Constraint Programming-based Column Generation

This paper surveys recent applications and advances of the Constraint Programming-based Column Generation framework, where the master subproblem is solved by traditional OR techniques, while the pricing subproblem is solved by Constraint Programming. This framework has been introduced to solve crew assignment problems, where complex regulations make the pricing subproblem demanding for traditional techniques, and then it has been applied to other contexts. The main benefits of using Constraint Programming are the expressiveness of its modeling language and the flexibility of its solvers. Recently, the Constraint Programming-based Column Generation framework has been applied to many other problems, ranging from classical combinatorial problems such as graph coloring and two dimensional bin packing, to application oriented problems, such as airline planning and resource allocation in wireless ad-hoc networks.     

Chemical trees enumeration algorithms

In the chemical community the need for representing chemical structures within a given family and of efficiently enumerating these structures suggested the use of computers and the implementation of fast enumeration algorithms. This paper considers the isomeric acyclic structures focusing on the enumeration of the alkane molecular family. For this family, Trinajsti et al. (1991) devised an enumeration algorithm which is the most widely known and utilized nowadays. Kvasnika and Pospichal (1991) have proposed an algorithmic scheme which, from the computational complexity point of view, can prove to be more efficient than the Trinajsti one, nevertheless, this algorithm, to the best of our knowledge, has never been implemented. Indeed an efficient implementation requires the introduction of non trivial data structures and other computational tricks. The main contribution of this paper consists of the definition of the implementation details of Kvasnika-Pospichals algorithm, in a comparison of Trinajstis, Kvasnika-Pospichals and two new algorithms, proposed here, in terms of both computational complexity analysis and running times.AMS classification: 05A15, 05C05, 05C30, 05C90Part of this work has been developed during a visit of the first two authors at the EPFL of Lausanne     

Poly(caprolactone‐co‐lactide)/perfluoropolyether block copolymers: Synthesis,thermal, and surface characterization

Poly[(caprolactone‐co‐lactide)‐b‐perfluoropolyether‐b‐(caprolactone‐co‐lactide)] copolymers (TXCLLA) were prepared by ring‐opening polymerization of D ,L ‐dilactide (LA2) and caprolactone (CL) in the presence of α,ω‐hydroxy terminated perfluoropolyether (Fomblin Z‐DOL TX) as macroinitiator and tin(II) 2‐ethylexanoate as catalyst. ¹H NMR analysis showed that LA2 is initially incorporated into the copolymer preferentially with respect to CL. A blocky structure of the polyester segment was also indicated by the sequence distribution analysis of the monomeric units. Differential scanning calorimetry analysis showed the compatibility between poly(lactide) (PLA) and poly(caprolactone) (PCL) blocks inside the amorphous phase with glass‐transition temperature values increasing from ?60 to ?15 °C by increasing the PLA content. Copolymers with high average length of CL blocks were semicrystalline with a melting temperature ranging from +35 to +47 °C. Surface analysis showed a high surface activity of TXCLLA copolymers with values of surface tension independent from the PLA/PCL content and very close to those of pure TX. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3588–3599, 2005     

Fluorinated vinyl ethers as new surface agents in the photocationic polymerization of vinyl ether resins

The syntheses of fluorinated vinyl ethers (H₂C?CHOCH₂CH₂C_nF_2n+1, n = 6 or 8) and their copolymerizations with bis(4‐vinyloxybutyl) isophthalate are reported. The fluorinated monomers were prepared by the transetherification of ethyl vinyl ether and fluorinated alcohols in a 75% yield. Added in low concentrations (0.1–3.0 wt %) to formulations containing bis(4‐vinyloxybutyl) isophthalate, they did not affect the kinetics of the cationic photopolymerization. The cured films were transparent and showed interesting properties in terms of wettability, hardness, cross‐cut adhesion, and chemical inertness. The fluoromonomers increased the hydrophobicity of the film surface, whereas the adhesion on various substrates such as glass and wood was unchanged. An increase in the methyl ethyl ketone resistance was also observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2890–2897, 2003     

Cationic photoinitiated copolymerization of 1-propenyl-vinyl ether systems

A kinetic investigation of the photoinitiated cationic copolymerization of 1-propenyl ethers with vinyl ethers monomers was performed by using FT-IR and 1H-NMR analysis. FT-IR results, obtained in bulk, indicate a higher reactivity of the vinyl ether with respect to the 1-propenyl ether double bond. 1H-NMR analysis, in CDCl₃ solution, confirms these results which agree with the literature data concerning monofunctional systems. The properties of the UV cured copolymerization products are investigated by DMTA analysis and discussed on the basis of the kinetic investigation results.     

Synthesis of new fluorinated allyl ethers for the surface modification of thiol–ene ultraviolet‐curable formulations

Thiol–ene photocurable systems based on a trifunctional thiol [trimethylolpropane tris‐(3‐mercaptopropanoate)] and two different multifunctional allyl ethers (trimethylolpropane triallyl ether and Boltorn U2, an allyl functional dendritic polyester) were examined. To these systems, small amounts (<1 wt %) of fluorinated allyl ethers were added for the modification of their surface properties. Two new fluorinated allyl ethers, 1H,1H‐perfluoro‐1‐heptylallyl ether and 1H,1H‐perfluoro‐1‐decylallyl ether, were synthesized for this purpose by allylation of the corresponding 1H,1H‐perfluoro alcohols. The fluorinated monomers, despite their very low concentrations, caused sharp changes in the surface properties of the films and in the solvent resistance without any changes in the curing conditions and bulk properties. Completely hydrophobic surfaces were obtained (as a result of the selective enrichment of the fluorinated monomers on the film surfaces) that depended on the monomer structure and its concentration. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2583–2590, 2002     

Optimizing base station location and configuration in UMTS networks

Radio planning and coverage optimization are critical issues when deploying and expanding third generation cellular systems. We investigate mixed integer programming models for locating and configuring base stations in UMTS networks so as to maximize coverage and minimize installation costs. The overall model considers both uplink and downlink directions, that we studied separately in Amaldi et al. (2002, 2003b). The two-stage Tabu Search algorithm we propose exploits solutions of a simplified model for the uplink direction to drastically reduce the computational time required to find good approximate solutions of the overall uplink and downlink model.Computational results obtained for realistic instances %with voice as well as data traffic are reported and discussed. Research carried out within the national project “Optimization, simulation and complexity in the design and management of telecommunication networks”funded by the Italian Ministry of Education, University and Scientific Research (MIUR).     

Constraint programming-based column generation

This paper surveys recent applications and advances of the constraint programming-based column generation framework, where the master subproblem is solved by traditional OR techniques, while the pricing subproblem is solved by constraint programming (CP). This framework has been introduced to solve crew assignment problems, where complex regulations make the pricing subproblem demanding for traditional techniques, and then it has been applied to other contexts. The main benefits of using CP are the expressiveness of its modeling language and the flexibility of its solvers. Recently, the CP-based column generation framework has been applied to many other problems, ranging from classical combinatorial problems such as graph coloring and two dimensional bin packing, to application oriented problems, such as airline planning and resource allocation in wireless ad hoc networks.