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  • Author or Editor: L. Muñoz x
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Abstract  

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 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.

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Abstract  

An automatic measurement system for activation analysis has been developed at the La Reina Nuclear Center of the Chilean Nuclear Energy Commission. A gamma-ray spectrometer equipped with an automatic sample changer is linked to an IBM-compatible PC/AT. The peripheral devices are interconnected and suitable software for routine operation have been prepared. The computer handles solenoid valves and microswitch sensors. The gamma-spectra are stored in the hard disk and later transferred to a main frame computer where all the information is processed to obtain final results. The system is in full operation and the operation manuals that have been prepared allow it to be used by people who are not trained in activation analysis.

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Abstract  

Eleven trace elements were determined in the hair of Chuquicamata copper mine workers and of children living in camp by means of neutron activation analysis. Comparative studies demonstrated that concentrations of certain elements were greater than those corresponding to the nonexposed populations. Arsenic exceeded the normal limit considered for this element by health organizations.

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Abstract  

The present study contributes preliminary data concerning the concentrations of eleven trace elements contained in Pacific Oysters (Crassostrea gigas) cultured in two different bays of Northern Chile, where heavy-metal pollution is already recognized as a problem. The trace element contents of this moullusc were studied at monthly intervals for 12 months (September 1987–August 1988). Copper and cadmium content was determined using radiochemical neutron activation analysis. Instrumental neutron activation analysis was used for the analysis of As, Br, Na, Se, Cr, Ag, Fe, Zn and Co. Various Standard Reference Materials were used to determine the accuracy of both methods. Significant differences were found comparing the contents of copper, cadmium and other elements during different seasons and in different locations of capture.

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Abstract  

Levels of essential and toxic trace elements in six marine species greatly in demand in the international market (canned pink clams, razor clams, clams, king crab, sardines, and frozen albacore tuna fish) were studied. A special laboratory adequately equipped for handling and preparing biological materials, is described. The elements As, Br, Na, Se, Hg, Cr, Fe, Zn and Rb were determined by INAA, while copper and cadmium content were determined using RNAA. Significant differences were found on comparing the contents of some toxic elements in mollusk and other samples of marine food. Various certified reference materials (CRMs) of the IAEA, NIST and NIES were analyzed for quality assurance purposes.

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Abstract  

Mercury pollution in the industrial environment of Chile has been studied using hair as a monitor. Data from samples representing people living in the non-polluted and also from the polluted areas show that, hair is an effective and convenient indicator of environmental mercury pollution in Chile. A major source of mercury pollution and its transport is contaminated water. Hair is found to concentrate mercury from water to an extent of 80 to 500 fold increase in hair concentration. This absorption occurs in a contact time of 24 h and thus provides a means of treating mercury containing water to reduce the mercury to acceptable levels. The capacity of hair for this purpose is about 0.2% which means that, with a kilogram of hair /valued at less than 25 cents/ nearly 20.000 litres of contaminated water /at 0.1 ppm mercury/ can be treated. This is an inexpensive and convenient alternative to conventional ion-exchange processes which are generally very expensive, particularly for developing countries.

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Abstract  

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.

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Abstract  

Metal poly(vinyl acetates) polymers were obtained by radical polymerization with azodiisobutyronitrile. The thermal stabilities of the metal polymers (M-PVAC) have been studied by thermogravimetry (TG) between 25 and 550°C under nitrogen flow. The decomposition temperature was obtained from the maximum of the first derivative from TG curve. The kinetic parameters of the thermal decomposition were determined by the Arrhenius equation. All these polymers degrade mainly in a single step with a very small second step, probably via a complex reaction. The kinetic data thus obtained show that the thermostabilities decrease in the order: Sb-PVAc∼Ge-PVAc>Bi-PVAc∼Cd-PCAc>Ag-PVAc∼PVAc>Zn-PVAc> Au-PVAc>In-PVAc>Sn-PVAc>Ga-PVAc>Pd-PVAc. Again, the thermal stability is dependent upon the metal incorporated in the backbone polymer. They loose weight after 320°C. The order of reaction from the thermal decomposition of these metal polymers was found to be −0.5 for the first step and 0 for the second. The pre-exponential factor, the reaction order and the activation energy of the decomposition for metal (PVAc) have been determined in most of them.

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Abstract

Tim-3 has opposing roles in innate and adaptive immunities. It not only dampens CD4+ and CD8+ T cells responses but also enhances the ability of macrophages to eliminate intracellular pathogens. After peroral infection with 100 cysts of Toxoplasma gondii genetically susceptible C57BL/6 mice develop an unchecked Th1 response associated with the development of small intestinal immunopathology. Here we report that upon infection with T. gondii, both susceptible C57BL/6 and resistant BALB/c mice exhibit increased frequencies of Tim-3+ cells in spleens and mesenteric lymph nodes. The number of Tim-3+ cells was significantly higher in C57BL/6 than in BALB/c mice. Tim-3 was expressed by macrophages, dendritic, natural killer, as well as CD4+ and CD8+ T cells. Highest frequencies of Tim-3+ cells were observed at the peak of Th1 responses (day 7 post infection) concurrent with the development of ileal immunopathology. Infected Tim-3-deficient BALB/c mice did not develop ileal immunopathology nor did their parasite loads differ from those in wildtype BALB/c mice. Thus, although Tim-3 is markedly upregulated upon infection and differentially regulated in susceptible and resistant mice upon infection with T. gondii, the absence of Tim-3 is not sufficient to overcome the genetic resistance of BALB/c mice to the development of Th1-driven small intestinal immunopathology.

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