A multigrid optimization algorithm for the numerical solution of quasilinear variational inequalities involving the p-Laplacian

In this paper we propose a multigrid optimization algorithm (MG/OPT) for the numerical solution of a class of quasilinear variational inequalities of the second kind. This approach is enabled by the fact that the solution of the variational inequality is given by the minimizer of a nonsmooth energy functional, involving the $p$-Laplace operator. We propose a Huber regularization of the functional and a finite element discretization for the problem. Further, we analyze the regularity of the discretized energy functional, and we are able to prove that its Jacobian is slantly differentiable. This regularity property is useful to analyze the convergence of the MG/OPT algorithm. In fact, we demonstrate that the algorithm is globally convergent by using a mean value theorem for semismooth functions. Finally, we apply the MG/OPT algorithm to the numerical simulation of the viscoplastic flow of Bingham, Casson and Herschel–Bulkley fluids in a pipe. Several experiments are carried out to show the efficiency of the proposed algorithm when solving this kind of fluid mechanics problems.     

Morphology and chain mobility of reactive blend nanocomposites of PP‐EVA/Clay

Polypropylene (PP)‐ethylene vinyl acetate (EVA)/clay nanocomposites were prepared via reactive blending using dicumyl peroxide (DCP) as an initiator with the goal of enhancing the interaction between both phases and modified nanoclay. The effect of the reactive blending and clay incorporation strategies (direct and masterbatch) on the blend and nanostructure morphology, and chain mobility of nanocomposites were studied. The chemical analysis showed the chemical bonding of PP‐EVA, which helped to enhance the interaction in the nanocomposites. The nanocomposites obtained from the direct clay strategy presented a co‐continuous morphology of bordering intercalated and agglomerated nanoclay sheets, while the nanocomposites obtained from the masterbatch strategy showed that blend morphology change from droplet to co‐continuous with the increase of EVA concentration, with intercalated/exfoliated nanoclay sheets located in the EVA domains and at the interface. The dynamic mechanical and creep‐recovery results showed different behavior for the both strategies in terms of chain mobility and relaxation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40897.     

Thermal stability of the immobilization process of horseradish peroxidase in electrospun polymeric nanofibers

The horseradish peroxidase enzyme (type VI 250 U mg^?1) was encapsulated in polymeric nanofibers using the electrospinning technique and successfully immobilized by the exposure to glutaraldehyde (GA) vapor in order to create covalent bonds between the polyivinilalcohol (PVA) polymeric chains and the enzyme molecules. The morphology of the nanofibers was analyzed by scanning electron microscopy (SEM) showing a diameter in the range of 100–200 nm. The presence of the enzyme in the electrospun nanofibers was confirmed by infrared spectroscopy (FTIR). The optimum crosslinking time was 1 h of exposure to GA vapor. The maximum percentage of the retained protein and the enzyme activity was obtained using the lowest initial enzyme concentration. The enzyme activity of the sample was retained after four reuse cycles. Differential scanning calorimetry (DSC) was used to study the thermal stability of the samples. The thermal study of the immobilized HRP enzyme provide for the first time additional information regarding the interaction of the HRP enzyme molecules with the PVA chains of the nanofiber matrix, as well as the effect of the crosslinking time in the glass transition temperature and the heat of fusion of the samples. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44811.     

Data analysis of the inactivation of foodborne microorganisms under high hydrostatic pressure to establish global kinetic parameters and influencing factors

The inactivation rate of foodborne microorganisms under high hydrostatic pressure (HHP) is influenced by factors such as substrate, species, strain, temperature, pH, and stage of growth of the cell. In this study, 445 D(P)-values from previously published data were analyzed, including those from bacterial spores, vegetative cells, and yeasts. Three secondary linear inactivation models with pressure and/or temperature as process parameters were tested to estimate global log D(P)-, z(P)-, and z(T)-values, and the influence of these parameters and additional factors was assessed. The results show that significant differences in microbial resistance are mainly the result of temperature, highlighting the need for its inclusion as a process parameter. Perhaps due to the large number of data and very distinct factors, the remaining factors showed no significant differences in microbial resistance, except in the case of Clostridium spp. in soy milk, which showed decreased resistance in this substrate compared with its behavior in other products. These results serve to establish priorities among factors influencing HHP inactivation and to estimate global kinetic parameters as a basis for setting target levels of inactivation. Moreover, they can be used as a benchmark for comparison of microbial HHP inactivation data gathered in future studies.     

Trichothecene genotypes and chemotypes in Fusarium graminearum strains isolated from wheat in Argentina

Argentina is the fourth largest exporter of wheat in the world. The main pathogen associated with Fusarium Head Blight (FHB) of wheat in Argentina is Fusarium graminearum lineage 7 also termed F. graminearum sensu stricto in the F. graminearum species complex, which can produce the Type B trichothecenes, usually deoxynivalenol (DON) and its acetylated forms (3-ADON and 15-ADON) or nivalenol (NIV). We used a multiplex PCR assay of Tri3, Tri7, and Tri13 to determine the trichothecene genotype of 116 strains F. graminearum collected from three locations in Argentina and then verified the chemotype by chemical analysis. PCR assays and chemical analyses gave the same results for all strains that produced trichothecenes. Most strains (> 92%) had the 15-ADON genotype, with the remaining strains having the DON/NIV genotype. We observed neither the NIV nor the 3-ADON genotypes amongst the strains evaluated. The nine strains with the DON/NIV genotype produced DON when analyzed chemically. Thus, the Argentinean populations of F. graminearum are similar to those from wheat elsewhere in the world, in that all the strains produced DON/15-ADON and belong to lineage 7. However approximately 8% of the strains tested were incorrectly diagnosed as DON/NIV producers with the current multiplex PCR and were only DON producers by chemical analysis.     

Effect of Fe3O4 nanoparticles on magnetic xerogel composites for enhanced removal of fluoride and arsenic from aqueous solution

Fe₃O₄ magnetic xerogel composites were prepared by polycondensation of resorcinol (R)–formaldehyde reaction via a sol–gel process in an aqueous solution through varying the molar ratio of Fe₃O₄ nanoparticles (MNPs), catalyst (C), and water (W) content. MNPs were obtained by co-precipitation (MC), oxidation of iron salts (MO), or solvothermal synthesis (MS). Both MNPs and magnetic xerogels were examined regarding the performance of arsenic and fluoride removal in a batch system. The MC-based MNPs had higher adsorption capacities for both fluoride (202.9 mg/g) and arsenic (3.2 mg/g) than other MNPs in optimum conditions. The X-ray diffraction, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy confirmed that Fe was composed into the polymeric matrix of magnetic xerogels that contained 0.59%–4.42% of Fe with a molar ratio of MNPs (M) to R between 0.01 and 0.10. With low R/C and optimum M/R ratios, an increase in the surface area of magnetic xerogels affected the fluoride and arsenic adsorption capacities. The magnetic xerogel composites with the MC-based MNPs prepared at a fixed R/C ratio (100) and at different R/W (0.05–0.06) and M/R (0.07–0.10) ratios had a high arsenic removal efficiency of 100% at an As(V) concentration of 0.1 mg/L and pH of 3.0. The maximum adsorption capacities of magnetic xerogels were approximately five times higher than those of the xerogels without MNP composites. Therefore, Fe₃O₄ nanoparticles enhanced the adsorption of arsenate and fluoride. The variations of alkaline catalyst and water content significantly affected the resulting properties of textural and surface chemistry of magnetic xerogel composites.     

Testing a pump unit by identification measurements of vibration signals

A procedure that operates using the theory of identification measurements of signals and a computerized vibration-monitoring device for an NM 12500-210 pump unit are described. It is shown that the state of an object that is being monitored can be represented by a cluster, an array of linguistic characteristics of model signals with known distribution laws of instantaneous values. A consecutivecomparison procedure is described for assessing the condition of each element in the cluster and of all the clusters that contain respective elements that are stored in a database.     

Modernization of Vibration Analyzers Based on Identification Measurements

A technology is described for revamping vibration analyzers by introducing an additional intelligent unit for analyzing temporal characteristics of measurement signals. The unit flowchart includes a database, storing expert appraisals, and a knowledgebase, constructed based on the method of identification measurements of the regularity/chaoticity properties in the characteristics of vibration signals using the technique of scales. A computer-aided device has been developed for studying the applicability of the proposed techniques. Results of the vibrodiagnostics of a pumpjack with this device are presented.     

Nanostructured rigid polyurethane foams with improved specific thermo-mechanical properties using bacterial nanocellulose as a hard segment

Rigid polyurethane foams (RPUFs) were synthesized with bacterial nanocellulose (BNC) at concentrations of up to 0.5 wt% using two insertion routes based on its reaction with the isocyanate precursor (ISO route) and the formation of a colloidal dispersion in the polyol precursor (POL route). The results indicated that, for BNC concentrations of only 0.1 wt%, drastic improvements of the specific elastic compressive modulus (+244.2%) and strength (+77.5%) were measured for foams with apparent density of 46.4^{+/− 4.7} Kg.m⁻³. The chemical reaction of BNC with the precursor was corroborated through the measurement of the isocyanate number and FTIR analysis. The BNC caused a significant nucleation effect, decreasing the cell size up to 39.7%. Differential scanning calorimetry analysis revealed that the BNC had a strong effect on post-cure enthalpy, particularly for the POL route. Dynamical mechanical thermal analysis under flexural conditions proved that, regardless of BNC concentration, the incorporation of BNC caused anisotropy and that the ISO route contributed to an enhanced damping factor at high temperatures. These results prove that the ISO route is a key aspect to achieve foamed nanocomposites with improved specific mechanical properties.