Role of spectator ions in influencing the properties of dopant-free ZnO nanocrystals

Towards fundamental studies and potential applications, achieving precise control over the generation of defects in pure ZnO nanocrystals has been always intriguing. Herein, we explored the rote of spectator ions (Co2+ and Ni2+) in influencing the functional properties of ZnO nanocrystals. The crystalline quality, phase purity, and composition of as-prepared samples were thoroughly established by powder X-ray diffraction, electron microscopy (TEM and STEM), and by Raman and X-ray photoelectron spectroscopies (XPS). Despite the presence of Co2+ and Ni2+ ions in the reaction mixture, STEM-energy dispersive spectroscopy (EDS), XPS analysis, and inductively-coupled plasma mass spectrometry (ICP-MS) revealed that the ZnO nanocrystals formed are dopant-free. Even so, their luminescence and magnetic properties were substantially different from those of pure ZnO nanocrystals synthesized using a similar methodology. We attribute the origin of these properties to the defects associated with ZnO nanocrystals generated under different but optimized conditions.

Development and Evaluation of Statistical Downscaling Models for Monthly Precipitation

Several statistical downscaling models have been developed in the past couple of decades to assess the hydrologic impacts of climate change by projecting the station-scale hydrological variables from large-scale atmospheric variables simulated by general circulation models (GCMs). This paper presents and compares different statistical downscaling models that use multiple linear regression (MLR), positive coefficient regression (PCR), stepwise regression (SR), and support vector machine (SVM) techniques for estimating monthly rainfall amounts in the state of Florida. Mean sea level pressure, air temperature, geopotential height, specific humidity, U wind, and V wind are used as the explanatory variables/predictors in the downscaling models. Data for these variables are obtained from the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis dataset and the Canadian Centre for Climate Modelling and Analysis (CCCma) Coupled Global Climate Model, version 3 (CGCM3) GCM simulations. The principal component analysis (PCA) and fuzzy c-means clustering method (FCM) are used as part of downscaling model to reduce the dimensionality of the dataset and identify the clusters in the data, respectively. Evaluation of the performances of the models using different error and statistical measures indicates that the SVM-based model performed better than all the other models in reproducing most monthly rainfall statistics at 18 sites. Output from the third-generation CGCM3 GCM for the A1B scenario was used for future projections. For the projection period 2001-10, MLR was used to relate variables at the GCM and NCEP grid scales. Use of MLR in linking the predictor variables at the GCM and NCEP grid scales yielded better reproduction of monthly rainfall statistics at most of the stations (12 out of 18) compared to those by spatial interpolation technique used in earlier studies.