Eladio Martinez

Environmental or lifestyle factors are likely to explain part of the heterogeneity in breast and ovarian cancer risk among BRCA1 and BRCA2 mutation carriers. We assessed parity as a risk modifier in 515 and 503 Spanish female carriers of mutations in BRCA1 and BRCA2, respectively. Hazard ratios (HR) and their corresponding 95% confidence intervals (CI) were estimated using weighted Cox proportional hazards regression, adjusted for year of birth and study centre. The results for ever being parous and number of live-births were very similar for carriers of mutations in both genes. For all mutation carriers combined, the estimated HR associated with ever having had a live-birth was 0.74 (95% confidence interval [CI] = 0.55–1.01, P = 0.06), and that associated with each live-birth was 0.87 (95%CI = 0.77–0.98, P = 0.02). The latter association was observed only in women aged 40 and above (HR = 0.81, 95%CI = 0.70–0.94, P = 0.004 vs. HR = 0.99, 95%CI = 0.83–1.18, P = 0.9 for women under age 40), and this trend was highly consistently observed for carriers of mutations in each gene. There was no evidence of an association between breast cancer risk and age at first birth for parous BRCA1 or BRCA2 mutation carriers (P-trend ≥ 0.3). The power to detect associations with ovarian cancer risk was much lower, especially for BRCA2 mutation carriers. Nevertheless, having a live-birth was associated with protection for BRCA1 mutation carriers (HR = 0.41, 95%CI = 0.18–0.94, P = 0.03), and a strong and consistent protective effect of age at first birth was observed for parous carriers of mutations in both genes (HR = 0.65, 95%CI = 0.52–0.83, P < 0.001). This is the third independent study to find that, as in the general population, parity appears to be associated with protection from breast cancer in women with mutations in BRCA1 and BRCA2. Parity appears to be protective for ovarian cancer in BRCA1 mutation carriers, but its role in BRCA2 mutation carriers remains unclear. Whether later age at first birth is also protective for ovarian cancer in mutation carriers requires further confirmation.

According to restriction site analyses of mitochondrial DNA, Drosophila subobscura shows a polymorphism that consists of two frequent haplotypes that are evenly distributed all over the Old World and several rare haplotypes never present in more than one locality. To ascertain the causes responsible for such distribution, three different mtDNA fragments from haplotypes I and II sampled in a population from Zürich have been partially sequenced. Only three silent nucleotide changes have been detected in the ND5 gene. One of them implies the loss of the HaeIII restriction site, which differentiates haplotype I from haplotype II. On the basis of these results as well as on others involving the geographic distribution of haplotypes I and II, they can be considered phenotypically equivalent. The sequencing study has been complemented with the analysis of cytonuclear disequilibria between mitochondrial haplotypes and different nuclear loci in four D. subobscura populations. As expected, no significant cytonuclear disequilibria have been found between haplotypes I and II. Moreover, when haplotypes I and II were pooled and compared with the rare, endemic haplotypes similar results were obtained.

El modelo de la escuela primaria exige de un maestro que por su nivel de preparación, sea capaz de garantizar la formación integral de sus escolares. En tal sentido, la presente investigación incursiona en una de las problemáticas acuciantes de esta educación “la preparación de los maestros de la escuela primaria, para favorecer la solidez de los conocimientos de los

Powders of ternary Mn–Ni–Co oxide negative temperature coefficient thermistors were synthesized by a low-temperature alternative route. The procedure allowed straightforward preparation without the addition of any binder, of highly densified Mn–Ni–Co–O semiconducting ceramics as cubic single-phase spinels, at relatively moderate temperature (≈1000 °C). A tentative cation distribution for the Mn1.5Ni0.6Co0.9O4 spinel oxide has been proposed, and its variation with temperature has also been considered. The dilatometric and X-ray powder diffraction studies carried out for Mn1.5Ni0.6Co0.9O4 showed that sintering takes place in a single stage between 900 and 1000 °C, and yields highly densified ceramic with an apparant density larger than 96% of the calculated X-ray density. Scanning electron microscopy showed different microstructures for the Mn1.5Ni0.6Co0.9O4 spinel oxide, depending on sintering conditions. The value of the sensitivity index, β=3068 K, indicates a good technological thermistor performance for this material. © 1998 Chapman & Hall

El artículo presenta la descripción discreta de superficies de contacto de elementos mecánicos cónicos elásticos, los cuales se usan para uniones eje cubo de rueda mediante deformación y fricción. El objetivo es predecir las regiones de contacto potencial de la unión, midiendo ...