Greater rate of decline in maximal aerobic capacity with age in physically active vs. sedentary healthy women

Using a meta-analytic approach, we recently reported that the rate of decline in maximal oxygen uptake (VO2 max) with age in healthy women is greatest in the most physically active and smallest in the least active when expressed in milliliters per kilogram per minute per decade. We tested this hypothesis prospectively under well-controlled laboratory conditions by studying 156 healthy, nonobese women (age 20-75 yr): 84 endurance-trained runners (ET) and 72 sedentary subjects (S). ET were matched across the age range for age-adjusted 10-km running performance. Body mass was positively related with age in S but not in ET. Fat-free mass was not different with age in ET or S. Maximal respiratory exchange ratio and rating of perceived exertion were similar across age in ET and S, suggesting equivalent voluntary maximal efforts. There was a significant but modest decline in running mileage, frequency, and speed with advancing age in ET. VO2 max (ml . kg-1 . min-1) was inversely related to age (P < 0.001) in ET (r = -0.82) and S (r = -0.71) and was higher at any age in ET. Consistent with our meta-analysic findings, the absolute rate of decline in VO2 max was greater in ET (-5.7 ml . kg-1 . min-1 . decade-1) compared with S (-3.2 ml . kg-1 . min-1 . decade-1; P < 0. 01), but the relative (%) rate of decline was similar (-9.7 vs -9. 1%/decade; not significant). The greater absolute rate of decline in VO2 max in ET compared with S was not associated with a greater rate of decline in maximal heart rate (-5.6 vs. -6.2 beats . min-1 . decade-1), nor was it related to training factors. The present cross-sectional findings provide additional evidence that the absolute, but not the relative, rate of decline in maximal aerobic capacity with age may be greater in highly physically active women compared with their sedentary healthy peers. This difference does not appear to be related to age-associated changes in maximal heart rate, body composition, or training factors.     

Photocurrent near-field microscopy of Schottky barriers

We used a combination of internal photoemission and of near-field optical microscopy (SNOM) to study the lateral variations in solid interface properties such as energy barriers and electron–hole recombination. In particular we investigated the fully formed Pt–GaP, Au–GaAs, Au–SiN _x –GaAs and PtSi–Si Schottky barriers. Our approach enabled us to measure large lateral variations in the photocurrent with spatial resolution on the nanometric scale. Due to the ability of SNOM to supply parallel topographic information, we observed photocurrent variations from zone to zone that only correlated in a few cases with local variations in surface morphology. We assigned the uncorrelated fluctuations to local variations in the interface stoichiometry, the presence of interface states induced by the metallic overlayer and to defect states at the junction. Furthermore, by tuning the photon energy and applied bias we were able to measure the surface distribution of the diffusion length.     

Classification of chirp signals using hierarchical Bayesianlearning and MCMC methods

This paper addresses the problem of classifying chirp signals using hierarchical Bayesian learning together with Markov chain Monte Carlo (MCMC) methods. Bayesian learning consists of estimating the distribution of the observed data conditional on each class from a set of training samples. Unfortunately, this estimation requires to evaluate intractable multidimensional integrals. This paper studies an original implementation of hierarchical Bayesian learning that estimates the class conditional probability densities using MCMC methods. The performance of this implementation is first studied via an academic example for which the class conditional densities are known. The problem of classifying chirp signals is then addressed by using a similar hierarchical Bayesian learning implementation based on a Metropolis-within-Gibbs algorithm     

Particle Number or Density Can Be Stereologically Estimated By Wedge Sections

The information derivable from the traces of a two-phase medium on the faces of a wedge probe close to its edge is systematically investigated. It is shown that in principle the integral of gaussian curvature over a smooth phase-phase interface can be estimated from this information. In simple terms, the method allows one to estimate the number of cherries in a cherry-cake (or more generally the Euler topological characteristic of the cavities in an Emmental cheese) on the basis of observations on and near the edge of a wedge-shaped slice of the cake (or cheese).     

On the choice of quadrats in stereology

It is described how inference concerning the geometrical structure of a two-phase specimen may be carried out on the basis of sampling subregions or ‘quadrats’. Two basically different situations are considered—firstly when the specimen itself is the centre of interest, and secondly when the specimen is only part of a larger body of interest Weighted random quadrats are shown to be useful in the first case. Serial and multistage sectioning, and the incorporation of supplementary information via Monte Carlo techniques, are also discussed.     

Interannual variability of solar energy generation in Australia

Australia has an abundant solar energy resource that is likely to be used for energy generation on a large scale. Variable sources of electricity generation require knowledge of the nature of their variability at all time scales. This study examines the effect that El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) have on solar radiation in Australia, in order to establish the role for seasonal forecasting of solar power. Calendar years are classified into their ENSO state using a sea surface temperature index. The ERA-Interim and NCEP reanalysis products are then used to estimate the effect of ENSO on global horizontal solar irradiance over the continent. A bootstrap technique is used to obtain confidence regions for the effect in both winter and summer. The main impact of ENSO occurs during winter over a large part of eastern Australia. Little impact was observed over the continent during summer. A similar analysis is conducted for the Indian Ocean Dipole (IOD) to ensure that the observed ENSO effect is not a manifestation of the IOD. This study indicates that the ENSO phenomenon may account for solar energy changes of more than 10% in some locations on a seasonal basis. We show that the solar radiation analysis is directly applicable to solar energy yield. Knowledge of this variability may influence the location of large solar generation plants. Also, there is a potential to predict solar energy a few months ahead by means of seasonal forecasting systems, which would help to assist with planning for electricity grid.     

High-temperature vibrational Raman spectroscopy of gaseous species for solid-oxide fuel cell research

This work reports the development of a novel high temperature, optically-accessed experimental facility and optical methods for Solid Oxide Fuel Cell (SOFC) research at the University of British Columbia (UBC). Vibrational Raman spectroscopy is applied to determine the flow-wise distributions of key gaseous species in a model Direct Internal Reforming (DIR) SOFC reformer fuelled with methane at operating temperatures of 600 and 700 °C. This work describes key aspects of the rig design for high temperature operation and details the in-situ calibration methodology developed to allow results to be reported in terms of mole fraction. A sample set of experimental results is presented and discussed. Elements of the reformer design and the operating characteristics of the apparatus that directly influence the results are identified. Potential applications of the apparatus are described.     

X-Ray Opaque Methacrylate Polymers for Biomedical Applications

The synthesis of a number of halogenated aromatic methacrylate monomers was achieved by (1) the esterification of hydroxyl-containing methacrylate esters with 2,3,5-tri-iodobenzoic acid and (2) by the nucleophilic addition of 2,3,5-tri-iodobenzoic acid, or polyhalogenated phenols, to 2,3-epoxypropyl methacrylate, yielding white crystalline products which were fully characterized. These monomers could be homopolymerized in the melt to produce clear, intensely X-ray opaque glasses possessing high refractive indices. The monomers themselves were soluble in a variety of methacrylate monomers with which they could be copolymerized to produce clear radiopaque materials. The stability of the homopolymers in an aqueous environment was excellent as was thermal stability, exhibiting little decomposition below 300°C. © 1997 SCI.