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181.
Vladimiro Cardenia Thaddao Waraho Maria Teresa Rodriguez-Estrada D. Julian McClements Eric A. Decker 《Journal of the American Oil Chemists' Society》2011,88(9):1409-1416
Phospholipids have been reported to inhibit lipid oxidation in bulk oils, but very little is known about their influence on
oxidation in oil-in-water emulsions. In the present study, the impact of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) on lipid oxidation was studied in 1% stripped soybean oil-in-water (O/W) emulsions as a function
of DOPC concentration and pH (3 and 7). At pH 7.0, DOPC inhibited lipid oxidation in O/W emulsions, while DOPC was prooxidative
at pH 3.0. DOPC did not affect emulsion droplet charge or size at either pH 3.0 or 7.0. The antioxidant activity at pH 7.0
was observed in a series of phospholipids (PL) that varied in fatty acid unsaturation level and chain length as well as type
of phosphate head group. Overall, phosphatidylcholine with either oleic or palmitic acid were the most effective at inhibiting
lipid hydroperoxide and hexanal formation of all of the PL tested. Antioxidant mechanism of PL could not be ascribed to their
ability to decompose lipid hydroperoxides. It might be possible that, at pH 7.0, the PL antioxidant activity is related to
their ability to form structures within the lipid phase of the emulsions droplets or to chelate metals. 相似文献
182.
Cláudio Nico Luís Rino Mariana Matos Rui Monteiro Florinda M. Costa Teresa Monteiro Manuel P.F. Graça 《Journal of the European Ceramic Society》2013,33(15-16):3077-3083
Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the production of capacitors, but these materials still require a further and exhaustive study. Understanding the dynamics of the oxidation process from NbO to Nb2O5 is essential to explain and control the properties of a niobium oxide based capacitors. In situ XRD analysis of NbO powders was performed from 100 to 1100 °C, which showed a temperature range where only amorphous phase is present. The capacitor anodes, formed from the same type of NbO powders, were then heat-treated in air from room-temperature (RT) to 550 °C and recorded with a video camera to see the colour shift. The presence of core–shell structures and the increase of the shell thickness/amount with temperature are visible in SEM. Finally, in situ spectroscopy studies were performed, in order to observe the interference spectra which are responsible for the observed colours. 相似文献
183.
Iron catalyst in the form of a thin layer was deposited directly onto silicon wafers in order to grow carbon nanotubes by a chemical vapor deposition process. The chemical and morphological transformations undergone during the process by the iron were monitored in situ by photoelectron spectroscopy and ex situ by SEM. We found that the growth of carbon nanotubes was successful only when the iron catalyst was previously oxidized. Metallic iron transformed to embedded iron silicide structures, unable to initiate nanotube growth. On the other hand, pre-oxidized iron led to the formation of superficial particles and showed only a partial conversion to silicide, which resulted in carbon nanotube growth, even at very low pressures. 相似文献
184.
A typical reliability-based design optimization (RBDO) problem is usually formulated as a stochastic optimization model where
the performance of a system is optimized with the reliability requirements being satisfied. Most existing RBDO methods divide
the problem into two sub-problems: one relates to reliability analysis, the other relates to optimization. Traditional approaches
nest the two sub-problems with the reliability analysis as the inner loop and the optimization as the outer loop. Such nested
approaches face the challenge of prohibitive computational expense that drives recent research focusing on decoupling the
two loops or even fundamentally transforming the two-loop structure into one deterministic optimization problem. While promising,
the potential issue in these computationally efficient approaches is the lowered accuracy. In this paper, a new decoupled
approach, which performs the two loops sequentially, is proposed. First, a deterministic optimization problem is solved to
locate the means of the uncertain design variables. After the mean values are determined, the reliability analysis is performed.
A new deterministic optimization problem is then restructured with a penalty added to each limit-state function to improve
the solution iteratively. Most existing research on decoupled approaches linearizes the limit-state functions or introduces
the penalty into the limit-state functions, which may suffer the approximation error. In this research, the penalty term is
introduced to change the right hand side (RHS) value of the deterministic constraints. Without linearizing or transforming
the formulations of limit-state function, this penalty-based approach effectively improves the accuracy of RBDO. Comparison
experiments are conducted to illustrate how the proposed method obtains improved solutions with acceptable computational cost
when compared to other RBDO approaches collected from literature. 相似文献
185.
The authors determined conditions for manufacturing PAN precursor fibers containing a system of two nanoadditives, montmorillonite (MMT), and hydroxyapatite (HAp) in their structure. The PAN precursor fibers thus obtained are characterized by a tenacity of more than 30 cN/tex and a total volume of pores at the level of 0.29 cm3/g. Furthermore, it was found that the use of nanoadditives entails the remodeling of the paracrystalline structure of PAN fibers into a strictly crystalline one. This is accompanied by a decrease in spacing between MMT layers combined with their partial exfoliation. The fibers thus obtained, after being carbonized, will be used for medical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
186.
Inês N. Ramos João M.R. Miranda Teresa R.S. Brandão Cristina L.M. Silva 《Journal of food engineering》2010
A computer program was developed, aiming at estimating water diffusivity parameters in a dynamic drying process with grapes, assessing the predictability of corresponding non-isothermal drying curves. It numerically solves Fick’s second law for a sphere, by explicit finite differences, in a shrinking system, with anisotropic properties and changing boundary conditions. 相似文献
187.
Ursula Fillat Montserrat Pepió Teresa Vidal M. Blanca Roncero 《Biomass & bioenergy》2010,34(12):1896-1905
Fiber crops constitute a good alternative to wood fiber for manufacturing pulp and paper. In fact, fiber plants like flax surpass wood fiber in some technical respects and also in the environmental benignity of their processing. In this work, flax fiber was subjected to environmentally friendly bleaching sequences in order to obtain a high-quality pulp. The totally chlorine-free sequences (TCF) used for this purpose (LE and LRE) included an enzyme treatment with laccase in the presence of HBT as mediator (L stage), an alkaline extraction (E stage) and a reductive treatment with NaBH4 (R stage). The operating conditions for the L stage (laccase and HBT doses, reaction time and oxygen pressure) were optimised by using a sequential statistical plan to assess their influence on pulp properties after the E stage.Mathematical models accurately predicting brightness and kappa number in terms of the previous four variables were developed based on which the most influential factors were the laccase and HBT rates, and treatment time. By contrast, oxygen pressures of 0.2–0.6 MPa in the reactor had no effect on brightness or kappa number. The flax pulp obtained contained some oxidized cellulose that was partially degraded in the alkaline extraction step and reduced viscosity as a result. The viscosity loss associated with the presence of oxidized cellulose in the control and enzyme-treated pulp samples was efficiently recovered by using a reductive stage with sodium borohydride. Effluent was also analysed in order to assess the environmental impact of the process. 相似文献
188.
The paper describes the findings from a study of students’ use and experience of technologies. A series of in-depth case studies were carried out across four subject disciplines, with data collected via survey, audio logs and interviews. The findings suggest that students are immersed in a rich, technology-enhanced learning environment and that they select and appropriate technologies to their own personal learning needs. The findings have profound implications for the way in which educational institutions design and support learning activities. 相似文献
189.
190.
Wine ageing in wood barrels is a traditional practice in quality wine-making areas. It is generally believed that the organoleptic characteristics of wines aged in barrels are deeply influenced by wood geographical origin, as well as by age of barrels (new or used). 相似文献