Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

Manganese is an essential micronutrient whose both excess and deficiency cause serious health problems. Determination of trace concentrations of manganese in environmental and food samples is difficult due to different factors, mainly to the low metal contents and to the complexity of the matrices. Therefore, sensitive techniques are necessary for determination of manganese. Some common techniques are time-consuming and expensive, but flame atomic absorption spectroscopy presents advantages such as low cost, operational facilities and good selectivity. However, a preconcentration step is required. The aim of this work was to incorporate a chelating agent (alizarin red S) on an anionic exchanger to improve the extraction of manganese (II) and its quantification by flame atomic absorption spectroscopy. The method was applied to the determination of manganese in synthetic solutions and in real samples (urban runoff and baby food).

Protected areas play a key role in conservation. According with the aforementioned, it is important to evaluate how the criteria for their selection and establishment have been modified over time. Here, we present the case studies of three countries of America, USA, Mexico and Costa Rica, analyzing three moments of their history from the establishment of the first natural areas selected by qualitative characteristics, to the consolidation of current systematic methodologies.

Zeolitic clays from the state of Guerrero were crushed and characterized by means of analysis of the particle size distribution by sieving. Later they were purified by magnetic separation assisted with ultrasonic bath (SMABU); also, by means of X-ray diffraction (XRD), the presence of the phases corresponding to the aluminosilicate tales such as clinoptilolite (Na2 (Al2Si7O18)) and corroborate the effect of the magnetic separation was verified. By means of X-ray energy dispersion spectrometry (EDS) the decrease in mass of the magnetic elements after separating the zeolitic clays was verified. By scanning electron microscopy (SEM) the morphology and particle sizes were observed; finally, the physical properties of the material were determined.  

The ozone in the stratosphere forms a very important atmospheric layer that helps the preservation of life on Earth, since without its presence the UV-C rays would reach directly to the population, generating different health problems to living beings. Scientific literature mention that the ozone layer has entered a phase of deterioration due to the presence of compounds derived from saturated hydrocarbons such as chlorofluorocarbons (CFC´s). Due to the growing concern of the scientific community, studies have been increased in order to understand the behavior or deterioration of the ozone layer, and to propose mitigation measures to stop this phenomenon. The objective of this work was to make a bibliographical review of the current state of deterioration of the ozone layer, and to know the possible causes and consequences of the same, also to raise awareness about the use of compounds that contribute to the deterioration of this layer.

In this work, we present results from observations and structural analyses made on outcropping fault planes in the eastern sector of the Sierra de Pachuca, where La Crucita, La Sotolera, and Colmenas hills, are located. On the studied fault planes, several sets of superposed slickenlines with different orientation are observed.  The orientations of the slickenlines can be grouped into two different sets, here interpreted as reactivation of faults in response to changes in the orientation of crustal stress.  We compared the older dip slip normal faulting with the younger oblique slip faulting. Our results strongly suggest the presence of a regional trans-tensional regime.

The diaphonization technique consists in making the soft tissues of an organism transparent in order to observe the bone and cartilaginous tissues. Specific dyes are used for these purposes, mainly red alizarin for bone. There are no standardized protocols for each species, since it is generalized for large groups, being the group of fishes one of the least defined. In this article a protocol of the technique was developed for the nun fish (Gymnocorymbus ternetzi), there are included, the necessary chemicals, and the costs in Mexican pesos.

In this work, we present a general ideas in birth-death processes,which are a particular kind of stochastic process. Wepresent birth-death process applied for some biological examples.We present a birth-death model used for modeling thebehaivoir in the number of infected individuals as an epidemiologicalproblem. This process has a finite transition probabilitiesmatrix, which all their entries are constants. The last partof the work, we present a infinite matrix and some ideas aboutthe solution on this problem, adapted to the epidemiologicalexample deal in the previous section.

Three sized Micropits were developed. Micropits were designed and fabricated using wet etching. MEMS fabrication consists of thin film deposition and patterned of several geometric structures. For Si substrate etching three layers SiO2/ Si3N4/ SiO2 were deposited and patterned. They were used as a mask. Micropit pattern was transferred by lift off technique. SiO2, Si3N4 layers and Si substrate were etched by HF, H3PO4 and KOH solutions. Si substrate has 7mm/h etching rate. Micropit micrographs were obtained by scanning electronic microscopy (SEM). Micropits are MEMS widely used in gas sensors, because they provide thermal isolation, Micropits will be used for gas microsensors, polisilicon microheater and gas sensor thin film will be deposited later. Today gas sensors have several applications in manufacturing & industry, such as, automotive, medicine/biomedical, consumer products, aerospace, chemical, optical displays, fluidics, wireless and optical communications.

In this work, soil subsidence will be described as an important factor in the deterioration of the architectural urban heritage, mainly due to the water pumping that is continued to the subsoil of Mexico City and specifically in soils with high compressibility clays, which generates a phenomenon of consolidation in the subsoil, with which differential subsidence originates in the base of the buildings displaced in these zones. Some buildings have structural deterioration due to this phenomenon of differential subsidence, so it becomes essential to study their structural behavior under this phenomenon, in order to obtain results and parameters that can be considered in the analysis of this type of property anywhere of the world with similar characteristics. A building is studied in a virtual way, through simulation with numerical support, in particular it is a temple located in the historic center of Mexico City with the mechanical and constructive properties of the materials typical of the colonial era. The conclusions of the case study should support, mainly, those involved in professional practice and the guild, in order to take into account the recommendations arising from the study and thereby raise awareness of the effects that I could have our built heritage in the short, medium and long term.

In order to initiate or increase tourist activity in certain localities, actions are taken to capitalize built, unbuilt, tangible and intangible heritage areas. These interventions are often low criteria and are carried out or promoted by the government at the federal, state and municipal levels, jointly or individually. Sometimes these interventions are favorable but other times they are counterproductive because they do not contribute to the preservation of heritage and lead to the creation of a ‘no place.’ In order to study this problem, a qualitative method based on interviews with local social actors was used to analyze three proposed variables. Among the findings are that not all the interventions made to contribute to a town contemplated all the possible repercussions. Such is the case of the terrace built on the river, which is abandoned and deteriorating. The purpose of the terrace was to move the tourism service providers to this area. The service providers are currently in front of the church and the central garden which endangers the permanence of the town in the Magic Towns Program (PPM), given that this program establishes that in the public space areas there should not be street vendors.