Model order reduction in hyperelasticity: a proper generalized decomposition approach

This paper deals with the extension of proper generalized decomposition methods to non‐linear problems, in particular, to hyperelasticity. Among the different approaches that can be considered for the linearization of the doubly weak form of the problem, we have implemented a new one that uses asymptotic numerical methods in conjunction with proper generalized decomposition to avoid complex consistent linearization schemes necessary in Newton strategies. This approach results in an approximation of the problem solution in the form of a series expansion. Each term of the series is expressed as a finite sum of separated functions. The advantage of this approach is the presence of only one tangent operator, identical for every term in the series. The resulting approach has proved to render very accurate results that can be stored in the form of a meta‐model in a very compact format. This opens the possibility to use these results in real‐time, reaching kHz feedback rates, or to be used in deployed, handheld devices such as smartphones and tablets. Copyright © 2013 John Wiley & Sons, Ltd.     

Heuristic algorithms for a storage location assignment problem in a chaotic warehouse

The extensive application of emerging technologies is revolutionizing warehouse management. These technologies facilitate working with complex and powerful warehouse management models in which products do not have assigned fixed locations (random storage). Random storage allows the utilization of the available space to be optimized. In this context, and motivated by a real problem, this article presents a model that looks for the optimal allocation of goods in order to maximize the storage space availability within the restrictions of the warehouse. For the proposed model a construction method, a local search algorithm and different metaheuristics have been developed. The introduced algorithms can also be used for other purposes such as to assess when and how it is convenient to perform relocation of stored items to improve the current level of storage space availability. Computational tests performed on a set of randomly generated and real warehouse instances show the effectiveness of the proposed methods.     

Influence of molecular weight on the electrification of linear polyethylenes during extrusion: Identification of two different mechanisms for charge generation

The phenomenon of electrification is the accumulation of electric charge in a material. Polymers may become electrified when subjected to intense friction during their processing or under working conditions and the accumulated electric charge may change their adhesion and friction properties. In this work, a study of the influence of molecular weight and chain mobility on the electrification of linear low‐density polyethylenes under continuous extrusion is presented. The use of different die materials, polymer processing additives, as well as slip and no slip flow conditions allowed the identification of two different mechanisms for electric charge generation in the melts; namely, the stripping of an electrical double layer acting in the absence of slip, and dynamic frictional electrification, or tribocharging acting under strong slip conditions. The magnitude of the electric charge was found to increase with polymer molecular weight and die length, and exhibited a local maximum as a function of the average velocity of the melt in both cases. The height of the maximum increased along with the molecular mobility. The experimental results were compared with the numerical solution of the equation of continuity for charge transport and it is shown that it does not describe the experimental results because it does not consider the additional mechanism of charge generation introduced by strong slip at the die wall. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

Ethylene Hydrogenation over Pt/Ga2O3/Al2O3 Catalysts

The effects of gallia addition on the Pt dispersion and the activity for ethylene hydrogenation at 0 °C were studied for Pt-supported catalysts as a function of the reduction temperature (350, 450, and 550 °C). The catalysts contained 0.5 wt.% Pt and were prepared by successive incipient wetness impregnations with Ga(NO₃)₃ and H₂PtCl₆ aqueous solutions. CO and H₂ chemisorption data indicated that, the addition of small amount of Ga₂O₃ caused an increase of the Pt dispersion and a decrease of ethylene conversion. Both of them decreased appreciably when Ga₂O₃ addition was increased, particularly, for the case where β-Ga₂O₃ was used as a support. The increase in reduction temperature magnified the negative effects of the gallia addition on dispersion and activity, although the addition of small amount of gallia improved the resistance to metal sintering. Results were interpreted in terms of the presence of reduced Ga species, which can encapsulate Pt particles.     

Hydrogeological characteristics of a groundwater-dependent ecosystem (La Lantejuela, Spain)

By means of a simple water balance model, together with hydrogeochemical and morphological interpretation, the hydrogeological characteristics of a series of playa lakes forming an endorheic complex within the Guadalquivir river basin in Southern Spain (La Lantejuela) have been evaluated. The lakes are demonstrated to be groundwater-dependent ecosystems. The main source of groundwater input to the lakes is from an unconfined detritic aquifer, the playa lakes being the natural discharge points from the aquifer within the endorheic complex. High rates of evaporation from the lakes induce a centripetal groundwater flow pattern. This water body has been disturbed by a combination of extensive drainage works and intensive groundwater abstraction. There is a need for a sustainable water management strategy for the whole catchment area. It is hoped this will be an issue addressed within the Guadalquivir river basin management plan in accordance with the requirements of the European Water Framework Directive (WFD).     

Inhibition of verocytotoxigenic Escherichia coli by antimicrobial peptides caseicin A and B and the factors affecting their antimicrobial activities

The antimic robial activities of caseicin A and B antimicrobial peptides (AMPs) were assessed against a selection of verocytotoxigenic Escherichia coli (VTEC) strains (n = 11), other bacterial pathogenic and spoilage bacteria (n = 7), using a model broth system. The ability of the AMPs to retain their antimicrobial activities against a strain of E. coli O157:H7 380-94 under various test conditions (pH, temperature, water activity, sodium chloride concentrations, inoculum size and the presence of competitive microflora) was assessed and the minimum inhibitory concentrations (MIC) and number of surviving E. coli O157:H7 calculated. The mean number of VTEC surviving after exposure to 2 mg/ml caseicin A and B was reduced by 4.96 and 4.19 log₁₀ cfu/ml compared to the respective controls. The susceptibility of E. coli O157:H7 to the caseicin AMPs decreased as temperature, pH, water activity and inoculum size were reduced. The presence of sodium chloride (0.5-2.5%) did not affect the activity of caseicin A (p > 0.05), however it did inhibit the activity of caseicin B. The presence of a competitive microflora cocktail did not significantly (p > 0.05) affect the activities of the AMPs for the majority of the concentrations tested. Using a quantitative PCR assay, the levels of verotoxins (vt1 and vt2) expressed by E. coli O157:H7 following exposure to a sub-inhibitory concentration (0.5 mg/ml) of caseicin A showed that the verotoxin levels did not differ from the levels produced by the control cultures. The antimicrobial activity of caseicin A against E. coli O157:H7 was also tested in a model rumen system, however concentrations of ≥ 2 mg/ml did not significantly (p > 0.05) reduce E. coli O157:H7 numbers in the model system over a 24 h period. The application of caseicin AMPs in food and/or animal production may be valuable in combination with other antimicrobials although further research is required.     

Biofilm formation on abiotic and biotic surfaces during Spanish style green table olive fermentation

In this work, the establishment of polymicrobial communities on the surfaces which come into contact with the brine during Spanish style Gordal cv. green olive fermentation when subjected to spontaneous or controlled processes (inoculated with Lactobacillus pentosus LPCO10 or 128/2) was studied. Scanning electron microscopy showed that L. pentosus and yeast populations were able to form mixed biofilms throughout the fermentation process on both abiotic (glass slide) and biotic (olive skin) surfaces. The biofilm architectures in both supports were completely different: on the glass slides only aggregates of L. pentosus and yeasts without any polymeric matrix surrounding them were found while on the skin of the fruits, true mature biofilms were observed. During fermentation, the lactic acid bacteria (LAB) population on the olives remained similar while that of yeasts increased progressively to reach similar levels at the end of the process (8-9 log CFU/cm(2)). Molecular analysis showed that different populations of L. pentosus and yeasts were the only microbial members of the biofilm formed during fermentation, regardless of inoculation. Hence, the green olive surface provides an appropriate environmental condition for the suitable development and formation of complex biofilms during controlled or natural table olive processing.     

Chemical characterisation of anthocyanins in tamarillo (Solanum betaceum Cav.) and Andes berry (Rubus glaucus Benth.) fruits

The anthocyanin composition of tamarillo (Solanum betaceum Cav., red variety) and Andes berry (Rubus glaucus Benth.) was determined by HPLC–PDA and HPLC–ESIMS. From the anthocyanin-rich extracts (AREs), pure compounds (1–7) were obtained by MLCCC (multilayer countercurrent chromatography) and further preparative HPLC, and their unequivocal structures were obtained by 1D and 2D NMR analyses. The new anthocyanin delphinidin 3-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside-3′-O-β-d-glucopyranoside, as well as the known cyanidin-3-O-rutinoside, pelargonidin-3-O-rutinoside, and delphinidin-3-O-rutinoside were identified as constituents of tamarillo fruit. Although the anthocyanin composition of Andes berry had been reported before in the literature, the unequivocal structure elucidation of the major compound, cyanidin-3-O-α-l-rhamnopyranosyl-(1 → 6)-O-β-d-xylopyranosyl-(1 → 2)-β-d-glucopyranoside, was achieved for the first time.