Étude de films de nanotubes de carbone dans le domaine de fréquences térahertz : propriété antiréfléchissante

Les expériences de spectroscopie ont été réalisées en collaboration avec Jean-François Allard du groupe de Denis Morris de l'Université de Sherbrooke.

Construction and experimental study of an elevation linear Fresnel reflector

This paper outlines a novel elevation linear Fresnel reflector (ELFR) and presents and validates theoretical models defining its thermal performance. To validate the models, a series of experiments were carried out for receiver temperatures in the range of 30-100 °C to measure the heat loss coefficient, gain in heat transfer fluid (HTF) temperature, thermal efficiency, and stagnation temperature. The heat loss coefficient was underestimated due to the model exclusion of collector end heat losses. The measured HTF temperature gains were found to have a good correlation to the model predictions - less than a 5% difference. In comparison to model predictions for the thermal efficiency and stagnation temperature, measured values had a difference of -39% to +31% and 22-38%, respectively. The difference between the measured and predicted values was attributed to the low-temperature region for the experiments. It was concluded that the theoretical models are suitable for examining linear Fresnel reflector (LFR) systems and can be adopted by other researchers.

Drag coefficient in a crystal suspension

A single air bubble rising in xanthan gum crystal suspension has been studied experimentally. The suspension was made by different concentrations of xanthan gum solutions with 0.23 mm polystyrene crystal particles. Drag co-efficient data and a new correlation of drag coefficient is presented for spherical and nonspherical bubbles in non-Newtonian crystal suspension. The correlation is developed in terms of the Reynolds number, Re and the bubble shape factor, � (the ratio between the surface equivalent sphere diameter to the volume equivalent sphere diameter). The experimental drag coefficient was found to be consistent with this new predicted correlation and published data over the ranges, 0.1

Development of the response coefficient-root function method for the transient vibration serviceability design of flat concrete floors

The vibration serviceability limit state is an important design consideration for two-way, suspended concrete floors that is not always well understood by many practicing structural engineers. Although the field of floor vibration has been extensively developed, at present there are no convenient design tools that deal with this problem. Results from this research have enabled the development of a much-needed, new method for assessing the vibration serviceability of flat, suspended concrete floors in buildings. This new method has been named, the Response Coefficient-Root Function (RCRF) method. Full-scale, laboratory tests have been conducted on a post-tensioned floor specimen at Queensland University of Technology’s structural laboratory. Special support brackets were fabricated to perform as frictionless, pinned connections at the corners of the specimen. A series of static and dynamic tests were performed in the laboratory to obtain basic material and dynamic properties of the specimen. Finite-element-models have been calibrated against data collected from laboratory experiments. Computational finite-element-analysis has been extended to investigate a variety of floor configurations. Field measurements of floors in existing buildings are in good agreement with computational studies. Results from this parametric investigation have led to the development of new approach for predicting the design frequencies and accelerations of flat, concrete floor structures. The RCRF method is convenient tool to assist structural engineers in the design for the vibration serviceability limit-state of in-situ concrete floor systems.

Anomalous Seebeck coefficient in boron carbides

Boron carbides exhibit an anomalously large Seebeck coefficient with a temperature coefficient that is characteristic of polaronic hopping between inequivalent sites. The inequivalence in the sites is associated with disorder in the solid. The temperature dependence of the Seebeck coefficient for materials prepared by different techniques provides insight into the nature of the disorder.

Using the Gini coefficient with BIOLOG substrate utilisation data to provide an alternative quantitative measure for comparing bacterial soil communities

A measure quantifying unequal use of carbon sources, the Gini coefficient (G), has been developed to allow comparisons of the observed functional diversity of bacterial soil communities. This approach was applied to the analysis of substrate utilisation data obtained from using BIOLOG microtiter plates in a study which compared decomposition processes in two contrasting plant substrates in two different soils. The relevance of applying the Gini coefficient as a measure of observed functional diversity, for soil bacterial communities is evaluated against the Shannon index (H) and average well colour development (AWCD), a measure of the total microbial activity. Correlation analysis and analysis of variance of the experimental data show that the Gini coefficient, the Shannon index and AWCD provided similar information when used in isolation. However, analyses based on the Gini coefficient and the Shannon index, when total activity on the microtiter plates was maintained constant (i.e. AWCD as a covariate), indicate that additional information about the distribution of carbon sources being utilised can be obtained. We demonstrate that the Lorenz curve and its measure of inequality, the Gini coefficient, provides not only comparable information to AWCD and the Shannon index but when used together with AWCD encompasses measures of total microbial activity and absorbance inequality across all the carbon sources. This information is especially relevant for comparing the observed functional diversity of soil microbial communities.

An accuracy assessment of ASTER stereo images-derived digital elevation model by using rational polynomial coefficient model

The along-track stereo images of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor with 15 m resolution were used to generate Digital Elevation Model (DEM) on an area with low and near Mean Sea Level (MSL) elevation in Johor, Malaysia. The absolute DEM was generated by using the Rational Polynomial Coefficient (RPC) model which was run on ENVI 4.8 software. In order to generate the absolute DEM, 60 Ground Control Pointes (GCPs) with almost vertical accuracy less than 10 meter extracted from topographic map of the study area. The assessment was carried out on uncorrected and corrected DEM by utilizing dozens of Independent Check Points (ICPs). Consequently, the uncorrected DEM showed the RMSEz of ± 26.43 meter which was decreased to the RMSEz of ± 16.49 meter for the corrected DEM after post-processing. Overall, the corrected DEM of ASTER stereo images met the expectations.

Atomic resolution of dielectric with low temperature coefficient

Ba(6-3x)Nd(8+2x)Ti(18)O(54) (BNTl14) is a high permittivity dielectric with low temperature coefficient (Tcf). Low coefficient of change of dielectric permittivity with temperature (Tcf) is an unusual materials property. The research is aimed at discovering how atomic structure relates to temperature coefficient. Sub-Ångström scanning transmission electron microscopy (STEM) is used to measure mixed occupancy of Nd and Ba in atomic columns. It was expected that phase separation would occur to accommodate mixing of dissimilar ions. However no evidence of phase separation was found. There is a good image match between experiment and high angle annular dark field (HAADF) simulation. Vacancies and excess Ba ions appear to be randomly arranged on the available sites which would result in distortion of TiO6 octahedra. The low Tcf may arise from TiO6 distortion.