Productos de investigación

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12585/8849

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A computational model for residual life assessment of dents generated by explosive loads in pipelines
(2003) Useche Vivero, Jairo; Gomez J.; Brebbia C.A.; Carlomagno G.M.; Anagnostopoulos P.
The present work develops a finite elements computational model that describes the process of dynamic deformation in pipelines under explosive loads. The mechanical response of the material is modeled by means of an elastoviscoplastic constitutive law based on the Johnson-Cook equation. The model allows understanding the process of generation of dents through the dynamics phenomena and of the development and distribution of stress and strain. The model also allows studying the distribution and magnitude of residual stress allowing identifying critical areas in the dent. It is validated by means of the correlation of main variables with data obtained in experiments of generation of dents under controlled conditions. The model predicts the experimental results in a high grade allowing corroborating hypothesis of failure and residual life proposals for the pipe impacted.
Use of deep learning algorithms for real-time detection of vessels in confined spaces using the Tensorflow framework
(2003-01) Sánchez, S A; Campillo Jiménez, Javier Eduardo; Martínez-Santos, J C
Over 4515 small boat accidents were registered in the United State of America in 2012, resulting in 651 causalities and 22% of the accidents took place between two boats. It is, therefore, one of the most interesting applications for image analysis and recognition using deep learning, collision avoidance in passenger boats. Advances in parallel computing, graphic processing unit technology and deep learning have facilitated real-time image processing. The main objective of this study was to compare the performance metrics for different deep learning algorithms using pre-trained data sets. The algorithms used were: faster region-based convolutional neural networks, region-based fully convolutional network, and single shot multibox detector using the feature extractors: residual neural network, inception and convolutional neural networks for mobile vision applications to detect generic boats in confined waterways. These models were coded in Python programming language, using the framework Tensorflow and OpenCV library for image processing. The algorithms were pre-trained using the free images database posted on the web, Microsoft COCO. The use of these pre-trained models allowed making use of computers without graphic processing unit. As a result, it was found that the faster region-based convolutional neural networks and region-based fully convolutional network method compared to the single shot multibox detector method offer a small advantage precision if speed detection is not required, but the single shot multibox detector method is useful for case detectors in real time, however it did not perform as accurate when detecting small objects.
Multispectral tracking of phytoplankton in the Colombian Caribbean
(2004) Caicedo V.V.O.; Gómez A.P.; Marcano O. A.; Paz J.L.
In a quantitative research study, the concentration and circulation of group of micro-organisms "phytoplankton" have been found through the images of the ocean colour in the Colombian Caribbean Sea. These images have been observed through the Sea Star satellite. The method logical procedure was to collect a number of ocean images at the 1A level of the sensor SeaWifs. This only covered the geographical area of study and the seasons of the year. The selection criterion was to give priority to the absence of clouds in the area. Afterwards, the images were analyzed to create mosaics in convenient periods to visualize the periodical changes of the micro-organisms. Thus, places with higher concentration of phytoplankton in the study site were identified. This led to quantitative analyses of the concentration level of the subject of study. To analyze the images analytic algorithms were used to fit the sensor. The atmospheric correction of the SeaWifs images was made with the SeaDas software to obtain levels two and three of the images. This was done to calculate the primary production of phytoplankton.
Finding a voice through research
(SAGE Publications Ltd, 2006) Lobo J.; Vizcaíno A.
One question guided this experimental study: What impact does the change from teacher training to educational research have on university teachers' methodology and attitudes to teaching? To find answers to this question, the researchers selected five teachers of English as a Foreign Language (EFL) at the language centre of a private university on the Caribbean Coast of Colombia and instructed them in the principles and procedures of action research. Semi-structured interviews were then conducted with each of the teachers involved, a focus group with students and class observations, and field notes were made. Most data sources were audio-taped and transcribed, and all were coded and analysed using qualitative methods. Results indicate that by carrying out research, these teachers, who find it very hard to make ends meet, were able to find a voice, articulate their ideas and propose new ways of teaching. They also found ways to see things differently, from a humanistic angle, and to empower themselves. Copyright © 2006, SAGE Publications.
Dynamic appropriations of domestic space
(2007) Trillos J.
This commentary is an attempt to provide a complementary vision to analyze the study carried out by Giorgi, Padiglione and Pontecorvo. Based on their data, the authors describe three main categories of home appropriation: predominant, proscriptions and incomplete appropriations, each one with clear definitions and descriptions. However, the authors acknowledge that the nature of the methodology and the duration of the study did not permit a thorough study of how these self-representations are constructed. For this reason, here we provide an alternative analysis of the study using the concepts of semiotic mediation and dialogical self, which could be used to propose future research in the field of meaning construction in the home. Copyright © 2007 SAGE Publications.
Applicability of the classic WACC concept in practice
(2007) Mian M.A.; Vélez-Pareja I.
A large percentage of companies use the discounted cash flow (DCF) approach as the primary technique for investment/project evaluation and the capital budgeting process. This approach requires forecasting the detailed cash flow of the project under evaluation and then discounting the resulting cash flow to the present value (Net Present Value-NPV) using an appropriate discount rate. The discount rate commonly used represents the Weighted Average Cost of Capital (WACC) of the firm. There is no scarcity of literature on this subject as the concept has been around for the last 50 years or so. Although most analysts believe the concept is simple and very well known, the irony is that its misinterpretation and misuse prevails. There are many versions of the WACC equation and each is specific to a certain cash flow. Therefore, using the classic WACC relationship in all cases may result in the calculation of an overly optimistic NPV. Depending on the cash flow pattern, the investment may show a positive NPV at the classic WACC but it will actually be losing equity. This paper highlights (a) pitfalls and misuses of the WACC, (b) interdependence between types of cash flow and WACC, (c) assumptions behind the WACC and whether these assumptions are realistic, and (d) alternative approaches to arrive at the correct net present value (NPV). Company CEOs, management, analysts, and other investors using the WACC for investment decisions need to be fully aware of its pitfalls and misuses. © 2007 by The Haworth Press.
Variation in experimentation styles and domain-specific knowledge
(2007) Córdoba M.; Larreamendy-Joerns J.
This study explored the relationship between experimental strategies and domain-specific knowledge within a task of scientific discovery. Groups of expert biologists, experimental psychologists, and lag people in both biology and experimentation were asked to solve a task on population ecology, which implied reaching an equilibrium between preys and predators through parameter manipulation. Success rates, depth and breath of search, and global styles of experimentation were-analyzed. Results indicated that experimentation styles are associated with the participants prior knowledge. Novices engaged in an extensive search through the scope of the problem, whereas expert participants focused their research process on a limited number of parameters.
The potential that ethical finance has to generate new investment alternatives in Colombia
(2008) Sierra González J.H.; Londoño Bedoya D.A.
This article examines the need for and the opportunity of developing ethical finance initiatives, specifically ethical banks and ethical investment funds, as alternatives to strengthen development in Colombia. The validity of such alternatives La is justified through the empirical verification of economic inequality, the limited depth of the traditional financial system, the lack of appropriate investment alternatives to the socioeconomic structure in this country, and the interest of the persons who will potentially acquire the proposed services. The last aspect is based on an analysis of the information obtained from a survey made in Bogotá to 350 persons. The proposals are justified by the available evidence regarding the limitations that the Colombian financial system has and the interest of the potential users of ethical finance initiatives. Likewise, this article proposes an in-depth study of the real possibilities and expected impacts of the proponed initiatives and the effective de involvement of interested social and economic stakeholders. Finally, it suggests several reflections for development in an immediate future to take into account the elements that are relevant to the Colombian context.
Editorial
(2008) Vélez Pareja I.
Forecasting foreign exchange rates in Colombia assuming PPP conditions: Empirical evidence using VAR
(2009) Fayad Hernández, Catherine; Fortich Mesa, Roberto Carlos; Vélez-Pareja, Ignacio
This document examines exchange rate forecasts during the 1995-2005 period, using a Purchasing Power of Parity Exchange Rate Model (PPPER). Our first finding is that the computed forecasts seem to validate the use of this model under certain conditions given that it performs well in predicting the behavior of the nominal exchange rate. Our second finding included a comparative analysis of out-of-sample forecasts (saving historical data) between the PPP-based forecast models and the Vector Autoregressive (VAR) model. The VAR has a better forecasting performance based on the RMSE, MAE, and U-Theil indicators. MAPE results measured on the first and second month-ahead forecasts indicate that the VAR model performs more poorly than the PPP-based models. © 2018 Tehran University of Medical Sciences. All rights reserved.
Bracing alternatives in tapered frames under wind loads
(2009) Rivera A.M.M.
The level of risk caused by forces of the nature could be reduced with an appropriate intervention of vulnerability, since such threats cannot be reduced. One of the alternatives to reduce the structural vulnerability of buildings is provide elements, such as bracing, to improve their behavior when they are subjected to forces arising from these threats. The reduction of vulnerability in buildings type warehouse is achieved with elements that help to absorb horizontal forces acting on it, such as bracing and wind bracing. Due to the limited information about the better way to distribute these elements to reach a good configuration of the structure, we present this document, where we will analyze different distributions for the bracing that provides the best cost-benefit.
Prospective analysis: Guidelines for forecasting financial statements
(Springer Berlin Heidelberg, 2009) Vélez-Pareja I.; Tham J.
In this chapter, we discuss some ideas that might be useful in forecasting financial statements based on historical data.1 The approaches and suggestions presented in this chapter assume that the analyst has access to some company information that is not usually found in publicly available financial statements. In forecasting financial statements, we start with the historical financial statements and from them we identify the patterns and relationships of different items, the implicit policies, growth rates, and so on. The usual practice is to examine historical financial statements to derive information from them that can be used to forecast financial statements. As all information needed cannot be obtained from historical statements, we assume that the information is available from the company's management. We show how we can find information not found in the statements. Finally, we develop a detailed example of a hypothetical firm to explain the procedure to forecast financial statements. We also critically examine the usual practice of using plugs in forecasting financial statements. The chapter is organized as follows: first, we present comments in a general form about the relevance of prospective analysis to nontraded firms. Specifically, we highlight the importance for these firms of having a financial model with which they can assess the value creation in the firm. In the second section, we review concepts in accounting and economics that are used in forecasting financial statements. We stress upon a financial statement that shows the detailed inflows and outflows of cash in the firm: the cash budget (CB). This is an important tool for managing a firm. We also review topics like Pareto law and Fisher equation. Fisher equation is the key to forecasting variables linked to inflation rate. We also review the indexes used to measure inflation. The chapter uses the Fisher equation to forecast interest rates and increases in prices. Special mention is devoted to a usual practice when forecasting: the plug. This is a practice that we do not recommend and show an alternate approach. The approach we propose in this chapter follows an accounting principle that is the basis of any accounting procedure: the Double Entry Principle. This principle guarantees consistent and error-free financial statements. We show with a simple example how the plug works and its limitations. Next, the reader will find what information is needed for forecasting financial statements and where and how to find it. We identify the procedure to identify policies that govern the working of a firm such as accounts receivable and payable (AR and AP), inventories, dividend payout, payments in advance, and the like. We also deal with the real-life problem of a firm with multiple products and/or services. Finally, we show some tools to perform sensitivity analysis for financial management and analysis. We also use this tool to check the consistency of the financial model. In the next two sections, we deal with the relevance of several accounting concepts. In particular, we briefly describe the CB. © 2009 Springer-Verlag Berlin Heidelberg.
Generating dynamic fuzzy models for prediction problems
(2009) Contreras J.; Acuña O.
In this paper we present a new method to generate interpretable fuzzy systems from training data. A fuzzy system is developed for nonlinear systems modeling and for system state forecasting. The antecedent partition uses triangular sets with 0.5 interpolations avoiding the presence of complex overlapping that happens in other methods. Singleton consequents are employed and least square method is used to adjust the consequents. This approach is not a hybrid system and does not employ other techniques, like neural network or genetic algorithm. Two benchmark problems have been used to illustrate our approach: the first one is an input-output NARMAX model, which is one of the most popular models in the neural and fuzzy literature; the second one is the chaotic, nonperiodic and nonconvergence Mackey-Glass series, commonly used to evaluate a time series forecasting scheme. ©2009 IEEE.
Concept maps as a didactic strategy for learning of concepts of cell biology in students of health sciences
(Universidad del Norte, 2009) Rúa D.L.A.; Goenaga I.A.Y.; Olite J.L.M.; Márquez J.S.H.; Molina R.E.F.
For students of health sciences, knowledge of biology is a cornerstone to successfully face the challenges presented to them related to this field of knowledge and to interpret specific phenomena of medical science and health. This paper shows the results of the use of the concept maps for meaningful learning of cellular biology concepts. Objective: to determine the effectiveness of the concept maps as a didactic strategy in the learning of concepts of cellular Biology in students of Health Sciences. Material and methods: It was worked with a cuasi-experimental design of pre-test and post-test with two intact groups: an experimental group (it used the concept maps as learning strategy) and a control group (it did not use the concept maps as learning strategy). The students were evaluated using a pre-test and post-test, built with multiple-choice questions with one answer in the levels of knowledge, comprehension and analysis of the cognitive domain of Bloom's Taxonomy. Results: In the post-test found no significant differences in the total number of questions. However significant differences were found between groups in the application level, observing better results in the experimental group. Conclusions: The concept maps gave students a tool to learn concepts of cell biology significantly. However, its effective use depends on factors such as motivation for learning, continuous training in mapping, significant contents of learning and implementation time.
Intentionality and interpersonal relations
(Springer New York, 2009) Trillos J.
The present commentary re-introduces Heider's (1958) common-sense psychology and his treatment of intentionality, comparing and contrasting his theoretical formulations with those of Elstrup (IPBS: Integrative Psychological & Behavioral Science 43:4, 2009). Special emphasis is made in all those aspects of Heider's theory that are related to the perception, interpretation, prediction and control of our behavior and that of another person. Also, different social aspects of interpersonal relations are presented. Finally, some ideas regarding different approaches to the study of attributing are discussed. © Springer Science + Business Media, LLC 2009.
Market value calculation and the solution of circularity between value and the weighted average cost of capital WACC
(2009) Vélez-Pareja, Ignacio; Tham, Joseph
Most finance textbooks present the Weighted Average Cost of Capital (WACC) calculation as: WACC = Kd×(1-T)×D% + Ke×E%, where Kd is the cost of debt before taxes, T is the tax rate, D% is the percentage of debt on total value, Ke is the cost of equity and E% is the percentage of equity on total value. All of them precise (but not with enough emphasis) that the values to calculate D% y E% are market values. Although they devote special space and thought to calculate Kd and Ke, little effort is made to the correct calculation of market values. This means that there are several points that are not sufficiently dealt with: Market values, location in time, occurrence of tax payments, WACC changes in time and the circularity in calculating WACC. The purpose of this note is to clear up these ideas, solve the circularity problem and emphasize in some ideas that usually are looked over. Also, some suggestions are presented on how to calculate, or estimate, the equity cost of capital. © 2009 Mackenzie Presbyterian University. All rights reserved.
Which cost of debt should be used in forecasting cash flows?
(2009-04-20) Vélez-Pareja, Ignacio
Frequently, analysts and teachers use the capitalized rate of interest for the cost of debt when forecasting and discounting cash flows. Others estimate the interest payments when forecasting annual financial statements or cash flows based on the average of debt calculated with the beginning and ending balance. Others use the end of year convention that calculates the yearly interest multiplying the beginning balance times its contractual cost. The use of one or other methods is critical for the definition of the tax savings. These approaches are illustrated with examples and the differences in using them. A simple proposal to solve the problem is presented.
Potential dividends and actual cash flows in equity valuation. A critical analysis
(2009-11-11) Vélez-Pareja, Ignacio; Magni, Carlo Alberto
Practitioners and most academics in valuation include changes in liquid assets (potential dividends) in the cash flows. This widespread and wrong practice is inconsistent with basic finance theory. We present economic, theoretical, and empirical arguments to support the thesis. Economic arguments underline that only flows of cash should be considered for valuation; theoretical arguments show how potential dividends lead to contradiction and to arbitrage losses. Empirical arguments, from recent studies, suggest that investors discount potential dividends with high discount rates, which means that changes in liquid assets are not value drivers. Hence, when valuing cash flows, we should consider only actual payments.
Potential dividends and actual cash flows.A regional Latin American analysis
(2009-11-26) Vélez-Pareja, Ignacio; Merlo, Mariano Germán; Vélez-Pareja, Ignacio; Londoño Bedoya, David Andrés; Sarmiento Sabogal, Julio Alejandro
We examine the value market assigns to components of the cash flow to equity including potential dividends. We study non financial publicly traded firms from five Latin American countries. The model includes four variables: market value of equity, dividends paid, change in equity investment and change in liquid assets (potential dividends) and are regressed with actual equity value as dependent variable. Tests applied give robust results. The main conclusions: Market assigns less than one dollar to a future dollar for any of the variables studied. Potential dividends destroy value. A dollar invested in liquid assets has a negative Net Present Value and it is not zero NPV investments. We confirm the agency costs of keeping undistributed cash flows.
Mayorships with efficacious, efficient and effective public managementpreviously planned during the political campaign [Alcaldías con gestión pública eficaz, eficiente y efectiva planeada desde la campaña política]
(2010) Álvarez L.Á.; Álvarez E.A.; Saldarriaga A.E.; Chica J.S.
In Colombian towns, public management is led by the mayor, appointed by popular election. During the political campaign, candidates implement different strategies to show the citizens they deserve to be elected. Political campaigns in Colombia use money as a factor of competitiveness. The present paper, deriving from the civic observatory in Cartagena de Indias, proposes an instruction manual to become a mayor candidate. The aforementioned instruction manual might be extended to all positions of popular election stressing on substantial changes in the electoral process as an influential element in the future public management.

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