[en] Microbially influenced corrosion or bio corrosion is a problem that generates heavy global economic losses (several billion euros per year). In spite of the progress made on the understanding of the underlying mechanisms, the complexity of the phenomenon has prevented finding definitive solutions to the problem and continues to inspire many research works. The participation in bio corrosion of catalytic mechanisms induced by weak acids was studied in this work. Another objective of the thesis has been to take advantage from catalytic phenomena found in bio corrosion research to apply them in other areas: energy production with biofuel cells or electrochemical hydrogen production in mild conditions. This work has shown that the presence of weak acids and amino acids inside bio-films could play a major role in steel bio corrosion accelerating the phenomenon through the catalysis of the water reduction reaction. The reversibility of this mechanism, discerned and proved here, could explain the corrosion increase when hydrogen is removed (bacterial consumption, agitation...). In addition, phosphates allow the production of hydrogen by electrolysis in mild pH conditions (pH 4.0 - 8.0) with an equal or better performance than those found in alkaline electrolysis. Finally, industrial materials like stainless steel and titanium could be used in the fabrication of enzymatic electrodes for biosensors or microsystems. The use of the glucose oxidase/glucose system in an aqueous fuel cell with a stainless steel cathode, allows the improvement of the cell performance thanks to the production of hydrogen peroxide that is easily reduced. Moreover, the use of materials with micro-structured surfaces like sandblasted steels deserve to be studied in detail to exploit the remarkable reactivity they present compared to smooth electrodes. (author)

[en] This paper analyzes the methods and difficulties for the integration of environmental externalisation into electricity systems decision-making processes. As a case study, it assesses the consequences of the internalization of externalisation into the Spanish power system. To that end, a model has been developed which is capable of incorporating these externalities, and which therefore allows for the determination of a socially efficient electricity system operation. The results show that, if externalities are internalised, the electricity system operation may be altered significantly, even when only part of the externalities are taken into account. (Author)

[en] A member of the β-quartz series (Li_0.73Al_0.73Si_1.27O₄) was synthesised using the ceramic method from precursor powders - Li₂CO₃,Al(NO₃)₃.9H₂O, Si(C₂H₅O)₄ - with identical composition. Crystallisation of the gel was obtained by heating the raw material at 800 deg. C for 12 h. The XRD pattern of the synthetic sample indicates a β-quartz structure with hexagonal symmetry. Thermoluminescence (TL) signals of annealed samples at 1200 deg. C for 12 h, and non-annealed samples, were measured in the UV blue region of the spectrum. The non-annealed irradiated β-quartz displays two TL peaks at 110 deg. C and 280 deg. C which, after different additional radiation doses (from 0.4 to 5 Gy), display high linearity. The other annealed irradiated aliquots show a similar behaviour and stronger linearity. Thermal treatments at high temperature (1200 deg. C) produce ionic self-diffusion and loss of lithium atoms through the open hexagonal channel of the β-quartz structure. These [AlO₄/Li⁺]⁰ defects are responsible for the high radiation sensitivity of the sample. (author)

[en] Necrosis of brain is an uncommon complication of radiation therapy and may mimic recurrent tumor. The authors of this paper compare gadolinium enhanced MR imaging and contrast-enhanced CT in children with radiation necrosis to determine which modality was more sensitive and if there were any features that would aid in differentiating radiation necrosis from recurrent tumor. The authors studied five children (aged 9-15 y) with radiation necrosis proved by autopsy, biopsy, or long-term follow-up. Three patients had received external beam radiation (dose 3,000-5,440 rad) for glioblastoma, medulloblastoma, and CNS leukemia. Two patients had I-125 seeds (estimated dose, 15,000 rad) implanated for local control of recurrent medulloblastoma. Gadolinium-enhanced MR imaging was followed by contrast-enhanced CT within 24 h

[en] Thermoluminescence (TL) emission spectra have been obtained from a well-characterised cross-hatch low microcline using a high sensitivity spectrometer. Tests of thermal stability at different temperatures show a continuous trap distribution with progressive changes in the glow curve shape, intensity and temperature position of the maximum peak. The results suggest that the characteristic 340 nm emission band of microcline is associated with the presence of cross-hatch twinning. The present contribution speculates that both the 340 nm and 380 nm spectra bands could be linked by thermal alkali self-diffusion through the twinning interfaces. (author)

[en] Chile has approximately 4,500 kilometers of continental coastline on the Pacific Ocean. It is therefore in a favorable position to develop fishing activities, since its waters contain a great variety of marine resources, namely, fish, shellfish and seaweeds. Fishing in Chile plays an important role in production. Metal contamination of the marine ecosystem is a pervasive and worldwide problem. Consequently, seafood consuming and exporting countries have gradually increased the need to improve the quality of their products in order to meet the required standards. In turn, this implies the need to adopt more efficient methods to analyze these resources by carrying out studies that will provide greater integral knowledge on the levels of essential and toxic trace elements found in seafood. In the present study, seasonal and geographical variability of some trace elements content of Pacific Oysters (Crassostrea Gigas) cultured, greatly demanded on the international market, are investigated. Samples for the analysis were collected from two different bays of Northern Chile, where heavy-metal pollution is already recognized as a problem. The trace elements content of this mollusk was studied at monthly intervals for 12 months (September 1987-August 1988). The determination of Cu was carried out using radiochemical neutron activation analysis and the other trace elements like Cd, As, Br, Na, Se, Cr, Fe, Zn and Co, were determined through neutron activation analysis in its purely instrumental form. NBS Standard Reference Materials were used to determine the accuracy of both methods. Significant differences were found comparing the content of copper and cadmium at the different seasons and locations of capture

[en] A purely instrumental neutron activation analysis method, using high resolution gamma-ray spectrometry with intrinsic Ge and Ge(Li) detectors, has been used for the analysis of trace elements in copper concentrate samples. Seven rare earth elements and eight other trace elements (Co, Zn, Se, Sb, La, Ce, Nd, Sm, Eu, Tb, Yb, Hf, Re, Th, U) were determined with good precision. Standard rocks were also analyzed to check the analytical procedure, and the results obtained are in good agreement with literature values. (author)

[en] The paper describes an analytical instrumental method for determining trace amounts of gold, based on the transformation of stable ¹⁹⁷Au into radioactive ¹⁹⁸Au through nuclear reactions and subsequent measurement of the radioactivity using automatic gamma spectrometry systems. Irradiation and counting times were optimized in order to use the available resources as efficiently as possible. As ¹⁹⁷Au has a large capture cross-section for thermal neutrons - an important attribute for such nuclear transformations - the method is extremely sensitive. Special care was taken in preparing the samples and determining the quantities to be analysed, as gold, in view of its chemical characteristics, is distributed non-uniformly throughout the mineral. Studies were carried out to resolve this problem. The quantitative detection limit obtained is 0.05 μg/g and the analysis accuracy is ±3%. (author). 3 refs, 2 tabs

[en] The main purpose of an analytical laboratory is to provide reliable information on the nature and composition of the materials submitted for analysis. This purpose can only be attained if analytical methodologies that have the attributes of accuracy, precision, specificity and sensitivity, among others, are used. The process by which these attributes are evaluated is called validation of the analytical method. The Chilean Nuclear Energy Commission's Neutron Activation Analysis Laboratory is applying a quality guarantee program to ensure the quality of its analytical results, which aims, as well, to attain accreditation for some of its measurements. Validation of the analytical methodologies used is an essential part of applying this program. There are many forms of validation, from comparison with reference techniques to participation in inter-comparison rounds. Certified reference materials were used in this work in order to validate the application of neutron activation analysis in determining As, Co, Na, Hg, Se and Fe in shellfish samples. The use of reference materials was chosen because it is a simple option that easily detects sources of systematic errors. Neutron activation analysis is an instrumental analytical method that does not need chemical treatment and that is based on processes which take place in the nuclei of atoms, making the matrix effects unimportant and different biological reference materials can be used. The following certified reference materials were used for validating the method used: BCR human hair 397, NRCC dogfish muscle DORM-2, NRCC -dogfish liver DOLT-2, NIST - oyster tissue 1566, NIES - mussel 6 and BCR - tuna fish 464. The reference materials were analyzed using the procedure developed for the shellfish samples and the above-mentioned elements were determined. With the results obtained, the parameters of accuracy, precision, detection limit, quantification limit and uncertainty associated with the method were determined for each element. The procedure was adopted as routine for validating analytical methodologies in the neutron activation analysis laboratory's quality guarantee program. (author)

[en] Seven trace elements were determined in milk formulas, powder milk and infant food. Instrumental neutron activation analysis was used for the analysis of Fe, Zn, Co, Cr and Rb, while As and Cu content was determined using radiochemical neutron activation analysis. Differences were found in the trace element content of foods of the same type. Milk formulas are comparable with human milk according to the results obtained for the elements analyzed. The samples of powder cow's milk presented similar concentrations of the elements studied. Liver with vegetables was found to have the highest Cu content. A meal prepared at home, made of beef and fresh vegetables showed a higher trace element content than its similar commercial one. An estimation of the daily intake of the elements analyzed was made and compared with minimum recommended daily ingestion. (author)