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

p-Nitrophenol (pNP) is a widely used compound for analytical determinations of several esterases (EC. 3.1.1.X), including lipases (E.C. 3.1.1.3). Most enzymatic measurements employ pNP derivatives such as esters, which are broken down by enzymatic hydrolysis, releasing pNP that is quantified by its absorbance at 410 nm. Although this type of methods was developed a few decades ago, the spectrophotometric analysis of pNP requires analytical measurements of pH and temperature to achieve reliable determinations. The aim of this paper is to offer a graphical update of how pH and temperature affect the p-nitrophenol absorbance at different wavelengths in lipase emulsified media, due to its relevance for the quantitative determination of lipase activity using spectrophotometric methods. To highlight the importance of each variable involved in this analysis, we dissolved pNP in emulsified media (for lipase activity quantification) at several pH values from 4.00 to 11.00, and measured its absorbance in a range of 270 nm – 500 nm and at several temperatures from 25°C to 50°C. The absorption patterns of pNP under the established conditions were graphed in 3D plots. The constructed 3D plots showed that, regardless of the temperature, below pH 6.00, pNP predominantly absorbs at 317 nm, due to the greater abundance of its protonated form, which is completely predominant at pH 3.50 and below. On the other hand, at pH 10.0 and above, the major absorption occurs at about 401 nm, confirming that the equilibrium is completely shifted to the pNP anionic form. These results also indicate that close to neutral pH value pNP, it displays a temperature dependence effect, increasing absorbance to 410 nm at higher temperatures. Due to many analytical determinations of enzymatic activities, the release of pNP is carried around pH 7.00. It is necessary to consider the determinant role of both pH and temperature over these measurements, how these variables must be strictly controlled, and how the calibration curves and blanks should take the reaction media pH and temperature into account.

The objective of this study was to determinate blood parameters and the presence of parasites in a wild population of tortugas deslizantes (Trachemys scripta emolli) during the dry season of 2013 in the Caño Negro Wildlife Refuge in Costa Rica. Individuals were captured from different gaps using nets. Blood samples were taken to determine chemical parameters of blood and hematocrit, as well as morphological values and body conditions. In addition, samples of feces and ectoparasites were collected. The hematocrit CI 95.0% was [14.7091, 18.7356] and no significant difference were found between sexes. The 95% CI for blood chemistry parameters were: AST (U/L) [87.6214, 148.929], CK (U/L) [1439.2, 2487.08], AU (umol/L) [68.22, 90.43 ], GLU (mmol/L) [4.26, 5.47], PHOS [0.46, 0.61], Ca (mmol/L) [1.99, 2.15], PT (g/L) [22.16, 24.44], K (mmol/L ) [3.31, 3.83], and Na (mmol/L) [127.92, 130.93]. A total of 21 fecal samples was obtained, of which 10 were positive for parasites (23.8% Strongyloides, 14.3% Ascaridia, 9.5% Coccidia, and 9.5% Pentastomid). A leech from the Rhynchobdellidae family was the only ectoparasite found (Placobdella sp.). None of the individuals were ill or had abscesses in relation to their morphological attributes.  Based on the results, the handling used does not represent a risk for this reptile population.

Herein, we report the physical, chemical, and biological treatment of wastewater generated in the teaching laboratories at Universidad Nacional, Costa Rica. Initial physicochemical treatment included neutralization and coagulation-flocculation, followed by a biological treatment with fungi (Aspergillus sp. and Penicillium dipodomyicola) or bacterias, the latter were isolated from the sludge from the campus’ wastewater treatment plant and the greywater collection tank at the School of Chemistry. The samples’ pH prior to treatment was ≤ 2, while COD ranged between 3000 and 30 000 mg/L. Gas chromatography-mass spectra analysis indicated the presence of 55 organic compounds in the wastewater, some of which reached undetectable concentrations after treatment. The fungi and the bacterial strain removed up to 50% of the substances, while the toxicity decreased with respect to time of exposure to the treatment. Results support the potential use of these microorganisms as bioremediators. Although the organic compounds were partially removed, the treated wastewater exhibited high toxicity for Daphnia magna (water flea). Further experiments with longer treatment times or other strains might be needed for effective removal of pollutants.

The study of the problems posed by teachers to their students and the characteristics that should be considered to enhance mathematical competences is an issue that has gained interest in recent years. However, most of these studies have been approached from an epistemic, technological, or cognitive point of view, without effectively considering what math teachers usually do to pose problems in their classes. In this sense, the objective of this article is to explore the pedagogical conceptions and practices of a group of elementary and secondary teachers from southern Chile about the selection of mathematical problems for their classes, and the criteria they use for such selection. The interest of this study stems from assuming that, in the classroom, teachers are the articulating vehicle of educational policies. Another motivation for this paper is the results of research in Mathematics Education. For this purpose, a questionnaire was presented which showed that teachers choose any of the following three mathematical problems: i) problems taken from textbooks, internet, and other resources; ii) problems adapted from textbooks, internet, or other resources (own variations); and iii) problems created by the teacher. In any case, there is a growing interest in teachers to pose problems with contexts that students feel close to and arouse interest from an emotional point of view. In addition, it was observed that the criteria used by teachers for posing math problems in the classroom implicitly contemplate the didactical suitability criteria proposed within the framework of the Onto-Semiotic Approach to Mathematical Knowledge and Instruction (OSA).

The aim of this research is to characterize the graphing practices in first semester Physical Engineering students in a lab context. An ethnographic methodology is used to collect data, and the paper follows a framework that considers Graphing a social practice. For the analysis, five components in scientific environments were used: ongoing concerns, standard practices, material resources, linguistic resources, and breakdowns. The intent is to account for the confrontations, difficulties, and participation of 44 students in the first semester of the Physical Engineering Program in the social graphing practice as they construct and interpret Cartesian graphs. A summary of the results obtained is presented, and a categorization of graphing components during the experimental practice is shown. This categorization allowed us to find some difficulties students exhibit when interpreting and constructing cartesian graphs.

This article seeks to show the importance of solving verbal mathematics problems, and the role of metacognitive regulation in this process. To do so, awareness will be raised in secondary school teachers regarding the use of problem-solving as an exploratory resource in the metacognitive strategies applied by students, which teachers may use as input to modify methodologies in the classroom, both individually and collectively. A theoretical framework focused on the use of problem solving is provided as a didactic resource, paying special attention to the representations students use during problem solving to facilitate their understanding of a problem. Quasi-experimental research was carried out on a non-random sample of 99 students from the first and third years of secondary school, who solved problems with guidance focused on handling numerical and geometrical concepts. The results show clear differences in the metacognitive strategies used by students during the solution of these types of problems; teachers must therefore adapt their guidance strategies based on the mathematical content addressed.

This paper analyses the transition from performance assessment to formative assessment, based on a propaedeutic project framework for college mathematics teaching. An exploratory qualitative study was conducted to analyze the changes in the professor assessment practices during first-year math courses, in which the different types of assessment are assigned integrative purposes to guide the learning process.  Data was gathered from interviews and tests applied by 21 college professors teaching the Math Foundations courses for the Engineering (MFI) and Economics and Business Administration (FMEA) Programs in the first semester of 2018.  Results reveal predominance of assessment practices based on quantitative judgment for grading purposes, as well as assessment practices based on academic performance as certification, in which grades objectively guarantee the level of mathematical knowledge acquired by the student. It is concluded that the challenge of configuring interactive assessment systems between the two existing types requires updating the professional competence of university professors.

This paper presents detailed aspects regarding the implementation of the Finite Element Method (FEM) to solve a Poisson’s equation with homogeneous boundary conditions. The aim of this paper is to clarify details of this implementation, such as the construction of algorithms, implementation of numerical experiments, and their results. For such purpose, the continuous problem is described, and a classical FEM approach is used to solve it. In addition, a multilevel technique is implemented for an efficient resolution of the corresponding linear system, describing and including some diagrams to explain the process and presenting the implementation codes in MATLAB®. Finally, codes are validated using several numerical experiments. Results show an adequate behavior of the preconditioner since the number of iterations of the PCG method does not increase, even when the mesh size is reduced.

This paper studied the belief system of future Chilean teachers of Early Childhood Education and Primary Education regarding their competencies to incorporate Education for Sustainable Development (EDS) in the classroom, specifically, in math classes. To this end, a survey was applied to 87 Primary Education preservice teachers and 58 Early Childhood Education preservice teachers, which was analyzed from an interpretative approach. Results are not clear regarding ESD and its scope, despite being valued. In addition, there is a clear need for training in this regard and the potential of mathematical education as a tool to incorporate ESD into the school classroom. It is concluded that ESD-related competencies need to be incorporated in initial and permanent teacher training programs in a transversal way, in our case for Mathematics Education.

The objective of this research was to determine the level of knowledge and perception of the Costa Rican population about water for human consumption, general concepts, the impact of human activities, the occurrence of extreme events and water management and governance. In 2016, a quantitative-descriptive study of population perception was carried out through a semi-structured survey in which 800 people were consulted, through calls to landlines. It was found that the Costa Ricans: a) perceived that water is a public good and that there is greater availability of water than there is in reality, b) 22 % indicated having supply problems, infrastructure and/or water quality, c) are aware of the contamination of water bodies and willing to pay more for the treatment of wastewater, d) perceived a negative impact due to floods and landslides and, e) 55 % agreed that water for consumption comes from wells and springs, but only 12 % and 36 % had a general notion of what an aquifer and groundwater is, respectively. It is concluded that education programs should include general concepts on groundwater, water management and governance and that the willingness to pay more for wastewater treatment should be taken into consideration by the institutions for the improvement of environmental sanitation.