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21.
J. Albino Aguiar C. C. de Souza Silva Y. P. Yadava D. A. Landinez Tellez J. M. Ferreira E. Montarroyos J. Guzman E. Chavira 《Journal of Low Temperature Physics》1999,117(3-4):969-973
We have fabricated and characterized Yba
2
Cu
3
O
7–
-Ba
2
HoSbO
6
a realized high T
c
superconductor - ceramic insulator composite system in which particles of the superconductor and ceramic insulator could coexist with well defined separated phases left intact by stringent processing conditions. All the composites exhibit superconductivity at 92K. EDX analysis show that element% and atomic% of the composites are in a good agreement with those of their respective components. SEM studies show homogenous surface morphology and particle size distribution. There is no detectable interface interaction between component grains and Ba
2
HoSbO
6
grains are distinguishably distributed in the Yba
2
Cu
3
O
7–
matrix. 相似文献
22.
Toledo Marante FJ García Castellano A Estévez Rosas F Quintana Aguiar J Bermejo Barrera J 《Journal of chemical ecology》2003,29(9):2049-2071
Phytotoxicity-based extraction and fractionation were employed to separate allelochemicals contained in an extract of Lethariella canariensis. Twelve phenolic substances were isolated from the phytotoxic fraction Letharal of the thalli. These were identified by spectroscopic methods, physicochemical constants, and HPLC chemical correlation, and determined to be atranol (2), chloroatranol (3), hematommic acid (4), chlorohematommic acid (5), methyl hematommate (6), methyl chlorohematommate (7) (new compound), ethyl hematommate (8), ethyl chlorohematommate (9), methyl -orsellinate (10), atranorin (11), chloroatranorin (12), and (+)-usnic acid (13). Further identification and quantification of these allelochemicals in the environment were conducted by HPLC. Several phenolic compounds showed moderate antimicrobial activity. The cytostatic activity of the polyphenols was investigated on U937 and HL-60 cells. All compounds were assayed, with the exception of 10. The Letharal mixture decreased cell viability in both cell lines. Protection against lipid peroxidation was investigated using brain homogenates. Compounds 2, 3, 6, 8, 11, and Letharal decreased H2O2/Fe+2 induced lipid peroxidation in a concentration-dependent manner, while 10 and 13 were unable to protect tissue against oxidative stress. 相似文献
23.
Surendran Rajesh Daniel A. Macedo Rubens M. Nascimento Graziele L. Souza Filipe M.L. Figueiredo Fernando M.B. Marques 《International Journal of Hydrogen Energy》2013
Europium-doped ceria (EDC, Ce0.9Eu0.1O2−δ)/alkaline carbonate (LNC, (Li,Na)2CO3) composite ceramics prepared through a one-step citrate-based route were analyzed by powder X-ray diffraction, infrared and laser Raman spectroscopies as well as scanning and transmission electron microscopy. The electrochemical behavior of the electrolyte material was studied by impedance spectroscopy in air, CO2 and N2 + H2 (90/10 vol%, respectively) gas mixtures, in the temperature range 300–600 °C. The sub micrometric and even nanosized ceramic particles appeared as merged inside the mixed carbonates, with modest grain to grain necking. The EDC/LNC composite electrolytes showed a conductivity of 0.27 S cm−1 at 600 °C in air, amongst the best ever reported, exceeding the usual requirements for fuel cell applications. 相似文献
24.
Janaina I. S. Aguiar Jéssica S. G. Neto Sarah M. Almeida Claudia R. E. Mansur 《应用聚合物科学杂志》2013,128(3):1390-1397
During extraction of crude oil, water is generally present in the oil. This water‐in‐oil (w/o) mixture undergoes turbulent flow that promotes sheer forces, resulting in the appearance of emulsions. These emulsions can be highly stable due to the presence of compounds with polar characteristics such as asphaltenes, which act as natural emulsifiers and form resistant films at the oil–water interface. Nonionic surfactants based on polyoxides are widely used to prevent the formation or to break down w/o emulsions. To shed more light on the destabilization mechanism of w/o emulsions promoted by these surfactants, in this study the techniques of tensiometry and Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR‐ATR) were applied to study the interface formed by poly(ethylene oxide)‐poly(propylene oxide) (PEO‐PPO) block copolymers and asphaltenic petroleum fractions. Initially, the critical micelle concentration of the copolymers in aqueous solution was determined. The results agreed with those found by tensiometry. The bottle test was used to evaluate the break‐down of the w/o emulsions in the presence of the PEO‐PPO block copolymers, and the results presented good agreement with those obtained by tensiometry and FTIR‐ATR. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
25.
S Giovanni-De-Simone AS Aguiar AR Gimenez K Novellino RS de Moura 《Canadian Metallurgical Quarterly》1997,16(8):809-818
An analytical procedure was developed to measure bromate residues in baked goods using a sequence of clean-up procedures followed by high performance liquid chromatography (HPLC) with a post-column reaction for oxidants. Deionized water was used to extract bromate from bread samples. The extract was treated with a C-18 solid phase extraction column to remove lipids, a cation exchange column with the silver cation to remove chloride, and an ultrafiltration membrane to remove proteins. Further treatment of the extract with the sodium form of a propylsulphonic acid ion exchange column was necessary to remove the silver that leached from the silver column. The method had a detection limit of 3 ng/g in baked goods. Recoveries of bromate from breads ranged from 73 to 86% at a fortified bromate level of 5-100 ng/g. Pullman-type white bread, produced by a sponge and dough method, was prepared in our laboratory for measurement of residual bromate. The dough was scaled in three different weights at different specific volumes (3.8, 4.1, 4.3), and samples of each of the three weights were baked for six different baking times ranging from 24 to 34 min. When bromate at a level of 25 mg/kg was added to flour, no residual bromate was detected in any of the samples, regardless of weight and baking time. 相似文献
26.
Márcia Moraes Cascaes Giselle Maria Skelding Pinheiro Guilhon Eloisa Helena de Aguiar Andrade Maria das Gra?as Bichara Zoghbi Lourivaldo da Silva Santos 《International journal of molecular sciences》2015,16(10):23881-23904
Myrcia is one of the largest genera of the economically important family Myrtaceae. Some of the species are used in folk medicine, such as a group known as “pedra-hume-caá” or “pedra-ume-caá” or “insulina vegetal” (insulin plant) that it is used for the treatment of diabetes. The species are an important source of essential oils, and most of the chemical studies on Myrcia describe the chemical composition of the essential oils, in which mono- and sesquiterpenes are predominant. The non-volatile compounds isolated from Myrcia are usually flavonoids, tannins, acetophenone derivatives and triterpenes. Anti-inflammatory, antinociceptive, antioxidant, antimicrobial activities have been described to Myrcia essential oils, while hypoglycemic, anti-hemorrhagic and antioxidant activities were attributed to the extracts. Flavonoid glucosides and acetophenone derivatives showed aldose reductase and α-glucosidase inhibition, and could explain the traditional use of Myrcia species to treat diabetes. Antimicrobial and anti-inflammatory are some of the activities observed for other isolated compounds from Myrcia. 相似文献
27.
Cross-sectional study with 270 children and their mothers in eight public and philanthropic daycare centers in the city of S?o Paulo, Brazil. The objective is to identify the determinants of exclusive breastfeeding (EBF) and breastfeeding (BF). The Mann-Whitney/ Wilcoxon test and survival analysis; Kaplan Meier curves and Cox multiple regression models were used for statistical analyses. The median of exclusive breastfeeding duration was 79.1 +/- 55.6 days and breastfeeding was 185.3 +/- 174.2 days. In multivariate analysis, the following risk factors of early weaning for exclusive breastfeeding were identified: pacifier use (HR = 1.65, 95% CI = 1.24 to 2.2); previous hospital admission (HR = 1.35, 95% CI = 1.01 to 1.80); mother working outside home (HR = 1.33, 95% CI = 1.00 to 1.76). For breastfeeding were identified: pacifier use (HR = 2.54, 95% CI = 1.87 to 3.45) and mother who works outside the home (HR = 1.51, 95% CI = 1.14-1.99). The results show that it is necessary to continue to promote and support breastfeeding, mainly the exclusive breastfeeding until six months of age. The daycare centers should incorporate this idea, once they may have direct control over some of the early weaning determinants, and are also good places to deliver messages and guidance on nutrition education to mothers and caregivers in contact with children under three years old. 相似文献
28.
Lizandra Viana Maurat da Rocha Paulo Sergio Rangel Cruz da Silva Eduardo Miguez Bastos da Silva Vinicius de Oliveira Aguiar Maria Inês Bruno Tavares 《应用聚合物科学杂志》2024,141(17):e54147
The cover image by Lizandra Viana Maurat da Rocha highlights one of our innovative biodegradable films, which incorporated molybdenum trioxide and zinc oxide into the poly(butylene adipate-co-terephthalate) matrix through casting. The photo emphasizes its partial transparency and homogeneity. Some analytical results reported as FTIR, TD-NMR, XRD and TGA validates nanomaterial's exceptional mechanical and chemical properties. Icons below underscore its potential as an eco-friendly food packaging,with bacteriostatic features and no formation of microplastics after disposal. DOI: 10.1002/app.55294
29.
R. L. Rodríguez-Suárez S. M. Rezende A. Azevedo F. M. Aguiar 《Journal of Superconductivity and Novel Magnetism》2010,23(1):33-35
Here we present a calculation for the linewidth of the spin-wave that is generated when a spin valve nanostructure is traversed
by a high-density spin-polarized direct current. In this case, the magnetization excitations are considered to be standing
spin-wave modes interacting through the four-magnon processes. We obtain an analytic expression for the effective nonlinear
dissipation rate of a magnetic spin-torque nano-oscillator, taking into account a nonlinear phenomenological model of magnetic
dissipation and the natural nonlinear contributions due to the demagnetizing fields. The calculation is applied for the general
case of the external magnetic field applied in an arbitrary direction. 相似文献
30.
E. Vasconcelos S. Fernandes J.L. Barroso de Aguiar F. Pacheco-Torgal 《Construction and Building Materials》2011,25(8):3213-3221
This paper presents results about the use of metakaolin based geopolymers mortars for retrofitting purposes. Two main situations are addressed, the use of geopolymeric mortars as a repairing layer or as a binding agent to insure the adhesion between CFRP sheets and the concrete substrate. Several compositions of metakaolin geopolymer mortars were executed by varying the percentage of sand/binder mass ratio and the concentration of sodium hydroxide. It was found that metakaolin geopolymer mortars show a high mechanical resistance and a relevant adhesion to the concrete substrate. Although their adhesion strength is lower than the one present by commercial pre-pack repair mortars, they are very cost-effective (5–10 times less expensive). On the other hand, the adhesion strength between CFRP and geopolymer mortars proved to be lower than expected which could be due to the fact that the composition of the geopolymeric mortars was not optimized and also to the fact that the CFRP used was not prone to this kind of application. 相似文献