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

Context: Among the sources of biodiesel, waste cooking oil is a potential alternative fuel to reduce the emission of greenhouse gases from diesel engines without considerable technological changes. Method:  In this study, the experiments were performed under stable conditions on a single-cylinder four-stroke diesel engine using three different blends of pure diesel fuel with biodiesel made from waste cooking oil (B10, B20 and B30) and commercial diesel fuel B5. The engine ran at variable speed between 1000 - 1600 rpm, at full load and variable engine loads corresponding to the effective power at 1600 rpm. Results: The experimental results show that smoke opacity of B10, B20, and B30 is lower compared to the commercial B5 at 0.3%, 24% and 46% respectively, when evaluated at nominal speed 1600 rpm and at full load. However, by increasing the engine load at a constant speed of 1600 rpm, smoke opacity reached its maximum value with B20 compared to other fuels used. Conclusions: It is feasible to use biodiesel made with waste cooking oil in blends with pure and commercial diesel to reduce the effects of toxic emissions such as particulate matter (soot) of diesel engines on the environment. Therefore, recycling waste cooking oil significantly reduces environmental problems.

Context: For years, the safe and effective measurement of high voltage signals has one of the major concerns of those conducting high voltage tests; in these cases, voltage divider represents one of the most important devices for laboratory measurement of signals (such as those generated by lightning). However, the divider must have adequate characteristics of nominal voltage, scale factor, and frequency response, so that the recorded signal is a reflection of the signal applied to the equipment under test. For example, the most commonly developed voltage dividers (resistive divider, capacitive divider, and damped capacitive divider) have their own characteristics that allow a good performance of the high voltage measurement and recording system. This paper presents the theoretical and practical aspects related to design, construction, and evaluation of a damped capacitive divider of 300 kV in order to evaluate the performance of the measurement and recording system in relation to the conversion stage. Method: Simulation tools such as MATHEMATICA® and PSPICE® were used for the design and evaluation of the voltage divider. These helped estimate the behavior of the divider components (damping resistor and low voltage arms). Additionally, laboratory equipment (frequency response meter and 300 kV voltage pulse generator) was used to verify the performance of the components. The experiments were based on frequency response tests, insulation capacity, and obtaining the scale factors according to national and international standards. Results: In the frequency response test performed on the damping resistor from 20 Hz to 1 MHz, the parasitic effects are negligible and the impedance of the resistor can be considered purely resistive. In the insulation capacity test, resistor can withstand voltage pulses of up to 10 kV without breaking the resistor insulation. Regarding the verification of the scale factors, the porcentage differences did not exceed the limit of peak voltage variation set by the standard. Conclusions: The results show the methodology developed was adequate for the design, construction, and simulation of the voltage divider. The electrical models suggested in the methodology were sufficient to obtain reliable results during simulations. Finally, the most important contributions of this work were the construction of a non-inductive damping resistor and the construction of an additional low-voltage branch.

Context: The upper basin of the Chaschuil river is found in the geomorphological provinces of the Cordillera Frontal and the Famatina System; it extends from the upper limit of the basin (26°45'6.35" S - 68°2'22.15" O) to the Aguas Calientes volcano (27°13'25,81" S - 68°19'5.48" O). The zone is inserted in the Pacific Ring of Fire, which is characterized by concentrating some of the most important subduction zones in the world, where intense seismic and volcanic activity is generated. Method: The volcanic geomorphological cartography was generated by statistical and numerical operations applied on the matrix data that make up the satellite image. For this analysis, the free software SOPI 3.0 was used to process the Landsat 7 and 8 satellite images of the years 2002 and 2015. The cartography was prepared using the free software QGIS 3.2.2 and Google Earth Pro. Results: The best results of digital processing were given in the visible bands and by different combinations of bands in RGB. Thirteen main volcanic systems, highly eroded and with associated pahoehoe lavas, are described, as well as secondary eruptions with rugged aa-type lavas superimposed on the more fluid lavas. Conclusions: The application of digital satellite image processing is an optimal tool for the study of volcanic structures, which allows their delimitation and classification.

Context: The protection functions of a generator - transformer group must guarantee its useful life when an abnormal operating condition arises, thus improving the reliability of the electric power service in the electric power system. When the V/Hz ratio of the group increases, saturation may occur in the magnetic core and induce a dispersion flow in the non-laminated components that are not designed to conduct it, and damage can occur in seconds. This is the reason why machines are protected with the ANSI 24 protection function (FDP). Methodology: This article presents the theory that justifies the implementation of the ANSI 24 protection function in a generator-transformer group, as well as the methodology to calculate each of the adjustment parameters in a SIEMENS 7UM62 multifunctional relay. The article explains the logical decision diagram in a clear and detailed way, identifying the settings, input signals (analog and binary), and output signals. The logical diagram was organized in three subdiagrams to facilitate understanding and to identify the causes that originate its alarm, start, trip, or block outputs. Results: The detailed decision diagram of the ANSI 24 protection function was obtained; the input adjustment criteria of the adjustment parameters and a detailed procedure for calculating each were described. In addition, the numerical results of all the adjustments for the generator-transformer group of Unit 1 of the Salvajina hydroelectric power station were obtained. Conclusions: The results of this research recommend obtaining the actual V/Hz heating characteristic or confirming the one delivered by the manufacturer of the equipment to be protected, so that it is possible to have greater precision in the adjustment parameters.

Context: Concrete production is characterized by a significant demand for energy and raw materials, and by emitting large amounts of greenhouse gases (GHG). Moreover, the processes of construction, maintenance, and demolition of buildings generate huge quantities of waste that require costly and environmentally sensitive disposal procedures. Therefore, several solutions are being investigated to reduce the environmental impact of the processes associated with the life cycle of concrete. Methodology: Through experimental tests, the physical and mechanical properties of three sustainable concrete mixtures were studied (concrete with recycled aggregates, concrete with partial replacement of Portland cement by fly ash, and cementitious composites reinforced with recycled fibers). Results: The use of coarse recycled aggregates degraded the mechanical characteristics of the concrete due to their greater porosity and water absorption capacity. However, the mixture made out of recycled aggregates and fly ash showed a synergistic effect, mitigating the adverse consequences mentioned. The post-cracking response of concrete reinforced with recycled steel fibers was characterized by a lower tenacity and ductility compared to composites with industrial fibers. Specifically, mixtures with recycled fibers showed a more pronounced softening stage. This revealed a lower efficiency of recycled fibers compared to industrial fibers. Conclusions: The experimental results showed that the incorporation of recycled materials led to a deterioration in the physical and mechanical behavior of the analyzed composites. However, the resulting properties exceeded the recommended minimum values required for their application as structural materials.

Context: This research evaluates the compressive strength of a mixed granular material composed of clay and sand, in order to optimize its design. Methodology: The factors studied were the cement content, the humidity, the compaction blows, and the clay/sand ratio. Additionally, an initial experimental design of 24 was performed. Results: The results allowed to identify that the significant factor is the cement content. On the other hand, a single-factor design with three levels (175; 200; and 225 Kg/m3) and two replicas was explored for optimization. Conclusions: The experimental design allowed to identify the optimal value of the cement content factor in the border of the selected experimental region (150 Kg/m3). Keywords: Sub base, stabilization, cement floor, ANOVA.

Context: This paper presents a participative educational proposal led by the cooperation network called “Construya Seguro y Sostenible,” to which the University Corporation Minuto de Dios, the Catholic University of Colombia, and the Pilot University of Colombia belong. Methodology: This research was developed from a non-experimental descriptive quantitative method, where forty-four (44) bad practices related to habitability in informal housing were identified. Results: These bad practices were translated into instructional objectives through learning units framed in a course proposal oriented to communities under the instructional model of Jerrold and Kemp. Conclusion: This initiative allowed to link 25 families of the Villas de Kennedy neighborhood in Bogotá, Colombia, with students and teachers linked to the Network who, through participatory work, socialized their findings and experiences.

Context: Nowadays, the images of the Earth surface and the algorithms for their classification are widely available. In particular, the algorithms are promising in the differentiating of cotton crops stages, but it is necessary to establish the capabilities of the different algorithms in order to identify their advantages, and disadvantages. Method: This paper describes the assessment process in which the Support Vector Machines (SVM) and random-forest technique (decision trees) are compared with the maximum likelihood estimation when differentiating the stages of cotton crops. A RapidEye satellite image of a geographic area in the municipality of San Pelayo, Cordoba (Colombia), is used for the study. Using a set of sampling polygons, a random sample of 6000 pixels was taken (2000 training and 4000 for validating the classifications.) Confusion matrices, and R (data processing and analysis software) were used during the validation process Results: The maximun likelihood estimation presented a correct classification percentage of 68.95%. SVM correctly classified 81.325% of the cases and the decision trees correctly classified 78.925%. The confidence test for the classifications showed non-overlapping intervals, and SVM obtained the highest values. Conclusions: It was possible to confirm the superiority of the technique based on support vector machines for the proposed verification zones. However, this technique requires a number of classes that comprehensively represent the variations of the image (in order to guarantee a minimum number of support vectors) to avoid confusion in the classification of non-sampled areas. This was less evident in the other two classification techniques analysed.

Context: The homeostasis of the Urban Train of Guadalajara (Mexico) experiences entropy relative to the conglomeration of users in the so-called rush hours. This leads to greater consumption of electrical energy in daily commutes; however, the weight coming from users can be used as thermodynamic negentropy to reduce their entropy levels. Therefore, the objective of this research is to determine the feasibility of using piezoelectricity in obtaining and consuming electrical energy for the operation of the system. Method: The research is based on the data provided by the Urban Electric Train System (SITEUR, in Spanish) and the Federal Electricity Commission (CFE). This information is triangulated along with data obtained in field exercises, and based on energy the supply and demand; then, the approximate weight of the users and the energy that the piezoelectric generation system can produce per person are calculated. Finally, the Entropy-Homeostasis-Negentropy (EHN) model is used to determine the homeostasis of piezoelectricity in the energy consumption of the urban electric train in the metropolis of Guadalajara. Results: The use of piezoelectricity can significantly improve efficiency and achieve energy optimization of urban mobility systems up to 89,7%; for example, the case of Line 2 of the SITEUR in Guadalajara. This improvement in efficiency is possible due to the homeostatic conditions of the system and the average influx during rush hours, when it reaches 83,059 users. Therefore, it is possible to generate thermodynamic negentropy through the electrical energy coming from the piezoelectric systems and the weight of the users. Conclusions: The energy produced by piezoelectricity that makes use of the users’ weight can be stored to power the lines of the urban electric train network. In this way, the efficiency of the energy consumption in daily commutes is improved, saving the company money and energy (through the reduced amount use of external energy to produce work).

Context: The geochemical characterization of archeological materials of obsidian or volcanic glass (used in the past for the preparation of lithic tools) allows to trace origin and infer forms of interaction and ranges of mobility of ancient human populations. The characterization of the geochemical composition of obsidian by analysis of Neutron Activation allows to determine with a good degree of certainty its origin; however, it is a costly and destructive technique, not recommended for archeological pieces. Other more accessible techniques, such as X Ray Fluorescence or Mass Spectrometry with inductively coupled plasma have been used successfully for this application but with a higher level of uncertainty. This work seeks to provide solutions through the use other non-destructive techniques that may be applicable to archeological heritage. Method: The mechanical properties of an obsidian sample were explored through ultrasound methods. The phase velocity and the attenuation of longitudinal waves were measured, and the density of the samples was quantified with gas pycnometry, which makes it possible to determine the dynamic elastic modules. Additionally, the same measurements were repeated on glass samples of industrial manufacture. Results: It was observed that the speed, density, and longitudinal modulus were higher for the industrial glass sample than for the obsidian sample. Conversely, the attenuation was greater in the case of obsidian, and a greater dependence on frequency was observed. Conclusions: The results obtained demonstrate the ability of the method to distinguish between materials with different chemical composition; thus, it would be useful in archeological studies. Moreover, the differences observed in the attenuation show that the method is sensitive to the microstructure of the material, so it would provide information not accessible by conventional archaeometry techniques.