Análisis de estabilidad de sistemas lineales invariantes en el tiempo y representados por matrices intervalo [por] Juan José Darío Delgado Romero

Tesis (Doctor en Ing. Eléctrica) U.A.N.L.

L'ensemble des EDO d'ordres 2 et 3 invariantes sous SL(2,R) et leur discrétisation préservant les symétries

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Factores asociados al no deseo del primer embarazo en adolescentes gestantes colombianas. Estudio exploratorio de la ENDS 2010

Introducción: El inicio de la vida sexual dispone a las jóvenes a sufrir de las consecuencias inherentes de esta actividad, entre ellas, el embarazo no deseado. Para efectos del presente estudio, se indago en el contexto nacional la asociación del no deseo del primer embarazo en adolescentes gestantes con diversos factores sociodemográficos, individuales y de servicios de salud. Metodología: Estudio exploratorio, descriptivo y analítico; la población estudiada proviene de la Encuesta Nacional de Demografía y Salud 2010. La selección de la población tuvo como criterio a mujeres menores de 20 años, que cursan con su primer embarazo al momento de la encuesta. Se realizaron análisis descriptivos, comparativos y asociativos. Resultados: Se seleccionaron 286 adolescentes colombianas en estado de su primer embarazo. 71,3% corresponden a embarazos no deseados y 28,7% a embarazos deseados al momento de la encuesta. Se encontró asociación estadística del no deseo del embarazo con la asistencia escolar actual OR 2.3 (IC95% 1.2 a 4.56), sentir que le ha hecho falta más educación sexual OR 1.94 (IC95% 1.11 a 3.36), decisión del embarazo en conjunto OR 0.05 (IC95% 0.02 a 0.1) y nivel educativo alto OR: 3.5 (IC 95% de 1,397 a 8,792). Conclusión: Existe asociación estadísticamente significativa del no deseo del embarazo y un nivel educativo alto alcanzado por la mujer y la edad del esposo. Se requieren de más estudios para verificar los demás resultados.

Activity beginnings and ends : a case study of three teachers.

Se investiga si los estilos de enseñanza pueden ser observados en el habla de tres profesores universitarios de lengua extranjera y describir este habla bajo un paradigma interpretativo.

'Roman' or 'native' bodies in Britain: the evidence of late Roman nail-cleaner strap-ends

This paper reviews late Roman `nail-cleaner strap-ends', a group of objects first discussed by Hawkes and Dunning (1961). The precise function of these objects is unclear as their shape suggests use as toilet instruments but the split socket suggests that they were part of belt-fittings. We suggest a detailed typology and discuss the dating evidence and the spatial distribution of the type. Regardless of their precise function, it is argued in this paper that nail-cleaner strap-ends of this type are unique to late Roman Britain and thus represent a distinct regional type. The use of nail-cleaner strap-ends can be viewed in the context of gender associations, military status and religious beliefs.

A simple method of calculating eigenvalues and resonances in domains with infinite regular ends

A new approach is presented for the solution of spectral problems on infinite domains with regular ends, which avoids the need to solve boundary-value problems for many trial values of the spectral parameter. We present numerical results both for eigenvalues and for resonances, comparing with results reported by Aslanyan, Parnovski and Vassiliev.

A review of Holocene rainforest ecotonal dynamics at opposite ends of the Amazon - Bolivia versus Colombia

In this review paper, the aim is to compare and contrast fossil pollen evidence for Holocene rainforest ecotonal dynamics at opposite ends of the Amazon basin – the southern ecotone in NE lowland Bolivia versus the northern ecotone in lowland Colombia. During the Holocene, tropical South America experienced major changes in precipitation (Silva Dias et al. 2009). Consideration of Amazonian rainforest dynamics over this time-frame may therefore provide important insights into rainforest responsiveness to climate change.

Unusually short tandem repeats appear to reach chromosome ends of Rhynchosciara americana (Diptera: Sciaridae)

The characterisation of sequences at chromosome ends of Rhynchosciara americana was continued with the screening of a genomic library using as a probe a short repeat identified in a previous report (M-22, 22 bp) which was found to be specific for noncentromeric termini of this species. Simple repeats, complex tandem and apparently dispersed repeats were present in the genomic clones analysed. Repetitive sequences do not define individual chromosome tips as they were found in all noncentromeric ends. A novel and unusually short tandem repeat type for dipteran chromosome ends (named M-16) composed of 16 nucleotides and frequently associated with M-22 arrays was characterised in this work. Islands of M-16 and M-22 tandem repeats were found in all the genomic clones analysed. Individual probes representative of each repetitive element hybridised not only to all noncentromeric ends of R. americana chromosomes but also to inter-telomeric bridges. This contrasted with the other repeat types which displayed sub-telomeric localisation as seen by double detection of hybridised probe and telomeric reverse transcriptase. Some stretches composed of M-16 and M-22 tandem repeats localised in different regions of the analysed genomic clones were either identical or showed sequence similarity that was unexpectedly higher than the mean sequence similarity observed among repeats within each of their tandem arrays. The occurrence of segmental duplications, as deduced by sequence analyses involving the two repeats that appeared to reach chromosome ends, might indicate the involvement of this type of duplication process in the chromosome end maintenance in this species.

Curiously composite structures of a retrotransposon and a complex repeat associated with chromosome ends of Rhynchosciara americana (Diptera: Sciaridae)

In Drosophila, telomere retrotransposons counterbalance the loss of telomeric DNA. The exceptional mechanism of telomere recovery characterized in Drosophila has not been found in lower dipterans (Nematocera). However, a retroelement resembling a telomere transposon and termed ""RaTART"" has been described in the nematoceran Rhynchosciara americana. In this work, DNA and protein sequence analyses, DNA cloning, and chromosomal localization of probes obtained either by PCR or by screening a genomic library were carried out in order to examine additional features of this retroelement. The analyses performed raise the possibility that RaTART represents a genomic clone composed of distinct repetitive elements, one of which is likely to be responsible for its apparent enrichment at chromosome ends. RaTART sequence in addition allowed to assess a novel subtelomeric region of R. americana chromosomes that was analyzed in this work after subcloning a DNA fragment from a phage insert. It contains a complex repeat that is located in the vicinity of simple and complex tandem repeats characterized previously. Quantification data suggest that the copy number of the repeat is significantly lower than that observed for the ribosomal DNA in the salivary gland of R. americana. A short insertion of the RaTART was identified in the cloned segment, which hybridized preferentially to subtelomeres. Like RaTART, it displays truncated sequences related to distinct retrotransposons, one of which has a conceptual translation product with significant identity with an endonuclease from a lepidopteran retrotransposon. The composite structure of this DNA stretch probably reflects mobile element activity in the subtelomeric region analyzed in this work.