Parametric-based brain Magnetic Resonance Elastography using a Rayleigh damping material model

The three-parameter Rayleigh damping (RD) model applied to time-harmonic Magnetic Resonance Elastography (MRE) has potential to better characterise fluid-saturated tissue systems. However, it is not uniquely identifiable at a single frequency. One solution to this problem involves simultaneous inverse problem solution of multiple input frequencies over a broad range. As data is often limited, an alternative elegant solution is a parametric RD reconstruction, where one of the RD parameters (μ_I or ρ_I) is globally constrained allowing accurate identification of the remaining two RD parameters. This research examines this parametric inversion approach as applied to in vivo brain imaging.     

Utility of a novel error-stepping method to improve gradient-based parameter identification by increasing the smoothness of the local objective surface: A case-study of pulmonary mechanics

Accurate model parameter identification relies on accurate forward model simulations to guide convergence. However, some forward simulation methodologies lack the precision required to properly define the local objective surface and can cause failed parameter identification.     

A nanoanalytical investigation of elemental distributions in high-k dielectric gate stacks on silicon

Two high-k gate stacks with the structure Si/SiO₂/HfO₂/TiN/poly-Si are characterised using nanoanalytical electron microscopy. The effect of two key changes to the processing steps during the fabrication of the stacks is investigated. Electron energy-loss spectroscopy is used to show that the TiN layer has a very similar composition whether it is deposited by PVD or ALD. Spectrum imaging in the electron microscope was used to profile the distribution of elements across the layers in the stack. It was found that when the anneal after HfO₂ deposition is carried out in a NH₃ atmosphere instead of an O₂ atmosphere, there is diffusion of N into the SiO₂ and HfO₂ layers. There is also significant intermixing of the layers at the interfaces for both wafers.     

A Technique for Rapid Gas Chromatography Analysis Applied to Ambient Organic Aerosol Measurements from the Thermal Desorption Aerosol Gas Chromatograph (TAG)

While automated techniques exist for the integration of individual gas chromatograph peaks, manual inspection of integration quality and peak choice is still required due to drifting retention times and changing peak shapes near detection limits. The feasibility of a simplified method to obtain multiple bulk species classes from complex gas chromatography data is investigated here with data from the thermal desorption aerosol gas chromatograph (TAG). Chromatograms were divided into many “chromatography bins” containing total eluting mass spectra (both from resolved species and unresolved complex mixture [UCM]), instead of only integrating resolved peaks as is performed in the traditional chromatography analysis method. Positive matrix factorization (PMF) was applied to the mass spectra of the chromatography bins to determine major factors contributing to the observed chemical composition. PMF factors are not highly sensitive to the specific PMF error estimation method applied. Increasing the number of chromatography bins that each chromatogram was divided into improved PMF results until reaching 400 bins. Increasing the number of bins above 400 does not significantly improve the PMF results. This is likely due to 400 bin separation providing bin widths (4.6 s) that match the narrowest peak widths (4.8 s) of compounds found in the TAG chromatograms. The bin-based method took only a small fraction of the time to complete compared to peak-integrated method, significantly saving operator time and effort. Finally, high-factor solutions (e.g., 20 factors) of bin-based PMF can separate many individual compounds, homologues compound series, and UCM from chromatography data.

Copyright 2014 American Association for Aerosol Research     

Spectral analysis of intercycle heart fluctuations in Xenopus laevis, conscious or spinalized, treated with calcium channel blockers. Part I

1. In this study, electrocardiographic second lead tracings were recorded and analyzed online and offline in the conscious and spinalized Xenopus laevis under control conditions and after treatment with at least two effective doses of racemic diltiazem, nifedipine and racemic verapamil hydrochlorides. 2. Heart rates (HR) and intercycle heart rate power spectra (IHRPS) were calculated in the various experimental conditions. 3. Dose-dependent bradycardia was found in most cases, which was associated with dose-related increases in the overall dynamic range of the largest peak of HR variability (increased IHRPS), this being particularly marked at the higher nifedipine dose. The frequency position of the largest peak was unchanged in the spinalized preparation, as well as in the various treatments. 4. These findings may contribute toward a more complete pharmacodynamic definition of calcium channel blockers in their current therapeutic use.     

Affective reactivity of speech in schizophrenia patients and their nonschizophrenic relatives.

This study compared levels of referential communication disturbance in speech samples from 41 stable schizophrenia outpatients, 46 parents of patients, and 23 nonpsychiatric control participants in affectively positive versus affectively negative conditions. The speech of the patients and parents showed elevated frequencies of reference failures in the affectively positive condition compared with control participants; the speech of the patients became more disordered in the affectively negative condition, whereas the speech of the parents did not. These results support the idea that referential communication disturbances reflect vulnerability, as well as overt illness, but that affective reactivity of these disturbances is associated mainly with the manifest illness. These findings are consistent with biological, cognitive, and psychological theories about the processes underlying stress responsiveness of schizophrenic symptoms more generally. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chemically Resolved Particle Fluxes Over Tropical and Temperate Forests

Chemically resolved submicron (PM₁) particle mass fluxes were measured by eddy covariance with a high resolution time-of-flight aerosol mass spectrometer over temperate and tropical forests during the BEARPEX-07 and AMAZE-08 campaigns. Fluxes during AMAZE-08 were small and close to the detection limit (<1 ng m^?2 s^?1) due to low particle mass concentrations (<1 μg m^?3). During BEARPEX-07, concentrations were five times larger, with mean mid-day deposition fluxes of ?4.8 ng m^?2 s^?1 for total nonrefractory PM₁ (V_ex,PM1 = ?1 mm s^?1) and emission fluxes of +2.6 ng m^?2 s^?1 for organic PM₁ (V_ex,org = +1 mm s^?1). Biosphere–atmosphere fluxes of different chemical components are affected by in-canopy chemistry, vertical gradients in gas-particle partitioning due to canopy temperature gradients, emission of primary biological aerosol particles, and wet and dry deposition. As a result of these competing processes, individual chemical components had fluxes of varying magnitude and direction during both campaigns. Oxygenated organic components representing regionally aged aerosol deposited, while components of fresh secondary organic aerosol (SOA) emitted. During BEARPEX-07, rapid in-canopy oxidation caused rapid SOA growth on the timescale of biosphere-atmosphere exchange. In-canopy SOA mass yields were 0.5–4%. During AMAZE-08, the net organic aerosol flux was influenced by deposition, in-canopy SOA formation, and thermal shifts in gas-particle partitioning. Wet deposition was estimated to be an order of magnitude larger than dry deposition during AMAZE-08. Small shifts in organic aerosol concentrations from anthropogenic sources such as urban pollution or biomass burning alters the balance between flux terms. The semivolatile nature of the Amazonian organic aerosol suggests a feedback in which warmer temperatures will partition SOA to the gas-phase, reducing their light scattering and thus potential to cool the region.

Copyright 2013 American Association for Aerosol Research     

Differences in pH optima and calcium requirements for maturation of the prohormone convertases PC2 and PC3 indicates different intracellular locations for these events

PC2 and PC3, which is also known as PC1, are subtilisin-like proteases that are involved in the intracellular processing of prohormones and proneuropeptides. Both enzymes are synthesized as propolypeptides that undergo proteolytic maturation within the secretory pathway. An in vitro translation/translocation system from Xenopus egg extracts was used to investigate mechanisms in the maturation of pro-PC3 and pro-PC2. Pro-PC3 underwent rapid (t1/2 < 10 min) processing of the 88-kDa propolypeptide at the sequence RSKR83 to generate the 80-kDa active form of the enzyme. This processing was blocked when the active site aspartate was changed to asparagine, suggesting that an autocatalytic mechanism was involved. In this system, processing of pro-PC3 was optimal between pH 7.0 and 8.0 and was not dependent on additional calcium. These results are consistent with pro-PC3 maturation occurring at an early stage in the secretory pathway, possibly within the endoplasmic reticulum, where the pH would be close to neutral and the calcium concentration less than that observed in later compartments. Processing of pro-PC2 in the Xenopus egg extract was much slower than that of pro-PC3 (t1/2 = 8 h). It exhibited a pH optimum of 5.5-6.0 and was dependent on calcium (K0.5 = 2-4 mM). The enzymatic properties of pro-PC2 processing were similar to that of the mature enzyme. Further studies using mutant pro-PC2 constructs suggested that cleavage of pro-PC2 was catalyzed by the mature 68-kDa PC2 molecule. The results were consistent with pro-PC2 maturation occurring within a late compartment of the secretory pathway that contains a high calcium concentration and low pH.