Nanopartículas de ferritas obtenidas mediante sonoquímica asistida con tratamiento térmico y su caracterización magnética.

Se sintetizaron nanopartículas de ferritas con diferente composición química y estructura cristalina: hexagonales, cúbicas y tipo perovskita de composición SrFe12O19, Fe3O4 y BiFeO3 respectivamente, mediante el método de sonoquímica asistida por tratamiento térmico. En cada experimento fueron disueltas cantidades estequiométricas de los polvos precursores en un disolvente compuesto de dietilenglicol (DEG) y agua destilada (10% v/v), las soluciones obtenidas fueron sometidas a irradiación de ultrasonido durante diferentes tiempos y diferentes potencias de sonicación en un rango de 90-240 W. Para evaluar las propiedades fisicoquímicas de los polvos obtenidos del proceso de síntesis, fueron caracterizados mediante difracción de Rayos X (DRX), magnetometría de muestra vibrante (MMV), microscopia de electrónica de barrido y de transmisión (SEM/TEM), calorimetría diferencial de barrido, análisis termogravimétrico (DSC/TGA) y espectroscopía fotoelectrónica de Rayos X (XPS). Finalmente, y con base a los resultados de la caracterización antes descrita, los polvos obtenidos que no mostraban la fase deseada fueron sometidos a la aplicación de un tratamiento térmico en un rango de temperaturas de 100 hasta 1050°C, posteriormente los polvos obtenidos del tratamiento térmico fueron caracterizados mediante las técnicas mencionadas anteriormente para la evaluación de sus propiedades fisicoquímicas

Design Strategy for Low-Power Consumption in Solar Trackers

The new energy generation technologies that transform the solar energy, require a high accuracy for the tracking of the solar vector path, which increases the system energy consumption and reduces the entire system performance. From an optimization approach, a novel design strategy for low-power trackers is proposed, which consists of two main stages, a first for the physical tracker design optimization, and a second for the design of the tracker behavior. For the validation of the proposed design strategy, the implementation is presented through the development of a solar tracker prototype. For the implementation of the second stage, three Tracking Error Minimization Strategies (TEMS) are proposed (PI, GPI, and cascade control), and four Energy Saving Strategies (ESS) are proposed. The presented experimental results show that the saving energy strategy can reduce the energy consumption in up to 27.2771% in tracking tasks with an absolute maximum tracking error of 0.08°, and obtaining a low-power prototype tracker with 5.4749 Wh energy consumption. The proposed design strategy allows the design of solar trackers with a balance between the energy consumption and the tracking error

Adaptive Active Disturbance Rejection Control of Solar Tracking Systems with Partially Known Model

In this article, the trajectory tracking control of a solar tracking system is tackled by means of an adaptive active disturbance rejection control scheme. The state and disturbance estimation system is based on the combination of a time varying identification system and an adaptive observer. The stability and robustness of the controller is mathematically tested by means of the second method of Lyapunov, and its effectiveness is experimentally tested in a robotic test bed, achieving both lower energy consumption and better tracking results with respect to a PID-based controller

Effect of Sonication Output Power on the Crystal Structure and Magnetism of SrFe12O19 Nanoparticles

We reported the effect of the sonication output power (SOP), from 120, 180, to 240 W, on the crystal structure, morphology, and magnetic properties of SrFe12O19 nanoparticles synthesized by sonochemical process assisted with heat treatment. X-ray Diffraction analysis of the obtained powder showed the formation of Fe3O4 with low crystallinity degree, which increased with the increase in SOP, together in a crystalline phase identified as SrCO3. The formation of SrFe12O19 started at 1073 K, and was completed at 1173 K. However, hexaferrite was obtained with the secondary phases α-Fe2O3 and SrFeO2.5. At 1323 K, the secondary phases vanished, and a single phase SrFe12O19 was detected. Vibrating Sample Magnetometry analysis showed that the SrFeO2.5 phase caused the formation of a hysteresis loop known as the Perminvar magnetic hysteresis loop. At 1323 K, the powder synthesized at 120 W showed a specific magnetization of 67.15 Am2/kg at 1.43 × 106 A/m, and coercivity of 4.69 × 104 A/m, with a spherical-like morphology and average particle size of 56.81 nm obtained by Scanning Electron Microscopy analysis. The increment of SOP promoted a high degree of crystallinity and decrease in crystal size. Additionally, it promoted the formation of secondary phases, induced agglomeration, and modified the morphology of the particles

Optimal Selection of the Control Strategy for Dual-Axis Solar Tracking Systems

This article proposes a methodology for the optimal selection of the control strategy for two-axis solar tracking systems, that simultaneously reduces tracking error and energy consumption in existing solar tracking systems, improving their overall performance. Begins with the characterization of the tracking system, then the constraint definition helps to pre-select the possible controllers. Subsequently, a selection stage is carried out from a heuristic approach, based on a multibody simulation analysis and an experimental analysis, and the feasible controllers for the application of the tracker are defined. Finally, a comparative analysis is carried out to find the best control strategy for the existing tracker and the solar application. The optimal selection approach was implemented in a solar tracking system for low-power photovoltaic applications. Based on the defined constraints, six control strategies were pre-selected, which were simulated and implemented in the physical system. The multibody simulation process allows the designer to know the dynamics of each controller, and in turn determine an approximation of the best configuration of the elements that compose it. This, with the aim of validating that each proposal is compatible with the application of the solar tracker, and that it can be taken to the real experimental environment. From the experimental results, the MPC controller shows the best performance. Well, although it has a greater error than other alternatives, its value is still below the permissible precision level (less than 2°) and in turn has the lowest energy consumption 0.7867 Wh. That is, a reduction ranging from 34 to 76% with respect to each performance of the alternatives considered. In addition, the dynamics of the control actions it performs are smoother, thus reducing wear on the actuators.Thus, the results obtained to support that with the proposed methodology the overall performance of solar tracking systems can be increased, significantly reducing tracking error and energy consumption

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)