural system. Electrochemical studies show that the phenoxyl/phenol couple of the model system is chemically reversible and thermodynamically capable of water oxidation.