Search Results

You are looking at 1 - 10 of 19 items for

  • Author or Editor: G. Rodríguez x
  • Refine by Access: All Content x
Clear All Modify Search

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.

Restricted access

In many occasions descriptive analysis consists of product-specific training where the samples to be measured are used during the training. Towards the end of the training period it is common practice to present these samples and reach a consensus on their profiles, which we have called Training Consensus Profiles (TCP). Following the TCP, the samples are scored by each assessor and the results are statistically analysed to obtain statistical profiles. The objective of the present work was to compare the TCP with the statistical profiles in samples from three different food categories: fernet (an herb-based alcoholic drink), mayonnaise, and spaghetti. General Procrustes analysis showed that the TCP and statistical profiles were similar. A case is made, that if this type of training and measurement are to be followed, the statistical measuring stage could be left aside, directly reporting the results obtained from the TCP. Advantages and limitations on reporting these TCP profiles are discussed.

Restricted access

The study of co-occurrence patterns has been extensively applied to propose assembly rules for community organization. Recently, a new interest has grown in the effect of gradients on these patterns and to analyze them through new approximations such as co-occurrence networks, through which keystone species can be identified. Neotropical floodplains represent interesting systems to study such patterns, because of their spatial heterogeneity, temporal variability and their high fish species richness. With this in mind, our goal was to study the co-occurrence patterns of fish in a segment of the Arauca River’s floodplain and the influence of the spatial and temporal variability on them. One stream and one floodplain lake were sampled with gill nets during 2014 – 2015 across a hydrological cycle and 5 matrices for each 5 sampled months in each water body were prepared to explore the co-occurrence patterns in each water body across months and 2 for the entire period, through a probabilistic pair-wise analysis of species co-occurrence that identified aggregated and segregated species pairs. With the observed cooccurrences × water body × month, the species weighted degrees and betweenness were calculated, and co-occurrence networks were constructed. The networks structures, in terms of the degrees of every species, were compared spatially and temporally through a generalized linear model. The stream showed the highest numbers of aggregated species pairs, and in general showed the most complex networks in terms of nodes, edges and degrees. The habitat type and the hydrological phases significantly influenced the structure of the fish co-occurrence networks. Two species, Loricariichthys brunneus and Pygocentrus cariba were identified as the core of the fish communities of the floodplain and as keystone species because they contribute to the connection of the networks by having a series of links with less frequent species.

Restricted access

Abstract  

Instrumental neutron activation analysis (INAA) is a well-known analytical method for nondestructive, sensitive and accurate determination of elemental composition of geological samples. In the present work twenty-two elements were determined by INAA in nine rhyolitic geological samples from a wolframium ore body Lela, located in the territory of Isla de la Juventud, Cuba. The obtained results are important for the preliminary geochemical evaluation of the studied rocks.

Restricted access

Abstract  

Instrumental neutron activation analysis (INAA) and gamma spectrometric analysis (GSA) were used for the determination of twenty-one elements in pegmatites of Loma Venturilla area, in Central Cuba. The application of both methods allowed the determination of K, Co, Cr, Sc, Rb, Cs, Ba, Ta, Hf, Th, U, La, Ce, Nd, Sm, Eu, Tb, Ho, Tm, Yb and Lu. The results were obtained with good precision and accuracy. The knowledge of such concentrations is particularly useful for geochemical investigations. The obtained concentration values can be used in studies on the petrogenesis of those rocks. The results facilitate the evaluation and estimation of the main process involved in the generation and differentiation of the melts from which the pegmatites were formed.

Restricted access

Abstract  

The state of trace concentrations of95Zr–95Nb and134Cs was studied at an initial pH>13 in an uranyl triperoxidate medium using the electromigration method. OH ions governing the potential are adsorbed on the colloidal Nb(V)-hydroxide which leads to an increase in its negative electric charge; while95Zr did not move during the procedure. However, the electrophoretic mobility of the134Cs could be explained in terms of their agglomerations attributed to the interaction of Cs+ ions with water molecules to give larger aggregations.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors:
L. Desdín García
,
G. Capote Rodríguez
,
A. Leyva Fabelo
, and
L. Calderín Hidalgo

Abstract  

This paper shows the influence of hardness on the beta backscattering coefficient from heat treated and plastic deformed carbon steel specimens. The observed effect cannot be explained as a change in the chemical composition of the sample (or effective atomic number). In order to explain the observed dependencies, it is necessary to take into account the structural defect and morphological changes of the different phases.

Restricted access

Abstract  

Se in Ni and Co concentration in concentrates obtained from the nickel industry has to be determined for quality control requirements in their commercialization. Analysis of Se at minor and trace levels is relatively complicated and destructive procedures are frequently required. In this work the determination of Se by epithemal neutron activation analysis (ENAA) in 17 samples from Cuban nickel industry was investigated. Application of ENAA allowed nondestructive determination of Se concentration down to ppm level in spite of the presence of high Co, Fe, Ni and Cr contents in the samples. For attenuation of the thermal neutron flux a Cd filter was utilized.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors:
G. Rodríguez
,
A. Rivero
,
J. Bermúdez
,
S. Guevara
,
J. Insfrán
, and
G. Zayas

Abstract  

In this work the determination of elemental composition of MIBI, MAG-3 and sodium phytate by INAA was investigated. Analytical information about the concentration and/or detection limits of some toxic elements (Hg, Cd, As, Se, Sb) and other trace element of interest (Fe, Cr, Co, Zn, Br) was obtained.

Restricted access

Abstract  

The electrophoretic mobility of some radionuclides has been measured to understand its attractive or repulsive tendencies towards other charged species in the medium. In this study, the chemical state of trace concentrations of88Y,103Ru,134Cs, and141Ce in the presence of UO 2 2+ , as a dominant component, in strongly alkaline aqueous solutions (pH>13) was characterized.88Y and141Ce settled almost completely as colloidal species; whereas103Ru,134Cs, and uranium remained as ions. These results closely correlate a procedure for defining both the composition of the water in contact with the fuel and the practical applicability of modified sorbents.

Restricted access