No abstract

Analysis of the nasal region in fossils of three theropod dinosaurs ( Nanotyrannus, Ornithomimus, and Dromaeosaurus ) and one ornithischian dinosaur ( Hypacrosaurus ) showed that their metabolic rates were significantly lower than metabolic rates in modern birds and mammals. In extant endotherms and ectotherms, the cross-sectional area of the nasal passage scales approximately with increasing body mass M at M 0.72 . However, the cross-sectional area of nasal passages in endotherms is approximately four times that of ectotherms. The dinosaurs studied here have narrow nasal passages that are consistent with low lung ventilation rates and the absence of respiratory turbinates.

Highly c-axis oriented zinc oxide (ZnO) thin films with a wurtzite structure have been grown on glass substrates by metal organic chemical vapor deposition. The influence of growth parameters on the luminescent properties of the ZnO layers is investigated. It is shown that the growth temperature and VI/II ratio strongly influence the luminescent properties of ZnO thin films. For the films grown at low temperatures (250–325°C) a broad violet emission band at about 3.1eV has been observed. As the growth temperature increases, ultraviolet emission dominates the spectra and deep level emission is suppressed. It is suggested that the violet emission depends on grain size and hence the width of the free-carrier depletion region at the particle surface; the narrower the depletion width compared to the grain size, the higher the intensity. The result suggests that the mechanism responsible for the violet emission is recombination of delocalized electrons close to the conduction band with holes trapped in neutral zinc vacancy (VZn0) centers. For films grown under different VI/II ratios, the spectra are increasingly dominated by deep level emission as the VI/II ratio is increased. This broad emission is resolved into three bands at ∼2.0, ∼2.3, and ∼2.5eV. Based on the growth conditions, possible origins are proposed and discussed.

The electrical properties of zinc oxide (ZnO) thin films of various thicknesses (0.3-4.4 µm) grown by metalorganic chemical vapour deposition on glass substrates have been studied by using temperature-dependent Hall-effect (TDH) measurements in the 18-300 K range. The high quality of the layers has been confirmed with x-ray diffraction, transmission electron microscopy, scanning electron microscopy and photoluminescence techniques. TDH measurements indicate the presence of a degenerate layer which significantly influences the low-temperature data. It is found that the measured mobility generally increases with increasing layer thickness, reaching a value of 120 cm 2 V −1 s −1 at room temperature for the 4.4 µm thick sample. The lateral grain size of the layers is also found to increase with thickness indicating a clear correlation between the size of the surface grains and the electrical properties of corresponding films. Theoretical fits to the Hall data suggest that the bulk conduction of the layers is dominated by a weakly compensated donor with activation energy in the 33-41 meV range and concentration of the order of 10 17 cm −3 , as well as a total acceptor concentration of mid-10 15 cm −3 . Grain boundary scattering is found to be an important limiting factor of the mobility throughout the temperature range considered.