Approximating the average daily surface albedo with respect to soil roughness and latitude

The present study explores the diurnal variations in blue-sky albedo (α) of soils under clear sky conditions with respect to surface roughness. Three roughness levels of ploughed and unploughed soil surfaces, developed from the same loessial material, were examined. The relation between α of the surfaces and the solar zenith angle, determined during the experiment, enabled us to predict the diurnal α variation of the surfaces throughout the year at a given latitude, between 75° S and 75° N. The optimal time (T _O) for measuring the soil albedo by an instantaneous observation was considered as the best represented time for the daily averaged value within an error lower than ±2%. It was found that the T _O, falling at different times depending on the soil surface roughness, limits the possibilities of data achievement by remote-sensing satellites along one of their sun-synchronous orbits.     

Organic‐polymer thin‐film transistors for active‐matrix flat‐panel displays?

Abstract— Organic‐polymer‐based thin‐film transistors (OP‐TFTs) look very promising for flexible, large‐area, and low‐cost organic electronics. In this paper, we describe devices based on spin‐coated organic polymer that reproducibly exhibit field‐effect mobility values around 5 × 10^?3 cm²/V‐sec. We also address fabrication, performance, and stability issues that are critical for the use of such devices in active‐matrix flat‐panel displays.     

Thermochemistry, lattice energetics and stability of hexahalogenohafnates

The enthalpies of thermal dissociation (Δ_dH) and formation (Δ_fH) found in the literature as well as the crystal lattice energies (E_c) of inorganic and organic hexahalogenohafnates (M^I₂(or M^{II)HfX2−₆}; M^I and M^II denote monovalent and divalent cations respectively and X denotes a halogen) are reviewed and discussed. The enthalpies of formation of the salts were evaluated using the above-mentioned Δ_dH values and known enthalpies of formation of products of decomposition. Combination of the enthalpies of formation of hexahalogenohafnates thus obtained or those of the literature with the literature values of the enthalpy of formation of cations and theoretically determined enthalpies of formation of HfX²⁻₆ (or electrostatic lattice energies of the salts) afforded lattice energies of the salts (or enthalpies of formation of gaseous HfX²⁻₆). Values of Δ_fH were also assessed taking theoretically obtained electrostatic lattice energies of the salts and enthalpies of formation of HfX²⁻₆ and literature or theoretically determined values of the enthalpy of formation of gaseous cations. The independent sets of crystal lattice energies and thermochemical radii for HfX²⁻₆ were obtained following the Kapustinskii—Yatsimirskii approach. Combination of the latter method with the thermochemical cycle afforded information on the influence of the dimensions of ions on the thermodynamic stability of hexahalogenohafnates with respect to dissociation and oxidation processes. The thermochemical quantities of experimental and theoretical origin correlate with each other reasonably well, thus increasing their reliability.     

Effect of the diffusion phenomena in the catalyst grain on the selectivity of a system of parallel-consecutive reactions involved in the process of n-heptane dehydrocyclization

Analytical relations were derived for analyzing the selectivity of consecutive-parallel reactions occurring under conditions of the reforming process. With these relations it is also possible to determine how the shape of the catalyst grain, as well as the kinetic and diffusion phenomena that govern the process, affects the efficiency of the desired final products.     

Large Eddy Simulation of mixing effects on the course of parallel chemical reactions and comparison with k-? modeling

The way in which reagents are mixed can have a large influence on the product distribution of chemical reactions. To model effects of mixing on various scales on the course of chemical reactions the method of Large Eddy Simulation (LES) of non-premixed, turbulent reactive flows of incompressible fluids is considered in this work. The subgrid modeling of chemical reaction is based on a beta distribution of the mixture fraction in combination with a conditional moment closure based on linear interpolation of local instantaneous reactant concentration values. The predictions obtained with LES are compared with experimental data for fast parallel chemical reactions, the fluid velocity measured using Particle Image Velocity (PIV) technique and the passive tracer concentration measured using the Planar Laser Induced Fluorescence (PLIF) technique. Predictions of the model based on LES are compared as well with results obtained using the non-equilibrium multiple-time-scale mixing model combined with a standard k-? model and employing similar conditional moment closure as LES, applied, however, at larger scale. All comparisons show a very good performance of the model based on LES.     

Nanoindentation of WC–Co hardmetals

WC–Co cemented carbide has been investigated using instrumented indentation with maximum applied loads from 0.1 to 10 mN. The hardness and indentation modulus of individual phases and the influence of crystallographic orientation of WC on the hardness and indentation modulus have been studied. The hardness of the Co binder was approximately 10 GPa and that of WC grains up to 50 GPa with relatively large scatter under the indentation load of 1 mN. Investigation of the role of crystallographic orientation of WC grains on hardness at 10 mN load revealed average values of H_ITbasal = 40.4 GPa (E_ITbasal = 674 GPa) and H_ITprismatic = 32.8 GPa (E_Itprismatic = 542 GPa), respectively. The scatter in the measured values at low indentation loads is caused by the effects of surface and sub-surface characteristics (residual stress, damaged region) and at higher loads by “mix-phase” volume below the indenter.     

Non-isothermal micromixing in turbulent liquids: Theory and experiment

Partial segregation of reagents occurs when reaction rates exceed mixing rates and frequently causes product distributions to be mixing-dependent. A simultaneous temperature segregation, whereby the temperature in a reaction zone differs from that in its surroundings, has rarely been considered when mixing reagents in the liquid phase. The Prandtl number is usually sufficiently small that engulfment, not thermal conduction, determines the local temperature. The engulfment model of micromixing can then be extended by a heat balance to specify this temperature. To evaluate this model, a new pair of fast competitive reactions (neutralisation and acetal hydrolysis) has been characterised thermochemically and kinetically. A Mettler RC1 calorimeter was operated under isothermal and adiabatic conditions with various stirrer speeds and HCl was slowly added to a mixture of NaOH and 2,2-dimethoxypropane. Measured hydrolysis yields compared quite well with the extended engulfment model, although temperature segregation was of minor importance. It was also unimportant in other reaction systems (simultaneous neutralisation and ester hydrolysis; diazo coupling) employed earlier to study micromixing. Suggestions for further work are made.