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1.
L.G. Casado I. García T. Csendes V.G. Ruíz 《Journal of Optimization Theory and Applications》2003,118(1):27-43
Based on the investigation carried out in Ref. 1, this paper incorporates new studies about the properties of inclusion functions on subintervals while a branch-and-bound algorithm is solving global optimization problems. It is found that the relative place of the global minimum value within the inclusion function value of the objective function at the current interval indicates mostly whether the given interval is close to a minimizer point. This information is used in a heuristic interval rejection rule that can save a considerable amount of computation. Illustrative examples are discussed and an extended numerical study shows the advantages of the new approach. 相似文献
2.
Carmen Izquierdo María Luisa Moyá Jose Luis Usero Julio Casado 《Monatshefte für Chemie / Chemical Monthly》1992,123(5):383-389
Summary A simple working method for the estimation of the aggregation numbers and core radii from weight measurements of sodium bis-2-ethylhexylsulphosuccinate (aerosol-OT orAOT)/decane/water microemulsions of several compositions is proposed.Starting out from the hypotheses that (i) the density of the water inside the droplets is the same as that of free water, (ii) all the surfactant is localized as interface, and (iii) the penetration of the organic phase into the interface is negligible, values for the aggregation number and core radii comparable to those determined using more sophisticated methods were obtained.The results/methodological simplicity ratio may be of great advantage in kinetic work on reaction mechanisms in microemulsions.
Abschätzung von Aggregationszahl und Radius von Mikroemulsionen
Zusammenfassung Es wird eine einfache Methode zur Abschätzung von Aggregationszahl und Core-Radius von Mikroemulsionen aus Gewichtsmessungen von Natriumbis-2-ethylhexylsulphosuccinat (aerosol-OT oderAOT)/Decan/Wasser-Mikroemulsionen verschiedener Zusammensetzung vorgeschlagen. Unter den Annahmen, daß (i) die Dichte von Wasser innerhalb der Aggregationen die gleiche als bei freiem Wasser ist, (ii) das ganze Emulsionsmittel in der Grenzfläche vorliegt und (iii) das Eindringen der organischen Phase in die Grenzfläche vernachlässigbar ist, können Werte für Aggregationszahlen und Core-Radien erhalten werden, die durchaus mit entsprechenden Werten aus aufwendigeren Methoden vergleichbar sind. Das Leistungsverhältnis (Ergebnisse/geringer Aufwand) ist sehr vorteilhaft und macht die Methode für kinetische Arbeiten zur Bestimmung von Reaktionsmechanismen in Mikroemulsionen interessant.相似文献
3.
A qualitative method for the screening of organophosphorus pesticides (OPs) that could present in different types of vegetables has been established and validated. A typical multi-residue extraction procedure of OPs using ethyl acetate and sodium sulphate has been applied. No clean-up was required after extraction, and concentrated extracts were analysed by gas chromatography with pulsed-flame photometric detection (GC-PFPD). Confirmation of compound identities was performed by gas chromatography with mass spectrometric detection (GC-MSD) in the electron impact (EI) mode with full scan acquisition. Retention time locking (RTL) software was used in order to improve the method capability of identification and confirmation. Spiked samples at pesticide concentrations equal to the maximum residue level (MRL) were used to check chromatographic performance and for validation studies. The proposed method allows a rapid and accurate identification of the studied OPs until the ng ml(-1) range for those whose use is forbidden, and above their MRL concentration for the rest. 相似文献
4.
María Pedrero Belén Casado F. Javier Manuel Villena Jose M. Pingarrón 《Fresenius' Journal of Analytical Chemistry》1994,349(7):546-551
An adsorptive stripping voltammetric method for the determination of the pesticide dinoseb (2-sec.-butyl-4,6-dinitrophenol) at the mercury film electrode is described. The deposition of the mercury film on a glassy carbon disk electrode was optimized. The temperature, at which the mercury film was deposited, was demonstrated to have a strong influence on the stripping peaks, the first one being much more intense than the second. A systematic study of the variables affecting the stripping response was carried out by differential pulse voltammetry. The results obtained have been compared with those at the HMDE; a significant improvement in the sensitivity of the method developed with the MFE was observed. Using a 300 s accumulation time, the limits of determination and detection were 3.6 × 10–10 and 1.1 × 10–10 mol L–1, respectively. The effect of the presence of several herbicides on the dinoseb response was also tested. The method has been applied to the determination of the pesticide in spiked apple juice at two concentration levels: 12.0 and 1.2 g L–1 of juice. 相似文献
5.
Summary We studied the mineral speciation of Cu, Zn and Hg in fly ash from a large thermal plant burning lignite. By applying various treatments carried out under different conditions and taking into account the solubility and physical properties (boiling and melting point, etc.) and the behaviour towards combustion of the different possible compounds, we concluded that the ash assayed contained 109.6, 114.4 and 14.30 g/g of zinc silicate, zinc oxide and/or zinc sulphide and metal zinc, respectively, as well as 24.5 g/g of copper silicate and 31.2 g/g of a mixture of copper oxide, sulphide and metal. The formation of these compounds in the combustion of lignite is discussed. 相似文献
6.
The reactivity of the fluorescent reagent calcein with the trivalent cations of the rare earths has been spectrofluorimetrically studied in aqueous solution. Optimum excitation and emission wavelengths were 492-497 and 519-522 nm, respectively. Optimum pH was in the range 6.0-9.2. The stoichiometry of the complexes was 1:1. A direct, rapid and sensitive method for the determination of rare earth mixtures has been proposed with a detection limit of 4.49x10(-8) M and a coefficient of variation of 0.82%. 相似文献
7.
Mauricio Alcolea Palafox Nerea Iza Manuel Gil Jos Luís Núez 《International journal of quantum chemistry》2002,89(1):25-47
A quantum chemical study of several complex monocyclic 4‐benzoyl‐4‐phenyl‐β‐lactam derivatives was carried out using cyclobutane, azetidine, 2‐azetidinone, 1‐methyl‐2‐azetidinone, and 3‐methyl‐2‐azetidinone as model compounds. The optimum geometry was obtained for the different conformations. The planarity of the ring was discussed in terms of the influence of the substituents on the amide resonance. To better analyze the amide resonance and the activity of the β‐lactam ring, a vibrational study was also carried out. To examine the influence of solvent polarity on the carbonyl bands, the Fourier transform–infrared (FT‐IR) spectra of the β‐lactam monocyclic derivatives were recorded in CCl4, C6H6, and CHCl3 solutions. The normal vibrations of the β‐lactam ring in the model compounds were characterized and used in the analysis of the β‐ring of more complex derivatives. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
8.
The reaction of [Rh4(mu-PyS2)2(cod)4] (PyS2 = 2,6-pyridinedithiolate, cod = 1,5-cyclooctadiene) with CF3SO3Me gave the cationic complex [Rh(4)(mu-PyS(2)Me)(2)(cod)4][CF3SO3]2 (1) with two 6-(thiomethyl)pyridine-2-thiolate bridging ligands from the attack of Me+ at the terminal sulfur atoms of the starting material. Under identical conditions [Rh4(mu-PyS2)2(tfbb)4] (tfbb = tetrafluorobenzobarrelene) reacted with CF3SO3Me to give the mixed-ligand complex [Rh(4)(mu-PyS2)(mu-PyS2Me)(tfbb)4][CF3SO3] 2. The nucleophilicity of the bridging ligands in the complexes [Rh4(mu-PyS2)2(diolefin)4] was exploited to prepare heteropolynuclear species. Reactions with [Au(PPh3)(Me2CO)][ClO4] gave the hexanuclear complexes [(PPh3)2Au2Rh4(mu-PyS2)2(diolefin)4][ClO4]2 (diolefin = cod (3), tfbb (4)). The structure of 4, solved by X-ray diffraction methods, showed the coordination of the [Au(PPh3)]+ fragments to the peripheral sulfur atoms in [Rh4(mu-PyS2)2(diolefin)4] along with their interaction with the neighbor rhodium atoms. Neutral coordination polymers of formula [ClMRh4(mu-PyS2)2(diolefin)4]n (M = Cu (5, 6), Au (7)) result from the self-assembly of alternating [Rh4(mu-PyS2)2(diolefin)4] ([Rh4]) blocks and MCl linkers. The formation of the infinite polymetallic chains was found to be chiroselective for M = Cu; one particular chain contains exclusively homochiral [Rh4] complexes. Cationic heterometallic coordination polymers of formula [MRh4(mu-PyS2)2(diolefin)4]n[BF4]n (M = Ag (8, 9), Cu (10, 11)) and [Rh5(mu-PyS2)2(diolefin)5]n[BF4]n (12, 13) result from the reactions of [Rh4] with [Cu(CH2CN)4]BF4, AgBF4, and [Rh(diolefin)(Me2CO)2]BF4, respectively. The heterometallic coordination polymers exhibit a weak electric conductivity in the solid state in the range (1.2-2.8) x 10(-7) S cm(-1). 相似文献
9.
A method is proposed for the treatment of data from a kinetic system of first order consecutive reactions by using an optimization procedure which converges to the correct solution of the two mathematically possible solutions and which does not need initial estimates of the parameters close to those to be determined.
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10.
Samuel González-Mancebo Javier Lacadena Yolanda García-Alonso Jesús Hernández-Benito Emilio Calle Julio Casado 《Monatshefte für Chemie / Chemical Monthly》2002,133(2):157-166
Summary. Nitrosation reactions of phenol, o-cresol, 2,6-dimethylphenol, o-tert-butylphenol, 2-hydroxyacetophenone, and 2-allylphenol in water and water/acetonitrile were studied. Kinetic monitoring of
the reactions was accomplished by spectrophotometric analysis of the nitrosated products at 345 nm. The dominant reaction
was C-nitrosation via a mechanism consisting of an attack on the nitrosatable substrate by NO+/NO2H2
+ followed by a slow proton transfer. The values of the rate constants of phenolic C-nitrosation were increased by electron
donating substituents, and a good Hammett correlation was observed with ρ = −6.1. The results also revealed the strong effect of pH and the permitivity of the reaction medium on the rate constant, whose maximum values were observed for pH ≈ 3, decreasing strongly for higher pH values. The study in water/acetonitrile with up to 25% acetonitrile showed that it is possible to inhibit the reaction strongly
by increasing the percentage of the organic component. The conclusions drawn show that (i) it is possible to predict the rate of nitrosation of phenolics as a function of the meta-substituents on the phenol ring and (ii) the nitrosation of phenolics can be strongly inhibited by increasing the pH of the reaction medium as well as by lowering its dielectric constant.
Received July 13, 2001. Accepted (revised) September 18, 2001 相似文献