A virtual trajectory model predicts differences in vocal fold kinematics in individuals with vocal hyperfunction

A simple, one degree of freedom virtual trajectory model of vocal fold kinematics was developed to investigate whether kinematic features of vocal fold movement confirm increased muscle stiffness. Model simulations verified that increases in stiffness were associated with changes in kinematic parameters, suggesting that increases in gesture rate would affect kinematic features to a lesser degree in vocal hyperfunction patients given the increased levels of muscle tension they typically employ to phonate. This hypothesis was tested experimentally in individuals with muscle tension dysphonia (MTD; N = 10) and vocal nodules (N = 10) relative to controls with healthy normal voice (N = 10) who were examined with trans-nasal endoscopy during a simple vocal fold abductory-adductory task. Kinematic measures in MTD patients were less affected by increased gesture rate, consistent with the hypothesis that these individuals have elevated typical laryngeal muscle tension. Group comparisons of the difference between medium and fast gesture rates (Mann-Whitney, one-tailed) showed statistically significant differences between the control and MTD individuals on the two kinematic features examined (p<0.05). Results in nodules participants were mixed and are discussed independently. The findings support the potential use of vocal fold kinematics as an objective clinical assay of vocal hyperfunction.     

Photogalvanic cells: Part XI. The thionine-coated electrode

Studies using ring-disc electrodes, cyclic voltammetry, optical absorption and X-ray photoelectron spectroscopy show that up to twenty monolayers of thionine can be irreversibly coated on to platinum or tin oxide electrodes. On such electrodes the electrode kinetics of the thionine-leucothionine couple are still reversible or quasi reversible. In contrast the reduction of Fe(III) is much slower on a coated electrode compared to a clean electrode. Koutecky-Levich plots show that there is a second potential-independent rate-limiting step. This blocking of the Fe(III) reduction means that the thionine coated electrode is the ideal electrode for a photogalvanic cell using the iron thionine system.     

Predicting shielding constants in solution using gauge invariant atomic orbital theory and the effective fragment potential method

A method to approximate ab initio shielding constants is presented, in which the ab initio density matrix is replaced in the gauge invariant atomic orbital formalism with the density matrix resulting from an effective fragment potential calculation. The resulting first-order density matrix is then iterated to self-consistency. The method is compared with fully ab initio gauge invariant atomic orbital restricted Hartree-Fock calculations on hydrogen chloride, water, and ammonia solutes with up to nine solvent water molecules using the 6-31G, 6-31G(d,p), and 6-31+G(d,p) basis sets. Using the 6-31G(d,p) basis sets, the average of the average absolute deviations for the three environments tested is 0.34 ppm. This is sufficiently accurate to allow for the identification of specific (1)H nuclei in a solvated molecule when the chemical shift between nuclei is not less than 1 ppm. The success of the method at this level of approximation is due to a cancellation of errors between the paramagnetic and diamagnetic terms of the shielding constant: the diamagnetic term is underestimated by roughly the same amount that the paramagnetic term is overestimated.     

The polymerization of styrene oxide by the triisobutylaluminum–water system

Styrene oxide has been polymerized by the triisobutylaluminum–water catalyst system. Kinetic studies of the effects of varying the monomer, triisobutylaluminum, and water concentrations in benzene solutions have been made. Styrene oxide was consumed in two reactions: an initial fast one producing trimer and a slower reaction forming higher molecular weight polymer.     

Dynamics of regioregular conducting polymer electrodes in response to electrochemical stimuli

We report thickness shear mode resonator acoustic wave data for films of regioregular poly(3-hexylthiophene) films exposed to acetonitrile solutions of LiClO4. Both the current- and acoustic wave-responses to constant (or slowly swept) potential show different regimes, whose characteristics, which are quite different to those of regiorandom electropolymerized films, can be interpreted in terms of crystalline and non-crystalline material. Oxidation of crystalline material, which occurs at low potentials, is dominated by anion transfer; as a result of the associated electrostatic effects, the film stiffens. Oxidation of non-crystalline material, which occurs at more positive potentials, involves significant solvent transfer; the solvent softens the film. We have been able to determine film thickness changes and shear modulus components (based on a homogeneous film model) (i) as functions of potential (ie. charge state) and of temperature at fixed potential, and (ii) as a function of time following a potential step. In each case, we have been able to rationalise the electrochemical and viscoelastic phenomena in terms of electrochemically controlled film composition, of which the most significant component is solvation state.     

Time-temperature superposition for viscoelastic properties of regioregular poly(3-hexylthiophene) films

Shear moduli were determined for chemically polymerized and solvent cast regioregular poly(3-hexylthiophene) films, using thickness shear mode acoustic wave resonators. The results are strikingly different to those for electropolymerized regiorandom poly(3-hexylthiophene) films. The time scale of the measurement was varied directly by use of higher harmonics of the acoustic wave resonator and indirectly via temperature. The significant variations in shear modulus with effective time scale can be "normalized"onto a stress master relaxation curve by using the concept of time-temperature superposition; this is the first time this has been demonstrated for electroactive films. The shift factors required to effect this normalization do not follow the classical Williams-Landel-Ferry (WLF) equation developed for long-range backbone motions of bulk polymers. Instead, they follow an Arrhenius-like behavior, commonly used to describe secondary motions of polymer side-chains. The activation enthalpy associated with this is independent of applied potential, is the same as for as cast (undoped) films, and is similar to that for rotation about a carbon-carbon single bond. These all point to the hexyl side-chains as the origins of the observed phenomena, consistent with the "melting point" separating two temperature-dependent phases and with the different molecular packing arrangements that would necessarily apply to regioregular and regiorandom materials.     

EFFECTS OF INORGANIC NITROGEN ON THE RESPONSE OF LEMNA CARBON DIOXIDE OUTPUT TO LIGHT QUALITY AND TIMING*

Abstract —The effects of various light/dark schedules on the time course of CO₂ output by axenic cultures of the short-day plant Lemna perpusilla 6746 differ substantially depending on whether the medium is N-less or contains NH₄ or NO₃ as the sole N source. The steady-state pattern achieved with a daily 1/4 h light pulse in N-less medium is essentially the same whether the light is red or far-red; on NO₃ or NH₄, however, the red and far-red patterns differ in form and suggest the action of a ‘Pfr-hourglass’ timer. In darkness, following either continuous light or entrainment to kh red light daily, CO₂ output oscillates for three or more circadian cycles on NH₄ medium and for at least two on N-less, but damps after a single cycle on NO₃. A schedule of 1/4 h red light every 12 h elicits a 24 h periodicity on NO₃ or NH₄ media and a 12 h periodicity on N-less medium, while a similar far-red schedule elicits a 12 h periodicity on all three. CO₂ output patterns on each of the media respond differently to varying the daily span of light from 1/4 to 6 to 12 h. These results are probably due to differential effects of changing N status on the proportion of total C O₂ arising from various metabolic reactions. They suggest that, rather than being a simple, unitary indicator, CO₂ output can be made to reflect different processes on different media, increasing its value as a real-time indicator of events underlying photoperiodism.     

Viscoelastic phenomena during electrochemical deposition of polyaniline films

Electrochemical quartz crystal microbalance (EQCM) and crystal admittance measurements were used to study the potentiodynamic electrodeposition of polyaniline films. Variations in peak admittance provided the distinction between acoustically thin and acoustically thick films. In the former instance, the Sauerbrey equation was used to interpret the EQCM frequency shift in gravimetric terms. In the latter case, admittance spectra were interpreted viscoelastically to yield shear storage and loss moduli. Variations in storage modulus with potential (within a given deposition cycle) and with number of deposition cycles (at a given potential) were small, covering the range 1.1–1.6 × 10⁷ dyn cm⁻². Variations in loss modulus were much more dramatic, increasing from very low levels typical of a simple fluid to values similar to the storage modulus. More subtle variations of both components within a single potential cycle were highlighted using a novel differential format. This revealed two peaks, correlating with the first film redox process and with further film oxidation/polymerization. Contribution to the International Workshop on Electrochemistry of Electroactive Materials (WEEM-2006), Repino, Russia, 24–29 June 2006.     

Stable copper-tin cluster compositions from high-temperature annealing

Copper-doped tin clusters can be thermally annealed to much more stable compositions with a substantially higher copper/tin ratio. The annealed clusters are only prominent over a narrow range of compositions: CuSn(10-15)+, Cu2Sn(12-18)+, Cu3Sn(15-21)+, Cu4Sn(18-(24)+, and Cu5Sn(21-(27)+. These compositions are close to those found for W(m)Si(n)+ clusters, raising the possibility that the Cu(m)Sn(n)+ clusters have core-shell geometries like those proposed for the W(m)Si(n)+ clusters. Increasing the number of copper atoms causes a change in the dissociation pattern from the fission processes that are characteristic of semiconductor clusters to the expulsion of individual atoms, which usually occurs for metal clusters. The change in the fragmentation pattern may result because the clusters rich in copper melt before they dissociate, while the pure tin clusters dissociate directly from a solidlike phase.