Stability,composition and properties of Li2FeSiO4 surfaces studied by DFT

Surface structures and energies of the Pmn2₁ polymorph of the electrode material Li₂FeSiO₄ are studied by first-principles calculations using density functional theory. In total, 29 surface terminations of stoichiometric polar and nonpolar slabs were studied. These surfaces were preselected by energy estimation via a model that accounts for bond cutting and additionally for polarity compensation in the case of polar surfaces. The model provides a way to quantify the most important contributions to the surface energy. Furthermore, we analyze the relaxation of surface atoms statistically. This clearly shows that SiO₄ tetrahedra are rather rigid whereas the local environment of Fe and Li can change strongly under relaxation near the surface. We furthermore compare results obtained by generalized gradient approximation (GGA) and GGA+U exchange correlation functionals. Thus, we estimate the thermodynamic equilibrium shape of Li₂FeSiO₄ by the Wulff construction scheme for stoichiometric surfaces obtaining crystallites that are terminated by {110}, {010}, and {001} surfaces.     

Low‐Temperature Oxidation of Carbon Monoxide with Gold(III) Ions Supported on Titanium Oxide

Au/TiO₂ catalysts prepared by a deposition–precipitation process and used for CO oxidation without previous calcination exhibited high, largely temperature‐independent conversions at low temperatures, with apparent activation energies of about zero. Thermal treatments, such as He at 623 K, changed the conversion–temperature characteristics to the well‐known S‐shape, with activation energies slightly below 30 kJ mol^?1. Sample characterization by XAFS and electron microscopy and a low‐temperature IR study of CO adsorption and oxidation showed that CO can be oxidized by gas‐phase O₂ at 90 K already over the freeze‐dried catalyst in the initial state that contained Au exclusively in the +3 oxidation state. CO conversion after activation in the feed at 303 K is due to Au^III‐containing sites at low temperatures, while Au⁰ dominates conversion at higher temperatures. After thermal treatments, CO conversion in the whole investigated temperature range results from sites containing exclusively Au⁰.     

Synthesis and Characterization of a Uranium(II) Monoarene Complex Supported by δ Backbonding

The low‐temperature (Ad,MeArO)₃mes}U] ( 1 ), with potassium spheres in the presence of a slight excess of 2.2.2‐cryptand, affords the quantitative conversion of 1 into the uranium(II) monoarene complex [K(2.2.2‐crypt)][((^Ad,MeArO)₃mes)U] ( 1‐K ). The molecular and electronic structure of 1‐K was established experimentally by single‐crystal X‐ray diffraction, variable‐temperature ¹H NMR and X‐band EPR spectroscopy, solution‐state and solid‐state magnetism studies, and optical absorption spectroscopy. The electronic structure of the complex was further investigated by DFT calculations. The complete body of evidence confirms that 1‐K is a uranium(II) monoarene complex with a 5f ⁴ electronic configuration supported by δ backbonding and that the nearly reversible, room‐temperature reduction observed for 1 at ?2.495 V vs. Fc/Fc⁺ is principally metal‐centered.     

Diagnosis of Toxoplasmosis Using a Synthetic Glycosylphosphatidylinositol Glycan

Around 2 billion people worldwide are infected with the apicomplexan parasite Toxoplasma gondii which induces a variety of medical conditions. For example, primary infection during pregnancy can result in fetal death or mental retardation of the child. Diagnosis of acute infections in pregnant women is challenging but crucially important as the drugs used to treat T. gondii infections are potentially harmful to the unborn child. Better, faster, more reliable, and cheaper means of diagnosis by using defined antigens for accurate serological tests are highly desirable. Synthetic pathogen‐specific glycosylphosphatidylinositol (GPI) glycan antigens are diagnostic markers and have been used to distinguish between toxoplasmosis disease states using human sera.     

Diffuse Reflectance Spectroscopy as a Tool to Measure the Absorption Coefficient in Skin: South African Skin Phototypes

In any laser skin treatment, the optical properties (absorption and scattering coefficients) are important parameters. The melanin content of skin influences the absorption of light in the skin. The spread in the values of the absorption coefficients for the South African skin phototypes are not known. A diffuse reflectance probe consisting of a ring of six light delivery fibers and a central collecting fiber was used to measure the diffused reflected light from the arms of 30 volunteers with skin phototypes I–V (on the Fitzpatrick scale). The absorption coefficient was calculated from these measurements. This real‐time in vivo technique was used to determine the absorption coefficient of sun‐exposed and ‐protected areas on the arm. The range of typical absorption coefficients for the South African skin phototypes is reported. The values for the darker South African skin types were much higher than was previously reported for darker skin phototypes. In the analysis, the contributions of the eumelanin and pheomelanin were separated, which resulted in improved curve fitting for volunteers of southern Asian ethnicity without compromising the other groups.     

Reversal of the Stereochemical Course of 1‐Methyl‐1H‐indole Addition to Cinnamaldehyde with cis‐5‐Benzyl‐(2‐fluoromethyl)‐2,3‐dimethylimidazolidin‐4‐ones as Catalysts – a Puzzling ‘Fluorine Effect’

Replacement of the cis‐Me group by CH₂F in the imidazolidinone organocatalyst specified in the title (so‐called McMillan generation‐I catalyst) leads to reversal of the product configuration in the title reaction. The topicity reversal in the nucleophilic addition step must arise either from cis‐addition with respect to the benzylic substituent of an (E)‐iminium ion intermediate or from trans‐addition to the corresponding (Z)‐iminium ion. Mechanistic investigations have not provided evidence for either one of these two possibilities, so far.     

Calculus of convex polyhedra and polyhedral convex functions by utilizing a multiple objective linear programming solver

ABSTRACT

The article deals with operations defined on convex polyhedra or polyhedral convex functions. Given two convex polyhedra, operations like Minkowski sum, intersection and closed convex hull of the union are considered. Basic operations for one convex polyhedron are, for example, the polar, the conical hull and the image under affine transformation. The concept of a P-representation of a convex polyhedron is introduced. It is shown that many polyhedral calculus operations can be expressed explicitly in terms of P-representations. We point out that all the relevant computational effort for polyhedral calculus consists in computing projections of convex polyhedra. In order to compute projections we use a recent result saying that multiple objective linear programming (MOLP) is equivalent to the polyhedral projection problem. Based on the MOLP solver bensolve a polyhedral calculus toolbox for Matlab and GNU Octave is developed. Some numerical experiments are discussed.     

Resonance ionization mass spectroscopy for trace analysis of neptunium

Resonance ionization mass spectroscopic (RIMS) measurements for trace analysis and spectroscopy of ²³⁷Np, the ecologically most important isotope of neptunium, are described. The chemical procedure for the separation of neptunium from aqueous samples as well as the preparation of filaments for RIMS are outlined. Several two- and three-step excitation schemes have been investigated in order to find suitable conditions for the sensitive detection of ²³⁷Np. Using a three-step, three-color excitation and ionization scheme an overall detection efficiency of 3×10^–8 was obtained, resulting in a detection limit of 4×10⁸ atoms (160 fg) of ²³⁷Np. The hyperfine structure splittings of the levels under investigation, which influence the detection limit, were measured. A new method to determine the first ionization potential (IP) was applied to neptunium yielding a value of IP=6.2655(2) eV.