Intensity and composition-dependent sign reversal of non-linearity in TiO_2/CeO_2 nanocomposites

CeO2/TiO2 composite nanoparticles with different Ce/Ti molar ratios have been successfully synthesized via sol-gel method. It was found that the band gap of the nanocomposite is tunable by varying Ce/Ti content. The nonlinear response of the sample was studied by using the nanosecond laser pulses from a Q switched Nd：Yag laser employing the Z-scan method. Open aperture Z-scan experiment revealed that with the increase in the CeO2 amount in the nanocomposite, the non-linearity of the composite increases, and it was assumed that this could be due to the modification of TiO2 dipole symmetry by the addition of CeO2. Closed aperture Z-scan experiment showed that when the CeO2 amount increases, positive nonlinear refraction decreases, and this could be attributed to the increase in the two photon absorption which subsequently suppresses the nonlinear refraction.

Morphophysiology of Germination among Seeds of Pau-rainha （Centrolobium paraense） Collected in the State of Roraima

This work intended to characterize the seed morphology, water absorption patterns and to determine the vigor among different colored seeds of the species Centrolobium paraense （Fabaceae）. For this purpose, samaras which were opened were collected from two sites---Agua Boa （AB） and Taiano （TAI） lo^ated in the state of Roraima, and the seeds screened by the coat coloration （light brown/intermediate brown/dark brown） for four conditions （two sites and two years of collection）. Evaluation of water absorption by the seeds at different periods, mass of 1,000 seeds, water content, electrical conductivity （EC）, seedling emergence and emergence velocity （EV） were performed. The water absorption by the seeds of Centrolobium paraense indicates coat permeability to water and distinct absorptions according to coat colorations. The EC test is efficient in determining the physiological quality of seeds of Centrolobium paraense. Seed coat coloration affects the physiological quality of the seeds of Centrolobium paraense. It is possible to distinguish the seeds of AB and TAI into two degrees of physiological quality, the light brown-colored seeds being more vigorous.

Experimental study on the influence of temperature and humidity on the thermal conductivity of building insulation materials

At present,thermal conductivity is usually taken as a constant value in the calculation of building energy con-sumption and load.However,in the actual use of building materials,they are exposed to the environment with continuously changing temperature and relative humidity.The thermal conductivity of materials will inevitably change with temperature and humidity,leading to deviations in the estimation of energy consumption in the building.Therefore,in this study,variations in the thermal conductivity of eight common building insulation materials(glass wool,rock wool,silica aerogel blanket,expanded polystyrene,extruded polystyrene,phenolic foam,foam ceramic and foam glass)with temperature(in the range of 20-60°C)and relative humidity(in the range of 0-100%)were studied by experimental methods.The results show that the thermal conductivity of these common building insulation materials increased approximately linearly with increasing temperature with maxi-mum growth rates from 3.9 to 22.7%in the examined temperature range.Due to the structural characteristics of materials,the increasing thermal conductivity of different materials varies depending on the relative humidity.The maximum growth rates of thermal conductivity with humidity ranged from 8.2 to 186.7%.In addition,the principles of selection of building insulation materials in different humidity regions were given.The research re-sults of this paper aim to provide basic data for the accurate value of thermal conductivity of building insulation materials and for the calculation of energy consumption.

Kinetics of fluorescence properties of Eu^(3+) ion in strontium-aluminiumbismuth-borate glasses

Eu3＋ doped strontium-aluminium-bismuth-borate glasses with the chemical composition（50–x）B2O3＋20Bi2O3＋7Al F3＋ 8Sr O＋15Sr F2＋x Eu2O3（where x=0.1 mol.%, 0.5 mol.%, 1.0 mol.% and 1.5 mol.%） were prepared by the conventional melt quenching technique.Structural properties of the prepared glasses were analysed through X-ray diffraction（XRD）, scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS） and Raman spectral techniques.Thermal stability of glass was analysed by differential thermal analysis（DTA） curve.Photoluminescence characteristics were studied using excitation, emission spectra and decay curves of Eu3＋ doped strontium-aluminium-bismuth-borate glasses.The Judd-Ofelt（J-O） intensity parameters, Ωλ（λ=2, 4 and 6） were obtained using emission spectra and was used to identify the nature of Eu3＋ ions with their surrounding ligands.Using J-O parameters the transition probabilities（A）, stimulated emission cross-sections σE p, branching ratios（βR） and radiative lifetimes（τmeas and τcal） were evaluated for the 5D0→7F J（J=0, 1, 2, 3 and 4） transition of Eu3＋ ions in the present glasses.The decay profiles were found to be non exponential for all the concentrations and the measured lifetimes（τmeas） were obtained from the decay profiles.The higher values of A, σE p, βR and quantum efficiency（η） for 5D0→7F2 emission transition at 617 nm confirmed the present glass was as active medium for red laser emission applications.