The surface properties of iron catalyst for ammonia synthesis

The reduction process and the surface properties of industrial prereduced triply and doubly promoted iron catalyst for ammonia synthesis have been studied using thermogravimetry, thermal desorption of N₂ and X-ray diffraction. The properties of both catalysts have been discussed on the basis of the double layer model of iron catalyst. A concept of facet formation on the active surface of the catalysts has been proposed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Distance sets of well-distributed planar sets for polygonal norms

LetX be a two-dimensional normed space, and letBX be the unit ball inX. We discuss the question of how large the set of extremal points ofBX may be ifX contains a well-distributed set whose distance set Δ satisfies the estimate |Δ∩[0,N]|≤CN ^3/2-ε. We also give a necessary and sufficient condition for the existence of a well-distributed set with |Δ∩[0,N]|≤CN.     

Basic inequalities for weighted entropies

The concept of weighted entropy takes into account values of different outcomes, i.e., makes entropy context-dependent, through the weight function. In this paper, we establish a number of simple inequalities for the weighted entropies (general as well as specific), mirroring similar bounds on standard (Shannon) entropies and related quantities. The required assumptions are written in terms of various expectations of weight functions. Examples are weighted Ky Fan and weighted Hadamard inequalities involving determinants of positive-definite matrices, and weighted Cramér-Rao inequalities involving the weighted Fisher information matrix.     

Liquid chromatography determination of natural dyes in extracts from historical Scottish textiles excavated from peat bogs

Textiles excavated from Scottish sites belonging now to the collections of the National Museums of Scotland, including seventeenth century textiles from peat bogs in the Scottish Highlands and Islands, were selected for analysis by high performance liquid chromatography with photodiode array detection (PDA HPLC) to detect whether any dyes remained and, if so, to identify their biological sources. Dye components were identified in 36 of the 81 samples analysed. Although it was not possible to identify the exact sources of the dyestuffs because of the wide-spread occurrence of these natural dyes components, the study has shown that textiles previously not thought to have been coloured had detectable traces of dye. Before the historical textiles were analyzed, an improved extraction procedure that combined the routine acid hydrolysis method with one using dimethylformamide (DMF) was applied. The DMF method enabled increased recovery of major flavonoid and anthraquinoid compounds, and very high efficiency of recovery of indigotin even in textiles with no colour visible, thereby complementing the acid hydrolysis method already in use. Extracts from historical thread samples were analysed by PDA HPLC using a reversed-phase gradient system comprising of a C18 column (150 mm x 4.6 mm i.d., 25 +/- 1 degrees C) with water, methanol and o-phosphoric acid at an eluent flow rate of 1.2 ml/min. A preliminary investigation to improve the detection limits further for a selection of natural dyes was made by comparing results from the 4.6mm internal diameter (i.d.) column with a narrow bore C18 column (2.1 mm i.d.). An increase in the detector response was observed for narrow-bore column proving its possibility of enhancement of sensitivity.     

Magnetite nanowires in MCM-41 type mesoporous silica templates

MCM-41 mesoporous material was chosen as a template of very small Fe₃O₄ particles. The results of structural and magnetic studies of magnetite nanowires are reported. The average length of these nanowires is about 70 nm and their diameter is 3 nm. Magnetite polycrystalline nanowires were characterized by means of X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy (MS). Almost 80% of the particles exist in a superparamagnetic state at room temperature. Mössbauer measurements also provided evidence that the composites displayed a distribution of magnetic particles by size. As a result, strong changes of superparamagnetic and magnetic relative contributions along with temperature were observed.     

Finite configurations in sparse sets

Let E ? ?ⁿ be a closed set of Hausdorff dimension α. For m > n, let{B₁, …, B_k} be n × (m ? n) matrices. We prove that if the system of matrices B_j is non-degenerate in a suitable sense, α is sufficiently close to n, and if E supports a probability measure obeying appropriate dimensionality and Fourier decay conditions, then for a range of m depending on n and k, the set E contains a translate of a non-trivial k-point configuration {B₁y, …, B_ky}. As a consequence, we are able to establish existence of certain geometric configurations in Salem sets (such as parallelograms in ?ⁿ and isosceles right triangles in ?²). This can be viewed as a multidimensional analogue of the result of [25] on 3-term arithmetic progressions in subsets of ?.     

Phase equilibria in the system FeVO4−Fe2WO6 in the solid state

A diagram of the phase equilibria established in the solid state in the system FeVO₄?Fe₂WO₆ was plotted on the basis of X-ray phase analysis and DTA. This system, one of the intersections of the three-component system Fe₂O₃?V₂O₅?WO₃, does not appear to be a real two-component system in the solid state.     

Diamino Acid Derivatives of Porphyrins Penetrate into Yeast Cells, Induce Photodamage, but Have No Mutagenic Effect

The yeast Saccharomyces cerevisiae was used as a model eukaryotic organism to study the uptake of diamino acid derivatives of porphyrins and their phototoxicity with particular emphasis on possible mutagenic effects. The water-soluble hematoporphyrin derivatives diarginate (HpD[Arg]₂) and 1-arginin di(N-amino acid)-protoporphyrinate used in this study are effective photosensitizers in tumor photodynamic therapy. Depending on the amino acid substituent, the porphyrin derivatives differ in their affinity for yeast cells. It is shown that HpD(Arg)₂ and PP(Met)₂ (Arg)₂ penetrate into the yeast cell and are metabolized. Both compounds sensitize yeast cells to photodamage but have no mutagenic effect on nuclear or mitochondrial genomes.     

Use of thermal analysis in the synthesis of vinylidenediphosphonic acid

Simultaneous TG-DTA was applied to establish the optimum conditions for the synthesis of vinylidenediphosphonates via the intramolecular dehydration of 1-hydroxyethylidenediphosphonate salts (Li, Na, K, Rb, NH₄, Ca and Ba). The tested salts underwent water elimination at different temperatures. Consequently, they are of different values for the synthesis of vinylidenedi phosphonates. The dibarium salt proved to be the best for this purpose, whereas the tetrammonium salt can not be used because of its uncontrolled thermal decomposition. The kinetic parameters do not reveal any influence of the metal cation on the intramolecular dehydration process.

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Zusammenfassung Simultane TG-DTA wurde eingesetzt, um die optimalen Bedingungen für die Synthese der Vinidylidendiphosphonate durch intramolekulare Wasserabspaltung aus den 1-Hydroxiethylidendiphosphaten des Li, Na, K, Rb, NH₄, Ca und Ba zu ermitteln. Aus den untersuchten Salzen wurde das Wasser bei verschiedenen Temperaturen abgespalten, sie sind daher unterschiedlich brauchbar zur Synthese der Vinylidenphosphonate. Das Bariumsalz erwies sich am geeignetsten, während das Tetra-ammoniumsalz wegen seiner unkontrollierten thermischen Zersetzung ungeeignet ist. Die kinetischen Parameter der intramolekularen Wasserabspaltung zeigen keinen Einfluss des vorhandenen Metallkations.

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