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41.
Liliana Fátima Bezerra de Lira Jose Geraldo Andrade Pacheco Eduardo Homem de Siqueira Cavalcanti Maria Fernanda Pimentel 《Microchemical Journal》2010,96(1):126-34
This paper evaluates analytical methods based on near infrared (NIR) and middle infrared (MIR) spectroscopy and multivariate calibration to monitor the stability of biodiesel. There was a focus on three parameters: oxidative stability index, acid number and water content. Ethylic and methylic biodiesel from different feedstocks were used in experiments of accelerated aging, in order to take into account the wide variety of oilseeds and feedstocks available in Brazil. Partial least squares (PLS) and multiple linear regression (MLR) models were developed. Different pre-processing techniques and spectral variable/regions selection algorithms were evaluated. For MLR models, the successive projection algorithm (SPA) was employed. Interval PLS (iPLS) and selection of variables taking into account the significant regression coefficients were used for PLS models. Results showed that both near and middle infrared regions, and all variable selection methods tested were efficient for predicting these three important quality parameters of B100, the root mean squares error of prediction (RMSEP) values being comparable to the reproducibility of the corresponding standard method for each property investigated. 相似文献
42.
Daniela de Araújo Viana Carolina de Albuquerque Lima Rejane Pereira Neves Cristina Souza Mota Keila Aparecida Moreira José Luiz de Lima-Filho Maria Taciana Holanda Cavalcanti Attilio Converti Ana Lúcia Figueiredo Porto 《Applied biochemistry and biotechnology》2010,162(3):830-842
Cow raw milk from dairy cooperatives was examined for its microbial composition. Among the isolates identified, 17.6% were
yeasts. The most frequent genus was Candida, although members belonging to the genera Brettanomyces, Dekkera, and Geotricum were also identified. Although qualitative and quantitative tests for extracellular proteolytic activity were positive for
all the species isolated, Candida buinensis showed the highest response (23.5 U/mg); therefore, it was selected for subsequent investigation. The results of fermentations
carried out at variable temperature, pH, and soybean flour concentration, according to a 23 full factorial design, demonstrated that this yeast ensured the highest production of extracellular proteases (573 U/mL)
when cultivated at 35 °C, pH 6.5, and using soybean flour concentrations in the range 0.1–0.5% (w/v). The cell-free supernatants showed the highest activity at 25 °C and pH 7.0, and satisfactory stability in the ranges 25–30 °C
and pH 7–9. The first-order rate constants of protease inactivation in the cell-free supernatants were calculated at different
temperatures from semi-log plots of the residual activity versus time and then used in Arrhenius and Eyring plots to estimate
the main thermodynamic parameters of thermoinactivation (E* = 40.0 kJ/mol; ΔH* = 37.3 kJ/mol; ΔS* = −197.5 J/mol K; ΔG* = 101 kJ/mol). 相似文献
43.
We investigate the decay of entanglement of generalized N-particle Greenberger-Horne-Zeilinger (GHZ) states interacting with independent reservoirs. Scaling laws for the decay of entanglement and for its finite-time extinction (sudden death) are derived for different types of reservoirs. The latter is found to increase with N. However, entanglement becomes arbitrarily small, and therefore useless as a resource, much before it completely disappears, around a time which is inversely proportional to the number of particles. We also show that the decay of multiparticle GHZ states can generate bound entangled states. 相似文献
44.
Analysis of ibuprofen enantiomers in rat plasma by liquid chromatography with tandem mass spectrometry 下载免费PDF全文
Juciane Lauren Cavalcanti Cardoso Vera Lucia Lanchote Maria Paula Marques Pereira Natália Valadares de Moraes José Salvador Lepera 《Journal of separation science》2014,37(8):944-949
A sensitive and selective method for the analysis of ibuprofen enantiomers by LC–MS/MS was developed and validated for the purpose of application in pharmacokinetic studies in small experimental animals. Aliquots of 200 μL plasma were submitted to liquid–liquid extraction with hexane/diisopropylether (50:50 v/v) in acid pH. Separation was accomplished in a Chirex® 3005 (250 × 4.6 mm, 5 μm) column at 25°C with a mobile phase that consisted of 0.01 M ammonium acetate in methanol at a flow rate of 1.1 mL/min. The mass spectrometer consisted of an ESI interface operating at negative ionization mode and multiple reaction monitoring. The transitions 205 > 161 and 240 > 197 were monitored for ibuprofen enantiomers and fenoprofen (internal standard), respectively. Method validation included the evaluation of the matrix effect, stability, linearity, lower LOQ, within‐run and between‐run precision, and accuracy. The lower LOQ was 25 ng/mL for each ibuprofen enantiomer, and the calibration curves showed good linearity in the range 0.025–50 μg/mL. The method was successfully applied in the investigation of pharmacokinetic disposition of ibuprofen enantiomers in rats treated orally with 25 mg/kg of the racemate. Enantioselective kinetic disposition was observed with accumulation of (+)‐(S)‐ibuprofen in rats following single oral administration. 相似文献
45.
D.C.J. Rezende F.O. Borges G.H. Cavalcanti M. Raineri M. Gallardo J. Reyna Almandos A.G. Trigueiros 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(12-13):2000-2006
The spectrum of four-times-ionized krypton (Kr V) has been observed in the 230–4900 Å wavelength range, resulting in 91 new classified lines. We were able to identify 21 new energy levels belonging to the 4s24p5d, 4s24p5s, 4s24p6s, 4s24p5p and 4s4p24d configurations. Relativistic Hartree–Fock calculations were used to predict energy levels and transitions. 相似文献
46.
M.M. Cavalcanti V.N. Domingos Cavalcanti P. Martinez 《Nonlinear Analysis: Theory, Methods & Applications》2008
The linear viscoelastic equation is considered. We prove uniform decay rates of the energy by assuming a nonlinear feedback acting on the boundary, without imposing any restrictive growth assumption on the damping term and strongly weakening the usual assumptions on the relaxation function. Our estimate depends both on the behavior of the damping term near zero and on the behavior of the relaxation function at infinity. 相似文献
47.
M. M. Cavalcanti V. N. Domingos Cavalcanti J. Ferreira 《Mathematical Methods in the Applied Sciences》2001,24(14):1043-1053
This paper is concerned with the non‐linear viscoelastic equation We prove global existence of weak solutions. Furthermore, uniform decay rates of the energy are obtained assuming a strong damping Δut acting in the domain and provided the relaxation function decays exponentially. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
48.
Marcelo M. Cavalcanti Valéria N. Domingos Cavalcanti Ryuichi Fukuoka Daniel Toundykov 《Applied Mathematics and Optimization》2014,69(1):83-122
Let $\mathcal{M}\subset\mathbb{R}^{3}$ be an oriented compact surface on which we consider the system: $$\left \{ \begin{array}{l@{\quad}l} u_{tt} - \Delta_{\mathcal{M}} u + a(x)g_{0}(u_{t})=0 & \text{in } \mathcal{M}\times\mathopen{]} 0,\infty[ ,\\ \partial_{\nu_{co}}u +u + b(x)g(u_t)=0 & \text{on } \partial \mathcal {M}\times\mathopen{]}0,+\infty[. \end{array} \right . $$ If $\mathcal{M}$ along with the localizers a, b and the nonlinear feedbacks g,g 0 satisfy certain conditions then uniform (but not necessarily exponential) decay rates of the finite energy of solutions can be established. We present a unified approach that bridges and extends a number of earlier results on stabilization of 2nd-order hyperbolic equations on manifolds. The methodology captures geometric requirements for damping acting simultaneously on subsets of the interior and of the boundary, and shows how placements of these feedbacks can complement each other depending on the underlying surface. In addition, the results conveniently incorporate the existing theory that allows elimination of geometric conditions from the controlled boundary (in absence of nearby interior damping), and elimination of damping entirely from certain boundary neighborhoods. The model also admits feedbacks that grow sub- or super-linearly not only at the origin, but also at infinity and demonstrates an interplay between the regularity of solutions and asymptotic energy decay rates. 相似文献
49.
Bruno Fonsêca Feitosa Charlene Maria de Alcntara Amanda Beatriz Sales de Lima Adriano SantAna Silva Alfredina dos Santos Araújo Mnica Tejo Cavalcanti Edna Mori Isaac Moura Araújo Pablo Antonio Maia de Farias Polrat Wilairatana Henrique Douglas Melo Coutinho 《Molecules (Basel, Switzerland)》2022,27(18)
The inappropriate use of synthetic antibiotics has become a global public health problem. Therefore, the study of new alternatives for the treatment of infectious diseases is relevant and natural bioactive products are on the rise. This study conducted a scientific prospection of bioactive natural products with promising applications in the chemical control of microorganisms. A systematic review of the most recent articles was performed according to the following three steps: (i) eligibility assessment, (ii) screening, and (iii) inclusion of articles and information extraction. There has been an increase in the number of scientific publications on bioactive natural products for microbial control in the CAPES and SciELO databases (2001–2021). Seventeen relevant articles were included, most of which focused on extracts. Ascorbic acid, chlorogenic acid, chrysin, and quercetin were the most cited compounds. Natural products were shown to be effective in inhibiting more than 30 microorganisms. A discussion was presented on the research trends. 相似文献
50.
Y. M. Gomes A. B. Carvalho M. L. Santos V. M. S. Cavalcanti L. Monjour 《Applied biochemistry and biotechnology》1992,33(3):183-192
Separation of the blood forms of trypanosomes from the blood of infected animals is difficult, especially in the case of Trypanosoma cruzi Y strain. Two procedures to isolate the Y strain blood forms of T. cruzi using polyvinyl pyrrolidone-coated silica (percoll) and histopaque are reported in this study. The recovery rates of parasites were 16 +/- 5 and 68 +/- 16%, respectively. The parasites isolated by these methods presented normal motility and morphology and were infective to albino mice with prepatent periods, parasitemia curves, and polymorphism patterns during the infection that were similar to those of control parasites. In addition, the preservation of surface antigens was confirmed by immunocytochemical studies. 相似文献