Absorption of ammonia in the melt of ammonium nitrate

The paper deals with the absorption of ammonia in a model fertilizer of ammonium nitrate. Volumetric overall mass transfer coefficient quantitatively characterizing the process was estimated on the basis of experimental data and kinetics modeling. The volumetric overall mass transfer coefficient depends on the temperature, content of water in the fertilizer and hydrodynamic conditions. Different hydrodynamic conditions were simulated by different speeds of the propeller stirrer. The empirical equation describing the volumetric overall mass transfer coefficient was proposed.     

Twilight of the EUSAMA diagnostic methodology

The article deals with recent failures of the EUSAMA methodology which is used for non-destructive testing of the car chassis without disassembling. Using simulated data, we perform an analysis of false-negative evaluation of car condition which occurs often on cars, which are actually in good technical shape. Suggested analysis is able to evaluate the changes introduced to the testing methodology directly on this particular group of chassis designs. The excitation stroke is identified as one of the main causes of methodology failure. The authors suggest that the stroke does not match the roughness profile of current roads. The authors propose certain adjustments of the EUSAMA methodology which should eliminate growing set of tests with contradictory diagnosis result. Suggested adjustments are tested by simulation as well. These adjustments involve changes either in software or hardware section of methodology. Significantly, the proposed adjustments can be easily applied to most EUSAMA testers already produced. However, it is assumed that the suggested methodology changes will be so significant, that new methodology cannot be labeled as EUSAMA anymore.     

Cation-Controlled Assembly of Polyoxotungstate-Based Coordination Networks

The Preyssler polyoxoanion, [NaP₅W₃₀O₁₁₀]¹⁴⁻ ({P₅W₃₀}), is used as a platform for evaluating the role of nonbridging cations in the formation of transition-metal-bridged polyoxometalate (POM) coordination frameworks. Specifically, the assembly architecture of Co²⁺-bridged frameworks is shown to be dependent on the identity and amount of alkali or alkaline-earth cations present during crystallization. The inclusion of Li⁺, Na⁺, K⁺, Mg²⁺, or Ca²⁺ in the framework synthesis is used to selectively synthesize five different Co²⁺-bridged {P₅W₃₀} structures. The influence of the competition between K⁺ and Co²⁺ for binding to {P₅W₃₀} in dictating framework assembly is evaluated. The role of ion pairing on framework assembly structure and available void volume is discussed. Overall, these results provide insight into factors governing the ability to achieve controlled assembly of POM-based coordination networks.     

The Affinity of Some Lewis Bases for Hexafluoroisopropanol as a Reference Lewis Acid: An ITC/DFT Study

To figure out the possible role of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) as well as to provide reference thermochemical data in solution, the formation of Lewis acid-base complexes between HFIP (Lewis acid) and a series of 8 different Lewis bases (3 sulfoxides, 3 Nsp² pyridine derivatives, 1 aromatic amine, 1 cyclic aliphatic ether) was examined by isothermal titration calorimetry (ITC) experiments and static density functional theory augmented with Dispersion (DFT−D) calculations. Measured ITC association enthalpy values (ΔH_a) lie between −9.3 and −14 kcal mol⁻¹. Computations including a PCM implicit solvation model produced similar exothermicity of association of all studied systems compared to the ITC data with ΔH_a values ranging from −8.5 to −12.7 kcal mol⁻¹. An additional set of calculations combining implicit and explicit solvation by chlorobenzene of the reactants, pointed out the relatively low interference of the solvent with the HFIP-base complexation: its main effect is to slightly enhance the Gibbs energy of the HFIP-Lewis base association. It is speculated that the interactions of bulk HFIP with Lewis bases therefore may significantly intervene in catalytic processes not only via the dynamic microstructuring of the medium but also more explicitly by affecting bonds’ polarization at the Lewis bases.     

Spectroscopic studies of folic acid adsorbed on various metal substrates: does the type of substrate play an essential role in temperature dependence of spectral features?

Folic acid is an essential nutrient involved in biosynthetic processes and cell growth. From an analytical point of view, folic acid can be used as an active part of sensors for substances with affinity to folic acid molecules. In biological environment, sensors can be exposed to temperatures that differ from room temperature. Thus, it is important to describe the influence of temperature on adsorbed molecules, especially on orientation of molecules towards the metal surface and on stability of adsorbed layer. Surface‐enhanced Raman scattering spectroscopy is a useful tool for investigation of architecture of molecular layers adsorbed on metal surfaces because the spectral features change with varying orientation of molecules towards the surface, as well as with changes in interactions among adsorbed molecules. In this study, folic acid was adsorbed on electrochemically prepared Au and Ag substrates, and both these substrates were exposed to temperature changes according to the temperature program consisting of stabilization, the substrate temperature at 10°C, at 50°C and back at 10°C. Decomposition of adsorbed folic acid at 50°C can be excluded on both metals, though the metal (Ag or Au) influences the arrangement of adsorbed molecules and its temperature‐induced changes. In the case of Ag substrate, significant and irreversible increase of certain Stokes band intensities is observed, whereas in the case of Au substrate, the band intensity increase is negligible. Experimental spectra were analyzed using principal component analysis and supplemented with calculated data for folic acid molecule adsorbed on small metal cluster using density functional theory. Moreover, it was proved that changes of surface plasmon resonance and collision frequency of Ag substrate are negligible in the studied temperature interval. Slight re‐orientation of adsorbed folic acid molecules was identified as the main source of band intensity variation in the spectra of folic acid adsorbed on Ag. Copyright © 2014 John Wiley & Sons, Ltd.     

Method for efficient prevention of gravity wave decoupling on rectangular semi-staggered grids

Generation of short gravity wave noise often occurs on semi-staggered rectangular grids as a result of sub-grid decoupling when there is a strong forcing in the mass field. In this study a numerical scheme has been proposed to prevent the generation of the gravity wave decoupling. The proposed numerical method provides efficient communication between decoupled gravity wave finite-difference solutions by a simple averaging of a term in the height tendency in the continuity equation. The proposed method is tested using a shallow water sink model developed for the purpose of this study. It has been demonstrated that this method outperforms other existing approaches. The new scheme is time efficient, based on explicit time integration and can be easily implemented. The proposed method is applicable in hydrodynamic models specified on semi-staggered B or E grids.     

Numerical evidence for critical behavior of the two-dimensional nonequilibrium zero-temperature random field Ising model

We give numerical evidence that the two-dimensional nonequilibrium zero-temperature random field Ising model exhibits critical behavior. Our findings are based on the results of scaling analysis and collapsing of data, obtained in extensive simulations of systems with sizes sufficiently large to clearly display the critical behavior.     

Athermal waveguides for optical communication wavelengths

We report on the design, fabrication, and characterization of temperature insensitive strip silicon-on-insulator racetrack resonators. The influence of various parameters, such as waveguide width, waveguide height, ring radius, coupling length, ring gap, and operating wavelength, on temperature-dependent wavelength shift is examined. A resonant wavelength shift of 0.2 pm/K at a 1550 nm wavelength is measured for 335 nm × 220 nm waveguides. A significant reduction of waveguide propagation losses, improved ring Q value, and higher extinction ratio are obtained after overlaying the silicon waveguides with a polymer cladding.     

Translocation of single-stranded DNA through the α-hemolysin protein nanopore in acidic solutions

The effect of acidic pH on the translocation of single-stranded DNA through the α-hemolysin pore is investigated. Two significantly different types of events, i.e. deep blockades and shallow blockades, are observed at low pH. The residence times of the shallow blockades are not significantly different from those of the DNA translocation events obtained at or near physiological pH, whereas the deep blockades have much larger residence times and blockage amplitudes. With a decrease in the pH of the electrolyte solution, the percentage of the deep blockades in the total events increases. Furthermore, the mean residence time of these long-lived events is dependent on the length of DNA, and also varies with the nucleotide base, suggesting that they are appropriate for use in DNA analysis. In addition to being used as an effective approach to affect DNA translocation in the nanopore, manipulation of the pH of the electrolyte solution provides a potential means to greatly enhance the sensitivity of nanopore stochastic sensing.