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Abstract  

The neutron reflection method was applied for the determination of the bound water content and its spread in lateritic mineral. The aim of the work was to study the influence of bound water on the accuracy of the moisture measurement. The distribution of bound water in the mineral can be described by a normal Gaussian curve.

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Journal of Thermal Analysis and Calorimetry
Authors:
J. Sacristán
,
R. Benavente
,
J. Pereña
,
E. Pérez
,
A. Bello
,
R. Rojas
,
R. Quijada
, and
F. Rabagliati

Abstract  

A series of high density polyethylenes (HDPE) were synthesized via homogeneous polymerization with metallocene catalyst in two different reactors (glass and stainless steel). The thermal and mechanical properties of the polyethylenes, synthesized with two types of reactor and different reaction parameters, are discussed.

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Abstract

Films of poly(vinylidene fluoride), PVDF, and poly(vinylidene fluoride – trifluoroethylene), P(VDF-TrFE), containing corn starch and latex of natural rubber as additives were produced by compressing/annealing forming blends visioning applications as biomaterials. Therefore, considering the possible applications of these blends, a basic characterization has been carried out targeting to infer on their thermomechanical properties. The polymer films (PVDF and P(VDF-TrFE)) with different percentage of additives were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC), and dynamical-mechanical analysis (DMA). The compressing/annealing process allowed discarding the necessity of using the solvents to dissolve either PVDF or P(VDF-TrFE), which are usually toxic to human. The results showed that the polymers do not interact chemically with the additives with the blends showing high thermal stability and elasticity modulus at the same order of magnitude of the bone, for instance. The SEM imaged revealed that the blends present morphological structures of typical physical mixtures where each material can be identified within the blends.

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Journal of Thermal Analysis and Calorimetry
Authors:
J. Pérez
,
R. Roque-Malherbe
,
C. González
, and
C. de las Pozas

Abstract  

The paper presents an application of thermodielectrical analysis in a geological material of industrial interest (bentonites). Thermodielectrical curves show noticeable differences in dependence of the cationic content and chemical nature of the cations, and also, with the cation position in the lattice.

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Abstract

In this paper, we want to support the idea of using a family of indices of similarity, that we call the Simpson's family indices or nestedness-based similarity functions (NBSF) for comparing operational geographic units (OGUs) (phytosociological relevés, animal traps, watersheds, administrative units, industrial areas, islands etc.). In these cases, similarity-dissimilarity depends, in addition to factors that induce replacement, also on factors that produce reduction or increment in the number of features within the same typology of OGUs (e.g., extent, reduction of fertility, anthropogenic pressure etc.). To keep into consideration this aspect, the indices are defined to be equal to 1 when the OGUs are completely nested. The results of the application to four simulated data sets prove that, when the data set does not show clear nested pattern, the use of NBSF produces results similar to the nestedness-free similarity functions, however since NBSF clearly detect nested situations, we should prefer their use in the circumstances where we think important to put in evidence nestedness. In conclusion, we support the idea of using both types of indices in order to improve the knowledge about the structure of any data set.

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Abstract  

The present work shows a methodology for the application of EDXRF with a X-ray tube, in the analysis of elements in the following matrices: microalgae, marine algae, marine sediments and corals. Various methods were applied: one using a relative external standard, a fundamental parameters method, an absolute method based on elemental sensitivity, a method which used X-ray fluorescence excitation measured in the back side of the sample for low contents heavy elements determination and a TRXRF method. The thin layer samples were prepared using a plastic resin. The analyzed samples of marine algae, marine sediments and corals belong to a marine ecosystem from the North of Havana City, the most affected area by natural metereological phenomena and human impact.

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Reaction Kinetics, Mechanisms and Catalysis
Authors:
M. R. Granados-Uribe
,
F. J. Lona-Ramírez
,
C. Pérez-Pérez
,
J. Barajas-Fernández
,
V. Rico Ramírez
, and
G. González-Alatorre

Abstract

The nitrosation of 1,3-dialkylureas was carried out in the presence of carboxylic acids and halides in an aqueous perchloric medium. The aim of this work was to validate the proposed mechanism for the nitrosation of such substrates. In accordance with the rate limiting step of the proposed mechanism, the protonic transfer to the solvent, basic catalysis and an absence of catalysis by halides should be observed. The Br⊘nsted parameters were determined by basic general catalysis.

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Abstract  

The infusion rate of a slug of tracer into an anchor agitated 100-liter batch mixer was characterized by a decay rate constant. This constant was then used to define a dimensionless mixing-rate number which was related to the stirrer Reynolds number. This correlationship allows the calculation of time or rotational speed needed to achieve any desired degree of uniformity of the mixture.99mTc was used as radiotracer and the mixing process was followed by a scintillation Nal(Tl) counter situated on the reactor wall near the injection point.

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Abstract  

The measurements of radioactivity in drinking water enable us to determine the exposure of the population to radiation through their usual consumption of water. An intensive study of the water supply in the city of Malaga has been carried out to determine both the gross alpha-and gross beta-activity concentrations. Gamma spectrometry was used in order to detect certain types of radionuclides. Results indicated that 95% of the water tested contained a gross alpha-radioactivity of less than 0.1 Bq/1, and 100% gross beta-activity of less than 1 Bq/1 — the activity limit recommended by the Spanish Regulatory Organization. Several factors were found to have an influence on radioactivity levels, such as total hardness, potassium and pH.

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