Carlos Ramírez

Ellipsometry and ab initio approaches to the refractive index of porous silicon

Spectroscopic ellipsometry is used to determine the complex refractive index (n−ik), porosity, and thickness of porous silicon (PSi) films. These films are obtained by anodizing p-type crystalline silicon in a hydrofluoric acid bath. After etching, PSi samples are heated to 750 °C in a controlled oxygen environment. A detailed analysis of the ellipsometry data is performed in order to determine the complex refractive index of PSi thin film. This frequency dependence of n and k is compared with the results of ab initio quantum mechanical calculations carried out by means of CASTEP codes within the density functional theory. The theoretical results show a diminution of the lattice constant as the oxygen content grows, in contrast to the hydrogen-saturated surface case.

Phenotypic stability and plasticity in GMP-derived cells as determined by their underlying regulatory network

Motivation Blood cell formation has been recognized as a suitable system to study celular differentiation mainly because of its experimental accessibility, and because it shows characteristics such as hierarchical and gradual bifurcated patterns of commitment, which are present in several developmental processes. Although hematopoiesis has been extensively studied and there is a wealth of molecular and cellular data about it, it is not clear how the underlying molecular regulatory networks define or restrict cellular differentiation processes. Here, we infer the molecular regulatory network that controls the differentiation of a blood cell subpopulation derived from the granulocyte-monocyte precursor (GMP), comprising monocytes, neutrophils, eosinophils, basophils and mast cells. Results We integrate published qualitative experimental data into a model to describe temporal expression patterns observed in GMP-derived cells. The model is implemented as a Boolean network, and its dynamical behavior is studied. Steady states of the network can be clearly identified with the expression profiles of monocytes, mast cells, neutrophils, basophils, and eosinophils, under wild-type and mutant backgrounds. Availability and implementation All scripts are publicly available at https://github.com/caramirezal/RegulatoryNetworkGMPModel. Contact lmendoza@biomedicas.unam.mx. Supplementary information Supplementary data are available at Bioinformatics online.

Adaptación de la Técnica de Impregnación Argéntica de Llombart para la Demostración de Fibras Nerviosas, en Cualquier Tejido en Cortes por Parafina

En la investigacion biologica sigue siendo necesaria la demostracion de la inervacion periferica en numerosos tejidos y organos. El objetivo de este trabajo fue rescatar y modernizar uno de los metodos mas constantes que hemos probado para demostrar la inervacion periferica. La tecnica de Llombart para fibras nerviosas se adapto en cortes por parafina de 7 µm en diferentes tejidos animales. La impregnacion argentica se hizo por goteo en camara humeda. Se demostraron en forma constante, precisa y seriada terminaciones nerviosas y corpusculos sensoriales, neuronas y fibras nerviosas perifericas. A pesar de la alta especificidad para fibras nerviosas, la tecnica no compromete el panorama tisular por lo que da bellas imagenes de conjunto. Sin ser una tecnica para argentafinidad, demuestra claramente dos tipos de celulas argentafines en las glandulas adrenales. La adicion de los reactivos metalicos en gotas y en camara humeda, ofrece una variante sumamente economica.