Improved sampled-data implementation of derivative-dependent control

We consider an LTI system of relative degree two that can be stabilized using the output and its derivative. The derivative is approximated using a finite difference, what leads to a time-delayed feedback. This feedback is analyzed using a Lyapunov-Krasovskii functional that compensates the derivative approximation error presented in an integral form. We show that if the derivative-dependent control exponentially stabilizes the system, then one can use consecutively sampled measurements to approximate the derivative and this approximation will preserve the stability if the sampling period is small enough. We provide linear matrix inequalities that allow to find admissible sampling period and can be used for robustness analysis with respect to system uncertainties. The results are demonstrated by two examples: 2D uncertain system and the Furuta pendulum

COYUNTURA ECONÓMICA, año 5, núm. 11, enero-abril 2023

El cierre de 2022 y el inicio de 2023 no han sido sencillos; venimos de tres años de estancamiento y bajo crecimiento. Comenzamos el año con una inflación alta y una recuperación económica lenta a pesar de algunos hechos que el actual gobierno considera positivos, como las crecientes remesas o la fortaleza del peso, que para algunos no son un reflejo positivo o que dependen de factores externos y por tanto no derivan de la fortaleza de la economía. Lo anterior, aunado al aumento de la desigualdad y a las crecientes necesidades sociales en todos los ámbitos dados los recortes presupuestales de los últimos tres años, ha derivado en que la presente administración tenga varios retos ante sí, entre los que destacan la reactivación de la economía y la recuperación de los empleos perdidos desde la pandemia. Expertos en el tema abordarán estos aspectos en el presente boletín titulado “Retos de política económica para el crecimiento y el desarrollo en México”

COYUNTURA ECONÓMICA, año 3, núm. 6, mayo - agosto 2021

Propuestas de recuperación de la crisis ocasionada por covid-19: farmacéuticas, análisis por región, violencia y buenos vivires

Adsorción de especies de arsénico en estructuras de imidazolato zeolíticas modificadas. Un estudio químico cuántico computacional

En este trabajo se estudiaron las interacciones electrónicas entre las especies As(III) y As(V) con una serie de estructuras de imidazolato zeoliticas (ZIF-8) con y sin defectos, utilizando cálculos periódicos de química cuántica computacional que implementa la teoría del funcional de densidad. Los defectos generados son: una vacancia de ligando, dos hidroxilos coordinados a los metales expuestos y dos dióxidos de azufre en los metales expuestos. La estructura con los metales expuestos disminuye la capacidad de adsorción debido a la reducción del 10% del área de la ventana y a su baja energía de interacción, mientras que la estructura con los grupos hidroxilo reduce en 7.82% el área de la ventana, pero presenta una quimisorción para ambas especies, -37.20 kcal/mol con el As(V) y -27.55 kcal/mol para el As(III), permitiendo su regeneración. Esto hace a la estructura ZIF-8 con hidroxilos la más adecuada para la remoción de las especies As.Computational chemistry calculation for periodic systems, through density functional theory, were performed to study the electronic interactions between arsenic species —As(III) and As(V)—, and a series of zeolitic imidazolate frameworks with and without defects. These defects are: a linker vacancy leaving open metal nodes, two hydroxyl groups filling the open metal nodes, and two sulfur dioxides filling the open metal nodes. The structure with the open metal defects diminishes ZIF-8 adsorption capacity, reducing 10% the window area and delivering a weak electrostatic interaction. In contrast, the structure with hydroxyl groups is the most suitable for the As species removal; although it reduces the window area by 7.82%, it shows a chemisorption energy of -37.20 kcal/mol for As(V) and -27.55 kcal/mol for As(III), these energies are small enough to allow the material regeneration

Estudio teórico-experimental de la adsorción en estado acuoso de arsénico sobre la MOF FeBTC

Con el objetivo de combatir la contaminación de metales pesados en el agua, en este trabajo se proponen dos materiales tipo MOF, la FeBTC y el compósito de FeBTC incorporado con nanopartículas de magnetita (Fe₃O₄-FeBTC), ambos sintetizados mediante el método simple en síntesis solvotermal. La obtención de estos materiales se confirmó mediante su caracterización por difracción de rayos-X, espectroscopia infrarroja, espectroscopia Raman y adsorción-desorción de nitrógeno. Los estudios cinéticos demostraron una buena descripción del fenómeno mediante el modelo de pseudo-segundo orden con un tiempo de equilibro alrededor de 100 min. A través de las isotermas de adsorción se determinó una transición energética de la superficie que favorece el proceso de adsorción al ser incorporadas nanopartículas de magnetita. Posteriormente, fue posible concluir que el fenómeno de fisisorción del metal en ambas MOF es quien gobierna el proceso. Lo anterior se confirmó al realizar el estudio termodinámico y fue corroborado mediante los ciclos de reutilización de los materiales y recuperación del metal. Finalmente, los estudios teóricos demuestran una interacción de la molécula de arsenito en los centros metálicos expuestos, evidencia confirmada mediante la caracterización después del proceso de adsorción mediante espectroscopia Raman.The principal objective of this work is to combat heavy metal contamination in water. Therefore, we propose two MOF-type materials FeBTC and the FeBTC composite, incorporated with magnetite nanoparticles (Fe₃O₄-FeBTC). Both synthesized employing the simple method in solvothermal synthesis. Their characterizationconfirmed obtaining these materials through X-ray diffraction, infrared spectroscopy, Raman spectroscopy and nitrogen adsorption-desorption. The kinetic studies demonstrated a good description of the phenomenon using the pseudosecond- order model with an equilibration time of around 100 min. Through the adsorption isotherms, an energy transition of the surface was determined that favors the adsorption process when the magnetite nanoparticles were incorporated. Subsequently, we concluded that the metal physisorption in both MOFs governs the process by conducting the thermodynamic study. Also, we corroborated this one through the cycles of reuse of materials and recovery of the metal. Finally, theoretical studies demonstrate an arsenite molecule interaction in the exposed metal centers, evidence confirmed by characterization after the adsorption process by Raman spectroscopy

On the transferability of three water models developed by adaptive force matching

Water is perhaps the most simulated liquid. Recently three water models have been developed following the adaptive force matching (AFM) method that provides excellent predictions of water properties with only electronic structure information as a reference. Compared to many other electronic structure based force fields that rely on fairly sophisticated energy expressions, the AFM water models use point-charge based energy expressions that are supported by most popular molecular dynamics packages. An outstanding question regarding simple force fields is whether such force fields provide reasonable transferability outside of their conditions of parameterization. A survey of three AFM water models, B3LYPD-4F, BLYPSP-4F, and WAIL are provided for simulations under conditions ranging from the melting point up to the critical point. By including ice-Ih configurations in the training set, the WAIL potential predicts the melting temperate, TM, of ice-Ih correctly. Without training for ice, BLYPSP-4F underestimates TM by about 15 K. Interestingly, the B3LYPD-4F model gives a TM 14 K too high. The overestimation of TM by B3LYPD-4F mostly likely reflects a deficiency of the B3LYP reference. The BLYPSP-4F model gives the best estimate of the boiling temperature TB and is arguably the best potential for simulating water in the temperature range from TM to TB. None of the three AFM potentials provides a good description of the critical point. Although the B3LYPD-4F model gives the correct critical temperature TC and critical density, there are good reasons to believe the agreement is reached fortuitously. Links to Gromacs input files for the three water models are provided at the end of the paper.Comment: 25 pages, 2 figure

An improved time-delay implementation of derivative-dependent feedback

We consider an LTI system of relative degree that can be stabilized using output derivatives. The derivatives are approximated by finite differences leading to a time-delayed feedback. We present a new method of designing and analyzing such feedback under continuous-time and sampled measurements. This method admits essentially larger time-delay/sampling period compared to the existing results and, for the first time, allows to use consecutively sampled measurements in the sampled-data case. The main idea is to present the difference between the derivative and its approximation in a convenient integral form. The kernel of this integral is hard to express explicitly but we show that it satisfies certain properties. These properties are employed to construct the Lyapunov–Krasovskii functional that leads to LMI-based stability conditions. If the derivative-dependent control exponentially stabilizes the system, then its time-delayed approximation stabilizes the system with the same decay rate provided the time-delay (for continuous-time measurements) or the sampling period (for sampled measurements) are small enough

Estudio del equilibrio tautomérico y reactividad del colorante Anaranjado Ácido 7 (AA7)

En el presente trabajo se preparó una solución acuosa de 40 ppm del colorante Anaranjado Acido 7 (AA7), a la cual se le realizaron ajustes en su pH en búsqueda del compuesto tautomérico (medio ácido y alcalino); para corroborar el cual se analizó mediante espectroscopia de UV-Vis; posteriormente se analizó el comportamiento químico de estas soluciones recurriendo a una reacción de oxidación con peróxido de hidrógeno (H₂O₂), confirmando así la importancia del medio de reacción que promueve el comportamiento tautomérico y modifica la degradación del compuesto. Por último se preparó la solución de colorante empleando diferentes concentraciones de etanol en agua (buscando la formación del compuesto tautomérico).In the present work an aqueous solution of 40 ppm of the dye Orange Acid 7 (AA7) was prepared, to which adjustments were made in its pH in search of the tautomeric compound (acid and alkaline medium); to corroborate which was analyzed by UV-Vis spectroscopy; afterwards, the chemical behavior ofthese solutions was analyzed using an oxidation reaction with hydrogen peroxide (H₂O₂), confirming the importance of the reaction medium that promotes tautomeric behavior and modifies the degradation of the compound. Finally, the dye solution was prepared using different concentrations of ethanol in water (seeking the formation ofthe tautomeric compound)

Incidence of retinopathy of prematurity type 1 and type 2 in a regional Hospital of Social Security in the state of Queretaro, Mexico (2017–2018)

Abstract Background Retinopathy of prematurity (ROP), the primary cause of blindness in children, is a potential complication for 7.7% of live births in Mexico. Given that less than one-third of all neonatal intensive care units follow Mexican National ROP guidelines, there have been few reports regarding the incidences of types 1 and 2 ROP. Methods This was a retrospective study that investigated the incidence and onset of ROP in a representative sample of children in Mexico. We analyzed the results obtained by the ROP Detection and Treatment Program, compliant with the Mexican National ROP guidelines, over a 1-year period. This study included 132 children who were born prematurely, were initially screened between October 2, 2017 and October 1, 2018, and underwent follow-up based on their risk group (in accordance with the Mexican National ROP guidelines). Results The mean gestational age (GA) at birth was 32 weeks and 3 days (32w3d) (95% CI, ± 3 days), and the mean birth weight (BW) was 1594 g (95% CI, ± 96 g). The clinical features were as follows: 36.4% had immature retina without ROP, 22.0% had mild ROP, 5.3% had type 2 ROP, 27.3% had type 1 ROP, and 1.5% had advanced disease. Premature children with ROP requiring treatment (i.e., type 1 ROP + advanced ROP) were born at an MGA of 30w4d (95% CI, ± 5d; range, 26–35 weeks); their MBW was 1316 g (95% CI, ± 110 g; range, 830–2220 g). Diagnosis of ROP requiring treatment was made at a mean postmenstrual age (PMA) of 37w3d (95% CI, ± 5d; range, 31w1d to 42w1d). Conclusion In Mexico, screening and close ophthalmological follow-up of children who present with risk factors of birth weight < 1750 g and gestational age ≤ 34 weeks, both of which are observed more frequently in children with type 1 ROP, appears essential for implementing timely treatments (within 72 h). This is particularly important for children with PMA between 36 and 38 weeks, which is considered to be the peak age for disease stages that require timely intervention