On homomorphisms between products of median algebras

Homomorphisms of products of median algebras are studied with particular attention to the case when the codomain is a tree. In particular, we show that all mappings from a product \({\mathbf{A_1} \times\ldots\times {\mathbf{A}_{n}}}\) of median algebras to a median algebra \({\mathbf{B}}\) are essentially unary whenever the codomain \({\mathbf{B}}\) is a tree. In view of this result, we also characterize trees as median algebras and semilattices by relaxing the defining conditions of conservative median algebras.     

Environmental scanning electron microscopy and microanalysis

It is shown that the environmental scanning electron microscope is the natural extension of the scanning electron microscope. The former incorporates all of the conventional functions of the latter and, in addition, it opens many new ways of looking at virtually any specimen, wet or dry, insulating or conducting. The environmental scanning electron microscope is characterised by the possibility of maintaining a gaseous pressure in the specimen chamber. All operational parameters can be varied within a range which is a function of pressure. It can be used with all types of gun and all basic modes of detection and, hence, it can be applied both to morphological and to microanalytical studies. It has opened many novel ways of looking at specimens and phenomena not previously accessible with scanning electron microscopy.     

Asymmetric induction—V : Effect of R on asymmetric induction in additions to abcC-COR compounds

The diastereomeric product ratios from reactions involving the addition of various reagents to the carbonyl of φCH₃HC-COR compounds varies over a wide range. This variation is interpreted as due partly to changes in the structure of the diastereomeric transition states with changes in the size of R. For example, when R is smaller than the φCH₃HC group the diastereomeric product ratios are close to those predicted on the assumption that 1 and 2 are the minimum energy diastereomeric transition states; and when R is larger than the φCH₃HC group, the diastereomeric product ratios are large and closer to those that one might expect if 5 and 6 were the minimum energy transition states.     

The algebra of majority consensus

In this note we show that a median algebra can be defined in terms of a singlen-ary operation for anyn5, so that besides symmetry and a majority condition only one additional identity is required. This provides a short axiomatic characterization of majority consensus for taxonomic structures.Presented by I. Rosenberg.     

Synthesis of enantiomerically pure tertiary 1,2-aminoalcohols by the highly diastereoselective reductive ring opening of oxazolidines

A number of enantiomerically pure 1,2-aminoalcohols containing tertiary nitrogen atoms bearing chiral substituents have been prepared by highly diastereoselective reductive ring cleavage of oxazolidines derived from ketones and pseudoephedrine or ephedrine. The ring cleavage occurs with retention of configuration.     

Unique trigonal prism encapsulated Ln complexes: a [Co(II)6Eu] and a [Co(II)6Dy] cage

The use of 2-amino-isobutyric acid in Co/Ln chemistry has led to the isolation of two unique [Co(II)(6)Ln(III)] 3d-4f metallic cages in which the Ln(III) centre (Ln = Eu, Dy) is encapsulated within a Co(II)(6) trigonal prism.     

Racemic 2,3,4-Triacyloxybutylarsonic Acids: A New Class of Arsonolipids with Three Acyl Chains

Abstract

A new class of arsonolipids, racemic 2,3,4-triacyloxybutylarsonic acids, having three fatty acyl chains per molecule have been prepared starting from the key compound 2,3,4-trihydroxybutylarsonic acid after investigating various acylating conditions in order to minimize the interference from As(III). Yields as high as 75% were obtained by adding neat acyl chloride dropwise to a cold (0°C) solution of diphenyl 2,3,4-trihydroxybutyldithioarsonite, pyridine, and catalytic amounts of 4-dimethylaminopyridine in dichloromethane. The new arsonolipids are glasses or soft solids, whose spectral properties are discussed.     

Mesoporous compound semiconductors from the reaction of metal ions with deltahedral [Ge9]4- clusters

We report the surfactant-directed assembly of mesoporous metal/germanium-based semiconducting materials from coupling of anionic (Ge 9) (4-) clusters with various linking metal ions. The resulting materials feature a metal/Ge 9 framework perforated by regular arrays of mesoporous channels. The permanent mesoporosity of the materials NU-MGe-2 (M = Sb, In, Sn, Pb, Cd), determined by N 2 physisorption measurements, corresponds to high internal BET surface areas from 127 to 277 m (2)/g and total pore volumes from 0.15 to 0.26 cm (3)/g. The mesoporous structures exhibit energy gaps in the range of 1.48-1.70 eV as well as strong photoluminescence at room temperature with emission energies varying from 740 to 845 nm. The emission depends on pore wall thickness and framework composition. The photoemission intensity in the mesoporous intermetallic germanium-based frameworks can be selectively suppressed by adsorbing electron-acceptor species such as tetracyanoethylene molecules but remains unchanged when exposed to electron-donor species such as tetrathiafulvalene molecules.