557 research outputs found
Improvement of in situ Pb isotope analysis by LA-ICP-MS using a 193 nm Nd : YAG laser
No full textWe have tested the capabilities of a new 193 nm Nd:YAG laser ablation system for in situ Pb-208/Pb-206 and Pb-207/Pb-206 measurements by LA-ICP-MS. Experiments were performed with MPI-DING (KL2-G, ML3B-G, ATHO-G, T1-G) and USGS (GSE-1G) reference glasses using the fast electrical scan mode (0.075 s per pass) of a single collector sector-field mass spectrometer. Mass discrimination was determined by sample-reference material (e. g., NIST SRM 612) bracketing with linear interpolation. We typically obtained an external precision for Pb-208/Pb-206 and Pb-207/Pb-206 of 0.05-0.2% RSD for 50-100 mu m three-spot analyses of the low-Pb (1-10 mu g g(-1)) MPI-DING glasses. The precision of Pb isotope ratio data of the high-Pb GSE-1G sample (366 mu g g(-1)) was <0.2% for spot sizes >= 10 mu m. Even 2 and 5 mu m spot size measurements could be performed with GSE-1G. The LA-ICP-MS isotope ratio data of the MPI-DING reference glasses agree within uncertainties (about 0.05% and 0.1% for Pb-208/Pb-206 and Pb-207/Pb-206, respectively, and 100 mm spot size analyses) with the reference values obtained from TIMS and solution MC-ICP-MS. A comparison of the 193 nm Nd:YAG laser results with those obtained from a 213 nm Nd:YAG laser system shows that there is almost a factor of two improvement in precision using the new 193 nm Nd: YAG laser. Because of lower sample consumption of the 193 nm Nd: YAG laser, the Pb detection efficiency (2.5 x 10(-3)) of the mass spectrometer is a factor of 2.5 higher than that using the 213 nm laser. Reasons for these improvements are the shorter wavelength (193 nm compared with 213 nm) and the shorter pulse width (2.8 ns compared to 5 ns) of the new laser ablation system. Thus, the mean particle size of the ablated material and the localized heating of the sample is reduced, leading to a more uniform mass discrimination
Estudo comparativo entre os métodos de Stoll e Kato quantitativo
No full textA autora realizou a contagem de ovos por gr. de fezes em 129 amostras de fezes pelos métodos de Kato e de Stoll, incluindo 100 casos de parasitismo por Ascaris lumbricoides, 100 por Trichuris trichiura, 70 por ancilostomideos e 40 por S. mansoni. Os resultados foram avaliados estatisticamente, evidenciando-se idênticos com as duas técnicas no que se refere a Ascaris lumbricoides, T. trichiuris e S. mansoni, mostrando-se, no entanto, o método de Stoll mais adequado para a contagem de ovos de ancilostomideos.The author examined 129 specimens of faeces using the techniques of Kato and Stoll. 100 cases of Ascaris lumbricoides infection, 100 of Trichocephalus trichiurus, 70 of hookworm infection and 40 of Schistosoma mansoni were detected. The number of eggs eliminated per gram of faeces was determined using the two methods. The results were statistically analysed using the comparative tests for the two methods at a significance levei of 0,05. The results showed that, for counting eggs, the two techniques presented equal results for A lumbricoides, T. trichiurus and Schistosoma mansoni, but the Stoll technique was more sensitive for hookworm
The Preparation and Preliminary Characterisation of Three Synthetic Andesite Reference Glass Materials (ARM-1, ARM-2, ARM-3) for In Situ Microanalysis
No full textThree synthetic reference glasses were prepared by directly fusing and stirring 3.8 kg of high-purity oxide powders to provide reference materials for microanalytical work. These glasses have andesitic major compositions and are doped with fifty-four trace elements in nearly identical abundance (500, 50, 5 mu µg g−1) using oxide powders or element solutions, and are named ARM-1, 2 and 3, respectively. We further document that sector-field (SF) ICP-MS (Element 2 or Element XR) is capable of sweeping seventy-seven isotopes (from 7Li to 238U, a total of sixty-eight elements) in 1 s and, thus, is able to quantify up to sixty-eight elements by laser sampling. Micro- and bulk analyses indicate that the glasses are homogeneous with respect to major and trace elements. This paper provides preliminary data for the ARM glasses using a variety of analytical techniques (EPMA, XRF, ICP-OES, ICP-MS, LA-Q-ICP-MS and LA-SF-ICP-MS) performed in ten laboratories. Discrepancies in the data of V, Cr, Ni and Tl exist, mainly caused by analytical limitations. Preliminary reference and information values for fifty-six elements were calculated with uncertainties [2 relative standard error (RSE)] estimated in the range of 1-20%
Chemical characterisation of the USGS reference glasses GSA-1G, GSC-1G, GSD-1G, GSE-1G, BCR-2G, BHVO-2G and BIR-1G using EPMA, ID-TIMS, ID-ICPMS and LA-ICPMS
No full textThe USGS reference glasses GSA-1G, GSC-1G, GSD-1G, GSE-1G, BCR-2G, BHVO-2G and BIR-1G were investigated by different analytical techniques. All these materials have a geological (basaltic) matrix and are therefore useful in igneous geochemistry as matrix-matched reference materials for microanalytical techniques. The new GS glasses have trace elements in groups at concentration levels of about 0.01, 5, 50 and 500 mu g g(-1). Their major element compositions have been determined by EPMA, and trace elements have been analysed by LA-ICP-MS and two isotope dilution techniques using TIMS and ICP-MS. EPMA and LA-ICP-MS analyses indicated that the USGS reference glasses are homogeneous at the mu m to mm scale with respect to major (variations 1-2%) and most trace elements (variations 14%). Trace element data obtained from the different analytical techniques agreed within an uncertainty of 1-5%, indicating that between method results are comparable. Therefore, the preliminary working values for the four USGS GS glasses calculated from these data have a low level of uncertainty
Kolonialer Rassismus, eugenisches Denken und Geschlecht. Auguste Forel und Otto Stoll in der Debatte um die "allgemeine Natur des Menschen" um 1900
No full textThrow Away your Computer and Get an Education (audio)
No full textDoes knowledge of computers equal a good education and a good job? Think again! Despite pressures for campus internet feeds in every venue, a quality education has little to do with computer and everything to do with the human interplay between student, professor and the body of knowledge. Yes, computers make it easy to look up facts and impress us with flashy graphics but they also discourage creativity. They encourage us t o copy what we see or read rather than come up with our own ideas and conclusions. Clifford Stoll, a leading authority on computer security and noted author, questions the dependency of the digital age. Are we better informed? Is our electorate more activ e? Are our citizens more involved in our communities? Has this revolution spawned more problems or solutions
Autoría, autoridad y verdad. Apuntes para una nueva lectura 'en frío' de la polémica Menchú-Stoll
No full textEste artículo versa sobre las condiciones que afectan la recepción de los textos que han sido ubicados bajo la rúbrica genérica testimonio en relación a la construcción de su autoría y de su condición de “verdad”. El análisis se concreta a partir de los procesos de interpretación que afectan un caso polémico, el de la recepción del testimonio mediado por Elizabeth Burgos,Me llamo Rigoberta Menchú y así me nació la conciencia (1983) una vez su referencialidad fue puesta en cuestión por el antropólogo David Stoll en el libro Rigoberta Menchú and the Story of All Poor Guatemalans (1999). Se parte de la hipótesis que toda posición de autor depende de elementos pragmáticos condicionados tanto por la filiación genérica o disciplinaria del texto en cuestión como por el lugar––social, político, simbólico–– que ocupa quien firma la obra en un determinado entorno. Palabras clave: testimonio, autoridad etnográfica, voces subalterna y autoría plural,This paper deals with the factors that affect the reception of those texts linked to the genre testimonio, in relation to the construction of their authorship and truth. It analyzes the interpretation processes that affect a controversial case: the reception of the work of Elizabeth Burgos, Me llamo Rigoberta Menchú y así me nació la conciencia (1983), once its documentary value was questioned by the anthropologist David Stoll in his book Rigoberta Menchú and the Story of All Poor Guatemalans (1999). The testimonio is an interesting genre where to show how the “author” function depends on pragmatic factors conditioned by the generic ordisciplinary affiliation of the text, as well as by the social, political or symbolical place occupied by the person(s) who sign(s) the book. Key words :testimonial writing, etnographic authority, subaltern voices and plural author
Autoría, autoridad y verdad. Apuntes para una nueva lectura 'en frío' de la polémica Menchú-Stoll
Get PDFEste artículo versa sobre las condiciones que afectan la recepción de los textos que han sido ubicados bajo la rúbrica genérica testimonio en relación a la construcción de su autoría y de su condición de “verdad”. El análisis se concreta a partir de los procesos de interpretación que afectan un caso polémico, el de la recepción del testimonio mediado por Elizabeth Burgos,Me llamo Rigoberta Menchú y así me nació la conciencia (1983) una vez su referencialidad fue puesta en cuestión por el antropólogo David Stoll en el libro Rigoberta Menchú and the Story of All Poor Guatemalans (1999). Se parte de la hipótesis que toda posición de autor depende de elementos pragmáticos condicionados tanto por la filiación genérica o disciplinaria del texto en cuestión como por el lugar––social, político, simbólico–– que ocupa quien firma la obra en un determinado entorno.
Palabras clave: testimonio, autoridad etnográfica, voces subalterna y autoría plural,
This paper deals with the factors that affect the reception of those texts linked to the genre testimonio, in relation to the construction of their authorship and truth. It analyzes the interpretation processes that affect a controversial case: the reception of the work of Elizabeth Burgos, Me llamo Rigoberta Menchú y así me nació la conciencia (1983), once its documentary value was questioned by the anthropologist David Stoll in his book Rigoberta Menchú and the Story of All Poor Guatemalans (1999). The testimonio is an interesting genre where to show how the “author” function depends on pragmatic factors conditioned by the generic ordisciplinary affiliation of the text, as well as by the social, political or symbolical place occupied by the person(s) who sign(s) the book.
Key words :testimonial writing, etnographic authority, subaltern voices and plural author
An automated iridium-strip heater for LA-ICP-MS bulk analysis of geological samples
No full textIn this paper we describe a flux-free fusion technique for the highly precise LA-ICP-MS bulk analysis of geological samples. For this purpose we have developed an automated iridium-strip heater with temperature and melt time control. To optimise the homogeneity of the fused glasses and to reduce possible depletion of volatile elements during melting, we undertook experiments with basaltic rock and glass powders using different melting temperatures (1300-1700 °C) and melting times (5-80 s). Major and trace element microanalysis was performed using EPMA and LA-ICP-MS. Homogeneous glasses were obtained for temperatures ≥ 1500 °C and melting times ≥ 10 s. High loss (20-90%) of highly volatile elements (e.g., Cs, Ge, Sn, Pb) was observed for high melting temperatures (≥ 1600 °C) and long melting times (80 s). Standard melting conditions (1600 °C, 10 s) represent a compromise, as the glasses were homogeneous with respect to major and trace elements and, at the same time, were not depleted in elements with condensation temperatures (at a pressure of 10-4 bar) higher than about 900 K (e.g., Zr, Hf, Ba, Sr, REE, U, Mo, Ni, Rb, Ga). Several international geological reference materials with SiO2 ranging between 47% m/m and 59% m/m were prepared using our standard melting conditions (1600 °C, 10 s) and subsequently analysed by LA-ICP-MS. These samples also include the new Brazilian basaltic reference material BRP-1. Matrix-matched calibration of the LA-ICP-MS data was performed using the basaltic reference glasses KL2-G, ML3B-G, BCR-2G and BHVO-2G. Most analytical data agreed within uncertainty at the 95% confidence level with the GeoReM preferred values published in the GeoReM database for reference materials of geological and environmental interest. To demonstrate routine bulk LA-ICP-MS analyses of geochemical and cosmochemical samples using the whole rock fusion technique, we also present trace element data for ocean island basalts from Lanai (Hawaii) and of Martian meteorites. © 2008 International Association of Geoanalysts
Notas sôbre a evolução da Sassurana - Megalopyge lanata (Stoll, 1780). (Lep., Heterocera, Megalopygidae)
No full textThis paper is a small contribution to the knowledge of Megalopyge lanata (Stoll, 1780). The caterpillars of this moth are called " Sassurana" and are very known by the fact of having the body densely covered with long hairs, among which are some setae connected with poison glands. They damage the leaves of a large number of plants, enclosed in at least 14 botanical families, being therefore poly-phagous. M. lanata has a great taxonomical importance for it being the type of the family Megalopygidae Berg, 1882. The Author presents some notes on the various common names used for it, on its known natural enemies and also about the biology, according to the observations made by him in the Laboratory of Zoology, of the Escola Superior de Agricultura "Luiz de Queiroz, São Paulo University, Brasil
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