Reduction of U(VI) Incorporated in the Structure of Hematite

U(VI) doped hematite was synthesized and exposed to two different organic reductants with E(0) of 0.23 and 0.70 V. A combination of HAADF-TEM and EXAFS provided evidence that uranium was incorporated in hematite in uranate, likely octahedral coordination. XPS indicated that structurally incorporated U(VI) was reduced to U(V), whereas non-incorporated U(VI) was reduced to U(IV). Specifically, the experiments indicate that U(V) was the dominant oxidation state of uranium in hematite around Eh -0.24 to -0.28 V and pH 7.7-8.6 for at least up to 5 weeks of reaction time. U(V), but not U(IV), was also detected in hematite at Eh +0.21 V (pH 7.1-7.3). The results support the hypothesis, based on previous experimental and theoretical work, that the stability field of U(V) is widened relative to U(IV) and U(VI) in uranate coordination environments where the coordination number of U is less than 8.     

Investigation of the abrasive water jet trajectory curvature inside the kerf

The paper is aimed at the implementation of new findings into the author's theoretical models of the abrasive water jet. Both the theoretical and the experimental works were performed to verify and specify the physical relationships among parameters of abrasive water jets used for cutting, the properties of cut materials and the output parameters of cutting, usually the depth of the cut. The model is based on up-to-date results. The new part of the model was designed to enable the calculation of the angle of the cutting head tilt so that the jet penetrating the material might exit it approximately along the normal to the material surface created at the point of jet axis entry. This model was experimentally verified on several tens of materials and its high reliability and applicability were confirmed on quasi-homogeneous materials.     

The Equivalent Electron Density Concept for Static and Dynamic Modeling of the IGBT Base in Soft- and Hard-Switching Applications

The transient and static behavior of an insulated gate bipolar transistor (IGBT) are analyzed through finite elements simulations and physically based equations. The standard model using a bipolar transistor driven by a MOSFET is abandoned for three partial voltage drops in series, each with its specific static and dynamic behavior. One voltage drop on the internal MOSFET, one on the base and one on the collector-base junction. It is found that the dynamic model can be drastically simplified by focusing on the equivalent electron density. This takes into account the most important phenomena related to the carrier mobilities, necessary for an accurate transient modeling. The specific behavior of the gate-collector capacitance in soft switching conditions is discussed. An equation set based on semiconductor physics is developed to determine the static operating points for each contribution. The importance of the minority carriers transit time in soft switching conditions is then shown. The similarity observed between the waveforms obtained through a finite element simulation and the waveforms obtained using the developed IGBT model within various external structures validates the proposed approach.     

The Influence of Thermal Expansion and Mass Loss on the Young’s Modulus of Ceramics During Firing

During the heating stage of the firing of a ceramic material, the mass \(m\) , length \(l\) , and diameter \(d\) of the sample alter their values depending on the temperature \(t\) . Young’s modulus \(E(f,m,l,d)\) measured by a sonic resonance method is also a function of the resonance frequency \(f\) . Therefore, three thermal analyses (TGA, TDA, modulated force TMA) must be performed to obtain correct values of Young’s modulus. The calculation of Young’s modulus can be simplified if TGA and/or TDA are omitted. This necessarily leads to partly incorrect results. If TGA is not performed, we have \(E[f(t),m_0 ,l(t),d(t)]\) and the relative difference \((\{E[f(t),m(t),l(t),d(t)]-E[f(t),m_0 ,l(t),d(t)]\}/E[f(t),m(t),l(t),d(t)])\) reaches 7 % for \(t> 650\,^\circ \text{ C}\) and less than 2 % for \(t< 500\,^\circ \text{ C}\) . If TDA is not performed, we have \(E[f(t),m(t),l_0 ,d_0 ]\) and the relative difference ( \(\{E[f(t),m(t),l(t),d(t)]-E[f(t),m(t),l_0 ,d_0 ]\}/E[f(t),m(t),l(t),d(t)])\) is less than 0.6 % for \(t < 1000\,^\circ \text{ C}\) . For the simplest case, we have \(E[f(t),m_0 ,l_0 ,d_0 ]\) and the relative difference ( \(\{E[f(t),m(t),l(t),d(t)]-E[f(t),m_0 ,l_0 ,d_0 ]\}/E[f(t),m(t),l(t),d(t)])\) is 7.5 % for \(t > 600\,^\circ \text{ C}\) and less than 2 % for \(t<500\,^\circ \text{ C}\) .     

An application of the self-organizing map in the non-Euclidean Traveling Salesman Problem

An application of the self-organizing map (SOM) to the Traveling Salesman Problem (TSP) has been reported by many researchers, however these approaches are mainly focused on the Euclidean TSP variant. We consider the TSP as a problem formulation for the multi-goal path planning problem in which paths among obstacles have to be found. We apply a simple approximation of the shortest path that seems to be suitable for the SOM adaptation procedure. The approximation is based on a geometrical interpretation of SOM, where weights of neurons represent nodes that are placed in the polygonal domain. The approximation is verified in a set of real problems and experimental results show feasibility of the proposed approach for the SOM based solution of the non-Euclidean TSP.     

Catalytic splitting of acetals to unsaturated ethers

Catalytic splitting of the dimethylacetals of heptanal, 3-cyclohexylpropanal, 3-cyclohexylbutanal, 3-phenylpropanal and 3-phenylbutanal to corresponding unsaturated ethers was studied in a gas phase. Acid catalysts were employed in the study. Reaction conditions favorable to high splitting selectivity to ethers were suggested. The original acetals as well as synthesized unsaturated methylethers revealed characteristic odoring properties.