Global optimization of large‐scale mixed‐integer linear fractional programming problems: A reformulation‐linearization method and process scheduling applications

Mixed‐integer linear fractional program (MILFP) is a class of mixed‐integer nonlinear programs (MINLP) where the objective function is the ratio of two linear functions and all constraints are linear. Global optimization of large‐scale MILFPs can be computationally intractable due to the presence of discrete variables and the pseudoconvex/pseudoconcave objective function. We propose a novel and efficient reformulation–linearization method, which integrates Charnes–Cooper transformation and Glover's linearization scheme, to transform general MILFPs into their equivalent mixed‐integer linear programs (MILP), allowing MILFPs to be globally optimized effectively with MILP methods. Extensive computational studies are performed to demonstrate the efficiency of this method. To illustrate its applications, we consider two batch scheduling problems, which are modeled as MILFPs based on the continuous‐time formulations. Computational results show that the proposed approach requires significantly shorter CPU times than various general‐purpose MINLP methods and shows similar performance than the tailored parametric algorithm for solving large‐scale MILFP problems. Specifically, it performs with respect to the CPU time roughly a half of the parametric algorithm for the scheduling applications. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4255–4272, 2013     

Stability of the lipid fraction of milk‐based infant formulas during storage

A study is made of the effects of storage (time and temperature) on the lipid fraction of four milk‐based adapted infant formulas with basically the same composition, though differing in the iron salt added (lactate or sulfate) and/or the vitamin E source (α‐tocopherol or α‐tocopherol acetate). Peroxide value, hydroperoxide C₁₈ percentage and thiobarbituric acid‐reactive substance (TBARS) content were used as indicators of lipid peroxidation. Fat contents remained stable throughout storage. Peroxide values increased from the first storage month and were affected by storage time, although they exhibited irregular behavior. Storage time and temperature affected hydroperoxide percentage, which was seen to be the earliest indicator of lipid oxidation, being measurable in newly manufactured formulas. TBARS values were only affected by storage time. No statistically significant differences were found among the four infant formulas for any of the lipid oxidation indicators.     

Supertoughness in Polysulfone/Poly(ethylene‐octene) Blends

Summary: Poly(sulfone of Bisphenol A) (PSU) based blends were obtained by melt blending PSU with up to 15 wt.‐% poly(ethylene‐octene) either modified with maleic anhydride (mPEO) or not (PEO). The dispersed particle size was small and similar in blends with PEO or mPEO. These facts indicated respectively that the interfacial tension was low and the lack of compatibilizing effect of mPEO. Some preferential presence of PEO in the outer surface of the specimens was observed, and was attributed to the large viscosity difference between the two components of the blends. This had no effect on the modulus of elasticity, but speeded up both the yield stress and ductility decreases at rubber contents above 3.25 wt.‐%. However, despite the immiscibility of the components, and thanks to the small particle size of the blends, super‐toughness was attained in the unmodified PSU/PEO blends. This was at PEO contents (3.25 wt.‐%) at which the modulus, yield stress and ductility of the blends were almost as good as those of pure PSU. It appeared that a change of the chemical nature of the rubber did not influence by itself super‐toughness, unless it was accompanied by either a morphological or adhesion change.

Impact strength of PSU‐based blends vs. PEO (○) or mPEO (?) content.     

Mechanical improvement of concrete by irradiated polypropylene fibers

Fiber reinforced concrete (FRC) contains fibers physically mixed with gravel, sand, cement, and water. So far, adequate mechanical performance of FRC has been obtained at high cost and using complex technologies; important here is the geometry and surface characteristics of the polymers. We have modified polymeric‐fiber surfaces by using gamma radiation. Irradiated polypropylene (PP) fibers were submitted to 0, 5, 10, 50, and 100 kGy of gamma irradiation dosages. First, tensile strength of PP fibers was evaluated, and then fibers blended at 0, 1.0, 1.5, and 2.0% in volume with Portland cement, gravel, sand, and water. The highest values of compressive strength were obtained with irradiated‐fibers at 10 kGy and 1.5% in volume of fiber. The result is 101 MPa, as compared to 35 MPa for simple concrete without fibers. POLYM. ENG. SCI., 45:1426–1431, 2005. © 2005 Society of Plastics Engineers     

Ozonation of Pyrolytic Aqueous Phase: Changes in the Content of Phenolic Compounds and Color

Ozonation on the phenols present in pyrolytic aqueous phases attained from biomass thermochemical conversion was evaluated. During ozonation, the dark color of original samples was found to decrease as a function of ozonation time. The oxidation kinetics of phenols was quantified by a method based on the color changes of samples. The oxidation profiles showed different behaviors and in some cases the phenols presented a positive correlation with the relative R color parameter, except eugenol, syringol, and vanillin which were markedly different. Finally, the color changes observed seem to be associated with the changes in the overall content of phenols and with the change in the molecular weight of the heavy fractions that include lignin oligomers.     

A Perinatal Palatable High-Fat Diet Increases Food Intake and Promotes Hypercholesterolemia in Adult Rats

The main goal of the present study was to evaluate the long-term effects of a perinatal palatable high-fat diet on the food intake and cholesterol profile of adult rats. Male Wistar rats (aged 22 days) were divided into two groups according to their mother’s diet during gestation and lactation (C _p, n = 10; pups from control mothers; and HL_p n = 10; pups from mothers fed a palatable high-fat diet). At the 76th day, pups were housed individually for 14 days, and daily food consumption was determined during a period of 6 days. Blood from 100-day-old rats was sampled by cardiac puncture. Fasting (12 h) serum glucose, total cholesterol, LDL-C, HDL-C, triglycerides (TG), and VLDL-C levels were determined. The measurement of food intake was higher in the animals submitted to a hyperlipidic diet during the perinatal period. Serum total cholesterol, LDL-C, HDL-C, TG, VLDL-C and glycemia were increased in the HL_p group compared to the control group. Our findings show that an early life environment with a high-fat diet can contribute to metabolic disease in later life.     

Dynamics and linear stability of charged jets in dielectric liquids

The physical system to be considered is a blade-plane configuration in a dielectric liquid. For high electric fields, injection from the blade takes place with ions of the same polarity. The Coulomb force acting upon the injected charges originates an electrohydrodynamic (EHD) flow, referred in what follows as the charged jet. A laminar solution of this EHD jet is obtained using similarity analysis. If transport of charge is dominated by convection, i.e., neglecting molecular diffusion and ion drift, and the electric field is assumed constant, the problem is mathematically equivalent to the bidimensional thermal plume in the limit of large Prandtl numbers. The authors examine the stability of this EHD jet using linear theory and parallel-flow approximations. Neutral stability curves are computed numerically in terms of a nondimensional parameter which is the electrical analogous to the Grashof number. Finally, some experimental observations are presented, followed by a short discussion. The role played by the viscosity correlates reasonable well with the theoretical analysis     

High-Impact PLA in Compatibilized PLA/PCL Blends: Optimization of Blend Composition and Type and Content of Compatibilizer

In this work, the effectiveness of seven commercial compatibilizers is tested in polylactide (PLA)/poly(ε-caprolactone) (PCL) blends with different compositions to obtain a high-impact PLA. None of the compatibilizers is effective for 90/10 and 80/20 PLA/PCL compositions, as no improvement of the impact strength is observed. For the 70/30 composition, compatibilizers having glycidyl methacrylate (GMA) and acrylate groups in their structure are proved the most effective, as the morphological change towards co-continuity induced by them leads to significant impact strength improvements (of ≈345% and 90% with respect to the neat PLA and the noncompatibilized PLA/PCL 70/30 blend, respectively). The 70/30 PLA/PCL composition, as it shows the best balance of properties, and the best compatibilizer (ElvaloyPTW) are chosen to carry out the optimization of the compatibilizer content. It is found that adding 6 phr to the blend results in highly toughened and ductile blends while maintaining a high modulus and yield strength values. Larger compatibilizer contents lead to even higher impact strength values, but the low-strain mechanical properties are notably reduced. Thus, in this work, a simple and easily scalable method to produce high-impact PLA is shown, as it implies the compounding of three commercially available components without involving any toxic solvents.