1,721,181 research outputs found
Finite element modeling of superplastic forming of friction stir processed AZ31B mg alloy
No full textSuperplastic forming (SPF) is considered to be a near net shape manufacturing technique, mainly adopted to realize aircraft and automotive parts, which requires relatively high tooling and assembly costs. Furthermore the tuning of the process is a non trivial operation since very limited reliable models have been developed to predict the complex geometries obtained through SPF. In such context several researches, based on finite element method (FEM,) have been conducted on the numerical optimization of conventional SPF processes. Friction Stir Processing (FSP) can be used combined with conventional SPF to enhance the superplastic material behavior by means of grain refinement treatment locally performed. From this point of view very few models have been developed to simulate the different superplastic behavior distinguishing the materials after the application of FSP. In this work free bulge forming tests of AZ31B Mg alloy was experimentally performed by means of blow forming laboratory-scale equipment as well as FEM analysis were conducted to simulate the SPF in two different cases: unprocessed and friction stir processed (FSProcessed) condition. The most relevant parameters of the constitutive numerical model were optimized by numerical-experimental comparison. More specifically material strength factor (K) and strain rate sensitivity index (m) were considered during the parametric optimization. Strain and thickness distributions were compared to the experimental measurements in order to individuate the optimized constitutive equations governing the superplastic behavior in both case studies
NHC ligand effects on Ru-catalyzed cross-metathesis of renewable materials
No full textAs petrochemical resources become increasingly scarce and expensive, much attention has been focused on renewable resources from biomass as alternative options for producing basic building blocks for chemical manufacturing. Catalytic olefin metathesis represents a powerful tool to transform biosourced structural motifs in valuable commodity, fine, and specialty chemicals. In that respect, the appropriate choice of the catalyst is the key issue of each metathesis transformation. The current study examines the influence of different N-heterocyclic carbene (NHC) ligands containing one or two N-alkyl substituents on the efficiency of Hoveyda–Grubbs-type catalysts in the cross-metathesis reaction of ethyl oleate with cis-1,4-diacetoxy-2-butene and cross-metathesis of eugenol acetate with cis-1,4-dichloro-2-butene. Interestingly, the introduction of alkyl N-substituents in the NHC ligand was revealed as beneficial for catalytic performances in the examined cross-metathesis (CM) reactions, leading to higher activity and/or selectivity than those observed in the presence of the classical, commercially available Hoveyda–Grubbs second generation catalyst (HGII)
Influence of some packaging materials and of natural tocopherols on the sensory properties of breakfast cereals
No full textThe combined effect of natural antioxidants and packaging materials on the quality decay of breakfast cereals during storage was evaluated. Corn flakes were produced on industrial scale, using different packages and adding natural tocopherols to the ingredients, and stored for 1 year. The samples were then submitted to sensory analysis and HS-solid phase microextraction/gas chromatography/mass spectrometry (SPME/GC/MS) analysis. The packaging had a significant influence on the sensory profile of the aged product: metallized polypropylene gave the highest levels of oxidation compounds and sensory defects. The sensory profile was improved using polypropylene and especially high-density polyethylene. Natural tocopherols reduced the sensory decay of the flakes and the oxidative evolution of the volatile profile. They gave the most remarkable improvement in polypropylene (either metallized or not) packs. Polypropylene showed a barrier effect on the scalping of volatiles outside of the pack. This led to higher levels of oxidation volatiles and faster rates of the further oxidative processes involving the volatiles. © The Author(s) 2013
Faba greens, globe Artichoke’s offshoots, crenate broomrape and summer squash greens: Unconventional vegetables of Puglia (Southern Italy) with good quality traits
No full textGlobe artichoke (Cynara cardunculus L. subsp. [L.] scolymus Hayek), summer squash (Cucurbita pepo L.) and faba bean (Vicia faba L.) are widely cultivated for their immature inflorescences, fruits and seeds, respectively. Nevertheless, in some areas of Puglia (Southern Italy), other organs of these species are traditionally used as vegetables, instead of being considered as by-products. Offshoots (so-called cardoni or carducci) of globe artichoke, produced during the vegetative growing cycle and removed by common cultural procedures, are used like to the cultivated cardoons (C. cardunculus L. var. altilis DC). The stems, petioles, flowers and smaller leaves of summer squash are used as greens (so-called cime di zucchini), like other leafy vegetables such as chicory (Cichorium intybus L.) and Swiss chard (Beta vulgaris L.). Also the plant apex of faba bean, about 5-10 cm long, obtained from the green pruning, are used as greens (so-called cime di fava) like spinach leaves. Moreover, crenate broomrape (Orobanche crenata Forssk.), a root parasite plant that produces devastating effects on many crops (mostly legumes), is used like asparagus (Asparagus officinalis L.) to prepare several traditional dishes. In this study ethnobotanical surveys and quality assessment of these unconventional vegetables were performed. For their content of fiber, offshoots of globe artichokes can be considered a useful food to bowel. Summer squash greens could be recommended as a vegetable to use especially in the case of hypoglycemic diets considering both content and composition of their carbohydrates. For their low content of nitrate, faba greens could be recommended as a substitute of nitrate-rich leafy vegetables. Crenate broomrape shows a high antioxidant activity and may be considered as a very nutritious agri-food product. Overall, the results of the present study indicate that offshoots of globe artichoke, summer squash greens, faba greens and crenate broomrape have good potential as novel foods, being nutritious and refined products. Their exploitation aiming to the obtainment of labeled and/or new potential ready-to-eat retail products could satisfy the demand for local functional foods
[OSSO]-bisphenolate metal complexes: A powerful and versatile tool in polymerization catalysis
No full textSince the report of the stereospecific polymerization of styrene dated 2003, metal complexes bearing [OSSO]-bisphenolate ligands have been successfully applied in different branches of homogeneous catalysis, de facto building a new research field. This review will focus on polymerization reactions promoted by these complexes, starting with those involving “traditional” monomers (such as fossil-derived olefins) up to more recent and green applications, like polymerization of terpenes or utilization of CO2 as a green building block
An “Omics” Approach for Lipid Oxidation in Foods: The Case of Free Fatty Acids in Bulk Purified Olive Oil
No full textMonitoring or preventing oxidation processes in foods, particularly heterogeneous systems or highly oxidizable lipids, has become a primary issue. Traditional approaches often fail in pursuing this aim. At the same time, the prediction in laboratory of the efficacy of antioxidant molecules and technologies often fails when challenging reality. A change in the traditional paradigm used to conceive oxidation processes and their monitoring could be a key. In the present work, an “omics” approach is suggested for the evaluation of oxidation in food lipids and of the role played by minor compounds. This holistic and comprehensive, hypothesis-generating approach is applied to a typical research case: highly-purified olive oil added with increasing amounts of purified free fatty acids (FFA). A comprehensive profile (“oxidome”) of oxidation products is outlined during the accelerated oxidation. The pathways considered are FFA and triacyglycerol oxidation, triacyglycerol polymerization, volatile compounds formation as well as their further oxidation. FFA affectes the overall balance of the oxidation pathways and consequently causes a drift in the evolution of the pattern of oxidation products. The balance between accelerating activity of FFA toward triacylglycerol oxidation and their high susceptibility to undergo oxidation turnes out to be dose-dependent and time-related, and shiftes the resulting oxidation profile of the oil. The omics approach to oxidation products profiling provides new insight into oxidation processes. “Oxidomics” could be helpful to deepen the insight into unresolved issues of oxidation, going beyond the usual single- or few-marker approach. Practical Applications: This research suggests a new paradigm for approaching food lipid oxidation. Unresolved practical issues regarding food spoilage and shelf-life, waste reduction, keeping of healthy properties are increasing along the increasing formulation of complex and dispersed systems, use of healthy highly unsaturated fatty acids and bioactive antioxidants, attention paid by consumers and industries to nutritional, sensory, health properties of foods. The new paradigm suggests going beyond the usually adopted single- or few-marker approach and to consider the pattern of oxidation reactions and products as a whole, in order to better describe and predict its changes and the effects of external factors as well as added molecules. “Oxidomics” is a new paradigm for lipid oxidation, with a holistic approach to the system and evaluating a pattern of oxidation products and its changes
An effort to improve the shelf life of breakfast cereals using natural mixed tocopherols
No full textAn experimental investigation was carried out with the aim of appraising the effects of natural tocopherols on lipid oxidation in extruded breakfast cereals. Corn flakes produced on an industrial scale, with and without added tocopherols and stored in commercial packing under shelf conditions, were compared using sensory evaluation and analyses of volatile compounds and triacylglycerol polymerization products. The sensory evaluation showed the effectiveness of tocopherols in limiting the development of off-flavour during storage. The analysis of the volatile compounds, focused on the secondary products of the lipid oxidation, showed that the antioxidant activity of tocopherols limited the evolution of the headspace towards a more intense oxidation, notably the further oxidation of hexanal into hexanoic acid (that reached 32% and 15% in the flakes, respectively, without and with added tocopherols, after 360 days). The percentage of hexanoic acid in the headspace positively correlated with almost all the descriptors of the defect considered for the sensory evaluation. The analysis of the triacylglycerol polymerization products confirmed the inhibiting action of tocopherols on lipid oxidative degradation. © 2007 Elsevier Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
