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Abstract  

We obtain inequalities for the weighted approximation error of Baskakov type operators and their derivatives. Such inequalities are valid for functions of polynomial growth and are expressed in terms of weighted moduli of continuity.

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Abstract  

The specific and non-specific interactions of twelve activated carbon cloth samples prepared from commercial cotton fabric, and that present different activation degrees are studied through the determination of immersion enthalpies in CCl4 and H2O, and in aqueous solutions of NaOH and HCl. The immersion enthalpies found for the solvents CCl4 and H2O are in a range of 5.49–45.84 and 1.77–7.76 J g−1, respectively. The enthalpic values for the materials in aqueous solutions of NaOH and HCl, allow characterizing the chemical surface of these materials, which are in a range of 6.63 and 21.49 J g−1, finding through them important relations in company with other characterizing techniques used in the study of these materials.

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Abstract  

The interactions among five samples of activated carbons, obtained from different lignocellulosic materials with different degrees of activation of approximately 20% and aqueous solutions of phenol and 4-nitro phenol are studied by means of the determination of immersion enthalpies. It is established that the obtained activated carbons are of a basic character and show values for the pH at the point of zero charge, pHPZC, that range from 7.4 to 9.7 and, in all cases, higher total basicity contents than the values obtained for total acidity. The immersion heat of the activated carbons in CCl4 and water is determined obtaining values which are higher for CCl4 immersion and vary from 31.4 to 48.6 J g−1. The hydrophobic factor, hf, it is calculated from the relation between of the immersion heat of the activated carbons in CCl4 and the immersion heat in water, the obtained values were 2.98 and 6.75, which are greater than 1 due to the greater values obtained in CCl4 when compared to the values obtained in water. Immersion enthalpies in phenol solution range from 7.6 to 13.9 J g−1 and for the case of 4-nitro phenol such enthalpies range from 12.7 to 20.5 J g−1; all the 5 samples studied showed a higher value for the heat of immersion in aqueous solutions of 4-nitro phenol.

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Thermal studies on metal complexes of 5-nitroso-pyrimidine derivatives

II. Thermal behaviour of Cd(II) complexes of 6-amino-5-nitroso-uracil derivatives

Journal of Thermal Analysis and Calorimetry
Authors:
M. Moreno-Carretero
and
J. Salas-Peregrín

The following cadmium(II) complexes of deprotonated 6-amino-5-nitroso-uracil (AH), deprotonated 6-amino-3-methyl-5-nitroso-uracil (BH) and neutral 6-amino-1-methyl-5--nitroso-uracil (CH) have been prepared and their thermal behaviour studied by TG and DSC techniques: CdA2 · 3 H2O, CdB2 · 2 H2O, CdB2 and CdCl2(CH)2 · 2 H2O.

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Thermal studies on metal complexes of 5-nitroso-pyrimidine derivatives

III. Thermal behaviour of Hg(II) complexes of 6-amino-5-nitrosouracil derivatives

Journal of Thermal Analysis and Calorimetry
Authors:
M. Moreno-Carretero
and
J. Salas-Peregrín

Four Hg(II) complexes, containing as ligands 6-amino-5-nitrosouracil (AH), 6-amino-3-methyl-5-nitrosouracil (BH) or 6-amino-1-methyl-5-nitrosouracil (CH), have been synthesized and their thermal behaviour studied by TG and DSC techniques: Hg3Cl6(AH)4, HgCl2(BH)2· 2 H2O, HgCl2(BH)2 · H2O and HgC2· 2 H2O.

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Abstract  

Activity concentrations of Pu radioisotopes and 241Am were determined in the organic and mineral layers of four soil sections collected in 1996, providing for the first time information on the levels of these radionuclides in soil samples from Romania. The investigated site was an alpine pasture located in the Charpathian Mountains, in an area found as one of the most affected in Romania after the Chernobyl accident. In the examined soil sections radioactive inventories were estimated to be 500 Bq/m2 for 241Pu, 115 Bq/m2 for 239+240Pu, 8 Bq/m2 for 238Pu and 50 Bq/m2 for 241Am. On the basis of activity ratios in the soil profile, the source of the radioactive release is discussed.

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Abstract  

Total acidity for a series of modified clays obtained from a natural vermiculite is determined through temperature programmed desorption (TPD) using ammonia as probe molecule. Results obtained for the acidity range from 15.1 to 68.5 meq/100 g. Immersion enthalpies of the clays in benzene, water and aqueous solutions of NH3 0.058 M and NaHCO3 0.053 M are determined. The results obtained show that immersion enthalpies in benzene and water are between −6.26 and −25.6 J g−1 and −2.10 and 5.55 J g−1, respectively and are smaller than the values obtained for the immersion enthalpies in the solutions. Immersion enthalpy values in NH3 solution are greater than the obtained using NaHCO3. Linear relations between the total acidity of the clays and the immersion enthalpies in the basic solutions are determined. An interaction factor using ammonia is calculated since the relation between the immersion enthalpy in ammonia solution and in water and it may be deduced that the relation with the total acidity is of second order tendency between them.

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Abstract  

A new solution-reaction isoperibol calorimeter was developed to measure enthalpies of solution and reaction. A new system of sample cell was developed to avoid the breaking of glass ampoules, hence making the sample cell reusable. The system is suitable for measuring molar enthalpies of solid-liquid and liquid-liquid interactions at different temperatures. The reproducibility and accuracy of the apparatus were tested by measuring the enthalpy of solution of KCl in water at 298.15 K and the enthalpy of protonation of THAM in HCl (0.1 M) at 298.15 K. The results showed the uncertainty taken as the reproducibility was ±0.3% and the difference with the literature values was within ±0.5%.

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