A Genetic Algorithm Based Approach for the Uncapacitated Continuous Location–Allocation Problem

A GA-based approach is introduced to address the continuous location–allocation problem. Selection and removal procedures based on groups of chromosomes instead of individual chromosomes are put forward and specific crossover and mutation operators that rely on the impact of the genes are proposed. A new operator that injects once in a while new chromosomes into the population is also introduced. This provides diversity within the search and attempts to avoid early convergence. This approach is tested on existing data sets using several runs to evaluate the robustness of the proposed GA approach.     

Synthesis and structural study of copolymers of l-lactic acid and bis(2-hydroxyethyl terephthalate)

Poly(ethylene terephthalate)-poly(lactic acid) (PET-PLLA) copolyesters were synthesized by the melt reaction of bis(2-hydroxyethyl terephthalate) (BHET) with l-lactic acid oligomers (OLLA) in the presence of SnCl₂, H₂O-p-toluene sulfonic acid, H₂O catalytic system. The ¹H and ¹³C NMR studies confirm the incorporation of lactate units in PET chains after reaction. Copolyesters containing nearly equimolar terephthalate/lactate ratio are not completely random and present some block-copolymer character, while the microstructure of PET-rich copolyesters is a random one. Due to a longer PET sequence length, the latter exhibit a melting point close to 210 °C while the other ones are amorphous. SEC/MALDI-TOF MS off-line coupling was used to obtain the absolute average molar masses of the copolyesters. The results indicate that the conventional polystyrene calibration method leads to a strong overestimation of PET-PLLA molar masses, while the determined by NMR is much closer to the SEC/MALDI value.     

Influence of a sudden expansion on slug flow characteristics in a horizontal two-phase flow: a pressure drop fluctuations analysis

Experimental investigations were conducted to study the evolution of air/water slug flow characteristics through a horizontal sudden expansion having a ratio of \(\sigma_{A}\)?=?0.444. A series of acquisition of differential pressure upstream and downstream were carried out leading to statistical as well as spectral analyses. The influences of both liquid and gas superficial velocities on flow behavior as well as standard deviation were studied. Substantial modifications of two-phase flow distribution were reported downstream the singularity with a quantitative reduction in standard deviation. Besides the fact that the slug flow regime didn’t persist downstream the singularity for low values of superficial phasic-velocities, the latter (\(J_{\ell }\) and \(J_{g}\)) seem to have no noticeable effects downstream the expansion. Reduction of slug frequency between upstream and downstream the singularity was also observed.     

Hybrid meta-heuristics with VNS and exact methods: alication to large unconditional and conditional vertex $$$$-centre roblems

Large-scale unconditional and conditional vertex \(p\)-centre problems are solved using two meta-heuristics. One is based on a three-stage approach whereas the other relies on a guided multi-start principle. Both methods incorporate Variable Neighbourhood Search, exact method, and aggregation techniques. The methods are assessed on the TSP dataset which consist of up to 71,009 demand points with \(p\) varying from 5 to 100. To the best of our knowledge, these are the largest instances solved for unconditional and conditional vertex \(p\)-centre problems. The two proposed meta-heuristics yield competitive results for both classes of problems.     

Poly(ester-amide)s Derived From Adipic Acid, 1,4-Butanediol and β-Alanine: Synthesis and Characterization

A series of polyesteramides (PEAs) differing in their amide/ester ratio, within a range of molar composition from 90/10 to 10/90, have been synthesized by a direct melt polycondensation of 1,4-butanediol, adipic acid and β-alanine. Their structure was fully characterized by FTIR and NMR spectroscopy. The resulting copolymers are amorphous, they are thermally stable to temperatures up to 330°C, and present increasing glass transition temperatures at increasing amide content.     

Customer Allocation in Maximum Capture Problems

The maximum capture (MAXCAP) model and its variants have been widely used to find the maximum capture that a firm can get as it enters a spatial market where there are already existing (competitor??s) facilities. While the model obtains the optimal demand capture, it however allows the customers to be assigned to the non-closest facility which may incur additional operating costs. A two stage method can be used that overcomes the drawback of the original model while requiring a negligible extra computational effort. To make the original model mathematically self contained and more concise two revised formulations of the problem RMAXCAP-1 and RMAXCAP-2 are proposed which assure that the customers patronize only their closest entering facilities. These models are tested on different sizes of datasets and their performances are compared.