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991.
The presence of pharmaceuticals in the environment is a very important problem that requires analytical solutions. The wide variety of matrices and, usually, the low pharmaceuticals levels in the environmental samples requires high sensitive and selective analytical procedures. Wastewaters are one of the more important sources of environmental pollutants but they are very complex matrices that need clean-up procedures prior the analysis. Hollow fiber-based liquid-phase microextraction (HF-LPME) is a relatively new technique used in analytical chemistry for sample pre-treatment that offers high selectivity and sensitivity compared to most traditional extraction techniques. The low organic solvent consumption derived from the use of HF-LPME is according to the current trends to a “Green Chemistry”, and Analytical Chemistry should follow these environmental good practices. This paper describes an extraction method using a polypropylene membrane supporting dihexyl ether (three-phase hollow fiber-based liquid-phase microextraction (HF-LPME)) for the direct analysis of three pharmaceuticals (salicylic acid (SAC), ibuprofen (IBU) and diclofenac (DIC)) in raw and treated wastewaters followed by a HPLC/MS-MS determination using a highly packed Pursuit® XRs Ultra 2.8 μm C18 column that allows high resolution using low flow-rates and, simultaneously, short retention times. Detection limits were 20, 100 and 300 ng L−1 for salicylic acid, diclofenac and ibuprofen, respectively. 相似文献
992.
Julio C. Ramos Fernández 《Applied mathematics and computation》2010,217(7):3392-3402
In this paper we use Young’s functions to define the Bloch-Orlicz spaces as a generalization of Bloch spaces. We study continuity, boundedness from below and compactness of composition operators on Bloch-Orlicz spaces. 相似文献
993.
Ana Lúcia Cardoso Manuela Ramos Silva Francisco Palacios Alberto A.C.C. Pais 《Tetrahedron》2010,66(39):7720-7725
Stereoselective inverse conjugate addition of carbonucleophiles to allenoates bearing a chiral auxiliary in the ester moiety afforded optically active α,β-unsaturated carboxylic esters bearing a new stereocenter at the δ position. The rationalization of the observed selectivity was supported by semi-empirical molecular orbital calculations. 相似文献
994.
995.
Higinio Ramos J. Vigo-Aguiar S. Natesan R. García-Rubio M. A. Queiruga 《Journal of mathematical chemistry》2010,48(1):38-54
In this article, we study the numerical solution of singularly perturbed non-linear autonomous initial-value problems by a
non-standard algorithm on layer-resolving nonuniform meshes. Here, we use the piecewise-uniform Shishkin meshes, and two other
nonuniform meshes which resolve the difficulties arising from the steep gradient of the solution in the initial layer. The
present method is intended for solving the nonlinear problem without linearization and provides third-order convergence results.
Linear stability of this method is studied. Numerical experiments are carried out to verify the efficiency and accuracy of
the method. 相似文献
996.
P. Lam Ramos D. J. Frías Fonseca M. A. González Garcia D. E. Aguiar Lambert J. R. Estévez Alvarez I. Pupo González D. R. López Sánchez 《Journal of Radioanalytical and Nuclear Chemistry》2001,247(3):583-587
The objective of the present study was the elaboration of a procedure for the determination of Y, La, Ce, Pr and Nd in soils by spectrophotometry with Arsenazo III preceded by a separation-concentration stage, which includes coprecipitation and ion exchange. Multielement analysis by energy dispersive X-ray fluorescence (including Y, La, Ce and Nd) and flame atomic absorption spectrophotometry was carried out simultaneously in order to obtain a general characterization of the soil samples. Certified reference materials and statistical intercomparison of the obtained results were used to evaluate the accuracy of the methods. The precision was examined by analyzing replicate samples. 相似文献
997.
S. Morales-Muñoz J. L. Luque-García M. J. Ramos M. J. Martínez-Bueno M. D. Luque de Castro 《Chromatographia》2005,62(1-2):69-74
An extraction method based on the use of a focused microwave-assisted Soxhlet extractor with subsequent gas chromatography separation and mass spectrometry detection is proposed for the analysis of environmental pollutants from marine sediments collected at the outflow of an urban wastewater treatment plant to the sea. For the extraction of compounds with different polarity, sequential extraction with dichloromethane and water was performed on each sample. The experimental variables were optimized by the experimental design methodology for both the organic and aqueous extractant. The total time required for quantitative extraction of triclosan, bisphenol A, estrone, estradiol, oxyfluorofen and permethrin was 75 min, a short time as compared with the 24 h Soxhlet extraction (diethylstilbestrol, 4-octylphenol, procymidone and 2,7/2,8-dichlorodibenzo-p-dioxin isomer pair).Revised: 10 March and 18 April 2005 相似文献
998.
Given a set of points S={p
1
,. . ., p
n
} in Euclidean d -dimensional space, we address the problem of computing the d -dimensional annulus of smallest width containing the set. We give a complete characterization of the centers of annuli which
are locally minimal in arbitrary dimension and we show that, for d=2 , a locally minimal annulus has two points on the inner circle and two points on the outer circle that interlace anglewise
as seen from the center of the annulus. Using this characterization, we show that, given a circular order of the points, there
is at most one locally minimal annulus consistent with that order and it can be computed in time O(n log n) using a simple algorithm. Furthermore, when points are in convex position, the problem can be solved in optimal Θ(n) time.
Received June 25, 1997, and in revised form March 5, 1998. 相似文献
999.
J. I. Ramos 《Applied Mathematical Modelling》1990,14(12):630-640
The equations describing the steady-state behavior of long annular liquid jets and liquid membranes in zero gravity are solved analytically as a function of the pressure difference across the jet or membrane, Weber number, and nozzle exit angle. The ranges of the parameters for which the analytical solutions are valid are determined, and analytical solutions of the mass absorption rate are obtained as a function of the Peclet and Weber numbers, nozzle exit angle, pressure difference, and thickness of the annular liquid jet. It is shown that the convergence length of annular liquid jets and liquid membranes increases as the Weber number, nozzle exit angle, and pressure coefficient are increased. It is also shown that the mass absoption rate increases as the nozzle exit angle, pressure coefficient, and Weber number are increased; however, the mass absorption rate decreases as the Peclet number and annular jet initial thickness-to-radius ratio are increased. 相似文献
1000.
Nash Equilibria for the Multiobjective Control of Linear Partial Differential Equations 总被引:3,自引:0,他引:3
Ramos A.M. Glowinski R. Periaux J. 《Journal of Optimization Theory and Applications》2002,112(3):457-498
This article is concerned with the numerical solution of multiobjective control problems associated with linear partial differential equations. More precisely, for such problems, we look for the Nash equilibrium, which is the solution to a noncooperative game. First, we study the continuous case. Then, to compute the solution of the problem, we combine finite-difference methods for the time discretization, finite-element methods for the space discretization, and conjugate-gradient algorithms for the iterative solution of the discrete control problems. Finally, we apply the above methodology to the solution of several tests problems. 相似文献