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Semi-empirical Model (semi-empirical + model)
Selected AbstractsSynthesis of Core,Shell Inorganic NanotubesADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Ronen Kreizman Abstract New materials and techniques pertaining to the synthesis of inorganic nanotubes have been ever increasing since the initiation of the field in 1992. Recently, WS2 nanotubes, which are produced now in large amounts, were filled with molten lead iodide salt by a capillary wetting process, resulting in PbI2@WS2 core,shell nanotubes. This work features progress in the synthesis of new core,shell nanotubes, including BiI3@WS2 nanotubes produced in a similar same manner. In addition, two new techniques for obtaining core,shell nanotubes are presented. The first is via electron-beam irradiation, i.e., in situ synthesis within a transmission electron microscope. This synthesis results in SbI3 nanotubes, observed either in a hollow core of WS2 ones (SbI3@WS2 nanotubes), or atop of them (WS2@SbI3 nanotubes). The second technique involves a gaseous phase reaction, where the layered product employs WS2 nanotubes as nucleation sites. In this case, the MoS2 layers most often cover the WS2 nanotube, resulting in WS2@MoS2 core,shell nanotubes. Notably, superstructures of the form MoS2@WS2@MoS2 are occasionally obtained. Using a semi-empirical model, it is shown that the PbI2 nanotubes become stable within the core of MoS2 nanotubes only above a critical core diameter of the host (>12,nm); below this diameter the PbI2 crystallizes as nanowires. These model calculations are in agreement with the current experimental observations, providing further support to the growth mechanism of such core,shell nanotubes. [source] Effects of pore aspect ratios on velocity prediction from well-log dataGEOPHYSICAL PROSPECTING, Issue 3 2002Jun Yan ABSTRACT We develop a semi-empirical model which combines the theoretical model of Xu and White and the empirical formula of Han, Nur and Morgan in sand,clay environments. This new model may be used for petrophysical interpretation of P- and S-wave velocities. In particular, we are able to obtain an independent estimation of aspect ratios based on log data and seismic velocity, and also the relationship between velocities and other reservoir parameters (e.g. porosity and clay content), thus providing a prediction of shear-wave velocity. To achieve this, we first use Kuster and Toksöz's theory to derive bulk and shear moduli in a sand,clay mixture. Secondly, Xu and White's model is combined with an artificial neural network to invert the depth-dependent variation of pore aspect ratios. Finally these aspect ratio results are linked to the empirical formula of Han, Nur and Morgan, using a multiple regression algorithm for petrophysical interpretation. Tests on field data from a North Sea reservoir show that this semi-empirical model provides simple but satisfactory results for the prediction of shear-wave velocities and the estimation of reservoir parameters. [source] Net regional ecosystem CO2 exchange from airborne and ground-based eddy covariance, land-use maps and weather observationsGLOBAL CHANGE BIOLOGY, Issue 3 2007F. MIGLIETTA Abstract Measurements of regional net ecosystem exchange (NEE) were made over a period of 21 days in summer 2002 in the South-Central part of the Netherlands and extrapolated to an area of 13 000 km2 using a combination of flux measurements made by a Sky Arrow ERA research aircraft, half-hourly eddy covariance data from four towers, half-hourly weather data recorded by three weather stations and detailed information on regional land use. The combination of this type of information allowed to estimate the net contribution of the terrestrial ecosystems to the overall regional carbon flux and to map dynamically the temporal and spatial variability of the fluxes. A regional carbon budget was calculated for the study period and the contributions of the different land uses to the overall regional flux, were assessed. Ecosystems were, overall, a small source of carbon to the atmosphere equivalent to to 0.23±0.025 g C m,2 day,1. When considered separately, arable and grasslands were a source of, respectively, 0.68±0.022 and 1.28±0.026 g C m,2 day,1. Evergreen and deciduous forests were instead a sink of ,1.42±0.015 g C m,2 day,1. During the study period, forests offset approximately 3.5% of anthropogenic carbon emission estimates obtained from inventory data. Lacking of a robust validation, NEE values obtained with this method were compared with independent state of art estimates of the regional carbon balance that were obtained by applying a semi-empirical model of NEE driven by MODIS satellite fAPAR data. The comparison showed an acceptable matching for the carbon balance of forest that was a sink in both cases, while a much larger difference for arable and grassland was found. Those ecosystems were a sink for satellite-based estimates while they were a source for the combined aircraft and tower estimates. Possible causes of such differences are discussed and partly addressed. The importance of new methods for determining carbon balance at the regional scale, is outlined. [source] A Tripodal Peptidic Titanium Phosphonate as a Homochiral Porous Solid Medium for the Heterogeneous Enantioselective Hydration of EpoxidesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Anat Milo Abstract A porous, homochiral titanium-phosphonate material based on a tripodal peptide scaffold was used as a heterogeneous reaction medium for the enantioselective hydration (>99%) of styrene oxide. This titanium-phosphonate material, which was shown to contain confined chiral spaces, was prepared by polymerization of L -leucine onto a tris(2-aminoethyl)amine initiator, followed by capping with phosphonate groups and completed by non-aqueous condensation with titanium isopropoxide. Circular dichroism confirmed that the peptide tethers yielded a secondary structure. X-ray powder diffraction and transmission electron microscopy supported by a semi-empirical model showed the likely formation of a porous, lamellar material that was quantified by nitrogen adsorption. [source] Rheological Characteristics of Pimento Purée: Theoretical InterpretationJOURNAL OF FOOD SCIENCE, Issue 7 2002E. Cepedaand ABSTRACT: Rheological characteristics of pimento purée were investigated at different temperatures (5 to 40 °C). The purée serum was a cloudy liquid (0to40 ,m particles) with Newtonian behavior, and flow activation energy of 25.9 kJ/ mol. The power law model was applied to fit the pseudoplastic behavior of pimento purée. The activation energy for flow, evaluated with the Arrhenius-Guzman equation, was low and depended on the variety. A modified Krieger-Dougherty model with 2 parameters was proposed to describe the effect of wet pulp fraction on the relative viscosity. In the semi-empirical model, the colloidal contribution to the viscosity at low shear rate and the parameter variations with the shear rate were considered. [source] A semi-empirical model of the infrared emission from galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008D. C. Ford ABSTRACT We present a semi-empirical model for the infrared emission of dust around star-forming sites in galaxies. Our approach combines a simple model of radiative transfer in dust clouds with a state-of-the-art model of the microscopic optical properties of dust grains pioneered by Draine & Li. In combination with the starburst99 stellar spectral synthesis package, this framework is able to produce synthetic spectra for galaxies which extend from the Lyman limit through to the far-infrared. We use it to probe how model galaxy spectra depend on the physical characteristics of their dust grain populations, and on the energy sources which heat that dust. We compare the predictions of our model with the 8- and 24-,m luminosities of sources in the Spitzer First Look Survey, and conclude by using the models to analyse the relative merits of various colour diagnostics in distinguishing systems out to a redshift of 2 with ongoing star formation from those with only old stellar populations. [source] Studies of Iron-Sulfur Covalency in the Model System and ProteinsCHINESE JOURNAL OF CHEMISTRY, Issue 9 2005Xiu-Juan Qin Abstract It was found that the highly covalent nature of the metal-ligand interactions in the Fe-S cluster clearly played an important role in determining the reactivity of the sites. A semi-empirical model, based on the Phillips theory of bonding was developed for quantitative explanation of covalency in Fe-S cluster, showing that Mossbauer spectroscopy and electronic absorption spectroscopy provided the direct experimental probe of covalency of Fe-S4 clusters. [source] | ||||||||||