RESUMO
The objective of this study was to identify the technological level used by dairy farmers in the northeastern region of Michoacán, Mexico, through a characterisation of small-scale dairy production units, as well as to learn about the socioeconomic conditions that have enabled them to survive in the current context. A semi-structured interview was applied to 114 production units, chosen by stratified random sampling. The interview included technological, production and socioeconomic aspects. Twenty-eight variables were initially explored and 12 were used for multivariate analysis, which included Principal Component Analysis, Hierarchical Cluster Analysis and K-means Cluster. The characterisation carried out showed that the production units that predominate in northeastern Michoacán have survived with a low technological level, having as strengths the diversification of their activities and the use of family labour. On the contrary, production units with a high technological level and high productivity are few and less diversified. This shows the need to generate differentiated public policies for each cluster, aimed at strengthening the aspects that have allowed them to survive and guaranteeing a market for their production, before promoting the use of technologies.
RESUMO
The present work presents an improved method to align the measurement scale mark in an immersion hydrometer calibration system of CENAM, the National Metrology Institute (NMI) of Mexico, The proposed method uses a vision system to align the scale mark of the hydrometer to the surface of the liquid where it is immersed by implementing image processing algorithms. This approach reduces the variability in the apparent mass determination during the hydrostatic weighing in the calibration process, therefore decreasing the relative uncertainty of calibration.
RESUMO
Se realizó un estudio comparativo entre pruebas de permutación y asintóticas, aplicadas a tablas de contingencia de dimensión R×C no ordenadas, utilizando como medida de comparación la diferencia entre el p-valor exacto y asintótico. Se analizaron cinco (05) ejemplos que presentan tablas de contingencia no ordenadas, publicados en la literatura científica internacional relacionados con estudios biomédicos, con el objeto de mostrar bajo cuales condiciones ambos enfoques difieren o convergen para las pruebas de independencia de Pearson, Razón de Verosimilitud y Freeman-Halton. Los resultados mostraron que el comportamiento de las metodologías exacta y asintótica depende del tamaño de muestra, dimensión, balanceo y dispersión de la tabla de contingencia y prueba aplicada. Para los casos estudiados se encontró que los p-valores exactos y asintóticos presentaron diferencias notables para tamaños de muestras pequeños; sobre todo en tablas de contingencia desbalanceadas y dispersas; y mostraron convergencia de los p-valores asintóticos a los exactos en la medida que el tamaño de muestra y dimensión de la tabla era mayor.
A comparative study between permutation and asymptotic tests applied to unordered R×C dimension contingency tables was carried out, using the difference between the exact p-value and the asymptotic one as comparison measurement. Five (05) biomedical research-paper results based on unordered contingency tables were examined from international scientific literature, analyzing how different or equivalent they appear using Pearson, Likelihood ratio and Freeman-Halton independency tests. Results revealed that both methodologies, exact and asymptotic, behave depending on sample size, dimensions, balance and dispersion of the contingency table, as well as on the test applied. The exact and asymptotic p-values showed striking differences for small sample sizes mainly in unbalanced and sparse contingency tables, but they converged as the sample size and table dimensions increased.
RESUMO
A heterogeneous population of ependymal cells lines the brain ventricles. The evidence about the origin and birth dates of these cell populations is scarce. Furthermore, the possibility that mature ependymal cells are born (ependymogenesis) or self-renewed (ependymal proliferation) postnatally is controversial. The present study was designed to investigate both phenomena in wild-type (wt) and hydrocephalic α-SNAP mutant (hyh) mice at different postnatal stages. In wt mice, proliferating cells in the ventricular zone (VZ) were only found in two distinct regions: the dorsal walls of the third ventricle and Sylvian aqueduct (SA). Most proliferating cells were monociliated and nestin+, likely corresponding to radial glial cells. Postnatal cumulative BrdU-labeling showed that most daughter cells remained in the VZ of both regions and they lost nestin-immunoreactivity. Furthermore, some labeled cells became multiciliated and GLUT-1+, indicating they were ependymal cells born postnatally. Postnatal pulse BrdU-labeling and Ki-67 immunostaining further demonstrated the presence of cycling multiciliated ependymal cells. In hydrocephalic mutants, the dorsal walls of the third ventricle and SA expanded enormously and showed neither ependymal disruption nor ventriculostomies. This phenomenon was sustained by an increased ependymogenesis. Consequently, in addition to the physical and geometrical mechanisms traditionally explaining ventricular enlargement in fetal-onset hydrocephalus, we propose that postnatal ependymogenesis could also play a role. Furthermore, as generation of new ependymal cells during postnatal stages was observed in distinct regions of the ventricular walls, such as the roof of the third ventricle, it may be a key mechanism involved in the development of human type 1 interhemispheric cysts.