Bull-free Berge graphs are perfect

Abull is the (self-complementary) graph with verticesa, b, c, d, e and edgesab, ac, bc, bd, ce; a graphG is calledBerge if neitherG not its complement contains a chordless cycle whose length is odd and at least five. We prove that bull-free Berge graphs are perfect; a part of our argument relies on a new property of minimal imperfect graphs.This work was done while both authors were at the School of Computer Science, McGill University; support by NSERC is gratefully acknowledged.     

Heterogeneous diastereoselective hydrogenation of pyridine and corresponding enamine covalently bound to pantolactone

The diastereoselective hydrogenation of 2-methyl nicotinic acid covalently bound to pantolactone was studied over supported metallic catalysts. With this chiral auxiliary, a two-steps reaction was observed with formation of tetrahydropyridine intermediate. The influence of different reaction parameters on the diastereoselectivity of the hydrogenation of pyridine and enamine substrates was studied.     

Adaptive perturbed neighbourhood search for the expanding capacity multiple-choice knapsack problem

In this paper, we develop a perturbed reactive-based neighbourhood search algorithm for the expanding constraint multiple-choice knapsack problem. It combines reactive tabu search with some specific neighbourhood search strategies to approximately solve the problem. The tests were conducted on randomly generated instances and executed in comparable benchmark scenarios to those of the literature. The results outperform those of the Cplex solver and demonstrate the high quality of the two approach versions.     

On uniqueness and existence of entropy solutions for a nonlinear parabolic problem with absorption

The aim of this paper is to study, for L ¹-data, the absorption problem of parabolic type : with Dirichlet boundary conditions and initial conditions. Here a satisfies the classical Leray-Lions hypotheses and β(x, ·) is the subdifferential ∂j(x, ·), where j is a convex function such that j(·, 0) = 0. Existence and uniqueness of an entropy solution is established.      

Diastereoselective heterogeneous catalytic hydrogenation of 2-methyl nicotinic acid using pyroglutamate chiral auxiliary

The diastereoselective hydrogenation of 2-methyl nicotinic acid covalently bound to proline ester or pyroglutamic ester over supported metallic catalyst yielded moderate diastereoselectivity (26%). The hydrogenation of the corresponding pyridinium salt was studied and similar de's were achieved.     

An Efficient Algorithm for the Knapsack Sharing Problem

The Knapsack Sharing Problem (KSP) is an NP-Hard combinatorial optimization problem, admitted in numerous real world applications. In the KSP, we have a knapsack of capacity c and a set of n objects, namely N, where each object j, j = 1,...,n, is associated with a profit p _j and a weight w _j. The set of objects N is composed of m different classes of objects J _i, i = 1,...,m, and N = ^m _i=1 J _i. The aim is to determine a subset of objects to be included in the knapsack that realizes a max-min value over all classes.In this article, we solve the KSP using an approximate solution method based upon tabu search. First, we describe a simple local search in which a depthparameter and a tabu list are used. Next, we enhance the algorithm by introducing some intensifying and diversifying strategies. The two versions of the algorithm yield satisfactory results within reasonable computational time. Extensive computational testing on problem instances taken from the literature shows the effectiveness of the proposed approach.     

Spectral Mapping Theorems for Neutron Transport, L1-Theory

This work deals with spectral mapping theorems for neutron transport semigroups in unbounded geometries and L¹ setting. The mathematical analysis relies on harmonic analysis of certain measure valued mappings related to Dyson-Phillips expansions and on some functional analytic results on the critical spectrum.     

Synthesis of Highly Fluorinated Aryl N-Acylsulfamates and Evaluation of Their Surfactant Properties

Abstract

Reaction of highly fluorinated carboxylic acids with aroxysulfonylisocyanates in the presence of triethylamine allowed the preparation of the corresponding highly fluorinated aroxy-N-sulfonylsulfamates. The reaction proceeds with good yield in toluene at room temperature or more rapidly in the same solvent at 60 °C. Surface tension measurement at the air/water interface showed that these compounds constitute new excellent nonionic surfactants exhibiting high surface activity in the range of the best nonionic fluoro surfactants, already described in the literature. The critical micelle concentration (CMC) has been calculated from the surface tension measurements on surface aqueous solutions.