Ingeniería e Investigación | Universidad Nacional de Colombia (National University of Colombia) (original) (raw)

Papers by Ingeniería e Investigación

38(3), 2018

This paper considers a no-wait flow shop scheduling (NWFS) problem, where the objective is to min... more This paper considers a no-wait flow shop scheduling (NWFS) problem, where the objective is to minimise the total flowtime.
We propose a genetic algorithm (GA) that is implemented in a spreadsheet environment. The GA functions as an add-in in the
spreadsheet. It is demonstrated that with proposed approach any criteria can be optimised without modifying the GA routine or
spreadsheet model. Furthermore, the proposed method for solving this class of problem is general purpose, as it can be easily
customised by adding or removing jobs and machines. Several benchmark problems already published in the literature are used
to demonstrate the problem-solving capability of the proposed approach. Benchmark problems set ranges from small (7-jobs, 7
machines) to large (100-jobs, 10-machines). The performance of the GA is compared with different meta-heuristic techniques used
in earlier literature. Experimental analysis demonstrate that solutions obtained in this research offer equal quality as compared to
algorithms already developed for NWFS problems.

In many countries, buildings are usually made of unreinforced clay masonry walls, especially in C... more In many countries, buildings are usually made of unreinforced clay masonry walls, especially in Colombia. These constructions have
low resistance and ductility, and are very vulnerable to seismic events, due to their low capacity of energy dissipation. This paper
reports the results obtained from a research project that evaluates the behavior of reinforced masonry walls under lateral loads. The
reinforcement was made using Carbon Fiber Reinforced Polymers (CFRP). In the test program, eight (8) clay masonry walls were built
using hollow brick. Four (4) of them were 1,23 m long and 1,90 m high and the remaining four (4) were 2,47 m long and 1,90 m
high. Four (4) walls were tested with a static lateral load and four (4) with a cyclic lateral load in its plane. Results revealed that the
presence of the reinforcement material significantly increased the ultimate load and deformation capacity, provided that the material
has a suitable anchoring system.

38(3), 2018

This research aims to analyze the influence of Engineering professors’ competencies on their perf... more This research aims to analyze the influence of Engineering professors’ competencies on their performance, as perceived by Engineering
students and graduates from a Brazilian federal public university. Regarding methodology, a set of Engineering educators’ competencies
were proposed, identified, and validated by exploratory factor analysis (EFA), parallel analysis, internal consistency (Cronbach’s
alpha), and partial confirmatory factor analysis (PCFA) in a sample of 139 Engineering students and graduates (engineers), who
answered a 35-item questionnaire. Results reveal three main competencies (namely, content-pedagogical knowledge, innovationinspiring
attitudes, and emotional skills) that further the research on the competencies of Engineering professors. First, contentpedagogical
knowledge is perceived by students as a single, merged competence. Second, Engineering students not only need
to develop innovation competencies, but Engineering educators also have to develop innovation-inspiring attitudes to motivate
students’ innovativeness. Third, emotional skills also play an important role in professors’ performance. Finally, the impact of these
competencies on Engineering educators’ performance was confirmed and analyzed by means of a logistic regression.

38(3), 2018

The aim of this paper is to evaluate the efficiency and productivity change of Paraná’s Credit Un... more The aim of this paper is to evaluate the efficiency and productivity change of Paraná’s Credit Union. The analysis considered 45 units
(each credit union researched), each of one with 10 variables in each period (8 inputs and 2 outputs). This evaluation has taken into
account quarterly credit union’s data, from January 2009 to July 2015 (27 periods). The methodology included Data Envelopment
Analysis (DEA), Principal Components Analysis (PCA) and Malmquist Index (MI) techniques. The results showed that DMUs 453,
498 and 517 were considered 100% efficient in all periods, making them ideal benchmarks. There was no case that a DMU was
not considered 100% efficient in at least one observation. The MI showed that the difference between the biggest and the smallest
average was significant (varying between 19.837 for DMU 251 and 0.926 for DMU 450). The average between all MI was 4,735 with
a standard deviation of 3,547, evidencing the different measures of efficiency between each DMU when compared to the others.

38(3), 2018

The textile industry is a generator of high volumes of waste water with a high content of polluta... more The textile industry is a generator of high volumes of waste water with a high content of pollutants such as azo dyes, which are
recalcitrant and persistent in the environment, these ones have been of interest in the last decades for the entities in charge of the care
of the environment. This study evaluated the ability to discolor of reactive black 5 (NR5) by a consortium and the microorganisms that
constitute Rhodotorula mucilaginosa, Galactomyces pseudocandidum and Escherichia coli free and immobilized in calcium alginate,
coffee husks and bagasse of sugar cane. The results show discoloration was evidenced, where the highest percentage corresponds
to G. pseudocandidum (90,05%) and the lowest to R. mucilaginosa (79,31%). When comparing the percentages of discoloration
between the free microorganisms and the immobilization matrices, it is observed that the former exhibit the highest percentages of
discoloration. In addition, there are no significant differences between using cane bagasse or coffee husks as immobilization matrix.

38(3), 2018

This paper demonstrates a study to improve the total harmonic distortion (THD) originated due to ... more This paper demonstrates a study to improve the total harmonic distortion (THD) originated due to excessive use of power electronic
(PE) equipment and non-linear loads. Shunt active power filter (SAPF) is used to mitigate the harmonics from the system because
it has the capability of minimizing the harmonic problems initiated by non-linear loads. The instantaneous reactive power (IRP)
p-q theory is used for the generation of reference signal and for the extraction of compensating components of the current. The
proportional integral (PI) controller and artificial neural network (ANN) have been employed in the DC-link controller and for current
errors adjustments. In this paper, both conventional hysteresis and adaptive hysteresis band current controller (HBCC) have been used
for the generation of gate pulses for the SAPF, which reduces THD in the source current to a value within IEEE specified standards,
without any phase error over the extensive range of adaptive HBCC strategy. Simulation results confirm that the SAPF with HBCC and
ANN performs the harmonic mitigation efficiently and maintains power factor (PF) close to unity.

38(3), 2018

This paper considers GSM cell system in which pure VAMOS technics is implemented. Traffic propert... more This paper considers GSM cell system in which pure VAMOS technics is implemented. Traffic properties of the system with VAMOS possibility (probability of unsuccessful pairing of connections in one timeslot and loss probability due to lack of idle channels) are determined. It is found dependence of these properties on the allowable power difference for successful pairing, on offered traffic and on environmental attenuation coefficient. The serving quality of this channel group is compared to an Erlang group with the same parameters. It is proved that probability of bad serving in the group of VAMOS channels is higher than in Erlang group with the same parameters, but not more than two times. The results obtained by calculation are proved comparing them to the results of simulation.

Mortar and paste with different composition were analyzed with X-ray diffraction and dispersive e... more Mortar and paste with different composition were analyzed with X-ray diffraction and dispersive energy spectrometry (EDS) with
coupled Electronic Scanning Microscope (SEM) to study the formation that appear after the setting reaction in the mortar made by
using glass powder, with a size of 16μ, as binder. Such analysis shows the occurrence of formations similar to C-S-H gels, but in
which, the Ca/Si ratio is lower than for typical C-S-H gels. In addition it was observed that the shape of the gels is slightly different
when the samples are preserved in water. These more filamentous formations and the presence of a larger number of Si molecules
causes the setting reaction to be maintained for a longer period of time and provide a certain capacity for self-regeneration without
external intervention, which makes it suitable for soil stabilization.

This paper shows the development of a decision tree for the classification of loads in a non-intr... more This paper shows the development of a decision tree for the classification of loads in a non-intrusive load monitoring (NILM) system implemented in a simple board computer (Raspberry Pi 3). The decision tree uses the total energy value of the power signal of an equipment, which is generated using a discrete wavelet transform and Parseval's theorem. The power consumption data of different types of equipment were obtained from a public access database for NILM applications. The best split point for the design of the decision tree was determined using the weighted average Gini index. The tree was validated using loads available in the same public access database.

This article shows the evaluation of the influence of two polymer wastes (crumb rubber – GCR and ... more This article shows the evaluation of the influence of two polymer wastes (crumb rubber – GCR and low density polyethylene – LDPE), a natural bitumen (Gilsonite - G) and a chemical component (Husil) on the physical, rheological and thermal properties of an asphalt cement (AC 60/70 penetration grade). Over a control asphalt and the modified asphalts were performed: penetration, softening point, ductility, ignition point, rheology (using a dynamic cut rheometer – DSR), Multi Stress Creep and Recovery (MSCR), linear amplitude sweep (LAS), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests. The results show that the four additives increase the stiffness and rutting resistance of the asphalts. Additionally, it reports an increase in fatigue cracking resistance when asphalt cement is modified with GCR, G and Husil. The additives give thermal stability to the asphalt cement, providing less mass loss (linked mostly to a less oxidation).

The purpose of this research is to apply methods of support vector machines (SVMs) for fast deter... more The purpose of this research is to apply methods of support vector machines (SVMs) for fast determination of earthquake depths using seismic records of the " El Rosal " station, near to the city of Bogotá – Colombia. The algorithm was trained with time signal descriptors of 863 seismic events acquired between January 1998 and October 2008. Only earthquakes with magnitude ≥ 2 M_L were contemplated, filtering its signals to remove diverse kind of noises not related to earth tremors. During training stages of SVM several combinations of kernel function exponent and complexity factor were considered for time signals of 5, 10 and 15 seconds along with earthquake magnitudes of 2.0, 2.5, 3.0 and 3.5 M_L. The best classification of SVM was obtained using time signals of 15 seconds and earthquake magnitudes of 3.5 M_L with kernel exponent of 10 and complexity factor of 2, showing accuracy of 0,6 ± 16,5 kilometers, which is good enough to be used in an early warning system for the city of Bogotá. It is recommended to provide this model with more recent seismic events in order to improve its accuracy.

Using simultaneous thermogravimetrical analysis coupled with mass spectroscopy, the pyrolysis of ... more Using simultaneous thermogravimetrical analysis coupled with mass spectroscopy, the pyrolysis of African palm husk, using several heat rates and programs was performed. Seven relations of mass/charge were followed of the evolved gas of the pyrolysis process, fitting the kinetics and the mass spectroscopy signals to the distributed activation energy model (DAEM) with different numbers of pseudo-components. Fitting with four pseudo-components proved to be the best for modeling the thermal degradation process. Kinetic parameters were not affected by the heating rate or program employed, which agrees with other reports for similar biomass. Methane, methanol formaldehyde, furfural were successfully fitted to the DAEM model, nevertheless CO 2 and NO 2 were not able to be represented by this model due to its production in secondary reactions in gaseous phase.

The effect of the pulse current, pulse on time and pulse off time on the surface roughness of AIS... more The effect of the pulse current, pulse on time and pulse off time on the surface roughness of AISI 304 stainless steel workpieces produced by electric discharge machining (EDM) using grade GSP-70 graphite electrodes was studied. A factorial design was performed, considering two levels for each of the three established parameters. From the statistical analysis, it was obtained that the pulse current and pulse on time are the most significant machining parameters on the obtained surface roughness values of the stainless steel AISI 304 workpieces machined by EDM. On the other hand, the regression analysis of a second order model was done to estimate the average roughness (Ra) in terms of the pulse current, pulse on time and pulse off time. Finally, the mean absolute percentage error (MAPE) of the roughness values estimated by the second order regression model and the roughness obtained experimentally is also presented.

This study evaluates the influence of incorporating two different types of recycled aggregates (R... more This study evaluates the influence of incorporating two different types of recycled aggregates (RA) from construction and demolition waste (CDW), brick ceramic aggregate (RA1) and crushed concrete aggregate (RA2), from the city of Bogotá, on the performance of pervious concrete under compression and flexural strength. The substitution of RA in the production of pervious concrete is outlined, taking into account five substitution levels. For the pervious concrete mixes, aggregates of sizes retained in a sieve of 1/2 " and 3/8 " were used. The pervious concrete mixes were submitted, 28 days later, to density tests, void content, compression and flexural strength and permeability. Such pervious concrete with RA reaches compression and flexural strength of up to 5,79 MPa and 2,14 MPa, respectively, which are within the allowed range by the ACI, reaching a permeability of 24,79 mm/s, value that is superior to the common characteristics of pervious concrete

The identification of irregular users is an important assignment in the recovery of energy in the... more The identification of irregular users is an important assignment in the recovery of energy in the distribution sector. This analysis requires low error levels to minimize non-technical electrical losses in power grid. However, the detection of fraudulent users who have billing does not present a generalized methodology. This issue is complex and varies according to the case study. This paper presents a novel methodology to identify residential fraudulent users by using intelligent systems. The proposed intelligent system consists of three fundamental modules. The first module performs the classification of users with similar power consumption curves using self-organizing maps and genetic algorithms. The second module allows carrying out the monthly electricity demand forecasting through of recursive adjustment of ARIMA models. The third module performs the detection of fraudulent users through an artificial neural network for pattern recognition. For the design and validation of the proposed intelligent system, several tests were performed in each developed module. The database used for the design and evaluation of the modules was constructed with data supplied by the energy distribution company of the Colombian Caribbean Region. The results obtained by the proposed intelligent system show a better performance versus the detection rates obtained by the company.

Manufacturing planning in small and medium enterprises (SMEs) uses a deterministic behavior, and ... more Manufacturing planning in small and medium enterprises (SMEs) uses a deterministic behavior, and the execution of these plans has a stochastic behavior. The evaluation of the manufacturing planning is based on a simple criterion as job on time or job delayed, without integrating conditions of uncertainty in the cycle times for each job. The aim of this paper is to propose a novel multidimensional stochastic Fuzzy Logic System (msFLS) approach to execute a plan with stochastic behavior in knitting SMEs and their evaluation. In this paper, two main contributions are identified. On one hand, the generation of a multi-dimensional diffuse system is proposed. Normal probability density function is used to generate multi linguistic variables to transform deterministic plans to stochastic plans in knitting SMEs. The fuzzy subsets or linguistic terms are labelled and categorized in a simple and clear language as poor (P), regular (R), good (G) and excellent (E). The Gaussian function was used as a membership function. On the other hand, the second contribution is the use of the sum of frequencies in the stage of implication for the multi-Fuzzy system. This research was validated through an integration of two different intelligent techniques such as the proposed novel msFLS and artificial neural networks. Neural networks were used as a generalization mechanism to perform any stochastic planning in the knitting companies. The inputs and outputs of the fuzzy system are used as training patterns in the neural network. The stages of the proposed approach are explicitly described and applied to random data and validated with real data of SMEs of the South of Guanajuato, Mexico. The proposed system had a positive response in the textile company, which continues to be used to carry out its manufacturing planning and the evaluation of its execution.

This paper presents the results from blast tests conducted on four 50 MPa concrete slabs with rei... more This paper presents the results from blast tests conducted on four 50 MPa concrete slabs with reinforcement ratios of 0,175% and 0,37%. Two of the slabs were retrofitted with 50 mm thick foam in order to investigate the potential of using the foam as a strengthening option. The slabs were simply supported on two sides. Non-confined PBX (Plastic bonded explosive) was molded with the form of a cylinder measuring 20 cm in height and 10,5 cm in diameter. The explosive was detonated at 2 m stand-off distance. The equivalent TNT mass of the explosive ranges from 2,58 to 2,72 kg for the four tests. Accelerometers, displacement and pressure gages were used to measure blast wave parameters and global response of the slabs. A high-speed digital camera in conjunction with a rugged notebook recorded images. Qualitative and quantitative results are included. Slabs retrofitted with foam showed a different pressure pattern as recorded by the sensors and resulted in higher displacement, acceleration and linear momentum.

In this work, steganography is implemented in photographs captured by an unmanned aerial vehicle ... more In this work, steganography is implemented in photographs captured by an unmanned aerial vehicle (drone), with the purpose of adding an identifier that indicates which device they are taken from so it works for the recovery of the origin. In the system, a new technique that modifies the least significant bit (LSB) is applied, using a mathematical model to generate the chaotic orbits, one of the parts selects the RGB channel (Red, Green or Blue) where the LSB is changed and the other is implemented to calculate the random position of the sub pixel to be modified in the selected channel. In addition, a comparison between the bit to be hidden and the LSB of the pixel of the image is performed to verify if it is not necessary to modify it, which lessens the alterations in the container image. It is a tool to capture photos remotely with the Ar.Drone 2.0, with the features needed to perform an analysis that uses correlation diagrams and histograms to verify if the integrity of the message is guaranteed or if changes in the stego-image are visible to the naked eye. On the other hand, a test was done on the Baboon image to compare the robustness of the proposed system with other investigations, evaluating the correlation, contrast, energy, homogeneity, MSE, PSNR and quality index. The results generated were compared with the work of other authors concluding our system provides greater security, integrity, high sensitivity to the keys, it is not linked to a single chaotic system and can be applied to hide imperceptibly all kinds of information, in: radiographs, videos, files, official documents, and other types of containers.

One of the main challenges in Macroergonomics is to develop a universal model to measure macroerg... more One of the main challenges in Macroergonomics is to develop a universal model to measure macroergonomic compatibility. As a first step to develop such model, it is necessary to validate the construct of macroergonomic compatibility (MC). MC refers to the ability of the different work system components and elements to complement the capabilities and limitations of employees in order to achieve companies’ goals. In that regard, to achieve this step, this paper analyzes the effects of MC of physical and psychological characteristics of employees over the performance of manufacturing systems measured by the clients, production processes, and the organizational performance of companies. Data was obtained from 188 employees of manufacturing systems by means of the Macroergonomic Compatibility Questionnaire (MCQ) in Chihuahua, Mexico. Also, data is analyzed to propose and test a hypothetical causal model of the relationships among the variables by using a Structural Equation Modeling (SEM) approach. Employees’ physical characteristics (weight, height, strength) are considered as independent variable. The highest direct effects values (ß) were found from physical characteristics to psychological characteristics (0,49), from clients to organizational performance (0,45), and from psychological characteristics to motivation and needs. Also, the highest total effects were found from physical characteristics to motivation and needs (0,517) and psychological characteristics (0,488) and from clients to organizational performance (0,454). Results of this model offer relevant knowledge to develop macroergonomic strategies for manufacturing systems in order to increase their competitiveness and support the design and improvement of these systems.

Consultas sobre el rectángulo vacío de mayor área en grandes conjuntos de datos de dos dimensione... more Consultas sobre el rectángulo vacío de mayor área en grandes conjuntos de datos de dos dimensiones, almacenados en memoria secundaria ABSTRACT-Let S be a set of points located in a rectangle R and q is a point that is not in S.-This article describes the design, implementation, and experimentation of different algorithms to solve the following two problems: (i) Maximum Empty Rectangle (MER), which consists in finding an empty rectangle with a maximum area contained in R and does not contain any point from S and (ii) Query Maximum Empty Rectangle (QMER), which consists in finding the rectangle with the same restrictions given for the MER problem but must also contain q. It is assumed that both problems have insufficient main memory to store all the objects in set S. According to literature, both problems are very practical in fields such as data mining and Geographic Information Systems (GIS). Specifically, the present study proposes two algorithms that assume that S is stored in secondary memory (mainly disk) and that it is impossible to store it completely in main memory. The first algorithm solves the QMER problem and consists of decreasing the size of S by using dominance areas and then processing the points that are not eliminated using an algorithm proposed by Orlowski (1990). The second algorithm solves the MER problem and consists of dividing R into four subrectangles that generate four subsets of similar size; these are processed using an algorithm proposed in Edmonds et al. (2003), and finally, the partial solutions are combined to obtain a global solution. For the purpose of verifying algorithm efficiency, results are shown for a series of experiments that consider synthetic and real data.

38(3), 2018