Application of a nonlinear viscoelastic model to glassy,particulate‐filled polymers

In previous studies, a nonlinear viscoelastic formalism for unfilled glassy polymers was developed, which employed a potential energy material clock. A wide variety of responses ranging from temperature‐dependent mechanical yield to enthalpy relaxation could be predicted accurately with one physical parameter set. The current investigation assessed the applicability of this approach to highly filled polymers (over 50 vol %). The particulate composites were treated as homogeneous continua, and model parameters were extracted directly from characterization tests developed for unfilled polymers. The predictions agreed surprisingly well with experimental data. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3135–3150, 2005     

Numerical analysis of four-wave mixing between picosecond mode-locked laser pulses in a tensile-strained bulk SOA

A numerical model of four-wave mixing between picosecond pulses in a tensile-strained bulk semiconductor optical amplifier is presented. The model utilizes a modified Schrödinger equation to model pulse propagation. The Schrödinger equation parameters such as the material gain first and second order dispersion, linewidth enhancement factors and optical loss coefficient were obtained using a previously developed steady-state model. The predicted four-wave mixing pulse characteristics show reasonably good agreement with experimental pulse characteristics obtained using Frequency Resolved Optical Gating. In particular simulations predict a large increase in the pulse pedestals of the FWM converted pulse, which is verified by experiment.     

Aberration-corrected STEM imaging of Ag on gamma-Al2O3.

Ag on gamma-alumina is a promising catalyst for hydrocarbon selective catalytic reduction in lean-burn gasoline and diesel engines for transportation applications. Although much is known about the mechanism of NOx reduction and the various intermediates, little agreement exists on the nature of the active silver species. In the present work, aberration-corrected STEM has provided new information about the nature of Ag on alumina both as impregnated and following treatments at various temperatures with exposure to simulated exhaust gas. Ex situ techniques have provided new insights into the evolution of Ag on alumina following exposure to temperature and simulated exhaust gas.     

Verifying the presence of low levels of neptunium in a uranium matrix with electron energy-loss spectroscopy

This paper examines the problems associated with analysis of low levels of neptunium in a uranium matrix with electron energy-loss spectroscopy (EELS) on the transmission electron microscope (TEM). The detection of neptunium in a matrix of uranium can be impeded by the occurrence of a plural scattering event from uranium (U-M₅ + U-O_4,5) that results in severe overlap on the Np-M₅ edge at 3665 eV. Low levels of Np (1600–6300 ppm) can be detected in a uranium solid, uranophane [Ca(UO₂)₂(SiO₃OH)₂(H₂O)₅], by confirming that the energy gap between the Np-M₅ and Np-M₄ edges is at 184 eV and showing that the M₄/M₅ ratio for the neptunium is smaller than that for uranium. The Richardson–Lucy deconvolution method was applied to energy-loss spectral images and was shown to increase the signal to noise ratio.     

Possibilities and pitfalls in quantifying the extent of cysteine sulfenic acid modification of specific proteins within complex biofluids

Background  

Cysteine sulfenic acid (Cys-SOH) plays important roles in the redox regulation of numerous proteins. As a relatively unstable posttranslational protein modification it is difficult to quantify the degree to which any particular protein is modified by Cys-SOH within a complex biological environment. The goal of these studies was to move a step beyond detection and into the relative quantification of Cys-SOH within specific proteins found in a complex biological setting--namely, human plasma.     

Benzenoid links

In this paper, we study new configurations of benzenoid hydrocarbons, called benzenoid links. Roughly speaking, a primitive corofusene is a closed narrow hexagonal ribbon with out-of-plane curvature 0. A primitive corofusene or the union of disjoint primitive corofusenes in \mathbbR³{\mathbb{R}^{3}} is called a benzenoid link. In this paper, we determine the minimum number of hexagons needed for a nontrivial benzenoid link in different senses. We also determine the structures of the smallest and the second smallest nontrivial benzenoid links of different types and their numbers of Kekule structures. We list all the benzenoid Hopf links of type III with 22–25 hexagons by their canonical codes in the appendix.     

Green's function for a third-order generalized right focal problem

We determine the Green's function for the third-order three-point generalized right focal boundary value problem

     

Simulation of ultrasonic focus aberration and correction through human tissue

Ultrasonic focusing in two dimensions has been investigated by calculating the propagation of ultrasonic pulses through cross-sectional models of human abdominal wall and breast. Propagation calculations used a full-wave k-space method that accounts for spatial variations in density, sound speed, and frequency-dependent absorption and includes perfectly matched layer absorbing boundary conditions. To obtain a distorted receive wavefront, propagation from a point source through the tissue path was computed. Receive focusing used an angular spectrum method. Transmit focusing was accomplished by propagating a pressure wavefront from a virtual array through the tissue path. As well as uncompensated focusing, focusing that employed time-shift compensation and time-shift compensation after backpropagation was investigated in both transmit and receive and time reversal was investigated for transmit focusing in addition. The results indicate, consistent with measurements, that breast causes greater focus degradation than abdominal wall. The investigated compensation methods corrected the receive focus better than the transmit focus. Time-shift compensation after backpropagation improved the focus from that obtained using time-shift compensation alone but the improvement was less in transmit focusing than in receive focusing. Transmit focusing by time reversal resulted in lower sidelobes but larger mainlobes than the other investigated transmit focus compensation methods.     

Ear-canal acoustic admittance and reflectance measurements in human neonates. II. Predictions of middle-ear in dysfunction and sensorineural hearing loss

This report describes relationships between middle-ear measurements of acoustic admittance and energy reflectance (YR) and measurements of hearing status using visual reinforcement audiometry in a neonatal hearing-screening population. Analyses were performed on 2638 ears in which combined measurements were obtained [Norton et al., Ear Hear. 21, 348-356 (2000)]. The measurements included distortion-product otoacoustic emissions (DPOAE), transient evoked otoacoustic emissions (TEOAE), and auditory brainstem responses (ABR). Models to predict hearing status using DPOAEs, TEOAEs, or ABRs were each improved by the addition of the YR factors as interactions, in which factors were calculated using factor loadings from Keefe et al. [J. Acoust. Soc. Am. 113, 389-406 (2003)]. This result suggests that information on middle-ear status improves the ability to predict hearing status. The YR factors were used to construct a middle-ear dysfunction test on 1027 normal-hearing ears in which DPOAE and TEOAE responses were either both present or both absent, the latter condition being viewed as indicative of middle-ear dysfunction. The middle-ear dysfunction test classified these ears with a nonparametric area (A) under the relative operating characteristic curve of A = 0.86, and classified normal-hearing ears that failed two-stage hearing-screening tests with areas A = 0.84 for DPOAE/ABR, and A = 0.81 for TEOAE/ABR tests. The middle-ear dysfunction test adequately generalized to a new sample population (A = 0.82).