Diurnal and Nocturnal Measurements of Aerosol Optical Depth at a Desert Site in Namibia

The Namibian desert is a candidate site for astrophysical observations with ground-based instrumentation, such as the High Energy Stereoscopic System experiment. For this kind of application, the characterization of the atmospheric transmittance is mandatory. In this context, a first campaign of both solar and lunar direct irradiance measurements has been performed from 7 July 1998 to 10 July 1998 on a desert plateau in Namibia. The aerosol optical depth in the visible range (330-700 nm) has been measured; we found daily values (at 483 nm) ranging from 0.10 to 0.26, while the nightly ones range from 2.5 2 10 m 3 up to 0.86. By means of a least square fitting procedure, the Ångström turbidity parameters have been estimated. ( f daily values 0.92 1 3.64, f nightly values 0.008 1 4.2; g daily values 0.06 1 0.56, g nightly values 0.001 1 0.68). Furthermore, a relationship between Ångström parameters and meteorological variables such as relative humidity and wind speed has been investigated. The results do not highlight any correlation, except for two diurnal data sets that show a negative correlation between the optical thickness and the wind speed. Although preliminary, our measurements allow us to have a first insight into characterizing the aerosol optical properties of the Namibian background aerosol. On the other hand, an extended campaign of measurements is needed for a full characterization of the site.     

Oxidation resistance of SIC-AlN ceramics coated by oxidation-assisted-pack cementation process

Liquid-phase-pressureless-sintered SiC-AlN-Y₂O₃ composites were coated by means of modified pack cementation process (OXPAC, OXidation-assisted-PAck Cementation) using rare-earth oxides, RE₂O₃ (RE = Sc, Er, Sm, Lu, Ho), as reactive powders. The coatings, composed by the oxidation products of SiC, AlN and rare-earth silicates, were adherent to the substrate, without porosity and with a thickness of 10 μm. The oxidation resistance of the coated SiC-AlN-Y₂O₃ ceramics was also investigated at 1500 °C for a period of 200 h. The coated samples showed specific weight gain lower than the uncoated and pre-oxidised samples. Furthermore, the specific weight gain linearly increased with the rare-earth cationic radius.     

Multivariate Analysis of <Superscript>1</Superscript>H-NMR Spectra of Genetically Characterized Extra Virgin Olive Oils and Growth Soil Correlations

Mono-varietal extra virgin olive oils were micro-extracted from drupes that were selectively collected from 28 trees distributed in five different Southern Italian Apulian areas. Nuclear Magnetic Resonance (NMR) profiles of these oil samples were correlated to the genetic (young green material) and soil (samples collected within the foliage projection) data of the tree of origin. Genetic analysis, performed on the samples using SSRs (Simple Sequence Repeats) by 9 microsatellite loci, confirmed the specific cultivar assignment (among Cima di Mola, Coratina, Ogliarola, and Oliva Rossa cultivars). Chemometric methods applied to ¹H-NMR spectroscopic data were used for cultivar and geographical origin discrimination of the studied extra virgin olive oils. Linear Discriminant Analysis (LDA) afforded a high reliability degree for discriminating cultivars (almost 90% of prediction ability), and a good assigning ability for the geographical origin (Ogliarola and Coratina samples used as subsets). Soil analyses were performed for each tree. Regression analysis was applied to soil composition in order to correlate available nutrients and total metals with the content of fatty acids and minor components present in monovarietal extra virgin olive oils. In the case of oleic and linoleic fatty acids, and for some terpenes, B, Cr, Mn, Zn were found to give significant correlations. Zn and Mn were the most significant trace elements for all the correlations found (p < 0.01). The results obtained (genetic, spectroscopic and soil analyses) are discussed as a multidisciplinary approach for setting up a strategy for a cultivar and/or geographic origin certification committed database construction.     

Simulation of the layer inversion phenomenon in binary liquid--fluidized beds by DEM–CFD with a drag law for polydisperse systems

Liquid-fluidized beds of particular binary mixtures exhibit the layer inversion phenomenon, a peculiar result of the mechanical equilibrium developing in such multiphase systems. Because of the crucial role of the hydrodynamic interaction, these are ideal test cases for assessing fluid-particle models in multi-particle CFD simulations. In the present work the layer inversion phenomenon is reproduced via Discrete Element Method (DEM) simulations, in which the drag force model for polydisperse systems described in Cello et al. (2010) is used. The simulations serve primarily to assess the suitability of the DEM–CFD approach and particularly the validity of the above drag model, although the results available may also prove very useful to investigate the prevailing mechanisms. To analyze a sufficiently broad variety of cases, involving different solid species, size ratios and operating conditions, three systems selected amongst the published literature are considered. The comparison of simulation and experimental observation is carried out in terms of overall bed and mixed layer interface heights, voidage and component distributions along bed height and time evolution of the species centers of mass. Simulations with liquid velocities below, above and at the critical inversion conditions are carried out. Additionally, simulations using a drag force model traditionally used for monodisperse beds are reported for comparison. The results not only demonstrate the importance of correctly accounting for the local size distribution in the bed, but also prove the validity of the overall computational approach. The predictions of the simulations are in good to excellent agreement with experiments, depending on the system considered, both in terms of critical velocity and, most notably, expansion of the individual components in the bed. The analysis of the hydrodynamics in the bed allows to investigate the local particle flow field, highlighting the presence of a steady irregular motion of the solids in apparently chaotic vortices continuously forming and disappearing, which is thought to be the mechanism responsible for mixing. The fluid–particle interaction forces exhibit a constant profile along bed height, even in the presence of a strongly non-uniform concentration profile.     

Surface modifications of molecularly imprinted polymers for improved template recognition in water media

New Restricted Access Materials—Molecularly Imprinted Polymers (RAM-MIP) were synthesized by using caffeine (CAFF), methacrylic acid (MAA), divinyl benzene (DVB) and glycidil methacrylate (GMA) as model template, functional monomer, crosslinking agent and pro-hydrophilic co-monomer, respectively. Furthermore, a screening of the ratio of functional monomer to template was performed. After the preliminary characterizations of conventional MIP prepared in absence of GMA, different GMA amounts were inserted in the pre-polymerization feeds and different reactions conditions were tested for GMA epoxide ring opening. In particular, perchloric acid, ammonia, lactic acid, glycine and triethylene glycol were chosen for this purpose. In perchloric acid and ammonia cases, a further modification was performed by phosphorylation and methylation procedures, respectively. Imprinting efficiency of all the obtained materials was evaluated by binding experiments using caffeine and its analogue theophylline both in organic and in water media. The increased hydrophilic characteristics of RAM polymers by water absorption measurement and protein binding experiments were performed.     

Polyamide 6 nanofibrous nonwovens via electrospinning

Electrospinning of Polyamide 6 (PA 6) in 2,2,2‐trifluoroethanol (TFE) was investigated for the fabrication of nanofibrous nonwoven membranes useful for separation systems. The effects of solution characteristics such as concentration and conductivity as well as the effects of processing conditions such as relative humidity and applied potential on the resultant nonwoven fibers were studied. By changing the relative humidity of the electrospinning chamber and the conductivity of the solvent, it is possible to modulate the fiber's size and consequently the porosity of the mats. The morphology of the electrospun PA 6 nanofibers was observed by scanning electron microscopy. The mechanical properties of the nanofibers were also studied. The results showed that PA 6 nanofibers having a diameter ranging from 100 to 600 nm, has been successfully prepared. The electrospun PA 6 nanofiber mats show good mechanical properties, such as a high‐tensile strength (12 ± 0.2 MPa) and elongation (300% ± 50%). The strength of the web was high enough to use as filter without the need of any supporting matrix and could be applicable in the field of self‐supporting membranes. The X‐ray and DSC analyses of the PA 6 electrospun fibers show the presence of the γ‐form of PA 6 crystallite that is usually obtained in the condition where a high stress of the fibers is applied. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Comment on the individual ion activities of Na+ and Cl− by Arce,Wilczek-Vera and Vera

Conventional values of activity coefficients of ionic species, in this case sodium and chloride ions in aqueous NaCl, have been published, as if these were the experimental values of individual ion activity coefficients, although no experimental method is really able to provide these separate quantities—but only the mean activity coefficients. A dangerous consequence is the possibility that scientists concerned with ionic solution theory may rely on such data, and derive wrong conclusions about the effectiveness of their theoretical work. This paper shows the reasons why the data in question have no relation to the ionic activity coefficients, which remain unknown, and are a mere artifact of the method adopted.