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101.
102.
Franco Van de Velde María E. Pirovani María S. Cámara Daniel R. Güemes Cecilia M. del H. Bernardi 《Food Analytical Methods》2012,5(5):1097-1104
Vitamin C or total ascorbic acid (TAA) in fruits can be assumed as ascorbic acid (AA) plus dehydroascorbic acid (DHA) content. The aim of this work was to optimize and validate, using experimental designs, a new high-performance liquid chromatographic method for vitamin C determination in strawberries. The mobile phase (MP) consisted of a 0.03 M sodium acetate/acetic acid buffer, 5% methanol. For optimization, a Box–Behnken design was used (three factors at three levels: (a) pH of MP, 3.8–5.8; (b) wavelength, 240–270 nm; and (c) flow rate, 0.5–1.2 ml min−1). Responses were: AA and TAA areas, peak widths, and retention times. A global optimization was performed using the Derringer desirability function, and a value of 0.84 was reached for the combination of design factors: A = 5.8, B = 251 nm, and C = 1.15 ml min−1. Method validation, using AA standard solutions, included: linearity study, limits of detection and quantification, and calibration and analytical sensitivity quantifications. Precision and accuracy were studied in strawberry extracts. The coefficients of variation (percent) were: AA, 1.5%; TAA, 1.8%, and DHA, 4.9%. Accuracy was evaluated with AA standard spiked in 30–150% range of the expected amount of analyte in real samples. The joint confidence elliptical region test and t test were employed for the study of the difference between recoveries (percent) and the ideal 100%. The robustness was analyzed using a fractional factorial design (34−2), and an AA recovery study after slight changes in operative variables was performed. The results indicate that the optimized method was linear, sensible, precise, accurate, and robust. 相似文献
103.
Francisco del Monte Willa Larsen John D. Mackenzie 《Journal of the American Ceramic Society》2000,83(6):1506-1512
Metastable tetragonal ZrO2 phase has been observed in ZrO2 –SiO2 binary oxides prepared by the sol–gel method. There are many studies concerning the causes of ZrO2 tetragonal stabilization in binary oxides such as Y3 O2 –ZrO2 , MgO–ZrO2 , or CaO–ZrO2 . In these binary oxides, oxygen vacancies cause changes or defects in the ZrO2 lattice parameters, which are responsible for tetragonal stabilization. Since oxygen vacancies are not expected in ZrO2 –SiO2 binary oxides, tetragonal stabilization should just be due to the difficulty of zirconia particles growing in the silica matrix. Furthermore, changes in the tetragonal ZrO2 crystalline lattice parameters of these binary oxides have recently been reported in a previous paper. The changes of the zirconia crystalline lattice parameters must result from the chemical interactions at the silica–zirconia interface (e.g., formation of Si–O–Zr bonds or Si–O− groups). In this paper, FT-IR and 29 Si NMR spectroscopy have been used to elucidate whether the presence of Si–O–Zr or Si–O− is responsible for tetragonal phase stabilization. Moreover, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy have also been used to study the crystalline characteristics of the samples. 相似文献
104.
Edgar Uquiche Ximena Fica Katherine Salazar José M. del Valle 《Journal of the American Oil Chemists' Society》2012,89(6):1135-1144
This work explored the possibility of using supercritical carbon dioxide (SC-CO2) to achieve fractionation of pre-pressed rapeseed (Brassica napus) cake oil at 30–50 MPa, at 40 or 80 °C, and increase the concentration of minor lipids (sterols, tocopherols, carotenoids) in the oil. Minor lipids are partially responsible for desirable antioxidant effects that protect against degradation and impart functional value to the oil. The weight and concentration of minor lipids in oil fractions collected during the first 60 min were analyzed. Cumulative oil yield increased with pressure, and with temperature at ≥40 MPa, but was lower at 80 °C than at 40 °C when working at pressure ≤35 MPa. Differences in solubility between the oil and minor lipids explained fractionation effects that were small for tocopherols. Unlike tocopherols, which are more soluble in SC-CO2 than the oil, sterols and carotenoids are less soluble than the oil, and their concentration increased in the later stages of extraction, particularly at ≥40 MPa, when there was not enough oil to saturate the CO2 phase. Because of the fractionating effects on rapeseed oil composition, there was an increase in the antioxidant activity of the oil in the second half as compared to the first half of the extraction. Consequently, this study suggests that SC-CO2 extraction could be used to isolate vegetable oil fractions with increased functional value. 相似文献
105.
Yo‐Han Seo Jurij Koruza Andreja Benčan Barbara Malič Jürgen Rödel Kyle G. Webber 《Journal of the American Ceramic Society》2014,97(5):1582-1588
The influence of second phase zirconia particles on the electrical properties and fracture behavior of various polycrystalline soft Pb(Zr1?xTix)O3 (PZT) compositions was investigated. PZT composites with yttria‐stabilized tetragonal zirconia particles exhibited enhanced crack resistance in comparison to monolithic compositions, regardless of the PZT composition. The addition of zirconia, however, was found to change the PZT composition through the diffusion of zirconium, resulting in variations in the observed piezoelectric and ferroelectric responses. Through the tailoring of the PZT matrix composition, the large electromechanical response and enhanced fracture toughness could be retained. The variation in both small and large signal properties is contrasted to fracture results and crystal structure changes, as determined by X‐ray diffraction. 相似文献
106.
J. Paulo García‐Sandoval A. Martín del Campo F. Bautista O. Manero Jorge E. Puig 《American Institute of Chemical Engineers》2018,64(6):2277-2292
The rheological behavior of micellar solutions is analyzed under nonhomogeneous velocity and stress flow conditions. The framework is based on the extended irreversible thermodynamics and the transient network formulation coupled to the underlying kinetics embodying two relevant processes: formation of wormlike chains from a free micellar solution through a thermally activated process and their flow induced degradation. The second kinetic process consists in the formation of entanglements from the free wormlike chains and their flow‐induced breakage. These processes are modeled in a coupled kinetic scheme constituted by a set of reversible kinetic equations describing the evolution in average of the three microstates (free short rod‐like micelles, free wormlike chains, and entangled wormlike chains) that reflect the complexity of macromolecular interactions. The predictions of the shear stress and first normal stress difference as a function of shear‐rate under banded flow are in good agreement with experimental data. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2277–2292, 2018 相似文献
107.
Beef production under different local husbandry systems might have meat sensory quality implications for the marketing of these products abroad. In order to assess the effect of finishing diet systems on beef quality, a trained sensory taste panel assessed meat aged for 20 days from 80 Uruguayan Hereford steers that were finished on one of the following diets: T1 = Pasture [4% of animal live weight (LW)], T2 = Pasture [3% LW plus concentrate (0.6% LW)], T3 = Pasture [3% LW plus concentrate (1.2% LW)], or T4 = Concentrate plus hay ad libitum. Beef odour and flavour intensities decreased with an increase in the energy content of the diet. The meat from T2 had the lowest acid flavour and strange odours intensities. In general, steers fed only concentrate plus hay (T4) produced meat that had an inferior sensory quality because they had more pronounced off-flavours and was tougher. 相似文献
108.
López Steven R.; Lara Ma. del Carmen; Kopelowicz Alex; Solano Susana; Foncerrada Hector; Aguilera Adrian 《Canadian Metallurgical Quarterly》2009,77(4):763
The authors developed and tested a 35-min psychoeducational program with the goal of increasing Spanish-speaking persons’ literacy of psychosis. The program uses popular cultural icons derived from music, art, and videos, as well as a mnemonic device—La CLAve (The Clue)—to increase (a) knowledge of psychosis, (b) efficacy beliefs that one can identify psychosis in others, (c) attributions to mental illness, and (d) professional help-seeking. Assessments were conducted before and after administering the program to both community residents (n = 57) and family caregivers of persons with schizophrenia (n = 38). For community residents, the authors observed increases across the 4 domains of symptom knowledge, efficacy beliefs, illness attributions, and recommended help-seeking. For caregivers, increases were observed in symptom knowledge and efficacy beliefs. La CLAve is a conceptually informed psychoeducational tool with a developing empirical base aimed at helping Spanish-speaking Latinos with serious mental illness obtain care in a timely manner. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
109.
Food traceability is essential to preserve the identity of unique quality traits against frauds or commercial disputes. Therefore, there is a growing demand of new traceability systems for the collection of information related to units/batches of food ingredients and products. 相似文献
110.
In this work, we give a complete picture of the behavior of the low intensity bootstrap of linear statistics. Our setup is given by triangular arrays of independent identically distributed random variables and different normalizations related to the rates of bootstrap intensities. We show that the behavior of this low intensity bootstrap coincides with that of partial sums of a number of summands equal to the bootstrap resampling size. Agreement on the limit laws for different (small) bootstrap sizes is thus shown to be closely related to domains of attraction of α-stable laws. As a byproduct, we obtain local distributional properties of Lévy processes. 相似文献