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51.
Vilar MR Botelho do Rego AM Ferraria AM Jugnet Y Noguès C Peled D Naaman R 《The journal of physical chemistry. B》2008,112(23):6957-6964
We present results from high-resolution electron energy loss spectroscopy (HREELS) and XPS studies of self-assembled monolayers of DNA. The monolayers are well-organized and display sharp vibrational peaks in the HREEL spectra. The electrons interact mainly with the backbone of the DNA. The XPS results indicate that, in most of the samples studied, the phosphates on the DNA are not charged. 相似文献
52.
An on-line derivatization strategy was developed for improving cobalt sensitivity using thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) as the analytical technique. This strategy involves the generation of a volatile cobalt compound, providing better sample vaporization efficiency. The effect of sodium diethyldithiocarbamate (DDTC) as complexing agent on the integrated absorbance signal was evaluated. Parameters including the pH of complex formation, complex concentration and volume, sample volume, flame gas composition and tube atomization configuration were optimized. A wide linear range (from 23 microg L(-1) to 3 mg L(-1); r(2)=0.9786) was obtained, with the best one (r(2)=0.9992) attained from 23 to 400 microg L(-1) with a sample throughput of 30 h(-1). The improvement in the detection power was 17-fold when compared to FAAS, which provides 7 microg L(-1) as the limit of detection when considered TS-FF-AAS technique. A relative standard deviation (n=10) of 4% for a cobalt solution containing 50 microg L(-1) was attained, and the accuracy of the procedure was evaluated through certified reference materials (IAEA-SL-1, lake sediment; and ISS-MURST-A1, Antarctic marine sediment). Good agreement between the results at the 95% confidence level was observed. 相似文献
53.
Karra-Châabouni M Bouaziz I Boufi S Botelho do Rego AM Gargouri Y 《Colloids and surfaces. B, Biointerfaces》2008,66(2):168-177
Rhizopus oryzae lipase (ROL) was immobilized by adsorption onto oxidized cellulose fibers and regenerated films. The maximum adsorption level increases with the raise in the amount of carboxylic groups on cellulose surface confirming that adsorption is being governed mainly by electrostatic interaction between the enzyme and the substrate. This hypothesis was further confirmed by zeta-potential measurements showing a decrease in the zeta-potential of the fibers after enzyme adsorption. XPS analysis showed an intensification of the N 1s peak attesting the presence of the enzyme on the surface. The effect of temperature, pH and solvent polarity on the immobilized enzyme activity and stability was investigated. The catalytic esterification of oleic acid with n-butanol has been carried on using hexane as an organic solvent. A high conversion yield was obtained (about 80%) at 37 degrees C with a molar ratio of oleic acid to butanol 1:1 and 150IU immobilized lipase. The adsorption achieved two successive cycles with the same efficiency, and started to lose its activity during the third cycle. 相似文献
54.
Luciano A. Leal Wiliam F. da Cunha Luiz F. Roncaratti Geraldo M. e Silva 《Molecular physics》2016,114(3-4):440-445
ABSTRACTBased on ab initio calculations, our research group has built an analytical ground-state potential energy surface (PES) for hydrogen peroxide– noble gas (Ng) interactions, such as H2O2–He, H2O2–Ne, H2O2–Ar, H2O2–Kr, and H2O2–Xe complexes. From this PES, it was verified that the Ng presence does not affect the equilibrium values of the H2O2 dihedral angles. This happens because the H2O2 intramolecular barriers have much higher energies than the atom–bond interaction within these complexes. From this point of view, it is indeed reasonable to consider the H2O2 system as a rigid rotor, frozen at its equilibrium configuration. We present in this work the torsional motion for the H2O2 isolated system, the vibration–rotation energy levels and spectroscopic constants for hydrogen peroxide–noble gas by using the aforementioned PES. The predicted H2O2 torsional motions are in good agreement with both theoretical and experimental results available in the literature. Regarding H2O2–Ng ro-vibrational energies and spectroscopic constants, it is the first time that these calculations are presented in the literature. The current theoretical predictions are expected to be useful in the future experimental investigations. 相似文献
55.
Gerlania S. Silva A. G. Souza J. R. Botelho M. C. D. Silva T. M. S. Silva 《Journal of Thermal Analysis and Calorimetry》2007,87(3):871-874
Cis-norbixin
isomer obtained by hydrolysis of cis-bixin and isolated by solvent extraction
from annatto seeds. The thermal decomposition data of the cis-norbixin samples
were analyzed by thermogravimetric analysis at different heating rates in
the 25–900°C temperature range. DSC curves showed that thermal decomposition
reactions for cis-norbixin occurred in the solid phase. The kinetic parameters,
such as activation energy and pre-exponential factor were determined using
integral and approximate methods: Coats–Redfern, Madhusudanan, Horowitz–Metzger
and Van Krevelen. F1 mechanism describes well the first stage of the thermal
decomposition. 相似文献
56.
Geraldo Lopes Crossetti Carlotta Bormioli Alberto Ripa Antonino Giarrusso Lido Porri 《Macromolecular rapid communications》1997,18(9):801-808
The soluble catalyst system methylaluminoxane (MAO)-Ni(acac), (acac: acetylacetonate) gives polystyrene consisting of an amorphous (aPS) and a crystalline isotactic (ips) fraction. Al(CH3)3, which is always present in commercial samples of MAO, decreases both polymer yield and stereospecificity. The polymer yield increases with increasing the MAO/Ni ratio but, at the same time, the iPS/aPS ratio decreases. Addition of N(C2H5)3 (mole ratio N/Ni = 1) increases the proportion of the isotactic fraction, while it decreases the polymer yield. A tentative interpretation of the stereospecificity is reported. 相似文献
57.
Luiz C. L. Botelho 《International Journal of Theoretical Physics》2009,48(6):1695-1700
We present a Wilson Loop evaluation of the binding energy of electric static charges in A.M. Polyakov’s Compact QED in R
4 through path integrals. 相似文献
58.
Eliane Gonçalves Gomes João Carlos Correia Baptista Soares de Mello Geraldo da Silva e Souza Lidia Angulo Meza João Alfredo de Carvalho Mangabeira 《Annals of Operations Research》2009,169(1):167-181
The aim of this paper is to use DEA models to evaluate sustainability in agriculture. Several variables are taken into account
and the resulting efficiency is measured by comparison. The performance of family farms is analysed here (variables: farmed
area, work force, and production). As agricultural sustainability depends on the maintenance of systems of production for
long periods of time, the models were run for the years of 1986 and 2002. Tiered DEA models were used to group farmers in
sustainability categories. Non-parametric regression models were used to identify the factors affecting the efficiency measurements.
All the results indicate that the majority of the farmers increased their efficiency along the time. These improvements may
support the existence of sustainability. 相似文献
59.
Silva PR Almeida VO Machado GB Benvenutti EV Costa TM Gallas MR 《Langmuir : the ACS journal of surfaces and colloids》2012,28(2):1447-1452
A dispersant for multiwall carbon nanotubes (MWCNTs) is proposed that fulfils the requirements of creating a uniform dispersion in the matrix and obtaining a good interface between CNTs and the matrix, and is soluble in generic nonpolar solvents. This dispersant is based on a long chain surfactant, called in this work dabcosil stearate, containing a stearate-based 18-carbon alkyl chain as an anion, and a silsesquioxane containing a bridged, positively charged 1,4-diazoniabicyclo[2.2.2]octane group. It provides not only a very good dispersion medium for the MWCNTs, but also a very good interface between MWCNTs and ceramic matrices, such as alumina and zirconia, prepared by the sol-gel method. 相似文献
60.
Geraldo Capannesi Alberto Rosada Maurizio Manigrasso Pasquale Avino 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(1):163-168
In geochemistry, the distribution of the Rare Earth Elements (REEs) in earth crust and mantle allows to understand geochemical
cycles and origin and age of igneous rocks. In this article REEs (Ce, Dy, Eu, La, Nd, Sm, Tb, and Yb), Th and U in ores of
the North-Latium (Bracciano area, Ceriti Mt., Fate Mt., Sabatini Mt., Vulsini Mt., Acqua Rossa basin), have been investigated
for evaluating the extraction feasibility for industrial applications. 107 samples were irradiated in the rotating rack of
the TRIGA Mark II reactor of the R.C. Casaccia (ENEA) at neutron flux of 2.6 × 1012
n × cm−2 × s−1 for 12 h together with primary and secondary standards. The gamma spectrometry measurements were performed after 8 h, 3 and
30 days of decay by means of HPGe detector (FWHM 1.75 keV at 1332.5 keV, peak/Compton ratio 55.1, relative efficiency of 22%)
connected to a multi-channel analyzer. The total REE mean content is 105 μg g−1, ranging widely between 2.23 and 410.5 μg g−1 (average coefficient of variation 112%). A similar behavior is found for Th and U: their average levels are 13.5 and 6.0 μg g−1, respectively. A quite good correlation between REEs and Th (and U) is found for Ceriti Mt. (r
2 > 0.8) whereas for the other areas the correlation is <0.7. The results obtained evidence the low U content in the investigated
locations. 相似文献