The retrieval of profile and chemical information from ground-based UV-visible spectroscopic measurements

An algorithm has been developed to retrieve altitude information at different diurnal stages for trace gas species by combining direct-sun and zenith-sky UV-visible differential slant column density (DSCD) measurements. DSCDs are derived here using differential optical absorption spectroscopy. Combining the complementary zenith-sky measurements (sensitive to the stratosphere) with direct-sun measurements (sensitive to the troposphere) allows this vertical distinction. Trace gas species such as BrO and NO₂ have vertical profiles with strong diurnal dependence. Information about the diurnal variation is simultaneously retrieved with the altitude distribution of the trace gas. The retrieval is a formal optimal estimation profile retrieval, allowing a complete assessment of information content and errors.     

Discount Weighted Regression

A recursive procedure for discounted multiple linear regression is described, together with a discounted estimator for the residual variance. The method is simple to program and involves no matrix inversion. Two examples are given.     

Superconductivity in a new ternary structure class of boride compounds

The occurrence of superconductivity at temperatures up to 9.6 K is reported for the system M(Rh_0.85Ru_0.15)₄B₄, where M can be Y or a rare earth element. In contrast, most members of the isostructural series MRu₄B₄ are either not superconducting or order magnetically instead. These materials were found to crystallize in a body-centered-tetragonal structure, with space group I⁴₁/acd and 8 formula units per unit cell. The atomic positions were determined through a structural study of the LuRu₄B₄ compound. These results are discussed with reference to the previously reported primitive tetragonal MRh₄B₄ system of superconducting or ferromagnetic compounds.     

A short formal synthesis of squalamine from a microbial metabolite

A short formal synthesis of squalamine is described, utilizing the biotransformation product 2, which is available in one step from commercially available 3-keto-23,24-bisnorchol-4-en-22-ol (1). Regioselective C-22 oxidation and C-24 sulfation of the corresponding alcohols in the presence of a free C-7 alcohol make for an efficient preparation of squalamine intermediate 11.     

Investigations of “soft-landed” Cd surface atoms via nuclear methods: hyperfine-field sign determination

Using refined preparation techniques, cadmium guest atoms have been positioned at different sites on the surfaces of nickel crystals. The magnetic hyperfine fields and the electric field gradients at the Cd nuclei were measured by time-dependent perturbed angular correlation (TDPAC) spectroscopy of the emitted gamma radiations. By measuring the combined interactions, electric field gradients and magnetic hyperfine fields can be unambiguously attributed to each surface site. The signs of the magnetic hyperfine fields are determined by applying an external magnetic field and choosing the appropriate γ-ray detector configuration. The measured fields correlate with the number of neighbouring host atoms. Band structure calculations confirm this finding and predict magnetic fields for various sp elements from the band structure of the s-like conduction electrons. The quadrupolar interactions are manifestations of the balance in the occupation of the guest p-sublevels. These results provide new information on the structure and formation of electronic configurations of sp elements in different local environments and will contribute to understanding electronic effects on surfaces.