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[en] An EIC 1 extrapolation chamber, flushed with a methan based tissue equivalent gas is presented. This measuring device serves as a reference instrument to calibrate in tissue absorbed dose beta beams from different irradiation facilities; point radioactive sources, sources used with beam flattening filters, large area sources simulated by moving a point source. The source to detector distance has to be greater than 3 cm, requiring a transfer dosemeter for smaller distances. Influence of these different irradiation geometries has been studied on several radioprotection instruments (babyline, individual dosemeter, ionisation chamber), using three radionucleides: 147Pm, 204Tl, 90Sr + 90Y
[fr]Une chambre a cavite variable type FWT.EIC.1 a circulation de gaz equivalent-tissu, a ete utilisee comme detecteur de reference pour caracteriser en dose dans les tissus divers faisceaux de rayonnement beta de configurations geometriques variees: source ponctuelle, faisceaux diffus, source etendue de diametre variable obtenue au moyen d'un dispositif de simulation par deplacement d'une source ponctuelle. Les limites d'utilisation de ce detecteur a proximite des sources (distance source-detecteur > 3 cm) ont montre la necessite de disposer d'un dosimetre de transfert. L'influence de ces diverses configurations geometriques d'irradiation sur la reponse de plusieurs appareils de radioprotection (Babyline, stylodosimetre, chambre d'ionisation) a ete etudiee pour trois radionucleides (147Pm, 204Tl, 90Sr + 90Y)
[en] At the beginning of the 1990s the restructuring of the industrial organization and the regulatory regimes are probably the most important economic and institutional phenomenon in electricity supply industries Latin America countries. This paper analyses the main characteristics of the restructuring in Chili and Brazil. Two major problems are driving this changes: the financial constraints and economic inefficiencies. Despite institutional barriers to privatization initiatives, the participation of new private companies in electricity supply industrial, specially in generation side, is becoming the common aspect of restructuring. This solution requires new regulatory options and new coordination mechanisms. In this context, the electricity companies may promote innovative strategies and adapt their long-term decisions. (authors). 2 tabs., 30 refs
[en] Contrast-enhanced ultrasound (CEUS), with the recent development of both contrast-specific imaging modalities and microbubble-based contrast agents, allows noninvasive quantification of microcirculation in vivo. Nevertheless, functional parameters obtained by modeling contrast uptake kinetics could be impaired by respiratory motion. Accordingly, we developed an automatic respiratory gating method and tested it on 35 CEUS hepatic datasets with focal lesions. Each dataset included fundamental mode and cadence contrast pulse sequencing (CPS) mode sequences acquired simultaneously. The developed method consisted in (1) the estimation of the respiratory kinetics as a linear combination of the first components provided by a principal components analysis constrained by a prior knowledge on the respiratory rate in the frequency domain, (2) the automated generation of two respiratory-gated subsequences from the CPS mode sequence by detecting end-of-inspiration and end-of-expiration phases from the respiratory kinetics. The fundamental mode enabled a more reliable estimation of the respiratory kinetics than the CPS mode. The k-means algorithm was applied on both the original CPS mode sequences and the respiratory-gated subsequences resulting in clustering maps and associated mean kinetics. Our respiratory gating process allowed better superimposition of manually drawn lesion contours on k-means clustering maps as well as substantial improvement of the quality of contrast uptake kinetics. While the quality of maps and kinetics was satisfactory in only 11/35 datasets before gating, it was satisfactory in 34/35 datasets after gating. Moreover, noise amplitude estimated within the delineated lesions was reduced from 62 ± 21 to 40 ± 10 (p < 0.01) after gating. These findings were supported by the low residual horizontal (0.44 ± 0.29 mm) and vertical (0.15 ± 0.16 mm) shifts found during manual motion correction of each respiratory-gated subsequence. The developed technique could be used as a basis for accurate quantification of perfusion parameters for the evaluation and follow-up of patients under antiangiogenic therapies.
[en] Time differential perturbed γ-γ angular correlation technique was used to measure the magnetic hyperfine field (MHF) at Tb sites in the intermetallic compound Tb3In5 using the 140La →140Ce nuclear probe. The measurements were carried out in the temperature range of 8 to 295 K. Two different temperature dependent magnetic frequencies were observed below 30 K, which were assigned as 140Ce substituting the two inequivalent Tb sites in the orthorhombic structure of Tb3In5. The temperature dependence of MHF also shows a possible deviation from an expected Brillouin-like behavior for temperatures below 18 K. A Neel transition at 27 K was observed from magnetization measurements in the samples. The magnetization as a function of the applied magnetic field was measured at two temperatures, 5 and 40 K, and the results show antiferromagnetic and a typical paramagnetic behavior, respectively. In both cases it was not observed saturation under high magnetic field.
[en] On September 13, 1987 a shielded 137Cs source was removed by two scavengers from a teletherapy unit in abandoned clinic in Goiania, Brazil, and was later broken open. The source was handled by many people from the time it was removed (Sept 13) until it was taken to the sanitary surveillance division (Sept 28). Many of these people (approximately 250) were exposed to large external and internal doses of radiation from the radioactive source; of these, 50 showed signal and symptoms of whole-body irradiation and local acute irradiation and also showed signs of external or internal contamination from ingested or absorbed 137Cs. Fourteen of those 50 developed moderate to severe bone marrow (BM) injury and required intensive medical care at a specialised unit in Rio de Janeiro. None were subjected to BM transplants. Ultimately, 4 of these casualties died of bleeding and sepsis despite the administration of GM-CSF (Granulocyte Macrophage Colony Stimulating Factor). Internal contamination due to ingestion or absorption of 137Cs was successfully removed by means of administration of Prussian Blue at doses ranging from 1.5-10.0 gm/day. Radiation induced skin injuries were observed in 28 patients requiring surgical and post-operative procedures. Since March 1988 a medical follow up protocol was established by NNEC and the Leide Das Neves Ferreira Foundation of the state of Goias, in order to prospectively follow more than 150 victims. The aim of this paper is to describe the main after-effects of the 137Cs accident in the last 4 years, giving emphasis on clinical, haematological, radiological and psychological aspects. (author)
[en] The magnetic relaxation of Co nanowires assemblies embedded in CeO2/SrTiO3(001) epilayers has been investigated by magnetization decay measurements. Two different samples were studied, with nanowires having distinct crystallographic structures and diameters of 3 and 5 nm. The structure of the nanowires was derived from high-resolution transmission electron microscopy analysis. The 3 nm diameter nanowires are made of hcp Co grains with the c-axis pointing along one of the four 〈111〉 directions of the CeO2 matrix, separated by fcc Co regions. In the 5 nm diameter nanowires, the grains are smaller and the density of stacking faults is much higher. The magnetic viscosity coefficient (S) of these two systems was measured as a function of the applied field and of the temperature. Analysis of the variation of S and of the activation volume for magnetization reversal reveals distinct behaviors for the two systems. In the nanowires assembly with 5 nm diameter, the results can be described by considering an energy barrier distribution related to shape anisotropy and are consistent with a thermally activated reversal of the magnetization. In contrast, the anomalous behavior of the 3 nm diameter wires indicates that additional sources of anisotropy have to be considered in order to describe the distribution of energy barriers and the reversal process. The distinct magnetic behaviors observed in these two systems can be rationalized by considering the grain structure of the nanowires and the resulting effective magnetocrystalline anisotropy.
[en] Gold anomalies in the Pau a-Pique deposits are present in anastomossed shear zones near the contact between the Group Aguapei conglomerates and the Tonalito Alvorada. These high-strain zones are subparallel to the regional shearing NW - SE, and they have a brittle-ductile structures. The gold ore is exploted from veins and disseminations in the conglomerates that were affected by hydrothermal alteration. The main hydrothermal minerals in the mineralized layer are quartz, tourmaline, pyrite, biotite, chlorite and white mica. These hydrothermal minerals present textures that indicate their post-tectonic growth due the circulation of mineralizing fluids in the late shearing stages. (author)
[en] We have revisited photoassociative ionization (PAI) in a cold sample of Na atoms. A two-color experiment was performed in a magneto-optical trap through the addition of a probe laser. The observation of a marked change in the PAI rate for a definite frequency range can be attributed to the influence of repulsive levels and a possible avoided crossing between long-range molecular levels