RF-coupling and cooling techniques of stored heavy ions

A tandem Penning trap system, the ISOLTRAP, is now used at the on-line mass separator ISOLDE at CERN, Geneva, for accurate mass measurements of short-lived nuclei. The mass of the stored ions is measured by the determination of the cyclotron frequency _c=qB/m in theB=6 T magnetic field of the trap. A new technique has been developed and implemented to allow reliable high-efficiency loading of the trap with radioactive heavy ions.     

Regiospecific syntheses of quinones using vinylketene acetals derived from unsaturated esters

A general method of annellating quinones in high yield has been devised using mixed vinylketene acetals obtained directly from the enolate ions of unsaturated esters.     

A Titration Microcalorimetric Study of the Effects of Halide Counterions on Vesicle-Forming Aggregation in Aqueous Solution of Branched-Chain Alkylpyridinium Surfactants

Titration microcalorimetry is used to study the influences of iodide, bromide, and chloride counterions on the aggregation of vesicle-forming 1-methyl-4-(2-pentylheptyl)pyridinium halide surfactants. Formation of vesicles by these surfactants was characterised using transmission electron microscopy. When the counterion is changed at 303 K through the series iodide, bromide, to chloride, the critical vesicular concentration (cvc) increases and the enthalpy of vesicle formation changes from exo- to endothermic. With increase in temperature to 333 K, vesicle formation becomes strongly exothermic. Increasing the temperature leads to a decrease in enthalpy and entropy of vesicle formation for all three surfactants. However the standard Gibbs energy for vesicle formation is, perhaps surprisingly, largely unaffected by an increase in temperature, as a consequence of a compensating change in both standard entropy and standard enthalpy of vesicle formation. Interestingly, standard isobaric heat capacities of vesicle formation are negative, large in magnitude but not strikingly dependent on the counterion. We conclude that the driving force for vesicle formation can be understood in terms of overlap of the thermally labile hydrophobic hydration shells of the alkyl chains. Copyright 2000 Academic Press.     

Effects of Adsorbed Polyaniline on Redox Process on MoO3 Surface

The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press.     

Synthesis of Coleon U

The recent publication by Matsumoto¹ of a synthesis of Coleon U²(1) prompts us to present our own preparation of this poly-hydroxy diterpene as the tri-O-methyl (12a) and tetra-O-methyl ethers (12b). In a previous communication³ we outlined our approach which is aimed at several similar natural products such as Coleon C⁴ (1b), Lycoxanthol⁵ (2), etc. and differs considerably from that of the Japanese group. Formally at least, the two syntheses start with the same material, (+) ferruginol methyl ether 5a. In our case the latter was prepared by recorded methods from methyl O-methyl podocarpate after introducing the iso-propyl sidechain⁶ (→4), transforming the C.4 methoxycarbonyl residue to a methyl⁷ (→5a, ferruginol methyl ether) which was oxidised at the benzylic position of the B ring to give sugiol methyl ether 5b.     

New Branch-and-Cut Algorithm for Bilevel Linear Programming

Linear mixed 0–1 integer programming problems may be reformulated as equivalent continuous bilevel linear programming (BLP) problems. We exploit these equivalences to transpose the concept of mixed 0–1 Gomory cuts to BLP. The first phase of our new algorithm generates Gomory-like cuts. The second phase consists of a branch-and-bound procedure to ensure finite termination with a global optimal solution. Different features of the algorithm, in particular, the cut selection and branching criteria are studied in details. We propose also a set of algorithmic tests and procedures to improve the method. Finally, we illustrate the performance through numerical experiments. Our algorithm outperforms pure branch-and-bound when tested on a series of randomly generated problems. Work of the authors was partially supported by FCAR, MITACS and NSERC grants.