Roxana Garcia-Andrade

Recent global disruptions have exposed the fragility of tightly coordinated supply chains, particularly under transportation and information delays, motivating the need for analytical tools to assess their stability limits. This study analyzes a two-echelon supply chain system to determine how delays affect stability and performance, with an emphasis on the role of feedback coordination. A continuous-time delay-differential modeling framework was developed to examine both uncoupled and coupled configurations. Stability is analyzed through characteristic equations, and explicit closed-form expressions for the critical delay threshold are derived as functions of the coupling gain and shipment rate. The uncoupled system is shown to exhibit delay-independent marginal stability but lacks the ability to regulate downstream inventory. In contrast, the coupled system achieves inventory regulation but introduces delay-dependent stability with a critical delay, beyond which oscillations grow unbounded. A key result revealed an inverse relationship between coupling strength and delay tolerance, highlighting a trade-off between responsiveness and robustness. An optimal control formulation further demonstrates that the stability constraints limit the achievable performance. These findings provide a theoretical explanation for the vulnerability of just-in-time systems and offer practical guidelines for resilient logistics design, enabling supply chain practitioners to quantify stability margins and balance coordination efficiency with robustness to transportation delays.

The optimal placement of robotic manipulators within industrial workstations is a critical problem that directly affects task feasibility, accessibility, and operational efficiency. Improper base positioning can lead to joint saturation, reduced manipulability, and limited workspace utilization. This work presents an optimization framework for determining the optimal base placement of robotic manipulators by maximizing a joint-centering performance index based on the κ-index, which quantifies the proximity of joint variables to their allowable limits. The proposed methodology integrates geometric accessibility constraints with a constrained optimization formulation to ensure feasible robot configurations within the workspace. Three optimization strategies—constrained nonlinear programming, gradient projection methods, and genetic algorithms—are evaluated and compared in terms of solution quality and computational performance. Numerical simulations are conducted using a planar 2-DOF manipulator to illustrate the proposed framework and to analyze the influence of workspace geometry on optimal base placement. Additionally, an industrial case study involving the ABB IRB 120 robotic manipulator is presented to assess the practical applicability of the proposed approach. The results demonstrate that the optimization framework improves joint distribution within the allowable limits and enhances robot accessibility across the task workspace. The proposed method provides a practical tool for intelligent workstation design and robotic cell layout optimization in modern industrial environments.

El desarrollo de software contemporáneo es una actividad de alta demanda cognitiva, caracterizada por interrupciones constantes que afectan la productividad del programador. La práctica habitual de recurrir a recursos externos para la resolución de errores provoca frecuentes cambios de contexto, generando sobrecarga mental y disminuyendo la eficiencia. Este proyecto de investigación tiene como objetivo general analizar, desde un enfoque teórico, cómo la implementación de un chat de asistencia inteligente embebido en un Entorno de Desarrollo Integrado (IDE) puede contribuir a la reducción de errores, la mejora de la productividad y la promoción de buenas prácticas en la programación. La metodología empleada se basa en un análisis documental cualitativo, una revisión bibliográfica de literatura reciente y una evaluación conceptual de la arquitectura, funcionamiento e impacto de dicha herramienta. El análisis concluye que un asistente integrado tiene un alto potencial para mitigar la carga cognitiva al reducir la conmutación de contexto y actuar como un sistema experto que asiste en la depuración y refactorización. Se identifica un impacto positivo significativo tanto en el ámbito profesional, al optimizar el flujo de trabajo, como en el educativo, al funcionar como un tutor personalizado. Sin embargo, se discuten los riesgos inherentes, principalmente la dependencia tecnológica, la pérdida de habilidades técnicas y los desafíos éticos relacionados con la privacidad y la responsabilidad del código.

This research communication aims to present three mathematical methods for analyzing inventory management in dynamic supply chains, starting from the basic definition in differential equations for inventory levels, which relates with production and demand rates. Initially, the study adopts a systemic perspective to examine the role of energy within a production–inventory system. Subsequently, the analysis focuses on inventory dynamics under parameters expressed in complex variables, with the aim of quantifying fluctuations in a generic production system and demonstrating the influence of inventory variation rates on system behavior. Finally, the investigation addresses the impact of variable capacity on production system inventories, drawing on analogies with corresponding physical systems to support the analysis.

Speed of convergence and robustness against disturbances affecting a dynamical system are of great importance in real-life applications. To satisfy these requirements, another approach called predefined time control has been developed in the last decade, which ensures the convergence of the states of a class of dynamical systems to the desired reference value in a time set by the control designer at will. However, previously proposed predefined time control algorithms have drawbacks that need to be tackled. For this reason, the authors present another form of predefined time control algorithm that can be coupled with any observer (in the case where not all the states of the system can be measured) or any other robust controller to robustify the system against matched disturbances. The development shows that the necessary form of the control law can be obtained using basic integration and backstepping. The performance of the control law is demonstrated through a series of numerical simulations utilizing the mathematical model of a permanent magnet synchronous motor (PMSM). The results show that the proposed control algorithm is, indeed, robust against any matched disturbance, and the convergence of the system states is ensured independently of any initial condition in the time set by the control designer at will.

In the present work, the design and implementation of a device capable of monitor the cardiac pulse by means of photoelectric sensors was carried out, using the oximetry technique and in turn the photometry. Heart rate monitoring has great relevance in the field of health and technology, due to the large number of cardiovascular diseases and millions of deaths worldwide annually. There are currently several heart rate counters with limitations that cannot send your information via internet or GPRS, and cannot be filed on a computer. This prototype was made, based on a microcontroller that receives an infrared sensor signal, once properly conditioned It can be transmitted to a computer. The information obtained can be analyzed and stored by medical specialists, as well as transmitted by Wi-Fi to an application of a remote device providing a service with the use of technologies.