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In order to reduce infant mortality in the municipality of Rio de Janeiro it is desired to encourage all mothers-to-be to attend the appropriate health care facilities. A 3-level hierarchical prenatal–neonatal health care system is described together with a basic model for optimising accessibility to facilities. A genetic algorithm to solve the basic model is developed and some numerical experience reported. Extensions to the basic model and planned future research are briefly indicated. 相似文献
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Roberto D. Galvão Luis Gonzalo Acosta Espejo Brian Boffey 《Annals of Operations Research》2006,143(1):31-44
A study has been carried out aimed at reducing perinatal mortality in the municipality of Rio de Janeiro through a better
distribution of health care facilities. The algorithmic aspects are detailed elsewhere and here the emphasis is on practical
issues and difficulties encountered.
A 3-level hierarchical model was developed. Both uncapacitated and capacitated versions are briefly described together with
some results based on actual data. The project brought to light many contradictions between OR theory and practice in developing
countries and, unfortunately, the models developed were not implemented by the municipality health authorities. Possible reasons
for this outcome are analysed. 相似文献
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Oxyethylene macrocyclic compounds (crown-ethers) act as ligands of intracrystalline cations of certain layered silicates as montmorillonites. Stable intercalation materials are formed which are used to prepare organic-inorganic membranes by encapsulating these intercalation compounds with a poly-butadiene thin coating. Electrochemical Impedance Spectroscopy (EIS) is used to study the resulting composite membranes in contact with aqueous electrolytes. From the impedance plots, the ionic resistance of the membranes is obtained. The thickness of the polybutadiene coating is an important factor determining the ability of ions to pass across the membrane. Marked differences in the ionic resistance are observed as a function of the nature of the interlayer macrocyclic compound. For non-intercalated montmorillonite membranes, the ionic resistance is strongly reduced, whereas for some crown-ether intercalated materials such as 18-crown-6 and dibenzo 24-crown-8, iono-selective membranes are obtained. Concerning the nature of the electrolyte, cations exhibiting greater hydration energies show higher difficulties to pass through the membrane and, consequently, the ionic resistance increases. 相似文献
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Preconcentration Systems Using Polyurethane Foam/Me-BDBD for Determination of Copper in Food Samples
Valfredo Azevedo Lemos Daniel Rodrigues Vieira Cleber Galvão Novaes Marcelo Eça Rocha Moacy Selis Santos Regina Terumi Yamaki 《Mikrochimica acta》2006,153(3-4):193-201
A new reagent, 6-[2′-(6′-methyl-benzothiazolylazo)]-1,2-dihydroxy-3,5-benzenedisulfonic acid (Me-BDBD), was synthesised and
used in on-line and off-line systems for copper preconcentration by solid-phase extraction. Spectrophotometry and Flame Atomic
Absorption Spectrometry (FAAS) were the detection techniques. Polyurethane foam loaded with Me-BDBD packed in a minicolumn
was used as sorbent in both systems. The spectral characteristics of Me-BDBD were investigated. The optimum pH values for
maximum sorption of the metal are between 7.0 and 8.5. Copper was desorbed with 0.05 and 0.50 mol L−1 hydrochloric acid solutions, for on-line and off-line systems, respectively. The effects of several foreign substances on
the adsorption of copper are reported. The enrichment factors obtained were 7 (on-line) and 26 (off-line) for the systems.
The proposed procedures allowed the determination of copper with detection limits of 3.4 and 1.4 μg L−1 (0.85 and 0.35 μg per gram of sample) for on-line and off-line systems, respectively. The precision of the procedures was
also calculated: 3.2 (on-line) and 1.9% (off-line). The validation of the procedures was carried out by analysis of certified
reference material. The copper contents in corn and rice flour and black tea samples were determined by applying the proposed
procedures. 相似文献
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Balderas-Hernández P Rojas-Hernández A Galván M Ramírez-Silva MT 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(3):569-577
The detailed analysis of the experimental spectrophotometric data obtained from solutions containing the acid-base indicator thymol blue (TB) and mercury(II) (Hg(II)) coupled with data processing by means of the SQUAD program, a chemical model was determined that includes the formation of complexes indicator-metal ion (HgTB and HgOTB), dimer species (H3TB2 and H4TB2) and monomer species (HTB and TB). The values of the overall formation constants (log beta) were calculated for the chemical equilibria involved: TB+Hg<-->HgTB log beta=16.047 +/- 0.043, TB+Hg+H2O<-->HgOHTB+H log beta=7.659 +/- 0.049, 2TB+4H<-->H4TB2 log beta=31.398 +/- 0.083, 2TB+3H<-->H3TB2 log beta=29.953 +/- 0.084 and H+TB<-->HTB-log beta=8.900. To compliment the present research, the values of the absorptivity coefficients are included for all the species involved, within a wide range of wavelengths (250-700 nm). The latter were used subsequently to carry simulations of the absorption spectra at various pH values, thus corroborating that the chemical model proposed is fully capable to describe the experimental information. Voltammetric study performed evidenced the formation of a complex with a 1:1 stoichiometry Hg(II):TB. 相似文献
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