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Robust Optimal Control of Linear-Type Dynamic Systems with Random Delays
No full textOur contribution deals with a class of Optimal Control Problems (OCPs) of dynamic systems with randomly varying time delays. We study the minimax-type OCPs associated with a family of delayed differential equations. The presented minimax dynamic optimization has a natural interpretation as a robustness (in optimization) with respect to the possible delays in control system under consideration. A specific structure of a delayed model makes it possible to reduce the originally given sophisticated OCP to an equivalent convex program in an Euclidean space. This analytic transformation implies a possibility to derive the necessary and sufficient optimality conditions for the original OCP. Moreover, it also allows consideration of the wide range of effective numerical procedures for the constructive treatment of the obtained convex-like OCP. The concrete computational methodology we follow in this paper involves a gradient projected algorithm. We give a rigorous formal analysis of the proposed solution approach and establish the necessary numerical consistence properties of the resulting robust optimization algorithm. © 201
Flexural behavior of ungrouted post-tensioned concrete masonry beams with unbonded bars
No full textPrecast and post-tensioned systems increase the efficiency of masonry beams in terms of labor and time of construction. This study is aimed at evaluating the flexural behavior of ungrouted post-tensioned concrete masonry beams, with eccentric bars, and the effect of the main design parameters on their structural performance when subjected to monotonic and unidirectional cyclic loading until failure. All beams failed in flexure by crushing of the masonry in the compression region. Masonry strength was the design parameter that had the most significant effect on the load-deflection behavior of post-tensioned masonry beams. The test results showed that the measured nonlinear load-deflection behavior and the correlation between bar stress increase and midspan deflection can be estimated using a multi-linear relationship. Beams tested under monotonic and unidirectional cyclic loading exhibited comparable load-deflection envelope response. © 2019 Elsevier Lt
Personal and entrepreneurial characteristics of nascent and active entrepreneurs: GUESSS Colombia study [Características personales y empresariales de emprendedores nacientes y activos: Estudio GUESSS Colombia]
No full textThis article identifies the main characteristics of nascent and active entrepreneurs. We use the information from the GUESSS Colombia 2013/2014 study. Main findings show that the rate of nascent and active entrepreneurs in Colombia is higher than worldwide and that the main industry sector of planned and existing firms are trade and ICT industries. Likewise, nascent entrepreneurs start up their firms with partners, while active entrepreneurs contribute with the majority of the equity, considering that they perform better than competitors and are optimistic with the growth of their firms. © 2018.Este artículo identifica las características de los emprendedores nacientes y activos. Se utiliza la información del estudio GUESSS Colombia 2013/2014, señalando que la tasa de emprendedores nacientes y activos es mayor que a nivel mundial, y que los principales sectores industriales para el emprendimiento son el comercial y el de TIC. Igualmente, los emprendedores nacientes inician sus empresas con socios, mientras que los emprendedores activos aportan la mayoría del capital de sus empresas, considerando que se desempeñan mejor que sus competidores y son optimistas con el crecimiento de sus firmas. © 2018
Hemodynamic and behavioral changes in older adults during cognitively demanding dual tasks
No full textIntroduction: Executive functions play a fundamental role in walking by integrating information from cognitive-motor pathways. Subtle changes in brain and behavior may help identify older adults who are more susceptible to executive function deficits with advancing age due to prefrontal cortex deterioration. This study aims to examine how older adults mitigate executive demands while walking during cognitively demanding tasks. Methods: Twenty healthy older adults (M = 71.8 years, SD = 6.4) performed simple reaction time (SRT), go/no-go (GNG), n-back (NBK), and double number sequence (DNS) cognitive tasks of increasing difficulty while walking (i.e., dual task). Functional near infra-red spectroscopy (fNIRS) was used to measure the hemodynamic response (i.e., oxy- [HbO2] and deoxyhemoglobin [HbR]) changes in the prefrontal cortex (PFC) during dual and single tasks (i.e., walking alone). In addition, performance was measured using gait speed (m/s), response time (s), and accuracy (% correct). Results: Using repeated measures ANOVAs, neural findings demonstrated a main effect of task such that ∆HbO2 (p =.047) and ∆HbR (p =.040) decreased between single and dual tasks. An interaction between task and cognitive difficulty (p =.014) revealed that gait speed decreased in the DNS between single and dual tasks. A main effect of task in response time indicated that the SRT response time was faster than all other difficulty levels (p <.001). Accuracy performance declined between single and dual tasks (p =.028) and across difficulty levels (p <.001) but was not significantly different between the NBK and DNS. Conclusion: Findings suggest that a healthy older adult sample might mitigate executive demands using an automatic locomotor control strategy such that shifting conscious attention away from walking during the dual tasks resulted in decreased ∆HbO2 and ∆HbR. However, decreased prefrontal activation was inefficient at maintaining response time and accuracy performance and may be differently affected by increasing cognitive demands. © 2021 The Authors. Brain and Behavior published by Wiley Periodicals LL
Optimization of aggregate production costs in textile companies [Optimización de costos de producción agregada en empresas del sector textil]
No full textThis article aims to optimize the aggregate production costs in textile companies sector through production strategies in the medium term. For this, an aggregate production planning model called PLAG is developed, which minimizes labor costs, inventory management costs, and production subcontracting costs. Unlike other models in the literature, the PLAG model considers characteristics of the textile sector related to fabric shrinkage, wastes due to product handling, new employees’ efficiency, training time, and manufacturing processes subcontracting, which makes it a comprehensive and effective model for companies in the textile industry. The proposed model is programmed and executed in GAMS, supported by an interface in MSExcel, which generates strategies for the improvement of the production capacity and the optimization of the production plan. © 2020, Universidad de Tarapaca. All rights reserved
Combustion of a hydrogen/carbon monoxide/carbon dioxide mixture in hot and diluted streams
No full textThis work presents an experimental investigation on the combustion behavior of a mixture of hydrogen, carbon monoxide and carbon dioxide in hot and diluted streams, like those obtain under flameless combustion regimes. A jet in a hot coflow burner was used to carry out the experiments. This burner consists of a central fuel jet surrounded by a combustion products stream, which comes from a premixed flame under lean conditions. In this way, it is possible to obtain high temperature and low oxygen concentration in the jet flame. Here, a mixture of 40% H2, 40% CO and 20% CO was issued through the jet nozzle. This composition corresponds to a renewable fuel known as syngas. Three oxygen composition in the oxidant stream were evaluated: 2.0%, 4.7% and 6.9%. Temperature and species concentration values were measured along axial and radial lines under a fix Reynolds's number. The results suggest that when oxygen concentration increases, CO and NO emissions of the total process decreases. © 2020 Published under licence by IOP Publishing Ltd
Phosphate removal from water using a hybrid material in a fixed-bed column
No full textIn this study, the removal and recovery of phosphorus (P) were evaluated on fixed-bed column systems using a hybrid adsorbent, i.e. HFeO. The effect of flow rates (1.0–2.5 mL/min) and bed heights (2–6 cm) was examined, and the experimental data were adjusted to the Thomas, Adams–Bohart and Yoon–Nelson models. The results indicate that for the flow rate of 1.0 mL/min and bed height of 2 cm, a maximum adsorption capacity of P (qTh) of 53.57 mg/g is obtained. 6% NaCl acts as the best eluting agent with a 97% efficiency of P desorption. Finally, it was found that HFeO is able to support up to three cycles of adsorption–desorption, decreasing its capacity of P adsorption by 26% with respect to the initial capacity. © 2018 Elsevier Lt
Impact of students' cultural values on the corporate entrepreneurship management linked to social responsibility
No full textThe present study tries to analyse the influence of students' cultural values on corporate entrepreneurship management associated with social responsibility. For that purpose, we adopt a multidisciplinary approach that combines stakeholders' issues, topics about corporate entrepreneurship, and innovation management concepts in a specific context where companies need to solve the stakeholders' needs in a new way. In this sense, and according to the scarce breakthrough about the inclusion of new actors in the corporate entrepreneurship process, we decide to review the literature about innovation - a near concept - that allows the participation of other players, different from employees. To then, define a quantitative sequential methodology that begins with the analysis of the gathered data through a classification tree, and finish with an artificial neural network. The study results find that only 14 of the 58 student's cultural values, impact and predict the corporate entrepreneurship management linked to social responsibility. A finding that we incorporate in a simulator that predicts the student's idea quality in the social responsibility framework, from 14 of their cultural values. Finally, we suggest the future verification of our results, in specific contexts that we do not consider like intellectual property issues, cost savings, and recruitment politics. Copyright © 2020 Inderscience Enterprises Ltd
Features of the energy spectrum of cosmic rays above 2.5×1018 eV using the pierre auger observatory
No full textWe report a measurement of the energy spectrum of cosmic rays above 2.5×1018 eV based on 215 030 events. New results are presented: at about 1.3×1019 eV, the spectral index changes from 2.51±0.03(stat)±0.05(syst) to 3.05±0.05(stat)±0.10(syst), evolving to 5.1±0.3(stat)±0.1(syst) beyond 5×1019 eV, while no significant dependence of spectral features on the declination is seen in the accessible range. These features of the spectrum can be reproduced in models with energy-dependent mass composition. The energy density in cosmic rays above 5×1018 eV is [5.66±0.03(stat)±1.40(syst)]×1053 erg Mpc-3. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI
The fourth industrial revolution, an opportunity for Civil Engineering. [Cuarta Revolución Industrial, una oportunidad para la Ingeniería Civil.]
No full textSince the last decades, development in technology and innovation has been the machine of the industrial transformation around the world, giving way to a new industrial revolution era called Industry 4.0, lending to improved productivity, competitiveness and sustainability of industry significantly, by changing the perspective of consumer market in a globalized world today. However, despite technological changes, industry of Civil Engineering has continued working as the last century, would depend significantly on manual labor, classical mechanics and, old operational and commercial models of the past century, resulting in a low productivity. For Civil Engineer it is time to takes advantage of new industrial revolution and begins to make a change in the traditional manual processes of production gradually, to move towards a digital and autonomous production in all its processes, from planning and design stages, until construction and maintenance stages. All these changes must be aligned with clear government policies in technology, innovation and development, creating new educational incentives and attract new talent to further develop technological skills in future professionals required by construction industry. © 2020 AISTI