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.     

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.     

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.     

Q value of the superallowed decay of 46V and its influence on Vud and the unitarity of the Cabibbo-Kobayashi-Maskawa matrix

The masses of the radioactive nuclei (46)V and its decay daughter (46)Ti have been measured with the Canadian Penning Trap on-line Penning trap mass spectrometer to a precision of 1 x 10(-8). A Q(EC) value of 7052.90(40) keV for the superallowed beta decay of (46)V is obtained from the difference of these two masses. With this precise Q value, the Ft value for this decay is determined with improved precision. An investigation of an earlier Q-value measurement for (46)V uncovers a set of 7 measurements that cannot be reconciled with modern data and affects previous evaluations of V(ud) from superallowed Fermi decays. A new evaluation, adding our new data and removing the discredited subset, yields new values for G(V) and V(ud). When combined with recent results for V(us), this yields modified constraints for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix and other extensions of the standard model.     

An exact algorithm for the network pricing problem

This work focuses on an improved exact algorithm for addressing an NP-hard network pricing problem. The method involves an efficient and partial generation of candidate solutions, a recursive scheme for generating improved upper bounds, and a column generation procedure for solving the network-structured subproblems. Its efficiency is assessed against both randomly generated instances involving three distinct topologies as well as instances based on real life situations in telecommunication and freight transportation.     

The proposed Penning trap mass spectrometer facility at TASCC

The proposed Penning trap mass spectrometer, to be located at the TASCC facility of the Chalk River Laboratories, is described. The facility will be used for precise atomic mass determinations among both stable and unstable nuclides. The unstable nuclides would be produced in heavy ion reactions using the TASCC facility. The products from these reactions would be collected using an He-jet transport system loaded with NaCl aerosols. After transport to a background free area, the nuclides of interest would be laser desorbed and resonantly ionized. Subsequently, these ions would be accumulated in a Paul trap, cooled and injected into a precision Penning trap mass spectrometer for mass analysis.     

Disjunctive cuts for continuous linear bilevel programming

This work shows how disjunctive cuts can be generated for a bilevel linear programming problem (BLP) with continuous variables. First, a brief summary on disjunctive programming and bilevel programming is presented. Then duality theory is used to reformulate BLP as a disjunctive program and, from there, disjunctive programming results are applied to derive valid cuts. These cuts tighten the domain of the linear relaxation of BLP. An example is given to illustrate this idea, and a discussion follows on how these cuts may be incorporated in an algorithm for solving BLP.     

Nuclear moments and charge radius changes in platinum isotopes

Isotope shift (IS) and hyperfine structure (HFS) measurements have been performed for^{185, 187, 189, 191, 195}Pt using the PILIS (Post ISOCELE Laser Isobar Separator) apparatus installed at the ISOCELE facility. Magnetic and quadrupole moments have been deduced from the HFS results. The charge radius changes determined for these odd nuclei from the IS results, added to the σ<r²> values of the even-A nuclei are compared to the results of lattice Hartree-Fock+BCS calculations for asymmetric solutions:¹⁸⁵Pt is confirmed to be prolate shaped whereas^{187, 189, 191}Pt are likely triaxial in their ground states.