Regressões lineares em geocronologia: isócronas, errócronas e pseudoisócronas

Several methods of linear regression reported in the literature for use in geochonology are discussed in order to guide geochronologists in the selection of an adequate model and also to distinguish among isochrons, errorchrons and pseudoisochrons. For Rb/Sr isochron methods, at least 6 models or statistical treatments are available, each one with its peculiarities. Based in two examples, we show that for cases when the experimental data points scatter within limits determined by the experimental errors, and using or not the weighted regression treatment, the resultant parameters are essentially concordant. The estimates of associated error, however especially for initial ratios, show variations by up to a factor of 7, depending upon the statistical procedure. In view of this fact and on the basis of simulated test data, we propose not only more adequate models, but also general criteria that must be observed in the selection of samples in order to obtain an isochron. If the data to be regressed show a scatter in excess of experimental error for geological reasons (open system), four regression models are available to treat the parameters defined in these cases as errorchrons. These models are briefly discussed in terms of their applications. In the Pb/U methods, in which the usual regression treatment is applied to obtain the best-fit line, some additional peculiarities are pointed outDiversos métodos de regressão linear propostos na literatura, para fins geocronológicos, são discutidos de modo a orientar os geocronólogos na escolha de modelos adequados e também distinguir entre isócronas, errócronas ou pseudoisócronas. No caso do método isocrôni co Rb/Sr, são disponíveis pelo menos 6 modelos ou abordagens estatísticas, cada qual com peculiaridades específicas. Exemplifica-se o caso em que os pontos se alinham dentro dos erros experimentais e utilizando modelos, adequados ou não, que empregam a técnica de pondera ção dos pontos, os parâmetros resultantes são praticamente concordantes, porém os erros podem variar até por um fator tão alto quanto 7, conforme a formulação estatística proposta. Em vista deste fato, propõem-se, com base também em exemplos, os modelos mais adequados e também critérios gerais que devem ser observados até na seleção de amostras para a obtenção de isócronas. Nos casos em que os pontos não se alinham dentro dos erros experimentais, por causas geológicas (sistema aberto), são abordados 4 dos modelos sugeridos e é feita também uma discussão em que casos seriam aplicáveis. No método da concórdia Pb/U, em que as regressões usuais também são aplicáveis para determinar a melhor reta, algumas particularidades adicionais são discutida

Um sistema nacional de aquisição e processamento de dados acoplado "on line" ao espectrômetro de massa de fonte sólida TH-5 (Varian Mat)

A VARIAN MAT solid source mass spectrometer, varían model MAT TH-5, used for geochronological applications has been coupled on line to a 16-bit HP-9825B computer. An appropriate digital voltimeter and interface, both supplied by Hewlett-Packard, complete the system. The developed prototype allows, through peak switching of 8 channels controlled by a Hall effect probe, isotopic analyses of all the elements which can be carried out by the thermal ionization method. This system has been used since 1983 with success, and the strontium measurements performed on 2 carbonate standards NBS-987 and SrN (E&A) agree, within experimental error, with results obtained in modem instruments. A similar system, with the same performance capabilities as the one described above, using an Apple computer and peripherals available in Brazil, has also been developed. The developed interface is provided with outputs to control external devices and accessories like solenoid valves, vacuum systems, scales, etc, common is mass spectrometry. The software, available in HPL and Applesoft languages, is provided with dinamic interference correction, Dodson's interpolation technique, rejection of the spurious ratios and computes all the common statistical parameters.Um espectrômetro de massa de fonte sólida da VARIAN MAT, modelo TH-5, utilizado em aplicações geocronológicas, foi acoplado "on line" ao microcomputador HP-9825B de 16 bits, tendo um voltímetro digital e interfaces apropriadas da Hewlett-Packard. O protótipo desenvolvido permite, através da técnica de "peak switching" de 8 canais controlados por uma sonda de efeito Hall, medidas isotópicas de todos os elementos analisáveis pelo método de ionização térmica. O sistema utilizado desde 1983, com amplo sucesso, rivaliza com os sistemas modernos conforme medidas efetuadas em 2 carbonatos padrões de estrôncio NBS-987 e SrN (E & A). Experiência semelhante, utilizando um microcomputador da linha Apple, periféricos e interface apropriados e inteiramente nacionais desenvolvidos para o sistema, reproduziu, de forma bastante adequada, a performance anterior. A interface desenvolvida, pela sua versatilidade, pode acionar periféricos e acessórios como válvulas solenóides, sistemas de vácuo, sistema de troca de escala, etc, operações comuns na espectrometria. O software, desenvolvido nas linguagens HPL e Applesoft, é provido de correção de interferência dinâmica, técnica de interpolação de Dodson, rejeição de razões espúrias e cálculos de todos os parâmetros estatísticos normais

Relationship between tooth loss and mortality in 80-year-old Japanese community-dwelling subjects

<p>Abstract</p> <p>Background</p> <p>Findings from several studies suggest associations between tooth loss and health outcomes, including malnutrition, poor quality of life, and mortality, in older individuals. However, limited information is available regarding whether those associations remain true in very elderly subjects after adequately considering confounding factors such as sex and smoking status. Herein, we determined whether the number of teeth in 80-year-old subjects is an independent predictor of mortality.</p> <p>Methods</p> <p>We initially contacted 1282 80-year-old community-dwelling individuals born in 1917, of whom 697 responded and participated in a baseline study, with follow-up examinations conducted 4 and 5.5 years later. Data from interviews and medical and oral examinations were obtained, and oral health was determined according to the number of teeth remaining in the oral cavity.</p> <p>Results</p> <p>A total of 108 and 157 subjects died in 4 years and 5.5 years, respectively, after the baseline study. Tooth loss was significantly associated with mortality at age 85.5, but not at age 84, after adjusting for potential confounders. When the analysis was stratified by sex, we found a stronger association in females in follow-up examinations conducted at both 4- and 5.5 years. On the other hand, the effect of tooth loss on mortality was not significantly different between smokers and non-smokers.</p> <p>Conclusion</p> <p>Tooth loss is a significant predictor of mortality independent of health factors, socio-economic status, and lifestyle in octogenarians, with a stronger association in females.</p

Characterization of the macrophage transcriptome in glomerulonephritis-susceptible and -resistant rat strains

Crescentic glomerulonephritis (CRGN) is a major cause of rapidly progressive renal failure for which the underlying genetic basis is unknown. WKY rats show marked susceptibility to CRGN, while Lewis rats are resistant. Glomerular injury and crescent formation are macrophage-dependent and mainly explained by seven quantitative trait loci (Crgn1-7). Here, we used microarray analysis in basal and lipopolysaccharide (LPS)-stimulated macrophages to identify genes that reside on pathways predisposing WKY rats to CRGN. We detected 97 novel positional candidates for the uncharacterised Crgn3-7. We identified 10 additional secondary effector genes with profound differences in expression between the two strains (>5-fold change, <1% False Discovery Rate) for basal and LPS-stimulated macrophages. Moreover, we identified 8 genes with differentially expressed alternatively spliced isoforms, by using an in depth analysis at probe-level that allowed us to discard false positives due to polymorphisms between the two rat strains. Pathway analysis identified several common linked pathways, enriched for differentially expressed genes, which affect macrophage activation. In summary, our results identify distinct macrophage transcriptome profiles between two rat strains that differ in susceptibility to glomerulonephritis, provide novel positional candidates for Crgn3-7, and define groups of genes that play a significant role in differential regulation of macrophage activity

Idades K-Ar de rochas alcalinas do Brasil meridional e Paraguai oriental: compilação e adaptação às novas constantes de decaimento

A compilation of 295 geochronological data of 52 alkaline occurrences from Southern Brazil and Eastern Paraguay is presented. These data, mostly available in previous publications, were recalculated, using the new decay constants recommended by STEIGER & JAEGER (1977) for the K-Ar method. The estimated analytical error of the age determined using experimental parameters is also indicated (COX & DALRYMPLE, 1967). This paper aims, specifically, at making ages published prior to 1977 compatible with recent data, allowing, for example, comparisons between ages obtained from a single alkaline massif or from neighbouring massifs. By calculating K-Ar ages using the constants recommended by STEIGER & JAEGER (op. cit.), there occurs an increase of 2.1 to 2.4% in the value of the age calculated with the previous constantsUma compilação de 295 dados geocronológicos de 52 ocorrências alcalinas do Brasil Meridional e Paraguai Oriental é apresentada. Estes dados, previamente publicados em sua quase totalidade, foram recalculados, utilizando-se as novas constantes de decaimento recomendadas por STEIGER & JAEGER (1977) para o método K-Ar. Indica-se, também, a estimativa do erro analítico da idade, determinada em função das condições experimentais (COX & DALRYMPLE 1967). O presente trabalho visa, especificamente, compatibilizar as idades publicadas anteriormente a 1977 com os dados mais recentes, permitindo, por exemplo, comparações entre idades de um mesmo maciço alcalino ou de maciços alcalinos vizinhos. Ao se calcular a idade K-Ar utilizando-se as constantes de STEIGER & JAEGER (op. cit.) ocorre um acréscimo de 2,1 a 2,4% no valor da idade calculada pelas constantes anteriore