Implementación del hidrógeno en la legislación mexicana para el desarrollo energético nacional

La energía es uno de los motores más importantes que mueven a las sociedades. El desarrollo de un sistema energético a base de hidrógeno (H2) está respaldado por dos grandes fuerzas, la seguridad energética y la problemática medioambiental. Considerando la celda de combustible de óxido sólido (SOFC) como el principal receptor del H2, se obtendría el potencial de crear un sistema energético eficiente, limpio y sostenible en las próximas décadas. El factor más importante a mejorar a corto plazo es el desarrollo de mejores sistemas de almacenamiento del H2. En México, el marco institucional para la promoción y aplicación de energías alternas es muy limitado, puesto que se prefiere desarrollar tecnologías para el aprovechamiento de fuentes tradicionales de energía; hay desconocimiento por parte de las autoridades de la magnitud y el posible aprovechamiento del H2 como fuente alterna de energía. La normativa mexicana no hace referencia al H2 como alternativa energética. Por ello, considerando todos los beneficios ambientales, económicos y sociales que se promueven con su uso y aplicación, es pertinente que se incorpore en el marco jurídico mexicano a fin de fomentar la investigación, promoción y aplicación de este elemento como fuente alterna de energía

Aportación a la Geografía Social de España: las diferencias regionales del empleo asalariado.

Sin resume

A Cholinergic Synaptically Triggered Event Participates in the Generation of Persistent Activity Necessary for Eye Fixation

An exciting topic regarding integrative properties of the nervous system is how transient motor commands or brief sensory stimuli are able to evoke persistent neuronal changes, mainly as a sustained, tonic action potential firing. A persisting firing seems to be necessary for postural maintenance after a previous movement. We have studied in vitro and in vivo the generation of the persistent neuronal activity responsible for eye fixation after spontaneous eye movements. Rat sagittal brainstem slices were used for the intracellular recording of prepositus hypoglossi (PH) neurons and their synaptic activation from nearby paramedian pontine reticular formation (PPRF) neurons. Single electrical pulses applied to the PPRF showed a monosynaptic glutamatergic projection on PH neurons, acting on AMPA-kainate receptors. Train stimulation of the PPRF area evoked a sustained depolarization of PH neurons exceeding (by hundreds of milliseconds) stimulus duration. Both duration and amplitude of this sustained depolarization were linearly related to train frequency. The train-evoked sustained depolarization was the result of interaction between glutamatergic excitatory burst neurons and cholinergic mesopontine reticular fibers projecting onto PH neurons, because it was prevented by slice superfusion with cholinergic antagonists and mimicked by cholinergic agonists. As expected, microinjections of cholinergic antagonists in the PH nucleus of alert behaving cats evoked a gaze-holding deficit consisting of a re-centering drift of the eye after each saccade. These findings suggest that a slow, cholinergic, synaptically triggered event participates in the generation of persistent activity characteristic of PH neurons carrying eye position signals.Unión Europea Grants BI04-CT98-0546España, Ministerio de Ciencia PB98-0011, BFI2000-00936, BFI2000-1190, y BFI2002-0137

Diversity of deep-sea echinoderms from Costa Rica

Echinoderms are a highly diverse group and one of the most conspicuous in the deep sea, playing ecological key roles. We present a review about the history of expeditions and studies on deep-sea echinoderms in Costa Rica, including an updated list of species. We used literature and information gathered from the databases of the California Academy of Sciences, the Benthic Invertebrate Collection of the Scripps Institution of Oceanography, the National Museum of Natural History, the Museum of Comparative Zoology and the Museo de Zoología from the Universidad de Costa Rica. A total of 124 taxa (76 confirmed species) have been collected from the Costa Rican deep sea, 112 found in the Pacific Ocean, 13 in the Caribbean Sea, and one species shared between the two basins. We report 22 new records for the Eastern Tropical Pacific, 46 for Central American waters, and 58 for Costa Rica. The most specious group was Ophiuroidea with 37 taxa, followed by Holothuroidea (34 taxa), Asteroidea (23 taxa), Echinoidea (17 taxa), and Crinoidea (11 taxa). The highest number of species (64) was found between 800 m and 1200 m depth. Only two species were found deeper than 3200 m. Further efforts on identification will be required for a better comprehension of the diversity of deep-sea echinoderms. Limited research has been done regarding the biology and ecology of deep-sea echinoderms in Costa Rica, so additional approaches will be necessary to understand their ecological functions.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR)UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Biodiversidad y Ecología Tropical (CIBET)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Análisis del Desgaste en Brocas Esféricas de Diamante de una Fresa Odontológica

Proyecto de Graduación (Bachillerato en Ingeniería en Materiales) Instituto Tecnológico de Costa Rica, Escuela de Ciencia e Ingeniería en Materiales, 2016This research work is presented as a quantitative analysis of wear generated on spherical diamond dental burs. To reproduce the clinical conditions in the most precise manner, a laboratory experiment was designed, in which burs from two different manufacturers were compared, each of them being used during 30-minute intervals in cavity preparations on extracted dental pieces. The change in mass and in the outer profile of each bur was quantified. In addition, by means of microscopic analysis, the different wear mechanisms involved during the use of the burs were observed and described. Finally, a comparison was made between the burs’ wear rate and unit price

Do ventricular repolarization interval ratios depend on heart rate and should they be rate-corrected?

QT interval decreases with increasing heart rate (HR), hence to define normal values of QT interval for different heart rates requires the application of a QT interval rate correction formula. However, the influence of HR on the ratios between several ventricular repolarization intervals, that can be useful as risk predictors of malignant ventricular arrhythmias is unknown. This study analyzes the influence of HR on QTp/QT, JTp/JT, Tpe/JTp, and Tpe/JT ratios on a healthy subject during exercise. The intervals were measured in V3 lead and the characteristic points of QRS complex and T wave were detected by computer algorithms based on the wavelet transform (WT). Exercise stress was graded according to the four initial stages of the Bruce protocol. The heart rate was divided into two ranges: less than 100 beats/min and from 100 beats/min to 185 beats/min. When HR exceeded 100 beats/min, QTp/QT and JTp/JT ratios increased whereas Tpe/JTp and Tpe/JT ratios decreased for increasing HR. However, when HR was below 100 beats/min, those same four ratios were independent from HR. As opposed to the QT interval, there is no need to correct QTp/QT, JTp/JT, Tpe/JTp, and Tpe/JT ratios when HR is below 100 beats/minPeer Reviewe

Spatial variability of ventricular activity intervals in normal subjects and old myocardial infarction patients

Increased dispersion of QT interval in the 12-lead ECG have been proposed as risk factor of ventricular arrhythmias in post myocardial infarction (post-MI) patients, but its sensitivity and specifity is low for diagnosis and/or prognosis. We evaluate dispersion in other ventricular activity intervals, in order to determine whether they improve the separation between 15 normal subjects and 15 post-MI patients compared with QT dispersion. All the interval ventricular activity dispersions measured in the Frank’s orthogonal leads (XYZ) are larger in post-MI patients than in normal subjects, but the differences are significant only for JTpeak (JTp) dispersion (p = 0.03). Therefore JTp dispersion could improve the identification of post-MI patients with risk of ventricular arrhythmiasPeer Reviewe